Protostellar Jets: The Revolution with ALMA

NASA Astrophysics Data System (ADS)

Podio, Linda

2017-11-01

Fast and collimated molecular jets as well as slower wide-angle outflows are observed since the earliest stages of the formation of a new star, when the protostellar embryo accretes most of its final mass from the dense parental envelope. Early theoretical studies suggested that jets have a key role in this process as they can transport away angular momentum thus allowing the star to form without reaching its break-up speed. However, an observational validation of these theories is still challenging as it requires to investigate the interface between jets and disks on scales of fractions to tens of AUs. For this reason, many questions about the origin and feedback of protostellar jets remain unanswered, e.g. are jets ubiquitous at the earliest stages of star formation? Are they launched by a magneto-centrifugal mechanism as suggested by theoretical models? Are they able to remove (enough) angular momentum? What is the jet/outflow feedback on the forming star-disk system in terms of transported mass/momentum and shock-induced chemical alterations? The advent of millimetre interferometers such as NOEMA and ALMA with their unprecedented combination of angular resolution and sensitivity are now unraveling the core of pristine jet-disk systems. While NOEMA allows to obtain the first statistically relevant surveys of protostellar jet properties and ubiquity, recent ALMA observations provide the first solid signatures of jet rotation and new insight on the chemistry of the protostellar region. I will review the most recent and exciting results obtained in the field and show how millimetre interferometry is revolutionising our comprehension of protostellar jets.

Formation of stellar clusters in magnetized, filamentary infrared dark clouds

NASA Astrophysics Data System (ADS)

Li, Pak Shing; Klein, Richard I.; McKee, Christopher F.

2018-01-01

Star formation in a filamentary infrared dark cloud (IRDC) is simulated over the dynamic range of 4.2 pc to 28 au for a period of 3.5 × 105 yr, including magnetic fields and both radiative and outflow feedback from the protostars. At the end of the simulation, the star formation efficiency is 4.3 per cent and the star formation rate per free-fall time is εff ≃ 0.04, within the range of observed values. The total stellar mass increases as ∼t2, whereas the number of protostars increases as ∼t1.5. We find that the density profile around most of the simulated protostars is ∼ρ ∝ r-1.5. At the end of the simulation, the protostellar mass function approaches the Chabrier stellar initial mass function. We infer that the time to form a star of median mass 0.2 M⊙ is about 1.4 × 105 yr from the median mass accretion rate. We find good agreement among the protostellar luminosities observed in the large sample of Dunham et al., our simulation and a theoretical estimate, and we conclude that the classical protostellar luminosity problem is resolved. The multiplicity of the stellar systems in the simulation agrees, to within a factor of 2, with observations of Class I young stellar objects; most of the simulated multiple systems are unbound. Bipolar protostellar outflows are launched using a subgrid model, and extend up to 1 pc from their host star. The mass-velocity relation of the simulated outflows is consistent with both observation and theory.

COPS-GREAT: CO in ProtoStars with GREAT

NASA Astrophysics Data System (ADS)

Kristensen, Lars

2013-10-01

Low-mass embedded protostars drive strong bipolar jets, which shock the surrounding gas on 100-1000 AU scales and entrain colder gas in outflows on 10,000 AU and larger scales. The aim of this proposal is to analyze the transition between shocks and entrainment and to quantify the mass in each component. We plan to do this by observing the CO 13-12 line with GREAT in five sources. Outflows from young protostars are a major source of feedback on both protostellar and cloud scales. However, our understanding of how they entrain or impact the protostellar envelope is still in its infancy. High-J CO observations are required to analyze in detail the transition where the outflowing gas goes from being colder (T ~ 100 K) entrained outflowing gas to being directly excited by the shocks causing the entrainment. These observations will allow us to quantify the amount of currently shocked gas with respect to the entrained gas, as well as examine shock properties as a function of velocity, and thereby quantify the feedback from a protostar on its natal material.

COPS-GREAT2: CO in ProtoStars with GREAT

NASA Astrophysics Data System (ADS)

Yildiz, Umut

Low-mass embedded protostars drive strong bipolar jets, which shock the surrounding gas on 100-1000 AU scales and entrain colder gas in outflows on 10,000 AU and larger scales. The aim of this proposal is to analyze the transition between shocks and entrainment and to quantify the mass in each component. We plan to do this by observing the CO 11-10 line with GREAT in nine sources. Outflows from young protostars are a major source of feedback on both protostellar and cloud scales. However, our understanding of how they entrain or impact the protostellar envelope is still in its infancy. High-J CO observations are required to analyze in detail the transition where the outflowing gas goes from being colder (T 100 K) entrained outflowing gas to being directly excited by the shocks causing the entrainment. These observations will allow us to quantify the amount of currently shocked gas with respect to the entrained gas, as well as examine shock properties as a function of velocity, and thereby quantify the feedback from a protostar on its natal material.

The chemical structure of the Class 0 protostellar envelope NGC 1333 IRAS 4A⋆⋆

NASA Astrophysics Data System (ADS)

Koumpia, E.; Semenov, D. A.; van der Tak, F. F. S.; Boogert, A. C. A.; Caux, E.

2017-07-01

Context. It is not well known what drives the chemistry of a protostellar envelope, in particular the role of the stellar mass and the protostellar outflows on the chemical enrichment of such environments. Aims: We study the chemical structure of the Class 0 protostellar envelope NGC 1333 IRAS 4A in order to (I) investigate the influence of the outflows on the chemistry; (II) constrain the age of our studied object; (III) compare it with a typical high-mass protostellar envelope. Methods: In our analysis we use JCMT line mapping (360-373 GHz) and HIFI pointed spectra (626.01-721.48 GHz). To study the influence of the outflow on the degree of deuteration, we compare JCMT maps of HCO+ and DCO+ with non-LTE (RADEX) models in a region that spatially covers the outflow activity of IRAS 4A. To study the envelope chemistry, we derive empirical molecular abundance profiles for the observed species using the Monte Carlo radiative transfer code (RATRAN) and adopting a 1D dust density/temperature profile from the literature. We use a combination of constant abundance profiles and abundance profiles that include jumps at two radii (T 100 K or T 30 K) to fit our observations. We compare our best-fit observed abundance profiles with the predictions from the time dependent gas grain chemical code (ALCHEMIC). Results: We detect CO, 13CO, C18O, CS, HCN, HCO+, N2H+, H2CO, CH3OH, H2O, H2S, DCO+, HDCO, D2CO, SO, SO2, SiO, HNC, CN, C2H and OCS. We divide the detected lines in three groups based on their line profiles: a) broad emission (FWHM = 4-11 km s-1), b) narrow emission (FWHM< 4 km s-1), and c) showing absorption features. The broad component is indicative of outflow activity, the narrow component arises from dynamically quiescent gas (I.e. envelope) and the absorption is a result of infall motions or the presence of foreground material. Our maps provide information about the spatial and velocity structure of many of the molecules mentioned above, including the deuterated species, making it possible to distinguish between envelope and outflow structures also spatially. The derived abundance profiles are based only on the narrow component (envelope) of the species and are reproduced by a 1D pseudo-time-dependent gas-grain chemical model for the outer envelope, with the exceptions of HCN, HNC, CN. These species along with the CO abundance require an enhanced UV field which points towards an outflow cavity. The abundances with respect to H2 are 1 to 2 orders of magnitude lower than those observed in the high mass protostellar envelope (AFGL 2591), while they are found to be similar within factors of a few when they are estimated with respect to CO. Differences in UV radiation intensity may also be responsible for such chemical differentiation, but temperature differences seem a more plausible explanation, especially the absence of a freeze-out zone in the high mass case. The CH3OH modeled abundance profile points towards an age of ≥4 × 104 yr for IRAS 4A. The spatial distribution of H2D+ differs from that of other deuterated species (I.e. DCO+, HDCO and D2CO), indicating an origin from a colder layer (<20 K) in the foreground, which is not seen in any other tracer. Conclusions: The observed abundances can be explained by passive heating towards the high mass protostellar envelope, while the presence of UV cavity channels become more important toward the low mass protostellar envelope (e.g. CO, HCO+). Based on Herschel observations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Reduced data (FITS files) are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/603/A88

A 100 au Wide Bipolar Rotating Shell Emanating from the HH 212 Protostellar Disk: A Disk Wind?

NASA Astrophysics Data System (ADS)

Lee, Chin-Fei; Li, Zhi-Yun; Codella, Claudio; Ho, Paul T. P.; Podio, Linda; Hirano, Naomi; Shang, Hsien; Turner, Neal J.; Zhang, Qizhou

2018-03-01

HH 212 is a Class 0 protostellar system found to host a “hamburger”-shaped dusty disk with a rotating disk atmosphere and a collimated SiO jet at a distance of ∼400 pc. Recently, a compact rotating outflow has been detected in SO and SO2 toward the center along the jet axis at ∼52 au (0.″13) resolution. Here we resolve the compact outflow into a small-scale wide-opening rotating outflow shell and a collimated jet, with the observations in the same S-bearing molecules at ∼16 au (0.″04) resolution. The collimated jet is aligned with the SiO jet, tracing the shock interactions in the jet. The wide-opening outflow shell is seen extending out from the inner disk around the SiO jet and has a width of ∼100 au. It is not only expanding away from the center, but also rotating around the jet axis. The specific angular momentum of the outflow shell is ∼40 au km s‑1. Simple modeling of the observed kinematics suggests that the rotating outflow shell can trace either a disk wind or disk material pushed away by an unseen wind from the inner disk or protostar. We also resolve the disk atmosphere in the same S-bearing molecules, confirming the Keplerian rotation there.

Modeling Jet and Outflow Feedback during Star Cluster Formation

NASA Astrophysics Data System (ADS)

Federrath, Christoph; Schrön, Martin; Banerjee, Robi; Klessen, Ralf S.

2014-08-01

Powerful jets and outflows are launched from the protostellar disks around newborn stars. These outflows carry enough mass and momentum to transform the structure of their parent molecular cloud and to potentially control star formation itself. Despite their importance, we have not been able to fully quantify the impact of jets and outflows during the formation of a star cluster. The main problem lies in limited computing power. We would have to resolve the magnetic jet-launching mechanism close to the protostar and at the same time follow the evolution of a parsec-size cloud for a million years. Current computer power and codes fall orders of magnitude short of achieving this. In order to overcome this problem, we implement a subgrid-scale (SGS) model for launching jets and outflows, which demonstrably converges and reproduces the mass, linear and angular momentum transfer, and the speed of real jets, with ~1000 times lower resolution than would be required without the SGS model. We apply the new SGS model to turbulent, magnetized star cluster formation and show that jets and outflows (1) eject about one-fourth of their parent molecular clump in high-speed jets, quickly reaching distances of more than a parsec, (2) reduce the star formation rate by about a factor of two, and (3) lead to the formation of ~1.5 times as many stars compared to the no-outflow case. Most importantly, we find that jets and outflows reduce the average star mass by a factor of ~ three and may thus be essential for understanding the characteristic mass of the stellar initial mass function.

YSO jets in the Galactic plane from UWISH2 - V. Jets and outflows in M17

NASA Astrophysics Data System (ADS)

Samal, M. R.; Chen, W. P.; Takami, M.; Jose, J.; Froebrich, D.

2018-07-01

Jets and outflows are the first signposts of stellar birth. Emission in the H2 1-0 S(1) line at 2.122- μm is a powerful tracer of shock excitation in these objects. Here we present the analysis of 2.0 × 0.8 deg2 data from the UK Wide-field Infrared Survey for H2 (UWISH2) in the 1-0 S(1) line to identify and characterize the outflows of the M17 complex. We uncover 48 probable outflows, of which 93 per cent are new discoveries. We identified driving source candidates for 60 per cent of outflows. Among the driving source candidate young stellar objects (YSOs), 90 per cent are protostars and the remaining 10 per cent are Class II YSOs. In comparison with results from other surveys, we suggest that H2 emission fades very quickly as the objects evolve from protostars to pre-main-sequence stars. We fit spectral energy distribution (SED) models to 14 candidate outflow-driving sources and conclude that the outflows of our sample are mostly driven by moderate-mass YSOs that are still actively accreting from their protoplanetary disc. We examined the spatial distribution of the outflows with the gas and dust distribution of the complex and observed that the filamentary dark cloud M17SWex, located on the south-western side of the complex, is associated with a greater number of outflows. We find that our results corroborate previous suggestions that, in the M17 complex, M17SWex is the most active site of star formation. Several of our newly identified outflow candidates are excellent targets for follow-up studies to understand better the very early phase of protostellar evolution.

Radiation transfer of models of massive star formation. III. The evolutionary sequence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yichen; Tan, Jonathan C.; Hosokawa, Takashi, E-mail: yichen.zhang@yale.edu, E-mail: jt@astro.ufl.edu, E-mail: takashi.hosokawa@phys.s.u-tokyo.ac.jp

2014-06-20

We present radiation transfer simulations of evolutionary sequences of massive protostars forming from massive dense cores in environments of high mass surface densities, based on the Turbulent Core Model. The protostellar evolution is calculated with a multi-zone numerical model, with the accretion rate regulated by feedback from an evolving disk wind outflow cavity. The disk evolution is calculated assuming a fixed ratio of disk to protostellar mass, while the core envelope evolution assumes an inside-out collapse of the core with a fixed outer radius. In this framework, an evolutionary track is determined by three environmental initial conditions: the core massmore » M{sub c} , the mass surface density of the ambient clump Σ{sub cl}, and the ratio of the core's initial rotational to gravitational energy β {sub c}. Evolutionary sequences with various M{sub c} , Σ{sub cl}, and β {sub c} are constructed. We find that in a fiducial model with M{sub c} = 60 M {sub ☉}, Σ{sub cl} = 1 g cm{sup –2}, and β {sub c} = 0.02, the final mass of the protostar reaches at least ∼26 M {sub ☉}, making the final star formation efficiency ≳ 0.43. For each of the evolutionary tracks, radiation transfer simulations are performed at selected stages, with temperature profiles, spectral energy distributions (SEDs), and multiwavelength images produced. At a given stage, the envelope temperature depends strongly on Σ{sub cl}, with higher temperatures in a higher Σ{sub cl} core, but only weakly on M{sub c} . The SED and MIR images depend sensitively on the evolving outflow cavity, which gradually widens as the protostar grows. The fluxes at ≲ 100 μm increase dramatically, and the far-IR peaks move to shorter wavelengths. The influence of Σ{sub cl} and β {sub c} (which determines disk size) are discussed. We find that, despite scatter caused by different M{sub c} , Σ{sub cl}, β {sub c}, and inclinations, sources at a given evolutionary stage appear in similar regions of color-color diagrams, especially when using colors with fluxes at ≳ 70 μm, where scatter due to inclination is minimized, implying that such diagrams can be useful diagnostic tools for identifying the evolutionary stages of massive protostars. We discuss how intensity profiles along or perpendicular to the outflow axis are affected by environmental conditions and source evolution and can thus act as additional diagnostics of the massive star formation process.« less

Nature of shocks revealed by SOFIA OI observations in the Cepheus E protostellar outflow

NASA Astrophysics Data System (ADS)

Gusdorf, A.; Anderl, S.; Lefloch, B.; Leurini, S.; Wiesemeyer, H.; Güsten, R.; Benedettini, M.; Codella, C.; Godard, B.; Gómez-Ruiz, A. I.; Jacobs, K.; Kristensen, L. E.; Lesaffre, P.; Pineau des Forêts, G.; Lis, D. C.

2017-06-01

Context. Protostellar jets and outflows are key features of the star-formation process, and primary processes of the feedback of young stars on the interstellar medium. Understanding the underlying shocks is necessary to explain how jet and outflow systems are launched, and to quantify their chemical and energetic impacts on the surrounding medium. Aims: We performed a high-spectral resolution study of the [OI]63μm emission in the outflow of the intermediate-mass Class 0 protostar Cep E-mm. The goal is to determine the structure of the outflow, to constrain the chemical conditions in the various components, and to understand the nature of the underlying shocks, thus probing the origin of the mass-loss phenomenon. Methods: We present observations of the O I 3P1 → 3P2, OH between 2Π1/2J = 3/2 and J = 1/2 at 1837.8 GHz, and CO (16-15) lines with the GREAT receiver onboard SOFIA towards three positions in the Cep E protostellar outflow: Cep E-mm (the driving protostar), Cep E-BI (in the southern lobe), and Cep E-BII (the terminal position in the southern lobe). Results: The CO (16-15) line is detected at all three positions. The [OI]63μm line is detected in Cep E-BI and BII, whereas the OH line is not detected. In Cep E-BII, we identify three kinematical components in O I and CO. These were already detected in CO transitions and relate to spatial components: the jet, the HH377 terminal bow-shock, and the outflow cavity. We measure line temperature and line integrated intensity ratios for all components. The O I column density is higher in the outflow cavity than in the jet, which itself is higher than in the terminal shock. The terminal shock is the region where the abundance ratio of O I to CO is the lowest (about 0.2), whereas the jet component is atomic (N(O I)/N(CO) 2.7). In the jet, we compare the [OI]63μm observations with shock models that successfully fit the integrated intensity of 10 CO lines. We find that these models most likely do not fit the [OI]63μm data. Conclusions: The high intensity of O I emission points towards the propagation of additional dissociative or alternative FUV-irradiated shocks, where the illumination comes from the shock itself. A picture emerges from the sample of low-to-high mass protostellar outflows, where similar observations have been performed, with the effects of illumination increasing with the mass of the protostar. These findings need confirmation with more observational constraints and a larger sample. This article uses Herschel-PACS data; Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.All spectra shown in Fig. 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A8

The SOFIA Massive (SOMA) Star Formation Survey. I. Overview and First Results

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Buizer, James M.; Shuping, Ralph; Liu, Mengyao

We present an overview and first results of the Stratospheric Observatory For Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the FORCAST instrument to image massive protostars from ∼10 to 40 μ m. These wavelengths trace thermal emission from warm dust, which in Core Accretion models mainly emerges from the inner regions of protostellar outflow cavities. Dust in dense core envelopes also imprints characteristic extinction patterns at these wavelengths, causing intensity peaks to shift along the outflow axis and profiles to become more symmetric at longer wavelengths. We present observational results for the first eight protostars in themore » survey, i.e., multiwavelength images, including some ancillary ground-based mid-infrared (MIR) observations and archival Spitzer and Herschel data. These images generally show extended MIR/FIR emission along directions consistent with those of known outflows and with shorter wavelength peak flux positions displaced from the protostar along the blueshifted, near-facing sides, thus confirming qualitative predictions of Core Accretion models. We then compile spectral energy distributions and use these to derive protostellar properties by fitting theoretical radiative transfer models. Zhang and Tan models, based on the Turbulent Core Model of McKee and Tan, imply the sources have protostellar masses m {sub *} ∼ 10–50 M {sub ⊙} accreting at ∼10{sup −4}–10{sup −3} M {sub ⊙} yr{sup −1} inside cores of initial masses M {sub c} ∼ 30–500 M {sub ⊙} embedded in clumps with mass surface densities Σ{sub cl} ∼ 0.1–3 g cm{sup −2}. Fitting the Robitaille et al. models typically leads to slightly higher protostellar masses, but with disk accretion rates ∼100× smaller. We discuss reasons for these differences and overall implications of these first survey results for massive star formation theories.« less

Chemical Evolution of Protostellar Matter

NASA Technical Reports Server (NTRS)

Langer, William D.; vanDishoeck, Ewine F.; Bergin, Edwin A.; Blake, Geoffrey A.; Tielens, Alexander G. G. M.; Velusamy, Thangasamy; Whittet, Douglas C. B.

2000-01-01

We review the chemical processes that are important in the evolution from a molecular cloud core to a protostellar disk. These cover both gas phase and gas grain interactions. The current observational and theoretical state of this field are discussed.

Theory of Bipolar Outflows from Accreting Hot Stars

NASA Astrophysics Data System (ADS)

Konigl, A.

1996-05-01

There is a growing number of observational indicators for the presence of bipolar outflows in massive, young stellar objects that are still accreting mass as part of their formation process. In particular, there is evidence that the outflows from these objects can attain higher velocities and kinetic luminosities than their lower-mass counterparts. Furthermore, the higher-mass objects appear to smoothly continue the correlation found in T Tauri stars between outflow and accretion signatures, and in several cases there are direct clues to the existence of a disk from optical and infrared spectroscopy. These results suggest that the disk--outflow connection found in low-mass pre--main-sequence stars extends to more massive objects, and that a similar physical mechanism may drive the outflows in both cases. In this presentation, I first critically examine the observational basis for this hypothesis, considering, among other things, the possibility that several low-luminosity outflows might occasionally masquerade as a single flow from a luminous object, and the effects that the radiation field of a hot star could have on the spectroscopic diagnostics of an accretion-driven outflow. I then go on to consider how the commonly invoked centrifugally driven wind models of bipolar outflows in low-mass stars would be affected by the various physical processes (such as photoionization, photoevaporation, radiation pressure, and stellar wind ram pressure) that operate in higher-mass stars. I conclude by mentioning some of the tantalizing questions that one could hope to address as this young field of research continues to develop (for example: is there a high-mass analog of the FU Orionis outburst phenomenon? Could one use observations of progressively more massive, and hence less convective, stars to elucidate the role of stellar magnetic fields in the accretion and outflow processes? Would it be possible to observationally identify massive stars that have reached the main sequence while they were still accreting? Does the evolution of protostellar disks differ in low-mass and high-mass objects?).

The HIFI spectral survey of AFGL 2591 (CHESS). I. Highly excited linear rotor molecules in the high-mass protostellar envelope

NASA Astrophysics Data System (ADS)

van der Wiel, M. H. D.; Pagani, L.; van der Tak, F. F. S.; Kaźmierczak, M.; Ceccarelli, C.

2013-05-01

Context. Linear rotor molecules such as CO, HCO+ and HCN are important probes of star-forming gas. For these species, temperatures of ≲ 50 K are sufficient to produce emission lines that are observable from the ground at (sub)millimeter wavelengths. Molecular gas in the environment of massive protostellar objects, however, is known to reach temperatures of several hundred K. To probe this, space-based far-infrared observations are required. Aims: We aim to reveal the gas energetics in the circumstellar environment of the prototypical high-mass protostellar object AFGL 2591. Methods: Rotational spectral line signatures of CO species, HCO+, CS, HCN and HNC from a 490-1240 GHz survey with Herschel/HIFI, complemented by ground-based JCMT and IRAM 30 m spectra, cover transitions in the energy range (Eup/k) between 5 K and ~ 300 K. Selected frequency settings in the highest frequency HIFI bands (up to 1850 GHz) extend this range to 750 K for 12C16O. The resolved spectral line profiles are used to separate and study various kinematic components. Observed line intensities are compared with a numerical model that calculates excitation balance and radiative transfer based on spherical geometry. Results: The line profiles show two emission components, the widest and bluest of which is attributed to an approaching outflow and the other to the envelope. We find evidence for progressively more redshifted and wider line profiles from the envelope gas with increasing energy level. This trend is qualitatively explained by residual outflow contribution picked up in the systematically decreasing beam size. Integrated line intensities for each species decrease as Eup/k increases from ≲ 50 to ~700 K. The H2 density and temperature of the outflow gas are constrained to ~105-106 cm-3 and 60-200 K. In addition, we derive a temperature between 9 and 17 K and N(H2) ~ 3 × 1021 cm-2 for a known foreground cloud seen in absorption, and N(H2) ≲ 1019 cm-2 for a second foreground component. Conclusions: Our spherical envelope model systematically underproduces observed line emission at Eup/k ≳ 150 K for all species. This indicates that warm gas should be added to the model and that the model's geometry should provide low optical depth pathways for line emission from this warm gas to escape, for example in the form of UV heated outflow cavity walls viewed at a favorable inclination angle. Physical and chemical conditions derived for the outflow gas are similar to those in the protostellar envelope, possibly indicating that the modest velocity (≲10 km s-1) outflow component consists of recently swept-up gas. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

A circumstellar disk associated with a massive protostellar object.

PubMed

Jiang, Zhibo; Tamura, Motohide; Fukagawa, Misato; Hough, Jim; Lucas, Phil; Suto, Hiroshi; Ishii, Miki; Yang, Ji

2005-09-01

The formation process for stars with masses several times that of the Sun is still unclear. The two main theories are mergers of several low-mass young stellar objects, which requires a high stellar density, or mass accretion from circumstellar disks in the same way as low-mass stars are formed, accompanied by outflows during the process of gravitational infall. Although a number of disks have been discovered around low- and intermediate-mass young stellar objects, the presence of disks around massive young stellar objects is still uncertain and the mass of the disk system detected around one such object, M17, is disputed. Here we report near-infrared imaging polarimetry that reveals an outflow/disk system around the Becklin-Neugebauer protostellar object, which has a mass of at least seven solar masses (M(o)). This strongly supports the theory that stars with masses of at least 7M(o) form in the same way as lower mass stars.

Shaping a high-mass star-forming cluster through stellar feedback. The case of the NGC 7538 IRS 1-3 complex

NASA Astrophysics Data System (ADS)

Frau, P.; Girart, J. M.; Zhang, Q.; Rao, R.

2014-07-01

Context. NGC 7538 IRS 1-3 is a high-mass star-forming cluster with several detected dust cores, infrared sources, (ultra)compact H II regions, molecular outflows, and masers. In such a complex environment, interactions and feedback among the embedded objects are expected to play a major role in the evolution of the region. Aims: We study the dust, kinematic, and polarimetric properties of the NGC 7538 IRS 1-3 region to investigate the role of the different forces in the formation and evolution of high-mass star-forming clusters. Methods: We performed SMA high angular resolution observations at 880 μm with the compact configuration. We developed the RATPACKS code to generate synthetic velocity cubes from models of choice to be compared to the observational data. To quantify the stability against gravitational collapse we developed the "mass balance" analysis that accounts for all the energetics on core scales. Results: We detect 14 dust cores from 3.5 M⊙ to 37 M⊙ arranged in two larger scale structures: a central bar and a filamentary spiral arm. The spiral arm presents large-scale velocity gradients in H13CO+ 4-3 and C17O 3-2, and magnetic field segments aligned well to the dust main axis. The velocity gradient is reproduced well by a spiral arm expanding at 9 km s-1 with respect to the central core MM1, which is known to power a large precessing outflow. The energy of the outflow is comparable to the spiral-arm kinetic energy, which dominates gravitational and magnetic energies. In addition, the dynamical ages of the outflow and spiral arm are comparable. On core scales, those embedded in the central bar seem to be unstable against gravitational collapse and prone to forming high-mass stars, while those in the spiral arm have lower masses that seem to be supported by non-thermal motions and magnetic fields. Conclusions: The NGC 7538 IRS 1-3 cluster seems to be dominated by protostellar feedback. The dusty spiral arm appears to be formed in a snowplow fashion owing to the outflow from the MM1 core. We speculate that the external pressure from the redshifted lobe of the outflow could trigger star formation in the spiral arm cores. This scenario would form a small cluster with a few central high-mass stars, surrounded by a number of low-mass stars formed through protostellar feedback. Based on observations carried out with the SMA telescope. The SMA is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics, and is funded by the Smithsonian Institution and the Academia Sinica (http://sma1.sma.hawaii.edu/).Final reduced SMA data cube is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A116

Magnetically Controlled Spasmodic Accretion during Star Formation. II. Results

NASA Astrophysics Data System (ADS)

Tassis, Konstantinos; Mouschovias, Telemachos Ch.

2005-01-01

The problem of the late accretion phase of the evolution of an axisymmetric, isothermal magnetic disk surrounding a forming star has been formulated in a companion paper. The ``central sink approximation'' is used to circumvent the problem of describing the evolution inside the opaque central region for densities greater than 1011 cm-3 and radii smaller than a few AU. Only the electrons are assumed to be attached to the magnetic field lines, and the effects of both negatively and positively charged grains are accounted for. After a mass of 0.1 Msolar accumulates in the central cell (forming star), a series of magnetically driven outflows and associated outward-propagating shocks form in a quasi-periodic fashion. As a result, mass accretion onto the protostar occurs in magnetically controlled bursts. We refer to this process as spasmodic accretion. The shocks propagate outward with supermagnetosonic speeds. The period of dissipation and revival of the outflow decreases in time, as the mass accumulated in the central sink increases. We evaluate the contribution of ambipolar diffusion to the resolution of the magnetic flux problem of star formation during the accretion phase, and we find it to be very significant albeit not sufficient to resolve the entire problem yet. Ohmic dissipation is completely negligible in the disk during this phase of the evolution. The protostellar disk is found to be stable against interchange-like instabilities, despite the fact that the mass-to-flux ratio has temporary local maxima.

ALMA Detection of Bipolar Outflows: Evidence for Low-mass Star Formation within 1 pc of Sgr A*

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, F.; Wardle, M.; Kunneriath, D.; Royster, M.; Wootten, A.; Roberts, D. A.

2017-12-01

We report the discovery of 11 bipolar outflows within a projected distance of 1 pc from Sgr A* based on deep ALMA observations of 13CO, H30α, and SiO (5-4) lines with subarcsecond and ˜1.3 km s-1 resolutions. These unambiguous signatures of young protostars manifest as approaching and receding lobes of dense gas swept up by the jets created during the formation and early evolution of stars. The lobe masses and momentum transfer rates are consistent with young protostellar outflows found throughout the disk of the Galaxy. The mean dynamical age of the outflow population is estimated to be {6.5}-3.6+8.1× {10}3 years. The rate of star formation is ˜5 × 10-4 {M}⊙ yr-1 assuming a mean stellar mass of ˜0.3 {M}⊙ . This discovery provides evidence that star formation is taking place within clouds surprisingly close to Sgr A*, perhaps due to events that compress the host cloud, creating condensations with sufficient self-gravity to resist tidal disruption by Sgr A*. Low-mass star formation over the past few billion years at this level would contribute significantly to the stellar mass budget in the central few parsecs of the Galaxy. The presence of many dense clumps of molecular material within 1 pc of Sgr A* suggests that star formation could take place in the immediate vicinity of supermassive black holes in the nuclei of external galaxies.

First Detection of Methanol in a Class O Protostellar Disk

NASA Technical Reports Server (NTRS)

Velusamy, T.; Langer, William D.; Goldsmith, Paul F.

2000-01-01

We report the detection of emission from methanol in a compact source coincident with the position of the L1157 infrared source, which we attribute to molecules in the disk surrounding this young, Class O protostellar object. In addition, we identify a spectral feature in the outflow corresponding to an ethanol transition. Using the Caltech Owens Valley Millimeter Array with a synthesized beam size of 2", we detect spatially unresolved methanol in the 2(sub k) - 1(sub k) transitions at 3mm, which is coincident in position with the peak of the continuum emission. The gas phase methanol could be located in the central region (< 100 AU radius) of a flat disk, or in an extended heated surface layer (approx. 200 AU radius) of a flared disk. The fractional abundance of methanol X(CH3OH) is approx. 2 x l0(exp -8) in the flat disk model, and 3 x l0(exp -7) for the flared disk. The fractional abundance is small in the disk as a whole, but considerably larger in the warm portions. This difference indicates that substantial chemical processing probably takes place in the disk via depletion and desorption. The methanol desorbed from the grains in the warm surface layers returns to the icy grain mantles in the cooler interior of the disk, where it is available to become part of the composition of solar system-like bodies, such as comets, formed in the outer circumstellar region. This first millimeter-wavelength detection of a complex organic molecule in a young protostellar disk has implications for disk structure and chemical evolution and for potential use as a temperature probe. The research of TV and WL was conducted at the Jet Propulsion Laboratory, California Institute of Technology with support from the National Aeronautics and Space Administration.

An Outflow-shaped Magnetic Field Toward the Class 0 Protostellar Source Serpens SMM1

NASA Astrophysics Data System (ADS)

Hull, Charles; Girart, Josep M.; Tychoniec, Lukasz; Rao, Ramprasad; Cortés, Paulo; Pokhrel, Riwaj; Zhang, Qizhou; Houde, Martin; Dunham, Michael; Kristensen, Lars; Lai, Shih-Ping; Li, Zhi-Yun; Plambeck, Richard

2018-01-01

The results from the polarization system at the Atacama Large Millimeter/submillimeter Array (ALMA) have begun both to expand and to confound our understanding of the role of the magnetic field in low-mass star formation. Here we show the highest resolution and highest sensitivity polarization images made to date toward the very young, intermediate-mass Class 0 protostellar source Serpens SMM1, the brightest source in the Serpens Main star-forming region. These ALMA observations achieve ~140 AU resolution, allowing us to probe dust polarization—and thus magnetic field orientation—in the innermost regions surrounding the protostar. By complementing these observations with polarization observations from the Submillimeter Array (SMA) and archival data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the James Clerk Maxwell Telescopes (JCMT), we can compare the magnetic field orientations at different spatial scales. We find major changes in the magnetic field orientation between large (~0.1 pc) scales—where the magnetic field is oriented E–W, perpendicular to the major axis of the dusty filament where SMM1 is embedded—and the intermediate and small scales probed by CARMA (~1000 au resolution), the SMA (~350 au resolution), and ALMA. The ALMA maps reveal that the redshifted lobe of the bipolar outflow is clearly shaping the magnetic field in SMM1 on the southeast side of the source. High-spatial-resolution continuum and spectral-line observations also reveal a tight (~130 au) protobinary system in SMM1-b, the eastern component of which is launching an extremely high-velocity, one-sided jet visible in both CO(2-1) and SiO(5-4); however, that jet does not appear to be shaping the magnetic field. These observations show that with the sensitivity and resolution of ALMA, we can now begin to understand the role that feedback (e.g., from protostellar outflows) plays in shaping the magnetic field in very young, star-forming sources like SMM1.

Water in star-forming regions with Herschel (WISH). II. Evolution of 557 GHz 110-101 emission in low-mass protostars

NASA Astrophysics Data System (ADS)

Kristensen, L. E.; van Dishoeck, E. F.; Bergin, E. A.; Visser, R.; Yıldız, U. A.; San Jose-Garcia, I.; Jørgensen, J. K.; Herczeg, G. J.; Johnstone, D.; Wampfler, S. F.; Benz, A. O.; Bruderer, S.; Cabrit, S.; Caselli, P.; Doty, S. D.; Harsono, D.; Herpin, F.; Hogerheijde, M. R.; Karska, A.; van Kempen, T. A.; Liseau, R.; Nisini, B.; Tafalla, M.; van der Tak, F.; Wyrowski, F.

2012-06-01

Context. Water is a key tracer of dynamics and chemistry in low-mass star-forming regions, but spectrally resolved observations have so far been limited in sensitivity and angular resolution, and only data from the brightest low-mass protostars have been published. Aims: The first systematic survey of spectrally resolved water emission in 29 low-mass (L < 40 L⊙) protostellar objects is presented. The sources cover a range of luminosities and evolutionary states. The aim is to characterise the line profiles to distinguish physical components in the beam and examine how water emission changes with protostellar evolution. Methods: H2O was observed in the ground-state 110-101 transition at 557 GHz (Eup/kB ~ 60 K) as single-point observations with the Heterodyne Instrument for the Far-Infrared (HIFI) on Herschel in 29 deeply embedded Class 0 and I low-mass protostars. Complementary far-IR and sub-mm continuum data (including PACS data from our programme) are used to constrain the spectral energy distribution (SED) of each source. H2O intensities are compared to inferred envelope properties, e.g., mass and density, outflow properties and CO 3-2 emission. Results: H2O emission is detected in all objects except one (TMC1A). The line profiles are complex and consist of several kinematic components tracing different physical regions in each system. In particular, the profiles are typically dominated by a broad Gaussian emission feature, indicating that the bulk of the water emission arises in outflows, not in the quiescent envelope. Several sources show multiple shock components appearing in either emission or absorption, thus constraining the internal geometry of the system. Furthermore, the components include inverse P-Cygni profiles in seven sources (six Class 0, one Class I) indicative of infalling envelopes, and regular P-Cygni profiles in four sources (three Class I, one Class 0) indicative of expanding envelopes. Molecular "bullets" moving at ≳50 km s-1 with respect to the source are detected in four Class 0 sources; three of these sources were not known to harbour bullets previously. In the outflow, the H2O/CO abundance ratio as a function of velocity is nearly the same for all line wings, increasing from 10-3 at low velocities (<5 km s-1) to ≳10-1 at high velocities (>10 km s-1). The water abundance in the outer cold envelope is low, ≳10-10. The different H2O profile components show a clear evolutionary trend: in the younger Class 0 sources the emission is dominated by outflow components originating inside an infalling envelope. When large-scale infall diminishes during the Class I phase, the outflow weakens and H2O emission all but disappears. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.org

Broad N2H+ Emission toward the Protostellar Shock L1157-B1

NASA Astrophysics Data System (ADS)

Codella, C.; Viti, S.; Ceccarelli, C.; Lefloch, B.; Benedettini, M.; Busquet, G.; Caselli, P.; Fontani, F.; Gómez-Ruiz, A.; Podio, L.; Vasta, M.

2013-10-01

We present the first detection of N2H+ toward a low-mass protostellar outflow, namely, the L1157-B1 shock, at ~0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30 m antenna. We observed emission at 93 GHz due to the J = 1-0 hyperfine lines. Analysis of this emission coupled with HIFI CHESS multiline CO observations leads to the conclusion that the observed N2H+(1-0) line originated from the dense (>=105 cm-3) gas associated with the large (20''-25'') cavities opened by the protostellar wind. We find an N2H+ column density of a few 1012 cm-2 corresponding to an abundance of (2-8) × 10-9. The N2H+ abundance can be matched by a model of quiescent gas evolved for more than 104 yr, i.e., for more than the shock kinematical age (sime2000 yr). Modeling of C-shocks confirms that the abundance of N2H+ is not increased by the passage of the shock. In summary, N2H+ is a fossil record of the pre-shock gas, formed when the density of the gas was around 104 cm-3, and then further compressed and accelerated by the shock.

Magnetically regulated collapse in the B335 protostar? I. ALMA observations of the polarized dust emission

NASA Astrophysics Data System (ADS)

Maury, A. J.; Girart, J. M.; Zhang, Q.; Hennebelle, P.; Keto, E.; Rao, R.; Lai, S.-P.; Ohashi, N.; Galametz, M.

2018-06-01

The role of the magnetic field during protostellar collapse is poorly constrained from an observational point of view, although it could be significant if we believe state-of-the-art models of protostellar formation. We present polarimetric observations of the 233 GHz thermal dust continuum emission obtained with ALMA in the B335 Class 0 protostar. Linearly polarized dust emission arising from the circumstellar material in the envelope of B335 is detected at all scales probed by our observations (50 to 1000 au). The magnetic field structure producing the dust polarization has a very ordered topology in the inner envelope, with a transition from a large-scale poloidal magnetic field, in the outflow direction, to strongly pinched in the equatorial direction. This is probably due to magnetic field lines being dragged along the dominating infall direction since B335 does not exhibit prominent rotation. Our data and their qualitative comparison to a family of magnetized protostellar collapse models show that, during the magnetized collapse in B335, the magnetic field is maintaining a high level of organization from scales 1000 au to 50 au: this suggests the field is dynamically relevant and capable of influencing the typical outcome of protostellar collapse, such as regulating the disc size in B335.

The Infrared Reflection Nebula Around the Protostellar System in S140

NASA Technical Reports Server (NTRS)

Harker, D.; Bregman, J.; Tielens, A. G. G. M.; Temi, P.; Rank, D.; Morrison, David (Technical Monitor)

1994-01-01

We have studied the protostellar system in S140 at 2.2, 3.1 and 3.45 microns using a 128x128 InSb array at the Lick Observatory 3m telescope. Besides the protostellar sources, the data reveal a bright infrared reflection nebula. We have developed a simple model of this region and derived the physical conditions. IRSI is surrounded by a dense dusty disk viewed almost edge-on. Photons leaking out through the poles illuminate almost directly north and south the inner edge of a surrounding shell of molecular gas, Analysis of the observed colors and intensities of the NIR light, using Mie scattering theory, reveal that the dust grains in the molecular cloud are somewhat larger than in the general diffuse interstellar medium. Moreover, the incident light has a "cool" color temperature, approximately equals 800K, and likely originates from a dust photosphere close to the protostar. Finally, we find little H2O ice associated with the dusty disk around IRSI. Most of the 3.1 micron ice extinction arises instead from cool intervening molecular cloud material. We have compared our infrared dust observations with millimeter and radio observations of molecular gas associated with this region. The large scale structure observable in the molecular gas is indicative of the interaction between the protostellar wind and the surrounding molecular cloud rather than the geometry of the protostellar disk. We conclude that S140 is a young blister formed by this outflow on the side of a molecular cloud and viewed edge-on.

The Mass Evolution of Protostellar Disks and Envelopes in the Perseus Molecular Cloud

NASA Astrophysics Data System (ADS)

Andersen, Bridget; Stephens, Ian; Dunham, Michael; Pokhrel, Riwaj; Jørgensen, Jes; Frimann, Søren

2018-01-01

In the standard picture for low-mass star formation, a dense molecular cloud undergoes gravitational collapse to form a protostellar system consisting of a new central star, a circumstellar disk, and a surrounding envelope of remaining material. The mass distribution of the system evolves as matter accretes from the large-scale envelope through the disk and onto the protostar. While this general picture is supported by simulations and indirect observational measurements, the specific timescales related to disk growth and envelope dissipation remain poorly constrained. We present a rigorous test of a method introduced by Jørgensen et al. (2009) to obtain observational mass measurements of disks and envelopes around embedded protostars from unresolved (resolution of ~1000 AU) observations. Using data from the recent Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey, we derive disk and envelope mass estimates for 59 protostellar systems in the Perseus molecular cloud. We compare our results to independent disk mass measurements from the VLA Nascent Disk and Multiplicity (VANDAM) survey and find a strong linear correlation. Then, leveraging the size and uniformity of our sample, we find no significant trend in protostellar mass distribution as a function of age, as approximated from bolometric temperatures. These results may indicate that the disk mass of a protostar is set near the onset of the Class 0 protostellar stage and remains roughly constant throughout the Class I protostellar stage.

Erratum: The Effects of Thermal Energetics on Three-dimensional Hydrodynamic Instabilities in Massive Protostellar Disks. II. High-Resolution and Adiabatic Evolutions

NASA Astrophysics Data System (ADS)

Pickett, Brian K.; Cassen, Patrick; Durisen, Richard H.; Link, Robert

2000-02-01

In the paper ``The Effects of Thermal Energetics on Three-dimensional Hydrodynamic Instabilities in Massive Protostellar Disks. II. High-Resolution and Adiabatic Evolutions'' by Brian K. Pickett, Patrick Cassen, Richard H. Durisen, and Robert Link (ApJ, 529, 1034 [2000]), the wrong version of Figure 10 was published as a result of an error at the Press. The correct version of Figure 10 appears below. The Press sincerely regrets this error.

Centrifugally driven winds from protostellar accretion discs - I. Formulation and initial results

NASA Astrophysics Data System (ADS)

Nolan, C. A.; Salmeron, R.; Federrath, C.; Bicknell, G. V.; Sutherland, R. S.

2017-10-01

Protostellar discs play an important role in star formation, acting as the primary mass reservoir for accretion on to young stars and regulating the extent to which angular momentum and gas is released back into stellar nurseries through the launching of powerful disc winds. In this study, we explore how disc structure relates to the properties of the wind-launching region, mapping out the regions of protostellar discs where wind launching could be viable. We combine a series of 1.5D semi-analytic, steady-state, vertical disc-wind solutions into a radially extended 1+1.5D model, incorporating all three diffusion mechanisms (Ohm, Hall and ambipolar). We observe that the majority of mass outflow via disc winds occurs over a radial width of a fraction of an astronomical unit, with outflow rates attenuating rapidly on either side. We also find that the mass accretion rate, magnetic field strength and surface density profile each have significant effects on both the location of the wind-launching region and the ejection/accretion ratio \\dot{M}_out/\\dot{M}_in. Increasing either the accretion rate or the magnetic field strength corresponds to a shift of the wind-launching region to smaller radii and a decrease in \\dot{M}_out/\\dot{M}_in, while increasing the surface density corresponds to launching regions at larger radii with increased \\dot{M}_out/\\dot{M}_in. Finally, we discover a class of disc winds containing an ineffective launching configuration at intermediate radii, leading to two radially separated regions of wind launching and diminished \\dot{M}_out/\\dot{M}_in. We find that the wind locations and ejection/accretion ratio are consistent with current observational and theoretical estimates.

The molecular gas content of the Pipe Nebula. I. Direct evidence of outflow-generated turbulence in B59?

NASA Astrophysics Data System (ADS)

Duarte-Cabral, A.; Chrysostomou, A.; Peretto, N.; Fuller, G. A.; Matthews, B.; Schieven, G.; Davis, G. R.

2012-07-01

Context. Star forming regions may share many characteristics, but the specific interplay between gravity, magnetic fields, large-scale dynamics, and protostellar feedback will have an impact on the star formation history of each region. The importance of feedback from outflows is a particular subject to debate, as we are yet to understand the details of their impact on clouds and star formation. Aims: The Pipe Nebula is a nearby molecular cloud hosting the B59 region as its only active star-forming clump. This paper focuses on the global dynamics of B59, its temperature structure, and its outflowing gas, with the goal of revealing the local and global impact of the protostellar outflows. Methods: Using HARP at the James Clerk Maxwell Telescope, we have mapped the B59 region in the J = 3 → 2 transition of 12CO to study the kinematics and energetics of the outflows, and the same transitions of 13CO and C18O to study the overall dynamics of the ambient cloud, the physical properties of the gas, and the hierarchical structure of the region. Results: The B59 region has a total of ~30 M⊙ of cold and quiescent material, mostly gravitationally bound, with narrow line widths throughout. Such low levels of turbulence in the non-star-forming regions within B59 are indicative of the intrinsic initial conditions of the cloud. On the other hand, close to the protostars the impact of the outflows is observed as a localised increase of both C18O line widths from ~0.3 km s-1 to ~1 km s-1, and 13CO excitation temperatures by ~2-3 K. The impact of the outflows is also evident in the low column density material which shows signs of being shaped by the outflow bow shocks as they pierce their way out of the cloud. Much of this structure is readily apparent in a dendrogram analysis of the cloud and demonstrates that when decomposing clouds using such techniques a careful interpretation of the results is needed. Conclusions: The low mass of B59 together with its intrinsically quiescent gas and small number of protostars, allows the identification of specific regions where the outflows from the embedded sources interact the dense gas. Our study suggests that outflows are an important mechanism for injecting and sustaining supersonic turbulence at sub-parsec size scales. We find that less than half of the outflow energy is deposited as turbulent energy of the gas, however this turbulent energy is sufficient to slow down the collapse of the region.

THE MASSIVE PROTOSTELLAR CLUSTER NGC 6334I AT 220 au RESOLUTION: DISCOVERY OF FURTHER MULTIPLICITY, DIVERSITY, AND A HOT MULTI-CORE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brogan, C. L.; Hunter, T. R.; Indebetouw, R.

2016-12-01

We present Very Large Array and Atacama Large Millimeter/submillimeter Array imaging of the deeply embedded protostellar cluster NGC 6334I from 5 cm to 1.3 mm at angular resolutions as fine as 0.″17 (220 au). The dominant hot core MM1 is resolved into seven components at 1.3 mm, clustered within a radius of 1000 au. Four of the components have brightness temperatures >200 K, radii ∼300 au, minimum luminosities ∼10{sup 4} L {sub ⊙}, and must be centrally heated. We term this new phenomenon a “hot multi-core.” Two of these objects also exhibit compact free–free emission at longer wavelengths, consistent withmore » a hypercompact H ii region (MM1B) and a jet (MM1D). The spatial kinematics of the water maser emission centered on MM1D are consistent with it being the origin of the high-velocity bipolar molecular outflow seen in CO. The close proximity of MM1B and MM1D (440 au) suggests a proto-binary or a transient bound system. Several components of MM1 exhibit steep millimeter spectral energy distributions indicative of either unusual dust spectral properties or time variability. In addition to resolving MM1 and the other hot core (MM2) into multiple components, we detect five new millimeter and two new centimeter sources. Water masers are detected for the first time toward MM4A, confirming its membership in the protocluster. With a 1.3 mm brightness temperature of 97 K coupled with a lack of thermal molecular line emission, MM4A appears to be a highly optically thick 240  L {sub ⊙} dust core, possibly tracing a transient stage of massive protostellar evolution. The nature of the strongest water maser source CM2 remains unclear due to its combination of non-thermal radio continuum and lack of dust emission.« less

The Massive Protostellar Cluster NGC 6334I at 220 au Resolution: Discovery of Further Multiplicity, Diversity, and a Hot Multi-core

NASA Astrophysics Data System (ADS)

Brogan, C. L.; Hunter, T. R.; Cyganowski, C. J.; Chandler, C. J.; Friesen, R.; Indebetouw, R.

2016-12-01

We present Very Large Array and Atacama Large Millimeter/submillimeter Array imaging of the deeply embedded protostellar cluster NGC 6334I from 5 cm to 1.3 mm at angular resolutions as fine as 0.″17 (220 au). The dominant hot core MM1 is resolved into seven components at 1.3 mm, clustered within a radius of 1000 au. Four of the components have brightness temperatures >200 K, radii ˜300 au, minimum luminosities ˜104 L ⊙, and must be centrally heated. We term this new phenomenon a “hot multi-core.” Two of these objects also exhibit compact free-free emission at longer wavelengths, consistent with a hypercompact H II region (MM1B) and a jet (MM1D). The spatial kinematics of the water maser emission centered on MM1D are consistent with it being the origin of the high-velocity bipolar molecular outflow seen in CO. The close proximity of MM1B and MM1D (440 au) suggests a proto-binary or a transient bound system. Several components of MM1 exhibit steep millimeter spectral energy distributions indicative of either unusual dust spectral properties or time variability. In addition to resolving MM1 and the other hot core (MM2) into multiple components, we detect five new millimeter and two new centimeter sources. Water masers are detected for the first time toward MM4A, confirming its membership in the protocluster. With a 1.3 mm brightness temperature of 97 K coupled with a lack of thermal molecular line emission, MM4A appears to be a highly optically thick 240 L ⊙ dust core, possibly tracing a transient stage of massive protostellar evolution. The nature of the strongest water maser source CM2 remains unclear due to its combination of non-thermal radio continuum and lack of dust emission.

Laboratory formation of a scaled protostellar jet by coaligned poloidal magnetic field.

PubMed

Albertazzi, B; Ciardi, A; Nakatsutsumi, M; Vinci, T; Béard, J; Bonito, R; Billette, J; Borghesi, M; Burkley, Z; Chen, S N; Cowan, T E; Herrmannsdörfer, T; Higginson, D P; Kroll, F; Pikuz, S A; Naughton, K; Romagnani, L; Riconda, C; Revet, G; Riquier, R; Schlenvoigt, H-P; Skobelev, I Yu; Faenov, A Ya; Soloviev, A; Huarte-Espinosa, M; Frank, A; Portugall, O; Pépin, H; Fuchs, J

2014-10-17

Although bipolar jets are seen emerging from a wide variety of astrophysical systems, the issue of their formation and morphology beyond their launching is still under study. Our scaled laboratory experiments, representative of young stellar object outflows, reveal that stable and narrow collimation of the entire flow can result from the presence of a poloidal magnetic field whose strength is consistent with observations. The laboratory plasma becomes focused with an interior cavity. This gives rise to a standing conical shock from which the jet emerges. Following simulations of the process at the full astrophysical scale, we conclude that it can also explain recently discovered x-ray emission features observed in low-density regions at the base of protostellar jets, such as the well-studied jet HH 154. Copyright © 2014, American Association for the Advancement of Science.

Protostellar Disk Instabilities and the Formation of Substellar Companions

NASA Astrophysics Data System (ADS)

Pickett, Brian K.; Durisen, Richard H.; Cassen, Patrick; Mejia, Annie C.

2000-09-01

Recent numerical simulations of self-gravitating protostellar disks have suggested that gravitational instabilities can lead to the production of substellar companions. In these simulations, the disk is typically assumed to be locally isothermal; i.e., the initial, axisymmetric temperature in the disk remains everywhere unchanged. Such an idealized condition implies extremely efficient cooling for outwardly moving parcels of gas. While we have seen disk disruption in our own locally isothermal simulations of a small, massive protostellar disk, no long-lived companions formed as a result of the instabilities. Instead, thermal and tidal effects and the complex interactions of the disk material prevented permanent condensations from forming, despite the vigorous growth of spiral instabilities. In order to compare our results more directly with those of other authors, we here present three-dimensional evolutions of an older, larger, but less massive protostellar disk. We show that potentially long-lived condensations form only for the extreme of local isothermality, and then only when severe restrictions are placed on the natural tendency of the protostellar disk to expand in response to gravitational instabilities. A more realistic adiabatic evolution leads to vertical and radial expansion of the disk but no clump formation. We conclude that isothermal disk calculations cannot demonstrate companion formation by disk fragmentation but only suggest it at best. It will be necessary in future numerical work on this problem to treat the disk thermodynamics more realistically.

Peering to the Heart of Massive Star Birth - II. A Survey of 8 Protostars

NASA Astrophysics Data System (ADS)

Tan, Jonathan

2012-10-01

We propose to follow-up our SOFIA FORCAST Basic Science observation of G35.20-0.74 with similar observations of seven other massive protostars, with a total time request of about 5 hours. Our goal is to use mid-infrared (MIR) and far-infrared (FIR) imaging, especially at wavelengths of 31 and 37 microns that are unique to SOFIA, to constrain detailed radiative transfer models of massive star formation. In particular, we show that if massive stars are forming from high mass surface density cores, then the observed MIR and FIR morphologies are strongly influenced by the presence of protostellar outflow cavities. For typical surface densities of ~1 g cm^2, the observed radiation at wavelengths less than about 30 microns escapes preferentially along the near-facing outflow cavity. At longer wavelengths we begin to see emission from the far-facing cavity, and thus the proposed SOFIA FORCAST observations are particularly powerful for constraining the properties of the star-forming core such as the mass surface density in the immediate vicinity of the protostar. Our full analysis will involve comparing these SOFIA FORCAST data with images at other wavelengths, including Spitzer IRAC (3 to 8 microns), ground-based (10 & 20 microns) and Herschel (70 microns), to derive flux profiles and spectral energy distributions as a function of projected distance along the outflow axis. These observations have the potential to: (1) test basic scenarios of massive star formation; (2) begin to provide detailed measurements such as the mass surface density structure of massive star-forming cores and the line-of-sight orientation, opening angle, degree of symmetry and dust content of their outflow cavities. With a sample of eight protostars in total we will begin to be able to search for trends in these properties with core mass surface density and protostellar luminosity.

ALMA Observations of the Galactic Center: SiO Outflows and High Mass Star Formation Near Sgr A

NASA Technical Reports Server (NTRS)

Yusef-Zadeh, F.; Royster, M.; Wardle, M.; Arendt, R.; Bushouse, H.; Gillessen, S.; Lis, D.; Pound, M. W.; Roberts, D. A.; Whitney, B.;

Heating, Cooling, and Gravitational Instabilities in Protostellar and Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Pickett, B. K.; Mejia, A. C.; Durisen, R. H.

2001-12-01

We present three-dimensional hydrodynamic simulations of protostellar disk models, in order to explore how the interplay between heating and cooling regulates significant gravitational instabilities. Artificial viscosity is used to treat irreversible heating, such as would occur in shocks; volumetric cooling at several different rates is also applied throughout a broad radial region of the disk. We study the evolution of a disk that is already unstable (due to the low value of the Toomre Q parameter), and a marginally unstable disk that is cooled towards instability. The evolutions have implications for the transport of mass and angular momentum in protostellar disks, the effects of gravitational instabilities on the vertical structure of the disks, and the formation of stellar and substellar companions on dynamic time scales due to disk instabilties. This work is supported by grants from the NASA Planetary Geology and Geophysics and Origins of Solar Systems Programs.

X-ray insights into star and planet formation.

PubMed

Feigelson, Eric D

2010-04-20

Although stars and planets form in cold environments, X-rays are produced in abundance by young stars. This review examines the implications of stellar X-rays for star and planet formation studies, highlighting the contributions of NASA's (National Aeronautics and Space Administration) Chandra X-ray Observatory. Seven topics are covered: X-rays from protostellar outflow shocks, X-rays from the youngest protostars, the stellar initial mass function, the structure of young stellar clusters, the fate of massive stellar winds, X-ray irradiation of protoplanetary disks, and X-ray flare effects on ancient meteorites. Chandra observations of star-forming regions often show dramatic star clusters, powerful magnetic reconnection flares, and parsec-scale diffuse plasma. X-ray selected samples of premain sequence stars significantly advance studies of star cluster formation, the stellar initial mass function, triggered star-formation processes, and protoplanetary disk evolution. Although X-rays themselves may not play a critical role in the physics of star formation, they likely have important effects on protoplanetary disks by heating and ionizing disk gases.

X-ray insights into star and planet formation

PubMed Central

Feigelson, Eric D.

2010-01-01

Although stars and planets form in cold environments, X-rays are produced in abundance by young stars. This review examines the implications of stellar X-rays for star and planet formation studies, highlighting the contributions of NASA’s (National Aeronautics and Space Administration) Chandra X-ray Observatory. Seven topics are covered: X-rays from protostellar outflow shocks, X-rays from the youngest protostars, the stellar initial mass function, the structure of young stellar clusters, the fate of massive stellar winds, X-ray irradiation of protoplanetary disks, and X-ray flare effects on ancient meteorites. Chandra observations of star-forming regions often show dramatic star clusters, powerful magnetic reconnection flares, and parsec-scale diffuse plasma. X-ray selected samples of premain sequence stars significantly advance studies of star cluster formation, the stellar initial mass function, triggered star-formation processes, and protoplanetary disk evolution. Although X-rays themselves may not play a critical role in the physics of star formation, they likely have important effects on protoplanetary disks by heating and ionizing disk gases. PMID:20404197

Uncovering the Protostars in Serpens South with ALMA: Continuum Sources and Their Outflow Activity

NASA Astrophysics Data System (ADS)

Plunkett, Adele; Arce, H.; Corder, S.; Dunham, M.

2017-06-01

Serpens South is an appealing protostellar cluster to study due the combination of several factors: (1) a high protostar fraction that shows evidence for very recent and ongoing star formation; (2) iconic clustered star formation along a filamentary structure; (3) its relative proximity within a few hundred parsecs. An effective study requires the sensitivity, angular and spectral resolution, and mapping capabilities recently provided with ALMA. Here we present a multi-faceted data set acquired from Cycles 1 through 3 with ALMA, including maps of continuum sources and molecular outflows throughout the region, as well as a more focused kinematical study of the protostar that is the strongest continuum source at the cluster center. Together these data span spatial scales over several orders of magnitude, allowing us to investigate the outflow-driving sources and the impact of the outflows on the cluster environment. Currently, we focus on the census of protostars in the cluster center, numbering about 20, including low-flux, low-mass sources never before detected in mm-wavelengths and evidence for multiplicity that was previously unresolved.

Water in embedded low-mass protostars: cold envelopes and warm outflows

NASA Astrophysics Data System (ADS)

Kristensen, Lars E.; van Dishoeck, Ewine; Mottram, Joseph; Schmalzl, Markus; Visser, Ruud

2015-08-01

As stars form, gas from the parental cloud is transported through the molecular envelope to the protostellar disk from which planets eventually form. Water plays a crucial role in such systems: it forms the backbone of the oxygen chemistry, it is a unique probe of warm and hot gas, and it provides a unique link between the grain surface and gas-phase chemistries. The distribution of water, both as ice and gas, is a fundamental question to our understanding of how planetary systems, such as the Solar System, form.The Herschel Space Observatory observed many tens of embedded low-mass protostars in a suite of gas-phase water transitions in several programs (e.g. Water in Star-forming regions with Herschel, WISH, and the William Herschel Line Legacy Survey, WILL), and related species (e.g. CO in Protostars with HIFI, COPS-HIFI). I will summarize what Herschel has revealed about the water distribution in the cold outer molecular envelope of low-mass protostars, and the warm gas in outflows, the two components predominantly traced by Herschel observations. I will present our current understanding of where the water vapor is in protostellar systems and the underlying physical and chemical processes leading to this distribution. Through these dedicated observational surveys and complementary modeling efforts, we are now at a stage where we can quantify where the water is during the early stages of star formation.

High-sensitivity survey of a pole-on disk-jet system around high mass YSOs

NASA Astrophysics Data System (ADS)

Motogi, Kazuhito; Walsh, Andrew; Hirota, Tomoya; Niinuma, Kotaro; Sugiyama, Koichiro; Fujisawa, Kenta; Yonekura, Yoshinori; Honma, Mareki; Sorai, Kazuo

2013-10-01

Recent theoretical works have suggested that detailed evolution of a high mass protostellar object highly depends on effective accretion rate and exact accretion geometry. Observational studies of the innermost accretion properties are, thus, an essential task in the ALMA era. High mass protostellar objects with a pole-on disk-jet system are, hence, excellent targets for such a study, since an outflow cavity reduces the total optical depth along the line-of-sight. Our previous studies have shown that some singular water maser sources called dominant blue-shifted masers (DBSMs) are plausible candidates of pole-on disk jet systems. There are, however, still two major problems as follows, (1) Some DBSMs can be a "fake", because of the significant variability of water masers. (2) It is difficult to verify the sources are really in pole-on geometry. The first problems can be checked with the thermal counterparts, and the second problem can be tested by morphologies of the class II CH3OH maser sources. We propose a high-sensitivity survey of real “pole-on” disk-jet systems towards the southern ten DBSMs. This new survey consists of multi-band observations between C/X/K/W bands. We will start from the C/X-continuum survey in this semester. Scientific goals in this semester are, (1) surveying radio jet activities with the C/X continuum emission, (2) estimating the inclination angle of disk-jet systems based on the morphologies of the CH3OH maser spots. (3) determining the exact positions of driving sources.

Nitrogen oxide in protostellar envelopes and shocks: the ASAI survey

NASA Astrophysics Data System (ADS)

Codella, C.; Viti, S.; Lefloch, B.; Holdship, J.; Bachiller, R.; Bianchi, E.; Ceccarelli, C.; Favre, C.; Jiménez-Serra, I.; Podio, L.; Tafalla, M.

2018-03-01

The high sensitivity of the IRAM 30-m Astrochemical Surveys At IRAM (ASAI) unbiased spectral survey in the mm window allows us to detect NO emission towards both the Class I object SVS13-A and the protostellar outflow shock L1157-B1. We detect the hyperfine components of the 2Π1/2J = 3/2 → 1/2 (at 151 GHz) and the 2Π1/2J = 5/2 → 3/2 (at 250 GHz) spectral pattern. The two objects show different NO profiles: (i) SVS13-A emits through narrow (1.5 km s-1) lines at the systemic velocity, while (ii) L1157-B1 shows broad (˜5 km s-1) blueshifted emission. For SVS13-A, the analysis leads to Tex ≥ 4 K, N(NO) ≤ 3 × 1015 cm-2, and indicates the association of NO with the protostellar envelope. In L1157-B1, NO is tracing the extended outflow cavity: Tex ≃ 4-5 K, and N(NO) = 5.5 ± 1.5 × 1015 cm-2. Using C18O, 13C18O, C17O, and 13C17O ASAI observations, we derive an NO fractional abundance less than ˜10-7 for the SVS13-A envelope, in agreement with previous measurements towards extended photodissociation regions (PDRs) and prestellar objects. Conversely, a definite X(NO) enhancement is measured towards L1157-B1, ˜6 × 10-6, showing that the NO production increases in shocks. The public code UCLCHEM was used to interpret the NO observations, confirming that the abundance observed in SVS13-A can be attained in an envelope with a gas density of 105 cm-3 and a kinetic temperature of 40 K. The NO abundance in L1157-B1 is reproduced with pre-shock densities of 105 cm-3 subjected to a ˜45 km s-1 shock.

Episodic accretion in binary protostars emerging from self-gravitating solar mass cores

NASA Astrophysics Data System (ADS)

Riaz, R.; Vanaverbeke, S.; Schleicher, D. R. G.

2018-06-01

Observations show a large spread in the luminosities of young protostars, which are frequently explained in the context of episodic accretion. We tested this scenario with numerical simulations that follow the collapse of a solar mass molecular cloud using the GRADSPH code, thereby varying the strength of the initial perturbations and temperature of the cores. A specific emphasis of this paper is to investigate the role of binaries and multiple systems in the context of episodic accretion and to compare their evolution to the evolution in isolated fragments. Our models form a variety of low-mass protostellar objects including single, binary, and triple systems in which binaries are more active in exhibiting episodic accretion than isolated protostars. We also find a general decreasing trend in the average mass accretion rate over time, suggesting that the majority of the protostellar mass is accreted within the first 105 years. This result can potentially help to explain the surprisingly low average luminosities in the majority of the protostellar population.

On the diversity and statistical properties of protostellar discs

NASA Astrophysics Data System (ADS)

Bate, Matthew R.

2018-04-01

We present results from the first population synthesis study of protostellar discs. We analyse the evolution and properties of a large sample of protostellar discs formed in a radiation hydrodynamical simulation of star cluster formation. Due to the chaotic nature of the star formation process, we find an enormous diversity of young protostellar discs, including misaligned discs, and discs whose orientations vary with time. Star-disc interactions truncate discs and produce multiple systems. Discs may be destroyed in dynamical encounters and/or through ram-pressure stripping, but reform by later gas accretion. We quantify the distributions of disc mass and radii for protostellar ages up to ≈105 yr. For low-mass protostars, disc masses tend to increase with both age and protostellar mass. Disc radii range from of order 10 to a few hundred au, grow in size on time-scales ≲ 104 yr, and are smaller around lower mass protostars. The radial surface density profiles of isolated protostellar discs are flatter than the minimum mass solar nebula model, typically scaling as Σ ∝ r-1. Disc to protostar mass ratios rarely exceed two, with a typical range of Md/M* = 0.1-1 to ages ≲ 104 yr and decreasing thereafter. We quantify the relative orientation angles of circumstellar discs and the orbit of bound pairs of protostars, finding a preference for alignment that strengths with decreasing separation. We also investigate how the orientations of the outer parts of discs differ from the protostellar and inner disc spins for isolated protostars and pairs.

From protostellar to pre-main-sequence evolution

NASA Astrophysics Data System (ADS)

D'Antona, F.

I summarize the status of pre-main-sequence evolutionary tracks starting from the first steps dating back to the concept of Hayashi track. Understanding of the dynamical protostellar phase in the vision of Palla & Stahler, who introduced the concept of the deuterium burning thermostat and of stellar birthline, provided for a long time a link between the dynamical and hydrostatic evolution. Disk accretion however changed considerably the view, but re-introducing some ambiguities which must still be solved. The limitations and uncertainties in the mass and age determination from models for young stellar objects are summarized, but the burning of light elements is still a powerful observational signature.

MOLECULAR OUTFLOWS FROM THE PROTOCLUSTER SERPENS SOUTH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakamura, Fumitaka; Higuchi, Aya; Sugitani, Kohji

2011-08-20

We present the results of CO (J = 3-2) and HCO{sup +} (J = 4-3) mapping observations toward a nearby embedded cluster, Serpens South, using the ASTE 10 m telescope. Our CO (J = 3-2) map reveals that many outflows are crowded in the dense cluster-forming clump that can be recognized as an HCO{sup +} clump with a size of {approx}0.2 pc and mass of {approx}80 M{sub sun}. The clump contains several subfragments with sizes of {approx}0.05 pc. By comparing the CO (J = 3-2) map with the 1.1 mm dust continuum image taken by AzTEC on ASTE, we findmore » that the spatial extents of the outflow lobes are sometimes anti-correlated with the distribution of the dense gas, and some of the outflow lobes apparently collide with the dense gas. The total outflow mass, momentum, and energy are estimated to be 0.6 M{sub sun}, 8 M{sub sun} km s{sup -1}, and 64 M{sub sun} km{sup 2} s{sup -2}, respectively. The energy injection rate due to the outflows is comparable to the turbulence dissipation rate in the clump, implying that the protostellar outflows can maintain the supersonic turbulence in this region. The total outflow energy seems only about 10% of the clump gravitational energy. We conclude that the current outflow activity is not enough to destroy the whole cluster-forming clump, and therefore star formation is likely to continue for several or many local dynamical times.« less

HELICAL MAGNETIC FIELDS IN THE NGC 1333 IRAS 4A PROTOSTELLAR OUTFLOWS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ching, Tao-Chung; Lai, Shih-Ping; Zhang, Qizhou

We present Submillimeter Array polarization observations of the CO J = 3–2 line toward NGC 1333 IRAS 4A. The CO Stokes I maps at an angular resolution of ∼1″ reveal two bipolar outflows from the binary sources of NGC 1333 IRAS 4A. The kinematic features of the CO emission can be modeled by wind-driven outflows at ∼20° inclined from the plane of the sky. Close to the protostars the CO polarization, at an angular resolution of ∼2.″3, has a position angle approximately parallel to the magnetic field direction inferred from the dust polarizations. The CO polarization direction appears to vary smoothly frommore » an hourglass field around the core to an arc-like morphology wrapping around the outflow, suggesting a helical structure of magnetic fields that inherits the poloidal fields at the launching point and consists of toroidal fields at a farther distance of outflow. The helical magnetic field is consistent with the theoretical expectations for launching and collimating outflows from a magnetized rotating disk. Considering that the CO polarized emission is mainly contributed from the low-velocity and low-resolution data, the helical magnetic field is likely a product of the wind–envelope interaction in the wind-driven outflows. The CO data reveal a PA of ∼30° deflection in the outflows. The variation in the CO polarization angle seems to correlate with the deflections. We speculate that the helical magnetic field contributes to ∼10° deflection of the outflows by means of Lorentz force.« less

The Reel Deal In 3D: The Spatio-Temporal Evolution of YSO Jets

NASA Astrophysics Data System (ADS)

Frank, Adam

2014-10-01

Jets are a ubiquitous phenomena in astrophysics, though in most cases their central engines are unresolvable. Thus the structure of the jets often acts as a proxy for understanding the objects creating them. Jets are also of interest in their own right, serving as critical examples of rapidly evolving astrophysical magnetized plasma systems. And while millions of CPU hours {at least} have been spent simulating the kinds of astrophysical plasma dynamics that occur routinely in jets, we rarely have had the chance to study their real-time evolution. In this proposal we seek to use a unique multi-epoch HST dataset of protostellar jets to carry forward an innovative theoretical, numerical and laboratory-based study of magnetized outflows and the plasma processes which determine their evolution. Our work will make direct and detailed contact with these HST data sets and will articulate newly-observed features of jet dynamics that have not been possible to explore before. Using numerical simulations and laboratory plasma studies we seek to articulate the full 3-D nature of new behaviors seen in the HST data. Our collaboration includes the use of scaled laboratory plasma experiments with hypersonic magnetized radiative jets. The MHD experiments have explored how jets break up into clumps via kink-mode instabilities. Therefore such experiments are directly relevant to the initial conditions in our models.

VLA Ammonia Observations of IRAS 16253-2429: A Very Young and Low Mass Protostellar System

NASA Technical Reports Server (NTRS)

Wiseman, Jennifer J.

2011-01-01

IRAS l6253-2429. the source of the Wasp-Waist Nebula seen in Spitzer IRAC images, is an isolated very low luminosity ("VeLLO") Class 0 protostar in the nearby rho Ophiuchi cloud. We present VLA ammonia mapping observations of the dense gas envelope feeding the central core accreting system. We find a flattened envelope perpendicular to the outflow axis, and gas cavities that appear to cradle the outflow lobes as though carved out by the flow and associated (apparently precessing) jet. Based on the NH3 (1,1) and (2,2) emission distribution, we derive the mass, velocity fields and temperature distribution for the envelope. We discuss the combined evidence for this source as possibly one of the youngest and lowest mass sources in formation yet known.

A precessing jet in the NGC2264G outflow

NASA Astrophysics Data System (ADS)

McCoey, Carolyn; Teixeira, P. S.; Fich, M.; Lada, C. J.

2007-05-01

We present new infrared imaging of the NGC 2264 G protostellar outflow region, obtained with the Spitzer Space Telescope. A jet in the red (eastern) outflow lobe is clearly detected in all four IRAC bands and, for the first time, is shown to continuously extend over the entire length of the red outflow lobe, as traced by CO observations. The jet also extends to a deeply embedded Class 0 source, VLA2, confirming previous suggestions that it is the driving source of the outflow. The images show that the easternmost part of the jet exhibits what appears to be multiple changes of direction. We consider two possible explanations for the jet morphology: (i) deflection of the jet off the walls of the outflow lobes as proposed by Fich & Lada (1997) and (ii) precession. The jet structure shown in the IRAC images can be largely, although not entirely, explained by a slowly precessing jet (period 8000 yr) that lies mostly on the plane of the sky. In either case it appears that the observed and inferred changes in the jet direction are sufficient to broaden the NGC 2264 G outflow to an extent comparable to that observed in the CO emission. P. S. T. acknowledges support from the scholarship SFRH/BD/13984/2003 awarded by the Fundaçao para a Ciencia e Tecnologia (Portugal). Both M. F. and C. M. are supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wolf-Chase, Grace; Arvidsson, Kim; Smutko, Michael, E-mail: gwolfchase@adlerplanetarium.org

We present the results of a narrow-band near-infrared imaging survey for Molecular Hydrogen emission-line Objects (MHOs) toward 26 regions containing high-mass protostellar candidates and massive molecular outflows. We have detected a total of 236 MHOs, 156 of which are new detections, in 22 out of the 26 regions. We use H{sub 2} 2.12 μ m/H{sub 2} 2.25 μ m flux ratios, together with morphology, to separate the signatures of fluorescence associated with photo-dissociation regions (PDRs) from shocks associated with outflows in order to identify the MHOs. PDRs have typical low flux ratios of ∼1.5–3, while the vast majority of MHOsmore » display flux ratios typical of C-type shocks (∼6–20). A few MHOs exhibit flux ratios consistent with expected values for J-type shocks (∼3–4), but these are located in regions that may be contaminated with fluorescent emission. Some previously reported MHOs have low flux ratios, and are likely parts of PDRs rather than shocks indicative of outflows. We identify a total of 36 outflows across the 22 target regions where MHOs were detected. In over half these regions, MHO arrangements and fluorescent structures trace features present in CO outflow maps, suggesting that the CO emission traces a combination of dynamical effects, which may include gas entrained in expanding PDRs as well as bipolar outflows. Where possible, we link MHO complexes to distinct outflows and identify candidate driving sources.« less

Revolution evolution: tracing angular momentum during star and planetary system formation

NASA Astrophysics Data System (ADS)

Davies, Claire Louise

2015-04-01

Stars form via the gravitational collapse of molecular clouds during which time the protostellar object contracts by over seven orders of magnitude. If all the angular momentum present in the natal cloud was conserved during collapse, stars would approach rotational velocities rapid enough to tear themselves apart within just a few Myr. In contrast to this, observations of pre-main sequence rotation rates are relatively slow (∼ 1 - 15 days) indicating that significant quantities of angular momentum must be removed from the star. I use observations of fully convective pre-main sequence stars in two well-studied, nearby regions of star formation (namely the Orion Nebula Cluster and Taurus-Auriga) to determine the removal rate of stellar angular momentum. I find the accretion disc-hosting stars to be rotating at a slower rate and contain less specific angular momentum than the disc-less stars. I interpret this as indicating a period of accretion disc-regulated angular momentum evolution followed by near-constant rotational evolution following disc dispersal. Furthermore, assuming that the age spread inferred from the Hertzsprung-Russell diagram constructed for the star forming region is real, I find that the removal rate of angular momentum during the accretion-disc hosting phase to be more rapid than that expected from simple disc-locking theory whereby contraction occurs at a fixed rotation period. This indicates a more efficient process of angular momentum removal must operate, most likely in the form of an accretion-driven stellar wind or outflow emanating from the star-disc interaction. The initial circumstellar envelope that surrounds a protostellar object during the earliest stages of star formation is rotationally flattened into a disc as the star contracts. An effective viscosity, present within the disc, enables the disc to evolve: mass accretes inwards through the disc and onto the star while momentum migrates outwards, forcing the outer regions of the disc to expand. I used spatially resolved submillimetre detections of the dust and gas components of protoplanetary discs, gathered from the literature, to measure the radial extent of discs around low-mass pre-main sequence stars of ∼ 1-10 Myr and probe their viscous evolution. I find no clear observational evidence for the radial expansion of the dust component. However, I find tentative evidence for the expansion ofthe gas component. This suggests that the evolution of the gas and dust components of protoplanetary discs are likely governed by different astrophysical processes. Observations of jets and outflows emanating from protostars and pre-main sequence stars highlight that it may also be possible to remove angular momentum from the circumstellar material. Using the sample of spatially resolved protoplanetary discs, I find no evidence for angular momentum removal during disc evolution. I also use the spatially resolved debris discs from the Submillimetre Common-User Bolometer Array-2 Observations of Nearby Stars survey to constrain the amount of angular momentum retained within planetary systems. This sample is compared to the protoplanetary disc angular momenta and to the angular momentum contained within pre-stellar cores. I find that significant quantities of angular momentum must be removed during disc formation and disc dispersal. This likely occurs via magnetic braking during the formation of the disc, via the launching of a disc or photo-evaporative wind, and/or via ejection of planetary material following dynamical interactions.

Water in star-forming regions with Herschel (WISH). V. The physical conditions in low-mass protostellar outflows revealed by multi-transition water observations

NASA Astrophysics Data System (ADS)

Mottram, J. C.; Kristensen, L. E.; van Dishoeck, E. F.; Bruderer, S.; San José-García, I.; Karska, A.; Visser, R.; Santangelo, G.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; van Kempen, T. A.; Liseau, R.; Nisini, B.; Tafalla, M.; van der Tak, F. F. S.; Wyrowski, F.

2014-12-01

Context. Outflows are an important part of the star formation process as both the result of ongoing active accretion and one of the main sources of mechanical feedback on small scales. Water is the ideal tracer of these effects because it is present in high abundance for the conditions expected in various parts of the protostar, particularly the outflow. Aims: We constrain and quantify the physical conditions probed by water in the outflow-jet system for Class 0 and I sources. Methods: We present velocity-resolved Herschel HIFI spectra of multiple water-transitions observed towards 29 nearby Class 0/I protostars as part of the WISH guaranteed time key programme. The lines are decomposed into different Gaussian components, with each component related to one of three parts of the protostellar system; quiescent envelope, cavity shock and spot shocks in the jet and at the base of the outflow. We then use non-LTE radex models to constrain the excitation conditions present in the two outflow-related components. Results: Water emission at the source position is optically thick but effectively thin, with line ratios that do not vary with velocity, in contrast to CO. The physical conditions of the cavity and spot shocks are similar, with post-shock H2 densities of order 105 - 108 cm-3 and H2O column densities of order 1016 - 1018 cm-2. H2O emission originates in compact emitting regions: for the spot shocks these correspond to point sources with radii of order 10-200 AU, while for the cavity shocks these come from a thin layer along the outflow cavity wall with thickness of order 1-30 AU. Conclusions: Water emission at the source position traces two distinct kinematic components in the outflow; J shocks at the base of the outflow or in the jet, and C shocks in a thin layer in the cavity wall. The similarity of the physical conditions is in contrast to off-source determinations which show similar densities but lower column densities and larger filling factors. We propose that this is due to the differences in shock properties and geometry between these positions. Class I sources have similar excitation conditions to Class 0 sources, but generally smaller line-widths and emitting region sizes. We suggest that it is the velocity of the wind driving the outflow, rather than the decrease in envelope density or mass, that is the cause of the decrease in H2O intensity between Class 0 and I sources. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.orgReduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A21

Dynamical evolution of young binaries and multiple systems

NASA Astrophysics Data System (ADS)

Reipurth, B.

Most stars, and perhaps all, are born in small multiple systems whose components interact, leading to chaotic dynamic behavior. Some components are ejected, either into distant orbits or into outright escapes, while the remaining components form temporary and eventually permanent binary systems. More than half of all such breakups of multiple systems occur during the protostellar phase, leading to the occasional ejection of protostars outside their nascent cloud cores. Such orphaned protostars are observed as wide companions to embedded protostars, and thus allow the direct study of protostellar objects. Dynamic interactions during early stellar evolution explain the shape and enormous width of the separation distribution function of binaries, from close spectroscopic binaries to the widest binaries.

The Wasp-Waist Nebula: VLA Ammonia Observations of the Molecular Core Envelope In a Unique Class 0 Protostellar System

NASA Technical Reports Server (NTRS)

Wiseman, Jennifer

2010-01-01

The Wasp-Waist Nebula was discovered in the IRAC c2d survey of the Ophiuchus starforming clouds. It is powered by a well-isolated, low-luminosity, low-mass Class 0 object. Its weak outflow has been mapped in the CO (3-2) transition with the JCMT, in 2.12 micron H2 emission with WIRC (the Wide-Field Infrared Camera) on the Hale 5-meter, and, most recently, in six H2 mid-infrared lines with the IRS (InfraRed Spectrograph) on-board the Spitzer Space Telescope; possible jet twisting structure may be evidence of unique core dynamics. Here, we report results of recent VLA ammonia mapping observations of the dense gas envelope feeding the central core protostellar system. We describe the morphology, kinematics, and angular momentum characteristics of this unique system. The results are compared with the envelope structure deduced from IRAC 8-micron absorption of the PAH (polycyclic aromatic hydrocarbon) background emission from the cloud.

IRAS01202+6133: A Possible Case of Protostellar Collapse Triggered by a Small HIIRegion

NASA Astrophysics Data System (ADS)

Kang, Sung-Ju; Kerton, C.

2012-01-01

The molecular gas surrounding an HII region is thought to be a place where star formation can be induced. One of the main questions in the study of star formation is how protostars accrete material from their parent molecular clouds and observations of infall motions are needed to provide direct evidence for accretion. This poster will present an analysis of submm spectroscopic observations of the submm/infrared source IRAS 01202+6133 located on the periphery of the HII region KR 120. HCO+(J=3-2) spectra of this source show a classic blue-dominated double-peaked profile indicative of infall motions that would be expected to occur in the envelope surrounding a young protostellar object. The HCO+ spectrum toward the core was fitted using models incorporating both outflow and infall components along with basic assumptions regarding excitation temperature trends within molecular cloud cores. Using the models, we derive physical properties of the infall kinematics and the envelope structure.

IRAS 01202+6133 : A Possible Case of Protostellar Collapse Triggered by a Small HII Region

NASA Astrophysics Data System (ADS)

Kang, Sung-Ju; Kerton, C.

2012-01-01

The molecular gas surrounding an HII region is thought to be a place where star formation can be induced. One of the main questions in the study of star formation is how protostars accrete material from their parent molecular clouds and observations of infall motions are needed to provide direct evidence for accretion. This poster will present an analysis of submm spectroscopic observations of the submm/infrared source IRAS 01202+6133 located on the periphery of the HII region KR 120. HCO+(J=3-2) spectra of this source show a classic blue-dominated double-peaked profile indicative of infall motions that would be expected to occur in the envelope surrounding a young protostellar object. The HCO+ spectrum toward the core was fitted using models incorporating both outflow and infall components along with basic assumptions regarding excitation temperature trends within molecular cloud cores. Using the models, we derive physical properties of the infall kinematics and the envelope structure.

TRACING INFALL AND ROTATION ALONG THE OUTFLOW CAVITY WALLS OF THE L483 PROTOSTELLAR ENVELOPE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leung, Gigi Y.C.; Lim, Jeremy; Takakuwa, Shigehisa

2016-12-10

Single-dish observations in CS(7–6) reveal emission extending out to thousands of au along the outflow axis of low-mass protostars and having a velocity gradient in the opposite direction to that of their outflows. This emission has been attributed to dense and warm gas flowing outward along the walls of bipolar outflow cavities. Here, we present combined single-dish and interferometric CS(7–6) maps for the low-mass protostar L483, revealing a newly discovered compact central component (radius ≲800 au) and previously unknown features in its extended component (visible out to ∼4000 au). The velocity gradient and skewed (toward the redshifted side) brightness distributionmore » of the extended component are detectable out to a radius of ∼2000 au, but not beyond. The compact central component exhibits a velocity gradient in the same direction as, but which is steeper than that of, the extended component. Furthermore, both components exhibit a velocity gradient with an approximately constant magnitude across the outflow axis, apparent in the extended component not just through but also away from the center out to 2000 au. We point out contradictions between our results and model predictions for outflowing gas and propose a new model in which all of the aforementioned emission can be qualitatively explained by gas inflowing along the outflow cavity walls of a rigidly rotating envelope. Our model also can explain the extended CS(7–6) emission observed around other low-mass protostars.« less

Studying the outflow-core interaction with ALMA Cycle 1 observations of the HH 46/47 molecular outflow

NASA Astrophysics Data System (ADS)

Zhang, Yichen; Arce, Hector G.; Mardones, Diego; Dunham, Michael; Garay, Guido; Noriega-Crespo, Alberto; Corder, Stuartt; Offner, Stella; Cabrit, Sylvie

2016-01-01

We present ALMA Cycle 1 observations of the HH 46/47 molecular outflow which is driven by a low-mass Class 0/I protostar. Previous ALMA Cycle 0 12CO observation showed outflow cavities produced by the entrainment of ambient gas by the protostellar jet and wide-angle wind. Here we present analysis of observation of 12CO, 13CO, C18O and other species using combined 12m array and ACA observations. The improved angular resolution and sensitivity allow us to detect details of the outflow structure. Specially, we see that the outflow cavity wall is composed of two or more layers of outflowing gas, which separately connect to different shocked regions along the outflow axis inside the cavity, suggesting the outflow cavity wall is composed of multiple shells entrained by a series of jet bow-shock events. The new 13CO and C18O data also allow us to trace relatively denser and slower outflow material than that traced by the 12CO. These species are only detected within about 1 to 2 km/s from the cloud velocity, tracing the outflow to lower velocities than what is possible using only the 12CO emission. Interestingly, the cavity wall of the red lobe appears at very low outflow velocities (as low as ~0.2 km/s). In addition, 13CO and C18O allow us to correct for the CO optical depth, allowing us to obtain more accurate estimates of the outflow mass, momentum and kinetic energy. Applying the optical depth correction significantly increases the previous mass estimate by a factor of 14. The outflow kinetic energy distribution shows that even though the red lobe is mainly entrained by jet bow-shocks, most of the outflow energy is being deposited into the cloud at the base of the outflow cavity rather than around the heads of the bow shocks. The estimated total mass, momentum, and energy of the outflow indicate that the outflow has the ability to disperse the parent core. We found possible evidence for a slowly moving rotating outflow in CS. Our 13CO and C18O observations also trace a circumstellar envelope with both rotation and infall motions.

AN EXPLORATION OF THE STATISTICAL SIGNATURES OF STELLAR FEEDBACK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyden, Ryan D.; Offner, Stella S. R.; Koch, Eric W.

2016-12-20

All molecular clouds are observed to be turbulent, but the origin, means of sustenance, and evolution of the turbulence remain debated. One possibility is that stellar feedback injects enough energy into the cloud to drive observed motions on parsec scales. Recent numerical studies of molecular clouds have found that feedback from stars, such as protostellar outflows and winds, injects energy and impacts turbulence. We expand upon these studies by analyzing magnetohydrodynamic simulations of molecular clouds, including stellar winds, with a range of stellar mass-loss rates and magnetic field strengths. We generate synthetic {sup 12}CO(1–0) maps assuming that the simulations aremore » at the distance of the nearby Perseus molecular cloud. By comparing the outputs from different initial conditions and evolutionary times, we identify differences in the synthetic observations and characterize these using common astrostatistics. We quantify the different statistical responses using a variety of metrics proposed in the literature. We find that multiple astrostatistics, including the principal component analysis, the spectral correlation function, and the velocity coordinate spectrum (VCS), are sensitive to changes in stellar mass-loss rates and/or time evolution. A few statistics, including the Cramer statistic and VCS, are sensitive to the magnetic field strength. These findings demonstrate that stellar feedback influences molecular cloud turbulence and can be identified and quantified observationally using such statistics.« less

The HIFI spectral survey of massive star-forming region AFGL 2591

NASA Astrophysics Data System (ADS)

Kazmierczak, Maja; van der Tak, Floris; Helmich, Frank; Chvarria, Luis; Wang, Kuo-Song; Ceccarelli, Cecilia

2013-07-01

AFGL 2591 is a massive protostellar object with a bipolar outflow. It has been widely studied before since it is a relatively isolated and nearby star-forming region. Here we present an overview of the Herschel/HIFI spectral survey, as a part of CHESS Key Project. The survey covers a frequency range from 480 up to 1240 GHz as well as some particular lines from 1267 to 1901 GHz. From the spectral survey a total of 32 species were identified. The data analysis is divided into various families of molecules, eg. CO and its isotopologues, nitrogen-bearing molecules, sulfur-bearing species, organic molecules. We will discuss different types of observed molecules and their physical parameters. The radial abundance profiles of some molecules will be presented to learn about the chemical processes leading to their formation and destruction. One of the studied molecule is ammonia, which is concentrated in the inner part of the protostellar envelope (when T > 100K i.e. where water ice evaporates), with the abundance of 3x10e-7.

A movie of accretion/ejection of material in a high-mass YSO in Orion BN/KL at radii comparable to the Solar System

NASA Astrophysics Data System (ADS)

Goddi, C.; Greenhill, L.; Humphreys, E.; Matthews, L.; Chandler, C.

2010-11-01

Around high-mass Young Stellar Objects (YSOs), outflows are expected to be launched and collimated by accretion disks inside radii of 100 AU. Strong observational constraints on disk-mediated accretion in this context have been scarce, largely owing to difficulties in probing the circumstellar gas at scales 10-100 AU around high-mass YSOs, which are on average distant (>1 Kpc), form in clusters, and ignite quickly whilst still enshrouded in dusty envelopes. Radio Source I in Orion BN/KL is the nearest example of a high-mass YSO, and only one of three YSOs known to power SiO masers. Using VLA and VLBA observations of different SiO maser transitions, the KaLYPSO project (http://www.cfa.harvard.edu/kalypso/) aims to overcome past observational limitations by mapping the structure, 3-D velocity field, and dynamical evolution of the circumstellar gas within 1000 AU from Source I. Based on 19 epochs of VLBA observations of v=1,2 SiO masers over ~2 years, we produced a movie of bulk gas flow tracing the compact disk and the base of the protostellar wind at radii < 100 AU from Source I. In addition, we have used the VLA to map 7mm SiO v=0 emission and track proper motions over 10 years. We identify a narrowly collimated outflow with a mean motion of 18 km/s at radii 100-1000 AU, along a NE-SW axis perpendicular to that of the disk traced by the v=1,2 masers. The VLBA and VLA data exclude alternate models that place outflow from Source I along a NW-SE axis. The analysis of the complete (VLBA and VLA) dataset provides the most detailed evidence to date that high-mass star formation occurs via disk-mediated accretion.

Protostellar collapse in a self-gravitating sheet

NASA Technical Reports Server (NTRS)

Hartmann, Lee; Boss, Alan; Calvet, Nuria; Whitney, Barbara

1994-01-01

We present preliminary calculations of protostellar cloud collapse starting from an isothermal, self-gravitating gaseous layer in hydrostatic equilibrium. This gravitationally unstable layer collapses into a flattened or toroidal density distribution, even in the absence of rotation or magnetic fields. We suggest that the flat infalling envelope recently observed in HL Tau by Hayashi et al.is the result of collapse from an initially nonspherical layer. We also speculate that the later evolution of such a flattened, collapsing envelope can produce a structure similar to the 'flared disk' invoked by Kenyon and Hartmann to explain the infrared excesses of many T Tauri stars.

The CHESS survey of the L1157-B1 bow-shock: Dissecting the water content

NASA Astrophysics Data System (ADS)

Busquet, Gemma; Lefloch, Bertrand; Benedettini, Milena; Ceccarelli, Cecilia; Codella, Claudio; Cabrit, Sylvie; Nisini, Brunella; Viti, Serena; Gómez-Ruiz, Arturo; Gusdorf, Antoine; Di Giorgio, Anna Maria; Wiesenfeld, Laurent

2013-07-01

Molecular outflows powered by young protostars strongly affect the kinematics and chemistry of the natal molecular cloud through strong shocks, resulting in an increase of the abundance of several species. In particular, water is a powerful tracer of shocked material due to its sensitivity to both physical conditions and chemical processes. The observations of the "Chemical Herschel Survey of Star forming regions" (CHESS) key program towards the shock region L1157-B1 offered a unique and comprehensive view of the water emission in a typical protostellar bow shock across the submillimeter and far-infrared window. A grand total of 13 water lines have been detected with the PACS and HIFI instruments, probing a wide range of excitation conditions and providing us with a detailed picture on both the kinematics and the spatial distribution of water emission. Several gas components have been identified coexisting in the L1157-B1 shock region. Large Velocity Gradient (LVG) analysis reveals that these components have different excitation conditions: i) a warm (T~250 K) and dense (n(H2)~10^6 cm-3) gas component seen also with the CO lines and associated with the partly dissociative shock produced by the impact of the protostellar jet against the bow shock; ii) a compact (size~5''), hot (T~700 K), and less dense (n(H2)~10^4 cm-3) gas component, and iii) an extended component associated with the B1 outflow cavity. These three components present clear differences in terms of water enrichment. Finally, we confront the physical and chemical properties of the H2O emission to the predictions of current shock models.

SCUBA and HIRES Results for Protostellar Cores in the MON OB1 Dark Cloud

NASA Astrophysics Data System (ADS)

Wolf-Chase, G.; Moriarty-Schieven, G.; Fich, M.; Barsony, M.

1999-05-01

We have used HIRES-processing of IRAS data and point-source modelling techniques (Hurt & Barsony 1996; O'Linger 1997; Barsony et al. 1998), together with submillimeter continuum imaging using the Submillimeter Common-User Bolometer Array (SCUBA) on the 15-meter James Clerk Maxwell Telescope (JCMT), to search CS cores in the Mon OB1 dark cloud (Wolf-Chase, Walker, & Lada 1995; Wolf-Chase & Walker 1995) for deeply embedded sources. These observations, as well as follow-up millimeter photometry at the National Radio Astronomy Observatory (NRAO) 12-meter telescope on Kitt Peak, have lead to the identification of two Class 0 protostellar candidates, which were previously unresolved from two brighter IRAS point sources (IRAS 06382+0939 & IRAS 06381+1039) in this cloud. Until now, only one Class 0 object had been confirmed in Mon OB1; the driving source of the highly-collimated outflow NGC 2264 G (Ward-Thompson, Eiroa, & Casali 1995; Margulis et al. 1990; Lada & Fich 1996), which lies well outside the extended CS cores. One of the new Class 0 candidates may be an intermediate-mass source associated with an H_2O maser, and the other object is a low-mass source which may be associated with a near-infrared jet, and possibly with a molecular outflow. We report accurate positions for the new Class 0 candidates, based on the SCUBA images, and present new SEDs for these sources, as well as for the brighter IRAS point sources. A portion of this work was performed while GWC held a President's Fellowship from the University of California. MB and GWC gratefully acknowledge financial support from MB's NSF CAREER Grant, AST97-9753229.

ALMA Observations of Dust Polarization and Molecular Line Emission from the Class 0 Protostellar Source Serpens SMM1

NASA Astrophysics Data System (ADS)

Hull, Charles L. H.; Girart, Josep M.; Tychoniec, Łukasz; Rao, Ramprasad; Cortés, Paulo C.; Pokhrel, Riwaj; Zhang, Qizhou; Houde, Martin; Dunham, Michael M.; Kristensen, Lars E.; Lai, Shih-Ping; Li, Zhi-Yun; Plambeck, Richard L.

2017-10-01

We present high angular resolution dust polarization and molecular line observations carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the Class 0 protostar Serpens SMM1. By complementing these observations with new polarization observations from the Submillimeter Array (SMA) and archival data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the James Clerk Maxwell Telescopes (JCMT), we can compare the magnetic field orientations at different spatial scales. We find major changes in the magnetic field orientation between large (˜0.1 pc) scales—where the magnetic field is oriented E-W, perpendicular to the major axis of the dusty filament where SMM1 is embedded—and the intermediate and small scales probed by CARMA (˜1000 au resolution), the SMA (˜350 au resolution), and ALMA (˜140 au resolution). The ALMA maps reveal that the redshifted lobe of the bipolar outflow is shaping the magnetic field in SMM1 on the southeast side of the source; however, on the northwestern side and elsewhere in the source, low-velocity shocks may be causing the observed chaotic magnetic field pattern. High-spatial-resolution continuum and spectral-line observations also reveal a tight (˜130 au) protobinary system in SMM1-b, the eastern component of which is launching an extremely high-velocity, one-sided jet visible in both {CO}(J=2\\to 1) and {SiO}(J=5\\to 4); however, that jet does not appear to be shaping the magnetic field. These observations show that with the sensitivity and resolution of ALMA, we can now begin to understand the role that feedback (e.g., from protostellar outflows) plays in shaping the magnetic field in very young, star-forming sources like SMM1.

Signatures of Young Star Formation Activity within Two Parsecs of Sgr A*

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, F.; Wardle, M.; Sewilo, M.; Roberts, D. A.; Smith, I.; Arendt, R.; Cotton, W.; Lacy, J.; Martin, S.; Pound, M. W.; Rickert, M.; Royster, M.

2015-07-01

We present radio and infrared observations indicating ongoing star formation activity inside the ˜2-5 pc circumnuclear ring at the Galactic center. Collectively these measurements suggest a continued disk-based mode of ongoing star formation has taken place near Sgr A* over the last few million years. First, Very Large Array observations with spatial resolution 2.″17 × 0.″81 reveal 13 water masers, several of which have multiple velocity components. The presence of interstellar water masers suggests gas densities that are sufficient for self-gravity to overcome the tidal shear of the 4× {10}6 {M}⊙ black hole. Second, spectral energy distribution modeling of stellar sources indicates massive young stellar object (YSO) candidates interior to the molecular ring, supporting in situ star formation near Sgr A* and appear to show a distribution similar to that of the counter-rotating disks of ˜100 OB stars orbiting Sgr A*. Some YSO candidates (e.g., IRS 5) have bow shock structures, suggesting that they have gaseous disks that are phototoevaporated and photoionized by the strong radiation field. Third, we detect clumps of SiO (2-1) and (5-4) line emission in the ring based on Combined Array for Research in Millimeter-wave Astronomy and Sub-Millimeter Array observations. The FWHM and luminosity of the SiO emission is consistent with shocked protostellar outflows. Fourth, two linear ionized features with an extent of ˜0.8 pc show blue and redshifted velocities between +50 and -40 km s-1, suggesting protostellar jet driven outflows with mass-loss rates of ˜ 5× {10}-5 {M}⊙ yr-1. Finally, we present the imprint of radio dark clouds at 44 GHz, representing a reservoir of molecular gas that feeds star formation activity close to Sgr A*.

Explaining the luminosity spread in young clusters: proto and pre-main sequence stellar evolution in a molecular cloud environment

NASA Astrophysics Data System (ADS)

Jensen, Sigurd S.; Haugbølle, Troels

2018-02-01

Hertzsprung-Russell diagrams of star-forming regions show a large luminosity spread. This is incompatible with well-defined isochrones based on classic non-accreting protostellar evolution models. Protostars do not evolve in isolation of their environment, but grow through accretion of gas. In addition, while an age can be defined for a star-forming region, the ages of individual stars in the region will vary. We show how the combined effect of a protostellar age spread, a consequence of sustained star formation in the molecular cloud, and time-varying protostellar accretion for individual protostars can explain the observed luminosity spread. We use a global magnetohydrodynamic simulation including a sub-scale sink particle model of a star-forming region to follow the accretion process of each star. The accretion profiles are used to compute stellar evolution models for each star, incorporating a model of how the accretion energy is distributed to the disc, radiated away at the accretion shock, or incorporated into the outer layers of the protostar. Using a modelled cluster age of 5 Myr, we naturally reproduce the luminosity spread and find good agreement with observations of the Collinder 69 cluster, and the Orion Nebular Cluster. It is shown how stars in binary and multiple systems can be externally forced creating recurrent episodic accretion events. We find that in a realistic global molecular cloud model massive stars build up mass over relatively long time-scales. This leads to an important conceptual change compared to the classic picture of non-accreting stellar evolution segmented into low-mass Hayashi tracks and high-mass Henyey tracks.

The effects of magnetic fields and protostellar feedback on low-mass cluster formation

NASA Astrophysics Data System (ADS)

Cunningham, Andrew J.; Krumholz, Mark R.; McKee, Christopher F.; Klein, Richard I.

2018-05-01

We present a large suite of simulations of the formation of low-mass star clusters. Our simulations include an extensive set of physical processes - magnetohydrodynamics, radiative transfer, and protostellar outflows - and span a wide range of virial parameters and magnetic field strengths. Comparing the outcomes of our simulations to observations, we find that simulations remaining close to virial balance throughout their history produce star formation efficiencies and initial mass function (IMF) peaks that are stable in time and in reasonable agreement with observations. Our results indicate that small-scale dissipation effects near the protostellar surface provide a feedback loop for stabilizing the star formation efficiency. This is true regardless of whether the balance is maintained by input of energy from large-scale forcing or by strong magnetic fields that inhibit collapse. In contrast, simulations that leave virial balance and undergo runaway collapse form stars too efficiently and produce an IMF that becomes increasingly top heavy with time. In all cases, we find that the competition between magnetic flux advection towards the protostar and outward advection due to magnetic interchange instabilities, and the competition between turbulent amplification and reconnection close to newly formed protostars renders the local magnetic field structure insensitive to the strength of the large-scale field, ensuring that radiation is always more important than magnetic support in setting the fragmentation scale and thus the IMF peak mass. The statistics of multiple stellar systems are similarly insensitive to variations in the initial conditions and generally agree with observations within the range of statistical uncertainty.

VizieR Online Data Catalog: Deconvolved Spitzer images of 89 protostars (Velusamy+, 2014)

NASA Astrophysics Data System (ADS)

Velusamy, T.; Langer, W. D.; Thompson, T.

2016-03-01

The sample of Class 0 protostars, H2 jets, and outflow sour selected for HiRes deconvolution of Spitzer images are listed in Table1. The majority of our target protostellar objects were selected from "The Youngest Protostars" webpage hosted by the University of Kent (http://astro.kent.ac.uk/protostars/old/), which are based on the young Class 0 objects compiled by Froebrich 2005 (cat. J/ApJS/156/169). In addition to these objects, our sample includes some Herbig-Haro (HH) sources and a few well known jet outflow sources. Our sample also includes one high-mass protostar (IRAS20126+4104; cf. Caratti o Garatti et al., 2008A&A...485..137C) to demonstrate the use of HiRes for such sources. Our choice for target selection was primarily based on the availability of Spitzer images in IRAC and MIPS bands in the archives and the feasibility for reprocessing based on the published Spitzer images wherever available. (1 data file).

Deuterated formaldehyde in the low-mass protostar HH212

NASA Astrophysics Data System (ADS)

Sahu, Dipen; Minh, Y. C.; Lee, Chin-Fei; Liu, Sheng-Yuan; Das, Ankan; Chakrabarti, S. K.; Sivaraman, Bhala

2018-04-01

HH212, a nearby (400 pc) object in Orion, is a class 0 protostellar system with a Keplerian disc and collimated bipolar SiO jets. Deuterated water, HDO, and a deuterated complex molecule, methanol (CH2DOH), have been reported in the source. Here, we report the HDCO (deuterated formaldehyde) line observation from Atacama Large Millimeter Array data to probe the inner region of HH212. We compare HDCO line with other molecular lines to understand the possible chemistry and physics of the source. The distribution of HDCO emission suggests that it may be associated with the base of the outflow. The emission also shows a rotation but it is not associated with the Keplerian rotation of disc or the rotating infalling envelope, rather it is associated with the outflow as previously seen in C34S. From the possible deuterium fractionation, we speculate that the gas phase formation of deuterated formaldehyde is active in the central hot region of the low-mass protostar system, HH212.

Very Large Array Ammonia Observations of the HH 111/HH 121 Protostellar System: A Detection of a New Source with a Peculiar Chemistry

NASA Astrophysics Data System (ADS)

Sewiło, Marta; Wiseman, Jennifer; Indebetouw, Remy; Charnley, Steven B.; Pineda, Jaime E.; Lindberg, Johan E.; Qin, Sheng-Li

2017-11-01

We present the results of Very Large Array NH3 (J,K)=(1,1) and (2,2) observations of the HH 111/HH 121 protostellar system. HH 111, with a spectacular collimated optical jet, is one of the most well-known Herbig-Haro objects. We report the detection of a new source, NH3-S, in the vicinity of HH 111/HH 121 (˜0.03 pc from the HH 111 jet source) in two epochs of the ammonia observations. This constitutes the first detection of this source, in a region that has been thoroughly covered previously by both continuum and spectral line interferometric observations. We study the kinematic and physical properties of HH 111 and the newly discovered NH3-S. We also use HCO+ and HCN (J=4-3) data obtained with the James Clerk Maxwell Telescope and archival Atacama Large Millimeter/submillimeter Array 13CO, 12CO, and C18O (J=2-1), N2D+ (J=3-2), and 13CS (J=5-4) data to gain insight into the nature of NH3-S. The chemical structure of NH3-S shows evidence for “selective freeze-out,” an inherent characteristic of dense cold cores. The inner part of NH3-S shows subsonic nonthermal velocity dispersions indicating a “coherent core,” while they increase in the direction of the jets. Archival near- to far-infrared data show no indication of any embedded source in NH3-S. The properties of NH3-S and its location in the infrared dark cloud suggest that it is a starless core located in a turbulent medium, with the turbulence induced by Herbig-Haro jets and associated outflows. More data are needed to fully understand the physical and chemical properties of NH3-S and if/how its evolution is affected by nearby jets.

Very Large Array Ammonia Observations of the HH 111/HH 121 Protostellar System: A Detection of a New Source with a Peculiar Chemistry

NASA Technical Reports Server (NTRS)

Sewilo, Marta; Wiseman, Jennifer; Indebetouw, Remy; Charnley, Steven B.; Pineda, Jaime E.; Lindberg, Johan E.; Qin, Sheng-Li

2017-01-01

We present the results of Very Large Array NH3 (J, K) = (1, 1) and (2, 2) observations of the HH 111/HH 121 protostellar system. HH 111, with a spectacular collimated optical jet, is one of the most well-known Herbig-Haro objects. We report the detection of a new source, NH3-S, in the vicinity of HH 111/HH 121 (approximately 0.03 parsecs from the HH 111 jet source) in two epochs of the ammonia observations. This constitutes the first detection of this source, in a region that has been thoroughly covered previously by both continuum and spectral line interferometric observations. We study the kinematic and physical properties of HH 111 and the newly discovered NH3-S. We also use HCO plus and HCN (J=4-3) data obtained with the James Clerk Maxwell Telescope and archival Atacama Large Millimeter/submillimeter Array (sup 13) CO, (sup 12) CO, and C (sup 18) O (J=2-1), N2D plus (J=3-2), and (sup 13) CS (J=5-4) data to gain insight into the nature of NH3-S. The chemical structure of NH3-S shows evidence for "selective freeze-out,"� an inherent characteristic of dense cold cores. The inner part of NH3-S shows subsonic nonthermal velocity dispersions indicating a "coherent core,"� while they increase in the direction of the jets. Archival near- to far-infrared data show no indication of any embedded source in NH3-S. The properties of NH3-S and its location in the infrared dark cloud suggest that it is a starless core located in a turbulent medium, with the turbulence induced by Herbig-Haro jets and associated outflows. More data are needed to fully understand the physical and chemical properties of NH3-S and if/how its evolution is affected by nearby jets.

Outflows, infall and evolution of a sample of embedded low-mass protostars. The William Herschel Line Legacy (WILL) survey

NASA Astrophysics Data System (ADS)

Mottram, J. C.; van Dishoeck, E. F.; Kristensen, L. E.; Karska, A.; San José-García, I.; Khanna, S.; Herczeg, G. J.; André, Ph.; Bontemps, S.; Cabrit, S.; Carney, M. T.; Drozdovskaya, M. N.; Dunham, M. M.; Evans, N. J.; Fedele, D.; Green, J. D.; Harsono, D.; Johnstone, D.; Jørgensen, J. K.; Könyves, V.; Nisini, B.; Persson, M. V.; Tafalla, M.; Visser, R.; Yıldız, U. A.

2017-04-01

Context. Herschel observations of water and highly excited CO (J > 9) have allowed the physical and chemical conditions in the more active parts of protostellar outflows to be quantified in detail for the first time. However, to date, the studied samples of Class 0/I protostars in nearby star-forming regions have been selected from bright, well-known sources and have not been large enough for statistically significant trends to be firmly established. Aims: We aim to explore the relationships between the outflow, envelope and physical properties of a flux-limited sample of embedded low-mass Class 0/I protostars. Methods: We present spectroscopic observations in H2O, CO and related species with Herschel HIFI and PACS, as well as ground-based follow-up with the JCMT and APEX in CO, HCO+ and isotopologues, of a sample of 49 nearby (d < 500 pc) candidate protostars selected from Spitzer and Herschel photometric surveys of the Gould Belt. This more than doubles the sample of sources observed by the WISH and DIGIT surveys. These data are used to study the outflow and envelope properties of these sources. We also compile their continuum spectral energy distributions (SEDs) from the near-IR to mm wavelengths in order to constrain their physical properties (e.g. Lbol, Tbol and Menv). Results: Water emission is dominated by shocks associated with the outflow, rather than the cooler, slower entrained outflowing gas probed by ground-based CO observations. These shocks become less energetic as sources evolve from Class 0 to Class I. Outflow force, measured from low-J CO, also decreases with source evolutionary stage, while the fraction of mass in the outflow relative to the total envelope (I.e. Mout/Menv) remains broadly constant between Class 0 and I. The median value of 1% is consistent with a core to star formation efficiency on the order of 50% and an outflow duty cycle on the order of 5%. Entrainment efficiency, as probed by FCO/Ṁacc, is also invariant with source properties and evolutionary stage. The median value implies a velocity at the wind launching radius of 6.3 km s-1, which in turn suggests an entrainment efficiency of between 30 and 60% if the wind is launched at 1 AU, or close to 100% if launched further out. L[O I] is strongly correlated with Lbol but not with Menv, in contrast to low-J CO, which is more closely correlated with the latter than the former. This suggests that [O I] traces the present-day accretion activity of the source while CO traces time-averaged accretion over the dynamical timescale of the outflow. H2O is more strongly correlated with Menv than Lbol, but the difference is smaller than low-J CO, consistent with water emission primarily tracing actively shocked material between the wind, traced by [O I], and the entrained molecular outflow, traced by low-J CO. L[O I] does not vary from Class 0 to Class I, unlike CO and H2O. This is likely due to the ratio of atomic to molecular gas in the wind increasing as the source evolves, balancing out the decrease in mass accretion rate. Infall signatures are detected in HCO+ and H2O in a few sources, but still remain surprisingly illusive in single-dish observations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

1961-2011: Fifty years of Hayashi tracks

NASA Astrophysics Data System (ADS)

Palla, Francesco

2012-09-01

Fifty years after the seminal paper by Prof. C. Hayashi, the field of pre-main sequence (PMS) evolution still plays a fundamental role in observational and theoretical astrophysics. In this contribution, I highlight the contribution made by Hayashi in establishing the theoretical foundation of early stellar evolution. Then, I discuss the changes of the classical theory introduced by the inclusion of protostellar evolution in PMS models and present selected results on young stars.

Reconstructing the history of water ice formation from HDO/H2O and D2O/HDO ratios in protostellar cores

NASA Astrophysics Data System (ADS)

Furuya, K.; van Dishoeck, E. F.; Aikawa, Y.

2016-02-01

Recent interferometer observations have found that the D2O/HDO abundance ratio is higher than that of HDO/H2O by about one order of magnitude in the vicinity of low-mass protostar NGC 1333-IRAS 2A, where water ice has sublimated. Previous laboratory and theoretical studies show that the D2O/HDO ice ratio should be lower than the HDO/H2O ice ratio, if HDO and D2O ices are formed simultaneously with H2O ice. In this work, we propose that the observed feature, D2O/HDO > HDO/H2O, is a natural consequence of chemical evolution in the early cold stages of low-mass star formation as follows: 1) majority of oxygen is locked up in water ice and other molecules in molecular clouds, where water deuteration is not efficient; and 2) water ice formation continues with much reduced efficiency in cold prestellar/protostellar cores, where deuteration processes are highly enhanced as a result of the drop of the ortho-para ratio of H2, the weaker UV radiation field, etc. Using a simple analytical model and gas-ice astrochemical simulations, which traces the evolution from the formation of molecular clouds to protostellar cores, we show that the proposed scenario can quantitatively explain the observed HDO/H2O and D2O/HDO ratios. We also find that the majority of HDO and D2O ices are likely formed in cold prestellar/protostellar cores rather than in molecular clouds, where the majority of H2O ice is formed. This work demonstrates the power of the combination of the HDO/H2O and D2O/HDO ratios as a tool to reveal the past history of water ice formation in the early cold stages of star formation, and when the enrichment of deuterium in the bulk of water occurred. Further observations are needed to explore if the relation, D2O/HDO > HDO/H2O, is common in low-mass protostellar sources.

On the tidal interaction between protostellar disks and companions

NASA Technical Reports Server (NTRS)

Lin, D. N. C.; Papaloizou, J. C. B.

1993-01-01

Formation of protoplanets and binary stars in a protostellar disk modifies the structure of the disk. Through tidal interactions, energy and angular momentum are transferred between the disk and protostellar or protoplanetary companion. We summarize recent progress in theoretical investigations of the disk-companion tidal interaction. We show that low-mass protoplanets excite density waves at their Lindblad resonances and that these waves are likely to be dissipated locally. When a protoplanet acquires sufficient mass, its tidal torque induces the formation of a gap in the vicinity of its orbit. Gap formation leads to the termination of protoplanetary growth by accretion. For proto-Jupiter to attain its present mass, we require that (1) the primordial solar nebula is heated by viscous dissipation; (2) the viscous evolution time scale of the nebula is comparable to the age of typical T Tauri stars with circumstellar disks; and (3) the mass distribution in the nebula is comparable to that estimated from a minimum-mass nebula model.

Spectroscopic diagnostics of organic chemistry in the protostellar environment

NASA Technical Reports Server (NTRS)

Charnley, S. B.; Ehrenfreund, P.; Kuan, Y. J.

2001-01-01

A combination of astronomical observations, laboratory studies, and theoretical modelling is necessary to determine the organic chemistry of dense molecular clouds. We present spectroscopic evidence for the composition and evolution of organic molecules in protostellar environments. The principal reaction pathways to complex molecule formation by catalysis on dust grains and by reactions in the interstellar gas are described. Protostellar cores, where warming of dust has induced evaporation of icy grain mantles, are excellent sites in which to study the interaction between gas phase and grain-surface chemistries. We investigate the link between organics that are observed as direct products of grain surface reactions and those which are formed by secondary gas phase reactions of evaporated surface products. Theory predicts observable correlations between specific interstellar molecules, and also which new organics are viable for detection. We discuss recent infrared observations obtained with the Infrared Space Observatory, laboratory studies of organic molecules, theories of molecule formation, and summarise recent radioastronomical searches for various complex molecules such as ethers, azaheterocyclic compounds, and amino acids.

The nature of very low luminosity objects (VeLLOs)

NASA Astrophysics Data System (ADS)

Vorobyov, Eduard I.; Elbakyan, Vardan; Dunham, Michael M.; Guedel, Manuel

2017-04-01

Aims: The nature of very low luminosity objects (VeLLOs) with the internal luminosity Lobj ≤ 0.1 L⊙ is investigated by means of numerical modeling coupling the core collapse simulations with the stellar evolution calculations. Methods: The gravitational collapse of a large sample of model cores in the mass range 0.1-2.0 M⊙ is investigated. Numerical simulations were started at the pre-stellar phase and terminated at the end of the embedded phase when 90% of the initial core mass had been accreted onto the forming protostar plus disk system. The disk formation and evolution was studied using numerical hydrodynamics simulations, while the formation and evolution of the central star was calculated using a stellar evolution code. Three scenarios for mass accretion from the disk onto the star were considered: hybrid accretion in which a fraction of accreted energy absorbed by the protostar depends on the accretion rate, hot accretion wherein a fraction of accreted energy is constant, and cold accretion wherein all accretion energy is radiated away. Results: Our conclusions on the nature of VeLLOs depend crucially on the character of protostellar accretion. In the hybrid accretion scenario, most VeLLOs (90.6%) are expected to be the first hydrostatic cores (FHSCs) and only a small fraction (9.4%) are true protostars. In the hot accretion scenario, all VeLLOs are FHSCs due to overly high photospheric luminosity of protostars. In the cold accretion scenario, on the contrary, the majority of VeLLOs belong to the Class I phase of stellar evolution. The reason is that the stellar photospheric luminosity, which sets the floor for the total internal luminosity of a young star, is lower in cold accretion, thus enabling more VeLLOs in the protostellar stage. VeLLOs are relatively rare objects occupying 7%-11% of the total duration of the embedded phase and their masses do not exceed 0.3 M⊙. When compared with published observations inferring a fraction of VeLLOs in the protostellar stage of 6.25%, we find that cold accretion provides a much better fit to observations than hybrid accretion (5.7% for cold accretion vs. 0.7% for hybrid accretion). Both accretion scenarios predict more VeLLOs in the Class I phase than in the Class 0 phase, in contrast to observations. Finally, when accretion variability with episodic bursts is artificially filtered out from our numerically derived accretion rates, the fraction of VeLLOs in the protostellar stage drops significantly, suggesting a causal link between the two phenomena.

Disk Accretion and the Stellar Birthline

NASA Astrophysics Data System (ADS)

Hartmann, Lee; Cassen, Patrick; Kenyon, Scott J.

1997-02-01

We present a simplified analysis of some effects of disk accretion on the early evolution of fully convective, low-mass pre-main-sequence stars. Our analysis builds on the previous seminal work of Stahler, but it differs in that the accretion of material occurs over a small area of the stellar surface, such as through a disk or magnetospheric accretion column, so that most of the stellar photosphere is free to radiate to space. This boundary condition is similar to the limiting case considered by Palla & Stahler for intermediate-mass stars. We argue that for a wide variety of disk mass accretion rates, material will be added to the star with relatively small amounts of thermal energy. Protostellar evolution calculated assuming this ``low-temperature'' limit of accretion generally follows the results of Stahler because of the thermostatic nature of deuterium fusion, which prevents protostars from contracting below a ``birthline'' in the H-R diagram. Our calculated protostellar radii tend to fall below Stahler's at higher masses; the additional energy loss from the stellar photosphere in the case of disk accretion tends to make the protostar contract. The low-temperature disk accretion evolutionary tracks never fall below the deuterium-fusion birthline until the internal deuterium is depleted, but protostellar tracks can lie above the birthline in the H-R diagram if the initial radius of the protostellar core is large enough or if rapid disk accretion (such as might occur during FU Ori outbursts) adds significant amounts of thermal energy to the star. These possibilities cannot be ruled out by either theoretical arguments or observational constraints at present, so that individual protostars might evolve along a multiplicity of birthlines with a modest range of luminosity at a given mass. Our results indicate that there are large uncertainties in assigning ages for the youngest stars from H-R diagram positions, given the uncertainty in birthline positions. Our calculations also suggest that the relatively low disk accretion rates characteristic of T Tauri stars below the birthline cause low-mass stars to contract only slightly faster than normal Hayashi track evolution, so that ages for older pre-main-sequence stars estimated from H-R diagram positions are relatively secure.

A young bipolar outflow from IRAS 15398-3359

NASA Astrophysics Data System (ADS)

Bjerkeli, P.; Jørgensen, J. K.; Brinch, C.

2016-03-01

Context. Changing physical conditions in the vicinity of protostars allow for a rich and interesting chemistry to occur. Heating and cooling of the gas allows molecules to be released from and frozen out on dust grains. These changes in physics, traced by chemistry as well as the kinematical information, allows us to distinguish between different scenarios describing the infall of matter and the launching of molecular outflows and jets. Aims: We aim to determine the spatial distribution of different species that are of different chemical origin. This is to examine the physical processes in play in the observed region. From the kinematical information of the emission lines we aim to determine the nature of the infalling and outflowing gas in the system. We also aim to determine the physical properties of the outflow. Methods: Maps from the Submillimeter Array (SMA) reveal the spatial distribution of the gaseous emission towards IRAS 15398-3359. The line radiative transfer code LIME is used to construct a full 3D model of the system taking all relevant components and scales into account. Results: CO, HCO+, and N2H+ are detected and shown to trace the motions of the outflow. For CO, the circumstellar envelope and the surrounding cloud also have a profound impact on the observed line profiles. N2H+ is detected in the outflow, but is suppressed towards the central region, perhaps because of the competing reaction between CO and H3+ in the densest regions as well as the destruction of N2H+ by CO. N2D+ is detected in a ridge south-west of the protostellar condensation and is not associated with the outflow. The morphology and kinematics of the CO emission suggests that the source is younger than ~1000 years. The mass, momentum, momentum rate, mechanical luminosity, kinetic energy, and mass-loss rate are also all estimated to be low. A full 3D radiative transfer model of the system can explain all the kinematical and morphological features in the system.

Infrared and Radio Observations of a Small Group of Protostellar Objects in the Molecular Core, L1251-C

NASA Astrophysics Data System (ADS)

Kim, Jungha; Lee, Jeong-Eun; Choi, Minho; Bourke, Tyler L.; Evans, Neal J., II; Di Francesco, James; Cieza, Lucas A.; Dunham, Michael M.; Kang, Miju

2015-05-01

We present a multi-wavelength observational study of a low-mass star-forming region, L1251-C, with observational results at wavelengths from the near-infrared to the millimeter. Spitzer Space Telescope observations confirmed that IRAS 22343+7501 is a small group of protostellar objects. The extended emission in the east-west direction with its intensity peak at the center of L1251A has been detected at 350 and 850 μm with the Caltech Submillimeter Observatory and James Clerk Maxwell telescopes, tracing dense envelope material around L1251A. The single-dish data from the Korean VLBI Network and TRAO telescopes show inconsistencies between the intensity peaks of several molecular emission lines and that of the continuum emission, suggesting complex distributions of molecular abundances around L1251A. The Submillimeter Array interferometer data, however, show intensity peaks of CO 2-1 and 13CO 2-1 located at the position of IRS 1, which is both the brightest source in the Infrared Array Camera image and the weakest source in the 1.3 mm dust-continuum map. IRS 1 is the strongest candidate for the driving source of the newly detected compact CO 2-1 outflow. Over the entire region (14‧ × 14‧) of L125l-C, 3 Class I and 16 Class II sources have been detected, including three young stellar objects (YSOs) in L1251A. A comparison between the average projected distance among the 19 YSOs in L1251-C and that among the 3 YSOs in L1251A suggests that L1251-C is an example of low-mass cluster formation where protostellar objects form in a small group.

VLTI + MIDI Study of the High Mass Protostellar Candidate NGC 3603 IRS 9A

NASA Astrophysics Data System (ADS)

Nürnberger, D. E. A.; Vehoff, S.; Hummel, C. A.; Duschl, W. J.

2010-02-01

The formation and early evolution of high mass stars is among the hottest topics in astrophysics. Interferometric studies of these young stars and their circumstellar environments (envelopes, disks and jets) at near and mid infrared wavelengths are still rare and in terms of data analysis/interpretation very challenging. We here report on observations of the high mass protostellar candidate NGC 3603 IRS 9A which we undertook with VLTI + MIDI in 2005, complemented by near and mid infrared imaging and spectroscopic data. We discuss our results obtained from dedicated modeling efforts, employing both DUSTY and MC3D radiative transfer codes for a selected number of source geometries and surface brightness distributions.

Water distribution in shocked regions of the NGC 1333-IRAS 4A protostellar outflow

NASA Astrophysics Data System (ADS)

Santangelo, G.; Nisini, B.; Codella, C.; Lorenzani, A.; Yıldız, U. A.; Antoniucci, S.; Bjerkeli, P.; Cabrit, S.; Giannini, T.; Kristensen, L. E.; Liseau, R.; Mottram, J. C.; Tafalla, M.; van Dishoeck, E. F.

2014-08-01

Context. Water is a key molecule in protostellar environments because its line emission is very sensitive to both the chemistry and the physical conditions of the gas. Observations of H2O line emission from low-mass protostars and their associated outflows performed with HIFI onboard the Herschel Space Observatory have highlighted the complexity of H2O line profiles, in which different kinematic components can be distinguished. Aims: The goal is to study the spatial distribution of H2O, in particular of the different kinematic components detected in H2O emission, at two bright shocked regions along IRAS 4A, one of the strongest H2O emitters among the Class 0 outflows. Methods: We obtained Herschel-PACS maps of the IRAS 4A outflow and HIFI observations of two shocked positions. The largest HIFI beam of 38'' at 557 GHz was mapped in several key water lines with different upper energy levels, to reveal possible spatial variations of the line profiles. A large velocity gradient (LVG) analysis was performed to determine the excitation conditions of the gas. Results: We detect four H2O lines and CO (16-15) at the two selected shocked positions. In addition, transitions from related outflow and envelope tracers are detected. Different gas components associated with the shock are identified in the H2O emission. In particular, at the head of the red lobe of the outflow, two distinct gas components with different excitation conditions are distinguished in the HIFI emission maps: a compact component, detected in the ground-state water lines, and a more extended one. Assuming that these two components correspond to two different temperature components observed in previous H2O and CO studies, the LVG analysis of the H2O emission suggests that the compact (about 3'', corresponding to about 700 AU) component is associated with a hot (T ~ 1000 K) gas with densities nH2 ~ (1-4) × 105 cm-3, whereas the extended (10''-17'', corresponding to 2400-4000 AU) one traces a warm (T ~ 300-500 K) and dense gas (nH2 ~ (3-5) × 107 cm-3). Finally, using the CO (16-15) emission observed at R2 and assuming a typical CO/H2 abundance of 10-4, we estimate the H2O/H2 abundance of the warm and hot components to be (7-10) × 10-7 and (3-7) × 10-5. Conclusions: Our data allowed us, for the first time, to resolve spatially the two temperature components previously observed with HIFI and PACS. We propose that the compact hot component may be associated with the jet that impacts the surrounding material, whereas the warm, dense, and extended component originates from the compression of the ambient gas by the propagating flow. PACS maps and HIFI spectra (FITS format) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568/A125

Magnetic Stars After the Hayashi Phase. I

NASA Astrophysics Data System (ADS)

Glagolevskij, Yu. V.

2016-06-01

The problems of the origin and evolution of magnetic stars based on analysis of observational data are discussed. It is assumed that magnetic stars acquire their major properties during the protostellar collapse stage. The properties of magnetic stars after the Hayashi phase are examined in detail.

The Formation and Fragmentation of Primordial Protostellar Discs

NASA Astrophysics Data System (ADS)

Clark, Paul C.; Glover, Simon C. O.; Smith, Rowan J.; Greif, Thomas H.; Klessen, Ralf S.; Bromm, Volker

2010-11-01

We study the formation and evolution of the protostellar discs that form around the first stars in the Universe. Using sink particles, we replace the gravitationally bound gas at densities higher than 1015 cm-3 and radii greater than 3 AU from the central protostellar core, with an accreting point mass that is able to gravitationally interact with the surrounding gas. We find the disc is gravitationally (or `Toomre') unstable, and is dominated by a strong m = 2 spiral mode. Although the angular momentum transport is dominated by a combination of gravitational torques and Reynolds stresses, which are extremely efficient mechanisms, the disc is unable to process the infalling material and grows increasingly gravitationally unstable. During the build-up of the disc, the temperature in the gas is regulated by a combination of H2 line cooling, collision-induced emission and H2 dissociation, which together help to offset heating from the gravitational collapse and feedback from the protostar. Once the disc starts to fragment, H2 dissociation keeps the gas almost isothermal as the collapse of the fragment progresses. The fragmentation occurs when the protostar/disc system is only 230 yr old and at a distance of ~20 AU from its sibling, by which point the central protostar has a mass of ~1 Msolar. Given the angular momentum of the new protostellar system, it is likely that the protostars will grow to become a massive binary system.

The near-infrared outflow and cavity of the proto-brown dwarf candidate ISO-Oph 200

NASA Astrophysics Data System (ADS)

Whelan, E. T.; Riaz, B.; Rouzé, B.

2018-03-01

In this Letter a near-infrared integral field study of a proto-brown dwarf candidate is presented. A 0.''5 blue-shifted outflow is detected in both H2 and [Fe II] lines at Vsys = (–35 ± 2) km s-1 and Vsys = (–51 ± 5) km s-1 respectively. In addition, slower ( ±10 km s-1) H2 emission is detected out to <5.''4, in the direction of both the blue and red-shifted outflow lobes but along a different position angle to the more compact faster emission. It is argued that the more compact emission is a jet and the extended H2 emission is tracing a cavity. The source extinction is estimated at Av = 18 ± 1 mag and the outflow extinction at Av = 9 ± 0.4 mag. The H2 outflow temperature is calculated to be 1422 ± 255 K and the electron density of the [Fe II] outflow is measured at 10 000 cm-3. Furthermore, the mass outflow rate is estimated at Ṁout [H2] = 3.8 × 10-10 M⊙ yr-1 and Ṁout[Fe II] = 1 × 10-8 M⊙ yr-1. Ṁout[Fe II] takes a Fe depletion of 88% into account. The depletion is investigated using the ratio of the [Fe II] 1.257 μm and [P II] 1.188 μm lines. Using the Paβ and Brγ lines and a range in stellar mass and radius Ṁacc is calculated to be (3–10) × 10-8 M⊙ yr-/1. Comparing these rates puts the jet efficiency in line with predictions of magneto-centrifugal models of jet launching in low mass protostars. This is a further case of a brown dwarf outflow exhibiting analogous properties to protostellar jets. Based on Observations collected with SINFONI at the Very Large Telescope on Cerro Paranal (Chile), operated by the European Southern Observatory (ESO). Program ID: 097.C-0732(A).

Deuterium chemistry in the young massive protostellar core NGC 2264 CMM3

NASA Astrophysics Data System (ADS)

Awad, Z.; Shalabiea, O. M.

2018-01-01

In this work we present the first attempt of modelling the deuterium chemistry in the massive young protostellar core NGC 2264 CMM3. We investigated the sensitivity of this chemistry to the physical conditions in its surrounding environment. The results showed that deuteration, in the protostellar gas, is affected by variations in the core density, the amount of gas depletion onto grain surfaces, the CR ionisation rate, but it is insensitive to variations in the H2 ortho-to-para ratio. Our results, also, showed that deuteration is often enhanced in less-dense, partially depleted (<85%), or cores that are exerted to high CR ionisation rates (≥6.5×10^{-17} s^{-1}). However, in NGC 2264 CMM3, decreasing the amount of gas depleted onto grains and enhancing the CR ionisation rate are often overestimating the observed values in the core. The best fit time to observations occurs around (1-5) × 104 yrs for core densities in the range (1-5)×106 cm^{-3} with CR ionisation rate between (1.7-6.5)×10^{-17} s^{-1}. These values are in agreement with the results of the most recent theoretical chemical model of CMM3, and the time range of best fit is, also, in-line with the estimated age of young protostellar objects. We conclude that deuterium chemistry in protostellar cores is: (i) sensitive to variations in the physical conditions in its environment, (ii) insensitive to changes in the H2 ortho-to-para ratio. We also conclude that the core NGC 2264 CMM3 is in its early stages of chemical evolution with an estimated age of (1-5)×104 yrs.

Formation of massive seed black holes via collisions and accretion

NASA Astrophysics Data System (ADS)

Boekholt, T. C. N.; Schleicher, D. R. G.; Fellhauer, M.; Klessen, R. S.; Reinoso, B.; Stutz, A. M.; Haemmerlé, L.

2018-05-01

Models aiming to explain the formation of massive black hole seeds, and in particular the direct collapse scenario, face substantial difficulties. These are rooted in rather ad hoc and fine-tuned initial conditions, such as the simultaneous requirements of extremely low metallicities and strong radiation backgrounds. Here, we explore a modification of such scenarios where a massive primordial star cluster is initially produced. Subsequent stellar collisions give rise to the formation of massive (104-105 M⊙) objects. Our calculations demonstrate that the interplay among stellar dynamics, gas accretion, and protostellar evolution is particularly relevant. Gas accretion on to the protostars enhances their radii, resulting in an enhanced collisional cross-section. We show that the fraction of collisions can increase from 0.1 to 1 per cent of the initial population to about 10 per cent when compared to gas-free models or models of protostellar clusters in the local Universe. We conclude that very massive objects can form in spite of initial fragmentation, making the first massive protostellar clusters viable candidate birth places for observed supermassive black holes.

Molecular ions in the protostellar shock L1157-B1

NASA Astrophysics Data System (ADS)

Podio, L.; Lefloch, B.; Ceccarelli, C.; Codella, C.; Bachiller, R.

2014-05-01

Aims: We perform a complete census of molecular ions with an abundance greater than ~10-10 in the protostellar shock L1157-B1. This allows us to study the ionisation structure and chemistry of the shock. Methods: An unbiased high-sensitivity survey of L1157-B1 performed with the IRAM-30 m and Herschel/HIFI as part of the CHESS and ASAI large programmes allows searching for molecular ions emission. Then, by means of a radiative transfer code in the large velocity gradient approximation, the gas physical conditions and fractional abundances of molecular ions are derived. The latter are compared with estimates of steady-state abundances in the cloud and their evolution in the shock calculated with the chemical model Astrochem. Results: We detect emission from HCO+, H13CO+, N2H+, HCS+, and for the first time in a shock, from HOCO+ and SO+. The bulk of the emission peaks at blue-shifted velocity, ~0.5-3 km s -1 with respect to systemic, has a width of ~3-7 km s-1 and is associated with the outflow cavities (Tkin ~ 20-70 K, nH2 ~ 105 cm-3). A high-velocity component up to -40 km s-1, associated with the primary jet, is detected in the HCO+ 1-0 line. Observed HCO+ and N2H+ abundances (XHCO+ ~ 0.7-3 × 10-8, XN2H+ ~ 0.4-8 × 10-9) agree with steady-state abundances in the cloud and with their evolution in the compressed and heated gas in the shock for cosmic rays ionisation rate ζ = 3 × 10-16 s-1. HOCO+, SO+, and HCS+ observed abundances (XHOCO+ ~ 10-9, XSO+ ~ 8 × 10-10, XHCS+ ~ 3-7 × 10-10), instead, are 1-2 orders of magnitude larger than predicted in the cloud; on the other hand, they are strongly enhanced on timescales shorter than the shock age (~2000 years) if CO2, S or H2S, and OCS are sputtered off the dust grains in the shock. Conclusions: The performed analysis indicates that HCO+ and N2H+ are a fossil record of pre-shock gas in the outflow cavity, whilst HOCO+, SO+, and HCS+ are effective shock tracers that can be used to infer the amount of CO2 and sulphur-bearing species released from dust mantles in the shock. The observed HCS+ (and CS) abundance indicates that OCS should be one of the main sulphur carrier on grain mantles. However, the OCS abundance required to fit the observations is 1-2 orders of magnitude larger than observed. Laboratory experiments are required to measure the reactions rates involving these species and to fully understand the chemistry of sulphur-bearing species. The molecular ions line spectra shown in Fig. 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/565/A64

The high-mass star-forming core G35.2N: what have we learnt from SOFIA and ALMA observations?

NASA Astrophysics Data System (ADS)

Zinnecker, Hans; Sandell, Goeran

2014-07-01

G35.2N is a luminouos, star forming core in a filamentary cloud at a distance of 2.2 kpc. It is associated with a thermal N-S radio jet and a misaligned NE-SW CO outflow observed both with SOFIA FORCAST (30 and 40 microns, ~4" resolution; Zhang, Tan, de Buizer et al. 2013) and with ALMA band 7 (850 micron line and continuum, 0.4" resolution; Sanchez-Monge, Cesaroni, Beltran et al. 2013, 2014). The ALMA observations revealed a NW-SE Keplerian rotating disk in the CH3CN molecule (Sanchez-Monge et al.) with an enclosed protostellar mass of 18 +/- 3 Mo, whose orientation is inconsistent with the N-S radio jet, and whose protostellar mass is marginally inconsistent with the one inferred from the SED modelling (20-34 Mo, L ~ 10(5) Lo; Zhang et al.) We review the various assumptions involved in the derivation of the disk interpretation and the SED modelling. The dynamical mass could be in the form of a close binary (two 9 Mo stars, say) in which case the predicted total luminosity would be 3 x 10(4) Lo, close to the actually observed one (as opposed to the modelled one, which takes into account the flashlight effect and unmeasured radiation that escapes along a bipolar cavity). One the other hand, if the inferred higher-luminosity model is correct, the disk interpretation of ALMA rotation curve may have to be challenged, and what seems like a nice disk might be a more complex dynamical structure, such as a warped or precessing disk around a binary protostar or a different (outflow-related) velocity-structure altogether. These observations show the complexity of the interpretation of multi-wavelength observations of high-mass star forming regions when viewed with different spatial resolutions.

The Nonisothermal Stage of Magnetic Star Formation. I. Formulation of the Problem and Method of Solution

NASA Astrophysics Data System (ADS)

Kunz, Matthew W.; Mouschovias, Telemachos Ch.

2009-03-01

We formulate the problem of the formation and subsequent evolution of fragments (or cores) in magnetically supported, self-gravitating molecular clouds in two spatial dimensions. The six-fluid (neutrals, electrons, molecular and atomic ions, positively charged, negatively charged, and neutral grains) physical system is governed by the radiation, nonideal magnetohydrodynamic equations. The magnetic flux is not assumed to be frozen in any of the charged species. Its evolution is determined by a newly derived generalized Ohm's law, which accounts for the contributions of both elastic and inelastic collisions to ambipolar diffusion and Ohmic dissipation. The species abundances are calculated using an extensive chemical-equilibrium network. Both MRN and uniform grain size distributions are considered. The thermal evolution of the protostellar core and its effect on the dynamics are followed by employing the gray flux-limited diffusion approximation. Realistic temperature-dependent grain opacities are used that account for a variety of grain compositions. We have augmented the publicly available Zeus-MP code to take into consideration all these effects and have modified several of its algorithms to improve convergence, accuracy, and efficiency. Results of magnetic star formation simulations that accurately track the evolution of a protostellar fragment from a density sime103 cm-3 to a density sime1015 cm-3, while rigorously accounting for both nonideal MHD processes and radiative transfer, are presented in a separate paper.

Dynamics of binary and planetary-system interaction with disks - Eccentricity changes

NASA Technical Reports Server (NTRS)

Atrymowicz, Pawel

1992-01-01

Protostellar and protoplanetary systems, as well as merging galactic nuclei, often interact tidally and resonantly with the astrophysical disks via gravity. Underlying our understanding of the formation processes of stars, planets, and some galaxies is a dynamical theory of such interactions. Its main goals are to determine the geometry of the binary-disk system and, through the torque calculations, the rate of change of orbital elements of the components. We present some recent developments in this field concentrating on eccentricity driving mechanisms in protoplanetary and protobinary systems. In those two types of systems the result of the interaction is opposite. A small body embedded in a disk suffers a decrease of orbital eccentricity, whereas newly formed binary stars surrounded by protostellar disks may undergo a significant orbital evolution increasing their eccentricities.

Dust Coagulation in Infalling Protostellar Envelopes I. Compact Grains

NASA Technical Reports Server (NTRS)

Yorke, H.; Suttner, G.; Lin, D.

1999-01-01

Dust plays a key role in the optical, thermodynamic and gas dynamical behavior of collapsing molecular cores. Because of relative velocities of the individual dust grains, coagulation and shattering can modify the grain size distribution and due to corresponding changes in the medium's opacity significantly influence the evolution during early phase of star formation.

Dust Coagulation in Infalling Protostellar Envelopes I. Compact Grains

NASA Technical Reports Server (NTRS)

Yorke, H.; Lin, D.; Suttner, G.

1999-01-01

Dust plays a key role in the optical, thermodynamic and gas dynamical behavior of collapsing molecular cores. Because of relative velocities of the individual dust grains, coagulation and shattering can modify the grain size distribution and -- due to corresponding changes in the medium's opacity significantly -- influence the evolution during early phases of star formation.

Course 6: Star Formation

NASA Astrophysics Data System (ADS)

Natta, A.

Contents 1 Introduction 2 Collapse of molecular cores 2.1 Giant molecular clouds and cores 2.2 Conditions for collapse 2.3 Free-fall collapse 2.4 Collapse of an isothermal sphere of gas 2.5 Collapse of a slowly rotating core 3 Observable properties of protostars 3.1 Evidence of infall from molecular line profiles 3.2 SEDs of protostars 3.3 The line spectrumof a protostar 4 Protostellar and pre-main-sequence evolution 4.1 The protostellar phase 4.2 Pre-main-sequence evolution 4.3 The birthline 5 Circumstellar disks 5.1 Accretion disks 5.2 Properties of steady accretion disks 5.3 Reprocessing disks 5.4 Disk-star interaction 6 SEDs of disks 6.1 Power-law disks 6.2 Long-wavelength flux and disk mass 6.3 Comparison with TTS observations: Heating mechanism 7 Disk properties from observations 7.1 Mass accretion rate 7.2 Inner radius 7.3 Masses 7.4 Sizes 8 Disk lifetimes 8.1 Ground-based near and mid-infrared surveys 8.2 Mid-infrared ISOCAMsurveys 8.3 ISOPHOT 60 microm survey 8.4 Surveys at millimeter wavelengths 9 Disk evolution 9.1 Can we observe the early planet formation phase? 9.2 Evidence for grain growth 9.3 Evidence of planetesimals 9.4 Where is the diskmass? 10 Secondary or debris disks 11 Summary

Laboratory Measurements for H3+ Deuteration Reactions

NASA Astrophysics Data System (ADS)

Bowen, Kyle; Hillenbrand, Pierre-Michel; Urbain, Xavier; Savin, Daniel Wolf

2018-06-01

Deuterated molecules are important chemical tracers of protostellar cores. At the ~106 cm-3 particle densities and ~20 K temperatures typical for protostellar cores, most molecules freeze onto dust grains. A notable exception is H3+ and its isotopologues. These become important carriers of positive charge in the gas, can couple to any ambient magnetic field, and can thereby alter the cloud dynamics. Knowing the total abundance of H3+ and its isotopologues is important for studying the evolution of protostellar cores. However, H3+ and D3+ have no dipole moment. They lack a pure rotational spectrum and are not observable at protostellar core temperatures. Fortunately H2D+ and D2H+ have dipole moments and a pure rotational spectrum that can be excited in protostellar cores. Observations of these two molecules, combined with astrochemical models, provide information about the total abundance of H3+ and all its isotopologues. The inferred abundances, though, rely on accurate astrochemical data for the deuteration of H3+ and its isotopologues.Here we present laboratory measurements of the rate coefficients for three important deuterating reactions, namely D + H3+/H2D+/D2H+ → H + H2D+/ D2H+/D3+. Astrochemical models currently rely on rate coefficients from classical (Langevin) or semi-classical methods for these reactions, as fully quantum-mechanical calculations are beyond current computational capabilities. Laboratory studies are the most tractable means of providing the needed data. For our studies we used our novel dual-source, merged fast-beams apparatus, which enables us to study reactions of neutral atoms and molecular ions. Co-propagating beams allow us to measure experimental rate coefficients as a function of collision energy. We extract cross section data from these results, which we then convolve with a Maxwell-Boltzmann distribution to generate thermal rate coefficients. Here we present our results for these three reactions and discuss some implications.

Characterization of methanol as a magnetic field tracer in star-forming regions

NASA Astrophysics Data System (ADS)

Lankhaar, Boy; Vlemmings, Wouter; Surcis, Gabriele; van Langevelde, Huib Jan; Groenenboom, Gerrit C.; van der Avoird, Ad

2018-02-01

Magnetic fields play an important role during star formation1. Direct magnetic field strength observations have proven particularly challenging in the extremely dynamic protostellar phase2-4. Because of their occurrence in the densest parts of star-forming regions, masers, through polarization observations, are the main source of magnetic field strength and morphology measurements around protostars2. Of all maser species, methanol is one of the strongest and most abundant tracers of gas around high-mass protostellar disks and in outflows. However, as experimental determination of the magnetic characteristics of methanol has remained largely unsuccessful5, a robust magnetic field strength analysis of these regions could hitherto not be performed. Here, we report a quantitative theoretical model of the magnetic properties of methanol, including the complicated hyperfine structure that results from its internal rotation6. We show that the large range in values of the Landé g factors of the hyperfine components of each maser line lead to conclusions that differ substantially from the current interpretation based on a single effective g factor. These conclusions are more consistent with other observations7,8 and confirm the presence of dynamically important magnetic fields around protostars. Additionally, our calculations show that (nonlinear) Zeeman effects must be taken into account to further enhance the accuracy of cosmological electron-to-proton mass ratio determinations using methanol9-12.

The star-forming cores in the centre of the Trifid nebula (M 20): from Herschel to the near-infrared

NASA Astrophysics Data System (ADS)

Tapia, M.; Persi, P.; Román-Zúñiga, C.; Elia, D.; Giovannelli, F.; Sabau-Graziati, L.

2018-04-01

A new detailed infrared (IR) study of eight star-forming dense condensations (TCs) in M 20, the Trifid nebula, is presented. The aim is to determine the physical properties of the dust in such globules and establish the presence and properties of their embedded protostellar and/or young stellar population. For this, we analysed new Herschel far-IR and Calar Alto near-IR images of the region, combined with Spitzer Infrared Array Camera (Spitzer/IRAC) archival observations. We confirm the presence of several young stellar objects (YSOs), most with mid-IR colours of Class II sources in all but one of the observed cores. Five TCs are dominated in the far-IR by Class I sources with bolometric luminosities between 100 and 500 L⊙. We report the discovery of a possible counterjet to HH 399 and its protostellar engine inside the photodissociation region TC2, as well as a bipolar outflow system, signposted by symmetric H2 emission knots, embedded in TC3. The present results are compatible with previous suggestions that star formation has been active in the region for some 3 × 105 yr, and that the most recent events in some of these TCs may have been triggered by the expansion of the H II region. We also obtained a revised value for the distance to M 20 of 2.0 ± 0.1 kpc.

OH masers towards IRAS 19092+0841

NASA Astrophysics Data System (ADS)

Edris, K. A.; Fuller, G. A.; Etoka, S.; Cohen, R. J.

2017-12-01

Context. Maser emission is a strong tool for studying high-mass star-forming regions and their evolutionary stages. OH masers in particular can trace the circumstellar material around protostars and determine their magnetic field strengths at milliarcsecond resolution. Aims: We seek to image OH maser emission towards high-mass protostellar objects to determine their evolutionary stages and to locate the detected maser emission in the process of high-mass star formation. Methods: In 2007, we surveyed OH maser emission towards 217 high-mass protostellar objects to study its presence. In this paper, we present follow-up MERLIN observations of a ground-state OH maser emission towards one of these objects, IRAS 19092+0841. Results: We detect emissions from the two OH main spectral lines, 1665 and 1667 MHz, close to the central object. We determine the positions and velocities of the OH maser features. The masers are distributed over a region of 5'' corresponding to 22 400 AU (or 0.1 pc) at a distance of 4.48 kpc. The polarization properties of the OH maser features are determined as well. We identify three Zeeman pairs from which we inferred a magnetic field strength of 4.4 mG pointing towards the observer. Conclusions: The relatively small velocity spread and relatively wide spacial distribution of the OH maser features support the suggestion that this object could be in an early evolutionary state before the presence of disk, jets or outflows.

Chemical segregation in the young protostars Barnard 1b-N and S. Evidence of pseudo-disk rotation in Barnard 1b-S

NASA Astrophysics Data System (ADS)

Fuente, A.; Gerin, M.; Pety, J.; Commerçon, B.; Agúndez, M.; Cernicharo, J.; Marcelino, N.; Roueff, E.; Lis, D. C.; Wootten, H. A.

2017-10-01

The extremely young Class 0 object B1b-S and the first hydrostatic core (FSHC) candidate, B1b-N, provide a unique opportunity to study the chemical changes produced in the elusive transition from the prestellar core to the protostellar phase. We present 40″ × 70″ images of Barnard 1b in the 13CO 1 → 0, C18O 1 → 0, NH2D 11,1a→ 10,1s, and SO 32→ 21 lines obtained with the NOEMA interferometer. The observed chemical segregation allows us to unveil the physical structure of this young protostellar system down to scales of 500 au. The two protostellar objects are embedded in an elongated condensation, with a velocity gradient of 0.2-0.4 m s-1 au-1 in the east-west direction, reminiscent of an axial collapse. The NH2D data reveal cold and dense pseudo-disks (R 500 - 1000 au) around each protostar. Moreover, we observe evidence of pseudo-disk rotation around B1b-S. We do not see any signature of the bipolar outflows associated with B1b-N and B1b-S, which were previously detected in H2CO and CH3OH, in any of the imaged species. The non-detection of SO constrains the SO/CH3OH abundance ratio in the high-velocity gas. Based on observations carried out with the IRAM Northern Extended Millimeter Array (NOEMA). IRAM is supported by INSU/ CNRS (France), MPG (Germany), and IGN (Spain).The reduced datacube is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/L3

Chemical evolution of the gas in C-type shocks in dark clouds

NASA Astrophysics Data System (ADS)

Nesterenok, A. V.

2018-07-01

A magnetohydrodynamic model of a steady, transverse C-type shock in a dense molecular cloud is presented. A complete gas-grain chemical network is taken into account: the gas-phase chemistry, the adsorption of gas species on dust grains, various desorption mechanisms, the grain surface chemistry, the ion neutralization on dust grains, the sputtering of grain mantles. The population densities of energy levels of ions CI, CII and OI and molecules H2, CO, H2O are computed in parallel with the dynamical and chemical rate equations. The large velocity gradient approximation is used in the line radiative transfer calculations. The simulations consist of two steps: (i) modelling of the chemical and thermal evolution of a static molecular cloud and (ii) shock simulations. A comparison is made with the results of publicly available models of similar physical systems. The focus of the paper is on the chemical processing of gas material and ice mantles of dust grains by the shock. Sputtering of ice mantles takes place in the shock region close to the temperature peak of the neutral gas. At high shock speeds, molecules ejected from ice mantles are effectively destroyed in hot gas, and their survival time is low—of the order of dozens of years. After a passage of high-speed C-type shock, a zone of high abundance of atomic hydrogen appears in the cooling postshock gas that triggers formation of complex organic species such as methanol. It is shown that abundances of some complex organic molecules (COMs) in the postshock region can be much higher than in the preshock gas. These results are important for interpretation of observations of COMs in protostellar outflows.

Generation of shockwave and vortex structures at the outflow of a boiling water jet

NASA Astrophysics Data System (ADS)

Alekseev, M. V.; Lezhnin, S. I.; Pribaturin, N. A.; Sorokin, A. L.

2014-12-01

Results of numerical simulation for shock waves and generation of vortex structures during unsteady outflow of boiling liquid jet are presented. The features of evolution of shock waves and vortex structures formation during unsteady outflow of boiling water are compared with corresponding structures during unsteady gas outflow.

Binary star formation: gravitational fragmentation followed by capture

NASA Astrophysics Data System (ADS)

Turner, J. A.; Chapman, S. J.; Bhattal, A. S.; Disney, M. J.; Pongracic, H.; Whitworth, A. P.

1995-11-01

We describe in detail one of a sequence of numerical simulations which realize the mechanism of binary star formation proposed by Pringle. In these simulations, collisions between stable molecular cloud clumps produce dense shocked layers, which cool radiatively and fragment gravitationally. The resulting fragments then condense to form protostellar discs, which at the same time fall together and, as a result of tidal and viscous interactions, capture one another to form binary systems. We refer to this mechanism as shock-induced gravitational fragmentation followed by capture, or SGF+C. When the initial clumps are sufficiently massive and/or the Mach number of the collision is sufficiently high, a large number (>~10) of protostellar discs is produced; under these circumstances, the layer fragments first into filaments, and then into beads along the filaments. The marriage of two protostellar discs in this way is `arranged' in the sense that the protostellar discs involved do not form independently. First, they both condense out of the same layer, and probably also out of the same filament within this layer; this significantly increases the likelihood of them interacting dynamically. Secondly, there tends to be alignment between the orbital and spin angular momenta of the interacting protostellar discs, reflecting the fact that these angular momenta derive mainly from the systematic global angular momentum of the off-axis collision which produced the layer; this alignment of the various angular momenta pre-disposes the discs to very dissipative interactions, thereby increasing the probability of producing a strongly bound, long-lasting union. It is a marriage because the binary orbit stabilizes itself rather quickly. Any subsequent orbit evolution, as the protostellar discs `mop up' the surrounding residual gas and interact tidally, tends to harden the orbit. Therefore, as long as a third body does not intervene, the union is binding. Even if a third body does intervene, provided the binary components are well matched (i.e. of comparable mass) and the third body is not too massive, such interventions will - more often than not - harden the orbit further. In two appendices we describe the code used in the simulations presented in this and the companion paper, and the tests performed to demonstrate the code's ability to handle the physical processes involved.

CCS Observations of the Protostellar Envelope of B335

NASA Technical Reports Server (NTRS)

Velusamy, T.; Kuiper, T. B. H.; Langer, W. D.

1995-01-01

Knowledge of the density, velocity and chemical profiles around protostars is of fundamental importance for testing dynamical models of protostar evolution and understanding the nature of the material falling onto circumstellar disks. Presented are single dish and interferometric spectral line observations of CCS towards the core of B335, a classic example of a young, low mass stellar object.

Eccentricity Evolution of Extrasolar Multiple Planetary Systems Due to the Depletion of Nascent Protostellar Disks

NASA Astrophysics Data System (ADS)

Nagasawa, M.; Lin, D. N. C.; Ida, S.

2003-04-01

Most extrasolar planets are observed to have eccentricities much larger than those in the solar system. Some of these planets have sibling planets, with comparable masses, orbiting around the same host stars. In these multiple planetary systems, eccentricity is modulated by the planets' mutual secular interaction as a consequence of angular momentum exchange between them. For mature planets, the eigenfrequencies of this modulation are determined by their mass and semimajor axis ratios. However, prior to the disk depletion, self-gravity of the planets' nascent disks dominates the precession eigenfrequencies. We examine here the initial evolution of young planets' eccentricity due to the apsidal libration or circulation induced by both the secular interaction between them and the self-gravity of their nascent disks. We show that as the latter effect declines adiabatically with disk depletion, the modulation amplitude of the planets' relative phase of periapsis is approximately invariant despite the time-asymmetrical exchange of angular momentum between planets. However, as the young planets' orbits pass through a state of secular resonance, their mean eccentricities undergo systematic quantitative changes. For applications, we analyze the eccentricity evolution of planets around υ Andromedae and HD 168443 during the epoch of protostellar disk depletion. We find that the disk depletion can change the planets' eccentricity ratio. However, the relatively large amplitude of the planets' eccentricity cannot be excited if all the planets had small initial eccentricities.

Formation of X-ray emitting stationary shocks in magnetized protostellar jets

NASA Astrophysics Data System (ADS)

Ustamujic, S.; Orlando, S.; Bonito, R.; Miceli, M.; Gómez de Castro, A. I.; López-Santiago, J.

2016-12-01

Context. X-ray observations of protostellar jets show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary. They are interpreted as shock diamonds. Aims: We investigate the physics that guides the formation of X-ray emitting stationary shocks in protostellar jets; the role of the magnetic field in determining the location, stability, and detectability in X-rays of these shocks; and the physical properties of the shocked plasma. Methods: We performed a set of 2.5-dimensional magnetohydrodynamic numerical simulations that modelled supersonic jets ramming into a magnetized medium and explored different configurations of the magnetic field. The model takes into account the most relevant physical effects, namely thermal conduction and radiative losses. We compared the model results with observations, via the emission measure and the X-ray luminosity synthesized from the simulations. Results: Our model explains the formation of X-ray emitting stationary shocks in a natural way. The magnetic field collimates the plasma at the base of the jet and forms a magnetic nozzle there. After an initial transient, the nozzle leads to the formation of a shock diamond at its exit which is stationary over the time covered by the simulations ( 40-60 yr; comparable with timescales of the observations). The shock generates a point-like X-ray source located close to the base of the jet with luminosity comparable with that inferred from X-ray observations of protostellar jets. For the range of parameters explored, the evolution of the post-shock plasma is dominated by the radiative cooling, whereas the thermal conduction slightly affects the structure of the shock. A movie is available at http://www.aanda.org

Velocity Space Evolution of Dayside Reconnection Outflow

NASA Astrophysics Data System (ADS)

Broll, J. M.; Fuselier, S. A.; Trattner, K. J.

2015-12-01

Magnetic reconnection is a universal phenomenon occurring when energy stored in a complicated magnetic field topology is released into the surrounding plasma as the field simplifies its configuration. At Earth's dayside magnetopause, reconnection is responsible for mass and energy input from the solar wind into the magnetosphere. We describe the evolution of the velocity-space evolution of plasma outflow from a dayside magnetic reconnection region. We analyze Cluster magnetopause crossings between 1 and 10 Earth radii from the reconnection X-line predicted by the maximum magnetic shear model. The effects of nonadiabatic processes, such as deformation of the profile due to finite-gyroradius-induced pitch-angle scattering and wave-particle interactions, are described. We compare observations and simulation results to describe the outflow evolution and infer the field-aligned distance between an observation and the reconnection site producing it.

The nearest X-ray emitting protostellar jet (HH 154) observed with Hubble

NASA Astrophysics Data System (ADS)

Bonito, R.; Fridlund, C. V. M.; Favata, F.; Micela, G.; Peres, G.; Djupvik, A. A.; Liseau, R.

2008-06-01

Context: The jet coming from the YSO binary L1551 IRS5 is the closest astrophysical jet known. It is therefore a unique laboratory for studies of outflow mechanisms and of the shocks occurring when expanding material hits the ambient medium as well as of how the related processes influence the star- (and planet-) forming process. Aims: The optical data are related to other data covering the spectrum from the optical band to X-rays with goal of understanding the energetics of low-mass star jets, in general, and of this jet in particular. We study the time evolution of the jet, by measuring the proper motions of knots as they progress outwards from the originating source. Methods: The nebulosities associated with the jet(s) from the protostellar binary L1551 IRS5 were imaged in a number of spectral bands using the Hubble Space Telescope. This allows the proper motion to be measured and permits a simple characterization of the physical conditions in different structures. To this end we developed a reproducible method of data analysis, which allows us to define the position and shape of each substructure observed within the protostellar jet. Using this approach, we derive the proper motion of the knots in the jet, as well as their flux variability and shock emission. Results: The time base over which HST observations were carried out is now about ten years. The sub-structures within the jet undergo significant morphological variations: some knots seem to disappear in a few years and collision between different knots, ejected at different epochs and maybe with different speed, may occur. The velocities along the jet vary between ~100 km s-1 and over 400 km s-1, with the highest speed corresponding to the knots at the base of the jet. Conclusions: There are indications that the HH 154 jet has been active relatively recently. Our results suggest the presence of a new shock front at the base of the jet identified with an internal working surface. From the analysis of the terminal and internal working surfaces within the jet, we find that the more likely scenario for the HH 154 jet is that of a jet traveling through a denser ambient medium (a “light jet”). These results are consistent with the Bonito et al. (2007) model predictions. Furthermore, there is strong evidence that the knots at the base of the northern jet correspond to the location where the highest velocity and the highest excitation component are measured along the jet. More important, this is the location where the X-ray source has been discovered. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #6127, #6411 & #10351.

The circumstellar disk response to the motion of the host star

NASA Astrophysics Data System (ADS)

Regály, Zs.; Vorobyov, E.

2017-05-01

Context. Grid-based hydrodynamics simulations of circumstellar disks are often performed in the curvilinear coordinate system, in which the center of the computational domain coincides with the motionless star. However, the center of mass may be shifted from the star due to the presence of any non-axisymmetric mass distribution. As a result, the system exerts a non-zero gravity force on the star, causing the star to move in response, which can in turn affect the evolution of the circumstellar disk. Aims: We aim at studying the effects of stellar motion on the evolution of protostellar and protoplanetary disks. In protostellar disks, a non-axisymmetric distribution of matter in the form of spiral arms and/or massive clumps can form due to gravitational instability. Protoplanetary disks can also feature non-axisymmetric structures caused by an embedded high-mass planet or a large-scale vortex formed at viscosity transitions. Methods: We use 2D grid-based numerical hydrodynamic simulations to explore the effect of stellar motion. We adopt a non-inertial polar coordinate system centered on the star, in which the stellar motion is taken into account by calculating the indirect potential caused by the non-axisymmetric disk, a high-mass planet, or a large-scale vortex. We compare the results of numerical simulations with and without stellar motion. Results: We found that the stellar motion has a moderate effect on the evolution history and the mass accretion rate in protostellar disks, reducing somewhat the disk size and mass, while having a profound effect on the collapsing envelope, changing its inner shape from an initially axisymmetric to a non-axisymmetric configuration. Protoplanetary disk simulations show that the stellar motion slightly reduces the width of the gap opened by a high-mass planet, decreases the planet migration rate, and strengthens the large-scale vortices formed at the viscosity transition. Conclusions: We conclude that the inclusion of the indirect potential is recommended in grid-based hydrodynamics simulations of circumstellar disks which use the curvilinear coordinate system.

Sharpless-76E: astrometry and outflows in a protostellar cluster

NASA Astrophysics Data System (ADS)

Chibueze, James O.; Hamabata, Hideo; Nagayama, Takumi; Omodaka, Toshihiro; Handa, Toshihiro; Sunada, Kazuyoshi; Nakano, Makoto; Ueno, Yuji

2017-04-01

Using VLBI Exploration of Radio Astrometry, we have conducted multi-epoch observations of the H2O masers associated with Sharpless 76E. The measured annual parallax is 0.521 ± 0.024 mas corresponding to the distance of 1.92^{+0.09}_{-0.08} kpc. From the parallax measurement, we obtained the peculiar motion of Sh2-76EMM1 (UMM1, VMM1, WMM1) to be (-9 ± 3, 10 ± 4, 6 ± 4) km s-1and Sh2-76EMM2 (UMM2, VMM2, WMM2) to be (-5 ± 12, 3 ± 14, -21 ± 22) km s-1, where U, V and W are directed towards the Galactic Centre, in the direction of Galactic rotation and towards the Galactic north pole, respectively. The internal motion of the H2O masers trace two separate bipolar outflows, one associated with Sh2-76EMM1 and the other with Sh2-76EMM2. The spectral energy distribution (SED) of Sh2-76EMM1 suggests it to be a class I YSO. We have only limited data points for the SED fit of Sh2-76EMM2, therefore can only speculate it to be probably a class II based on its comparative K-band and H-band magnitudes.

Star formation inside a galactic outflow.

PubMed

Maiolino, R; Russell, H R; Fabian, A C; Carniani, S; Gallagher, R; Cazzoli, S; Arribas, S; Belfiore, F; Bellocchi, E; Colina, L; Cresci, G; Ishibashi, W; Marconi, A; Mannucci, F; Oliva, E; Sturm, E

2017-04-13

Recent observations have revealed massive galactic molecular outflows that may have the physical conditions (high gas densities) required to form stars. Indeed, several recent models predict that such massive outflows may ignite star formation within the outflow itself. This star-formation mode, in which stars form with high radial velocities, could contribute to the morphological evolution of galaxies, to the evolution in size and velocity dispersion of the spheroidal component of galaxies, and would contribute to the population of high-velocity stars, which could even escape the galaxy. Such star formation could provide in situ chemical enrichment of the circumgalactic and intergalactic medium (through supernova explosions of young stars on large orbits), and some models also predict it to contribute substantially to the star-formation rate observed in distant galaxies. Although there exists observational evidence for star formation triggered by outflows or jets into their host galaxy, as a consequence of gas compression, evidence for star formation occurring within galactic outflows is still missing. Here we report spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448. The inferred star-formation rate in the outflow is larger than 15 solar masses per year. Star formation may also be occurring in other galactic outflows, but may have been missed by previous observations owing to the lack of adequate diagnostics.

Limits on the location of planetesimal formation in self-gravitating protostellar discs

NASA Astrophysics Data System (ADS)

Clarke, C. J.; Lodato, G.

2009-09-01

In this Letter, we show that if planetesimals form in spiral features in self-gravitating discs, as previously suggested by the idealized simulations of Rice et al., then in realistic protostellar discs, this process will be restricted to the outer regions of the disc (i.e. at radii in excess of several tens of au). This restriction relates to the requirement that dust has to be concentrated in spiral features on a time-scale that is less than the (roughly dynamical) lifetime of such features, and that such rapid accumulation requires spiral features whose fractional amplitude is not much less than unity. This in turn requires that the cooling time-scale of the gas is relatively short, which restricts the process to the outer disc. We point out that the efficient conversion of a large fraction of the primordial dust in the disc into planetesimals could rescue this material from the well-known problem of rapid inward migration at an approximate metre-size scale and that in principle the collisional evolution of these objects could help to resupply small dust to the protostellar disc. We also point out the possible implications of this scenario for the location of planetesimal belts inferred in debris discs around main sequence stars, but stress that further dynamical studies are required in order to establish whether the disc retains a memory of the initial site of planetesimal creation.

Astrochemical evolution along star formation: Overview of the IRAM Large Program ASAI

NASA Astrophysics Data System (ADS)

Lefloch, Bertrand; Bachiller, R.; Ceccarelli, C.; Cernicharo, J.; Codella, C.; Fuente, A.; Kahane, C.; López-Sepulcre, A.; Tafalla, M.; Vastel, C.; Caux, E.; González-García, M.; Bianchi, E.; Gómez-Ruiz, A.; Holdship, J.; Mendoza, E.; Ospina-Zamudio, J.; Podio, L.; Quénard, D.; Roueff, E.; Sakai, N.; Viti, S.; Yamamoto, S.; Yoshida, K.; Favre, C.; Monfredini, T.; Quitián-Lara, H. M.; Marcelino, N.; Roberty, H. Boechat; Cabrit, S.

2018-04-01

Evidence is mounting that the small bodies of our Solar System, such as comets and asteroids, have at least partially inherited their chemical composition from the first phases of the Solar System formation. It then appears that the molecular complexity of these small bodies is most likely related to the earliest stages of star formation. It is therefore important to characterize and to understand how the chemical evolution changes with solar-type protostellar evolution. We present here the Large Program "Astrochemical Surveys At IRAM" (ASAI). Its goal is to carry out unbiased millimeter line surveys between 80 and 272 GHz of a sample of ten template sources, which fully cover the first stages of the formation process of solar-type stars, from prestellar cores to the late protostellar phase. In this article, we present an overview of the surveys and results obtained from the analysis of the 3 mm band observations. The number of detected main isotopic species barely varies with the evolutionary stage and is found to be very similar to that of massive star-forming regions. The molecular content in O- and C- bearing species allows us to define two chemical classes of envelopes, whose composition is dominated by either a) a rich content in O-rich complex organic molecules, associated with hot corino sources, or b) a rich content in hydrocarbons, typical of Warm Carbon Chain Chemistry sources. Overall, a high chemical richness is found to be present already in the initial phases of solar-type star formation.

On the origin of jets from disc-accreting magnetized stars

NASA Astrophysics Data System (ADS)

Lovelace, Richard V. E.; Romanova, Marina M.; Lii, Patrick; Dyda, Sergei

2014-09-01

A brief review of the origin of jets from disc-accreting rotating magnetized stars is given. In most models, the interior of the disc is characterized by a turbulent viscosity and magnetic diffusivity ("alpha" discs) whereas the coronal region outside the disc is treated using ideal magnetohydrodynamics (MHD). Extensive MHD simulations have established the occurrence of long-lasting outflows in the case of both slowly and rapidly rotating stars. (1) Slowly rotating stars exhibit a new type of outflow, conical winds. Conical winds are generated when stellar magnetic flux is bunched up by the inward motion of the accretion disc. Near their region of origin, the winds have a thin conical shell shape with half opening angle of ˜30°. At large distances, their toroidal magnetic field collimates the outflow forming current carrying, matter dominated jets. These winds are predominantly magnetically and not centrifugally driven. About 10-30% of the disc matter from the inner disc is launched in the conical wind. Conical winds may be responsible for episodic as well as long lasting outflows in different types of stars. (2) Rapidly rotating stars in the "propeller regime" exhibit two-component outflows. One component is similar to the matter dominated conical wind, where a large fraction of the disc matter may be ejected in this regime. The second component is a high-velocity, low-density magnetically dominated axial jet where matter flows along the open polar field lines of the star. The axial jet has a mass flux of about 10% that of the conical wind, but its energy flux, due to the Poynting flux, can be as large as for the conical wind. The jet's magnetically dominated angular momentum flux causes the star to spin down rapidly. Propeller-driven outflows may be responsible for protostellar jets and their rapid spin-down. When the artificial requirement of symmetry about the equatorial plane is dropped, the conical winds are found to come alternately from one side of the disc and then the other, even for the case where the stellar magnetic field is a centered axisymmetric dipole. Recent MHD simulations of disc accretion to rotating stars in the propeller regime have been done with no turbulent viscosity and no diffusivity. The strong turbulence observed is due to the magneto-rotational instability. This turbulence drives accretion in the disc and leads to episodic conical winds and jets.

Probing changes of dust properties along a chain of solar-type prestellar and protostellar cores in Taurus with NIKA

NASA Astrophysics Data System (ADS)

Bracco, A.; Palmeirim, P.; André, Ph.; Adam, R.; Ade, P.; Bacmann, A.; Beelen, A.; Benoît, A.; Bideaud, A.; Billot, N.; Bourrion, O.; Calvo, M.; Catalano, A.; Coiffard, G.; Comis, B.; D'Addabbo, A.; Désert, F.-X.; Didelon, P.; Doyle, S.; Goupy, J.; Könyves, V.; Kramer, C.; Lagache, G.; Leclercq, S.; Macías-Pérez, J. F.; Maury, A.; Mauskopf, P.; Mayet, F.; Monfardini, A.; Motte, F.; Pajot, F.; Pascale, E.; Peretto, N.; Perotto, L.; Pisano, G.; Ponthieu, N.; Revéret, V.; Rigby, A.; Ritacco, A.; Rodriguez, L.; Romero, C.; Roy, A.; Ruppin, F.; Schuster, K.; Sievers, A.; Triqueneaux, S.; Tucker, C.; Zylka, R.

2017-08-01

The characterization of dust properties in the interstellar medium is key for understanding the physics and chemistry of star formation. Mass estimates are crucial to determine gravitational collapse conditions for the birth of new stellar objects in molecular clouds. However, most of these estimates rely on dust models that need further observational constraints to capture the relevant parameter variations depending on the local environment: from clouds to prestellar and protostellar cores. We present results of a new study of dust emissivity changes based on millimeter continuum data obtained with the NIKA camera at the IRAM-30 m telescope. Observing dust emission at 1.15 mm and 2 mm allows us to constrain the dust emissivity index, β, in the Rayleigh-Jeans tail of the dust spectral energy distribution far from its peak emission, where the contribution of other parameters (I.e. dust temperature) is more important. Focusing on the Taurus molecular cloud, one of the most famous low-mass star-forming regions in the Gould Belt, we analyze the emission properties of several distinct objects in the B213 filament. This subparsec-sized region is of particular interest since it is characterized by a collection ofevolutionary stages of early star formation: three prestellar cores, two Class 0/I protostellar cores and one Class II object. We are therefore able to compare dust properties among a sequence of sources that likely derive from the same parent filament. By means of the ratio of the two NIKA channel maps, we show that in the Rayleigh-Jeans approximation, βRJ varies among the objects: it decreases from prestellar cores (βRJ 2) to protostellar cores (βRJ 1) and the Class II object (βRJ 0). For one prestellar and two protostellar cores, we produce a robust study using available Herschel data to constrain the dust temperature of the sources. By using the Abel transform inversion technique we derive accurate radial temperature profiles that allow us to obtain radial β profiles. We find systematic spatial variations of β in the protostellar cores that are not observed in the prestellar core. While in the former case β decreases toward the center (with β varying between 1 and 2), in the latter it remains constant (β = 2.4 ± 0.3). Moreover, the dust emissivity index appears anticorrelated with the dust temperature. We discuss the implication of these results in terms of dust grain evolution between pre- and protostellar cores. Based on observations carried out under project number 146-13 with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).The FITS file of the published maps is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/604/A52

Nonaxisymmetric evolution in protostellar disks

NASA Technical Reports Server (NTRS)

Laughlin, Gregory; Bodenheimer, Peter

1994-01-01

We present a two-dimensional, multigridded hydrodynamical simulation of the collapse of an axisymmetric, rotating, 1 solar mass protostellar cloud, which forms a resolved, hydrotastic disk. The code includes the effects of physical viscosity, radiative transfer and radiative acceleration but not magnetic fields. We examine how the disk is affected by the inclusion of turbulent viscosity by comparing a viscous simulation with an inviscid model evolved from the same initial conditions, and we derive a disk evolutionary timescale on the order of 300,000 years if alpha = 0.01. Effects arising from non-axisymmetric gravitational instabilities in the protostellar disk are followed with a three-dimensional SPH code, starting from the two-dimensional structure. We find that the disk is prone to a series of spiral instabilities with primary azimulthal mode number m = 1 and m = 2. The torques induced by these nonaxisymmetric structures elicit material transport of angular momentum and mass through the disk, readjusting the surface density profile toward more stable configurations. We present a series of analyses which characterize both the development and the likely source of the instabilities. We speculate that an evolving disk which maintains a minimum Toomre Q-value approximately 1.4 will have a total evolutionary span of several times 10(exp 5) years, comparable to, but somewhat shorter than the evolutionary timescale resulting from viscous turbulence alone. We compare the evolution resulting from nonaxisymmetric instabilities with solutions of a one-dimensional viscous diffusion equation applied to the initial surface density and temperature profile. We find that an effective alpha-value of 0.03 is a good fit to the results of the simulation. However, the effective alpha will depend on the minimum Q in the disk at the time the instability is activated. We argue that the major fraction of the transport characterized by the value of alpha is due to the action of gravitational torques, and does not arise from inherent viscosity within the smoothed particle hydrodynamics method.

Cold Ion Outflow Modulated by the Solar Wind Energy Input and Tilt of the Geomagnetic Dipole

NASA Astrophysics Data System (ADS)

Li, Kun; Wei, Y.; André, M.; Eriksson, A.; Haaland, S.; Kronberg, E. A.; Nilsson, H.; Maes, L.; Rong, Z. J.; Wan, W. X.

2017-10-01

The solar wind energy input into the Earth's magnetosphere-ionosphere system drives ionospheric outflow, which plays an important role in both the magnetospheric dynamics and evolution of the atmosphere. However, little is known about the cold ion outflow with energies lower than a few tens of eV, as the direct measurement of cold ions is difficult because a spacecraft gains a positive electric charge due to the photoemission effect, which prevents cold ions from reaching the onboard detectors. A recent breakthrough in the measurement technique using Cluster spacecraft revealed that cold ions dominate the ion population in the magnetosphere. This new technique yields a comprehensive data set containing measurements of the velocities and densities of cold ions for the years 2001-2010. In this paper, this data set is used to analyze the cold ion outflow from the ionosphere. We found that about 0.1% of the solar wind energy input is transformed to the kinetic energy of cold ion outflow at the topside ionosphere. We also found that the geomagnetic dipole tilt can significantly affect the density of cold ion outflow, modulating the outflow rate of cold ion kinetic energy. These results give us clues to study the evolution of ionospheric outflow with changing global magnetic field and solar wind condition in the history.

Alternative paradigm for the cosmic objects formation: New prospects

NASA Astrophysics Data System (ADS)

Harutyunian, Haik A.

2017-12-01

We consider here briefly the cosmogonic concept suggested by Viktor Ambartsumian in the last century for explaining the formation of cosmic objects. He grounded his concept using the observational facts available in 40s-60s of the last century. The analysis of observational data allowed him to conclude that cosmic objects formation takes place up to nowadays. The second and more "heretical" conclusion he arrived at persuades that the origination and further evolution of cosmic objects goes on in course of gradual decay of proto-stellar matter at all hierarchical levels. We argue that this approach appeared first time in Ambartsumian's papers devoted to the problems of quantum electrodynamics. Later on his concept on objects formation due to decay of protostellar dense matter was rejected because the known laws of physics do not allow existence of huge masses consisted of superdense matter. We bring to the readers' attention, that the discovery of dark energy changes the situation drastically and opens new rooms for the ideas forgotten by the scientific community.

DEEPLY EMBEDDED PROTOSTELLAR POPULATION IN THE 20 km s{sup −1} CLOUD OF THE CENTRAL MOLECULAR ZONE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Xing; Gu, Qiusheng; Zhang, Qizhou

2015-12-01

We report the discovery of a population of deeply embedded protostellar candidates in the 20 km s{sup −1} cloud, one of the massive molecular clouds in the Central Molecular Zone (CMZ) of the Milky Way, using interferometric submillimeter continuum and H{sub 2}O maser observations. The submillimeter continuum emission shows five 1 pc scale clumps, each of which further fragments into several 0.1 pc scale cores. We identify 17 dense cores, among which 12 are gravitationally bound. Among the 18 H{sub 2}O masers detected, 13 coincide with the cores and probably trace outflows emanating from the protostars. There are also 5more » gravitationally bound dense cores without H{sub 2}O maser detection. In total, the 13 masers and 5 cores may represent 18 protostars with spectral types later than B1 or potentially growing more massive stars at earlier evolutionary stages, given the non-detection in the centimeter radio continuum. In combination with previous studies of CH{sub 3}OH masers, we conclude that the star formation in this cloud is at an early evolutionary phase, before the presence of any significant ionizing or heating sources. Our findings indicate that star formation in this cloud may be triggered by a tidal compression as it approaches pericenter, similar to the case of G0.253+0.016 but with a higher star formation rate, and demonstrate that high angular resolution, high-sensitivity maser, and submillimeter observations are promising techniques to unveil deeply embedded star formation in the CMZ.« less

INFALLING–ROTATING MOTION AND ASSOCIATED CHEMICAL CHANGE IN THE ENVELOPE OF IRAS 16293–2422 SOURCE A STUDIED WITH ALMA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oya, Yoko; López-Sepulcre, Ana; Watanabe, Yoshimasa

2016-06-20

We have analyzed rotational spectral line emission of OCS, CH{sub 3}OH, HCOOCH{sub 3}, and H{sub 2}CS observed toward the low-mass Class 0 protostellar source IRAS 16293–2422 Source A at a sub-arcsecond resolution (∼0.″6 × 0.″5) with ALMA. Significant chemical differentiation is found on a scale of 50 au. The OCS line is found to trace well the infalling–rotating envelope in this source. On the other hand, the distributions of CH{sub 3}OH and HCOOCH{sub 3} are found to be concentrated around the inner part of the infalling–rotating envelope. With a simple ballistic model of the infalling–rotating envelope, the radius of themore » centrifugal barrier (a half of the centrifugal radius) and the protostellar mass are evaluated from the OCS data to be from 40 to 60 au and from 0.5 to 1.0 M {sub ⊙}, respectively, assuming the inclination angle of the envelope/disk structure to be 60° (90° for the edge-on configuration). Although the protostellar mass is correlated with the inclination angle, the radius of the centrifugal barrier is not. This is the first indication of the centrifugal barrier of the infalling–rotating envelope in a hot corino source. CH{sub 3}OH and HCOOCH{sub 3} may be liberated from ice mantles by weak accretion shocks around the centrifugal barrier and/or by protostellar heating. The H{sub 2}CS emission seems to come from the disk component inside the centrifugal barrier in addition to the envelope component. The centrifugal barrier plays a central role not only in the formation of a rotationally supported disk but also in the chemical evolution from the envelope to the protoplanetary disk.« less

Circumstellar Disks and Outflows in Turbulent Molecular Cloud Cores: Possible Formation Mechanism for Misaligned Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsumoto, Tomoaki; Machida, Masahiro N.; Inutsuka, Shu-ichiro, E-mail: matsu@hosei.ac.jp

2017-04-10

We investigate the formation of circumstellar disks and outflows subsequent to the collapse of molecular cloud cores with the magnetic field and turbulence. Numerical simulations are performed by using an adaptive mesh refinement to follow the evolution up to ∼1000 years after the formation of a protostar. In the simulations, circumstellar disks are formed around the protostars; those in magnetized models are considerably smaller than those in nonmagnetized models, but their size increases with time. The models with stronger magnetic fields tend to produce smaller disks. During evolution in the magnetized models, the mass ratios of a disk to amore » protostar is approximately constant at ∼1%–10%. The circumstellar disks are aligned according to their angular momentum, and the outflows accelerate along the magnetic field on the 10–100 au scale; this produces a disk that is misaligned with the outflow. The outflows are classified into two types: a magnetocentrifugal wind and a spiral flow. In the latter, because of the geometry, the axis of rotation is misaligned with the magnetic field. The magnetic field has an internal structure in the cloud cores, which also causes misalignment between the outflows and the magnetic field on the scale of the cloud core. The distribution of the angular momentum vectors in a core also has a non-monotonic internal structure. This should create a time-dependent accretion of angular momenta onto the circumstellar disk. Therefore, the circumstellar disks are expected to change their orientation as well as their sizes in the long-term evolutions.« less

Astrochemical evolution along star formation: overview of the IRAM Large Program ASAI

NASA Astrophysics Data System (ADS)

Lefloch, Bertrand; Bachiller, R.; Ceccarelli, C.; Cernicharo, J.; Codella, C.; Fuente, A.; Kahane, C.; López-Sepulcre, A.; Tafalla, M.; Vastel, C.; Caux, E.; González-García, M.; Bianchi, E.; Gómez-Ruiz, A.; Holdship, J.; Mendoza, E.; Ospina-Zamudio, J.; Podio, L.; Quénard, D.; Roueff, E.; Sakai, N.; Viti, S.; Yamamoto, S.; Yoshida, K.; Favre, C.; Monfredini, T.; Quitián-Lara, H. M.; Marcelino, N.; Boechat-Roberty, H. M.; Cabrit, S.

2018-07-01

Evidence is mounting that the small bodies of our Solar system, such as comets and asteroids, have at least partially inherited their chemical composition from the first phases of the Solar system formation. It then appears that the molecular complexity of these small bodies is most likely related to the earliest stages of star formation. It is therefore important to characterize and to understand how the chemical evolution changes with solar-type protostellar evolution. We present here the Large Program `Astrochemical Surveys At IRAM' (ASAI). Its goal is to carry out unbiased millimetre line surveys between 80 and 272 GHz of a sample of 10 template sources, which fully cover the first stages of the formation process of solar-type stars, from pre-stellar cores to the late protostellar phase. In this paper, we present an overview of the surveys and results obtained from the analysis of the 3 mm band observations. The number of detected main isotopic species barely varies with the evolutionary stage and is found to be very similar to that of massive star-forming regions. The molecular content in O- and C-bearing species allows us to define two chemical classes of envelopes, whose composition is dominated by either (a) a rich content in O-rich complex organic molecules, associated with hot corino sources, or (b) a rich content in hydrocarbons, typical of warm carbon-chain chemistry sources. Overall, a high chemical richness is found to be present already in the initial phases of solar-type star formation.

Towards a population synthesis model of self-gravitating disc fragmentation and tidal downsizing II: the effect of fragment-fragment interactions

NASA Astrophysics Data System (ADS)

Forgan, D. H.; Hall, C.; Meru, F.; Rice, W. K. M.

2018-03-01

It is likely that most protostellar systems undergo a brief phase where the protostellar disc is self-gravitating. If these discs are prone to fragmentation, then they are able to rapidly form objects that are initially of several Jupiter masses and larger. The fate of these disc fragments (and the fate of planetary bodies formed afterwards via core accretion) depends sensitively not only on the fragment's interaction with the disc, but also with its neighbouring fragments. We return to and revise our population synthesis model of self-gravitating disc fragmentation and tidal downsizing. Amongst other improvements, the model now directly incorporates fragment-fragment interactions while the disc is still present. We find that fragment-fragment scattering dominates the orbital evolution, even when we enforce rapid migration and inefficient gap formation. Compared to our previous model, we see a small increase in the number of terrestrial-type objects being formed, although their survival under tidal evolution is at best unclear. We also see evidence for disrupted fragments with evolved grain populations - this is circumstantial evidence for the formation of planetesimal belts, a phenomenon not seen in runs where fragment-fragment interactions are ignored. In spite of intense dynamical evolution, our population is dominated by massive giant planets and brown dwarfs at large semimajor axis, which direct imaging surveys should, but only rarely, detect. Finally, disc fragmentation is shown to be an efficient manufacturer of free-floating planetary mass objects, and the typical multiplicity of systems formed via gravitational instability will be low.

Millimeter and Submillimeter Survey of the R Coronae Australis Region

NASA Astrophysics Data System (ADS)

Groppi, Christopher E.; Kulesa, Craig; Walker, Christopher; Martin, Christopher L.

2004-09-01

Using a combination of data from the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO), the Arizona Radio Observatory Kitt Peak 12 m telescope, and the Arizona Radio Observatory 10 m Heinrich Hertz Telescope, we have studied the most active part of the R CrA molecular cloud in multiple transitions of carbon monoxide, HCO+, and 870 μm continuum emission. Since R CrA is nearby (130 pc), we are able to obtain physical spatial resolution as high as 0.01 pc over an area of 0.16 pc2, with velocity resolution finer than 1 km s-1. Mass estimates of the protostar driving the millimeter-wave emission derived from HCO+, dust continuum emission, and kinematic techniques point to a young, deeply embedded protostar of ~0.5-0.75 Msolar, with a gaseous envelope of similar mass. A molecular outflow is driven by this source that also contains at least 0.8 Msolar of molecular gas with ~0.5 Lsolar of mechanical luminosity. HCO+ lines show the kinematic signature of infall motions, as well as bulk rotation. The source is most likely a Class 0 protostellar object not yet visible at near-IR wavelengths. With the combination of spatial and spectral resolution in our data set, we are able to disentangle the effects of infall, rotation, and outflow toward this young object.

THE SPINDLE: AN IRRADIATED DISK AND BENT PROTOSTELLAR JET IN ORION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bally, John; Youngblood, Allison; Ginsburg, Adam, E-mail: John.Bally@colorado.edu, E-mail: Allison.Youngblood@colorado.edu, E-mail: Adam.Ginsburg@colorado.edu

2012-09-10

We present Hubble Space Telescope observations of a bent, pulsed Herbig-Haro jet, HH 1064, emerging from the young star Parenago 2042 embedded in the H II region NGC 1977 located about 30' north of the Orion Nebula. This outflow contains eight bow shocks in the redshifted western lobe and five bow shocks in the blueshifted eastern lobe. Shocks within a few thousand AU of the source star exhibit proper motions of {approx}160 km s{sup -1} but motions decrease with increasing distance. Parenago 2042 is embedded in a proplyd-a photoevaporating protoplanetary disk. A remarkable set of H{alpha} arcs resembling a spindlemore » surround the redshifted (western) jet. The largest arc with a radius of 500 AU may trace the ionized edge of a circumstellar disk inclined by {approx}30 Degree-Sign . The spindle may be the photoionized edge of either a {approx}3 km s{sup -1} FUV-driven wind from the outer disk or a faster MHD-powered flow from an inner disk. The HH 1064 jet appears to be deflected north by photoablation of the south-facing side of a mostly neutral jet beam. V2412 Ori, located 1' west of Parenago 2042 drives a second bent flow, HH 1065. Both HH 1064 and 1065 are surrounded by LL Ori-type bows marking the boundary between the outflow cavity and the surrounding nebula.« less

Probing the CO and methanol snow lines in young protostars. Results from the CALYPSO IRAM-PdBI survey

NASA Astrophysics Data System (ADS)

Anderl, S.; Maret, S.; Cabrit, S.; Belloche, A.; Maury, A. J.; André, Ph.; Codella, C.; Bacmann, A.; Bontemps, S.; Podio, L.; Gueth, F.; Bergin, E.

2016-06-01

Context. So-called snow lines, indicating regions where abundant volatiles freeze out onto the surface of dust grains, play an important role for planet growth and bulk composition in protoplanetary disks. They can already be observed in the envelopes of the much younger, low-mass Class 0 protostars, which are still in their early phase of heavy accretion. Aims: We aim to use the information on the sublimation regions of different kinds of ices to understand the chemistry of the envelope, its temperature and density structure, and the history of the accretion process. This information is crucial to get the full picture of the early protostellar collapse and the subsequent evolution of young protostars. Methods: As part of the CALYPSO IRAM Large Program, we have obtained observations of C18O, N2H+, and CH3OH towards nearby Class 0 protostars with the IRAM Plateau de Bure interferometer at sub-arcsecond resolution. For four of these sources, we have modeled the emission using a chemical code coupled with a radiative transfer module. Results: We observe an anti-correlation of C18O and N2H+ in NGC 1333-IRAS4A, NGC 1333-IRAS4B, L1157, and L1448C, with N2H+ forming a ring (perturbed by the outflow) around the centrally peaked C18O emission. This emission morphology, which is due to N2H+ being chemically destroyed by CO, reveals the CO and N2 ice sublimation regions in these protostellar envelopes with unprecedented resolution. We also observe compact methanol emission towards three of the sources. Based on our chemical model and assuming temperature and density profiles from the literature, we find that for all four sources the CO snow line appears further inwards than expected from the binding energy of pure CO ices (~855 K). The emission regions of models and observations match for a higher value of the CO binding energy of 1200 K, corresponding to a dust temperature of ~24 K at the CO snow line. The binding energy for N2 ices is modeled at 1000 K, also higher than for pure N2 ices. Furthermore, we find very low CO abundances inside the snow lines in our sources, about an order of magnitude lower than the total CO abundance observed in the gas on large scales in molecular clouds before depletion sets in. Conclusions: The high CO binding energy may hint at CO being frozen out in a polar ice environment like amorphous water ice or in non-polar CO2-rich ice. The low CO abundances are comparable to values found in protoplanetary disks, which may indicate an evolutionary scenario where these low values are already established in the protostellar phase. Based on observations carried out under project number U052 with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

Massive outflow properties suggest AGN fade slowly

NASA Astrophysics Data System (ADS)

Zubovas, Kastytis

2018-01-01

Massive large-scale active galactic nucleus (AGN) outflows are an important element of galaxy evolution, being a way through which the AGN can affect most of the host galaxy. However, outflows evolve on time-scales much longer than typical AGN episode durations, therefore most AGN outflows are not observed simultaneously with the AGN episode that inflated them. It is therefore remarkable that rather tight correlations between outflow properties and AGN luminosity exist. In this paper, I show that such correlations can be preserved during the fading phase of the AGN episode, provided that the AGN luminosity evolves as a power law with exponent αd ∼ 1 at late times. I also show that subsequent AGN episodes that illuminate an ongoing outflow are unlikely to produce outflow momentum or energy rates rising above the observed correlations. However, there may be many difficult-to-detect outflows with momentum and energy rates lower than expected from the current AGN luminosity. Detailed observations of AGN outflow properties might help constrain the activity histories of typical and/or individual AGN.

Dissecting the Butterfly: Dual Outflows in the Dual AGN NGC 6240

NASA Astrophysics Data System (ADS)

Mueller Sanchez, Francisco; Comerford, Julie; Nevin, Rebecca; Davies, Richard; Treister, Ezequiel; Privon, George

2018-01-01

Current theories of galaxy evolution invoke some kind of feedback (from the stars or the supermassive black hole) to explain the properties of galaxies. However, numerical simulations and observations have not been able to evaluate the real impact of feedback in galaxies. This is largely because most studies have focused on studying stellar feedback or AGN feedback alone, instead of considering the combined effect of both. In fact, this is an unexplored territory for observations due to the difficulty of separating the contribution from the two sources.In this contribution I present the discovery of a dual outflow of different species of gas in the prototypical merging galaxy NGC 6240 using HST imaging, long-slit and integral-eld spectroscopy: an AGN-driven outflow of highly-ionized gas to the northeast and a starburst-driven outflow of ionized hydrogen to the northwest. The AGN outflow extends up to 4 kpc along a position angle of 56 degrees, has a conical shape with an opening angle of 52 degrees and a maximum line-of-sight velocity of 350 km/s. The WFC3 images also reveal a bubble of Halpha emission in the northwest, which has no counterpart in [O III], consistent with a scenario in which the starburst is ionizing and driving outflowing winds which inflate the bubble at an expansion velocity of 380 km/s. Assuming a spherical geometry for the starburst-driven bubble and a conical geometry for the AGN-driven outflow, we estimate mass outflow rates of 26 Msun/yr and 62 Msun/yr, respectively. We conclude that the AGN contribution to the evolution of the merger remnant and the formation of outflowing winds is signicant in the central 5 kpc of NGC 6240.

An X-Ray/SDSS Sample: Observational Characterization of The Outflowing Gas

NASA Astrophysics Data System (ADS)

Perna, Michele; Brusa, M.; Lanzuisi, G.; Mignoli, M.

2016-10-01

Powerful ionised AGN-driven outflows, commonly detected both locally and at high redshift, are invoked to contribute to the co-evolution of SMBH and galaxies through feedback phenomena. Our recent works (Brusa+2015; 2016; Perna+2015a,b) have shown that the XMM-COSMOS targets with evidence of outflows collected so far ( 10 sources) appear to be associated with low X-ray kbol corrections (Lbol /LX ˜ 18), in spite of their spread in obscuration, in the locations on the SFR-Mstar diagram, in their radio emission. A higher statistical significance is required to validate a connection between outflow phenomena and a X-ray loudness. Moreover, in order to validate their binding nature to the galaxy fate, it is crucial to correctly determine the outflow energetics. This requires time consuming integral field spectroscopic (IFS) observations, which are, at present, mostly limited to high luminosity objectsThe study of SDSS data offers a complementary strategy to IFS efforts. I will present physical and demographic characterization of the AGN-galaxy system during the feedback phase obtained studying a sample of 500 X-ray/SDSS AGNs, at z<0.8. Outflow velocity inferred from [OIII]5007 emission line profile has been related to optical (e.g., [OIII] and bolometric luminosities, Eddington ratio, stellar velocity dispersion) and X-ray properties (intrinsic X-ray luminosity, obscuration and X-ray kbol correction), to determine what drives ionised winds. Several diagnostic line ratios have been used to infer the physical properties of the ionised outflowing gas. The knowledge of these properties can reduce the actual uncertainties in the outflow energetics by a factor of ten, pointing to improve our understanding of the AGN outflow phenomenon and its impact on galaxy evolution.

Observations of the Evolution of Ion Outflow During a Sawtooth Event

NASA Astrophysics Data System (ADS)

Lund, E. J.; Nowrouzi, N.; Kistler, L. M.; Cai, X.; Frey, H. U.

2015-12-01

Sawtooth oscillations are one of several convection modes known to exist in the magnetosphere. Recent simulations have suggested that O+^+ ions transported from the high-latitude ionosphere to the magnetotail can drive sawtooth events. We present observational case studies of sawtooth events using data from FAST near the noon-midnight meridional plane, Cluster in the magnetotail, GOES and LANL energetic particle sensors at geosynchronous orbit, and ACE solar wind data to investigate the evolution of ion outflow during sawtooth events and the question of whether O+^+ outflow from one tooth helps to drive subsequent teeth. We find that oxygen enters the tail from the lobes after each tooth onset, the oxygen fraction in the magnetotail often increases after a tooth onset, and that the oxygen fraction of outflowing ions increases after a tooth event both in the cusp and on the nightside. However, a significant amount of low energy oxygen (≲1 keV) can end up in the dayside inner magnetosphere.

Feedback and Feeding in the Context of Galaxy Evolution with SPICA: Direct Characterisation of Molecular Outflows and Inflows

NASA Astrophysics Data System (ADS)

González-Alfonso, E.; Armus, L.; Carrera, F. J.; Charmandaris, V.; Efstathiou, A.; Egami, E.; Fernández-Ontiveros, J. A.; Fischer, J.; Granato, G. L.; Gruppioni, C.; Hatziminaoglou, E.; Imanishi, M.; Isobe, N.; Kaneda, H.; Koziel-Wierzbowska, D.; Malkan, M. A.; Martín-Pintado, J.; Mateos, S.; Matsuhara, H.; Miniutti, G.; Nakagawa, T.; Pozzi, F.; Rico-Villas, F.; Rodighiero, G.; Roelfsema, P.; Spinoglio, L.; Spoon, H. W. W.; Sturm, E.; van der Tak, F.; Vignali, C.; Wang, L.

2017-11-01

A far-infrared observatory such as the SPace Infrared telescope for Cosmology and Astrophysics, with its unprecedented spectroscopic sensitivity, would unveil the role of feedback in galaxy evolution during the last 10 Gyr of the Universe (z = 1.5-2), through the use of far- and mid-infrared molecular and ionic fine structure lines that trace outflowing and infalling gas. Outflowing gas is identified in the far-infrared through P-Cygni line shapes and absorption blueshifted wings in molecular lines with high dipolar moments, and through emission line wings of fine-structure lines of ionised gas. We quantify the detectability of galaxy-scale massive molecular and ionised outflows as a function of redshift in AGN-dominated, starburst-dominated, and main-sequence galaxies, explore the detectability of metal-rich inflows in the local Universe, and describe the most significant synergies with other current and future observatories that will measure feedback in galaxies via complementary tracers at other wavelengths.

Lunar and Planetary Science XXXV: Ancient Mars Water and Landforms

NASA Technical Reports Server (NTRS)

2004-01-01

Titles in this section include: 1) Giant Lowland Polygons: Relics of an Ancient Martian Ocean? 2) Lake Shorelines: Earth Analogs for Hypothesized Martian Coastal Features; 3) Complex Evolution of Paleolacustrine Systems on Mars: An Example from the Holden Crater; 4) Geomorphology and Hydraulics of Ma'adim Vallis, Mars, During a Noachian/Hesperian Boundary Paleoflood; 5) Geologic Evolution of Dao Vallis, Mars; 6) Advances in Reconstructing the Geologic History of the Chryse Region Outflow Channels on Mars; 7) Ravi Vallis, Mars - Paleoflood Origin and Genesis of Secondary Chaos Zones; 8) Walla Walla Vallis and Wallula Crater: Two Recently Discovered Martian Features Record Aqueous History; 9) Tharsis Recharge: a Source of Groundwater for Martian Outflow Channels; 10) Factors Controlling Water Volumes and Release Rates in Martian Outflow Channels; 11) Significance of Confined Cavernous Systems for Outflow Channel Water Sources, Reactivation Mechanisms and Chaos Formation; 12) Systematic Differences in Topography of Martian and Terrestrial Drainage Basins; 13) Waves on Seas of Mars and Titan: Wind-Tunnel Experiments on Wind-Wave Generation in Extraterrestrial Atmospheres.

Figuring Out Gas and Galaxies in Enzo (FOGGIE): Simulating effects of feedback on galactic outflows

NASA Astrophysics Data System (ADS)

Morris, Melissa Elizabeth; Corlies, Lauren; Peeples, Molly; Tumlinson, Jason; O'Shea, Brian; Smith, Britton

2018-01-01

The circumgalactic medium (CGM) is the region beyond the galactic disk in which gas is accreted through pristine inflows from the intergalactic medium and expelled from the galaxy by stellar feedback in large outflows that can then be recycled back onto the disk. These gas cycles connect the galactic disk with its cosmic environment, making the CGM a vital component of galaxy evolution. However, the CGM is primarily observed in absorption, which can be difficult to interpret. In this study, we use high resolution cosmological hydrodynamic simulations of a Milky Way mass halo evolved with the code Enzo to aid the interpretation of these observations. In our simulations, we vary feedback strength and observe the effect it has on galactic outflows and the evolution of the galaxy’s CGM. We compare the star formation rate of the galaxy with the velocity flux and mass outflow rate as a function of height above the plane of the galaxy in order to measure the strength of the outflows and how far they extend outside of the galaxy.This work was supported by The Space Astronomy Summer Program at STScI and NSF grant AST-1517908.

The MYStIX Infrared-Excess Source Catalog

NASA Astrophysics Data System (ADS)

Povich, Matthew S.; Kuhn, Michael A.; Getman, Konstantin V.; Busk, Heather A.; Feigelson, Eric D.; Broos, Patrick S.; Townsley, Leisa K.; King, Robert R.; Naylor, Tim

2013-12-01

The Massive Young Star-Forming Complex Study in Infrared and X-rays (MYStIX) project provides a comparative study of 20 Galactic massive star-forming complexes (d = 0.4-3.6 kpc). Probable stellar members in each target complex are identified using X-ray and/or infrared data via two pathways: (1) X-ray detections of young/massive stars with coronal activity/strong winds or (2) infrared excess (IRE) selection of young stellar objects (YSOs) with circumstellar disks and/or protostellar envelopes. We present the methodology for the second pathway using Spitzer/IRAC, 2MASS, and UKIRT imaging and photometry. Although IRE selection of YSOs is well-trodden territory, MYStIX presents unique challenges. The target complexes range from relatively nearby clouds in uncrowded fields located toward the outer Galaxy (e.g., NGC 2264, the Flame Nebula) to more distant, massive complexes situated along complicated, inner Galaxy sightlines (e.g., NGC 6357, M17). We combine IR spectral energy distribution (SED) fitting with IR color cuts and spatial clustering analysis to identify IRE sources and isolate probable YSO members in each MYStIX target field from the myriad types of contaminating sources that can resemble YSOs: extragalactic sources, evolved stars, nebular knots, and even unassociated foreground/background YSOs. Applying our methodology consistently across 18 of the target complexes, we produce the MYStIX IRE Source (MIRES) Catalog comprising 20,719 sources, including 8686 probable stellar members of the MYStIX target complexes. We also classify the SEDs of 9365 IR counterparts to MYStIX X-ray sources to assist the first pathway, the identification of X-ray-detected stellar members. The MIRES Catalog provides a foundation for follow-up studies of diverse phenomena related to massive star cluster formation, including protostellar outflows, circumstellar disks, and sequential star formation triggered by massive star feedback processes.

Decoupling of magnetic fields in collapsing protostellar envelopes and disc formation and fragmentation

NASA Astrophysics Data System (ADS)

Zhao, Bo; Caselli, Paola; Li, Zhi-Yun; Krasnopolsky, Ruben

2018-02-01

Efficient magnetic braking is a formidable obstacle to the formation of rotationally supported discs (RSDs) around protostars in magnetized dense cores. We have previously shown, through 2D (axisymmetric) non-ideal magnetohydrodynamic simulations, that removing very small grains (VSGs: ∼10 Å to few 100 Å) can greatly enhance ambipolar diffusion and enable the formation of RSDs. Here, we extend the simulations of disc formation enabled by VSG removal to 3D. We find that the key to this scenario of disc formation is that the drift velocity of the magnetic field almost cancels out the infall velocity of the neutrals in the 102-103 au scale 'pseudo-disc' where the field lines are most severely pinched and most of protostellar envelope mass infall occurs. As a result, the bulk neutral envelope matter can collapse without dragging much magnetic flux into the disc-forming region, which lowers the magnetic braking efficiency. We find that the initial discs enabled by VSG removal tend to be Toomre-unstable, which leads to the formation of prominent spiral structures that function as centrifugal barriers. The piling-up of infall material near the centrifugal barrier often produces dense fragments of tens of Jupiter masses, especially in cores that are not too strongly magnetized. Some fragments accrete on to the central stellar object, producing bursts in mass accretion rate. Others are longer lived, although whether they can survive for a long term to produce multiple systems remains to be ascertained. Our results highlight the importance of dust grain evolution in determining the formation and properties of protostellar discs and potentially multiple systems.

Observations of Superwinds in Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Marlowe, A. T.; Heckman, T. M.; Wyse, R.; Schommer, R.

1993-12-01

Dwarf galaxies are important in developing our understanding of the formation and evolution of galaxies, and of the structure in the universe. The concept of supernova-driven mass outflows is a vital ingredient in theories of the structure and evolution of dwarfs galaxies. We have begun a detailed multi-waveband search for outflows in starbursting dwarf galaxies, and have obtained Fabry-Perot images and Echelle spectra of 20 nearby actively-star-forming dwarf galaxies. In about half the sample, the Fabry-Perot Hα images show loops and filaments with sizes of one to a few kpc. The Echelle spectra taken through the loops and filaments show kinematics consistent with expanding bubble-like structures. We describe these data, and present seven dwarfs in our sample that have the strongest evidence of outflows.

AGN outflows and feedback twenty years on

NASA Astrophysics Data System (ADS)

Harrison, C. M.; Costa, T.; Tadhunter, C. N.; Flütsch, A.; Kakkad, D.; Perna, M.; Vietri, G.

2018-03-01

It is twenty years since the seminal works by Magorrian and co-authors and by Silk and Rees, which, along with other related work, ignited an explosion of publications connecting active galactic nucleus (AGN)-driven outflows to galaxy evolution. With a surge in observations of AGN outflows, studies are attempting to test AGN feedback models directly using the outflow properties. With a focus on outflows traced by optical and CO emission lines, we discuss significant challenges that greatly complicate this task, from both an observational and theoretical perspective. We highlight the observational uncertainties involved and the assumptions required when deriving kinetic coupling efficiencies (that is, outflow kinetic power as a fraction of AGN luminosity) from typical observations. Based on recent models we demonstrate that extreme caution should be taken when comparing observationally derived kinetic coupling efficiencies to coupling efficiencies from fiducial feedback models.

OUTFLOW AND METALLICITY IN THE BROAD-LINE REGION OF LOW-REDSHIFT ACTIVE GALACTIC NUCLEI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shin, Jaejin; Woo, Jong-Hak; Nagao, Tohru

2017-01-20

Outflows in active galactic nuclei (AGNs) are crucial to understand in investigating the co-evolution of supermassive black holes (SMBHs) and their host galaxies since outflows may play an important role as an AGN feedback mechanism. Based on archival UV spectra obtained with the Hubble Space Telescope and IUE , we investigate outflows in the broad-line region (BLR) in low-redshift AGNs ( z < 0.4) through detailed analysis of the velocity profile of the C iv emission line. We find a dependence of the outflow strength on the Eddington ratio and the BLR metallicity in our low-redshift AGN sample, which ismore » consistent with earlier results obtained for high-redshift quasars. These results suggest that BLR outflows, gas accretion onto SMBHs, and past star formation activity in host galaxies are physically related in low-redshift AGNs as in powerful high-redshift quasars.« less

The Production of Cold Gas Within Galaxy Outflows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scannapieco, Evan

2017-03-01

I present a suite of three-dimensional simulations of the evolution of initially hot material ejected by starburst-driven galaxy outflows. The simulations are conducted in a comoving frame that moves with the material, tracking atomic/ionic cooling, Compton cooling, and dust cooling and destruction. Compton cooling is the most efficient of these processes, while the main role of atomic/ionic cooling is to enhance density inhomogeneities. Dust, on the other hand, has little effect on the outflow evolution, and is rapidly destroyed in all the simulations except for the case with the smallest mass flux. I use the results to construct a simplemore » steady-state model of the observed UV/optical emission from each outflow. The velocity profiles in this case are dominated by geometric effects, and the overall luminosities are extremely strong functions of the properties of the host system, as observed in ultra-luminous infrared galaxies (ULIRGs). Furthermore the luminosities and maximum velocities in several models are consistent with emission-line observations of ULIRGs, although the velocities are significantly greater than observed in absorption-line studies. It may be that absorption line observations of galaxy outflows probe entrained cold material at small radii, while emission-line observations probe cold material condensing from the initially hot medium at larger distances.« less

Effect of angular momentum alignment and strong magnetic fields on the formation of protostellar discs

NASA Astrophysics Data System (ADS)

Gray, William J.; McKee, Christopher F.; Klein, Richard I.

2018-01-01

Star-forming molecular clouds are observed to be both highly magnetized and turbulent. Consequently, the formation of protostellar discs is largely dependent on the complex interaction between gravity, magnetic fields, and turbulence. Studies of non-turbulent protostellar disc formation with realistic magnetic fields have shown that these fields are efficient in removing angular momentum from the forming discs, preventing their formation. However, once turbulence is included, discs can form in even highly magnetized clouds, although the precise mechanism remains uncertain. Here, we present several high-resolution simulations of turbulent, realistically magnetized, high-mass molecular clouds with both aligned and random turbulence to study the role that turbulence, misalignment, and magnetic fields have on the formation of protostellar discs. We find that when the turbulence is artificially aligned so that the angular momentum is parallel to the initial uniform field, no rotationally supported discs are formed, regardless of the initial turbulent energy. We conclude that turbulence and the associated misalignment between the angular momentum and the magnetic field are crucial in the formation of protostellar discs in the presence of realistic magnetic fields.

Outflow and Accretion Physics in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

McGraw, Sean Michael

2016-09-01

This dissertation focuses on placing observational constraints on outflows and accretion disks in active galactic nuclei (AGN) for the purpose of better understanding the physics of super-massive black holes (SMBHs) and their evolution with the host galaxy over cosmic time. Quasar outflows and their importance in SMBH-host galaxy co-evolution can be further understood by analyzing broad absorption lines (BALs) in rest-frame UV spectra that trace a range of wind conditions. We quantify the properties of the flows by conducting BAL variability studies using multiple-epoch spectra acquired primarily from MDM Observatory and from the Sloan Digital Sky Survey. Iron low-ionization BALs (FeLoBALs) are a rare type of outflow that may represent a transient phase in galaxy evolution, and we analyze the variations in 12 FeLoBAL quasars with redshifts between 0.7 ≤ z ≤ 1.9 and rest frame timescales between ˜10 d to 7.6 yr. We investigate BAL variability in 71 quasar outflows that exhibit P V absorption, a tracer of high column density gas (i.e. NH ≥ 1022 cm -2), in order to quantify the energies and momenta of the flows. We also characterize the variability patterns of 26 quasars with mini-BALs, an interesting class of absorbers that may represent a distinct phase in the evolution of outflows. Low-luminosity AGN (LLAGN) are important objects to study since their prominence in the local Universe suggest a possible evolution from the quasar era, and their low radiative outputs likely indicate a distinct mode of accretion onto the SMBH. We probe the accretion conditions in the LLAGN NGC 4203 by estimating the SMBH mass, which is obtained by modeling the 2-dimensional velocity field of the nebular gas using spectra from the Hubble Space Telescope. We detect significant BAL and mini-BAL variability in a subset of quasars from each of our samples, with measured rest-frame variability time-scales from days to years and over multiple years on average. Variable wavelength intervals are associated with high-ionization species such as C IV and N V, low-ionization lines including Mg II and Al III, and ground and excited states from Fe II multiplets. The detected BAL and mini-BAL variations in a subset of sources provide evidence supporting scenarios involving either transverse motions of gas or ionization changes within the absorbers. We conclude that some outflows in our samples likely exist on the order of 0.01-1 pc from the SMBH, and the possibility remains that we are tracing outflowing gas on larger scales within limits ranging from ≤10 pc to ≤1 kpc from the central source. We estimate outflow kinetic luminosities between ˜10 6 and 1 times the bolometric luminosity of the quasar, indicating that the BAL outflows we probe likely possess a range of energies and only some absorber energies are likely sufficient for AGN feedback processes. We estimate the SMBH mass in the LLAGN in NGC 4203 to be ˜1.1x10 7 solar masses within a factor of ˜2. This mass estimate in conjunction with theoretical predictions is consistent with the existence of a two-component accretion flow in the nucleus of NGC 4203, consisting of a hot, advection-dominated torus at small radii connected with a thin, radiatively efficient disk at larger scales. These results provide a significant increase in the information available for quasar outflow properties and the conditions in low-luminosity accretion disks, and will inform future observational and theoretical studies that attempt to construct a more complete picture of AGN and their effects on the surrounding environments.

Hierarchical Fragmentation in the Perseus Molecular Cloud: From the Cloud Scale to Protostellar Objects

NASA Astrophysics Data System (ADS)

Pokhrel, Riwaj; Myers, Philip C.; Dunham, Michael M.; Stephens, Ian W.; Sadavoy, Sarah I.; Zhang, Qizhou; Bourke, Tyler L.; Tobin, John J.; Lee, Katherine I.; Gutermuth, Robert A.; Offner, Stella S. R.

2018-01-01

We present a study of hierarchical structure in the Perseus molecular cloud, from the scale of the entire cloud (≳ 10 pc) to smaller clumps (∼1 pc), cores (∼0.05–0.1 pc), envelopes (∼300–3000 au), and protostellar objects (∼15 au). We use new observations from the Submillimeter Array (SMA) large project “Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES)” to probe the envelopes, and recent single-dish and interferometric observations from the literature for the remaining scales. This is the first study to analyze hierarchical structure over five scales in the same cloud complex. We compare the number of fragments with the number of Jeans masses in each scale to calculate the Jeans efficiency, or the ratio of observed to expected number of fragments. The velocity dispersion is assumed to arise either from purely thermal motions or from combined thermal and non-thermal motions inferred from observed spectral line widths. For each scale, thermal Jeans fragmentation predicts more fragments than observed, corresponding to inefficient thermal Jeans fragmentation. For the smallest scale, thermal plus non-thermal Jeans fragmentation also predicts too many protostellar objects. However, at each of the larger scales thermal plus non-thermal Jeans fragmentation predicts fewer than one fragment, corresponding to no fragmentation into envelopes, cores, and clumps. Over all scales, the results are inconsistent with complete Jeans fragmentation based on either thermal or thermal plus non-thermal motions. They are more nearly consistent with inefficient thermal Jeans fragmentation, where the thermal Jeans efficiency increases from the largest to the smallest scale.

Massive black hole factories: Supermassive and quasi-star formation in primordial halos

NASA Astrophysics Data System (ADS)

Schleicher, Dominik R. G.; Palla, Francesco; Ferrara, Andrea; Galli, Daniele; Latif, Muhammad

2013-10-01

Context. Supermassive stars and quasi-stars (massive stars with a central black hole) are both considered as potential progenitors for the formation of supermassive black holes. They are expected to form from rapidly accreting protostars in massive primordial halos. Aims: We explore how long rapidly accreting protostars remain on the Hayashi track, implying large protostellar radii and weak accretion luminosity feedback. We assess the potential role of energy production in the nuclear core, and determine what regulates the evolution of such protostars into quasi-stars or supermassive stars. Methods: We followed the contraction of characteristic mass shells in rapidly accreting protostars, and inferred the timescales for them to reach nuclear densities. We compared the characteristic timescales for nuclear burning with those for which the extended protostellar envelope can be maintained. Results: We find that the extended envelope can be maintained up to protostellar masses of 3.6 × 108 ṁ3 M⊙, where ṁ denotes the accretion rate in solar masses per year. We expect the nuclear core to exhaust its hydrogen content in 7 × 106 yr. If accretion rates ṁ ≫ 0.14 can still be maintained at this point, a black hole may form within the accreting envelope, leading to a quasi-star. Alternatively, the accreting object will gravitationally contract to become a main-sequence supermassive star. Conclusions: Due to the limited gas reservoir in typical 107 M⊙ dark matter halos, the accretion rate onto the central object may drop at late times, implying the formation of supermassive stars as the typical outcome of direct collapse. However, if high accretion rates are maintained, a quasi-star with an interior black hole may form.

Magnetic Protostars

NASA Astrophysics Data System (ADS)

Glagolevskij, Yu. V.

2015-09-01

A possible variant of the evolution of magnetic protostars "before the Hayashi phase" is discussed. Arguments are given in support of the following major properties of magnetic stars: (1) global magnetic dipole fields with predominant orientation of the magnetic lines of force in the plane of the equator of revolution; (2) slow rotation; (3) complex, two and three dipole structures of the magnetic field in a large part of the stars; (4) partition of stars into magnetic and normal in a proportion of 1:10 occurs during the period when the protostellar clouds undergo gravitational collapse "before the Hayashi phase."

Two separate outflows in the dual supermassive black hole system NGC 6240

NASA Astrophysics Data System (ADS)

Müller-Sánchez, F.; Nevin, R.; Comerford, J. M.; Davies, R. I.; Privon, G. C.; Treister, E.

2018-04-01

Theoretical models and numerical simulations have established a framework of galaxy evolution in which galaxies merge and create dual supermassive black holes (with separations of one to ten kiloparsecs), which eventually sink into the centre of the merger remnant, emit gravitational waves and coalesce. The merger also triggers star formation and supermassive black hole growth, and gas outflows regulate the stellar content1-3. Although this theoretical picture is supported by recent observations of starburst-driven and supermassive black hole-driven outflows4-6, it remains unclear how these outflows interact with the interstellar medium. Furthermore, the relative contributions of star formation and black hole activity to galactic feedback remain unknown7-9. Here we report observations of dual outflows in the central region of the prototypical merger NGC 6240. We find a black-hole-driven outflow of [O iii] to the northeast and a starburst-driven outflow of Hα to the northwest. The orientations and positions of the outflows allow us to isolate them spatially and study their properties independently. We estimate mass outflow rates of 10 and 75 solar masses per year for the Hα bubble and the [O iii] cone, respectively. Their combined mass outflow is comparable to the star formation rate10, suggesting that negative feedback on star formation is occurring.

Two separate outflows in the dual supermassive black hole system NGC 6240.

PubMed

Müller-Sánchez, F; Nevin, R; Comerford, J M; Davies, R I; Privon, G C; Treister, E

2018-04-01

Theoretical models and numerical simulations have established a framework of galaxy evolution in which galaxies merge and create dual supermassive black holes (with separations of one to ten kiloparsecs), which eventually sink into the centre of the merger remnant, emit gravitational waves and coalesce. The merger also triggers star formation and supermassive black hole growth, and gas outflows regulate the stellar content 1-3 . Although this theoretical picture is supported by recent observations of starburst-driven and supermassive black hole-driven outflows 4-6 , it remains unclear how these outflows interact with the interstellar medium. Furthermore, the relative contributions of star formation and black hole activity to galactic feedback remain unknown 7-9 . Here we report observations of dual outflows in the central region of the prototypical merger NGC 6240. We find a black-hole-driven outflow of [O III] to the northeast and a starburst-driven outflow of Hα to the northwest. The orientations and positions of the outflows allow us to isolate them spatially and study their properties independently. We estimate mass outflow rates of 10 and 75 solar masses per year for the Hα bubble and the [O III] cone, respectively. Their combined mass outflow is comparable to the star formation rate 10 , suggesting that negative feedback on star formation is occurring.

Quantifying the AGN-driven outflows in ULIRGs (QUADROS) II: evidence for compact outflow regions from HST [OIII] imaging observations

NASA Astrophysics Data System (ADS)

Tadhunter, C.; Zaurín, J. Rodríguez; Rose, M.; Spence, R. A. W.; Batcheldor, D.; Berg, M. A.; Ramos Almeida, C.; Spoon, H. W. W.; Sparks, W.; Chiaberge, M.

2018-05-01

The true importance of the warm, AGN-driven outflows for the evolution of galaxies remains uncertain. Measurements of the radial extents of the outflows are key for quantifying their masses and kinetic powers, and also establishing whether the AGN outflows are galaxy-wide. Therefore, as part of a larger project to investigate the significance of warm, AGN-driven outflows in the most rapidly evolving galaxies in the local universe, here we present deep Hubble Space Telescope (HST) narrow-band [OIII]λ5007 observations of a complete sample of 8 nearby ULIRGs with optical AGN nuclei. Combined with the complementary information provided by our ground-based spectroscopy, the HST images show that the warm gas outflows are relatively compact for most of the objects in the sample: in three objects the outflow regions are barely resolved at the resolution of HST (0.065 < R[OIII] < 0.12 kpc); in a further four cases the outflows are spatially resolved but with flux weighted mean radii in the range 0.65 < R[OIII] < 1.2 kpc; and in only one object (Mrk273) is there clear evidence for a more extended outflow, with a maximum extent of R[OIII] ˜ 5 kpc. Overall, our observations show little evidence for the galaxy-wide outflows predicted by some models of AGN feedback.

Substructures In Protostellar Discs: Spirals, Gaps (And Warps)

NASA Astrophysics Data System (ADS)

Lodato, Giuseppe

2016-07-01

The advent of high resolution imaging of protostellar discs, both in the sub-mm (thanks to ALMA) and in the near infrared, has radically changed our understanding of the evolution of such discs and of the planet formation process occuring within them. While in the past disc were modeled as simplified, axi-symmetric structures, often characterized by simple radial power-law for density and temperature, we now need more advanced modeling, able to describe the substructures observed. Such modeling needs to take into account both the gas component, that dominates the dynamics and the line emission, and the dust, which is responsible for the continuum mm band emission. Here, I review several aspects of such modeling. I will discuss the theory and some hydrodynamical simulations describing: (a) spiral density waves, for example induced by gravitational instabilities in young and massive discs; (b) gaps induced by the presence of a forming planet in the disc, with particular emphasis on the spectacular case of HL Tau, that we have recently successfully modeled; (c) warps, which are expected to develop in circumbinary discs, or in discs where a planet has been put on a very inclined orbit.

SEAC4RS Data and Information Page

Atmospheric Science Data Center

2015-07-01

... deep convection throughout the troposphere; to determine the evolution of gases and aerosols in deep convective outflow and the implications ... influence of biomass burning and pollution, their temporal evolution, and ultimately, impacts on meteorological processes which can, in ...

Characterizing Quasar Outflows I: Sample, Spectral Measurements

NASA Astrophysics Data System (ADS)

Ganguly, Rajib; Christenson, D. H.; Richmond, J. M.; Derseweh, J. A.; Robbins, J. M.; Townsend, S. L.; Stark, M. A.

2012-05-01

Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 11000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) measurements of UV emission line and continuum parameters. In this poster, we subjectively divide these quasars into four categories: broad absorption-line quasars (2700 objects), associated absorption-line quasars (1700 objects), reddened quasars (160 objects), and unabsorbed/unreddened quasars (6300 objects). We present measurements of the absorption (velocities, velocity widths, equivalent widths), composite spectral profiles of outflows as a function of velocity, as well as measurements of the continuum and CIV, MgII, and FeII emission-line properties. In accompanying posters, we add photometry from the rest-frame X-ray (ROSAT and Chandra), EUV (GALEX), optical (2MASS), and infrared (WISE) bands to complete the SED. The continuum and emission-line measurements from the SDSS spectra and accompanying photometry provides estimates on the black hole masses, bolometric luminsosities, and SED. We consider empirically how these affect the outflow properties. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program.

Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

NASA Astrophysics Data System (ADS)

Andrews, Brett H.; Weinberg, David H.; Schönrich, Ralph; Johnson, Jennifer A.

2017-02-01

Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the stellar initial mass function, the SN Ia delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in [O/Fe]-[Fe/H] and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]-[Fe/H] unlike the observed bimodality (separate high-α and low-α sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present [X/Fe]-[Fe/H] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of α-elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at https://github.com/bretthandrews/flexCE.

Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrews, Brett H.; Weinberg, David H.; Schönrich, Ralph

Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the stellar initial mass function, the SN Ia delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in [O/Fe]–[Fe/H] and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracksmore » in [O/Fe]–[Fe/H] unlike the observed bimodality (separate high- α and low- α sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present [X/Fe]–[Fe/H] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of α -elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at https://github.com/bretthandrews/flexCE.« less

Simulating Supernovae Driven Outflows in Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Rodriguez, Jaimee-Ian

2018-01-01

Galactic outflows, or winds, prove to be a necessary input for galactic simulations to produce results comparable to observation, for it solves issues caused by what previous literature dubbed the “angular momentum catastrophe.” While it is known that the nature of outflows depends on the nature of the Interstellar Medium (ISM), the mechanisms behind outflows are still not completely understood. We investigate the driving force behind galactic outflows and the factors that influence their behavior, hypothesizing that supernovae within the galaxy drive these winds. We study isolated, high-resolution, smooth particle hydrodynamic simulations, focusing specifically on dwarf galaxies due to their shallow potential wells, which allow for more significant outflows. We find that outflows follow star formation (and associated supernovae) suggesting the causal relationship between the two. Furthermore, simulations with higher diffusivity differ little in star formation rate, but show significantly lower outflow rates, suggesting that environmental factors that have little effect on regulating star formation can greatly influence outflows, and so efficient outflows can be driven by a constant rate of supernovae, depending on ISM behavior. We are currently analyzing disk morphology and ambient density in order to comprehend the effect of supernovae on the immediate interstellar gas. By attaining greater understanding of the origin of galactic outflows, we will be able to not only improve the accuracy of simulations, we will also be able to gain greater insight into galactic formation and evolution, as outflows and resultant inflows may be vital to the regulation of galaxies throughout their lifetimes.

An Archival COS Study of Multi-phase Galactic Outflows and Their Dependence on Host Galaxy Properties

NASA Astrophysics Data System (ADS)

Chisholm, John

2013-10-01

Galactic outflows have become vital for understanding galaxy evolution. Outflows have been used to explain the mass-metallicity relation, the star formation history of the universe, and the shape of the baryonic mass function. However, few studies have focused on the basic question of how outflow velocities depend upon the physical properties of their host galaxies. Here we propose an archival project utilizing 52 COS spectra of local star-forming galaxies spanning four decades of star formation rate, and stellar mass. We will preform a self-consistent analysis of trends between galactic properties {star formation rate, stellar mass, specific star formation rate and star formation rate surface density} and outflow velocities measured from interstellar metal absorption lines {e.g., CII 1335}. We will extend this analysis to different gas phases - cold, warm, and hot - to gain a more comprehensive understanding of the physics of multi-phase outflows. The trends we observe will provide insights into the feedback process and will be crucial new benchmarks for simulations.

Survey Observations to Study Chemical Evolution from High-mass Starless Cores to High-mass Protostellar Objects. I. HC3N and HC5N

NASA Astrophysics Data System (ADS)

Taniguchi, Kotomi; Saito, Masao; Sridharan, T. K.; Minamidani, Tetsuhiro

2018-02-01

We carried out survey observations of HC3N and HC5N in the 42‑45 GHz band toward 17 high-mass starless cores (HMSCs) and 35 high-mass protostellar objects (HMPOs) with the Nobeyama 45 m radio telescope. We have detected HC3N from 15 HMSCs and 28 HMPOs, and HC5N from 5 HMSCs and 14 HMPOs, respectively. The average values of the column density of HC3N are found to be (5.7+/- 0.7) × {10}12 and (1.03+/- 0.12)×{10}13 cm‑2 in HMSCs and HMPOs, respectively. The average values of the fractional abundance of HC3N are derived to be (6.6+/- 0.8)× {10}-11 and (3.6+/- 0.5)× {10}-11 in HMSCs and HMPOs, respectively. We find that the fractional abundance of HC3N decreases from HMSCs to HMPOs using the Kolmogorov–Smirnov test. On the other hand, its average value of the column density slightly increases from HMSCs to HMPOs. This may imply that HC3N is newly formed in dense gas in HMPO regions. We also investigate the relationship between the column density of HC3N in HMPOs and the luminosity-to-mass ratio (L/M), a physical evolutional indicator. The column density of HC3N tends to decrease with the increase of the L/M ratio, which suggests that HC3N is destroyed by the stellar activities.

A grid of one-dimensional low-mass star formation collapse models

NASA Astrophysics Data System (ADS)

Vaytet, N.; Haugbølle, T.

2017-02-01

Context. Numerical simulations of star formation are becoming ever more sophisticated, incorporating new physical processes in increasingly realistic set-ups. These models are being compared to the latest observations through state-of-the-art synthetic renderings that trace the different chemical species present in the protostellar systems. The chemical evolution of the interstellar and protostellar matter is very topical, with more and more chemical databases and reaction solvers available online to the community. Aims: The current study was developed to provide a database of relatively simple numerical simulations of protostellar collapse as a template library for observations of cores and very young protostars, and for researchers who wish to test their chemical modelling under dynamic astrophysical conditions. It was also designed to identify statistical trends that may appear when running many models of the formation of low-mass stars by varying the initial conditions. Methods: A large set of 143 calculations of the gravitational collapse of an isolated sphere of gas with uniform temperature and a Bonnor-Ebert-like density profile was undertaken using a 1D fully implicit Lagrangian radiation hydrodynamics code. The parameter space covered initial masses from 0.2 to 8 M⊙, temperatures of 5-30 K, and radii 3000 ≤ R0 ≤ 30 000 AU. Results: A spread due to differing initial conditions and optical depths, was found in the thermal evolutionary tracks of the runs. Within less than an order of magnitude, all first and second Larson cores had masses and radii essentially independent of the initial conditions. Radial profiles of the gas density, velocity, and temperature were found to vary much more outside of the first core than inside. The time elapsed between the formation of the first and second cores was found to strongly depend on the first core mass accretion rate, and no first core in our grid of models lived for longer than 2000 years before the onset of the second collapse. Conclusions: The end product of a protostellar cloud collapse, the second Larson core, is at birth a canonical object with a mass and radius of about 3 MJ and 8 RJ, independent of its initial conditions. The evolution sequence which brings the gas to stellar densities can, however, proceed in a variety of scenarios, on different timescales or along different isentropes, but each story line can largely be predicted by the initial conditions. All the data from the simulations are publicly available. The figures and raw data for every simulation output can be found at this address: http://starformation.hpc.ku.dk/grid-of-protostars. Copies of the outputs, as well as Table C.1, are also available in the form of static electronic tables at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A116

The Launching of Cold Clouds by Galaxy Outflows. I. Hydrodynamic Interactions with Radiative Cooling

NASA Astrophysics Data System (ADS)

Scannapieco, Evan; Brüggen, Marcus

2015-06-01

To better understand the nature of the multiphase material found in outflowing galaxies, we study the evolution of cold clouds embedded in flows of hot and fast material. Using a suite of adaptive mesh refinement simulations that include radiative cooling, we investigate both cloud mass loss and cloud acceleration under the full range of conditions observed in galaxy outflows. The simulations are designed to track the cloud center of mass, enabling us to study the cloud evolution at long disruption times. For supersonic flows, a Mach cone forms around the cloud, which damps the Kelvin-Helmholtz instability but also establishes a streamwise pressure gradient that stretches the cloud apart. If time is expressed in units of the cloud crushing time, both the cloud lifetime and the cloud acceleration rate are independent of cloud radius, and we find simple scalings for these quantities as a function of the Mach number of the external medium. A resolution study suggests that our simulations accurately describe the evolution of cold clouds in the absence of thermal conduction and magnetic fields, physical processes whose roles will be studied in forthcoming papers.

RADIO OBSERVATIONS OF THE STAR FORMATION ACTIVITIES IN THE NGC 2024 FIR 4 REGION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Minho; Kang, Miju; Lee, Jeong-Eun, E-mail: minho@kasi.re.kr

Star formation activities in the NGC 2024 FIR 4 region were studied by imaging centimeter continuum sources and water maser sources using several archival data sets from the Very Large Array. The continuum source VLA 9 is elongated in the northwest–southeast direction, consistent with the FIR 4 bipolar outflow axis, and has a flat spectrum in the 6.2–3.6 cm interval. The three water maser spots associated with FIR 4 are also distributed along the outflow axis. One of the spots is located close to VLA 9, and another one is close to an X-ray source. Examinations of the positions ofmore » compact objects in this region suggest that the FIR 4 cloud core contains a single low-mass protostar. VLA 9 is the best indicator of the protostellar position. VLA 9 may be a radio thermal jet driven by this protostar, and it is unlikely that FIR 4 contains a high-mass young stellar object (YSO). A methanol 6.7 GHz maser source is located close to VLA 9, at a distance of about 100 AU. The FIR 4 protostar must be responsible for the methanol maser action, which suggests that methanol class II masers are not necessarily excited by high-mass YSOs. Also discussed are properties of other centimeter continuum sources in the field of view and the water masers associated with FIR 6n. Some of the continuum sources are radio thermal jets, and some are magnetically active young stars.« less

X-ray diving in the center of Sh2-129: looking for the driving source of Ou4

NASA Astrophysics Data System (ADS)

Grosso, Nicolas

2012-10-01

The outflow phenomenon is associated both with the early and the last phase of the stellar evolution. Recently, a unique bipolar outflow with an angular size of 1.2 degrees was discovered in the blister HII region Sh2-129. Ou4, nicknamed "The Giant Squid", is to our knowledge the bipolar outflow with the largest angular size ever found. We propose joint XMM-Newton/EPIC (35 ks) and Chandra/HRC-I (16 ks) observations to look for the driving source of Ou4 and to clarify the nature of this object.

Efficient radiative transfer techniques in hydrodynamic simulations

NASA Astrophysics Data System (ADS)

Mercer, A.; Stamatellos, D.; Dunhill, A.

2018-05-01

Radiative transfer is an important component of hydrodynamic simulations as it determines the thermal properties of a physical system. It is especially important in cases where heating and cooling regulate significant processes, such as in the collapse of molecular clouds, the development of gravitational instabilities in protostellar discs, disc-planet interactions, and planet migration. We compare two approximate radiative transfer methods which indirectly estimate optical depths within hydrodynamic simulations using two different metrics: (i) the gravitational potential and density of the gas (Stamatellos et al.), and (ii) the pressure scale-height (Lombardi et al.). We find that both methods are accurate for spherical configurations e.g. in collapsing molecular clouds and within clumps that form in protostellar discs. However, the pressure scale-height approach is more accurate in protostellar discs (low and high-mass discs, discs with spiral features, discs with embedded planets). We also investigate the β-cooling approximation which is commonly used when simulating protostellar discs, and in which the cooling time is proportional to the orbital period of the gas. We demonstrate that the use of a constant β cannot capture the wide range of spatial and temporal variations of cooling in protostellar discs, which may affect the development of gravitational instabilities, planet migration, planet mass growth, and the orbital properties of planets.

Pre-biotic molecules in shocks: the case of L1157

NASA Astrophysics Data System (ADS)

Mendoza, Edgar; Lefloch, Bertrand; López-Sepulcre, Ana; Ceccarelli, Cecilia; Codella, Claudio; Boechat-Roberty, Heloisa M.; Bachiller, Rafael

2015-08-01

Interstellar molecules with a peptide link -NH-C(=O)-, like formamide (NH2CHO) and isocyanic acid (HNCO) are notably interesting for their potential role in pre-biotic chemistry. For first time, we report the detection of both molecules towards the protostellar shock L1157-B1 and L1157-B2, with the IRAM 30m telescope. Analysis of the line profiles shows that the emission arises from the outflow cavities associated with B1 and B2. From a simple rotational diagram analysis, molecular abundance of ≈ (0.4-1.1)×10-8 and (3.3-8.8)×10-8 are derived for NH2CHO and HNCO, respectively. The shock regions B1 and B2 appear to be among the richest Galactic sources of HNCO and NH2CHO molecules. We have observed a narrow linear correlation between their abundances, suggesting that the two species are chemically related. Comparison with astrochemical models favours molecule formation on ice grain mantles, with NH2CHO generated from hydrogenation of HNCO.

Radio Videos of Orion Protostars (with X-ray Colors!)

NASA Astrophysics Data System (ADS)

Forbrich, Jan; Wolk, Scott; Menten, Karl; Reid, Mark; Osten, Rachel

2013-07-01

High-energy processes in Young Stellar Objects (YSOs) can be observed both in X-rays and in the centimetric radio wavelength range. While the past decade has brought a lot of progress in the field of X-ray observations of YSOs, (proto)stellar centimetric radio astronomy has only recently begun to catch up with the advent of the newly expanded Karl G. Jansky Very Large Array (JVLA). The enhanced sensitivity is fundamentally improving our understanding of YSO radio properties by providing unprecedented sensitivity and thus spectral as well as temporal resolution. As a result, it is becoming easier to disentangle coronal-type nonthermal radio emission emanating from the immediate vicinity of YSOs from thermal emission on larger spatial scales, for example ionized material at the base of outflows. Of particular interest is the correlation of the by now relatively well-characterized X-ray flaring variability with the nonthermal radio variability. We present first results of multi-epoch simultaneous observations using Chandra and the JVLA, targeting the Orion Nebula Cluster and highlighting the capabilities of the JVLA for radio continuum observations of YSOs.

Connecting the small scale to the large scale: young massive stars and their environments from the Red MSX Source Survey.

NASA Astrophysics Data System (ADS)

Figura, Charles C.; Urquhart, James S.; Morgan, Lawrence

2015-01-01

We have conducted a detailed multi-wavelength investigation of a variety of massive star forming regions in order to characterise the impact of the interactions between the substructure of the dense protostellar clumps and their local environment, including feedback from the embedded proto-cluster.A selection of 70 MYSOs and HII regions identified by the RMS survey have been followed up with observations of the ammonia (1,1) and (2,2) inversion transitions made with the KFPA on the GBT. These maps have been combined with archival CO data to investigate the thermal and kinematic structure of the extended envelopes down to the dense clumps. We complement this larger-scale picture with high resolution near- and mid-infrared images to probe the properties of the embedded objects themselves.We present an overview of several sources from this sample that illustrate some of the the interactions that we observe. We find that high molecular column densities and kinetic temperatures are coincident with embedded sources and with shocks and outflows as exhibited in gas kinematics.

Evolution of CO lines in time-dependent models of protostellar disk formation

NASA Astrophysics Data System (ADS)

Harsono, D.; Visser, R.; Bruderer, S.; van Dishoeck, E. F.; Kristensen, L. E.

2013-07-01

Context. Star and planet formation theories predict an evolution in the density, temperature, and velocity structure as the envelope collapses and forms an accretion disk. While continuum emission can trace the dust evolution, spectrally resolved molecular lines are needed to determine the physical structure and collapse dynamics. Aims: The aim of this work is to model the evolution of the molecular excitation, line profiles, and related observables during low-mass star formation. Specifically, the signatures of disks during the deeply embedded stage (Menv > M⋆) are investigated. Methods: The semi-analytic 2D axisymmetric model of Visser and collaborators has been used to describe the evolution of the density, stellar mass, and luminosity from the pre-stellar to the T-Tauri phase. A full radiative transfer calculation is carried out to accurately determine the time-dependent dust temperatures. The time-dependent CO abundance is obtained from the adsorption and thermal desorption chemistry. Non-LTE near-IR (NIR), far-IR (FIR), and submm lines of CO have been simulated at a number of time steps. Results: In single dish (10-20'' beams), the dynamics during the collapse are best probed through highly excited 13CO and C18O lines, which are significantly broadened by the infall process. In contrast to the dust temperature, the CO excitation temperature derived from submm/FIR data does not vary during the protostellar evolution, consistent with C18O observations obtained with Herschel and from ground-based telescopes. The NIR spectra provide complementary information to the submm lines by probing not only the cold outer envelope but also the warm inner region. The NIR high-J (≥8) absorption lines are particularly sensitive to the physical structure of the inner few AU, which does show evolution. The models indicate that observations of 13CO and C18O low-J submm lines within a ≤1″ (at 140 pc) beam are well suited to probe embedded disks in Stage I (Menv < M⋆) sources, consistent with recent interferometric observations. High signal-to-noise ratio subarcsec resolution data with ALMA are needed to detect the presence of small rotationally supported disks during the Stage 0 phase and various diagnostics are discussed. The combination of spatially and spectrally resolved lines with ALMA and at NIR is a powerful method to probe the inner envelope and disk formation process during the embedded phase. Appendices are available in electronic form at http://www.aanda.org

Dense cavity walls traced by CS in the L1157-B1 protostellar shocked region

NASA Astrophysics Data System (ADS)

Gomez-Ruiz, Arturo; Codella, Claudio; Lefloch, Bertrand; Benedettini, Milena; Busquet, Gemma; Nisini, Brunella; Ceccarelli, Cecilia; Cabrit, Sylvie; Viti, Serena

2013-07-01

In the framework of the CHESS Key Program, an unbiased spectral survey performed with Herschel and IRAM, in the frequency range from 97 to 600 GHz, have provided a chemical census of the protostellar shock L1157-B1. Here we focus on the study of carbon monosulfide (CS), a standard tracer of high-density gas. We have detected a total of 18 emission lines, with E_u up to 183 K, due to four isotopologues (^12C^32S, ^12C^34S, ^13C^32S, and ^12C^33S). The unprecedented sensitivity of the survey allow us to carefully analyze the line profiles. These profiles can be well fitted by two exponential laws: I ∝ exp(-|v/v0|) with v0 = 4.4, and 2.5 km s-1. Remarkably these two exponential laws are the same as those found in the CO line profiles by Lefloch et al. (2012), and named g2 and g3 components, respectively. These components have been related to the cavity walls produced by the B1 shock and the older B2 shock, respectively. An important characteristic of the lines profiles is that the emission of high-J CS transitions (E_u > 60 K) comes only from the g2 component. Using the LVG approximation, the CS solutions constrain n >= 10^4.5 cm^-3. In addition, when contrasted with the CO results (that already constrained T_k of 90 K and 40 K for g2 and g3, respectively), we see that the LVG can provide strong constrains to the gas density, in this case about 5 x 10^5 cm^-3 for both g2 and g3 components. Thus, the combination of CO and CS is a powerful tool to constrain both n and T_k. Our CS observations show therefore that this molecule is highlighting the dense cavity walls produced by the episodic outflow.

Herschel Observations of Protostellar and Young Stellar Objects in Nearby Molecular Clouds: The DIGIT Open Time Key Project

NASA Astrophysics Data System (ADS)

Green, Joel D.; DIGIT OTKP Team

2010-01-01

The DIGIT (Dust, Ice, and Gas In Time) Open Time Key Project utilizes the PACS spectrometer (57-210 um) onboard the Herschel Space Observatory to study the colder regions of young stellar objects and protostellar cores, complementary to recent observations from Spitzer and ground-based observatories. DIGIT focuses on 30 embedded sources and 64 disk sources, and includes supporting photometry from PACS and SPIRE, as well as spectroscopy from HIFI, selected from nearby molecular clouds. For the embedded sources, PACS spectroscopy will allow us to address the origin of [CI] and high-J CO lines observed with ISO-LWS. Our observations are sensitive to the presence of cold crystalline water ice, diopside, and carbonates. Additionally, PACS scans are 5x5 maps of the embedded sources and their outflows. Observations of more evolved disk sources will sample low and intermediate mass objects as well as a variety of spectral types from A to M. Many of these sources are extremely rich in mid-IR crystalline dust features, enabling us to test whether similar features can be detected at larger radii, via colder dust emission at longer wavelengths. If processed grains are present only in the inner disk (in the case of full disks) or from the emitting wall surface which marks the outer edge of the gap (in the case of transitional disks), there must be short timescales for dust processing; if processed grains are detected in the outer disk, radial transport must be rapid and efficient. Weak bands of forsterite and clino- and ortho-enstatite in the 60-75 um range provide information about the conditions under which these materials were formed. For the Science Demonstration Phase we are observing an embedded protostar (DK Cha) and a Herbig Ae/Be star (HD 100546), exemplars of the kind of science that DIGIT will achieve over the full program.

Star formation quenching in quasar host galaxies

NASA Astrophysics Data System (ADS)

Carniani, Stefano

2017-10-01

Galaxy evolution is likely to be shaped by negative feedback from active galactic nuclei (AGN). In the whole range of redshifts and luminosities studied so far, galaxies hosting an AGN frequently show fast and extended outflows consisting in both ionised and molecular gas. Such outflows could potentially quench the start formation within the host galaxy, but a clear evidence of negative feedback in action is still missing. Hereby I will analyse integral-field spectroscopic data for six quasars at z ˜2.4 obtained with SINFONI in the H- and K-band. All the quasars show [OIII]λ5007 line detection of fast, extended outflows. Also, the high signal-to-noise SINFONI observations allow the identification of faint narrow Hα emission (FWHM < 500 km/s), which is spatially extended and associated with star formation in the host galaxy. On paper fast outflows are spatially anti-correlated with star-formation powered emission, i.e. star formation is suppressed in the area affected by the outflow. Nonetheless as narrow, spatially-extended Hα emission, indicating star formation rates of at least 50 - 100 M⊙/yr, has been detected, either AGN feedback is not affecting the whole host galaxy, or star formation is completely quenched only by several feedback episodes. On the other hand, a positive feedback scenario, supported by narrow emission in Hα extending along the edges of the outflow cone, suggests that galaxy-wide outflows could also have a twofold role in the evolution of the host galaxy. Finally, I will present CO(3-2) ALMA data for three out of the six QSOs observed with SINFONI. Flux maps obtained for the CO(3-2) transition suggest that molecular gas within the host galaxy is swept away by fast winds. A negative-feedback scenario is supported by the inferred molecular gas mass in all three objects, which is significantly below what observed in non-active main-sequence galaxies at high-z.

Characterizing Quasar Outflows III: SEDs, and Bolometric Luminosity Estimates

NASA Astrophysics Data System (ADS)

Richmond, Joseph; Robbins, J. M.; Ganguly, R.; Stark, M. A.; Christenson, D. H.; Derseweh, J. A.; Townsend, S. L.

2012-05-01

Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 11000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) measurements of UV emission line and continuum parameters. In this poster, we add photometry from both the Two Micron All-Sky Survey (2MASS) and from the Wide-Field Infrared Survey Explorer (WISE). 2MASS photometry covers the rest-frame optical regime of these qusars, while the WISE W1, W2, and W3 bands cover the rest-frame wavelength ranges 0.9-1.27 micron, 1.35-1.75 micron, and 2.52-5.51 micron, respectively. The preliminary release of WISE data cover 3800 of our quasars. In an accompnying poster, we have subjectively divided these quasars into four categories: broad absorption-line quasars (2700 objects), associated absorption-line quasars (1700 objects), reddened quasars (160 objects), and unabsorbed/unreddened quasars (6300 objects). Here, we present average SEDs for these subsamples, estimates of bolometric luminosity, and explore changes in SED based on both outflow properties and quasar physical properties. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program.

Characterizing Quasar Outflows II: The Incidence of the Highest Velocity Outflows

NASA Astrophysics Data System (ADS)

Stark, Michele A.; Ganguly, R.; Christenson, D. H.; Richmond, J. M.; Derseweh, J. A.; Robbins, J. M.; Townsend, S. L.

2012-05-01

Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 11000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) measurements of UV emission line and continuum parameters. In an accompanying poster, we subjectively divide these quasars into four categories (broad absorption-line quasars, associated absorption-line quasars, reddened quasars, and unabsorbed/unreddened quasars). This subjective scheme is limited with regard to classifying narrow absorption-line systems (NALs). With single epoch, low dispersion SDSS spectra, we cannot distinguish between cosmologically intervening NALs, and intrinsic NALs that appear at large velocity offsets. In this poster, we tackle this uncertainty statistically by considering the incidence of both CIV and MgII NALs as a function of velocity, and how this distribution changes with quasar properties. We expect that absorption by intervening structures should not vary with quasar property. Other accompanying posters add photometry from rest-frame X-ray through the infrared (WISE) to complete the SED, which we utilize in these efforts. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program.

Characterizing the origin and impact of the most extreme molecular outflows in the nearby universe

NASA Astrophysics Data System (ADS)

Gowardhan, Avani; Riechers, Dominik A.; Spoon, Henrik; Farrah, Duncan

2018-01-01

Observations over the last decade have revealed that feedback in the form of molecular gas outflows is ubiquitous in local ultra luminous infrared galaxies (ULIRGs). Such outflows can clear the nuclear environments of gas and dust, quench star formation and active galactic nuclei (AGN) growth, and they are a key step in the evolution of dust-obscured AGN to optically luminous quasars. We here present multi-spectral line observations of feedback in the two most powerful molecular gas outflows in the local universe. We spatially resolve the outflows to determine their kinematics and structure and find that they can drive out the molecular gas and quench star formation within ~ few Myr. Applying mid-IR diagnostics to constrain the relative contributions of AGN and nuclear starburst activity, we find that starburst activity plays a significant role in driving the outflow. We discuss the implications for future studies of feedback in the local universe and obscured AGN at high redshift, which is a key target population for JWST and ALMA over the next decade.

SPECTROSCOPY ALONG MULTIPLE, LENSED SIGHT LINES THROUGH OUTFLOWING WINDS IN THE QUASAR SDSS J1029+2623

DOE Office of Scientific and Technical Information (OSTI.GOV)

Misawa, Toru; Inada, Naohisa; Ohsuga, Ken

2013-02-01

We study the origin of absorption features on the blue side of the C IV broad emission line of the large-separation lensed quasar SDSS J1029+2623 at z{sub em} {approx} 2.197. The quasar images, produced by a foreground cluster of galaxies, have a maximum separation angle of {theta} {approx} 22.''5. The large angular separation suggests that the sight lines to the quasar central source can go through different regions of outflowing winds from the accretion disk of the quasar, providing a unique opportunity to study the structure of outflows from the accretion disk, a key ingredient for the evolution of quasarsmore » as well as for galaxy formation and evolution. Based on medium- and high-resolution spectroscopy of the two brightest images conducted at the Subaru telescope, we find that each image has different intrinsic levels of absorptions, which can be attributed either to variability of absorption features over the time delay between the lensed images, {Delta}t {approx} 744 days, or to the fine structure of quasar outflows probed by the multiple sight lines toward the quasar. While both these scenarios are consistent with the current data, we argue that they can be distinguished with additional spectroscopic monitoring observations.« less

THE LAUNCHING OF COLD CLOUDS BY GALAXY OUTFLOWS. II. THE ROLE OF THERMAL CONDUCTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brüggen, Marcus; Scannapieco, Evan

2016-05-01

We explore the impact of electron thermal conduction on the evolution of radiatively cooled cold clouds embedded in flows of hot and fast material as it occurs in outflowing galaxies. Performing a parameter study of three-dimensional adaptive mesh refinement hydrodynamical simulations, we show that electron thermal conduction causes cold clouds to evaporate, but it can also extend their lifetimes by compressing them into dense filaments. We distinguish between low column-density clouds, which are disrupted on very short times, and high-column density clouds with much longer disruption times that are set by a balance between impinging thermal energy and evaporation. Wemore » provide fits to the cloud lifetimes and velocities that can be used in galaxy-scale simulations of outflows in which the evolution of individual clouds cannot be modeled with the required resolution. Moreover, we show that the clouds are only accelerated to a small fraction of the ambient velocity because compression by evaporation causes the clouds to present a small cross-section to the ambient flow. This means that either magnetic fields must suppress thermal conduction, or that the cold clouds observed in galaxy outflows are not formed of cold material carried out from the galaxy.« less

Relativistic MHD simulations of collision-induced magnetic dissipation in Poynting-flux-dominated jets/outflows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Wei

2015-07-21

The question of the energy composition of the jets/outflows in high-energy astrophysical systems, e.g. GRBs, AGNs, is taken up first: Matter-flux-dominated (MFD), σ < 1, and/or Poynting-flux-dominated (PFD), σ >1? The standard fireball IS model and dissipative photosphere model are MFD, while the ICMART (Internal-Collision-induced MAgnetic Reconnection and Turbulence) model is PFD. Motivated by ICMART model and other relevant problems, such as “jets in a jet” model of AGNs, the author investigates the models from the EMF energy dissipation efficiency, relativistic outflow generation, and σ evolution points of view, and simulates collisions between high-σ blobs to mimic the situation ofmore » the interactions inside the PFD jets/outflows by using a 3D SRMHD code which solves the conservative form of the ideal MHD equations. σ b,f is calculated from the simulation results (threshold = 1). The efficiency obtained from this hybrid method is similar to the efficiency got from the energy evolution of the simulations (35.2%). Efficiency is nearly σ independent, which is also confirmed by the hybrid method. σ b,i - σ b,f provides an interesting linear relationship. Results of several parameter studies of EMF energy dissipation efficiency are shown.« less

The early evolution of protostellar disks

NASA Technical Reports Server (NTRS)

Stahler, Steven W.; Korycansky, D. G.; Brothers, Maxwell J.; Touma, Jihad

1994-01-01

We consider the origin and intital growth of the disks that form around protostars during the collapse of rotating molecular cloud cores. These disks are assumed to be inviscid and pressure free, and to have masses small compared to those of their central stars. We find that there exist three distinct components-an outer disk, in which shocked gas moves with comparable azimuthal and radical velocities; and inner disk, where material follows nearly circular orbits, but spirals slowly toward the star because of the drag exerted by adjacent onfalling matter, and a turbulent ring adjoining the first two regions. Early in the evolution, i.e., soon after infalling matter begins to miss the star, only the outer disk is present, and the total mass acceration rate onto the protostar is undiminished. Once the outer disk boundary grows to more than 2.9 times the stellar radius, first the ring, and then the inner disk appear. Thereafter, the radii of all three components expand as t(exp 3). The mass of the ring increase with time and is always 13% of the total mass that has fallen from the cloud. Concurrently with the buildup of the inner disk and ring, the accretion rate onto the star falls off. However, the protostellar mass continue to rise, asymptotically as t(exp 1/4). We calculated the radiated flux from the inner and outer disk components due to the release of gravitational potential energy. The flux from the inner disk is dominant and rises steeply toward the stellar surface. We also determine the surface temperature of the inner disk as a function of radius. The total disk luminosity decreases slowly with time, while the contributions from the ring and inner disk both fall as t(exp -2).

Episodic accretion: the interplay of infall and disc instabilities

NASA Astrophysics Data System (ADS)

Kuffmeier, Michael; Frimann, Søren; Jensen, Sigurd S.; Haugbølle, Troels

2018-04-01

Using zoom-simulations carried out with the adaptive mesh-refinement code RAMSES with a dynamic range of up to 227 ≈ 1.34 × 108 we investigate the accretion profiles around six stars embedded in different environments inside a (40 pc)3 giant molecular cloud, the role of mass infall and disc instabilities on the accretion profile, and thus on the luminosity of the forming protostar. Our results show that the environment in which the protostar is embedded determines the overall accretion profile of the protostar. Infall on to the circumstellar disc may trigger gravitational disc instabilities in the disc at distances of around ˜10 to ˜50 au leading to rapid transport of angular momentum and strong accretion bursts. These bursts typically last for about ˜10 to a ˜100 yr, consistent with typical orbital times at the location of the instability, and enhance the luminosity of the protostar. Calculations with the stellar evolution code MESA show that the accretion bursts induce significant changes in the protostellar properties, such as the stellar temperature and radius. We apply the obtained protostellar properties to produce synthetic observables with RADMC3D and predict that accretion bursts lead to observable enhancements around 20 to 200 μm in the spectral energy distribution of Class 0 type young stellar objects.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McLaughlin, J. A.; Verth, G.; Fedun, V.

We investigate the long-term evolution of an initially buoyant magnetic flux tube emerging into a gravitationally stratified coronal hole environment and report on the resulting oscillations and outflows. We perform 2.5-dimensional nonlinear numerical simulations, generalizing the models of McLaughlin et al. and Murray et al. We find that the physical mechanism of oscillatory reconnection naturally generates quasi-periodic vertical outflows, with a transverse/swaying aspect. The vertical outflows consist of both a periodic aspect and evidence of a positively directed flow. The speed of the vertical outflow (20-60 km s{sup -1}) is comparable to those reported in the observational literature. We alsomore » perform a parametric study varying the magnetic strength of the buoyant flux tube and find a range of associated periodicities: 1.75-3.5 minutes. Thus, the mechanism of oscillatory reconnection may provide a physical explanation to some of the high-speed, quasi-periodic, transverse outflows/jets recently reported by a multitude of authors and instruments.« less

Herschel GASPS spectral observations of T Tauri stars in Taurus. Unraveling far-infrared line emission from jets and discs

NASA Astrophysics Data System (ADS)

Alonso-Martínez, M.; Riviere-Marichalar, P.; Meeus, G.; Kamp, I.; Fang, M.; Podio, L.; Dent, W. R. F.; Eiroa, C.

2017-07-01

Context. At early stages of stellar evolution young stars show powerful jets and/or outflows that interact with protoplanetary discs and their surroundings. Despite the scarce knowledge about the interaction of jets and/or outflows with discs, spectroscopic studies based on Herschel and ISO data suggests that gas shocked by jets and/or outflows can be traced by far-IR (FIR) emission in certain sources. Aims: We want to provide a consistent catalogue of selected atomic ([OI] and [CII]) and molecular (CO, H2O, and OH) line fluxes observed in the FIR, separate and characterize the contribution from the jet and the disc to the observed line emission, and place the observations in an evolutionary picture. Methods: The atomic and molecular FIR (60-190 μm) line emission of protoplanetary discs around 76 T Tauri stars located in Taurus are analysed. The observations were carried out within the Herschel key programme Gas in Protoplanetary Systems (GASPS). The spectra were obtained with the Photodetector Array Camera and Spectrometer (PACS). The sample is first divided in outflow and non-outflow sources according to literature tabulations. With the aid of archival stellar/disc and jet/outflow tracers and model predictions (PDRs and shocks), correlations are explored to constrain the physical mechanisms behind the observed line emission. Results: Outflow sources exhibit brighter atomic and molecular emission lines and higher detection rates than non-outflow sources. The line detection fractions decrease with SED evolutionary status (from Class I to Class III). We find correlations between [OI] 63.18 μm and [OI] 6300 Å, o-H2O 78.74 μm, CO 144.78 μm, OH 79.12+79.18 μm, and the continuum flux at 24 μm. The atomic line ratios can be explain either by fast (Vshock > 50 km s-1) dissociative J-shocks at low densities (n 103 cm-3) occurring along the jet and/or PDR emission (G0 > 102, n 103-106 cm-3). To account for the [CII] absolute fluxes, PDR emission or UV irradiation of shocks is needed. In comparison, the molecular emission is more compact and the line ratios are better explained with slow (Vshock < 40 km s-1) C-type shocks with high pre-shock densities (104-106 cm-3), with the exception of OH lines, that are better described by J-type shocks. Disc models alone fail to reproduce the observed molecular line fluxes, but a contribution to the line fluxes from UV-illuminated discs and/or outflow cavities is expected. Far-IR lines dominate disc cooling at early stages and weaken as the star+disc system evolves from Class I to Class III, with an increasing relative disc contribution to the line fluxes. Conclusions: Models which take into account jets, discs, and their mutual interaction are needed to disentangle the different components and study their evolution. The much higher detection rate of emission lines in outflow sources and the compatibility of line ratios with shock model predictions supports the idea of a dominant contribution from the jet/outflow to the line emission, in particular at earlier stages of the stellar evolution as the brightness of FIR lines depends in large part on the specific evolutionary stage. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

The Impact of Modeling Assumptions in Galactic Chemical Evolution Models

NASA Astrophysics Data System (ADS)

Côté, Benoit; O'Shea, Brian W.; Ritter, Christian; Herwig, Falk; Venn, Kim A.

2017-02-01

We use the OMEGA galactic chemical evolution code to investigate how the assumptions used for the treatment of galactic inflows and outflows impact numerical predictions. The goal is to determine how our capacity to reproduce the chemical evolution trends of a galaxy is affected by the choice of implementation used to include those physical processes. In pursuit of this goal, we experiment with three different prescriptions for galactic inflows and outflows and use OMEGA within a Markov Chain Monte Carlo code to recover the set of input parameters that best reproduces the chemical evolution of nine elements in the dwarf spheroidal galaxy Sculptor. This provides a consistent framework for comparing the best-fit solutions generated by our different models. Despite their different degrees of intended physical realism, we found that all three prescriptions can reproduce in an almost identical way the stellar abundance trends observed in Sculptor. This result supports the similar conclusions originally claimed by Romano & Starkenburg for Sculptor. While the three models have the same capacity to fit the data, the best values recovered for the parameters controlling the number of SNe Ia and the strength of galactic outflows, are substantially different and in fact mutually exclusive from one model to another. For the purpose of understanding how a galaxy evolves, we conclude that only reproducing the evolution of a limited number of elements is insufficient and can lead to misleading conclusions. More elements or additional constraints such as the Galaxy’s star-formation efficiency and the gas fraction are needed in order to break the degeneracy between the different modeling assumptions. Our results show that the successes and failures of chemical evolution models are predominantly driven by the input stellar yields, rather than by the complexity of the Galaxy model itself. Simple models such as OMEGA are therefore sufficient to test and validate stellar yields. OMEGA is part of the NuGrid chemical evolution package and is publicly available online at http://nugrid.github.io/NuPyCEE.

SURFACE AND LIGHTNING SOURCES OF NITROGEN OXIDES OVER THE UNITED STATES: MAGNITUDES, CHEMICAL EVOLUTION, AND OUTFLOW

EPA Science Inventory

We use observations from two aircraft during the ICARTT campaign over the eastern United States and North Atlantic during summer 2004, interpreted with a global 3-D model of tropospheric chemistry (GEOS-Chem) to test current understanding of regional sources, chemical evolution...

The Effects of FUV Radiation on C-Shocks: Implications for Water and Other O-bearing Species

NASA Astrophysics Data System (ADS)

Kaufman, Michael; Melick, Gary; Tolls, Volker

2015-08-01

Protostellar outflows have long been known to drive endothermic reactions that produce high abundances of oxygen-bearing species. Models of shocks in well-shielded gas made the strong prediction that essentially all of the pre-shock oxygen gets driven into water, so that the post-shock water abundances are order 10-4. Herschel observations, however, including those from the key program “Water in Star Forming Regions with Herschel (WISH)” show that for most sources, the shocked gas water abundances of are far lower, 10-7 - 10-5.This pattern of lower-than-predicted water abundance has led us to consider that our C-shock model (Kaufman & Neufeld 1996) is incomplete. In particular, we did not previously take into account that many outflow sources have higher than average far-ultraviolet radiation fields within their outflow cavities. Strong FUV radiation has important effects on the structure of C-shocks: the ionization fraction is larger than in well-shielded gas, decreasing the coupling length between neutrals and ions, and leading to higher temperatures and a lower breakdown speeds; the pre-shock gas composition, including the presence of ice mantles and the dominant charge carriers, is strongly affected; and abundant species such as water are diminished by photodissociation in the cooled down stream gas.In addition to the normal parameters of density, shock velocity, and magnetic field strength, we now include the external FUV field strength and the extinction between the FUV source and the shock. We use the results of a detailed PDR model to compute pre-shock chemical conditions, including the ionization fraction, the increase of which decreases the maximum velocities of C- shocks. FUV also keeps oxygen in the gas phase, making more available for H2O formarion ; however, photodissociation beyond the temperature peak keeps the average H2O abundance down. We present comparisons of our model results with the inferred water abundances and with observations of H2O, CO, O and OH lines from the Herschel archive.

Fast Outflow of Molecular Gas in the Seyfert Galaxy IC 5063

NASA Astrophysics Data System (ADS)

Morganti, Raffaella; Oosterloo, T.; Oonk, R.; Tadhunter, C.

2017-11-01

AGN-driven gas outflows may play an important role in the evolution of galaxies, as they impact on the growth on the central supermassive black hole as well on the star formation of the host galaxy. Much of the detailed physics of these gas outflows, and their actual impact on the host galaxy, is still not well understood. We present a detailed analysis, using ALMA observations, of the radio-jet driven outflow of molecular gas in the nearby radio-loud Seyfert galaxy IC 5063 which allows to derive important physical parameters of the gas and the outflow which, in turn, provide crucial input to numerical models. In recent years, a surprising result in the field of AGN-driven outflows has been that the cold phases of the gas (atomic and molecular) in some galaxies are the massive components of these outflows, despite the huge amounts of energy involved in driving these outflows. However, why most of the outflowing gas should be molecular/atomic, and in general, what are the physical conditions of the gas in the outflows and what really drives them, are still open questions. We present the results obtained from ALMA observations of multiple CO transitions and other molecules of what appears to be a textbook case of a jet-driven multi- phase outflow in the central regions of the Seyfert galaxy IC 5063. The data on multiple transitions allow us to derive the physical conditions in the different regions of the outflowing molecular gas. The signature of the impact of the radio jet is clearly seen in the spatial distribution of the excitation temperature and pressure of the outflowing gas, with the highest excitation and pressure found for the gas with the highest outflow velocities. We obtain a detailed three- dimensional picture of the outflow, and its kinematics, and find that outflowing molecular gas is present across the entire region co-spatial with the radio plasma, providing unambiguous evidence that the radio jets/cocoon are responsible for the outflow. The detailed information about the physical condition of the gas in a fast outflow will serve as template for the signatures of the impact of a radio plasma jet on a gas-rich ISM and its associated star formation, and guide the studies of outflows in other galaxies, including higher redshift objects.

3D modelling of HCO+ and its isotopologues in the low-mass proto-star IRAS16293-2422

NASA Astrophysics Data System (ADS)

Quénard, D.; Bottinelli, S.; Caux, E.; Wakelam, V.

2018-07-01

Ions and electrons play an important role in various stages of the star formation process. By following the magnetic field of their environment and interacting with neutral species, they slow down the gravitational collapse of the proto-star envelope. This process (known as ambipolar diffusion) depends on the ionization degree, which can be derived from the HCO+ abundance. We present a study of HCO+ and its isotopologues (H13CO+ , HC18O+ , DCO+ , and D13CO+) in the low-mass proto-star IRAS16293-2422. The structure of this object is complex, and the HCO+emission arises from the contribution of a young NW-SE outflow, the proto-stellar envelope, and the foreground cloud. We aim at constraining the physical parameters of these structures using all the observed transitions. For the young NW-SE outflow, we derive Tkin= 180-220 K and n(H2) = (4-7)× 106 cm-3 with an HCO+abundance of (3-5)× 10-9. Following previous studies, we demonstrate that the presence of a cold (Tkin≤ 30 K) and low density [n(H2) ≤ 1 × 104 cm-3] foreground cloud is also necessary to reproduce the observed line profiles. We have used the gas-grain chemical code NAUTILUS to derive the HCO+ abundance profile across the envelope and the external regions where X(HCO+) ≳ 1 × 10-9 dominate the envelope emission. From this, we derive an ionization degree of 10-8.9 ≲ x( e) ≲ 10-7.9. The ambipolar diffusion time-scale is ˜5 times the free-fall time-scale, indicating that the magnetic field starts to support the source against gravitational collapse and the magnetic field strength is estimated to be 6-46μG.

IRAS 16253–2429: THE FIRST PROTO-BROWN DWARF BINARY CANDIDATE IDENTIFIED THROUGH THE DYNAMICS OF JETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsieh, Tien-Hao; Lai, Shih-Ping; Belloche, Arnaud

2016-07-20

The formation mechanism of brown dwarfs (BDs) is one of the long-standing problems in star formation because the typical Jeans mass in molecular clouds is too large to form these substellar objects. To answer this question, it is crucial to study a BD in the embedded phase. IRAS 16253–2429 is classified as a very low-luminosity object (VeLLO) with an internal luminosity of <0.1 L {sub ⊙}. VeLLOs are believed to be very low-mass protostars or even proto-BDs. We observed the jet/outflow driven by IRAS 16253–2429 in CO (2–1), (6–5), and (7–6) using the IRAM 30 m and Atacama Pathfinder Experimentmore » telescopes and the Submillimeter Array (SMA) in order to study its dynamical features and physical properties. Our SMA map reveals two protostellar jets, indicating the existence of a proto-binary system as implied by the precessing jet detected in H{sub 2} emission. We detect a wiggling pattern in the position–velocity diagrams along the jet axes, which is likely due to the binary orbital motion. Based on this information, we derive the current mass of the binary as ∼0.032 M{sub ⊙}. Given the low envelope mass, IRAS 16253–2429 will form a binary that probably consist of one or two BDs. Furthermore, we found that the outflow force as well as the mass accretion rate are very low based on the multi-transition CO observations, which suggests that the final masses of the binary components are at the stellar/substellar boundary. Since IRAS 16253 is located in an isolated environment, we suggest that BDs can form through fragmentation and collapse, similar to low-mass stars.« less

First Large-scale Herbig-Haro Jet Driven by a Proto-brown Dwarf

NASA Astrophysics Data System (ADS)

Riaz, B.; Briceño, C.; Whelan, E. T.; Heathcote, S.

2017-07-01

We report the discovery of a new Herbig-Haro jet, HH 1165, in SOAR narrow-band imaging of the vicinity of the σ Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow shocks at the apparent ends of the flow. The Hα image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M1701117), with a total (dust+gas) mass of ˜36 M Jup and a bolometric luminosity of ˜0.1 L ⊙. High-resolution VLT/UVES spectra of M1701117 show a wealth of emission lines indicative of strong outflow and accretion activity. SOAR/Goodman low-resolution spectra along the jet axis show an asymmetrical morphology for HH 1165. We find a puzzling picture wherein the northwest part exhibits a classical HH jet running into a pre-dominantly neutral medium, while the southern part resembles an externally irradiated jet. The C-shaped bending in HH 1165 may be produced by the combined effects from the massive stars in the ionization front to the east, the σ Orionis core to the west, and the close proximity to the B2-type star HR 1950. HH 1165 shows all of the signatures to be considered as a scaled-down version of parsec-length HH jets, and can be termed as the first sub-stellar analog of a protostellar HH jet system.

Water in the envelopes and disks around young high-mass stars

NASA Astrophysics Data System (ADS)

van der Tak, F. F. S.; Walmsley, C. M.; Herpin, F.; Ceccarelli, C.

2006-03-01

Single-dish spectra and interferometric maps of (sub-)millimeter lines of H218O and HDO are used to study the chemistry of water in eight regions of high-mass star formation. The spectra indicate HDO excitation temperatures of ~110 K and column densities in an 11'' beam of ˜2×1014 cm-2 for HDO and ˜2×1017 cm-2 for H2O, with the N(HDO)/N(H2O) ratio increasing with decreasing temperature. Simultaneous observations of CH3OH and SO2 indicate that 20-50% of the single-dish line flux arises in the molecular outflows of these objects. The outflow contribution to the H218O and HDO emission is estimated to be 10-20%. Radiative transfer models indicate that the water abundance is low (~10-6) outside a critical radius corresponding to a temperature in the protostellar envelope of ≈100 K, and "jumps" to H2O/H2 ~ 10-4 inside this radius. This value corresponds to the observed abundance of solid water and together with the derived HDO/H2O abundance ratios of ~10-3 suggests that the origin of the observed water is evaporation of grain mantles. This idea is confirmed in the case of AFGL 2591 by interferometer observations of the HDO 110-111, H218O 313-220 and SO2 120,12-111,11 lines, which reveal compact (Ø ~ 800 AU) emission with a systematic velocity gradient. This size is similar to that of the 1.3 mm continuum towards AFGL 2591, from which we estimate a mass of ≈0.8 M⊙, or ~5% of the mass of the central star. We speculate that we may be observing a circumstellar disk in an almost face-on orientation.

First Large-scale Herbig–Haro Jet Driven by a Proto-brown Dwarf

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riaz, B.; Briceño, C.; Heathcote, S.

2017-07-20

We report the discovery of a new Herbig–Haro jet, HH 1165, in SOAR narrow-band imaging of the vicinity of the σ Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow shocks at the apparent ends of the flow. The H α image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M1701117), withmore » a total (dust+gas) mass of ∼36 M {sub Jup} and a bolometric luminosity of ∼0.1 L {sub ⊙}. High-resolution VLT/UVES spectra of M1701117 show a wealth of emission lines indicative of strong outflow and accretion activity. SOAR/Goodman low-resolution spectra along the jet axis show an asymmetrical morphology for HH 1165. We find a puzzling picture wherein the northwest part exhibits a classical HH jet running into a pre-dominantly neutral medium, while the southern part resembles an externally irradiated jet. The C-shaped bending in HH 1165 may be produced by the combined effects from the massive stars in the ionization front to the east, the σ Orionis core to the west, and the close proximity to the B2-type star HR 1950. HH 1165 shows all of the signatures to be considered as a scaled-down version of parsec-length HH jets, and can be termed as the first sub-stellar analog of a protostellar HH jet system.« less

3D modelling of HCO+ and its isotopologues in the low-mass proto-star IRAS16293-2422

NASA Astrophysics Data System (ADS)

Quénard, D.; Bottinelli, S.; Caux, E.; Wakelam, V.

2018-04-01

Ions and electrons play an important role in various stages of the star formation process. By following the magnetic field of their environment and interacting with neutral species, they slow down the gravitational collapse of the proto-star envelope. This process (known as ambipolar diffusion) depends on the ionisation degree, which can be derived from the HCO+abundance. We present a study of HCO+and its isotopologues (H13CO+, HC18O+, DCO+, and D13CO+) in the low-mass proto-star IRAS16293-2422. The structure of this object is complex, and the HCO+emission arises from the contribution of a young NW-SE outflow, the proto-stellar envelope and the foreground cloud. We aim at constraining the physical parameters of these structures using all the observed transitions. For the young NW-SE outflow, we derive Tkin = 180 - 220 K and n(H2) = (4 - 7) × 106 cm-3 with an HCO+abundance of (3 - 5) × 10-9. Following previous studies, we demonstrate that the presence of a cold (Tkin≤30 K) and low density (n(H2) ≤ 1 × 104 cm-3) foreground cloud is also necessary to reproduce the observed line profiles. We have used the gas-grain chemical code NAUTILUS to derive the HCO+abundance profile across the envelope and the external regions where X(HCO+)≳ 1 × 10-9 dominate the envelope emission. From this, we derive an ionisation degree of 10-8.9 ≲ x(e) ≲ 10-7.9. The ambipolar diffusion timescale is ˜5 times the free-fall timescale, indicating that the magnetic field starts to support the source against gravitational collapse and the magnetic field strength is estimated to be 6 - 46 μG.

The SPH consistency problem and some astrophysical applications

NASA Astrophysics Data System (ADS)

Klapp, Jaime; Sigalotti, Leonardo; Rendon, Otto; Gabbasov, Ruslan; Torres, Ayax

2017-11-01

We discuss the SPH kernel and particle consistency problem and demonstrate that SPH has a limiting second-order convergence rate. We also present a solution to the SPH consistency problem. We present examples of how SPH implementations that are not mathematically consistent may lead to erroneous results. The new formalism has been implemented into the Gadget 2 code, including an improved scheme for the artificial viscosity. We present results for the ``Standard Isothermal Test Case'' of gravitational collapse and fragmentation of protostellar molecular cores that produce a very different evolution than with the standard SPH theory. A further application of accretion onto a black hole is presented.

Synthetic observations of protostellar multiple systems

NASA Astrophysics Data System (ADS)

Lomax, O.; Whitworth, A. P.

2018-04-01

Observations of protostars are often compared with synthetic observations of models in order to infer the underlying physical properties of the protostars. The majority of these models have a single protostar, attended by a disc and an envelope. However, observational and numerical evidence suggests that a large fraction of protostars form as multiple systems. This means that fitting models of single protostars to observations may be inappropriate. We produce synthetic observations of protostellar multiple systems undergoing realistic, non-continuous accretion. These systems consist of multiple protostars with episodic luminosities, embedded self-consistently in discs and envelopes. We model the gas dynamics of these systems using smoothed particle hydrodynamics and we generate synthetic observations by post-processing the snapshots using the SPAMCART Monte Carlo radiative transfer code. We present simulation results of three model protostellar multiple systems. For each of these, we generate 4 × 104 synthetic spectra at different points in time and from different viewing angles. We propose a Bayesian method, using similar calculations to those presented here, but in greater numbers, to infer the physical properties of protostellar multiple systems from observations.

ORPHANED PROTOSTARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reipurth, Bo; Connelley, Michael; Mikkola, Seppo

2010-12-10

We explore the origin of a population of distant companions ({approx}1000-5000 AU) to Class I protostellar sources recently found by Connelley and coworkers, who noted that the companion fraction diminished as the sources evolved. Here, we present N-body simulations of unstable triple systems embedded in dense cloud cores. Many companions are ejected into unbound orbits and quickly escape, but others are ejected with insufficient momentum to climb out of the potential well of the cloud core and associated binary. These loosely bound companions reach distances of many thousands of AU before falling back and eventually being ejected into escapes asmore » the cloud cores gradually disappear. We use the term orphans to denote protostellar objects that are dynamically ejected from their placental cloud cores, either escaping or for a time being tenuously bound at large separations. Half of all triple systems are found to disintegrate during the protostellar stage, so if multiple systems are a frequent outcome of the collapse of a cloud core, then orphans should be common. Bound orphans are associated with embedded close protostellar binaries, but escaping orphans can travel as far as {approx}0.2 pc during the protostellar phase. The steep climb out of a potential well ensures that orphans are not kinematically distinct from young stars born with a less violent pre-history. The identification of orphans outside their heavily extincted cloud cores will allow the detailed study of protostars high up on their Hayashi tracks at near-infrared and in some cases even at optical wavelengths.« less

Volcanic Structures Within Niger and Dao Valles, Mars, and Implications for Outflow Channel Evolution and Hellas Basin Rim Development

NASA Astrophysics Data System (ADS)

Korteniemi, J.; Kukkonen, S.

2018-04-01

Outflow channel formation on the eastern Hellas rim region is traditionally thought to have been triggered by activity phases of the nearby volcanoes Hadriacus and Tyrrhenus Montes: As a result of volcanic heating subsurface volatiles were mobilized. It is, however, under debate, whether eastern Hellas volcanism was in fact more extensive, and if there were volcanic centers separate from the identified central volcanoes. This work describes previously unrecognized structures in the Niger-Dao Valles outflow channel complex. We interpret them as volcanic edifices: cones, a shield, and a caldera. The structures provide evidence of an additional volcanic center within the valles and indicate volcanic activity both prior to and following the formation of the outflow events. They expand the extent, type, and duration of volcanic activity in the Circum-Hellas Volcanic Province and provide new information on interaction between volcanism and fluvial activity.

On the X-Ray Low- and High-Velocity Outflows in Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Ramirez, J. M.; Tombesi, F.

2012-01-01

An exploration of the relationship between bolometric luminosity and outflow velocity for two classes of X-ray outflows in a large sample of active galactic nuclei has been performed. We find that line radiation pressure could be one physical mechanism that might accelerate the gas we observe in warm absorber, v approx. 100-1000 km/s, and on comparable but less stringent grounds the ultrafast outflows, v approx. 0.03-0.3c. If comparable with the escape velocity of the system, the first is naturally located at distances of the dusty torus, '" I pc, and the second at subparsec scales, approx.0.01 pc, in accordance with large set of observational evidence existing in the literature. The presentation of this relationship might give us key clues for our understanding of the different physical mechanisms acting in the centre of galaxies, the feedback process and its impact on the evolution of the host galaxy.

Depletion of chlorine into HCl ice in a protostellar core. The CHESS spectral survey of OMC-2 FIR 4

NASA Astrophysics Data System (ADS)

Kama, M.; Caux, E.; López-Sepulcre, A.; Wakelam, V.; Dominik, C.; Ceccarelli, C.; Lanza, M.; Lique, F.; Ochsendorf, B. B.; Lis, D. C.; Caballero, R. N.; Tielens, A. G. G. M.

2015-02-01

Context. The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout of various carriers of elements with abundances <10-5 has not yet been well studied. Aims: Our aim here is to study the depletion of chlorine in the protostellar core, OMC-2 FIR 4. Methods: We observed transitions of HCl and H2Cl+ towards OMC-2 FIR 4 using the Herschel Space Observatory and Caltech Submillimeter Observatory facilities. Our analysis makes use of state of the art chlorine gas-grain chemical models and newly calculated HCl-H2 hyperfine collisional excitation rate coefficients. Results: A narrow emission component in the HCl lines traces the extended envelope, and a broad one traces a more compact central region. The gas-phase HCl abundance in FIR 4 is 9 × 10-11, a factor of only 10-3 that of volatile elemental chlorine. The H2Cl+ lines are detected in absorption and trace a tenuous foreground cloud, where we find no depletion of volatile chlorine. Conclusions: Gas-phase HCl is the tip of the chlorine iceberg in protostellar cores. Using a gas-grain chemical model, we show that the hydrogenation of atomic chlorine on grain surfaces in the dark cloud stage sequesters at least 90% of the volatile chlorine into HCl ice, where it remains in the protostellar stage. About 10% of chlorine is in gaseous atomic form. Gas-phase HCl is a minor, but diagnostically key reservoir, with an abundance of ≲10-10 in most of the protostellar core. We find the [35Cl]/[37Cl] ratio in OMC-2 FIR 4 to be 3.2 ± 0.1, consistent with the solar system value. Appendices are available in electronic form at http://www.aanda.org

A Study of PG Quasar-Driven Outflows with COS

NASA Astrophysics Data System (ADS)

Hamann, Frederick

2013-10-01

Quasar outflows are an important part of the quasar phenomenon, but many questions remain about their energetics, physical properties and the role they might play in providing feedback to host galaxy evolution. We searched our own COS far-UV observations from the QUEST survey and other large COS programs to find a sample of 6 bright PG quasars with broad {FWHM > 400 km/s} high velocity {v > 1000 km/s} absorption lines that clearly form in quasar-driven winds. These quasars can fill an important gap in our understanding between local Seyferts with low-speed winds and high-redshift quasars with extreme BAL outflows. They are also well-studied at other wavelengths, with some evidence for the quasars driving galaxy-scale blowouts and shutting down star formation. But almost nothing is known about the quasar outflows themselves. We propose a detailed study of these 6 outflow quasars using new COS FUV observations to 1} expand the existing wavelength coverage across critical lines that are diagnostic of the outflow physical conditions, kinetic energies, and metallicities, and 2} check for line variability as an indicator of the outflow structure and locations. This quasar sample includes unusual cases with many low-abundance {PV 1118,1128 and SIV 1063} and excited-state lines {SIV 1073*, CIII* 1175, CII* 1335} that will provide unprecedented constraints on the outflow properties, plus the first known OVI-only mini-BAL outflow {no lower ions detected} for which we will cover NeVIII 770,780 to probe the highest ionization gas. The high FUV sensitivity of COS is uniquely able to measure this wide range of outflow lines in low-redshift quasars with no Lya forest contamination.

Transport pathways for Asian pollution outflow over the Pacific: Interannual and seasonal variations

NASA Astrophysics Data System (ADS)

Liu, Hongyu; Jacob, Daniel J.; Bey, Isabelle; Yantosca, Robert M.; Duncan, Bryan N.; Sachse, Glen W.

2003-10-01

The meteorological pathways contributing to Asian pollution outflow over the Pacific are examined with a global three-dimensional model analysis of CO observations from the Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission (February-April 2001). The model is used also to place the TRACE-P observations in an interannual (1994-2001) and seasonal context. The major process driving Asian pollution outflow in spring is frontal lifting ahead of southeastward-moving cold fronts (the leading edge of cold surges) and transport in the boundary layer behind the cold fronts. Orographic lifting over central and eastern China combines with the cold fronts to promote the transport of Chinese pollution to the free troposphere. Outflow of seasonal biomass burning in Southeast Asia during spring takes place mostly by deep convection but also by northeastward transport and frontal lifting, mixing with the anthropogenic outflow. Boundary layer outflow over the western Pacific is largely devoid of biomass burning influence. European and African (biomass burning) plumes in Asian outflow during TRACE-P were weak (<60 ppbv and 20 ppbv CO, respectively) and were not detectable in the observations because of superposition of the much larger Asian pollution signal. Spring 2001 (La Niña) was characterized by unusually frequent cold surge events in the Asian Pacific rim and strong convection in Southeast Asia, leading to unusually strong boundary layer outflow of anthropogenic emissions and convective outflow of biomass burning emissions in the upper troposphere. The Asian outflow flux of CO to the Pacific is found to vary seasonally by a factor of 3-4 (maximum in March and minimum in summer). The March maximum results from frequent cold surge events and seasonal biomass burning emissions.

Transport Pathways for Asian Pollution Outflow Over the Pacific: Interannual and Seasonal Variations

NASA Technical Reports Server (NTRS)

Liu, Hong-Yu; Jacob, Daniel J.; Bey, Isabelle; Yantosca, Robert M.; Duncan, Bryan N.; Sachse, Glen W.

2003-01-01

The meteorological pathways contributing to Asian pollution outflow over the Pacific are examined with a global three-dimensional model analysis of CO observations from the Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission (February-April 2001). The model is used also to place the TRACE-P observations in an interannual (1994-2001) and seasonal context. The major process driving Asian pollution outflow in spring is frontal lifting ahead of southeastward-moving cold fronts (the leading edge of cold surges) and transport in the boundary layer behind the cold fronts. Orographic lifting over central and eastern China combines with the cold fronts to promote the transport of Chinese pollution to the free troposphere. Outflow of seasonal biomass burning in Southeast Asia during spring takes place mostly by deep convection but also by northeastward transport and frontal lifting, mixing with the anthropogenic outflow. Boundary layer outflow over the western Pacific is largely devoid of biomass burning influence. European and African (biomass burning) plumes in Asian outflow during TRACE-P were weak (less than 60 ppbv and 20 ppbv CO, respectively) and were not detectable in the observations because of superposition of the much larger Asian pollution signal. Spring 2001 (La Nina) was characterized by unusually frequent cold surge events in the Asian Pacific rim and strong convection in Southeast Asia, leading to unusually strong boundary layer outflow of anthropogenic emissions and convective outflow of biomass burning emissions in the upper troposphere. The Asian outflow flux of CO to the Pacific is found to vary seasonally by a factor of 3-4 (maximum in March and minimum in summer). The March maximum results from frequent cold surge events and seasonal biomass burning emissions.

The COS revolution of AGN outflow science

NASA Astrophysics Data System (ADS)

Arav, Nahum

2016-10-01

HST/COS has opened a new discovery space for quasar outflow science. Specifically, it provides high quality FUV spectra covering the diagnostic-rich 500A-1050A rest-frame of medium redshift objects. We have published three refereed papers based on the analysis of such data that were supported by our concluded COS archive program, in which we reported: a) a new population of very high ionization outflows, b) robust cases of two-ionization-phase outflows, which are the missing link between UV AGN outflows and x-ray warm absorbers, and most importantly c) spectral diagnostics that allowed us to determine the distance of the outflows from the central source. The latter is a cardinal issue in the field as many researchers believe that most outflows are situated close to the accretion disk ( 0.01 pc) while the few reliable measurements show distances of 10-10,000 pc. Therefore, every empirical distance measurement is of importance. Our archive based publication also demonstrates that quasar outflows have sufficient energy to match theoretical predictions for AGN feedback influencing galaxy evolution.We propose to continue this successful archive program. Thus far we've analyzed about 300 COS G130M and G160M orbits of AGN observations. There are roughly 900 additional orbits that satisfy our criteria and will be available within a year. Based on our published survey, we expect that these 900 orbits will yield about 20-30 additional very-high ionization outflows and 4-6 cases of distance and kinetic luminosity determinations, all in cosmologically important luminous-quasars.

Ice-dammed lake drainage evolution at Russell Glacier, west Greenland

NASA Astrophysics Data System (ADS)

Carrivick, Jonathan L.; Tweed, Fiona S.; Ng, Felix; Quincey, Duncan J.; Mallalieu, Joseph; Ingeman-Nielsen, Thomas; Mikkelsen, Andreas B.; Palmer, Steven J.; Yde, Jacob C.; Homer, Rachel; Russell, Andrew J.; Hubbard, Alun

2017-11-01

Glaciological and hydraulic factors that control the timing and mechanisms of glacier lake outburst floods (GLOFs) remain poorly understood. This study used measurements of lake level at fifteen minute intervals and known lake bathymetry to calculate lake outflow during two GLOF events from the northern margin of Russell Glacier, west Greenland. We used measured ice surface elevation, interpolated subglacial topography and likely conduit geometry to inform a melt enlargement model of the outburst evolution. The model was tuned to best-fit the hydrograph’s rising limb and timing of peak discharge in both events; it achieved Mean Absolute Errors of < 5 %. About one third of the way through the rising limb, conduit melt enlargement became the dominant drainage mechanism. Lake water temperature, which strongly governed the enlargement rate, preconditioned the high peak discharge and short duration of these floods. We hypothesize that both GLOFs were triggered by ice dam flotation, and localised hydraulic jacking sustained most of their early-stage outflow, explaining the particularly rapid water egress in comparison to that recorded at other ice-marginal lakes. As ice overburden pressure relative to lake water hydraulic head diminished, flow became confined to a subglacial conduit. This study has emphasised the inter-play between ice dam thickness and lake level, drainage timing, lake water temperature and consequently rising stage lake outflow and flood evolution.

Exploring the engines of molecular outflows

NASA Astrophysics Data System (ADS)

Testi, Leonardo

1995-03-01

Water vapour masers and CO outflows are well known to be associated with the youngest phases of evolution of massive stellar objects. Nevertheless, up to now there is a lack of high resolution multiwavelength study of the regions containing these objects. Using the VLA, the CSO and the TIRGO equipped with the new Near-Infrared (NIR) camera ARNICA, we have begun a systematic study of water maser/CO outflow regions. These new high resolution and high sensitivity data have proved to be very useful in probing the star formation activity and the connection between infrared and radio sources. Here we report the results obtained in a preliminary sub- sample of objects. The NIR data showed that both the maser spots and the large- scale outflows tend to be associated to the most embedded and probably younger sources of the infrared clusters. Infrared emission lines observed with narrow band filters show the presence of jet-like structures in most of the sources observed. Water masers, jet-like and Herbig-Haro-like infrared structures, and CO outflows enable to probe ejection phenomena at all spacial scales ranging from 0.01 to 1 parsec.

The kinematics and morphology of cool galactic winds and halo gas from galaxies at 0.3 < z < 1.4

NASA Astrophysics Data System (ADS)

Rubin, Kate H. R.

Large-scale redshift surveys tracing the evolution of the luminous components of galaxies have revealed both an increase in the number density of "red and dead" galaxies and a concomitant decline in the star formation rates (SFRs) of blue galaxies since z ˜ 1. The latter is predicted to be due to a decreasing cool gas supply over time; whereas the former may be explained by the theory of merger-driven galaxy evolution, which suggests that the merging of blue galaxies expels the interstellar medium (ISM), thereby quenching star formation in the remnant. While these theoretical explanations provide robust predictions for the evolution of the gaseous components of distant galaxies, we have few direct measurements of the location and kinematics of cool gas around galaxies beyond the local universe. This thesis uses three complementary observational techniques to provide new constraints on the kinematics and morphology of cool gas in galaxies at 0.3 < z < 1.4. First, we use spectra of ˜470 galaxies at 0.7 < z < 1.5 drawn from the Team Keck Treasury Redshift Survey to study absorption line profiles for the Mg II lambdalambda2796, 2803 and Fe II lambdalambda2586, 2600 transitions, which probe cool, photoionized gas with temperature T ˜ 10 4 K. By coadding several sub-samples of galaxy spectra, we identify gaseous outflows via the Doppler shift of the absorption lines, and find that outflows are ubiquitous in galaxies having SFR > 10 M⊙ yr-1 and stellar masses ≳1010.5M⊙ . By comparing these results to those of Weiner et al. (2009), who present a similar study of outflows in star-forming galaxies at z ˜ 1.4, we find that these outflows persist in high-mass galaxies as they age between z ˜ 1.4 and z ˜ 1. Using HST/ACS imaging of our galaxy sample, we present evidence for a weak trend of increasing outflow absorption strength with increasing galaxy SFR surface density (SigmaSFR). Theoretical studies suggest that a minimum SigmaSFR must be exceeded in the host galaxy for outflows to be driven by either radiation pressure or thermalized energy from supernovae. To test this directly, we use a similar technique to probe cool gas kinematics in the individual Keck/LRIS spectra of a sample of ˜120 galaxies at 0.3 < z < 1.4. These data permit modeling of Mg II and Fe II absorption lines to obtain, e.g., the cool gas outflow velocity and covering fraction. Using Spitzer/MIPS and GALEX imaging to determine SFRs in concert with HST/ACS imaging which enables measurements of the size of star-forming regions, we compare outflow velocity to SigmaSFR. We find that while we detect outflows over a range 0.005 M⊙ yr-1 kpc-2 < Sigma SFR < 1 M⊙ yr-1 kpc-2, outflows occur more frequently with increasing SigmaSFR. The absorption line studies described above provide strong constraints on, e.g., the cool gas velocities. However, they provide only weak constraints on the radial extent and morphology of the gas. Knowledge of the spatial extent of the outflow is essential for accurately estimating its mass and energy; measurements of these rates are in turn crucial to understanding the role of outflows in driving galaxy evolution. Next, we show that emission in Mg II and Fe II* fine-structure lines can provide novel constraints on the spatial extent of an outflow. We identify a starburst galaxy at z = 0.69 which exhibits emission and absorption in Mg II, yielding a P Cygni-like line profile. We demonstrate that this emission is spatially broader than the continuum emission and the emission from H II regions, and associate the Mg II and Fe II* emission with resonance-line scattering and fluorescence in the outflow. These features are common at z ˜ 1, and in principle yield the first direct constraint on the radial extent of the outflow in many distant galaxies. Finally, we present a study of the cool gas around a single galaxy at z = 0.47 using spectroscopy of a bright background galaxy at z = 0.7 at a transverse distance of 16.5 h-170 kpc. While cool halo gas is typically studied along sightlines to background QSOs, the use of background galaxies offers several advantages over more traditional techniques. Because the background galaxy is spatially extended, we probe absorption over a large (> 4 h-170 kpc) area in the foreground halo, and find that the gas exhibits a large velocity dispersion and high covering fraction over this area. Spectroscopy of the foreground host galaxy reveals that it experienced a burst of star formation ˜1 Gyr ago, and we suggest that the absorbing gas in the halo was most likely ejected or tidally stripped during this past violent event. As such, these results again place a novel constraint on the radial extent of cool gas originating in the ISM of a distant galaxy.

Interferometric Mapping of Perseus Outflows with MASSES

NASA Astrophysics Data System (ADS)

Stephens, Ian; Dunham, Michael; Myers, Philip C.; MASSES Team

2017-01-01

The MASSES (Mass Assembly of Stellar Systems and their Evolution with the SMA) survey, a Submillimeter Array (SMA) large-scale program, is mapping molecular lines and continuum emission about the 75 known Class 0/I sources in the Perseus Molecular Cloud. In this talk, I present some of the key results of this project, with a focus on the CO(2-1) maps of the molecular outflows. In particular, I investigate how protostars inherit their rotation axes from large-scale magnetic fields and filamentary structure.

Protostellar Interferometric Line Survey (PILS): Constraining the formation of complex organic molecules with ALMA

NASA Astrophysics Data System (ADS)

Jorgensen, Jes K.; Coutens, Audrey; Bourke, Tyler L.; Favre, Cecile; Garrod, Robin; Lykke, Julie; Mueller, Holger; Oberg, Karin I.; Schmalzl, Markus; van der Wiel, Matthijs; van Dishoeck, Ewine; Wampfler, Susanne F.

2015-08-01

Understanding how, when and where complex organic and potentially prebiotic molecules are formed is a fundamental goal of astrochemistry and an integral part of origins of life studies. Already now ALMA is showing its capabilities for studies of the chemistry of solar-type stars with its high sensitivity for faint lines, high spectral resolution which limits line confusion, and high angular resolution making it possible to study the structure of young protostars on solar-system scales. We here present the first results from a large unbiased survey “Protostellar Interferometric Line Survey (PILS)” targeting one of the astrochemical template sources, the low-mass protostellar binary IRAS 16293-2422. The survey is more than an order of magnitude more sensitive than previous surveys of the source and provide imaging down to 25 AU scales (radius) around each of the two components of the binary. An example of one of the early highlights from the survey is unambiguous detections of the (related) prebiotic species glycolaldehyde, ethylene glycol (two lowest energy conformers), methyl formate and acetic acid. The glycolaldehyde-ethylene glycol abundance ratio is high in comparison to comets and other protostars - but agrees with previous measurements, e.g., in the Galactic Centre clouds possibly reflecting different environments and/or evolutionary histories. Complete mapping of this and other chemical networks in comparison with detailed chemical models and laboratory experiments will reveal the origin of complex organic molecules in a young protostellar system and investigate the link between these protostellar stages and the early Solar System.

Protostellar Disk Evolution over Million-year Timescales with a Prescription for Magnetized Turbulence

NASA Astrophysics Data System (ADS)

Landry, Russell; Dodson-Robinson, Sarah E.; Turner, Neal J.; Abram, Greg

2013-07-01

Magnetorotational instability (MRI) is the most promising mechanism behind accretion in low-mass protostellar disks. Here we present the first analysis of the global structure and evolution of non-ideal MRI-driven T-Tauri disks on million-year timescales. We accomplish this in a 1+1D simulation by calculating magnetic diffusivities and utilizing turbulence activity criteria to determine thermal structure and accretion rate without resorting to a three-dimensional magnetohydrodynamical (MHD) simulation. Our major findings are as follows. First, even for modest surface densities of just a few times the minimum-mass solar nebula, the dead zone encompasses the giant planet-forming region, preserving any compositional gradients. Second, the surface density of the active layer is nearly constant in time at roughly 10 g cm-2, which we use to derive a simple prescription for viscous heating in MRI-active disks for those who wish to avoid detailed MHD computations. Furthermore, unlike a standard disk with constant-α viscosity, the disk midplane does not cool off over time, though the surface cools as the star evolves along the Hayashi track. Instead, the MRI may pile material in the dead zone, causing it to heat up over time. The ice line is firmly in the terrestrial planet-forming region throughout disk evolution and can move either inward or outward with time, depending on whether pileups form near the star. Finally, steady-state mass transport is an extremely poor description of flow through an MRI-active disk, as we see both the turnaround in the accretion flow required by conservation of angular momentum and peaks in \\dot{M}(R) bracketing each side of the dead zone. We caution that MRI activity is sensitive to many parameters, including stellar X-ray flux, grain size, gas/small grain mass ratio and magnetic field strength, and we have not performed an exhaustive parameter study here. Our 1+1D model also does not include azimuthal information, which prevents us from modeling the effects of Rossby waves.

PROTOSTELLAR DISK EVOLUTION OVER MILLION-YEAR TIMESCALES WITH A PRESCRIPTION FOR MAGNETIZED TURBULENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Landry, Russell; Dodson-Robinson, Sarah E.; Turner, Neal J.

2013-07-10

Magnetorotational instability (MRI) is the most promising mechanism behind accretion in low-mass protostellar disks. Here we present the first analysis of the global structure and evolution of non-ideal MRI-driven T-Tauri disks on million-year timescales. We accomplish this in a 1+1D simulation by calculating magnetic diffusivities and utilizing turbulence activity criteria to determine thermal structure and accretion rate without resorting to a three-dimensional magnetohydrodynamical (MHD) simulation. Our major findings are as follows. First, even for modest surface densities of just a few times the minimum-mass solar nebula, the dead zone encompasses the giant planet-forming region, preserving any compositional gradients. Second, themore » surface density of the active layer is nearly constant in time at roughly 10 g cm{sup -2}, which we use to derive a simple prescription for viscous heating in MRI-active disks for those who wish to avoid detailed MHD computations. Furthermore, unlike a standard disk with constant-{alpha} viscosity, the disk midplane does not cool off over time, though the surface cools as the star evolves along the Hayashi track. Instead, the MRI may pile material in the dead zone, causing it to heat up over time. The ice line is firmly in the terrestrial planet-forming region throughout disk evolution and can move either inward or outward with time, depending on whether pileups form near the star. Finally, steady-state mass transport is an extremely poor description of flow through an MRI-active disk, as we see both the turnaround in the accretion flow required by conservation of angular momentum and peaks in M-dot (R) bracketing each side of the dead zone. We caution that MRI activity is sensitive to many parameters, including stellar X-ray flux, grain size, gas/small grain mass ratio and magnetic field strength, and we have not performed an exhaustive parameter study here. Our 1+1D model also does not include azimuthal information, which prevents us from modeling the effects of Rossby waves.« less

The formation of protostellar binaries in primordial minihalos

NASA Astrophysics Data System (ADS)

Riaz, R.; Bovino, S.; Vanaverbeke, S.; Schleicher, D. R. G.

2018-06-01

The first stars are known to form in primordial gas, either in minihalos with about 106 M⊙ or so-called atomic cooling halos of about 108 M⊙. Simulations have shown that gravitational collapse and disk formation in primordial gas yield dense stellar clusters. In this paper, we focus particularly on the formation of protostellar binary systems, and aim to quantify their properties during the early stage of their evolution. For this purpose, we combine the smoothed particle hydrodynamics code GRADSPH with the astrochemistry package KROME. The GRADSPH-KROME framework is employed to investigate the collapse of primordial clouds in the high-density regime, exploring the fragmentation process and the formation of binary systems. We observe a strong dependence of fragmentation on the strength of the turbulent Mach number M and the rotational support parameter β. Rotating clouds show significant fragmentation, and have produced several Pop. III proto-binary systems. We report maximum and minimum mass accretion rates of 2.31 × 10-1 M⊙ yr-1 and 2.18 × 10-4 M⊙ yr-1. The mass spectrum of the individual Pop III proto-binary components ranges from 0.88 M⊙ to 31.96 M⊙ and has a sensitive dependence on the Mach number M as well as on the rotational parameter β. We also report a range from ˜0.01 to ˜1 for the mass ratio of our proto-binary systems.

First Science Observations with SOFIA/FORCAST: 6-37 μm Imaging of Orion BN/KL

NASA Astrophysics Data System (ADS)

De Buizer, James M.; Morris, Mark R.; Becklin, E. E.; Zinnecker, Hans; Herter, Terry L.; Adams, Joseph D.; Shuping, Ralph Y.; Vacca, William D.

2012-04-01

The Becklin-Neugebauer/Kleinmann-Low (BN/KL) region of the Orion Nebula is the nearest region of high-mass star formation in our galaxy. As such, it has been the subject of intense investigation at a variety of wavelengths, which have revealed it to be brightest in the infrared to submillimeter wavelength regime. Using the newly commissioned SOFIA airborne telescope and its 5-40 μm camera FORCAST, images of the entire BN/KL complex have been acquired. The 31.5 and 37.1 μm images represent the highest resolution observations (lsim4'') ever obtained of this region at these wavelengths. These observations reveal that the BN object is not the dominant brightness source in the complex at wavelengths >= 31.5 μm and that this distinction goes instead to the source IRc4. It was determined from these images and derived dust color temperature maps that IRc4 is also likely to be self-luminous. A new source of emission has also been identified at wavelengths >= 31.5 μm that coincides with the northeastern outflow lobe from the protostellar disk associated with radio source I.

Quasars Outflows As A Function of SED - An Empirical Approach

NASA Astrophysics Data System (ADS)

Richmond, Joseph M.; Ganguly, Rajib

2015-08-01

Feedback from quasars (jets, outflows, and luminosity) is now recognized as a vital phase in describing galaxy evolution, growth, and star formation efficiency. Regarding outflows, roughly 60% are observed to have outflowing gas appearing at large velocities and with a variety of velocity dispersions. The most extreme observed form of these outflows appears in the ultraviolet spectrum of 15-20% of objects. Understanding the physics of these outflows is important for both astrophysical and cosmological reasons. Establishing empirical relationships to test the theoretical models of how these outflows are driven (and hence, how they impact their surroundings) is currently plagued by having too few objects, where other parameters like the black hole mass or accretion rate, may add to the scatter. We aim to fix this by using a systematic study of a large sample of objects. As a follow up to a previous study, we have identified a sample of nearly 11000 z=1.7-2 quasars using archived data from the Sloan Digital Sky Survey (Data Release 7), of which roughly 4400 appear to show outflows according to the visual inspection. The specific redshift range is chosen to feature both the Mg II 2800 emission line as well as wavelengths extending to nearly 20,000 km/s blueward of the C IV 1549 emission line. Our goals for this study are: (1) To temper our visual inspection schemes with a more automated, computer-driven scheme; (2) To measure the properties of the outflows (velocity, velocity dispersion, equivalent width, ionization); (3) To supplement the SDSS spectra with photometric measurements from GALEX, 2MASS, and WISE to further characterize the spectral energy distributions (SEDs) and dust content; (4) To form spectral composites to investigate possible SED changes with outflow properties; and (5) To use published estimates of the quasar physical properties (black hole mass, accretion rate, etc.) to fully establish in an empirical way the complex dependencies between the properties of the outflow, and the physical properties of the system.

The Stability of Radiatively Cooling Jets. 2: Nonlinear Evolution

NASA Technical Reports Server (NTRS)

Stone, James M.; Xu, Jianjun; Hardee, Philip

1997-01-01

We use two-dimensional time-dependent hydrodynamical simulations to follow the growth of the Kelvin-Helmholtz (K-H) instability in cooling jets into the nonlinear regime. We focus primarily on asymmetric modes that give rise to transverse displacements of the jet beam. A variety of Mach numbers and two different cooling curves are studied. The growth rates of waves in the linear regime measured from the numerical simulations are in excellent agreement with the predictions of the linear stability analysis presented in the first paper in this series. In the nonlinear regime, the simulations show that asymmetric modes of the K-H instability can affect the structure and evolution of cooling jets in a number of ways. We find that jets in which the growth rate of the sinusoidal surface wave has a maximum at a so-called resonant frequency can be dominated by large-amplitude sinusoidal oscillations near this frequency. Eventually, growth of this wave can disrupt the jet. On the other hand, nonlinear body waves tend to produce low-amplitude wiggles in the shape of the jet but can result in strong shocks in the jet beam. In cooling jets, these shocks can produce dense knots and filaments of cooling gas within the jet. Ripples in the surface of the jet beam caused by both surface and body waves generate oblique shock "spurs" driven into the ambient gas. Our simulations show these shock "spurs" can accelerate ambient gas at large distances from the jet beam to low velocities, which represents a new mechanism by which low-velocity bipolar outflows may be driven by high-velocity jets. Rapid entrainment and acceleration of ambient gas may also occur if the jet is disrupted. For parameters typical of protostellar jets, the frequency at which K-H growth is a maximum (or highest frequency to which the entire jet can respond dynamically) will be associated with perturbations with a period of - 200 yr. Higher frequency (shorter period) perturbations excite waves associated with body modes that produce internal shocks and only small-amplitude wiggles within the jet. The fact that most observed systems show no evidence for large-amplitude sinusoidal oscillation leading to disruption is indicative that the perturbation frequencies are generally large, consistent with the suggestion that pro- tostellar jets arise from the inner regions (r less than 1 AU) of accretion disks.

A near-infrared spectroscopic survey of massive jets towards extended green objects

NASA Astrophysics Data System (ADS)

Caratti o Garatti, A.; Stecklum, B.; Linz, H.; Garcia Lopez, R.; Sanna, A.

2015-01-01

Context. Protostellar jets and outflows are the main outcome of the star formation process, and their analysis can provide us with major clues about the ejection and accretion history of young stellar objects (YSOs). Aims: We aim at deriving the main physical properties of massive jets from near-infrared (NIR) observations, comparing them to those of a large sample of jets from low-mass YSOs, and relating them to the main features of their driving sources. Methods: We present a NIR imaging (H2 and Ks) and low-resolution spectroscopic (0.95-2.50 μm) survey of 18 massive jets towards GLIMPSE extended green objects (EGOs), driven by intermediate- and high-mass YSOs, which have bolometric luminosities (Lbol) between 4 × 102 and 1.3 × 105 L⊙. Results: As in low-mass jets, H2 is the primary NIR coolant, detected in all the analysed flows, whereas the most important ionic tracer is [Fe ii], detected in half of the sampled jets. Our analysis indicates that the emission lines originate from shocks at high temperatures and densities. No fluorescent emission is detected along the flows, regardless of the source bolometric luminosity. On average, the physical parameters of these massive jets (i.e. visual extinction, temperature, column density, mass, and luminosity) have higher values than those measured in their low-mass counterparts. The morphology of the H2 flows is varied, mostly depending on the complex, dynamic, and inhomogeneous environment in which these massive jets form and propagate. All flows and jets in our sample are collimated, showing large precession angles. Additionally, the presence of both knots and jets suggests that the ejection process is continuous with burst episodes, as in low-mass YSOs. We compare the flow H2 luminosity with the source bolometric luminosity confirming the tight correlation between these two quantities. Five sources, however, display a lower LH2/Lbol efficiency, which might be related to YSO evolution. Most important, the inferred LH2 vs. Lbol relationship agrees well with the correlation between the momentum flux of the CO outflows and the bolometric luminosities of high-mass YSOs indicating that outflows from high-mass YSOs are momentum driven, as are their low-mass counterparts. We also derive a less stringent correlation between the inferred mass of the H2 flows and Lbol of the YSOs, indicating that the mass of the flow depends on the driving source mass. Conclusions: By comparing the physical properties of jets in the NIR, a continuity from low- to high-mass jets is identified. Massive jets appear as a scaled-up version of their low-mass counterparts in terms of their physical parameters and origin. Nevertheless, there are consistent differences such as a more variegated morphology and, on average, stronger shock conditions, which are likely due to the different environment in which high-mass stars form. Based on observations collected at the European Southern Observatory La Silla, Chile, 080.C-0573(A), 083.C-0846(A).Appendices are available in electronic form at http://www.aanda.org

THE BARYON CYCLE AT HIGH REDSHIFTS: EFFECTS OF GALACTIC WINDS ON GALAXY EVOLUTION IN OVERDENSE AND AVERAGE REGIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadoun, Raphael; Shlosman, Isaac; Choi, Jun-Hwan

2016-10-01

We employ high-resolution cosmological zoom-in simulations focusing on a high-sigma peak and an average cosmological field at z ∼ 6–12 in order to investigate the influence of environment and baryonic feedback on galaxy evolution in the reionization epoch. Strong feedback, e.g., galactic winds, caused by elevated star formation rates (SFRs) is expected to play an important role in this evolution. We compare different outflow prescriptions: (i) constant wind velocity (CW), (ii) variable wind scaling with galaxy properties (VW), and (iii) no outflows (NW). The overdensity leads to accelerated evolution of dark matter and baryonic structures, absent from the “normal” region,more » and to shallow galaxy stellar mass functions at the low-mass end. Although CW shows little dependence on the environment, the more physically motivated VW model does exhibit this effect. In addition, VW can reproduce the observed specific SFR (sSFR) and the sSFR–stellar mass relation, which CW and NW fail to satisfy simultaneously. Winds also differ substantially in affecting the state of the intergalactic medium (IGM). The difference lies in the volume-filling factor of hot, high-metallicity gas, which is near unity for CW, while such gas remains confined in massive filaments for VW, and locked up in galaxies for NW. Such gas is nearly absent from the normal region. Although all wind models suffer from deficiencies, the VW model seems to be promising in correlating the outflow properties with those of host galaxies. Further constraints on the state of the IGM at high z are needed to separate different wind models.« less

The Baryon Cycle at High Redshifts: Effects of Galactic Winds on Galaxy Evolution in Overdense and Average Regions

NASA Astrophysics Data System (ADS)

Sadoun, Raphael; Shlosman, Isaac; Choi, Jun-Hwan; Romano-Díaz, Emilio

2016-10-01

We employ high-resolution cosmological zoom-in simulations focusing on a high-sigma peak and an average cosmological field at z ˜ 6-12 in order to investigate the influence of environment and baryonic feedback on galaxy evolution in the reionization epoch. Strong feedback, e.g., galactic winds, caused by elevated star formation rates (SFRs) is expected to play an important role in this evolution. We compare different outflow prescriptions: (I) constant wind velocity (CW), (II) variable wind scaling with galaxy properties (VW), and (III) no outflows (NW). The overdensity leads to accelerated evolution of dark matter and baryonic structures, absent from the “normal” region, and to shallow galaxy stellar mass functions at the low-mass end. Although CW shows little dependence on the environment, the more physically motivated VW model does exhibit this effect. In addition, VW can reproduce the observed specific SFR (sSFR) and the sSFR-stellar mass relation, which CW and NW fail to satisfy simultaneously. Winds also differ substantially in affecting the state of the intergalactic medium (IGM). The difference lies in the volume-filling factor of hot, high-metallicity gas, which is near unity for CW, while such gas remains confined in massive filaments for VW, and locked up in galaxies for NW. Such gas is nearly absent from the normal region. Although all wind models suffer from deficiencies, the VW model seems to be promising in correlating the outflow properties with those of host galaxies. Further constraints on the state of the IGM at high z are needed to separate different wind models.

Strong Stellar-driven Outflows Shape the Evolution of Galaxies at Cosmic Dawn

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fontanot, Fabio; De Lucia, Gabriella; Hirschmann, Michaela

We study galaxy mass assembly and cosmic star formation rate (SFR) at high redshift (z ≳ 4), by comparing data from multiwavelength surveys with predictions from the GAlaxy Evolution and Assembly (gaea) model. gaea implements a stellar feedback scheme partially based on cosmological hydrodynamical simulations, which features strong stellar-driven outflows and mass-dependent timescales for the re-accretion of ejected gas. In previous work, we have shown that this scheme is able to correctly reproduce the evolution of the galaxy stellar mass function (GSMF) up to z ∼ 3. We contrast model predictions with both rest-frame ultraviolet (UV) and optical luminosity functionsmore » (LFs), which are mostly sensitive to the SFR and stellar mass, respectively. We show that gaea is able to reproduce the shape and redshift evolution of both sets of LFs. We study the impact of dust on the predicted LFs, and we find that the required level of dust attenuation is in qualitative agreement with recent estimates based on the UV continuum slope. The consistency between data and model predictions holds for the redshift evolution of the physical quantities well beyond the redshift range considered for the calibration of the original model. In particular, we show that gaea is able to recover the evolution of the GSMF up to z ∼ 7 and the cosmic SFR density up to z ∼ 10.« less

Sedimentary patterns in perched spring travertines near Granada (Spain) as indicators of the paleohydrological and paleoclimatological evolution of a karst massif

NASA Astrophysics Data System (ADS)

Martín-Algarra, Agustín.; Martín-Martín, Manuel; Andreo, Bartolomé; Julià, Ramón; González-Gómez, Cecilio

2003-10-01

Perched spring travertines of the Granada basin (South Spain) constitute a perched system with four well-defined steps, which are formed by several facies associations deposited in different sub-environments (travertine pools, dams and cascades). These perched travertines are considered as a freshwater reef system with a facies zonation and stratigraphic architecture closely resembling that of marine reef terraces and prograding carbonate platforms. The travertine deposits have been dated by 230Th/ 234U and 14C methods. As in other Mediterranean areas, the travertine deposition occurred episodically during warm and wet interglacial periods coinciding with isotopic stages 9, 7 and 5, and with the transition between isotopic stages 2/1. During these periods, underground dissolution, large outflow in the springs and subsequent calcium carbonate precipitation occurred. In the same way that evolution of reef systems indicates sea level changes, the geomorphology, age and architecture of perched spring travertine systems may be used to interpret former climatically controlled changes in outflow, in base level marked by the altitude of springs and in the chemistry of spring waters. Thus, aggradation or climbing progradation may indicate an increase of outflow at the spring, progradation with toplap is due to a stable base level and, conversely, dowlapping progradation may signify that the base level was gradually dropping. Therefore, the travertines can be considered semiquantitative indicators of the paleohydrological evolution of karstic massifs and used as an important terrestrial proxy climate record.

The HST-pNFL program: Mapping the Fluorescent Emission of Galactic Outflows

NASA Astrophysics Data System (ADS)

Heckman, Timothy

2017-08-01

Galactic outflows associated with star formation are believed to play a crucial role in the evolution of galaxies and the IGM. Most of our knowledge about outflows has come from down-the-barrel UV absorption spectroscopy of star-forming galaxies. However, absorption-line data alone provide only indirect information about the radial structure of the gas flows, which introduces large systematic uncertainties in some of the most important quantities, such as the outflow rate, the mass loading factor, and the momentum, metal, and energy fluxes. Recent spectroscopic observations of star-forming galaxies with large (projected physical) apertures have revealed non-resonant (fluorescent) emission in the UV, e.g., FeII* and SiII*, that can be naturally produced by spatially extended emission from the same outflowing material traced in absorption. Encouraged by the most recent observations of FeII* emission by the SDSS-IV/eBOSS survey (Zhu et al. 2015), we propose a pilot program to use narrow-band filter UVIS F280N images to map the extended FeII* 2626 and 2613 fluorescent emission in a carefully-chosen sample of 4 starburst galaxies at z=0.065, and COS G130M to obtain down-the- barrel spectra for SiII absorption and SiII* emission. This HST pilot program can provide unique information about the spatial structure of galactic outflows and can potentially lead to a revolution in our understanding of outflow physics and its impact on galaxies and the IGM.

Robust boundary treatment for open-channel flows in divergence-free incompressible SPH

NASA Astrophysics Data System (ADS)

Pahar, Gourabananda; Dhar, Anirban

2017-03-01

A robust Incompressible Smoothed Particle Hydrodynamics (ISPH) framework is developed to simulate specified inflow and outflow boundary conditions for open-channel flow. Being purely divergence-free, the framework offers smoothed and structured pressure distribution. An implicit treatment of Pressure Poison Equation and Dirichlet boundary condition is applied on free-surface to minimize error in velocity-divergence. Beyond inflow and outflow threshold, multiple layers of dummy particles are created according to specified boundary condition. Inflow boundary acts as a soluble wave-maker. Fluid particles beyond outflow threshold are removed and replaced with dummy particles with specified boundary velocity. The framework is validated against different cases of open channel flow with different boundary conditions. The model can efficiently capture flow evolution and vortex generation for random geometry and variable boundary conditions.

[Kelvin-Helmholtz instability in protostellar jets

NASA Technical Reports Server (NTRS)

Stone, James; Hardee, Philip

1996-01-01

NASA grant NAG 5 2866, funded by the Astrophysics Theory Program, enabled the study the Kelvin-Helmholtz instability in protostellar jets. In collaboration with co-investigator Philip Hardee, the PI derived the analytic dispersion relation for the instability in including a cooling term in the energy equation which was modeled as one of two different power laws. Numerical solutions to this dispersion relation over a wide range of perturbation frequencies, and for a variety of parameter values characterizing the jet (such as Mach number, and density ratio) were found It was found that the growth rates and wavelengths associated with unstable roots of the dispersion relation in cooling jets are significantly different than those associated with adiabatic jets, which have been studied previously. In collaboration with graduate student Jianjun Xu (funded as a research associate under this grant), hydrodynamical simulations were used to follow the growth of the instability into the nonlinear regime. It was found that asymmetric surface waves lead to large amplitude, sinusoidal distortions of the jet, and ultimately to disruption Asymmetric body waves, on the other hand, result in the formation of shocks in the jet beam in the nonlinear regime. In cooling jets, these shocks lead to the formation of dense knots and filaments of gas within the jet. For sufficiently high perturbation frequencies, however, the jet cannot respond and it remains symmetric. Applying these results to observed systems, such as the Herbig-Haro jets HH34, HH111 and HH47 which have been observed with the Hubble Space Telescope, we predicted that some of the asymmetric structures observed in these systems could be attributed to the K-H modes, but that perturbations on timescales associated with the inner disk (about 1 year) would be too rapid to cause disruption. Moreover, it was discovered that weak shock 'spurs' in the ambient gas produced by ripples in the jet surface due to nonlinear, modes of surface and/or body waves could accelerate the ambient gas to low velocity. This latter effect represents a new mechanism by which supersonic jets can accelerate low velocity outflows.

Subliminal expansion in NGC1275

NASA Astrophysics Data System (ADS)

Backer, Donald C.

The neraby, active galaxy NGC 1275 (3C 84, z = 0.018) has been the subject of many investigations in the past 20 years. The author reviews the evolution of the microwave flux density and the structure seen in 10.7 GHz VLBI images. Then he summarizes recent VLBI observations at 22 GHz and 90 GHz. Rapid changes in the core and the presence of a "hot spot" in the outflowing material are prominent features of these short-wavelength VLBI data. The case for subluminal proper velocities of the outflow is strong.

Demographics and Case Studies of Galactic Outflows in the Local Universe

NASA Astrophysics Data System (ADS)

Rupke, David

2017-07-01

Galactic outflows driven by both star formation and active black holes are an important driver of galaxy evolution. The local universe is a sensitive laboratory for understanding the scaling relations that characterize these winds and the physics that govern them. I will review what we know from statistical studies about the prevalance and properties of nearby galactic winds and how these properties depend on those of the host galaxy or power source. I will also highlight detailed case studies of key objects that illustrate the multiphase structure of these winds.

The Space Infrared Interferometric Telescope (SPIRIT): High-Resolution Imaging and Spectroscopy in the Far-Infrared (Preprint)

DTIC Science & Technology

2007-01-01

primary scientific objectives: (1) Learn how planetary systems form from protostellar disks , and how they acquire their inhomogeneous composition; (2...characterize the family of extrasolar planetary systems by imaging the structure in debris disks to understand how and where planets of different...scientific objectives: (1) Learn how planetary systems form from protostellar disks , and how they acquire their inhomogeneous composition; (2

Planet Forming Protostellar Disks

NASA Technical Reports Server (NTRS)

Lubow, Stephen

1998-01-01

The project achieved many of its objectives. The main area of investigation was the interaction of young binary stars with surrounding protostellar disks. A secondary objective was the interaction of young planets with their central stars and surrounding disks. The grant funds were used to support visits by coinvestigators and visitors: Pawel Artymowicz, James Pringle, and Gordon Ogilvie. Funds were also used to support travel to meetings by Lubow and to provide partial salary support.

SDSS J163459.82+204936.0: A Ringed Infrared-luminous Quasar with Outflows in Both Absorption and Emission Lines

NASA Astrophysics Data System (ADS)

Liu, Wen-Juan; Zhou, Hong-Yan; Jiang, Ning; Wu, Xufen; Lyu, Jianwei; Shi, Xiheng; Shu, Xinwen; Jiang, Peng; Ji, Tuo; Wang, Jian-Guo; Wang, Shu-Fen; Sun, Luming

2016-05-01

SDSS J163459.82+204936.0 is a local (z = 0.1293) infrared-luminous quasar with L IR = 1011.91 {L}⊙ . We present a detailed multiwavelength study of both the host galaxy and the nucleus. The host galaxy, appearing as an early-type galaxy in the optical images and spectra, demonstrates violent, obscured star formation activities with SFR ≈ 140 {M}⊙ yr-1, estimated from either the polycyclic aromatic hydrocarbon emission or IR luminosity. The optical to NIR spectra exhibit a blueshifted narrow cuspy component in Hβ, He I λλ5876, 10830, and other emission lines consistently with an offset velocity of ≈900 {km} {{{s}}}-1, as well as additional blueshifting phenomena in high-ionization lines (e.g., a blueshifted broad component of He I λ10830 and the bulk blueshifting of [O III]λ5007), while there exist blueshifted broad absorption lines (BALs) in Na I D and He I λλ3889, 10830, indicative of the active galactic nucleus outflows producing BALs and emission lines. Constrained mutually by the several BALs in the photoionization simulations with Cloudy, the physical properties of the absorption line outflow are derived as follows: density 104 < n H ≲ 105 cm-3, ionization parameter 10-1.3 ≲ U ≲ 10-0.7 , and column density 1022.5 ≲ N H ≲ 1022.9 cm-2, which are similar to those derived for the emission line outflows. This similarity suggests a common origin. Taking advantages of both the absorption lines and outflowing emission lines, we find that the outflow gas is located at a distance of ˜48-65 pc from the nucleus and that the kinetic luminosity of the outflow is 1044-1046 {erg} {{{s}}}-1. J1634+2049 has a off-centered galactic ring on the scale of ˜30 kpc that is proved to be formed by a recent head-on collision by a nearby galaxy for which we spectroscopically measure the redshift. Thus, this quasar is a valuable object in the transitional phase emerging out of dust enshrouding as depicted by the co-evolution scenario invoking galaxy merger (or violent interaction) and quasar feedback. Its proximity enables our further observational investigations in detail (or tests) of the co-evolution paradigm.

A Model for Protostellar Cluster Luminosities and the Impact on the CO–H2 Conversion Factor

NASA Astrophysics Data System (ADS)

Gaches, Brandt A. L.; Offner, Stella S. R.

2018-02-01

We construct a semianalytic model to study the effect of far-ultraviolet (FUV) radiation on gas chemistry from embedded protostars. We use the protostellar luminosity function (PLF) formalism of Offner & McKee to calculate the total, FUV, and ionizing cluster luminosity for various protostellar accretion histories and cluster sizes. We2 compare the model predictions with surveys of Gould Belt star-forming regions and find that the tapered turbulent core model matches best the mean luminosities and the spread in the data. We combine the cluster model with the photodissociation region astrochemistry code, 3D-PDR, to compute the impact of the FUV luminosity from embedded protostars on the CO-to-H2 conversion factor, X CO, as a function of cluster size, gas mass, and star formation efficiency. We find that X CO has a weak dependence on the FUV radiation from embedded sources for large clusters owing to high cloud optical depths. In smaller and more efficient clusters the embedded FUV increases X CO to levels consistent with the average Milky Way values. The internal physical and chemical structures of the cloud are significantly altered, and X CO depends strongly on the protostellar cluster mass for small efficient clouds.

Protostellar accretion traced with chemistry. High-resolution C18O and continuum observations towards deeply embedded protostars in Perseus

NASA Astrophysics Data System (ADS)

Frimann, Søren; Jørgensen, Jes K.; Dunham, Michael M.; Bourke, Tyler L.; Kristensen, Lars E.; Offner, Stella S. R.; Stephens, Ian W.; Tobin, John J.; Vorobyov, Eduard I.

2017-06-01

Context. Understanding how accretion proceeds is a key question of star formation, with important implications for both the physical and chemical evolution of young stellar objects. In particular, very little is known about the accretion variability in the earliest stages of star formation. Aims: Our aim is to characterise protostellar accretion histories towards individual sources by utilising sublimation and freeze-out chemistry of CO. Methods: A sample of 24 embedded protostars are observed with the Submillimeter Array (SMA) in context of the large program "Mass Assembly of Stellar Systems and their Evolution with the SMA" (MASSES). The size of the C18O-emitting region, where CO has sublimated into the gas-phase, is measured towards each source and compared to the expected size of the region given the current luminosity. The SMA observations also include 1.3 mm continuum data, which are used to investigate whether or not a link can be established between accretion bursts and massive circumstellar disks. Results: Depending on the adopted sublimation temperature of the CO ice, between 20% and 50% of the sources in the sample show extended C18O emission indicating that the gas was warm enough in the past that CO sublimated and is currently in the process of refreezing; something which we attribute to a recent accretion burst. Given the fraction of sources with extended C18O emission, we estimate an average interval between bursts of 20 000-50 000 yr, which is consistent with previous estimates. No clear link can be established between the presence of circumstellar disks and accretion bursts, however the three closest known binaries in the sample (projected separations <20 AU) all show evidence of a past accretion burst, indicating that close binary interactions may also play a role in inducing accretion variability.

Gravitational Instabilities in Circumstellar Disks

NASA Astrophysics Data System (ADS)

Kratter, Kaitlin; Lodato, Giuseppe

2016-09-01

Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review, we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small-scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability supplemented with a survey of numerical simulations that aim to capture the nonlinear evolution. We emphasize the role of thermodynamics and large-scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analytic predictions and numerical results. In the next part of our review, we focus on the astrophysical consequences of the instability. We show that the disks most likely to be gravitationally unstable are young and relatively massive compared with their host star, Md/M*≥0.1. They will develop quasi-stable spiral arms that process infall from the background cloud. Although instability is less likely at later times, once infall becomes less important, the manifestations of the instability are more varied. In this regime, the disk thermodynamics, often regulated by stellar irradiation, dictates the development and evolution of the instability. In some cases the instability may lead to fragmentation into bound companions. These companions are more likely to be brown dwarfs or stars than planetary mass objects. Finally, we highlight open questions related to the development of a turbulent cascade in thin disks and the role of mode-mode coupling in setting the maximum angular momentum transport rate in thick disks.

Outflow activities in the young high-mass stellar object G23.44-0.18

NASA Astrophysics Data System (ADS)

Ren, Jeremy Zhiyuan; Liu, Tie; Wu, Yuefang; Li, Lixin

2011-07-01

We present an observational study towards the young high-mass star-forming region G23.44-0.18 using the Submillimeter Array. Two massive, radio-quiet dusty cores MM1 and MM2 are observed in 1.3-mm continuum emission and dense molecular gas tracers including thermal CH3OH, CH3CN, HNCO, SO, and OCS lines. The 12CO (2-1) line reveals a strong bipolar outflow originating from MM2. The outflow consists of a low-velocity component with wide-angle quasi-parabolic shape and a more compact and collimated high-velocity component. The overall geometry resembles the outflow system observed in the low-mass protostar which has a jet-driven fast flow and entrained gas shell. The outflow has a dynamical age of 6 × 103 yr and a mass loss rate ˜10-3 M ⊙ yr-1. A prominent shock emission in the outflow is observed in SO and OCS, and also detected in CH3OH and HNCO. We investigated the chemistry of MM1, MM2 and the shocked region. The dense core MM2 have molecular abundances of three to four times higher than those in MM1. The abundance excess, we suggest, can be a net effect of the stellar evolution and embedded shocks in MM2 that calls for further inspection.

Catastrophic ice lake collapse in Aram Chaos, Mars

NASA Astrophysics Data System (ADS)

Roda, Manuel; Kleinhans, Maarten G.; Zegers, Tanja E.; Oosthoek, Jelmer H. P.

2014-07-01

Hesperian chaotic terrains have been recognized as the source of outflow channels formed by catastrophic outflows. Four main scenarios have been proposed for the formation of chaotic terrains that involve different amounts of water and single or multiple outflow events. Here, we test these scenarios with morphological and structural analyses of imagery and elevation data for Aram Chaos in conjunction with numerical modeling of the morphological evolution of the catastrophic carving of the outflow valley. The morphological and geological analyses of Aram Chaos suggest large-scale collapse and subsidence (1500 m) of the entire area, which is consistent with a massive expulsion of liquid water from the subsurface in one single event. The combined observations suggest a complex process starting with the outflow of water from two small channels, followed by continuous groundwater sapping and headward erosion and ending with a catastrophic lake rim collapse and carving of the Aram Valley, which is synchronous with the 2.5 Ga stage of the Ares Vallis formation. The water volume and formative time scale required to carve the Aram channels indicate that a single, rapid (maximum tens of days) and catastrophic (flood volume of 9.3 × 104 km3) event carved the outflow channel. We conclude that a sub-ice lake collapse model can best explain the features of the Aram Chaos Valley system as well as the time scale required for its formation.

Radio jets clearing the way through galaxies: the view from Hi and molecular gas

NASA Astrophysics Data System (ADS)

Morganti, Raffaella

2015-03-01

Massive gas outflows are considered a key component in the process of galaxy formation and evolution. Because of this, they are the topic of many studies aimed at learning more about their occurrence, location and physical conditions as well as the mechanism(s) at their origin. This contribution presents recent results on two of the best examples of jet-driven outflows traced by cold and molecular gas. Thanks to high-spatial resolution observations, we have been able to locate the region where the outflow occurs. This appears to be coincident with bright radio features and regions where the interaction between radio plasma jet and ISM is known to occur, thus strongly supporting the idea of jet-driven outflows. We have also imaged the distribution of the outflowing gas. The results clearly show the effect that expanding radio jets and lobes have on the ISM. This appears to be in good agreement with what predicted from numerical simulations. Furthermore, the results show that cold gas is associated with these powerful phenomena and can be formed - likely via efficient cooling - even after a strong interaction and fast shocks. The discovery of similar fast outflows of cold gas in weak radio sources is further increasing the relevance that the effect of the radio plasma can have on the surrounding medium and on the host galaxy.

Convective scale interaction: Arc cloud lines and the development and evolution of deep convection

NASA Technical Reports Server (NTRS)

Purdom, James Francis Whitehurst

1986-01-01

Information is used from satellite data and research aircraft data to provide new insights concerning the mesoscale development and evolution of deep convection in an atmosphere typified by weak synoptic-scale forcing. The importance of convective scale interaction in the development and evolution of deep convection is examined. This interaction is shown to manifest itself as the merger and intersection of thunderstorm outflow boundaries (arc cloud lines) with other convective lines, areas or boundaries. Using geostationary satellite visible and infrared data convective scale interaction is shown to be responsible for over 85 percent of the intense convection over the southeast U.S. by late afternoon, and a majority of that area's afternoon rainfall. The aircraft observations provided valuable information concerning critically important regions of the arc cloud line: (1) the cool outflow region, (2) the density surge line interface region; and (3) the sub-cloud region above the surge line. The observations when analyzed with rapid scan satellite data, helped in defining the arc cloud line's life cycle as 3 evolving stages.

The limited role of recombination energy in common envelope removal

NASA Astrophysics Data System (ADS)

Grichener, Aldana; Sabach, Efrat; Soker, Noam

2018-05-01

We calculate the outward energy transport time by convection and photon diffusion in an inflated common envelope and find this time to be shorter than the envelope expansion time. We conclude therefore that most of the hydrogen recombination energy ends in radiation rather than in kinetic energy of the outflowing envelope. We use the stellar evolution code MESA and inject energy inside the envelope of an asymptotic giant branch star to mimic energy deposition by a spiraling-in stellar companion. During 1.7 years the envelope expands by a factor of more than 2. Along the entire evolution the convection can carry the energy very efficiently outwards, to the radius where radiative transfer becomes more efficient. The total energy transport time stays within several months, shorter than the dynamical time of the envelope. Had we included rapid mass loss, as is expected in the common envelope evolution, the energy transport time would have been even shorter. It seems that calculations that assume that most of the recombination energy ends in the outflowing gas might be inaccurate.

Linear analysis of the evolution of nearly polar low-mass circumbinary discs

NASA Astrophysics Data System (ADS)

Lubow, Stephen H.; Martin, Rebecca G.

2018-01-01

In a recent paper Martin & Lubow showed through simulations that an initially tilted disc around an eccentric binary can evolve to polar alignment in which the disc lies perpendicular to the binary orbital plane. We apply linear theory to show both analytically and numerically that a nearly polar aligned low-mass circumbinary disc evolves to polar alignment and determine the alignment time-scale. Significant disc evolution towards the polar state around moderately eccentric binaries can occur for typical protostellar disc parameters in less than a typical disc lifetime for binaries with orbital periods of order 100 yr or less. Resonant torques are much less effective at truncating the inner parts of circumbinary polar discs than the inner parts of coplanar discs. For polar discs, they vanish for a binary eccentricity of unity. The results agree with the simulations in showing that discs can evolve to a polar state. Circumbinary planets may then form in such discs and reside on polar orbits.

Characterizing the long-range transport of black carbon aerosols during Transport and Chemical Evolution over the Pacific (TRACE-P) experiment.

PubMed

Verma, Sunita; Worden, John; Payra, Swagata; Jourdain, Line; Shim, Changsub

2009-07-01

A major aircraft experiment Transport and Chemical Evolution over the Pacific (TRACE-P) mission over the NW Pacific in March-April 2001 was conducted to better understand how outflow from the Asian continent affects the composition of the global atmosphere. In this paper, a global climate model, GEOS-Chem is used to investigate possible black carbon aerosol contributions from TRACE-P region. Our result depicts that absorbing black carbon ("soot") significantly outflow during lifting to the free troposphere through warm conveyor belt and convection associated with this lifting. The GEOS-Chem simulation results show significant transport of black carbon aerosols from Asian regions to the Western Pacific region during the spring season. As estimated by GEOS-Chem simulations, approximately 25% of the black carbon concentrations over the western pacific originate from SE Asia in the spring.

Stellar physics. Observing the onset of outflow collimation in a massive protostar.

PubMed

Carrasco-González, C; Torrelles, J M; Cantó, J; Curiel, S; Surcis, G; Vlemmings, W H T; van Langevelde, H J; Goddi, C; Anglada, G; Kim, S-W; Kim, J-S; Gómez, J F

2015-04-03

The current paradigm of star formation through accretion disks, and magnetohydrodynamically driven gas ejections, predicts the development of collimated outflows, rather than expansion without any preferential direction. We present radio continuum observations of the massive protostar W75N(B)-VLA 2, showing that it is a thermal, collimated ionized wind and that it has evolved in 18 years from a compact source into an elongated one. This is consistent with the evolution of the associated expanding water-vapor maser shell, which changed from a nearly circular morphology, tracing an almost isotropic outflow, to an elliptical one outlining collimated motions. We model this behavior in terms of an episodic, short-lived, originally isotropic ionized wind whose morphology evolves as it moves within a toroidal density stratification. Copyright © 2015, American Association for the Advancement of Science.

The JCMT Transient Survey: Detection of Submillimeter Variability in a Class I Protostar EC 53 in Serpens Main

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoo, Hyunju; Cho, Jungyeon; Lee, Jeong-Eun

During the protostellar phase of stellar evolution, accretion onto the star is expected to be variable, but this suspected variability has been difficult to detect because protostars are deeply embedded. In this paper, we describe a submillimeter luminosity burst of the Class I protostar EC 53 in Serpens Main, the first variable found during our dedicated JCMT/SCUBA-2 monitoring program of eight nearby star-forming regions. EC 53 remained quiescent for the first six months of our survey, from 2016 February to August. The submillimeter emission began to brighten in 2016 September, reached a peak brightness of 1.5 times the faint state,more » and has been decaying slowly since 2017 February. The change in submillimeter brightness is interpreted as dust heating in the envelope, generated by a luminosity increase of the protostar of a factor of ≥4. The 850 μ m light curve resembles the historical K -band light curve, which varies by a factor of ∼6 with a 543 period and is interpreted as accretion variability excited by interactions between the accretion disk and a close binary system. The predictable detections of accretion variability observed at both near-infrared and submillimeter wavelengths make the system a unique test-bed, enabling us to capture the moment of the accretion burst and to study the consequences of the outburst on the protostellar disk and envelope.« less

Nonaxisymmetric Dynamic Instabilities of Rotating Polytropes. II. Torques, Bars, and Mode Saturation with Applications to Protostars and Fizzlers

NASA Astrophysics Data System (ADS)

Imamura, James N.; Durisen, Richard H.; Pickett, Brian K.

2000-01-01

Dynamic nonaxisymmetric instabilities in rapidly rotating stars and protostars have a range of potential applications in astrophysics, including implications for binary formation during protostellar cloud collapse and for the possibility of aborted collapse to neutron star densities at late stages of stellar evolution (``fizzlers''). We have recently presented detailed linear analyses for polytropes of the most dynamically unstable global modes, the barlike modes. These produce bar distortions in the regions near the rotation axis but have trailing spiral arms toward the equator. In this paper, we use our linear eigenfunctions to predict the early nonlinear behavior of the dynamic instability and compare these ``quasi-linear'' predictions with several fully nonlinear hydrodynamics simulations. The comparisons demonstrate that the nonlinear saturation of the barlike instability is due to the self-interaction gravitational torques between the growing central bar and the spiral arms, where angular momentum is transferred outward from bar to arms. We also find a previously unsuspected resonance condition that accurately predicts the mass of the bar regions in our own simulations and in those published by other researchers. The quasi-linear theory makes other accurate predictions about consequences of instability, including properties of possible end-state bars and increases in central density, which can be large under some conditions. We discuss in some detail the application of our results to binary formation during protostellar collapse and to the formation of massive rotating black holes.

First detection of a THz water maser in NGC 7538-IRS1 with SOFIA and new 22 GHz e-MERLIN maps

NASA Astrophysics Data System (ADS)

Herpin, F.; Baudry, A.; Richards, A. M. S.; Gray, M. D.; Schneider, N.; Menten, K. M.; Wyrowski, F.; Bontemps, S.; Simon, R.; Wiesemeyer, H.

2017-10-01

Context. The formation of massive stars (M> 10M⊙, L > 103L⊙) is still not well understood. Accumulating a large amount of mass infalling within a single entity in spite of radiation pressure is possible if, in addition to several other conditions, enough thermal energy is released. Despite numerous water line observations over a broad range of energies obtained with the Herschel Space Observatory, observations were not able to trace the emission from the hot core around the newly forming protostellar object in most of the sources. Aims: We wish to probe the physical conditions and water abundance in the inner layers of the host protostellar object NGC 7538-IRS1 using a highly excited H2O line. Water maser models predict that several THz water masers should be detectable in these objects. We therefore aim to detect the o-H2O 82,7-73,4 line in a star forming region for the first time. Model calculations have predicted this line to show maser action. Methods: We present SOFIA observations of the o-H2O 82,7-73,4 line at 1296.41106 GHz and a 616-523 22 GHz e-MERLIN map of the region (the very first 22 GHz images made after the e-MERLIN upgrade). In order to be able to constrain the nature of the emission - thermal or maser - we used near-simultaneous observations of the 22 GHz water maser performed with the Effelsberg radiotelescope and e-MERLIN. A thermal water model using the RATRAN radiative transfer code is presented based on HIFI pointed observations. Molecular water abundances are derived for the hot core. Results: The o-H2O 82,7-73,4 line is detected toward NGC 7538-IRS1 with one feature at the source velocity (-57.7 kms-1) and another one at -48.4 kms-1. We propose that the emission at the source velocity is consistent with thermal excitation and is excited in the innermost part of the IRS1a, in the closest circumstellar environment of the massive protostellar object. The other emission is very likely the first detection of a water THz maser line, pumped by shocks due to the IRS1b outflow, in a star-forming region. Assuming thermal excitation of the THz line, the water abundance in the hot core of NGC 7538-IRS1 is estimated to be 5.2 × 10-5 with respect to H2. The reduced spectra and maps (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/A52

Origin of warm and hot gas emission from low-mass protostars: Herschel-HIFI observations of CO J = 16-15. I. Line profiles, physical conditions, and H2O abundance

NASA Astrophysics Data System (ADS)

Kristensen, L. E.; van Dishoeck, E. F.; Mottram, J. C.; Karska, A.; Yıldız, U. A.; Bergin, E. A.; Bjerkeli, P.; Cabrit, S.; Doty, S.; Evans, N. J.; Gusdorf, A.; Harsono, D.; Herczeg, G. J.; Johnstone, D.; Jørgensen, J. K.; van Kempen, T. A.; Lee, J.-E.; Maret, S.; Tafalla, M.; Visser, R.; Wampfler, S. F.

2017-09-01

Context. Through spectrally unresolved observations of high-J CO transitions, Herschel Photodetector Array Camera and Spectrometer (PACS) has revealed large reservoirs of warm (300 K) and hot (700 K) molecular gas around low-mass protostars. The excitation and physical origin of this gas is still not understood. Aims: We aim to shed light on the excitation and origin of the CO ladder observed toward protostars, and on the water abundance in different physical components within protostellar systems using spectrally resolved Herschel-HIFI data. Methods: Observations are presented of the highly excited CO line J = 16-15 (Eup/kB = 750 K) with the Herschel Heterodyne Instrument for the Far Infrared (HIFI) toward a sample of 24 low-mass protostellar objects. The sources were selected from the Herschel "Water in Star-forming regions with Herschel" (WISH) and "Dust, Ice, and Gas in Time" (DIGIT) key programs. Results: The spectrally resolved line profiles typically show two distinct velocity components: a broad Gaussian component with an average FWHM of 20 km s-1 containing the bulk of the flux, and a narrower Gaussian component with a FWHM of 5 km s-1 that is often offset from the source velocity. Some sources show other velocity components such as extremely-high-velocity features or "bullets". All these velocity components were first detected in H2O line profiles. The average rotational temperature over the entire profile, as measured from comparison between CO J = 16-15 and 10-9 emission, is 300 K. A radiative-transfer analysis shows that the average H2O/CO column-density ratio is 0.02, suggesting a total H2O abundance of 2 × 10-6, independent of velocity. Conclusions: Two distinct velocity profiles observed in the HIFI line profiles suggest that the high-J CO ladder observed with PACS consists of two excitation components. The warm PACS component (300 K) is associated with the broad HIFI component, and the hot PACS component (700 K) is associated with the offset HIFI component. The former originates in either outflow cavity shocks or the disk wind, and the latter in irradiated shocks. The low water abundance can be explained by photodissociation. The ubiquity of the warm and hot CO components suggest that fundamental mechanisms govern the excitation of these components; we hypothesize that the warm component arises when H2 stops being the dominant coolant. In this scenario, the hot component arises in cooling molecular H2-poor gas just prior to the onset of H2 formation. High spectral resolution observations of highly excited CO transitions uniquely shed light on the origin of warm and hot gas in low-mass protostellar objects. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Structure and Evolution of an Undular Bore on the High Plains and Its Effects on Migrating Birds.

NASA Astrophysics Data System (ADS)

Locatelli, John D.; Stoelinga, Mark T.; Hobbs, Peter V.; Johnson, Jim

1998-06-01

On 18 September 1992 a series of thunderstorms in Nebraska and eastern Colorado, which formed south of a synoptic-scale cold front and north of a Rocky Mountain lee trough, produced a cold outflow gust front that moved southeastward into Kansas, southeastern Colorado, and Oklahoma around sunset. When this cold outflow reached the vicinity of the lee trough, an undular bore developed on a nocturnally produced stable layer and moved through the range of the Dodge City WSR-88D Doppler radar. The radar data revealed that the undular bore, in the leading portion of a region of northwesterly winds about 45 km wide by 4 km high directly abutting the cold outflow, developed five undulations over the course of 3 h. Contrary to laboratory tank experiments, observations indicated that the solitary waves that composed the bore probably did not form from the enveloping of the head of the cold air outflow by the stable layer and the breaking off of the head of the cold air outflow. The synoptic-scale cold front subsequently intruded on the surface layer of air produced by the cold outflow, but there was no evidence for the formation of another bore.Profiler winds, in the region affected by the cold air outflow and the undular bore, contained signals from nocturnally, southward-migrating birds (most likely waterfowl) that took off in nonfavorable southerly winds and remained aloft for several hours longer than usual, thereby staying ahead of the turbulence associated with the undular bore.

Wind from the black-hole accretion disk driving a molecular outflow in an active galaxy.

PubMed

Tombesi, F; Meléndez, M; Veilleux, S; Reeves, J N; González-Alfonso, E; Reynolds, C S

2015-03-26

Powerful winds driven by active galactic nuclei are often thought to affect the evolution of both supermassive black holes and their host galaxies, quenching star formation and explaining the close relationship between black holes and galaxies. Recent observations of large-scale molecular outflows in ultraluminous infrared galaxies support this quasar-feedback idea, because they directly trace the gas from which stars form. Theoretical models suggest that these outflows originate as energy-conserving flows driven by fast accretion-disk winds. Proposed connections between large-scale molecular outflows and accretion-disk activity in ultraluminous galaxies were incomplete because no accretion-disk wind had been detected. Conversely, studies of powerful accretion-disk winds have until now focused only on X-ray observations of local Seyfert galaxies and a few higher-redshift quasars. Here we report observations of a powerful accretion-disk wind with a mildly relativistic velocity (a quarter that of light) in the X-ray spectrum of IRAS F11119+3257, a nearby (redshift 0.189) optically classified type 1 ultraluminous infrared galaxy hosting a powerful molecular outflow. The active galactic nucleus is responsible for about 80 per cent of the emission, with a quasar-like luminosity of 1.5 × 10(46) ergs per second. The energetics of these two types of wide-angle outflows is consistent with the energy-conserving mechanism that is the basis of the quasar feedback in active galactic nuclei that lack powerful radio jets (such jets are an alternative way to drive molecular outflows).

Evidence for Fluorescent Fe II Emission from Extended Low Ionization Outflows in Obscured Quasars

NASA Astrophysics Data System (ADS)

Wang, Tinggui; Ferland, Gary J.; Yang, Chenwei; Wang, Huiyuan; Zhang, Shaohua

2016-06-01

Recent studies have shown that outflows in at least some broad absorption line (BAL) quasars are extended well beyond the putative dusty torus. Such outflows should be detectable in obscured quasars. We present four WISE selected infrared red quasars with very strong and peculiar ultraviolet Fe II emission lines: strong UV Fe II UV arising from transitions to ground/low excitation levels, and very weak Fe II at wavelengths longer than 2800 Å. The spectra of these quasars display strong resonant emission lines, such as C IV, Al III and Mg II but sometimes, a lack of non-resonant lines such as C III], S III and He II. We interpret the Fe II lines as resonantly scattered light from the extended outflows that are viewed nearly edge-on, so that the accretion disk and broad line region are obscured by the dusty torus, while the extended outflows are not. We show that dust free gas exposed to strong radiation longward of 912 Å produces Fe II emission very similar to that observed. The gas is too cool to collisionally excite Fe II lines, accounting for the lack of optical emission. The spectral energy distribution from the UV to the mid-infrared can be modeled as emission from a clumpy dusty torus, with UV emission being reflected/scattered light either by the dusty torus or the outflow. Within this scenario, we estimate a minimum covering factor of the outflows from a few to 20% for the Fe II scattering region, suggesting that Fe II BAL quasars are at a special stage of quasar evolution.

Oceanographic Mower Cruise

NASA Astrophysics Data System (ADS)

Valencia, J.; Ercilla, G.; Hernández-Molina, F. J.; Casas, D.

2015-04-01

The MOWER Cruise has executed a geophysics and geologic expedition in the Gulf of Cádiz (sector adjacent to the Strait of Gibraltar) and west off Portugal, in the framework of the coordinate research project MOWER "Erosive features and associated sandy deposits generated by the Mediterranean Outflow Water (MOW) around Iberia: paleoceanographic, sedimentary & economic implications" (CTM 2012-39599-C03). The main aim of this project is to identify and study the erosional features (terraces and channels) and associated sedimentary deposits (sandy contourites) generated by the Mediterranean Water Masses around the middle continental slope of Iberia (The Mediterranean Outflow Water - MOW - in the Atlantic margins), their Pliocene and Quaternary evolution and their paleoceanographic, sedimentary and economic implications. This objective directly involves the study of alongslope (contourite) processes associated with the MOW and across-slope (turbiditic flows, debris flows, etc.) processes in the sedimentary stacking pattern and evolution of the Iberian margins. The MOWER project and cruise are related to the Integrated Ocean Drilling Program (IODP) Expedition 339 (Mediterranean Outflow). It is also linked and coordinated with CONDRIBER Project "Contourite drifts and associated mass-transport deposits along the SW Iberia margin - implications to slope stability and tsunami hazard assessment" (2013-2015) funded by the Fundação para a Ciência e Tecnologia, Portugal (PTDC/GEO-GEO/4430/2012).

Supernova-driven outflows and chemical evolution of dwarf spheroidal galaxies

PubMed Central

Qian, Yong-Zhong; Wasserburg, G. J.

2012-01-01

We present a general phenomenological model for the metallicity distribution (MD) in terms of [Fe/H] for dwarf spheroidal galaxies (dSphs). These galaxies appear to have stopped accreting gas from the intergalactic medium and are fossilized systems with their stars undergoing slow internal evolution. For a wide variety of infall histories of unprocessed baryonic matter to feed star formation, most of the observed MDs can be well described by our model. The key requirement is that the fraction of the gas mass lost by supernova-driven outflows is close to unity. This model also predicts a relationship between the total stellar mass and the mean metallicity for dSphs in accord with properties of their dark matter halos. The model further predicts as a natural consequence that the abundance ratios [E/Fe] for elements such as O, Mg, and Si decrease for stellar populations at the higher end of the [Fe/H] range in a dSph. We show that, for infall rates far below the net rate of gas loss to star formation and outflows, the MD in our model is very sharply peaked at one [Fe/H] value, similar to what is observed in most globular clusters. This result suggests that globular clusters may be end members of the same family as dSphs. PMID:22411827

Supernova-driven outflows and chemical evolution of dwarf spheroidal galaxies.

PubMed

Qian, Yong-Zhong; Wasserburg, G J

2012-03-27

We present a general phenomenological model for the metallicity distribution (MD) in terms of [Fe/H] for dwarf spheroidal galaxies (dSphs). These galaxies appear to have stopped accreting gas from the intergalactic medium and are fossilized systems with their stars undergoing slow internal evolution. For a wide variety of infall histories of unprocessed baryonic matter to feed star formation, most of the observed MDs can be well described by our model. The key requirement is that the fraction of the gas mass lost by supernova-driven outflows is close to unity. This model also predicts a relationship between the total stellar mass and the mean metallicity for dSphs in accord with properties of their dark matter halos. The model further predicts as a natural consequence that the abundance ratios [E/Fe] for elements such as O, Mg, and Si decrease for stellar populations at the higher end of the [Fe/H] range in a dSph. We show that, for infall rates far below the net rate of gas loss to star formation and outflows, the MD in our model is very sharply peaked at one [Fe/H] value, similar to what is observed in most globular clusters. This result suggests that globular clusters may be end members of the same family as dSphs.

Probing the Active Galactic Nuclei using optical spectroscopy

NASA Astrophysics Data System (ADS)

Vivek, M.

Variability studies offer one of the best tools for understanding the physical conditions present in regions close to the central engine in an AGN. We probed the various properties of AGN through time variability studies of spectral lines in the optical wavelengths using the 2m telescope in IUCAA Girawali observatory. The absorption line variability studies are mainly concentrated in understanding the nature of outflows in quasars. Quasar outflows have a huge impact on the evolution of central supermassive blackholes, their host galaxies and the surrounding intergalactic medium. Studying the variability in these Broad Absorption Lines (BALs) can help us understand the structure, evolution, and basic physical properties of these outflows. We conducted a repeated Low ionization BAL monitoring program with 27 LoBALs (Low Ionization BALs) at z 0.3-2.1 covering timescales from 3.22 to 7.69 years in the quasar rest frame. We see a variety of phenomena, including some BALs that either appeared or disappeared completely and some BALs which do not vary over the observation period. In one case, the excited fine structure lines have changed dramatically. One source shows signatures of radiative acceleration. Here, we present the results from this program. Emission line studies are concentrated in understanding the peculiar characteristics of a dual-AGN source SDSS J092712.64+294344.0.

Near-Surface Flow Fields Deduced Using Correlation Tracking and Time-Distance Analysis

NASA Technical Reports Server (NTRS)

DeRosa, Marc; Duvall, T. L., Jr.; Toomre, Juri

1999-01-01

Near-photospheric flow fields on the Sun are deduced using two independent methods applied to the same time series of velocity images observed by SOI-MDI on SOHO. Differences in travel times between f modes entering and leaving each pixel measured using time-distance helioseismology are used to determine sites of supergranular outflows. Alternatively, correlation tracking analysis of mesogranular scales of motion applied to the same time series is used to deduce the near-surface flow field. These two approaches provide the means to assess the patterns and evolution of horizontal flows on supergranular scales even near disk center, which is not feasible with direct line-of-sight Doppler measurements. We find that the locations of the supergranular outflows seen in flow fields generated from correlation tracking coincide well with the locations of the outflows determined from the time-distance analysis, with a mean correlation coefficient after smoothing of bar-r(sub s) = 0.840. Near-surface velocity field measurements can used to study the evolution of the supergranular network, as merging and splitting events are observed to occur in these images. The data consist of one 2048-minute time series of high-resolution (0.6" pixels) line-of-sight velocity images taken by MDI on 1997 January 16-18 at a cadence of one minute.

Toward a Prescription for Feedback from Quasar Outflows

NASA Astrophysics Data System (ADS)

Ganguly, Rajib; Bourjaily, M.; Munsell, J.; Brotherton, M. S.; Bhattacharjee, A.; Runnoe, J.; Charlton, J. C.; Eracleous, M.

2011-01-01

Models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, distance, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 14000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) estimates of the quasar black hole mass. To this, we are adding photometry from GALEX, 2MASS, and ROSAT in an effort to characterize more fully the quasar SEDs. ROSAT photometry provides estimates of the level of soft X-ray absorption, which helps regulate the velocity of outflows. GALEX photometry samples the extreme ultraviolet range where several high ionization species, that may be present in the outflows, absorb light. 2MASS photometry samples the rest-frame optical, where the effects of absorption and dust reddening are minimal, yield better estimates of the bolometric luminosity (hence, Eddington ratio). In this poster, we will present preliminary measurements of the amount of absorption in the soft X-ray and extreme ultraviolet bands as a function of both outflow properties and quasar physical properties. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program.

The mass-metallicity relations for gas and stars in star-forming galaxies: strong outflow versus variable IMF

NASA Astrophysics Data System (ADS)

Lian, Jianhui; Thomas, Daniel; Maraston, Claudia; Goddard, Daniel; Comparat, Johan; Gonzalez-Perez, Violeta; Ventura, Paolo

2018-02-01

We investigate the mass-metallicity relations for the gaseous (MZRgas) and stellar components (MZRstar) of local star-forming galaxies based on a representative sample from Sloan Digital Sky Survey Data Release 12. The mass-weighted average stellar metallicities are systematically lower than the gas metallicities. This difference in metallicity increases towards galaxies with lower masses and reaches 0.4-0.8 dex at 109 M⊙ (depending on the gas metallicity calibration). As a result, the MZRstar is much steeper than the MZRgas. The much lower metallicities in stars compared to the gas in low-mass galaxies imply dramatic metallicity evolution with suppressed metal enrichment at early times. The aim of this paper is to explain the observed large difference in gas and stellar metallicity and to infer the origin of the mass-metallicity relations. To this end we develop a galactic chemical evolution model accounting for star formation, gas inflow and outflow. By combining the observed mass-metallicity relation for both gas and stellar components to constrain the models, we find that only two scenarios are able to reproduce the observations. Either strong metal outflow or a steep initial mass function (IMF) slope at early epochs of galaxy evolution is needed. Based on these two scenarios, for the first time we successfully reproduce the observed MZRgas and MZRstar simultaneously, together with other independent observational constraints in the local Universe. Our model also naturally reproduces the flattening of the MZRgas at the high-mass end leaving the MZRstar intact, as seen in observational data.

A STUDY OF RADIO POLARIZATION IN PROTOSTELLAR JETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cécere, Mariana; Velázquez, Pablo F.; De Colle, Fabio

2016-01-10

Synchrotron radiation is commonly observed in connection with shocks of different velocities, ranging from relativistic shocks associated with active galactic nuclei, gamma-ray bursts, or microquasars, to weakly or non-relativistic flows such as those observed in supernova remnants. Recent observations of synchrotron emission in protostellar jets are important not only because they extend the range over which the acceleration process works, but also because they allow us to determine the jet and/or interstellar magnetic field structure, thus giving insights into the jet ejection and collimation mechanisms. In this paper, we compute for the first time polarized (synchrotron) and non-polarized (thermal X-ray)more » synthetic emission maps from axisymmetrical simulations of magnetized protostellar jets. We consider models with different jet velocities and variability, as well as a toroidal or helical magnetic field. Our simulations show that variable, low-density jets with velocities of ∼1000 km s{sup −1} and ∼10 times lighter than the environment can produce internal knots with significant synchrotron emission and thermal X-rays in the shocked region of the leading bow shock moving in a dense medium. While models with a purely toroidal magnetic field show a very large degree of polarization, models with a helical magnetic field show lower values and a decrease of the degree of polarization, in agreement with observations of protostellar jets.« less

Protostellar hydrodynamics: Constructing and testing a spacially and temporally second-order accurate method. 2: Cartesian coordinates

NASA Technical Reports Server (NTRS)

Myhill, Elizabeth A.; Boss, Alan P.

1993-01-01

In Boss & Myhill (1992) we described the derivation and testing of a spherical coordinate-based scheme for solving the hydrodynamic equations governing the gravitational collapse of nonisothermal, nonmagnetic, inviscid, radiative, three-dimensional protostellar clouds. Here we discuss a Cartesian coordinate-based scheme based on the same set of hydrodynamic equations. As with the spherical coorrdinate-based code, the Cartesian coordinate-based scheme employs explicit Eulerian methods which are both spatially and temporally second-order accurate. We begin by describing the hydrodynamic equations in Cartesian coordinates and the numerical methods used in this particular code. Following Finn & Hawley (1989), we pay special attention to the proper implementations of high-order accuracy, finite difference methods. We evaluate the ability of the Cartesian scheme to handle shock propagation problems, and through convergence testing, we show that the code is indeed second-order accurate. To compare the Cartesian scheme discussed here with the spherical coordinate-based scheme discussed in Boss & Myhill (1992), the two codes are used to calculate the standard isothermal collapse test case described by Bodenheimer & Boss (1981). We find that with the improved codes, the intermediate bar-configuration found previously disappears, and the cloud fragments directly into a binary protostellar system. Finally, we present the results from both codes of a new test for nonisothermal protostellar collapse.

Far-ultraviolet Observations of Outflows from Infrared-luminous Galaxies

NASA Astrophysics Data System (ADS)

Leitherer, Claus; Chandar, Rupali; Tremonti, Christy A.; Wofford, Aida; Schaerer, Daniel

2013-08-01

We obtained medium-resolution ultraviolet (UV) spectra between 1150 and 1450 Å of the four UV-bright, infrared-luminous starburst galaxies IRAS F08339+6517, NGC 3256, NGC 6090, and NGC 7552 using the Cosmic Origins Spectrograph on board the Hubble Space Telescope. The selected sightlines toward the starburst nuclei probe the properties of the recently formed massive stars and the physical conditions in the starburst-driven galactic superwinds. Despite being metal-rich and dusty, all four galaxies are strong Lyα emitters with equivalent widths ranging between 2 and 13 Å. The UV spectra show strong P Cygni-type high-ionization features indicative of stellar winds and blueshifted low-ionization lines formed in the interstellar and circumgalactic medium. We detect outflowing gas with bulk velocities of ~400 km s-1 and maximum velocities of almost 900 km s-1. These are among the highest values found in the local universe and comparable to outflow velocities found in luminous Lyman-break galaxies at intermediate and high redshift. The outflow velocities are unlikely to be high enough to cause escape of material from the galactic gravitational potential. However, the winds are significant for the evolution of the galaxies by transporting heavy elements from the starburst nuclei and enriching the galaxy halos. The derived mass outflow rates of ~100 M ⊙ yr-1 are comparable to or even higher than the star formation rates. The outflows can quench star formation and ultimately regulate the starburst as has been suggested for high-redshift galaxies.

New methods and astrophysical applications of adaptive mesh fluid simulations

NASA Astrophysics Data System (ADS)

Wang, Peng

The formation of stars, galaxies and supermassive black holes are among the most interesting unsolved problems in astrophysics. Those problems are highly nonlinear and involve enormous dynamical ranges. Thus numerical simulations with spatial adaptivity are crucial in understanding those processes. In this thesis, we discuss the development and application of adaptive mesh refinement (AMR) multi-physics fluid codes to simulate those nonlinear structure formation problems. To simulate the formation of star clusters, we have developed an AMR magnetohydrodynamics (MHD) code, coupled with radiative cooling. We have also developed novel algorithms for sink particle creation, accretion, merging and outflows, all of which are coupled with the fluid algorithms using operator splitting. With this code, we have been able to perform the first AMR-MHD simulation of star cluster formation for several dynamical times, including sink particle and protostellar outflow feedbacks. The results demonstrated that protostellar outflows can drive supersonic turbulence in dense clumps and explain the observed slow and inefficient star formation. We also suggest that global collapse rate is the most important factor in controlling massive star accretion rate. In the topics of galaxy formation, we discuss the results of three projects. In the first project, using cosmological AMR hydrodynamics simulations, we found that isolated massive star still forms in cosmic string wakes even though the mega-parsec scale structure has been perturbed significantly by the cosmic strings. In the second project, we calculated the dynamical heating rate in galaxy formation. We found that by balancing our heating rate with the atomic cooling rate, it gives a critical halo mass which agrees with the result of numerical simulations. This demonstrates that the effect of dynamical heating should be put into semi-analytical works in the future. In the third project, using our AMR-MHD code coupled with radiative cooling module, we performed the first MHD simulations of disk galaxy formation. We find that the initial magnetic fields are quickly amplified to Milky-Way strength in a self-regulated way with amplification rate roughly one e-folding per orbit. This suggests that Milky Way strength magnetic field might be common in high redshift disk galaxies. We have also developed AMR relativistic hydrodynamics code to simulate black hole relativistic jets. We discuss the coupling of the AMR framework with various relativistic solvers and conducted extensive algorithmic comparisons. Via various test problems, we emphasize the importance of resolution studies in relativistic flow simulations because extremely high resolution is required especially when shear flows are present in the problem. Then we present the results of 3D simulations of supermassive black hole jets propagation and gamma ray burst jet breakout. Resolution studies of the two 3D jets simulations further highlight the need of high resolutions to calculate accurately relativistic flow problems. Finally, to push forward the kind of simulations described above, we need faster codes with more physics included. We describe an implementation of compressible inviscid fluid solvers with AMR on Graphics Processing Units (GPU) using NVIDIA's CUDA. We show that the class of high resolution shock capturing schemes can be mapped naturally on this architecture. For both uniform and adaptive simulations, we achieve an overall speedup of approximately 10 times faster execution on one Quadro FX 5600 GPU as compared to a single 3 GHz Intel core on the host computer. Our framework can readily be applied to more general systems of conservation laws and extended to higher order shock capturing schemes. This is shown directly by an implementation of a magneto-hydrodynamic solver and comparing its performance to the pure hydrodynamic case.

Small Scale Chemical Segregation Within Keplerian Disk Candidate G35.20-0.74N

NASA Astrophysics Data System (ADS)

Allen, Veronica; van der Tak, Floris; Sánchez-Monge, Álvaro; Cesaroni, Riccardo; Beltrán, Maria T.

2016-06-01

In the study of high-mass star formation, hot cores are empirically defined stages where chemically rich emission is detected toward a massive protostar. It is unknown whether the physical origin of this emission is a disk, inner envelope, or outflow cavity wall and whether the hot core stage is common to all massive stars. With the advent of the highly sensitive sub-millimeter interferometer, ALMA, the ability to chemically characterize high mass star forming regions other than Orion has become possible. In the up-and-coming field of observational astrochemistry, these sensitive high resolution observations have opened up opportunities to find small scale variations in young protostellar sources.We have done an in depth analysis of high spatial resolution (~1000 AU) Cycle 0 ALMA observations of the high mass star forming region G35.20-0.74N, where Sánchez-Monge et al (2013) found evidence for Keplerian rotation. After further chemical analysis, numerous complex organic species have been identified in this region and we notice an interesting asymmetry in the distribution of the Nitrogen-bearing species within this source. In my talk, I will briefly outline the case for the disk and the consequences for this hypothesis following the chemical segregation we have seen.

The AstroBiology Explorer (ABE) MIDEX Mission Concept: Using Infrared Spectroscopy to Identify Organic Molecules in Space

NASA Technical Reports Server (NTRS)

Sandford, Scott A.; Ennico, Kimberly; Allamandola, Louis; Bregman, Jesse; Greene, Thomas; Hudgins, Douglas

2002-01-01

One of the principal means by which organic compounds are detected and identified in space is by infrared spectroscopy. Past IR telescopic and laboratory studies have shown that much of the carbon in the interstellar medium (ISM) is in complex organic species but the distribution, abundance and evolutionary relationships of these materials are not well understood. The Astrobiology Explorer (ABE) is a MIDEX mission concept designed to conduct IR spectroscopic observations to detect and identify these materials and address outstanding problems in astrobiology, astrochemistry, and astrophysics. ABE's core science program includes observations of planetary nebulae and stellar outflows, protostellar objects, Solar System objects, and galaxies, and lines of sight through dense molecular clouds and the diffuse ISM. ABE is a cryogenically-cooled 60 cm diameter space telescope equipped with 3 cross-dispersed R-2000 spectrometers that share a single common slit. Each spectrometer measures one spectral octave and together cover the entire 2.5-20 micron region simultaneously. The spectrometers use state-of-the-art InSb and Si:As 1024x1024 pixel detectors. ABE would operate in a heliocentric, Earth drift-away orbit and have a core science mission lasting approximately 1.5 years. ABE is currently under study at NASA's Ames Research Center in collaboration with Ball Aerospace and Technologies Corp.

ALMA Observations of a Misaligned Binary Protoplanetary Disk System in Orion

NASA Astrophysics Data System (ADS)

Williams, Jonathan P.; Mann, Rita K.; Di Francesco, James; Andrews, Sean M.; Hughes, A. Meredith; Ricci, Luca; Bally, John; Johnstone, Doug; Matthews, Brenda

2014-12-01

We present Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a wide binary system in Orion, with projected separation 440 AU, in which we detect submillimeter emission from the protoplanetary disks around each star. Both disks appear moderately massive and have strong line emission in CO 3-2, HCO+ 4-3, and HCN 3-2. In addition, CS 7-6 is detected in one disk. The line-to-continuum ratios are similar for the two disks in each of the lines. From the resolved velocity gradients across each disk, we constrain the masses of the central stars, and show consistency with optical-infrared spectroscopy, both indicative of a high mass ratio ~9. The small difference between the systemic velocities indicates that the binary orbital plane is close to face-on. The angle between the projected disk rotation axes is very high, ~72°, showing that the system did not form from a single massive disk or a rigidly rotating cloud core. This finding, which adds to related evidence from disk geometries in other systems, protostellar outflows, stellar rotation, and similar recent ALMA results, demonstrates that turbulence or dynamical interactions act on small scales well below that of molecular cores during the early stages of star formation.

Externally Heated Protostellar Cores in the Ophiuchus Star-Forming Region

NASA Technical Reports Server (NTRS)

Lindberg, Johan E.; Charnley, Steven B.; Jorgensen, Jes K.; Cordiner, Martin A.; Bjerkeli, Per

2017-01-01

We present APEX 218 GHz observations of molecular emission in a complete sample of embedded protostars in the Ophiuchus star-forming region. To study the physical properties of the cores, we calculate H2CO and c-C3H2 rotational temperatures, both of which are good tracers of the kinetic temperature of the molecular gas. We find that the H2CO temperatures range between 16K and 124K, with the highest H2CO temperatures toward the hot corino source IRAS 16293-2422 (69-124 K) and the sources in the rho Oph A cloud (23-49 K) located close to the luminous Herbig Be star S1, which externally irradiates the rho Oph A cores. On the other hand, the c-C3H2 rotational temperature is consistently low (7-17 K) in all sources. Our results indicate that the c-C3H2 emission is primarily tracing more shielded parts of the envelope whereas the H2CO emission (at the angular scale of the APEX beam; 3600 au in Ophiuchus) mainly traces the outer irradiated envelopes, apart from in IRAS?16293-2422, where the hot corino emission dominates. In some sources, a secondary velocity component is also seen, possibly tracing the molecular outflow.

3-D MHD disk wind simulations of protostellar jets

NASA Astrophysics Data System (ADS)

Staff, Jan E.; Koning, Nico; Ouyed, Rachid; Tanaka, Kei; Tan, Jonathan C.

2016-01-01

We present the results of large scale, three-dimensional magnetohydrodynamics simulations of disk winds for different initial magnetic field configurations. The jets are followed from the source to distances, which are resolvable by HST and ALMA observations. Our simulations show that jets are heated along their length by many shocks. The mass of the protostar is a free parameter that can be inserted in the post processing of the data, and we apply the simulations to both low mass and high mass protostars. For the latter we also compute the expected diagnostics when the outflow is photoionized by the protostar. We compute the emission lines that are produced, and find excellent agreement with observations. For a one solar mass protostar, we find the jet width to be between 20 and 30 au while the maximum velocities perpendicular to the jet are found to be 100 km s-1. The initially less open magnetic field configuration simulations result in a wider, two-component jet; a cylindrically shaped outer jet surrounding a narrow and much faster, inner jet. For the initially most open magnetic field configuration the kink mode creates a narrow corkscrew-like jet without a clear Keplerian rotation profile and even regions where we observe rotation opposite to the disk (counter-rotating). This is not seen in the less open field configurations.

THE DETECTION OF A HOT MOLECULAR CORE IN THE LARGE MAGELLANIC CLOUD WITH ALMA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shimonishi, Takashi; Onaka, Takashi; Kawamura, Akiko

We report the first detection of a hot molecular core outside our Galaxy based on radio observations with ALMA toward a high-mass young stellar object (YSO) in a nearby low metallicity galaxy, the Large Magellanic Cloud (LMC). Molecular emission lines of CO, C{sup 17}O, HCO{sup +}, H{sup 13}CO{sup +}, H{sub 2}CO, NO, SiO, H{sub 2}CS, {sup 33}SO, {sup 32}SO{sub 2}, {sup 34}SO{sub 2}, and {sup 33}SO{sub 2} are detected from a compact region (∼0.1 pc) associated with a high-mass YSO, ST11. The temperature of molecular gas is estimated to be higher than 100 K based on rotation diagram analysis ofmore » SO{sub 2} and {sup 34}SO{sub 2} lines. The compact source size, warm gas temperature, high density, and rich molecular lines around a high-mass protostar suggest that ST11 is associated with a hot molecular core. We find that the molecular abundances of the LMC hot core are significantly different from those of Galactic hot cores. The abundances of CH{sub 3}OH, H{sub 2}CO, and HNCO are remarkably lower compared to Galactic hot cores by at least 1–3 orders of magnitude. We suggest that these abundances are characterized by the deficiency of molecules whose formation requires the hydrogenation of CO on grain surfaces. In contrast, NO shows a high abundance in ST11 despite the notably low abundance of nitrogen in the LMC. A multitude of SO{sub 2} and its isotopologue line detections in ST11 imply that SO{sub 2} can be a key molecular tracer of hot core chemistry in metal-poor environments. Furthermore, we find molecular outflows around the hot core, which is the second detection of an extragalactic protostellar outflow. In this paper, we discuss the physical and chemical characteristics of a hot molecular core in the low metallicity environment.« less

Protostellar jets in the NIR: interaction with the ISM and correlation with the exciting source evolutionary phase

NASA Astrophysics Data System (ADS)

Caratti o Garatti, Alessio

2006-03-01

I present an in-depth near-IR (NIR) analysis of a sample of H2 jets from young embedded sources to compare the physical, kinematical properties and cooling mechanisms of the different flows. The sample comprises 23 outflows driven by Class 0 and I sources having low-intermediate solar luminosity (1-600 L(sun)). For such an analysis, I have utilized narrow band images centered on the H2 (2.12 micron) and [FeII] (1.64 micron) spectral lines, low resolution spectra (R~600) in the range 1-2.5 micron and high resolution spectra (R~10000) centered on H2 (2.12 micron) and [FeII] (1.64 micron) lines. At NIR wavelengths these two tracers (H2,[FeII]) are the main coolants of the gas, that is excited by strong radiative shocks. Narrow band images have been used to detect such shocked regions in both ionic and molecular components. [FeII] have been observed in ~74% of the outflows which in some cases indicate the presence of embedded Herbig Haro (HH) like objects. H2 line ratios have been used to estimate the visual extinction and the average temperature of the molecular gas. A(V) values range from ~2 to ~15 mag, while average temperatures range between ~2000 and ~4000 K. In several knots, however, a stratification of temperatures is found with maximum values up to 5000 K. Such a stratification is more commonly observed in those knots which also show [FeII] emission, while a thermalized gas at a single temperature is generally found in knots emitting only in molecular lines. Combining narrow band imaging with the parameters derived from the spectroscopic analysis, it was possible to measure the total luminosity of the H2 and [FeII] shocked regions (L(H2) and L([FeII])) in each flow. H2 is the major NIR coolant with an average L(H2)/L([FeII]) ratio of ~10^2. About 83% of the sources have a L(H2)/L(bol) ratio ~0.04, irrespective of the Class of the driving source, while a smaller group of sources (mostly Class I) have L(H2)/L(bol) an order of magnitude smaller. Such a separation reveals the non-homogeneous behaviour of Cl ass I, where sources with very different outflow activity can be found. These less luminous jets are originated by older sources, where L(bol) is not dominated anymore by the accretion luminosity. This is confirmed by a further analysis conducted on jets from six intermediate and high mass sources, four of them not included in the original sample. They have a faster evolution with respect to the low mass ones and thus only a fraction of their L(bol) is due to the accretion luminosity. For these objects I find a defined separation between the two Classes in the L(H2)-L(bol) plot. Viceversa, there is a straight correlation between L(H2) and L(acc) for all these sources. Finally, I compare the derived jet physical parameters to theoretical shock models. The observed H2 emission in the HH objects can be mostly reproduced by models of J-type shocks with magnetic precursors.

The SILCC project - III. Regulation of star formation and outflows by stellar winds and supernovae

NASA Astrophysics Data System (ADS)

Gatto, Andrea; Walch, Stefanie; Naab, Thorsten; Girichidis, Philipp; Wünsch, Richard; Glover, Simon C. O.; Klessen, Ralf S.; Clark, Paul C.; Peters, Thomas; Derigs, Dominik; Baczynski, Christian; Puls, Joachim

2017-04-01

We study the impact of stellar winds and supernovae on the multiphase interstellar medium using three-dimensional hydrodynamical simulations carried out with FLASH. The selected galactic disc region has a size of (500 pc)2 × ±5 kpc and a gas surface density of 10 M⊙ pc-2. The simulations include an external stellar potential and gas self-gravity, radiative cooling and diffuse heating, sink particles representing star clusters, stellar winds from these clusters that combine the winds from individual massive stars by following their evolution tracks, and subsequent supernova explosions. Dust and gas (self-) shielding is followed to compute the chemical state of the gas with a chemical network. We find that stellar winds can regulate star (cluster) formation. Since the winds suppress the accretion of fresh gas soon after the cluster has formed, they lead to clusters that have lower average masses (102-104.3 M⊙) and form on shorter time-scales (10-3-10 Myr). In particular, we find an anticorrelation of cluster mass and accretion time-scale. Without winds, the star clusters easily grow to larger masses for ˜5 Myr until the first supernova explodes. Overall, the most massive stars provide the most wind energy input, while objects beginning their evolution as B-type stars contribute most of the supernova energy input. A significant outflow from the disc (mass loading ≳1 at 1 kpc) can be launched by thermal gas pressure if more than 50 per cent of the volume near the disc mid-plane can be heated to T > 3 × 105 K. Stellar winds alone cannot create a hot volume-filling phase. The models that are in best agreement with observed star formation rates drive either no outflows or weak outflows.

Direct observations of seasonal exchange through the Bab el Mandab Strait

NASA Astrophysics Data System (ADS)

Murray, Stephen P.; Johns, William

The exchange flow between the Red Sea and the Gulf of Aden-Indian Ocean through the Bab el Mandab Strait was measured continuously for 10 months, June 1995-March 1996. ADCP and temperature-salinity chain moorings allow an unprecedented look at the magnitude and seasonal evolution of the inflow layer from the Gulf of Aden, and the high salinity outflow layer from the Red Sea. The timing, structure, and evolution of the summer season mid-depth intrusion of cold, low salinity water into the Red Sea from the Gulf of Aden is measured for the complete intrusion cycle of 1995. We unexpectedly find the deep outflow still strong in June 1995, with speeds of 0.6 m/sec and transport of 0.4 Sv (1 Sv = 106 m³/sec). From July to mid-September, the deep outflow persists but is attenuated to speeds of 0.2 m/sec and transport of 0.05 Sv. The dominant summer feature, the cold low salinity intermediate layer intrusion, persists for 3 months, occupies 70% of the water column in the Strait and carries approximately 1.7 × 1012 m³ of cold nutrient-rich water into the Red Sea. The winter regime begins in mid-September, is fully developed by early November, and continues to the end of our first observation interval in March 1996. Speeds in the lower layer are 0.8-1.0 m/sec and 0.4-0.6 m/sec in the upper layer. At maximum exchange in mid-February, outflow transport reaches 0.7 Sv. Ubiquitous oscillations in current and salinity at synoptic and intraseasonal periods appear closely related to fluctuations in the along-channel wind forcing and perhaps to coastally-trapped waves.

Chemical Ionization Mass Spectrometry-Based Measurements of HO2 and RO2 During TRACE-P

NASA Technical Reports Server (NTRS)

Cantrell, Christopher A.; Eisele, Fred L.

2004-01-01

The Transport and Chemical Evolution over the Pacific (TRACE-P) mission extends NASA's Global Tropospheric Experiment (GTE) series of campaigns. TRACE-P was an aircraft-based campaign that was part of a larger ground-based and aircraft-based program (APARE) under the auspices of the International Global Atmospheric Chemistry (IGAC) program. TRACE-P was designed to (1) determine the chemical composition of Asian outflow over the western Pacific, and to (2) determine the chemical evolution of the Asian outflow. These objectives were addressed through a variety of observations and numerical modeling exercises. In particular, the goals included sampling strategies that would improve understanding of the budgets of odd hydrogen species (OH and HO2), budgets of NOx (NO, NO2, and their reservoirs), and impacts of oxidants produced in the outflow on air quality in the United States. The NASA DC-8 and P-3B aircraft were deployed in the March and April, 2001 out of primary bases of operation in Hong Kong and Yokota Air Base in Japan. These two aircraft have complementary capabilities which allow high altitude and long range impacts, as well as low altitude, local impacts to be assessed. In order to quantify the composition and evolution of Asian outflow, it is important to quantify as many species as possible including photochemically active species (e.g. NO2, CH2O, O3, acetone, etc.), sources species (VOCs, CO, NOx, SO2, aerosols), reactive intermediates including free radicals (OH, HO2, RO2, and their reservoirs), and end products (nitric acid, sulfuric acid, secondary aerosols, etc.). The more complete the measurement suite, the more tightly constrained the numerical modeling can be (within the uncertainties of the measurements). The numerical models range in sophistication from simple steady state box models (as employed in this study) to multi-dimensional chemical transport models. Data were collected on approximately 20 flights of the DC-8 and 21 flights of the P-3B. Observations from both aircraft were used in the present analysis, but primarily focused on the P-3B flights since that was the platform on which the peroxy radical instrumentation was based.

An X-ray/SDSS sample. I. Multi-phase outflow incidence and dependence on AGN luminosity

NASA Astrophysics Data System (ADS)

Perna, M.; Lanzuisi, G.; Brusa, M.; Mignoli, M.; Cresci, G.

2017-07-01

Aims: The connection between the growth of super-massive black holes (SMBHs) and the evolution of their host galaxies is nowadays well established, although the underlying mechanisms explaining their mutual relations are still debated. Multi-phase fast, massive outflows have been postulated to play a crucial role in this process. The aim of this work is to constrain the nature and the fraction of outflowing gas in active galactic nuclei (AGNs) as well as the nuclear conditions possibly at the origin of such phenomena. Methods: We present a large spectroscopic sample of X-ray detected SDSS AGNs at z< 0.8 with a high signal-to-noise ratio in the [O III]λ5007 line to unveil the faint wings of the emission profile associated with AGN-driven outflows. We used X-ray and optical flux ratio diagnostics to select the sample. We derived physical and kinematic characterization by re-analysing optical (and X-ray) spectra. Results: We derive the incidence of ionized ( 40%) and atomic (<1%) outflows covering a wide range of AGN bolometric luminosity from 1042 to 1046 erg/s. We also derive bolometric luminosities and X-ray bolometric corrections to test whether the presence of outflows is associated with an X-ray loudness, as suggested by our recent results obtained by studying high-z QSOs. Conclusions: We study the relations between the outflow velocity inferred from [O III] kinematic analysis and different AGN power tracers, such as black hole mass (MBH), [O III], and X-ray luminosity. We show a well-defined positive trend between outflow velocity and LX, for the first time, over a range of 5 order of magnitudes. Overall, we find that in the QSO-luminosity regime and at MBH> 108M⊙ the fraction of AGNs with outflows becomes >50%. Finally, we discuss our results about X-ray bolometric corrections and outflow incidence in cold and ionized phases in the context of an evolutionary sequence allowing two distinct stages for the feedback phase: first, an initial stage characterized by X-ray/optical obscured AGNs, in which the atomic gas is still present in the ISM and the outflow processes involve all the gas components and, second, a later stage associated with unobscured AGNs, in which the line of sight has been cleaned and the cold components have been heated or exhausted.

Intrinsic, Narrow N V Absorption Reveals a Clumpy Outflow in z < 0.4 Radio-Loud Quasars

NASA Astrophysics Data System (ADS)

DeMarcy, Bryan; Serra, Viktoriah; Culliton, Chris; Ganguly, Rajib; Runnoe, Jessie; Charlton, Jane; Eracleous, Michael; Misawa, Toru; Narayanan, Anand

2018-01-01

Quasar outflows are often invoked in models for galaxy evolution to inject energy and momentum into the gas in the host galaxy and influence its star formation history. Thus, the study of quasar outflows is essential for understanding galaxy evolution. N V absorption systems within the associated region (|Δv| ≤ 5000 km s-1) of the quasar are thought to be intrinsic since many show evidence for partial covering of the quasar. A recent archival study of quasar spectra taken with COS/G130M or G160M found 39/181 radio-quiet quasars show intrinsic N V absorption, while none of the 31 radio-loud quasars have N V absorption detected (Culliton et al. 2017). Further investigation of these radio-loud quasars showed a clear bias towards compact morphologies as revealed by FIRST 1.4 GHz imaging and comparatively flat radio spectra. This suggests we are viewing more face-on orientations which prevent us from seeing absorption outflows. The cause for such bias within the HST archive is still unknown; however, it could explain the lack of radio-loud intrinsic N V absorption seen by Culliton et al. (2017). Alternatively, the quasar wind structure may be fundamentally different between radio-loud and radio-quiet objects. We used COS/G130M or G160M to obtain rest-frame UV spectra (1195 Å - 1250 Å) of 14 low-redshift SDSS radio-loud quasars which show lobe-dominated FIRST morphologies to distinguish between these possibilities. Intrinsic N V absorption was detected in 6 of our 14 quasars. This suggests the lack of detections in the archival study was a result of an orientation effect/sampling bias rather than to differences in wind structure between radio-loud and radio-quiet quasars. Interestingly, we find significant overlap in radio core fractions between quasars with and without N V detection. Quasars in our sample with N V detection span a range of core fractions from < 0.01 up to 0.89 while those without detected N V range from 0.04 up to 0.93. A laminar outflow with a small opening angle would be difficult to explain given this overlap in radio core fractions. Our observations suggest a clumpy, sporadic outflow is the more likely explanation.

Formation and Recondensation of Complex Organic Molecules During Protostellar Luminosity Outbursts

NASA Technical Reports Server (NTRS)

Taquet, Vianney; Wirstrom, Eva S.; Charnley, Steven B.

2016-01-01

During the formation of stars, the accretion of surrounding material toward the central object is thought to undergo strong luminosity outbursts followed by long periods of relative quiescence, even at the early stages of star formation when the protostar is still embedded in a large envelope. We investigated the gas-phase formation and recondensation of the complex organic molecules (COMs) di-methyl ether and methyl formate, induced by sudden ice evaporation processes occurring during luminosity outbursts of different amplitudes in protostellar envelopes. For this purpose, we updated a gas-phase chemical network forming COMs in which ammonia plays a key role. The model calculations presented here demonstrate that ion-molecule reactions alone could account for the observed presence of di-methyl ether and methyl formate in a large fraction of protostellar cores without recourse to grain-surface chemistry, although they depend on uncertain ice abundances and gas-phase reaction branching ratios. In spite of the short outburst timescales of about 100 years, abundance ratios of the considered species higher than 10% with respect to methanol are predicted during outbursts due to their low binding energies relative to water and methanol which delay their recondensation during cooling. Although the current luminosity of most embedded protostars would be too low to produce complex organics in the hot-core regions that are observable with current sub-millimetric interferometers, previous luminosity outburst events would induce the formation of COMs in extended regions of protostellar envelopes with sizes increasing by up to one order of magnitude.

Formation and Recondensation of Complex Organic Molecules during Protostellar Luminosity Outbursts

NASA Astrophysics Data System (ADS)

Taquet, Vianney; Wirström, Eva S.; Charnley, Steven B.

2016-04-01

During the formation of stars, the accretion of surrounding material toward the central object is thought to undergo strong luminosity outbursts followed by long periods of relative quiescence, even at the early stages of star formation when the protostar is still embedded in a large envelope. We investigated the gas-phase formation and recondensation of the complex organic molecules (COMs) di-methyl ether and methyl formate, induced by sudden ice evaporation processes occurring during luminosity outbursts of different amplitudes in protostellar envelopes. For this purpose, we updated a gas-phase chemical network forming COMs in which ammonia plays a key role. The model calculations presented here demonstrate that ion-molecule reactions alone could account for the observed presence of di-methyl ether and methyl formate in a large fraction of protostellar cores without recourse to grain-surface chemistry, although they depend on uncertain ice abundances and gas-phase reaction branching ratios. In spite of the short outburst timescales of about 100 years, abundance ratios of the considered species higher than 10% with respect to methanol are predicted during outbursts due to their low binding energies relative to water and methanol which delay their recondensation during cooling. Although the current luminosity of most embedded protostars would be too low to produce complex organics in the hot-core regions that are observable with current sub-millimetric interferometers, previous luminosity outburst events would induce the formation of COMs in extended regions of protostellar envelopes with sizes increasing by up to one order of magnitude.

The Metallicity Evolution of Low Mass Galaxies: New Contraints at Intermediate Redshift

NASA Technical Reports Server (NTRS)

Henry, Alaina; Martin, Crystal L.; Finlator, Kristian; Dressler, Alan

2013-01-01

We present abundance measurements from 26 emission-line-selected galaxies at z approx. 0.6-0.7. By reaching stellar masses as low as 10(exp 8) M stellar mass, these observations provide the first measurement of the intermediate-redshift mass-metallicity (MZ) relation below 10(exp 9)M stellar mass. For the portion of our sample above M is greater than 10(exp 9)M (8/26 galaxies), we find good agreement with previous measurements of the intermediate-redshift MZ relation. Compared to the local relation, we measure an evolution that corresponds to a 0.12 dex decrease in oxygen abundances at intermediate redshifts. This result confirms the trend that metallicity evolution becomes more significant toward lower stellar masses, in keeping with a downsizing scenario where low-mass galaxies evolve onto the local MZ relation at later cosmic times. We show that these galaxies follow the local fundamental metallicity relation, where objects with higher specific (mass-normalized) star formation rates (SFRs) have lower metallicities. Furthermore, we show that the galaxies in our sample lie on an extrapolation of the SFR-M* relation (the star-forming main sequence). Leveraging the MZ relation and star-forming main sequence (and combining our data with higher-mass measurements from the literature), we test models that assume an equilibrium between mass inflow, outflow, and star formation.We find that outflows are required to describe the data. By comparing different outflow prescriptions, we show that momentum, driven winds can describe the MZ relation; however, this model underpredicts the amount of star formation in low-mass galaxies. This disagreement may indicate that preventive feedback from gas heating has been overestimated, or it may signify a more fundamental deviation from the equilibrium assumption.

Inflow/Outflow Conditions for Unsteady Aerodynamics and Aeroacoustics in Nonuniform Flow

NASA Technical Reports Server (NTRS)

Atassi, Oliver V.; Grady, Joseph E. (Technical Monitor)

2003-01-01

The effect of a nonuniform mean flow on the normal modes; the inflow/outflow nonreflecting boundary conditions; and the sound power are studied. The normal modes in an annular duct are computed using a spectral method in combination with a shooting method. The swirl causes force imbalance which couples the acoustic and vortical modes. The acoustic modes are distinguished from the vortical modes by their large pressure and small vorticity content. The mean swirl also produces a Doppler shift in frequency. This results in more counter-spinning modes cut-on at a given frequency than modes spinning with the swirl. Nonreflecting boundary conditions are formulated using the normal mode solutions. The inflow/outflow boundary conditions are implemented in a linearized Euler scheme and validated by computing the propagation of acoustic and vortical waves in a duct for a variety of swirling mean flows. Numerical results show that the evolution of the vortical disturbances is sensitive to the inflow conditions and the details of the wake excitations. All three components of the wake velocity must be considered to correctly compute the wake evolution and the blade upwash. For high frequencies, the acoustic-vortical mode coupling is weak and a conservation equation for the acoustic energy can be derived. Sound power calculations show significant mean flow swirl effects, but mode interference effects are small.

Off-axis Gamma-ray Burst Afterglow Modeling Based on a Two-dimensional Axisymmetric Hydrodynamics Simulation

NASA Astrophysics Data System (ADS)

van Eerten, Hendrik; Zhang, Weiqun; MacFadyen, Andrew

2010-10-01

Starting as highly relativistic collimated jets, gamma-ray burst outflows gradually slow down and become nonrelativistic spherical blast waves. Although detailed analytical solutions describing the afterglow emission received by an on-axis observer during both the early and late phases of the outflow evolution exist, a calculation of the received flux during the intermediate phase and for an off-axis observer requires either a more simplified analytical model or direct numerical simulations of the outflow dynamics. In this paper, we present light curves for off-axis observers covering the long-term evolution of the blast wave, calculated from a high-resolution two-dimensional relativistic hydrodynamics simulation using a synchrotron radiation model. We compare our results to earlier analytical work and calculate the consequence of the observer angle with respect to the jet axis both for the detection of orphan afterglows and for jet break fits to the observational data. We confirm earlier results in the literature finding that only a very small number of local type Ibc supernovae can harbor an orphan afterglow. For off-axis observers, the observable jet break can be delayed up to several weeks, potentially leading to overestimation of the beaming-corrected total energy. In addition we find that, when using our off-axis light curves to create synthetic Swift X-ray data, jet breaks are likely to remain hidden in the data.

First results from the CALYPSO IRAM-PdBI survey. II. Resolving the hot corino in the Class 0 protostar NGC 1333-IRAS2A

NASA Astrophysics Data System (ADS)

Maury, A. J.; Belloche, A.; André, Ph.; Maret, S.; Gueth, F.; Codella, C.; Cabrit, S.; Testi, L.; Bontemps, S.

2014-03-01

Aims: We investigate the origin of complex organic molecules (COMs) in the gas phase around the low-mass Class 0 protostar NGC 1333-IRAS2A, to determine if the COM emission lines trace an embedded disk, shocks from the protostellar jet, or the warm inner parts of the protostellar envelope. Methods: In the framework of the CALYPSO IRAM Plateau de Bure survey, we obtained large bandwidth spectra at sub-arcsecond resolution towards NGC 1333-IRAS2A. We identify the emission lines towards the central protostar and perform Gaussian fits to constrain the size of the emitting region for each of these lines, tracing various physical conditions and scales. Results: The emission of numerous COMs such as methanol, ethylene glycol, and methyl formate is spatially resolved by our observations. This allows us to measure, for the first time, the size of the COM emission inside the protostellar envelope, finding that it originates from a region of radius 40-100 AU, centered on the NGC 1333-IRAS2A protostellar object. Our analysis shows no preferential elongation of the COM emission along the jet axis, and therefore does not support the hypothesis that COM emission arises from shocked envelope material at the base of the jet. Down to similar sizes, the dust continuum emission is well reproduced with a single power-law envelope model, and therefore does not favor the hypothesis that COM emission arises from the thermal sublimation of grains embedded in a circumstellar disk. Finally, the typical scale ~60 AU observed for COM emission is consistent with the size of the inner envelope where Tdust > 100 K is expected. Our data therefore strongly suggest that the COM emission traces the hot corino in IRAS2A, i.e., the warm inner envelope material where the icy mantles of dust grains evaporate because they are passively heated by the central protostellar object. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).CALYPSO stands for Continuum And Lines in Young ProtoStellar Objects.Appendix A, Tables 1, 2, and Figs. 3, 4 are available in electronic form at http://www.aanda.orgThe integrated emission maps shown in Fig. 3 are available in electronic form at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/563/L2

Measurement of Selected Organic Trace Gases During TRACE-P

NASA Technical Reports Server (NTRS)

Atlas, Elliot

2004-01-01

Major goals of the TRACE-P mission were: 1) to investigate the chemical composition of radiatively important gases, aerosols, and their precursors in the Asian outflow over the western Pacific, and 2) to describe and understand the chemical evolution of the Asian outflow as it is transported and mixed into the global troposphere. The research performed as part of this proposal addressed these major goals with a study of the organic chemical composition of gases in the TRACE-P region. This work was a close collaboration with the Blake/Rowland research group at UC-Irvine, and they have provided a separate report for their funded effort.

Numerical Simulations of Turbulent Molecular Clouds Regulated by Radiation Feedback Forces. II. Radiation-Gas Interactions and Outflows

NASA Astrophysics Data System (ADS)

Raskutti, Sudhir; Ostriker, Eve C.; Skinner, M. Aaron

2017-12-01

Momentum deposition by radiation pressure from young, massive stars may help to destroy molecular clouds and unbind stellar clusters by driving large-scale outflows. We extend our previous numerical radiation hydrodynamic study of turbulent star-forming clouds to analyze the detailed interaction between non-ionizing UV radiation and the cloud material. Our simulations trace the evolution of gas and star particles through self-gravitating collapse, star formation, and cloud destruction via radiation-driven outflows. These models are idealized in that we include only radiation feedback and adopt an isothermal equation of state. Turbulence creates a structure of dense filaments and large holes through which radiation escapes, such that only ˜50% of the radiation is (cumulatively) absorbed by the end of star formation. The surface density distribution of gas by mass as seen by the central cluster is roughly lognormal with {σ }{ln{{Σ }}}=1.3{--}1.7, similar to the externally projected surface density distribution. This allows low surface density regions to be driven outwards to nearly 10 times their initial escape speed {v}{esc}. Although the velocity distribution of outflows is broadened by the lognormal surface density distribution, the overall efficiency of momentum injection to the gas cloud is reduced because much of the radiation escapes. The mean outflow velocity is approximately twice the escape speed from the initial cloud radius. Our results are also informative for understanding galactic-scale wind driving by radiation, in particular, the relationship between velocity and surface density for individual outflow structures and the resulting velocity and mass distributions arising from turbulent sources.

The Properties and Prevalence of Galactic Outflows at z ~ 1 in the Extended Groth Strip

NASA Astrophysics Data System (ADS)

Kornei, Katherine A.; Shapley, Alice E.; Martin, Crystal L.; Coil, Alison L.; Lotz, Jennifer M.; Schiminovich, David; Bundy, Kevin; Noeske, Kai G.

2012-10-01

We investigate galactic-scale outflowing winds in 72 star-forming galaxies at z ~ 1 in the Extended Groth Strip. Galaxies were selected from the DEEP2 survey and follow-up LRIS spectroscopy was obtained covering Si II, C IV, Fe II, Mg II, and Mg I lines in the rest-frame ultraviolet. Using Galaxy Evolution Explorer (GALEX), Hubble Space Telescope (HST), and Spitzer imaging available for the Extended Groth Strip, we examine galaxies on a per-object basis in order to better understand both the prevalence of galactic outflows at z ~ 1 and the star-forming and structural properties of objects experiencing outflows. Gas velocities, measured from the centroids of Fe II interstellar absorption lines, are found to span the interval [-217, +155] km s-1. We find that ~40% (10%) of the sample exhibits blueshifted Fe II lines at the 1σ (3σ) level. We also measure maximal outflow velocities using the profiles of the Fe II and Mg II lines; we find that Mg II frequently traces higher velocity gas than Fe II. Using quantitative morphological parameters derived from the HST imaging, we find that mergers are not a prerequisite for driving outflows. More face-on galaxies also show stronger winds than highly inclined systems, consistent with the canonical picture of winds emanating perpendicular to galactic disks. In light of clumpy galaxy morphologies, we develop a new physically motivated technique for estimating areas corresponding to star formation. We use these area measurements in tandem with GALEX-derived star formation rates (SFRs) to calculate SFR surface densities. At least 70% of the sample exceeds an SFR surface density of 0.1 M ⊙ yr-1 kpc-2, the threshold necessary for driving an outflow in local starbursts. At the same time, the outflow detection fraction of only 40% in Fe II absorption provides further evidence for an outflow geometry that is not spherically symmetric. We see a ~3σ trend between outflow velocity and SFR surface density, but no significant trend between outflow velocity and SFR. Higher resolution data are needed in order to test the scaling relations between outflow velocity and both SFR and SFR surface density predicted by theory. Based, in part, on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

Towards a Population Synthesis Model of Objects formed by Self-Gravitating Disc Fragmentation and Tidal Downsizing

NASA Astrophysics Data System (ADS)

Forgan, Duncan; Rice, Ken

2013-07-01

Recently, the gravitational instability (GI) model of giant planet and brown dwarf formation has been revisited and recast into what is often referred to as the "tidal downsizing" hypothesis. The fragmentation of self-gravitating protostellar discs into gravitationally bound embryos - with masses of a few to tens of Jupiter masses, at semi major axes above 30 - 40 AU - is followed by a combination of grain sedimentation inside the embryo, radial migration towards the central star and tidal disruption of the embryo's upper layers. The properties of the resultant object depends sensitively on the timescales upon which each process occurs. Therefore, GI followed by tidal downsizing can theoretically produce objects spanning a large mass range, from terrestrial planets to giant planets and brown dwarfs. Whether such objects can be formed in practice, and what proportions of the observed population they would represent, requires a more involved statistical analysis. We present a simple population synthesis model of star and planet formation via GI and tidal downsizing. We couple a semi-analytic model of protostellar disc evolution to analytic calculations of fragmentation, initial embryo mass, grain growth and sedimentation, embryo migration and tidal disruption. While there are key pieces of physics yet to be incorporated, it represents a first step towards a mature statistical model of GI and tidal downsizing as a mode of star and planet formation. We show results from four runs of the population synthesis model, varying the opacity law and the strength of migration, as well as investigating the effect of disc truncation during the fragmentation process.

The Properties of Planck Galactic Cold Clumps in the L1495 Dark Cloud

NASA Astrophysics Data System (ADS)

Tang, Mengyao; Liu, Tie; Qin, Sheng-Li; Kim, Kee-Tae; Wu, Yuefang; Tatematsu, Ken’ichi; Yuan, Jinghua; Wang, Ke; Parsons, Harriet; Koch, Patrick M.; Sanhueza, Patricio; Ward-Thompson, D.; Tóth, L. Viktor; Soam, Archana; Lee, Chang Won; Eden, David; Di Francesco, James; Rawlings, Jonathan; Rawlings, Mark G.; Montillaud, Julien; Zhang, Chuan-Peng; Cunningham, M. R.

2018-04-01

Planck Galactic Cold Clumps (PGCCs) possibly represent the early stages of star formation. To understand better the properties of PGCCs, we studied 16 PGCCs in the L1495 cloud with molecular lines and continuum data from Herschel, JCMT/SCUBA-2, and the PMO 13.7 m telescope. Thirty dense cores were identified in 16 PGCCs from 2D Gaussian fitting. The dense cores have dust temperatures of T d = 11–14 K, and H2 column densities of {N}{{{H}}2} = (0.36–2.5) × 1022 cm‑2. We found that not all PGCCs contain prestellar objects. In general, the dense cores in PGCCs are usually at their earliest evolutionary stages. All the dense cores have non-thermal velocity dispersions larger than the thermal velocity dispersions from molecular line data, suggesting that the dense cores may be turbulence-dominated. We have calculated the virial parameter α and found that 14 of the dense cores have α <2, while 16 of the dense cores have α >2. This suggests that some of the dense cores are not bound in the absence of external pressure and magnetic fields. The column density profiles of dense cores were fitted. The sizes of the flat regions and core radii decrease with the evolution of dense cores. CO depletion was found to occur in all the dense cores, but is more significant in prestellar core candidates than in protostellar or starless cores. The protostellar cores inside the PGCCs are still at a very early evolutionary stage, sharing similar physical and chemical properties with the prestellar core candidates.

Can Gas Outflows Explain The Strong Lyα Emission Of Lyman Alpha Emitters?

NASA Astrophysics Data System (ADS)

Hashimoto, Takuya; Ouchi, M.; Shimasaku, K.; Nakajima, K.; Ono, Y.; Rauch, M.

2012-05-01

Lyman alpha emitters (LAEs) are galaxies commonly seen at high redshift, probably playing an important role in galaxy evolution as building blocks of massive galaxies. The most interesting feature of LAEs is strong Lyα emission, because Lyα photons produced in a galaxy are expected to be easily absorbed by dust in the ISM before escaping the galaxy due to their resonant nature. Previous studies have suggested that outflow may help their escape thanks to reduced cross sections of outflowing (ie, redshifted) neutral hydrogen atoms. Although the presence of outflows can be examined from the offset of the Lyα emission from the systemic velocity defined by Hα emission, there are only four LAEs with reliable detection of Hα emission. We present the results of Magellan/MMIRS and Keck/NIRSPEC spectroscopic observations of five LAEs at z˜2.2 from our wide-field narrow-band survey with Subaru/Suprime-Cam. We successfully detect Hα emission for five objects. After eliminating an AGN contaminated object, we measure the velocityoffset between Lyα and Hα (Δ v_Lyα) for the remaining four, to find that three have a positive offset, suggesting an outflow. Since three among the four from the the literature also have an outflow, we conclude that ˜75% of LAEs have an outflow, with velocities of 75-280 km/s. We then use these eight LAEs to examine how the Lyα strength defined by Lyα escape fraction (f_esc) and/or Lyα equivalent width (EW(Lyα)) depend on other physical quantities including those derived from SED fitting. Contrary to our expectation, we find that both f_esc and EW(Lyα) decrease with Δ v_Lyα. Thus, although LAEs do have outflow, high outflow velocities are not the primary cause of strong Lyα emission. We also find that the Lyα strength does not depend on E(B-V). However, we find that objects with a clumpier gas distribution may have higher f_esc.

The WISSH quasars project. I. Powerful ionised outflows in hyper-luminous quasars

NASA Astrophysics Data System (ADS)

Bischetti, M.; Piconcelli, E.; Vietri, G.; Bongiorno, A.; Fiore, F.; Sani, E.; Marconi, A.; Duras, F.; Zappacosta, L.; Brusa, M.; Comastri, A.; Cresci, G.; Feruglio, C.; Giallongo, E.; La Franca, F.; Mainieri, V.; Mannucci, F.; Martocchia, S.; Ricci, F.; Schneider, R.; Testa, V.; Vignali, C.

2017-02-01

Models and observations suggest that both the power and effects of AGN feedback should be maximised in hyper-luminous (LBol > 1047 erg s-1) quasars, I.e. objects at the brightest end of the AGN luminosity function. In this paper, we present the first results of a multiwavelength observing programme, focusing on a sample of WISE/SDSS selected hyper-luminous (WISSH) broad-line quasars at z ≈ 1.5-5. The WISSH quasars project has been designed to reveal the most energetic AGN-driven outflows, estimate their occurrence at the peak of quasar activity, and extend the study of correlations between outflows and nuclear properties up to poorly investigated, extreme AGN luminosities, I.e. LBol 1047 - 1048 erg s-1. We present near-infrared, long-slit LBT/LUCI1 spectroscopy of five WISSH quasars at z ≈ 2.3 - 3.5, showing prominent [OIII] emission lines with broad (FWHM 1200-2200 km s-1) and skewed profiles. The luminosities of these broad [OIII] wings are the highest measured so far, with L[OIII]broad ≳ 5 × 1044 erg s-1, and reveal the presence of powerful ionised outflows with associated mass outflow rates Ṁ ≳ 1700M⊙ yr-1 and kinetic powers Ėkin ≳ 1045 erg s-1. Although these estimates are affected by large uncertainties because of the use of [OIII] as a tracer of ionised outflows and the very basic outflow model adopted here, these results suggest that in our hyper-luminous targets the AGN is highly efficient at pushing large amounts of ionised gas outwards. Furthermore, the mechanical outflow luminosities measured for WISSH quasars correspond to higher percentages ( 1-3%) of LBol than those derived for AGN with lower LBol. Our targets host very massive (MBH ≳ 2 × 109M⊙) black holes that are still accreting at a high rate (I.e. a factor of 0.4-3 of the Eddington limit). These findings clearly demonstrate that WISSH quasars offer the opportunity to probe the extreme end of both luminosity and supermassive black holes (SMBH) mass functions and revealing powerful ionised outflows that are able to affect the evolution of their host galaxies.

A Sleeping Giant Awakened: Reignition of AGN Activity, Reborn Star Formation, and a Multiphase Outflow in one of the Largest Radio Galaxies Known

NASA Astrophysics Data System (ADS)

Tremblay, Grant; O'Dea, Christopher; Labiano, Alvaro; Baum, Stefi; McDermid, Richard; Combes, Francoise; Garcia-Burillo, Santiago; Davis, Timothy

2014-08-01

3C 236 is the second largest known radio galaxy and one of the largest objects in the known Universe. Its central AGN has recently reignited after a 10 Myr dormancy period, giving rise to a very young and compact radio source and a 1000 km/sec outflow of warm ionized and atomic HI gas. We propose GMOS-N IFU observations to resolve this outflow, determine its driver, and estimate the relative coupling efficiencies between the warm ionized, atomic, and cold molecular gas phases. We will assemble a much-needed spatially resolved Balmer decrement (extinction map) across the dramatic double dust lanes of this source, enabling high spatial resolution star formation rate, efficiency, and gas excitation and velocity maps. These will address several mysteries related to the very high star formation efficiency and the unique nature of the multiphase outflow in this source. 3C 236 is such a remarkable galaxy that whatever the results of the proposed observations, they will have wide-ranging implications for the triggering of star formation and AGN activity, their possibly coupled co-evolution, and the feedback effects of the latter on the former.

Mapping the Extent of M82's outlfows with VIRUS-P

NASA Astrophysics Data System (ADS)

Indahl, Briana; Hill, Gary J.; Drory, Niv; McLinden, Emily

2017-06-01

Starburst-driven outflows (SBDOs) and other feedback processes play a critical role in the evolution of galaxies through the regulation and disruption of star formation. However, our ability to observe and quantify feedback from SBDOs directly has been limited by the inability to obtain the spectroscopy needed for physical diagnostics over the large areas of local SBDOs. We present integral field spectroscopy taken with the George and Cynthia Mitchell Spectrograph (VIRUS-P) on the 2.7 meter Harlan J. Smith Telescope at McDonald Observatory mapping the full extent of M82’s northern outflow out to ~12kpc covering ~139 square arcminutes. We measured line ratios ([OIII]/Hβ, [OI]/Hα, [NII]/Hα), [SII]/Hα) for each spaxel in our fields. Using Ionization Diagnostic Diagrams (IDDs) we spatially map shock dominated regions which we show trace the biconical structure of the outflow. M82 is a local galaxy (z~0.000677) and the classical example of a starburst galaxy with vigorous outflows. As a result it has been comprehensively studied for nearly 50 years. However, we present the most sensitive and extensive map of the warm ionized gas to date from the disk to the Hα cap at ~12kpc.

Collapse and Fragmentation Models of Tidally Interacting Molecular Cloud Cores. IV. Initial Slow Rotation and Magnetic Field Support

NASA Astrophysics Data System (ADS)

Sigalotti, Leonardo Di G.; Klapp, Jaime

2000-03-01

Fragmentation has long been advocated as the primary mechanism for explaining the observed binary frequency among pre-main-sequence stars and, more recently, for explaining the emerging evidence for binary and multiple protostellar systems. The role of magnetic fields and ambipolar diffusion is essential to understand how dense cloud cores begin dynamic collapse and eventually fragment into protostars. Here we consider new numerical models of the gravitational collapse and fragmentation of slowly rotating molecular cloud cores, including the effects of magnetic support and ambipolar diffusion. The starting point of the evolution is provided by a magnetically stable (subcritical) condensation that results from adding a magnetic field pressure, B2/8π [with the field strength given by the scaling relation B=B0(ρ/ρ0)1/2], to a reference state consisting of a thermally supercritical (α~0.36), slowly rotating (β~0.037), Gaussian cloud core of prolate shape and central density ρ0. The effects of ambipolar diffusion are approximated by allowing the reference field strength B0 to gradually decrease over a timescale of 10 free-fall times. The models also include the effects of tidal interaction due to a gravitational encounter with another protostar, and so they may apply to low-mass star formation within a cluster-forming environment. The results indicate that the magnetic forces delay the onset of dynamic collapse, and hence of fragmentation, by an amount of time that depends on the initial central mass-to-flux ratio. Compared with previous magnetic collapse calculations of rapidly rotating (β=0.12) clouds, lower initial rotation (β~0.037) is seen to result in much shorter delay periods, thus anticipating binary fragmentation. In general, the results show that the models are still susceptible to fragment into binary systems. Intermediate magnetic support (η~0.285) and low tidal forces (τ<~0.201) may lead to final triple or quadruple protostellar systems, while increasing the size of η and τ always results in final binary protostellar cores. The formed binary systems have separations of ~200-350 AU, suggesting that the recently observed peaks around ~90 AU and 215 AU for T Tauri stars may be explained by the collapse and fragmentation of initially slowly rotating magnetic cloud cores with β<~0.04.

Submillimeter astronomy and the problem of star formation

NASA Technical Reports Server (NTRS)

Harwit, M.

1984-01-01

Sources that have traditionally been called 'protostars,' because they were strong emitters of infrared radiation embedded in dust clouds, are now recognized to be 'newly formed' stars instead. Recent developments in submillimeter astronomy should permit a redoubling of efforts to find bodies that are the actual predecessors of newly formed stars. This renewed search for true protostars will be aided by advances that have occurred in submillimeter spectroscopy; these will permit an analysis of the physical conditions and chemical constitution of cooler protostellar clouds, and may provide insight into circumstances favoring protostellar collapse.

Interaction of tectonic and depositional processes that control the evolution of the Iberian Gulf of Cadiz margin

USGS Publications Warehouse

Maldonado, A.; Nelson, C.H.

1999-01-01

This study provides an integrated view of the growth patterns and factors that controlled the evolution of the Gulf of Cadiz continental margin based on studies of the tectonic, sedimentologic and oceanographic history of the area. Seven sedimentary regimes are identified, but there are more extensive descriptions of the late Cenozoic regimes because of the larger data base. The regimes of the Mesozoic passive margin include carbonate platforms, which become mixed calcareous-terrigenous deposits during the Late Cretaceous-early Tertiary. The Oligocene and Early Miocene terrigenous regimes developed, in contrast, over the active and transcurrent margins near the African-Iberian plate boundary. The top of the Gulf of Cadiz olistostrome, emplaced in the Late Miocene, is used as a key horizon to define the 'post-orogenic' depositional regimes. The Late Miocene progradational margin regime is characterized by a large terrigenous sediment supply to the margin and coincides with the closing of the Miocene Atlantic-Mediterranean gateways. The terrigenous drift depositional regime of the Early Pliocene resulted from the occurrence of high eustatic sea level and the characteristics of the Mediterranean outflow currents that developed after the opening of the Strait of Gibraltar. The Late Pliocene and Quaternary regimes are dominated by sequences of deposits related to cycles of high and low sea levels. Deposition of shelf-margin deltas and slope wedges correlate with regressive and low sea level regimes caused by eustasy and subsidence. During the highstand regimes of the Holocene, inner shelf prograding deltas and deep-water sediment drifts were developed under the influence of the Atlantic inflow and Mediterranean outflow currents, respectively. A modern human cultural regime began 2000 years ago with the Roman occupation of Iberia; human cultural effects on sedimentary regimes may have equalled natural factors such as climate change. Interplay of tectonic and oceanographic controls dominated the evolution of the Cadiz margin during the Cenozoic. Depositional sequences formed where the tectonic setting provided the accommodation space and the shape of the deposits has been greatly influenced by the strong unidirectional Atlantic inflow currents on the shelf and Mediterranean outflow currents on the slope. The entire cycle of the inflow and outflow deposition along the margin has been controlled first by the tectonic evolution of the Betic and Rif gateways, which become closed during the Late Miocene, and after the Messinian by the opening of the Strait of Gibraltar. Strong current development during eustatic sea level highstands of the Pliocene and Quaternary has controlled deposition because of maximum sill depths at Gibraltar for water circulation. Lowstand sea levels slowed circulation and resulted in mud drapes over the slope and regressive stratigraphic sequences over the shelf. More recently, the human industrial revolution has caused heavy metal contamination of sediment and water over the Cadiz margin. Human activity also has affected sedimentation rates because of deforestation that caused increased depositional rates near undammed rivers and decreased rates where rivers have been dammed. Future research efforts will need to focus on: (1) the effect of increased Mediterranean outflow caused by river damming plus global warming and the increased outflow as a potential trigger for new ice ages; (2) assessments of geologic hazards for planning man-made shoreline structures, developing offshore petroleum resources and maintaining undersea communications cables; and (3) confirmation of the general geologic history of the Cadiz margin.

The Composition of the Protosolar Disk and the Formation Conditions for Comets

NASA Astrophysics Data System (ADS)

Willacy, K.; Alexander, C.; Ali-Dib, M.; Ceccarelli, C.; Charnley, S. B.; Doronin, M.; Ellinger, Y.; Gast, P.; Gibb, E.; Milam, S. N.; Mousis, O.; Pauzat, F.; Tornow, C.; Wirström, E. S.; Zicler, E.

2015-12-01

Conditions in the protosolar nebula have left their mark in the composition of cometary volatiles, thought to be some of the most pristine material in the solar system. Cometary compositions represent the end point of processing that began in the parent molecular cloud core and continued through the collapse of that core to form the protosun and the solar nebula, and finally during the evolution of the solar nebula itself as the cometary bodies were accreting. Disentangling the effects of the various epochs on the final composition of a comet is complicated. But comets are not the only source of information about the solar nebula. Protostellar disks around young stars similar to the protosun provide a way of investigating the evolution of disks similar to the solar nebula while they are in the process of evolving to form their own solar systems. In this way we can learn about the physical and chemical conditions under which comets formed, and about the types of dynamical processing that shaped the solar system we see today.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coughlin, Eric R., E-mail: eric_coughlin@berkeley.edu

We present the exact solutions for the collapse of a spherically symmetric cold (i.e., pressureless) cloud under its own self-gravity, valid for arbitrary initial density profiles and not restricted to the realm of self-similarity. These solutions exhibit a number of remarkable features, including the self-consistent formation of and subsequent accretion onto a central point mass. A number of specific examples are provided, and we show that Penston’s solution of pressureless self-similar collapse is recovered for polytropic density profiles; importantly, however, we demonstrate that the time over which this solution holds is fleetingly short, implying that much of the collapse proceedsmore » non-self-similarly. We show that our solutions can naturally incorporate turbulent pressure support, and we investigate the evolution of overdensities—potentially generated by such turbulence—as the collapse proceeds. Finally, we analyze the evolution of the angular velocity and magnetic fields in the limit that their dynamical influence is small, and we recover exact solutions for these quantities. Our results may provide important constraints on numerical models that attempt to elucidate the details of protostellar collapse when the initial conditions are far less idealized.« less

Formation of wide binaries by turbulent fragmentation

NASA Astrophysics Data System (ADS)

Lee, Jeong-Eun; Lee, Seokho; Dunham, Michael M.; Tatematsu, Ken'ichi; Choi, Minho; Bergin, Edwin A.; Evans, Neal J.

2017-08-01

Understanding the formation of wide-binary systems of very low-mass stars (M ≤ 0.1 solar masses, M⊙) is challenging 1,2,3 . The most obvious route is through widely separated low-mass collapsing fragments produced by turbulent fragmentation of a molecular core4,5. However, close binaries or multiples from disk fragmentation can also evolve to wide binaries over a few initial crossing times of the stellar cluster through tidal evolution6. Finding an isolated low-mass wide-binary system in the earliest stage of formation, before tidal evolution could occur, would prove that turbulent fragmentation is a viable mechanism for (very) low-mass wide binaries. Here we report high-resolution ALMA observations of a known wide-separation protostellar binary, showing that each component has a circumstellar disk. The system is too young7 to have evolved from a close binary, and the disk axes are misaligned, providing strong support for the turbulent fragmentation model. Masses of both stars are derived from the Keplerian rotation of the disks; both are very low-mass stars.

Astrophysics of brown dwarfs; Proceedings of the Workshop, George Mason University, Fairfax, VA, Oct. 14, 15, 1985

NASA Technical Reports Server (NTRS)

Kafatos, Minas C. (Editor); Harrington, Robert S. (Editor); Maran, Stephen P. (Editor)

1986-01-01

Various reports on theoretical and observational studies of brown dwarfs (BDs) are presented. The topics considered include: astrometric detection of BDs, search for substellar companions to nearby stars using IR imaging, constraints on BD mass function from optical and IR searches, properties of stellar objects near the main sequence mass limit, search for low-mass stellar companions with the HF precision velocity technique, dynamical search for substellar objects, search for BDs in the IRAS data base, deep CCD survey for low mass stars in the disk and halo, the Berkeley search for a faint solar companion, the luminosity function for late M stars, astronomic search for IR dwarfs, and the role of the Space Telescope in the detection of BDs. Also addressed are: theoretical significance of BDs, evolution of super-Jupiters, compositional indicators in IR spectra of BDs, evolution of BDs and the evolutionary status of VB8B, the position of BDs on universal diagrams, theoretical determination of the minimum protostellar mass, Population II BDs and dark halos.

Studies of Circumstellar Disk Evolution

NASA Technical Reports Server (NTRS)

Hartmann, Lee W.

2004-01-01

Spitzer Space Telescope infrared data for our program on disk evolution has been taken (the main IRAC - 3-8 micron exposures; the 24 and 70 micron MIPS data are to come later). We now have deep maps in the four IRAC bands of the 3-Myr-old cluster Trumpler 37, and the 10-Myr-old cluster NGC 7160. Analysis of these data has now begun. We will be combining these data with our ground-based photometric and spectroscopic data to obtain a complete picture of disk frequency as a function of mass through this important age range, which spans the likely epoch of (giant) planet formation in most systems. Analysis of the SIRTF data, and follow-on ground-based spectroscopy on the converted MMT telescope using the wide-field, fiber-fed, multiobject spectrographs, Hectospec and Hectochelle, will be the major activity during the next year.Work was also performed on the following: protoplanetary disk mass accretion rates in very low-mass stars; the inner edge of T Tauri disks; accretion in intermediate-mass T Tauri stars (IMPS); and the near-infrared spectra of the rapidly-accreting protostellar disks FU Ori and V1057 Cyg.

Quasar Feedback in the Ultraluminous Infrared Galaxy F11119+3257: Connecting the Accretion Disk Wind with the Large-scale Molecular Outflow

NASA Astrophysics Data System (ADS)

Veilleux, S.; Bolatto, A.; Tombesi, F.; Meléndez, M.; Sturm, E.; González-Alfonso, E.; Fischer, J.; Rupke, D. S. N.

2017-07-01

In Tombesi et al., we reported the first direct evidence for a quasar accretion disk wind driving a massive (>100 M ⊙ yr-1) molecular outflow. The target was F11119+3257, an ultraluminous infrared galaxy (ULIRG) with unambiguous type 1 quasar optical broad emission lines. The energetics of the accretion disk wind and molecular outflow were found to be consistent with the predictions of quasar feedback models where the molecular outflow is driven by a hot energy-conserving bubble inflated by the inner quasar accretion disk wind. However, this conclusion was uncertain because the mass outflow rate, momentum flux, and mechanical power of the outflowing molecular gas were estimated from the optically thick OH 119 μm transition profile observed with Herschel. Here, we independently confirm the presence of the molecular outflow in F11119+3257, based on the detection of ˜±1000 km s-1 blue- and redshifted wings in the CO(1-0) emission line profile derived from deep ALMA observations obtained in the compact array configuration (˜2.″8 resolution). The broad CO(1-0) line emission appears to be spatially extended on a scale of at least ˜7 kpc from the center. Mass outflow rate, momentum flux, and mechanical power of (80-200) {R}7-1 M ⊙ yr-1, (1.5-3.0) {R}7-1 L AGN/c, and (0.15-0.40)% {R}7-1 {L}{AGN}, respectively, are inferred from these data, assuming a CO-to-H2 conversion factor appropriate for a ULIRG (R 7 is the radius of the outflow normalized to 7 kpc, and L AGN is the AGN luminosity). These rates are time-averaged over a flow timescale of 7 × 106 yr. They are similar to the OH-based rates time-averaged over a flow timescale of 4 × 105 yr, but about a factor of 4 smaller than the local (“instantaneous” ≲105 yr) OH-based estimates cited in Tombesi et al. The implications of these new results are discussed in the context of time-variable quasar-mode feedback and galaxy evolution. The need for an energy-conserving bubble to explain the molecular outflow is also reexamined.

FORMATION AND RECONDENSATION OF COMPLEX ORGANIC MOLECULES DURING PROTOSTELLAR LUMINOSITY OUTBURSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taquet, Vianney; Wirström, Eva S.; Charnley, Steven B.

2016-04-10

During the formation of stars, the accretion of surrounding material toward the central object is thought to undergo strong luminosity outbursts followed by long periods of relative quiescence, even at the early stages of star formation when the protostar is still embedded in a large envelope. We investigated the gas-phase formation and recondensation of the complex organic molecules (COMs) di-methyl ether and methyl formate, induced by sudden ice evaporation processes occurring during luminosity outbursts of different amplitudes in protostellar envelopes. For this purpose, we updated a gas-phase chemical network forming COMs in which ammonia plays a key role. The modelmore » calculations presented here demonstrate that ion–molecule reactions alone could account for the observed presence of di-methyl ether and methyl formate in a large fraction of protostellar cores without recourse to grain-surface chemistry, although they depend on uncertain ice abundances and gas-phase reaction branching ratios. In spite of the short outburst timescales of about 100 years, abundance ratios of the considered species higher than 10% with respect to methanol are predicted during outbursts due to their low binding energies relative to water and methanol which delay their recondensation during cooling. Although the current luminosity of most embedded protostars would be too low to produce complex organics in the hot-core regions that are observable with current sub-millimetric interferometers, previous luminosity outburst events would induce the formation of COMs in extended regions of protostellar envelopes with sizes increasing by up to one order of magnitude.« less

Dusty Disks, Diffuse Clouds, and Dim Suns: Galactic Science with the Infrared Spectrograph on the Spitzer Space Telescope

NASA Technical Reports Server (NTRS)

Roellig, T. L.; Watson, D. M.; Uchida, K. I.; Forrest, W. J.; VanCleve, J. E.; Herter, T. L.; Sloan, G. C.; Furlan, E.; Wilson, J. C.; Bernard-Salas, J.

2004-01-01

The Infrared Spectrograph (IRS) on the Spitzer Space Telescope has now been in routine science operations since Dec. 14,2003. The IRS Science Team has used a portion of their guaranteed time to pursue three major science themes in galactic astronomy: the evolution of protostellar disks and debris disks; the composition and evolution of diffuse matter and clouds in the interstellar medium; and the composition and structure of brown dwarfs and low-mass main-sequence stars. We report here on the results from the first five months of IRS observations in these programs. Full IRS Spectra have already been obtained for large samples of YSO/protoplanetary disks in the Taurus and TW Hya associations, and or debris disks around main-sequence stars, in which many aspects of the evolution of planetary systems can be addressed for the first time. As anticipated, the mid-infrared IRS observations of brown dwarfs have yielded important new information about their atmospheres, including the identification of NH3 and measurements of new methane features. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work was provided by NASA's Office of Space Science.

Dusty Disks, Diffuse Clouds, and Dim Suns - Galactic Science with the Infrared Spectrograph on the Spitzer Space Telescope

NASA Astrophysics Data System (ADS)

Roellig, T. L.; Watson, D. M.; Uchida, K. I.; Forrest, W. J.; Van Cleve, J. E.; Herter, T. L.; Sloan, G. C.; Furlan, E.; Wilson, J. C.; Bernard-Salas, J.; Saumon, D.; Leggett, S.; Chen, C.; Kemper, F.; Hartmann, L.; Marley, M.; Cushing, M.; Mainzer, A. K.; Kirkpatrick, D.; Jura, M.; Houck, J. R.

2004-05-01

The Infrared Spectrograph (IRS) on the Spitzer Space Telescope has now been in routine science operations since Dec. 14, 2003. The IRS Science Team has used a portion of their guaranteed time to pursue three major science themes in galactic astronomy: the evolution of protostellar disks and debris disks; the composition and evolution of diffuse matter and clouds in the interstellar medium; and the composition and structure of brown dwarfs and low-mass main-sequence stars. We report here on the results from the first five months of IRS observations in these programs. Full IRS Spectra have already been obtained for large samples of YSO/protoplanetary disks in the Taurus and TW Hya associations, and of debris disks around main-sequence stars, in which many aspects of the evolution of planetary systems can be addressed for the first time. As anticipated, the mid-infrared IRS observations of brown dwarfs have yielded important new information about their atmospheres, including the identification of NH3 and measurements of new methane features. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work was provided by NASA's Office of Space Science.

Is Episodic Accretion Necessary to Resolve the Luminosity Problem in Low-Mass Protostars?

NASA Astrophysics Data System (ADS)

Sevrinsky, Raymond Andrew; Dunham, Michael

2017-01-01

In this contribution, we compare the results of protostellar accretion simulations for scenarios both containing and lacking episodic accretion activity. We determine synthetic observational signatures for collapsing protostars by taking hydrodynamical simulations predicting highly variable episodic accretion events, filtering out the stochastic behavior by applying power law fits to the mass accretion rates onto the disk and central star, and using the filtered rates as inputs to two-dimensional radiative transfer calculations. The spectral energy distributions generated by these calculations are used to calculate standard observational signatures of Lbol and Tbol, and compared directly to a sample of 230 embedded protostars. We explore the degree to which these continually declining accretion models successfully reproduce the observed spread of protostellar luminosities, and examine their consistency with the prior variable models to investigate the degree to which episodic accretion bursts are necessary in protostellar formation theories to match observations of field protostars. The SAO REU program is funded in part by the National Science Foundation REU and Department of Defense ASSURE programs under NSF Grant no. 1262851, and by the Smithsonian Institution.

A High-definition View Of The Circum-nuclear Regions In Nearby Seyferts With Chandra And HST

NASA Astrophysics Data System (ADS)

Wang, Junfeng; Fabbiano, G.; Elvis, M.; Risaliti, G.; Karovska, M.; Zezas, A.; Mundell, C. G.

2011-09-01

To improve our understanding of AGN feedback, it is crucial to evaluate the true role of outflows on galaxy evolution observationally. I will present new results from the CHandra survey of Extended Emission-line Regions in nearby Seyfert galaxies (CHEERS), which aims to examine feedback in action in much greater detail than at high redshift. Findings from Chandra studies of the circum-nuclear region in the archetypal Seyfert 1 galaxy NGC 4151 will be discussed in detail. Exploiting Chandra's highest possible resolution, we find evidence for X-ray emission from interaction between radio outflow and the optical narrow-line region clouds, in addition to the emission from photoionized gas.

Evolution of the global water cycle on Mars: The geological evidence

NASA Technical Reports Server (NTRS)

Baker, V. R.; Gulick, V. C.

1993-01-01

The geological evidence for active water cycling early in the history of Mars (Noachian geological system or heavy bombardment) consists almost exclusively of fluvial valley networks in the heavily cratered uplands of the planet. It is commonly assumed that these landforms required explanation by atmospheric processes operating above the freezing point of water and at high pressure to allow rainfall and liquid surface runoff. However, it has also been documented that nearly all valley networks probably formed by subsurface outflow and sapping erosion involving groundwater outflow prior to surface-water flow. The prolonged ground-water flow also requires extensive water cycling to maintain hydraulic gradients, but is this done via rainfall recharge, as in terrestrial environments?

Outflows in low-mass galaxies at z >1

NASA Astrophysics Data System (ADS)

Maseda, Michael V.; MUSE GTO Consortium

2017-03-01

Star formation histories of local dwarf galaxies, derived through resolved stellar populations, appear complex and varied. The general picture derived from hydrodynamical simulations is one of cold gas accretion and bursty star formation, followed by feedback from supernovae and winds that heat and eject the central gas reservoirs. This ejection halts star formation until the material cools and re-accretes, resulting in an episodic SFH, particularly at stellar masses below ~ 109 M⊙. Such feedback has often been cited as the driving force behind the observed slowly-rising rotation curves in local dwarfs, due to an under-density of dark matter compared to theoretical models, which is one of the primary challenges to LCDM cosmology. However, these events have not yet been directly observed at high-redshift. Recently, using HST imaging and grism spectroscopy, we have uncovered an abundant population of low-mass galaxies (M* < 109 M⊙) at z = 1 - 2 that are undergoing strong bursts of star formation, in agreement with the theoretical predictions. These Extreme Emission Line Galaxies, with high specific SFRs and shallow gravitational potential wells, are ideal places to test the theoretical prediction of strong feedback-driven outflows. Here we use deep MUSE spectroscopy to search these galaxies for signatures of outflowing material, namely kinematic offsets between absorption lines (in the restframe optical and UV), which trace cool gas, and the nebular emission lines, which define the systemic redshift of the galaxy. Although the EELGs are intrinsically very faint, stacked spectra reveal blueshifted velocity centroids for Fe II absorption, which is indicative of outflowing cold gas. This represents the first constraint on outflows in M* < 109 M⊙ galaxies at z = 1 - 2. These outflows should regulate the star formation histories of low-mass galaxies at early cosmic times and thus play a crucial role in galaxy growth and evolution.

Ionized and Neutral Outflows in the QUEST QSOs

NASA Astrophysics Data System (ADS)

Veilleux, Sylvain

2011-10-01

The role of galactic winds in gas-rich mergers is of crucial importance to understand galaxy and SMBH evolution. In recent months, our group has had three major scientific breakthroughs in this area: {1} The discovery with Herschel of massive molecular {OH-absorbing} outflows in several ULIRGs, including the nearest quasar, Mrk 231. {2} The independent discovery from mm-wave interferometric observations in the same object of a spatially resolved molecular {CO-emitting} wind with estimated mass outflow rate 3x larger than the star formation rate and spatially coincident with blueshifted neutral {Na ID-absorbing} gas in optical long-slit spectra. {3} The unambiguous determination from recent Gemini/IFU observations that the Na ID outflow in this object is wide-angle, thus driven by a QSO wind rather than a jet. This powerful outflow may be the long-sought "smoking gun" of quasar mechanical feedback purported to transform gas-rich mergers. However, our Herschel survey excludes all FIR-faint {UV-bright} "classic" QSOs by necessity. So here we propose a complementary FUV absorption-line survey of all FIR-bright -and- FIR-faint QSOs from the same parent sample. New {19 targets} and archival {11} spectra will be used to study, for the first time, the gaseous environments of QSOs as a function of host properties and age across the merger sequence ULIRG -> QSO. These data will allow us to distinguish between ionized & neutral quasar-driven outflows, starburst-driven winds, and tidal debris around the mergers. They will also be uniquely suited for a shallow but broad study of the warm & warm-hot intergalactic media, complementary to on-going surveys that are deeper but narrower.

AGN-enhanced outflows of low-ionization gas in star-forming galaxies at 1.7 < z < 4.6*

NASA Astrophysics Data System (ADS)

Talia, M.; Brusa, M.; Cimatti, A.; Lemaux, B. C.; Amorin, R.; Bardelli, S.; Cassarà, L. P.; Cucciati, O.; Garilli, B.; Grazian, A.; Guaita, L.; Hathi, N. P.; Koekemoer, A.; Le Fèvre, O.; Maccagni, D.; Nakajima, K.; Pentericci, L.; Pforr, J.; Schaerer, D.; Vanzella, E.; Vergani, D.; Zamorani, G.; Zucca, E.

2017-11-01

Fast and energetic winds are invoked by galaxy formation models as essential processes in the evolution of galaxies. These outflows can be powered either by star formation (SF) and/or active galactic nucleus (AGN) activity, but the relative dominance of the two mechanisms is still under debate. We use spectroscopic stacking analysis to study the properties of the low-ionization phase of the outflow in a sample of 1330 star-forming galaxies (SFGs) and 79 X-ray-detected (1042 < LX < 1045 erg s-1) Type 2 AGN at 1.7 < z < 4.6 selected from a compilation of deep optical spectroscopic surveys, mostly zCOSMOS-Deep and VIMOS Ultra Deep Survey (VUDS). We measure mean velocity offsets of ˜- 150 km s-1 in the SFGs, while in the AGN sample the velocity is much higher (˜- 950 km s-1), suggesting that the AGN is boosting the outflow up to velocities that could not be reached only with the SF contribution. The sample of X-ray AGN has on average a lower SF rate than non-AGN SFGs of similar mass: this, combined with the enhanced outflow velocity in AGN hosts, is consistent with AGN feedback in action. We further divide our sample of AGN into two X-ray luminosity bins: we measure the same velocity offsets in both stacked spectra, at odds with results reported for the highly ionized phase in local AGN, suggesting that the two phases of the outflow may be mixed only up to relatively low velocities, while the highest velocities can be reached only by the highly ionized phase.

The circum-Chryse region as a possible example of a hydrologic cycle on Mars: Geologic observations and theoretical evaluation

NASA Technical Reports Server (NTRS)

Moore, Jeffrey M.; Clow, Gary D.; Davis, Wanda L.; Gulick, Virginia C.; Janke, David R.; Mckay, Christopher P.; Stoker, Carol R.; Zent, Aaron P.

1995-01-01

The transection and superposition relationships among channels, chaos, surface materials units, and other features in the circum-Chryse region of Mars were used to evaluate relative age relationships and evolution of flood events. Channels and chaos in contact (with one another) were treated as single discrete flood-carved systems. Some outflow channel systems form networks and are inferred to have been created by multiple flood events. Within some outflow channel networks, several separate individual channel systems can be traced to a specific chaos which acted as flood-source area to that specific flood channel. Individual flood-carved systems were related to widespread materials units or other surface features that served as stratigraphic horizons. Chryse outflow channels are inferred to have formed over most of the perceivable history of Mars. Outflow channels are inferred to become younger with increasing proximity to the Chryse basin. The relationship of subsequent outflow channel sources to the sources of earlier floods is inferred to disfavor episodic flooding due to the progresssive tapping of a juvenile near-surface water supply. Instead, we propose the circum-Chryse region as a candidate site of past hydrological recycling. The discharge rates necessary to carve the circum-Chryse outflow channels would have inevitably formed temporary standing bodies of H2O on the Martian surface where the flood-waters stagnated and pooled (the Chryse basin is topographically enclosed). These observations and inferences have led us to formulate and evaluate two hypotheses. Our numerical evaluations indicate that of these two hypotheses formulated, the groundwater seep cycle seems by far the more viable. Further observations from forthcoming missions may permit the determination of which mechanisms may have operated to recycle the Chryse flood-waters.

Mapping the solar wind HI outflow velocity in the inner heliosphere by coronagraphic ultraviolet and visible-light observations

NASA Astrophysics Data System (ADS)

Dolei, S.; Susino, R.; Sasso, C.; Bemporad, A.; Andretta, V.; Spadaro, D.; Ventura, R.; Antonucci, E.; Abbo, L.; Da Deppo, V.; Fineschi, S.; Focardi, M.; Frassetto, F.; Giordano, S.; Landini, F.; Naletto, G.; Nicolini, G.; Nicolosi, P.; Pancrazzi, M.; Romoli, M.; Telloni, D.

2018-05-01

We investigated the capability of mapping the solar wind outflow velocity of neutral hydrogen atoms by using synergistic visible-light and ultraviolet observations. We used polarised brightness images acquired by the LASCO/SOHO and Mk3/MLSO coronagraphs, and synoptic Lyα line observations of the UVCS/SOHO spectrometer to obtain daily maps of solar wind H I outflow velocity between 1.5 and 4.0 R⊙ on the SOHO plane of the sky during a complete solar rotation (from 1997 June 1 to 1997 June 28). The 28-days data sequence allows us to construct coronal off-limb Carrington maps of the resulting velocities at different heliocentric distances to investigate the space and time evolution of the outflowing solar plasma. In addition, we performed a parameter space exploration in order to study the dependence of the derived outflow velocities on the physical quantities characterising the Lyα emitting process in the corona. Our results are important in anticipation of the future science with the Metis instrument, selected to be part of the Solar Orbiter scientific payload. It was conceived to carry out near-sun coronagraphy, performing for the first time simultaneous imaging in polarised visible-light and ultraviolet H I Lyα line, so providing an unprecedented view of the solar wind acceleration region in the inner corona. The movie (see Sect. 4.2) is available at https://www.aanda.org

Optimal layout design of obstacles for panic evacuation using differential evolution

NASA Astrophysics Data System (ADS)

Zhao, Yongxiang; Li, Meifang; Lu, Xin; Tian, Lijun; Yu, Zhiyong; Huang, Kai; Wang, Yana; Li, Ting

2017-01-01

To improve the pedestrian outflow in panic situations by suitably placing an obstacle in front of the exit, it is vital to understand the physical mechanism behind the evacuation efficiency enhancement. In this paper, a robust differential evolution is firstly employed to optimize the geometrical parameters of different shaped obstacles in order to achieve an optimal evacuation efficiency. Moreover, it is found that all the geometrical parameters of obstacles could markedly influence the evacuation efficiency of pedestrians, and the best way for achieving an optimal pedestrian outflow is to slightly shift the obstacle from the center of the exit which is consistent with findings of extant literature. Most importantly, by analyzing the profiles of density, velocity and specific flow, as well as the spatial distribution of crowd pressure, we have proven that placing an obstacle in panic situations does not reduce or absorb the pressure in the region of exit, on the contrary, promotes the pressure to a much higher level, hence the physical mechanism behind the evacuation efficiency enhancement is not a pressure decrease in the region of exit, but a significant reduction of high density region by effective separation in space which finally causes the increasing of escape speed and evacuation outflow. Finally, it is clearly demonstrated that the panel-like obstacle is considerably more robust and stable than the pillar-like obstacle to guarantee the enhancement of evacuation efficiency under different initial pedestrian distributions, different initial crowd densities as well as different desired velocities.

Truncation of the Binary Distribution Function in Globular Cluster Formation

NASA Astrophysics Data System (ADS)

Vesperini, E.; Chernoff, David F.

1996-02-01

We investigate a population of primordial binaries during the initial stage of evolution of a star cluster. For our calculations we assume that equal-mass stars form rapidly in a tidally truncated gas cloud, that ˜10% of the stars are in binaries, and that the resulting star cluster undergoes an epoch of violent relaxation. We study the collisional interaction of the binaries and single stars, in particular, the ionization of the binaries and the energy exchange between binaries and single stars. We find that for large N systems (N > 1000), even the most violent beginning leaves the binary distribution function largely intact. Hence, the binding energy originally tied up in the cloud's protostellar pairs is preserved during the relaxation process, and the binaries are available to interact at later times within the virialized cluster.

EXTERNALLY HEATED PROTOSTELLAR CORES IN THE OPHIUCHUS STAR-FORMING REGION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindberg, Johan E.; Charnley, Steven B.; Cordiner, Martin A.

We present APEX 218 GHz observations of molecular emission in a complete sample of embedded protostars in the Ophiuchus star-forming region. To study the physical properties of the cores, we calculate H{sub 2}CO and c -C{sub 3}H{sub 2} rotational temperatures, both of which are good tracers of the kinetic temperature of the molecular gas. We find that the H{sub 2}CO temperatures range between 16 K and 124 K, with the highest H{sub 2}CO temperatures toward the hot corino source IRAS 16293-2422 (69–124 K) and the sources in the ρ Oph A cloud (23–49 K) located close to the luminous Herbigmore » Be star S1, which externally irradiates the ρ Oph A cores. On the other hand, the c -C{sub 3}H{sub 2} rotational temperature is consistently low (7–17 K) in all sources. Our results indicate that the c -C{sub 3}H{sub 2} emission is primarily tracing more shielded parts of the envelope whereas the H{sub 2}CO emission (at the angular scale of the APEX beam; 3600 au in Ophiuchus) mainly traces the outer irradiated envelopes, apart from in IRAS 16293-2422, where the hot corino emission dominates. In some sources, a secondary velocity component is also seen, possibly tracing the molecular outflow.« less

Veiling and Accretion Around the Young Binary Stars S and VV Corona Australis

NASA Astrophysics Data System (ADS)

Sullivan, Kendall; Prato, Lisa; Avilez, Ian

2018-01-01

S CrA and VV CrA are two young binary star systems with separations of 170 AU and 250 AU, respectively, in the southern star-forming region Corona Australis. The spectral types of the four stars in these two systems are similar, approximately K7 to M1, hence the stellar masses are also similar. The study of young stars just emerging from their natal cloud cores at the very limits of observability allows us to probe the extreme environments in which planet formation begins to occur. Stars in this early evolutionary stage can have circumstellar or circumbinary disks, and sometimes remnants of the envelopes which surrounded them during the protostellar stage. Envelopes accrete onto disks and disks in turn accrete onto the central stars, triggering elevated continuum emission, line emission, outflows, and stellar winds. This violent stage marks the onset of the epoch of planet formation. Using high-resolution near-infrared, H-band spectroscopy from the Keck II telescope using the NIRSPEC instrument over 4-6 epochs, we are probing the chaotic environment surrounding the four stars in these systems. We determine the spectral types for VV CrA A and B for the first time, and examine the variable veiling and emission occurring around each of these stars. This research was supported in part by NSF grants AST-1461200 and AST-1313399.

Resolving the Circumgalactic Medium in the NEPHTHYS Simulations

NASA Astrophysics Data System (ADS)

Richardson, Mark Lawrence Albert; Devriendt, Julien; Slyz, Adrianne; Rosdahl, Karl Joakim; Kimm, Taysun

2018-01-01

NEPHTHYS is a RAMSES Cosmological-zoom galaxy simulation suite investigating the impact of stellar feedback (winds, radiation, and type Ia and II SNe) on z > 1 ~L* galaxies and their environments. NEPHTHYS has ~10 pc resolution in the galaxy, where the scales driving star formation and the interaction of stellar feedback with the ISM can begin to be resolved. As outflows, winds, and radiation permeate through the circumgalactic medium (CGM) they can heat or cool gas, and deposit metals throughout the CGM. Such material in the CGM is seen by spectroscopic studies of distant quasars, where CGM gas of foreground galaxies is observed in absorption. It is still unclear what the origin and evolution of this gas is. To help answer this, NEPHTHYS includes additional refinement in the CGM, refining it to an unrivaled 80 pc resolution. I will discuss how this extra resolution is crucial for resolving the complex structure of outflows and accretion in the CGM. Specifically, the metal mass and covering fraction of metals and high energy ions is increased, while the better resolved outflows leads to a decrease in the overall baryon content of galaxy halos, and individual outflow events can have larger velocities. Our results suggest that absorption observations of CGM are tracing a clumpy column of gas with multiple kinematic components.

Recent Chandra/HETGS and NuSTAR observations of the quasar PDS 456 and its Ultra-Fast Outflow

NASA Astrophysics Data System (ADS)

Boissay Malaquin, Rozenn; Marshall, Herman L.; Nowak, Michael A.

2018-01-01

Evidence is growing that the interaction between outflows from active galactic nuclei (AGN) and their surrounding medium may play an important role in galaxy evolution, i.e. in the regulation of star formation in galaxies, through AGN feedback processes. Indeed, powerful outflows, such as the ultra-fast outflows (UFOs) that can reach mildly relativistic velocities of 0.2-0.4c, could blow away a galaxy’s reservoir of star-forming gas and hence quench the star formation in host galaxies. The low-redshift (z=0.184) radio-quiet quasar PDS 456 has showed the presence of a strong and blueshifted absorption trough in the Fe K band above 7 keV, that has been associated with the signature of such a fast and highly ionized accretion disk wind of a velocity of 0.25-0.3c. This persistent and variable feature has been detected in many observations of PDS 456, in particular by XMM-Newton, Suzaku and NuSTAR, together with other blueshifted absorption lines in the soft energy band (e.g. Nardini et al. 2015, Reeves et al. 2016). I will present here the results of the analysis of recent and contemporaneous high-resolution Chandra/HETGS and NuSTAR observations of PDS 456, and compare them with the previous findings.

Photospheric Emission from Stratified Jets

NASA Astrophysics Data System (ADS)

Ito, Hirotaka; Nagataki, Shigehiro; Ono, Masaomi; Lee, Shiu-Hang; Mao, Jirong; Yamada, Shoichi; Pe'er, Asaf; Mizuta, Akira; Harikae, Seiji

2013-11-01

We explore photospheric emissions from stratified two-component jets, wherein a highly relativistic spine outflow is surrounded by a wider and less relativistic sheath outflow. Thermal photons are injected in regions of high optical depth and propagated until the photons escape at the photosphere. Because of the presence of shear in velocity (Lorentz factor) at the boundary of the spine and sheath region, a fraction of the injected photons are accelerated using a Fermi-like acceleration mechanism such that a high-energy power-law tail is formed in the resultant spectrum. We show, in particular, that if a velocity shear with a considerable variance in the bulk Lorentz factor is present, the high-energy part of observed gamma-ray bursts (GRBs) photon spectrum can be explained by this photon acceleration mechanism. We also show that the accelerated photons might also account for the origin of the extra-hard power-law component above the bump of the thermal-like peak seen in some peculiar bursts (e.g., GRB 090510, 090902B, 090926A). We demonstrate that time-integrated spectra can also reproduce the low-energy spectrum of GRBs consistently using a multi-temperature effect when time evolution of the outflow is considered. Last, we show that the empirical E p-L p relation can be explained by differences in the outflow properties of individual sources.

The terrestrial plasma source - A new perspective in solar-terrestrial processes from Dynamics Explorer

NASA Technical Reports Server (NTRS)

Chappell, Charles R.

1988-01-01

The geospace environment has been viewed as a mixing bowl for plasmas of both solar and terrestrial origin. The present perspective on the nature of the supply mechanisms has undergone a radical evolution over the past decade, particularly during the five years of the Dynamics Explorer mission. During this period, the terrestrial source has increased in importance in both magnitude and character of ionospheric outflow. These outflows include the classical polar wind, the cleft ion fountain, the auroral ion fountain, and the polar cap. The earth can be envisioned as a multifaceted fountain which ejects particles from different spatial locations spread around the globe. These particles exhibit a range of masses from 1 to 32 amu and a range of energies from 1 eV to 10 keV. The total flux of this ionospheric outflow is very large: adequate to supply the entire magnetospheric particle population. And the implications of the outflow are significant across a broad spectrum of solar-terrestrial processes ranging from sources of magnetospheric plasmas, to influences on ionospheric density and temperature structure, to energy transfer in phenomena such as stable auroral red arcs. The Dynamics Explorer mission has made a major contribution in the characterization of the terrestrial plasma source.

Quasar Spectral Energy Distributions As A Function Of Physical Property

NASA Astrophysics Data System (ADS)

Townsend, Shonda; Ganguly, R.; Stark, M. A.; Derseweh, J. A.; Richmond, J. M.

2012-05-01

Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). In turn, models of outflows have shown particular sensitivity to the shape of the spectral energy distribution (SED), depending on the UV luminosity to transfer momentum to the gas, the X-ray luminosity to regulate how efficiently that transfer can be, etc. To investigate how SED changes with physical properties, we follow up on Richards et al. (2006), who constructed SEDs with varying luminosity. Here, we construct SEDs as a function of redshift, and physical property (black hole mass, bolometric luminosity, Eddington ratio) for volume limited samples drawn from the Sloan Digital Sky Survey, with photometry supplemented from 2MASS, WISE, GALEX, ROSAT, and Chandra. To estimate black hole masses, we adopt the scaling relations from Greene & Ho (2005) based on the H-alpha emission line FWHM. This requires redshifts less than 0.4. To construct volume-limited subsamples, we begin by adopting g=19.8 as a nominal limiting magnitude over which we are guaranteed to detect z<0.4 quasars. At redshift 0.4, we are complete down to Mg=-21.8, which yields 3300 objects from Data Release 7. At z=0.1, we are complete down to Mg=-18.5. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program.

Mapping and dating based evolution studies of the Niger Vallis outflow channel, Mars

NASA Astrophysics Data System (ADS)

Kukkonen, S.; Kostama, V.-P.

2018-04-01

Niger Vallis is one of the four large outflow channel systems in the eastern Hellas rim region of Mars. Niger, as well as the other nearby valles, is assumed to have been carved by water and later covered by ice-rich deposits. Thus, it plays a significant role both in the fluvial and glacial evolution of the region. This work presents the photogeological mapping and crater count dating results of the Niger Vallis system achieved based on the images of the ConTeXt (CTX) and High Resolution Imaging Science Experiment (HiRISE) cameras of Mars Reconnaissance Orbiter (MRO). The results show that Niger Vallis formed in at least two stages. The southern branch of Niger Vallis originated from Ausonia Cavus, ∼3.7-3.9 Ga ago, whereas the northern branch formed from Peraea Cavus, ∼3.3-3.4 Ga ago. Both of the time scales correspond to the volcanic activity phases of the nearby highland volcanoes of Tyrrhenus and Hadriacus Montes. The fluvial activity of Niger Vallis was not, however, as intense as the activity of the other nearby outflow channels, and it seems to have weakened soon after the formation of the northern branch. The outflow channel was resurfaced again ∼0.9-1.5 Ga ago, probably by regional fluvial activity. After that, the floor of Niger Vallis was covered by lineated valley fills and corresponding ice-rich deposits, the formation of which ended ∼220-470 Ma ago, or not later than ∼110 Ma ago. Although the origin of the deposits was probably related to contemporary climate conditions, the emplacement of some deposits, or even their formation, may have been contributed by impact events. After lineated valley fill formation, the region was resurfaced several times, probably because of changes in regional climatic or endogenic circumstances.

Long-range pollution transport during the MILAGRO-2006 campaign: a case study of a major Mexico City outflow event using free-floating altitude-controlled balloons

NASA Astrophysics Data System (ADS)

Voss, P. B.; Zaveri, R. A.; Flocke, F. M.; Mao, H.; Hartley, T. P.; Deamicis, P.; Deonandan, I.; Contreras-Jiménez, G.; Martínez-Antonio, O.; Figueroa Estrada, M.; Greenberg, D.; Campos, T. L.; Weinheimer, A. J.; Knapp, D. J.; Montzka, D. D.; Crounse, J. D.; Wennberg, P. O.; Apel, E.; Madronich, S.; de Foy, B.

2010-08-01

One of the major objectives of the Megacities Initiative: Local And Global Research Observations (MILAGRO-2006) campaign was to investigate the long-range transport of polluted Mexico City Metropolitan Area (MCMA) outflow and determine its downwind impacts on air quality and climate. Six research aircraft, including the National Center for Atmospheric Research (NCAR) C-130, made extensive chemical, aerosol, and radiation measurements above MCMA and more than 1000 km downwind in order to characterize the evolution of the outflow as it aged and dispersed over the Mesa Alta, Sierra Madre Oriental, Coastal Plain, and Gulf of Mexico. As part of this effort, free-floating Controlled-Meteorological (CMET) balloons, commanded to change altitude via satellite, made repeated profile measurements of winds and state variables within the advecting outflow. In this paper, we present an analysis of the data from two CMET balloons that were launched near Mexico City on the afternoon of 18 March 2006 and floated downwind with the MCMA pollution for nearly 30 h. The repeating profile measurements show the evolving structure of the outflow in considerable detail: its stability and stratification, interaction with other air masses, mixing episodes, and dispersion into the regional background. Air parcel trajectories, computed directly from the balloon wind profiles, show three transport pathways on 18-19 March: (a) high-altitude advection of the top of the MCMA mixed layer, (b) mid-level outflow over the Sierra Madre Oriental followed by decoupling and isolated transport over the Gulf of Mexico, and (c) low-level outflow with entrainment into a cleaner northwesterly jet above the Coastal Plain. The C-130 aircraft intercepted the balloon-based trajectories three times on 19 March, once along each of these pathways; in all three cases, peaks in urban tracer concentrations and LIDAR backscatter are consistent with MCMA pollution. In comparison with the transport models used in the campaign, the balloon-based trajectories appear to shear the outflow far more uniformly and decouple it from the surface, thus forming a thin but expansive polluted layer over the Gulf of Mexico that is well aligned with the aircraft observations. These results provide critical context for the extensive aircraft measurements made during the 18-19 March MCMA outflow event and may have broader implications for modelling and understanding long-range transport.

EVLA Observation of Centimeter Continuum Emission from Protostars in Serpens South

NASA Astrophysics Data System (ADS)

Kern, Nicholas S.; Tobin, John J.; Keown, Jared A.; Gutermuth, Robert A.

2015-01-01

Serpens South is a protocluster with an unusually high abundance of Class 0 and I protostars, suggesting it is in a very early phase of star formation and may eventually form a star cluster. Following its discovery in 2008 with the Spitzer space telescope, infrared and millimeter observations and analysis quickly followed, however, Serpens South has yet to be fully explored in the radio. Radio observations at centimeter wavelengths have long been used as a tool to probe the dynamical processes of young protostars that are still heavily shrouded in their protostellar envelopes and thus cannot be seen at longer wavelengths. Radio observations then become an important tool in understanding Serpens South due to its young age. To this end, we have conducted EVLA C band continuum observations of the central region of the Serpens South protostellar cluster in order to map the centimeter continuum emission in a region of high Class 0 / I protostellar surface density. We report the detection of centimeter emission corresponding to protostars identified by Spitzer, and to protostars identified but blended by Herschel. We characterize their centimeter emission, and put them in context with previous Spitzer and Herschel infrared and far-infrared observations, as well as IRAM millimeter observations. Additionally, we make an assessment of the protostars' bolometric luminosity, and compare them to the known protostellar 3.6 cm to 6.0 cm luminosity vs. bolometric luminosity relation. With the EVLA, we present a mid-resolution map of centimeter emission from the central region of Serpens South with the highest sensitivity to date, with a beam size of ~5 arcseconds and rms on the order of 15 microJansky.

Revealing H2D+ Depletion and Compact Structure in Starless and Protostellar Cores with ALMA

NASA Astrophysics Data System (ADS)

Friesen, R. K.; Di Francesco, J.; Bourke, T. L.; Caselli, P.; Jørgensen, J. K.; Pineda, J. E.; Wong, M.

2014-12-01

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the submillimeter dust continuum and H2D+ 110-111 emission toward two evolved, potentially protostellar cores within the Ophiuchus molecular cloud, Oph A SM1 and SM1N. The data reveal small-scale condensations within both cores, with mass upper limits of M <~ 0.02 M ⊙ (~20 M Jup). The SM1 condensation is consistent with a nearly symmetric Gaussian source with a width of only 37 AU. The SM1N condensation is elongated and extends 500 AU along its major axis. No evidence for substructure is seen in either source. A Jeans analysis indicates that these sources are unlikely to fragment, suggesting that both will form single stars. H2D+ is only detected toward SM1N, offset from the continuum peak by ~150-200 AU. This offset may be due to either heating from an undetected, young, low-luminosity protostellar source or first hydrostatic core, or HD (and consequently H2D+) depletion in the cold center of the condensation. We propose that SM1 is protostellar and that the condensation detected by ALMA is a warm (T ~ 30-50 K) accretion disk. The less concentrated emission of the SM1N condensation suggests that it is still starless, but we cannot rule out the presence of a low-luminosity source, perhaps surrounded by a pseudodisk. These data observationally reveal the earliest stages of the formation of circumstellar accretion regions and agree with theoretical predictions that disk formation can occur very early in the star formation process, coeval with or just after the formation of a first hydrostatic core or protostar.

Signs of Early-stage Disk Growth Revealed with ALMA

NASA Astrophysics Data System (ADS)

Yen, Hsi-Wei; Koch, Patrick M.; Takakuwa, Shigehisa; Krasnopolsky, Ruben; Ohashi, Nagayoshi; Aso, Yusuke

2017-01-01

We present ALMA 1.3 mm continuum, 12CO, C18O, and SO data for the Class 0 protostars Lupus 3 MMS, IRAS 15398-3559, and IRAS 16253-2429 at resolutions of ˜100 au. By measuring a rotational profile in C18O, a 100 au Keplerian disk around a 0.3 M⊙ protostar is observed in Lupus 3 MMS. No 100 au Keplerian disks are observed in IRAS 15398-3559 and IRAS 16253-2429. Nevertheless, embedded compact (<30 au) continuum components are detected. The C18O emission in IRAS 15398-3559 shows signatures of infall with a constant angular momentum. IRAS 16253-2429 exhibits signatures of infall and rotation, but its rotational profile is unresolved. By fitting the C18O data with our kinematic models, the protostellar masses and the disk radii are inferred to be 0.01 M⊙ and 20 au in IRAS 15398-3559, and 0.03 M⊙ and 6 au in IRAS 16253-2429. By comparing the specific angular momentum profiles from 10,000 au to 100 au in eight Class 0 and I protostars, we find that the evolution of envelope rotation can be described with conventional inside-out collapse models. In comparison with a sample of 18 protostars with known disk radii, our results reveal signs of disk growth, with the disk radius increasing as {{M}* }0.8+/- 0.14 or {t}1.09+/- 0.37 in the Class 0 stage, where M* is the protostellar mass and t is the age. The disk growth rate slows down in the Class I stage. In addition, we find a hint that the mass accretion rate declines as {t}-0.26+/- 0.04 from the Class 0 to the Class I stages.

Tharsis-triggered Flood Inundations of the Lowlands of Mars

NASA Technical Reports Server (NTRS)

Fairen, Alberto G.; Dohm, James M.; Baker, Victor R.; dePablo, Miguel A.

2003-01-01

Throughout the recorded history of Mars, liquid water has distinctly shaped its landscape, including the prominent circum-Chryse and the northwestern slope valleys outflow channel systems [1], and the extremely flat northern plains topography at the distal reaches of these outflow channel systems.Basing on the ideas of episodic greenhouse atmosphere and water stability on the lowlands of Mars [3], a conceptual scheme for water evolution and associated geomorphologic features on the northern plains can be proposed. This model highlights Tharsis-triggered flood inundations and their direct impact on shaping the northern plains, as well as making possible the existence of fossil and/or extant life.Possible biologic evolution throughout the resulting different climatic and hydrologic conditions would account for very distinct metabolic pathways for hypothesized organisms capable of surviving and perhaps evolving in each aqueous environment, those that existed in the dry and cold periods between the flood inundations, and those organisms that could survive both extremes. Terrestrial microbiota, chemolithotrophic and heterotrophic bacteria, provide exciting analogues for such potential extremophile existence in Mars, especially where long-lived, magmatic-driven hydrothermal activity is indicated [14].

Dust, ice and gas in time (DIGIT): Herschel and Spitzer spectro-imaging of SMM3 and SMM4 in Serpens

NASA Astrophysics Data System (ADS)

Dionatos, O.; Jørgensen, J. K.; Green, J. D.; Herczeg, G. J.; Evans, N. J.; Kristensen, L. E.; Lindberg, J. E.; van Dishoeck, E. F.

2013-10-01

Context. Mid- and far-infrared observations of the environment around embedded protostars reveal a plethora of high excitation molecular and atomic emission lines. Different mechanisms for the origin of these lines have been proposed, including shocks induced by protostellar jets and radiation or heating by the embedded protostar of its immediate surroundings. Aims: By studying of the most important molecular and atomic coolants, we aim at constraining the physical conditions around the embedded protostars SMM3 and SMM4 in the Serpens molecular cloud core and measuring the CO/H2 ratio in warm gas. Methods: Spectro-imaging observations from the Spitzer Infrared Spectrograph (IRS) and the Herschel Photodetector Array Camera and Spectrometer (PACS) provide an almost complete wavelength coverage between 5 and 200 μm. Within this range, emission from all major molecular (H2, CO, H2O and OH) and many atomic ([OI], [CII], [FeII], [SiII] and [SI]) coolants of excited gas are detected. Emission line maps reveal the morphology of the observed emission and indicate associations between the different species. The excitation conditions for molecular species are assessed through rotational diagrams. Emission lines from major coolants are compared to the results of steady-state C- and J-type shock models. Results: Line emission tends to peak at distances of ~10-20″ from the protostellar sources with all but [CII] peaking at the positions of outflow shocks seen in near-IR and sub-millimeter interferometric observations. The [CII] emission pattern suggests that it is most likely excited from energetic UV radiation originating from the nearby flat-spectrum source SMM6. Excitation analysis indicates that H2 and CO originate in gas at two distinct rotational temperatures of ~300 K and 1000 K, while the excitation temperature for H2O and OH is ~100-200 K. The morphological and physical association between CO and H2 suggests a common excitation mechanism, which allows direct comparisons between the two molecules. The CO/H2 abundance ratio varies from ~10-5 in the warmer gas up to ~10-4 in the hotter regions. Shock models indicate that C-shocks can account for the observed line intensities if a beam filling factor and a temperature stratification in the shock front are considered. C-type shocks can best explain the emission from H2O. The existence of J-shocks is suggested by the strong atomic/ionic (except for [CII]) emission and a number of line ratio diagnostics. Dissociative shocks can account for the CO and H2 emission in a single excitation temperature structure. Conclusions: The bulk of cooling from molecular and atomic lines is associated with gas excited in outflow shocks. The strong association between H2 and CO constrain their abundance ratio in warm gas. Both C- and J-type shocks can account for the observed molecular emission; however, J-shocks are strongly suggested by the atomic emission and provide simpler and more homogeneous solutions for CO and H2. The variations in the CO/H2 abundance ratio for gas at different temperatures can be interpreted by their reformation rates in dissociative J-type shocks, or the influence of both C and J shocks. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices A-C are available in electronic form at http://www.aanda.org

The Metallicity Evolution of Low-mass Galaxies: New Constraints at Intermediate Redshift

NASA Astrophysics Data System (ADS)

Henry, Alaina; Martin, Crystal L.; Finlator, Kristian; Dressler, Alan

2013-06-01

We present abundance measurements from 26 emission-line-selected galaxies at z ~ 0.6-0.7. By reaching stellar masses as low as 108 M ⊙, these observations provide the first measurement of the intermediate-redshift mass-metallicity (MZ) relation below 109 M ⊙. For the portion of our sample above M > 109 M ⊙ (8/26 galaxies), we find good agreement with previous measurements of the intermediate-redshift MZ relation. Compared to the local relation, we measure an evolution that corresponds to a 0.12 dex decrease in oxygen abundances at intermediate redshifts. This result confirms the trend that metallicity evolution becomes more significant toward lower stellar masses, in keeping with a downsizing scenario where low-mass galaxies evolve onto the local MZ relation at later cosmic times. We show that these galaxies follow the local fundamental metallicity relation, where objects with higher specific (mass-normalized) star formation rates (SFRs) have lower metallicities. Furthermore, we show that the galaxies in our sample lie on an extrapolation of the SFR-M * relation (the star-forming main sequence). Leveraging the MZ relation and star-forming main sequence (and combining our data with higher-mass measurements from the literature), we test models that assume an equilibrium between mass inflow, outflow, and star formation. We find that outflows are required to describe the data. By comparing different outflow prescriptions, we show that momentum, driven winds can describe the MZ relation; however, this model underpredicts the amount of star formation in low-mass galaxies. This disagreement may indicate that preventive feedback from gas heating has been overestimated, or it may signify a more fundamental deviation from the equilibrium assumption. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

VizieR Online Data Catalog: Young clumps embedded in IRDC (Traficante+, 2015)

NASA Astrophysics Data System (ADS)

Traficante, A.; Fuller, G. A.; Peretto, N.; Pineda, J. E.; Molinari, S.

2015-06-01

Photometric parameters for 667 starless clumps (sources identified at 160um with a counterpart at 250 and 350um) and 1056 protostellar clumps (sources identified at 160um with a counterpart at 70, 250 and 350um). Photometric parameters obtained with Hyper photometry code (2015A&A...574A.119T). The photometry is corrected for aperture and colour corrections. The parameter list is the standard Hyper output (see description below). SED fit parameters for 650 starless clumps and 1034 protostellar clumps (all clumps with good SED fitting: Chi2<10, Temperature<40K. See the paper for details) (4 data files).

Brine evolution and mineral deposition in hydrologically open evaporite basins

USGS Publications Warehouse

Sanford, W.E.; Wood, W.W.

1991-01-01

A lumped-parameter, solute mass-balance model is developed to define the role of water outflow from a well-mixed basin. A mass-balance model is analyzed with a geochemical model designed for waters with high ionic strengths. Two typical waters, seawater and a Na-HCO3 ground water, are analyzed to illustrate the control that the leakage ratio (or hydrologic openness of the basin) has on brine evolution and the suite and thicknesses of evaporite minerals deposited. The analysis suggests that brines evolve differently under different leakage conditions. -from Authors

Knotty protostellar jets as a signature of episodic protostellar accretion?

NASA Astrophysics Data System (ADS)

Vorobyov, Eduard I.; Elbakyan, Vardan G.; Plunkett, Adele L.; Dunham, Michael M.; Audard, Marc; Guedel, Manuel; Dionatos, Odysseas

2018-05-01

Aims: We aim to study the causal link between the knotty jet structure in CARMA 7, a young Class 0 protostar in the Serpens South cluster, and episodic accretion in young protostellar disks. Methods: We used numerical hydrodynamics simulations to derive the protostellar accretion history in gravitationally unstable disks around solar-mass protostars. We compared the time spacing between luminosity bursts Δτmod, caused by dense clumps spiralling on the protostar, with the differences of dynamical timescales between the knots Δτobs in CARMA 7. Results: We found that the time spacing between the bursts have a bi-modal distribution caused by isolated and clustered luminosity bursts. The former are characterized by long quiescent periods between the bursts with Δτmod = a few × (103-104) yr, whereas the latter occur in small groups with time spacing between the bursts Δτmod = a few × (10-102) yr. For the clustered bursts, the distribution of Δτmod in our models can be fit reasonably well to the distribution of Δτobs in the protostellar jet of CARMA 7, if a certain correction for the (yet unknown) inclination angle with respect to the line of sight is applied. The Kolmogorov-Smirnov test on the model and observational data sets suggests the best-fit values for the inclination angles of 55-80°, which become narrower (75-80°) if only strong luminosity bursts are considered. The dynamical timescales of the knots in the jet of CARMA 7 are too short for a meaningful comparison with the long time spacings between isolated bursts in our models. Moreover, the exact sequences of time spacings between the luminosity bursts in our models and knots in the jet of CARMA 7 were found difficult to match. Conclusions: Given the short time that has passed since the presumed luminosity bursts (tens to hundreds years), a possible overabundance of the gas-phase CO in the envelope of CARMA 7 compared to what could be expected from the current luminosity may be used to confirm the burst nature of this object. More sophisticated numerical models and observational data on jets with longer dynamical timescales are needed to further explore the possible causal link between luminosity bursts and knotty jets.

On the effect of galactic outflows in cosmological simulations of disc galaxies

NASA Astrophysics Data System (ADS)

Valentini, Milena; Murante, Giuseppe; Borgani, Stefano; Monaco, Pierluigi; Bressan, Alessandro; Beck, Alexander M.

2017-09-01

We investigate the impact of galactic outflow modelling on the formation and evolution of a disc galaxy, by performing a suite of cosmological simulations with zoomed-in initial conditions (ICs) of a Milky Way-sized halo. We verify how sensitive the general properties of the simulated galaxy are to the way in which stellar feedback triggered outflows are implemented, keeping ICs, simulation code and star formation (SF) model all fixed. We present simulations that are based on a version of the gadget3 code where our sub-resolution model is coupled with an advanced implementation of smoothed particle hydrodynamics that ensures a more accurate fluid sampling and an improved description of gas mixing and hydrodynamical instabilities. We quantify the strong interplay between the adopted hydrodynamic scheme and the sub-resolution model describing SF and feedback. We consider four different galactic outflow models, including the one introduced by Dalla Vecchia & Schaye (2012) and a scheme that is inspired by the Springel & Hernquist (2003) model. We find that the sub-resolution prescriptions adopted to generate galactic outflows are the main shaping factor of the stellar disc component at low redshift. The key requirement that a feedback model must have to be successful in producing a disc-dominated galaxy is the ability to regulate the high-redshift SF (responsible for the formation of the bulge component), the cosmological infall of gas from the large-scale environment, and gas fall-back within the galactic radius at low redshift, in order to avoid a too high SF rate at z = 0.

GBT Detection of Polarization-Dependent HI Absorption and HI Outflows in Local ULIRGs and Quasars

NASA Technical Reports Server (NTRS)

Teng, Stacy H.; Veilleux, Sylvain; Baker, Andrew J.

2013-01-01

We present the results of a 21-cm HI survey of 27 local massive gas-rich late-stage mergers and merger remnants with the Green Bank Telescope (GBT). These remnants were selected from the Quasar/ULIRG Evolution Study (QUEST) sample of ultraluminous infrared galaxies (ULIRGs; L(sub 8 - 1000 micron) > 10(exp 12) solar L) and quasars; our targets are all bolometrically dominated by active galactic nuclei (AGN) and sample the later phases of the proposed ULIRG-to-quasar evolutionary sequence. We find the prevalence of HI absorption (emission) to be 100% (29%) in ULIRGs with HI detections, 100% (88%) in FIR-strong quasars, and 63% (100%) in FIR-weak quasars. The absorption features are associated with powerful neutral outflows that change from being mainly driven by star formation in ULIRGs to being driven by the AGN in the quasars. These outflows have velocities that exceed 1500 km/s in some cases. Unexpectedly, we find polarization-dependent HI absorption in 57% of our spectra (88% and 63% of the FIR-strong and FIR-weak quasars, respectively). We attribute this result to absorption of polarized continuum emission from these sources by foreground HI clouds. About 60% of the quasars displaying polarized spectra are radio-loud, far higher than the approx 10% observed in the general AGN population. This discrepancy suggests that radio jets play an important role in shaping the environments in these galaxies. These systems may represent a transition phase in the evolution of gas-rich mergers into "mature" radio galaxies.

Temporal changes in the geographic distribution, elevation, and potential origin of the Martian outflow channels

NASA Technical Reports Server (NTRS)

Tribe, S.; Clifford, S. M.

1993-01-01

Observational evidence of outflow channel activity on Mars suggests that water was abundant in the planet's early crust. However, with the decline in the planet's internal heat flow, a freezing front developed within the regolith that propagated downward with time and acted as a thermodynamic sink for crustal H2O. One result of this thermal evolution is that, if the initial inventory of water on Mars was small, the cryosphere may have grown to the point where all the available water was taken up as ground ice. Alternatively, if the inventory of H2O exceeds the current pore volume of the cryosphere, then Mars has always possessed extensive bodies of subpermafrost groundwater. We have investigated the relative age, geographic distribution, elevation, and geologic setting of the outflow channels in an effort to accomplish the following: (1) identify possible modes of origin and evolutionary trends in their formation; (2) gain evidence regarding the duration and spatial distribution of groundwater in the crust; and (3) better constraint estimates of the planetary inventory of H2O.

A Panchromatic View of Star-Forming Regions in the Magellanic Clouds: Characterizing Physical and Evolutionary Parameters of 1,000 Young Stellar Objects

NASA Astrophysics Data System (ADS)

Carlson, Lynn R.

2010-01-01

I discuss newly discovered Young Stellar Objects (YSOs) in several star-forming regions in the Magellanic Clouds. I exploit the synergy between infrared photometry from the Spitzer SAGE (Surveying the Agents of Galaxy Evolution) legacy programs, near-infrared and optical photometry from ground-based surveys, and HST imaging to characterize young stellar populations. This reveals a variety of Main Sequence Stars and Proto-Stars over a wide range of evolutionary stages. Through SED fitting, I characterize the youngest, embedded, infrared-bright YSOs. Complementary color-Magnitude analysis and isochrone fitting of optical data allows a statistical description of more evolved, unembedded stellar and protostellar populations within these same regions. I examine the early evolution of Magellanic star clusters, including propagating and triggered star formation, and take a step toward characterizing evolutionary timescales for YSOs. In this talk, I present an overview of the project and exemplify the analysis by focusing on NGC 602 in the SMC and Henize 206 in the LMC as examples. The SAGE Project is supported by NASA/Spitzer grant 1275598 and NASA NAG5-12595.

The X-ray evolution of inflows and outflows in active galactic nuclei

NASA Astrophysics Data System (ADS)

Saez, Cristian

The evolution of the space density of AGNs might have spectral counterparts which could be observable in X-rays. The main objective of this thesis is to study the spectral properties of AGNs in X-rays in order to increase our current knowledge of AGN evolution. In chapter 2, we present results from a statistical analysis of 173 bright radio-quiet AGNs selected from the Chandra Deep Field-North and Chandra Deep Field-South surveys (hereafter, CDFs) in the redshift range of 0.1 ≲z≲ 4. We find that the X-ray power-law photon index (Gamma) of radio-quiet AGNs is correlated with their 2--10 keV rest-frame X-ray luminosity ( LX) at the > 99.5% confidence level in two redshift bins, 0.3 ≲z≲ 0.96, and 1.5 ≲z≲ 3.3 and is slightly less significant in the redshift bin 0.96 ≲z≲ 1.5. The X-ray spectral slope steepens as the X-ray luminosity increases for AGNs in the luminosity range 1042 to 1045 erg s-1. Combining our results from the CDFs with those from previous studies in the redshift range 1.5 ≲z≲ 3.3, we find that the Gamma -- L X correlation has a null-hypothesis probability of 1.6 x 10 -9. We investigate the redshift evolution of the correlation between the power-law photon index and the hard X-ray luminosity and find that the slope and offset of a linear fit to the correlation change significantly (at the > 99.9% confidence level) between redshift bins of 0.3 ≲z≲ 0.96 and 1.5 ≲z≲ 3.3. We explore physical scenarios explaining the origin of this correlation and its possible evolution with redshift in the context of steady corona models focusing on its dependency on variations of the properties of the hot corona with redshift. In chapter 3, we present results from three Suzaku observations of the z = 3.91 gravitationally lensed broad absorption line quasar APM 08279+5255. We detect strong and broad absorption at rest-frame energies of ≲ 2 keV (low-energy) and 7--12 keV (high-energy). The detection of these features confirms the results of previous long-exposure (80--90 ks) Chandra and XMM-Newton observations. The low and high-energy absorption is detected in both the back-illuminated (BI) and front-illuminated (FI) Suzaku XIS spectra (with an F-test significance of ≳ 99%). We interpret the low-energy absorption as arising from a low-ionization absorber with log (NH/cm-2) ˜ 23 and the high-energy absorption as due to lines arising from highly ionized (2.75 ≲ log xi ≲ 4.0; where xi is the ionization parameter) iron in a near-relativistic outflowing wind. Assuming this interpretation we find that the velocities in the outflow range between 0.1c and 0.6c. We constrain the angle between the outflow direction of the X-ray absorber and our line of sight to be ≲ 36°. We also detect likely variability of the absorption lines (at the ≳ 99.9% and ≳ 98% significance levels in the FI and BI spectra, respectively) with a rest-frame time scale of ˜1 month. Assuming that the detected high-energy absorption features arise from Fe XXV, we estimate that the fraction of the total bolometric energy injected over the quasar's lifetime into the intergalactic medium in the form of kinetic energy to be ≳ 10%. In chapter 4, we present an expansion of our previous work on the study of X-ray outflows on APM 08279+5255. The main conclusions from our multi-epoch spectral analysis of Chandra, XMM-Newton and Suzaku observations of the z = 3.91 gravitationally lensed broad absorption line (BAL) quasar APM 08279+5255 are: (1) In every observation we confirm the presence of two strong features, one at rest-frame energies between 1--4 keV, and the other between 7--18 keV. (2) The low-energy absorption is interpreted as arising (1--4 keV rest-frame) from a low-ionization absorber with log (N H/cm-2) ˜ 23 and the high-energy absorption (7--18 keV rest-frame) as due to lines arising from highly ionized (3 ≲ log xi ≲ 4; where xi is the ionization parameter) iron in a near-relativistic outflowing wind. Assuming this interpretation, we find that the velocities on the outflow could get up to ˜ 0.7c. We also present results obtained from fits to all the long exposure observations of APM 08279+5255 with a new outflow model. (Abstract shortened by UMI.)

The Bright Gamma-Ray Burst 991208: Tight Constraints on Afterglow Models from Observations of the Early-Time Radio Evolution

NASA Astrophysics Data System (ADS)

Galama, T. J.; Bremer, M.; Bertoldi, F.; Menten, K. M.; Lisenfeld, U.; Shepherd, D. S.; Mason, B.; Walter, F.; Pooley, G. G.; Frail, D. A.; Sari, R.; Kulkarni, S. R.; Berger, E.; Bloom, J. S.; Castro-Tirado, A. J.; Granot, J.

2000-10-01

The millimeter wavelength emission from GRB 991208 is the second brightest ever detected, yielding a unique data set. We present here well-sampled spectra and light curves over more than two decades in frequency for a 2 week period. This data set has allowed us for the first time to trace the evolution of the characteristic synchrotron self-absorption frequency νa, peak frequency νm, and the peak flux density Fm; we obtain νa~t-0.15+/-0.23, νm~t-1.7+/-0.7, and Fm~t-0.47+/-0.20. From the radio data we find that models of homogeneous or wind-generated ambient media with a spherically symmetric outflow can be ruled out. A model in which the relativistic outflow is collimated (a jet) can account for the observed evolution of the synchrotron parameters, the rapid decay at optical wavelengths, and the observed radio-to-optical spectral flux distributions that we present here, provided that the jet transition has not been fully completed in the first 2 weeks after the event. These observations provide additional evidence that rapidly decaying optical/X-ray afterglows are due to jets and that such transitions either develop very slowly or perhaps never reach the predicted asymptotic decay F(t)~t-p.

The formation of stellar systems from interstellar molecular clouds.

PubMed

Gehrz, R D; Black, D C; Solomon, P M

1984-05-25

Star formation, a crucial link in the chain of events that led from the early expansion of the universe to the formation of the solar system, continues to play a major role in the evolution of many galaxies. Observational and theoretical studies of regions of ongoing star formation provide insight into the physical conditions and events that must have attended the formation of the solar system. Such investigations also elucidate the role played by star formation in the evolutionary cycle which appears to dominate the chemical processing of interstellar material by successive generations of stars in spiral galaxies like our own. New astronomical facilities planned for development during the 1980's could lead to significant advances in our understanding of the star formation process. Efforts to identify and examine both the elusive protostellar collapse phase of star formation and planetary systems around nearby stars will be especially significant.

TWO-STAGE FRAGMENTATION FOR CLUSTER FORMATION: ANALYTICAL MODEL AND OBSERVATIONAL CONSIDERATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bailey, Nicole D.; Basu, Shantanu, E-mail: nwityk@uwo.ca, E-mail: basu@uwo.ca

2012-12-10

Linear analysis of the formation of protostellar cores in planar magnetic interstellar clouds shows that molecular clouds exhibit a preferred length scale for collapse that depends on the mass-to-flux ratio and neutral-ion collision time within the cloud. We extend this linear analysis to the context of clustered star formation. By combining the results of the linear analysis with a realistic ionization profile for the cloud, we find that a molecular cloud may evolve through two fragmentation events in the evolution toward the formation of stars. Our model suggests that the initial fragmentation into clumps occurs for a transcritical cloud onmore » parsec scales while the second fragmentation can occur for transcritical and supercritical cores on subparsec scales. Comparison of our results with several star-forming regions (Perseus, Taurus, Pipe Nebula) shows support for a two-stage fragmentation model.« less

Dust Coagulation in Protoplanetary Accretion Disks

NASA Technical Reports Server (NTRS)

Schmitt, W.; Henning, Th.; Mucha, R.

1996-01-01

The time evolution of dust particles in circumstellar disk-like structures around protostars and young stellar objects is discussed. In particular, we consider the coagulation of grains due to collisional aggregation. The coagulation of the particles is calculated by solving numerically the non-linear Smoluchowski equation. The different physical processes leading to relative velocities between the grains are investigated. The relative velocities may be induced by Brownian motion, turbulence and drift motion. Starting from different regimes which can be identified during the grain growth we also discuss the evolution of dust opacities. These opacities are important for both the derivation of the circumstellar dust mass from submillimeter/millimeter continuum observations and the dynamical behavior of the disks. We present results of our numerical studies of the coagulation of dust grains in a turbulent protoplanetary accretion disk described by a time-dependent one-dimensional (radial) alpha-model. For several periods and disk radii, mass distributions of coagulated grains have been calculated. From these mass spectra, we determined the corresponding Rosseland mean dust opacities. The influence of grain opacity changes due to dust coagulation on the dynamical evolution of a protostellar disk is considered. Significant changes in the thermal structure of the protoplanetary nebula are observed. A 'gap' in the accretion disk forms at the very frontier of the coagulation, i.e., behind the sublimation boundary in the region between 1 and 5 AU.

Physical and Chemical Properties of Protocluster Clumps and Massive Young Stellar Objects Associated to Infrared Dark Clouds

NASA Astrophysics Data System (ADS)

Gomez Gonzalez, Laura

2012-01-01

The study of high-mass stars is important not only because of the effects they produce in their environment through outflows, expanding HII regions, stellar winds, and eventually supernova shock waves, but also because they play a crucial role in estimating star formation rates in other galaxies. Although we have an accepted evolutionary scenario that explains (isolated) low-mass star formation, the processes that produce massive stars (M_star > 8 M_sol) and star clusters, especially their earliest stages, are not well understood. The newly discovered class of interstellar clouds now termed infrared dark clouds (IRDCs) represent excellent laboratories to study the earliest stages of high-mass star formation given that some of the clumps within them are known to have high masses (~100's M_sol), high densities (n > 10^5 cm^-3), and low temperatures (10-20K) as expected for the birthplaces of high-mass stars. Some questions remain unanswered: Do IRDCs harbor the very early stages of high-mass star formation, i.e., the pre-protocluster phase? If so, how do they compare with low-mass star formation sites? Is there chemical differentiation in IRDC clumps? What is the mass distribution of IRDCs? In this dissertation and for the first time, a catalog of 12529 IRDC candidates at 24 um has been created using archival data from the MIPSGAL/Spitzer survey, as a first step in searching for the massive pre-protocluster clumps. From this catalog, a sample of ~60 clumps has been selected in order to perform single-pointing observations with the IRAM 30m, Effelsberg 100m, and APEX 12m telescopes. One IRDC clump seems to be a promising candidate for being in the pre-protocluster phase. In addition, molecular line mapping observations have been performed on three clumps within IRDCs and a detailed chemical study of 10 molecular lines has been carried out. A larger difference in column densities and abundances has been found between these clumps and high-m! ass protostellar objects than between these clumps and low-mass pre-stellar cores and protostellar objects. A non-LTE Monte Carlo code was used to model the N_2H^+ (1-0) and (3-2) lines in order to constrain the physical properties of two clumps. Six IRDC complexes have been mapped in the 870 um dust continuum emission with the LABOCA instrument on the APEX 12m telescope. Line observations have been carried out in order to obtain temperature and kinematic distances of selected clumps. Physical properties such as masses, effective radii, and column densities have been obtained. The mass spectrum of these clumps has been fitted with a power-law whose best-fitting index is alpha =-1.60. This value is consistent with the CO clump mass function reported in the literature. A relation between the dust emission at 870 um and the degree of extinction (contrast) at 24 um has been obtained by combining dust emission observations and extinction studies. A study with the Plateau de Bure Interferometer of a core in an archetypal filamentary IRDC at few arcsecond resolution has been carried out to determine its physical and chemical structure. Extended 4.5 um emission, "wings" in the CH_3OH 2_k -> 1_k spectra, and a CH_3OH abundance enhancement provide evidence of an outflow in the East-West direction. In addition, a gradient of ~4 km/s in the same direction has been found, which is interpreted as being produced by an outflow(s)-cloud interaction. Finally, Very Large Array interferometric observations of the 7_0-6_1 A^+ (class I) methanol maser transition at 44 GHz toward three high-mass star-forming regions have been carried out in order to provide accurate maser positions and parameters. For all three sources, the masers were well-separated from the HII region, with projected distances ranging from 0.1 to 0.3 pc.

Ultrafast outflows disappear in high-radiation fields

NASA Astrophysics Data System (ADS)

Pinto, C.; Alston, W.; Parker, M. L.; Fabian, A. C.; Gallo, L. C.; Buisson, D. J. K.; Walton, D. J.; Kara, E.; Jiang, J.; Lohfink, A.; Reynolds, C. S.

2018-05-01

Ultrafast outflows (UFOs) are the most extreme winds launched by active galactic nuclei (AGN) due to their mildly relativistic speeds (˜0.1-0.3c) and are thought to significantly contribute to galactic evolution via AGN feedback. Their nature and launching mechanism are however not well understood. Recently, we have discovered the presence of a variable UFO in the narrow-line Seyfert 1 IRAS 13224-3809. The UFO varies in response to the brightness of the source. In this work we perform flux-resolved X-ray spectroscopy to study the variability of the UFO and found that the ionization parameter is correlated with the luminosity. In the brightest states the gas is almost completely ionized by the powerful radiation field and the UFO is hardly detected. This agrees with our recent results obtained with principal component analysis. We might have found the tip of the iceberg: the high ionization of the outflowing gas may explain why it is commonly difficult to detect UFOs in AGN and possibly suggest that we may underestimate their actual feedback. We have also found a tentative correlation between the outflow velocity and the luminosity, which is expected from theoretical predictions of radiation-pressure-driven winds. This trend is rather marginal due to the Fe XXV-XXVI degeneracy. Further work is needed to break such degeneracy through time-resolved spectroscopy.

Discovery of an Outflow from Radio Observations of the Tidal Disruption Event ASASSN-14li

NASA Astrophysics Data System (ADS)

Alexander, K. D.; Berger, E.; Guillochon, J.; Zauderer, B. A.; Williams, P. K. G.

2016-03-01

We report the discovery of transient radio emission from the nearby optically discovered tidal disruption event (TDE) ASASSN-14li (distance of 90 Mpc), making it the first typical TDE detected in the radio, and unambiguously pointing to the formation of a non-relativistic outflow with a kinetic energy of ≈(4-10) × 1047 erg, a velocity of ≈12,000-36,000 km s-1, and a mass of ≈3 × 10-5-7 × 10-4 M⊙. We show that the outflow was ejected on 2014 August 11-25, in agreement with an independent estimate of the timing of super-Eddington accretion based on the optical, ultraviolet, and X-ray observations, and that the ejected mass corresponds to about 1%-10% of the mass accreted in the super-Eddington phase. The temporal evolution of the radio emission also uncovers the circumnuclear density profile, ρ (R)\\propto {R}-2.5 on a scale of about 0.01 pc, a scale that cannot be probed via direct measurements even in the nearest supermassive black holes. Our discovery of radio emission from the nearest well-studied TDE to date, with a radio luminosity lower than all previous limits, indicates that non-relativistic outflows are ubiquitous in TDEs, and that future, more sensitive, radio surveys will uncover similar events.

Constraining Engine Paradigms of Pre-Planetary Nebulae Using Kinematic Properties of their Outflows

NASA Astrophysics Data System (ADS)

Blackman, E.

2014-04-01

Binary interactions and accretion plausibly conspire to produce the ubiquitous collimated outflows from planetary nebulae (PN) and their presumed pre-planetary nebulae (PPN) progenitors. But which accretion engines are viable? The difficulty in observationally resolving the engines warrants indirect constraints. I discuss how momentum outflow data for PPN can be used to determine the minimum required accretion rate for presumed main sequence (MS) or white dwarf (WD) accretors by comparing to several example accretion rates inferred from published models. While the main goal is to show the method in anticipation of more data and better theoretical constraints, taking the present results at face value already rule out modes of accretion: Bondi-Hoyle Lyttleton (BHL) wind accretion and wind Roche lobe overflow (M-WRLOF, based on Mira parameters) are too feeble for all 19/19 objects for a MS accretor. For a WD accretor, BHL is ruled out for 18/19 objects and M-WRLOF for 15/19 objects. Roche lobe overflow from the primary can accommodate 7/19 objects but only common envelope evolution accretion modes seem to be able to accommodate all 19 objects. Sub-Eddington rates for a MS accretor are acceptable but 8/19 would require super-Eddington rates for a WD. I also briefly discuss a possible anti-correlation between age and maximum observed outflow speed, and the role of magnetic fields.

Gas Flows in Dual Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Mueller Sanchez, Francisco; Comerford, Julia M.; Davies, Richard; Treister, Ezequiel; Privon, George C.; Nevin, Becky

2018-06-01

Dual Active Galactic Nuclei (AGN) are the Rosetta stone to understand the role of galaxy mergers in triggering nuclear activity and regulating black hole (BH) and galaxy growth. But very little is known about the physical processes required to effectively trigger AGN activity and regulate the growth of the two BHs. The work I will present here characterizes for the first time the properties of the stars, gas (molecular, ionized, and highly-ionized) and dust in all the confirmed dual AGN at z < 0.05, using Keck/OSIRIS, VLT/SINFONI, SOFIA/FORCAST, and HST data. I will focus on the interplay between the several complex processes observed in dual AGN, using as an example the prototypical merger system NGC 6240: vigorous star formation, two AGNs, outflowing winds of ionized gas, rippling dust and gas lanes, and tidal tails. In this galaxy, we observe for the first time a dual outflow of different species of gas: an AGN-driven outflow of highly-ionized gas to the northeast and a starburst-driven outflow of ionized hydrogen to the northwest. This shows that stellar feedback and supermassive black hole feedback can work in tandem to regulate the stellar growth of a galaxy after a merger event. These results open a new door to studies of dual AGN and AGN pairs in general, and enable dual AGN to be used, for the first time, for studies of galaxy evolution.

The Gaseous Environments of Quasars: Outflows, Feedback & Cold Mode Accretion

NASA Astrophysics Data System (ADS)

Chen, Chen; Hamann, Fred

2018-06-01

The early stages of massive galaxy evolution can involve galaxy-scale outflows driven by a starburst or a central quasar and cold-mode accretion (infall) that adds to the mass buildup in the galaxies. I will describe three related studies that use quasar absorption lines to measure outflows, infall, and the general gaseous environments of quasars across a range of spatial scales. The three studies are: 1) High-resolution spectroscopy with Keck-HIRES and VLT-UVES to study associated absorption lines (AALs) that have redshifts greater than the emission redshifts indicating infall and/or rich multi-component AAL complexes that might be interstellar clouds in the host galaxies that have been shredded and dispersed by a fast unseen quasar-driven wind. The data provide strong constraints on the gas kinematics, spatial structure, column densities, metallicities, and energetics. 2) A complete inventory of high-velocity CIV 1548,1550 mini-BAL outflows in quasars using high-resolution high signal-to-noise spectra in the public VLT-UVES and Keck-HIRES archives. This sensitive mini-BAL survey fills an important niche between previous work on narrow absorption lines (NALs) and the much-studied broad absorption lines (BALs) to build a more complete picture of quasar outflows. I will report of the mini-BAL statistics, the diversity of lines detected, and some tests for correlations with the quasar properties. We find, for example, that mini-BALs at v > 4000 km/s in at least 10% of 511 quasars studied, including 1% at v > 0.1 c. Finally, 3) Use the much larger database of NALs measured in 262,449 BOSS quasars by York et al. (in prep.) to study their potential relationships to the quasars and, specifically, their origins in quasar outflows. This involves primarily comparisons of the incidence and properties of NALs at different velocity shifts to other measured properties of the quasars such as BAL outflows, emission line characteristics, radio-loudness, and red colors. We find, for example, that the extreme high-velocity NALs (0.1 ‑ 0.2c) correlate strongly with AALs, indicating that a significant fraction of these NALs is ejected from the quasars.

Inter-annual variability and long term predictability of exchanges through the Strait of Gibraltar

NASA Astrophysics Data System (ADS)

Boutov, Dmitri; Peliz, Álvaro; Miranda, Pedro M. A.; Soares, Pedro M. M.; Cardoso, Rita M.; Prieto, Laura; Ruiz, Javier; García-Lafuente, Jesus

2014-03-01

Inter-annual variability of calculated barotropic (netflow) and simulated baroclinic (inflow and outflow) exchanges through the Strait of Gibraltar is analyzed and their response to the main modes of atmospheric variability is investigated. Time series of the outflow obtained by high resolution simulations and estimated from in-situ Acoustic Doppler Current Profiler (ADCP) current measurements are compared. The time coefficients (TC) of the leading empirical orthogonal function (EOF) modes that describe zonal atmospheric circulation in the vicinity of the Strait (1st and 3rd of Sea-Level Pressure (SLP) and 1st of the wind) show significant covariance with the inflow and outflow. Based on these analyses, a regression model between these SLP TCs and outflow of the Mediterranean Water was developed. This regression outflow time series was compared with estimates based on current meter observations and the predictability and reconstruction of past exchange variability based on atmospheric pressure fields are discussed. The simple regression model seems to reproduce the outflow evolution fairly reasonably, with the exception of the year 2008, which is apparently anomalous without available physical explanation yet. The exchange time series show a reduced inter-annual variability (less than 1%, 2.6% and 3.1% of total 2-day variability, for netflow, inflow and outflow, respectively). From a statistical point of view no clear long-term tendencies were revealed. Anomalously high baroclinic fluxes are reported for the years of 2000-2001 that are coincident with strong impact on the Alboran Sea ecosystem. The origin of the anomalous flow is associated with a strong negative anomaly (~ - 9 hPa) in atmospheric pressure fields settled north of Iberian Peninsula and extending over the central Atlantic, favoring an increased zonal circulation in winter 2000/2001. These low pressure fields forced intense and durable westerly winds in the Gulf of Cadiz-Alboran system. The signal of this anomaly is also seen in time coefficients of the most significant EOF modes. The predictability of the exchanges for future climate is discussed.

Long-range pollution transport during the MILAGRO-2006 campaign: a case study of a major Mexico City outflow event using free-floating altitude-controlled balloons

NASA Astrophysics Data System (ADS)

Voss, P. B.; Zaveri, R. A.; Flocke, F. M.; Mao, H.; Hartley, T. P.; Deamicis, P.; Deonandan, I.; Contreras-Jiménez, G.; Martínez-Antonio, O.; Figueroa Estrada, M.; Greenberg, D.; Campos, T. L.; Weinheimer, A. J.; Knapp, D. J.; Montzka, D. D.; Crounse, J. D.; Wennberg, P. O.; Apel, E.; Madronich, S.; de Foy, B.

2010-02-01

One of the major objectives of the Megacities Initiative: Local And Global Research Observations (MILAGRO-2006) campaign was to investigate the long-range transport of polluted Mexico City Metropolitan Area (MCMA) outflow and determine its downwind impacts on air quality and climate. Six research aircraft, including the National Center for Atmospheric Research (NCAR) C-130, made extensive chemical, aerosol, and radiation measurements above MCMA and more than 1000 km downwind in order to characterize the evolution of the outflow as it aged and dispersed over the Mesa Alta and Gulf of Mexico. As part of this effort, free-floating Controlled-Meteorological (CMET) balloons, commanded to change altitude via satellite, made repeated profile measurements of winds and state variables within the advecting outflow. In this paper, we present an analysis based on the data from two CMET balloons that were launched near Mexico City on the afternoon of 18 March 2006 and floated downwind with the MCMA pollution for nearly 30 h. The repeating profile measurements show the evolving structure of the outflow in considerable detail: its stability and stratification, interaction with other air masses, mixing episodes, and dispersion into the regional background. Air parcel trajectories, computed directly from the balloon wind profiles, show three different transport pathways on 18-19 March: (a) high-altitude advection of the top of the MCMA mixed layer, (b) mid-level outflow over the Sierra Madre Oriental followed by decoupling and isolated transport over the Gulf, and (c) low-altitude outflow with entrainment into a cleaner westerly jet below the plateau. The C-130 aircraft intercepted the balloon-based trajectories three times on 19 March, once along each of these pathways. In all three cases, distinct peaks in the urban tracer signatures and LIDAR backscatter imagery were consistent with MCMA pollution. The coherence of the high-altitude outflow was well preserved after one day whereas that lower in the atmosphere was more widely dispersed over the same time period. Other C-130 intercepts of polluted air are shown to have likely originated outside of MCMA. These findings, and the aircraft intercepts in particular, should prove useful in answering a range of scientific questions pertaining to the transport, transformation, and downwind impacts of megacity air pollution.

Quasar feedback revealed by giant molecular outflows

NASA Astrophysics Data System (ADS)

Feruglio, C.; Maiolino, R.; Piconcelli, E.; Menci, N.; Aussel, H.; Lamastra, A.; Fiore, F.

2010-07-01

In the standard scenario for galaxy evolution young star-forming galaxies transform into red bulge-dominated spheroids, where star formation has been quenched. To explain this transformation, a strong negative feedback generated by accretion onto a central super-massive black hole is often invoked. The depletion of gas resulting from quasar-driven outflows should eventually stop star-formation across the host galaxy and lead the black hole to “suicide” by starvation. Direct observational evidence for a major quasar feedback onto the host galaxy is still missing, because outflows previously observed in quasars are generally associated with the ionized component of the gas, which only accounts for a minor fraction of the total gas content, and typically occurrs in the central regions. We used the IRAM PdB Interferometer to observe the CO(1-0) transition in Mrk 231, the closest quasar known. Thanks to the wide band we detected broad wings of the CO line, with velocities of up to 750 km s-1 and spatially resolved on the kpc scale. These broad CO wings trace a giant molecular outflow of about 700 M_⊙/year, far larger than the ongoing star-formation rate (~200 M_⊙/year) observed in the host galaxy. This wind will totally expel the cold gas reservoir in Mrk 231 in about 107 yrs, therefore halting the star-formation activity on the same timescale. The inferred kinetic energy in the molecular outflow is ~1.2 × 1044 erg/s, corresponding to a few percent of the AGN bolometric luminosity, which is very close to the fraction expected by models ascribing quasar feedback to highly supersonic shocks generated by radiatively accelerated nuclear winds. Instead, the contribution by the SNe associated with the starburst fall short by several orders of magnitude to account for the kinetic energy observed in the outflow. The direct observational evidence for quasar feedback reported here provides solid support to the scenarios ascribing the observed properties of local massive galaxies to quasar-induced large-scale winds.

WPVS 007: Dramatic Broad Absorption Line Variability in a Narrow-line Seyfert 1

NASA Astrophysics Data System (ADS)

Cooper, Erin M.; Leighly, K.; Hamann, F. W.; Grupe, D.; Dietrich, M.

2014-01-01

Blue-shifted broad absorption lines are the manifestation of gaseous outflows in astrophysical phenomena. In active galaxies, these outflowing winds may play a key role in the central engine physics by removing angular momentum and in influencing host galaxy evolution by imparting energy and chemically enriched gas to the surrounding medium. AGN wind variability affords us a valuable tool to study this still poorly understood phenomenon. The existence of a high velocity broad line outflow in WPVS007 is especially extraordinary, as Seyfert-luminosity active galaxies are unexpected to produce them. With its lower luminosity and compact size, the NLS1 galaxy WPVS007 (M_V=-19.7, z=0.02882) provides us the ability to study even colossal variability on merely human timescales. Since its 1996 FOS observation, displaying miniBALs but no true broad absorption lines, WPVS007 has experienced a short but rich history of UV BAL variability. By the 2003 FUSE observation, WPVS007 had developed a BAL with v_max ~ 6000km/s, indicating an optically thick, high velocity outflow. We present the 2010 and 2013 June and December HST COS spectra. Between 2003 and 2010, both the maximum and minimum outflow velocity had increased substantially. As of 2013 June, the continuum emission has since dimmed by a factor of ~2 and the BALs have appeared to weaken, with both decreased maximum and minimum velocities. Such dramatic shifts in BAL velocity are unprecedented, as BAL variability is typically confined to changes in optical depth. What is the nature of the variability in this BAL wind? The upcoming (as of the writing of this abstract) December observation should give us more insight into tackling that question, whether it be the transient response of a continuous flow to a fluctuating continuum or perhaps the continued decline of a discrete outflow event.

Does an Intrinsic Magnetic Field Inhibit or Enhance Planetary Ionosphere Outflow and Loss?

NASA Astrophysics Data System (ADS)

Strangeway, R. J.; Russell, C. T.; Luhmann, J. G.; Moore, T. E.; Foster, J. C.; Barabash, S. V.; Nilsson, H.

2017-12-01

A characteristic feature of the planets Earth, Venus and Mars is the observation of the outflow of ionospheric ions, most notably oxygen. The oxygen ion outflow is frequently assumed to be a proxy for the loss of water from the planetary atmosphere. In terms of global outflow rates for the Earth the rate varies from 1025 to 1026 s-1, depending on geomagnetic activity. For both Venus and Mars global rates of the order 5x1024 s-1 have been reported. Venus and Mars do not have a large-scale intrinsic magnetic field, and there are several pathways for atmospheric and ionospheric loss. At Mars, because of its low gravity, neutral oxygen can escape through dissociative recombination. At Venus only processes related to the solar wind interaction with the planet such as sputtering and direct scavenging of the ionosphere by the solar wind can result in oxygen escape. At the Earth the intrinsic magnetic field forms a barrier to the solar wind, but reconnection of the Earth's magnetic field with the Interplanetary Magnetic Field allows solar wind energy and momentum to be transferred into the magnetosphere, resulting in ionospheric outflows. Observations of oxygen ions at the dayside magnetopause suggest that at least some of these ions escape. In terms of the evolution of planetary atmospheres how the solar-wind driven escape rates vary for magnetized versus umagnetized planets is also not clear. An enhanced solar wind dynamic pressure will increase escape from the unmagnetized planets, but it may also result in enhanced reconnection at the Earth, increasing outflow and loss rates for the Earth as well. Continued improvement in our understanding of the different pathways for ionospheric and atmospheric loss will allow us to determine how effective an intrinsic planetary field is in preserving a planetary atmosphere, or if we have to look for other explanations as to why the atmospheres of Venus and Mars have evolved to their desiccated state.

Microbial contributions to coupled arsenic and sulfur cycling in the acid-sulfide hot spring Champagne Pool, New Zealand.

PubMed

Hug, Katrin; Maher, William A; Stott, Matthew B; Krikowa, Frank; Foster, Simon; Moreau, John W

2014-01-01

Acid-sulfide hot springs are analogs of early Earth geothermal systems where microbial metal(loid) resistance likely first evolved. Arsenic is a metalloid enriched in the acid-sulfide hot spring Champagne Pool (Waiotapu, New Zealand). Arsenic speciation in Champagne Pool follows reaction paths not yet fully understood with respect to biotic contributions and coupling to biogeochemical sulfur cycling. Here we present quantitative arsenic speciation from Champagne Pool, finding arsenite dominant in the pool, rim and outflow channel (55-75% total arsenic), and dithio- and trithioarsenates ubiquitously present as 18-25% total arsenic. In the outflow channel, dimethylmonothioarsenate comprised ≤9% total arsenic, while on the outflow terrace thioarsenates were present at 55% total arsenic. We also quantified sulfide, thiosulfate, sulfate and elemental sulfur, finding sulfide and sulfate as major species in the pool and outflow terrace, respectively. Elemental sulfur concentration reached a maximum at the terrace. Phylogenetic analysis of 16S rRNA genes from metagenomic sequencing revealed the dominance of Sulfurihydrogenibium at all sites and an increased archaeal population at the rim and outflow channel. Several phylotypes were found closely related to known sulfur- and sulfide-oxidizers, as well as sulfur- and sulfate-reducers. Bioinformatic analysis revealed genes underpinning sulfur redox transformations, consistent with sulfur speciation data, and illustrating a microbial role in sulfur-dependent transformation of arsenite to thioarsenate. Metagenomic analysis also revealed genes encoding for arsenate reductase at all sites, reflecting the ubiquity of thioarsenate and a need for microbial arsenate resistance despite anoxic conditions. Absence of the arsenite oxidase gene, aio, at all sites suggests prioritization of arsenite detoxification over coupling to energy conservation. Finally, detection of methyl arsenic in the outflow channel, in conjunction with increased sequences from Aquificaceae, supports a role for methyltransferase in thermophilic arsenic resistance. Our study highlights microbial contributions to coupled arsenic and sulfur cycling at Champagne Pool, with implications for understanding the evolution of microbial arsenic resistance in sulfidic geothermal systems.

Compact objects at the heart of outflows in large and small systems

NASA Astrophysics Data System (ADS)

Sell, Paul Harrison

2013-12-01

This thesis focuses on studying and assessing high-energy feedback generated by both stellar mass and supermassive compact objects. From these two perspectives, I help bridge the gap in understanding how jets and winds can transform their much larger environments in thousands to millions of years, astronomically short timescales. I have acquired X-ray and optical data that aim to elucidate the role these objects play in powering parsec-scale shockwaves in the ISM and in driving kiloparsec-scale outflows in galaxies. I present Chandra X-ray imaging, Hubble Space Telescope imaging, and WIYN Hydra multi-object optical spectroscopic observations. The data reveal the morphologies of the systems and constrain on a range of interesting parameters: power, outflow velocity, density, accretion efficiency, and timescale. My analysis provides perspective on the importance of black holes, both large and small, and neutron stars for driving outflows into the interstellar and intergalactic medium. On kiloparsec scales, I explore the nature of what appear to be merging or recently merging post-starburst galaxies with very high-velocity winds. This work is part of a multiwavelength effort to characterize the niche these galaxies fill in the larger scheme of galaxy evolution. My focus is on the accretion activity of the coalescing supermassive black holes in their cores. This work leads us to compare the relative importance of a massive starburst to the supermassive black holes in the cores of the galaxies. On parsec scales, I present case studies of two prominent microquasars, Galactic X-ray binaries with jets, Circinus X-1 and Cygnus X-1. In the case of Circinus X-1, I present very deep follow-up observations of parsec-scale shock plumes driven by a powerful, bipolar jet. In the case of Cygnus X-1, I present follow-up observations to probe a recently discovered outflow near the binary. I calculate robust, physically motivated limits on the total power needed to drive the outflows in both of these systems.

Induced massive star formation in the trifid nebula?

PubMed

Cernicharo; Lefloch; Cox; Cesarsky; Esteban; Yusef-Zadeh; Mendez; Acosta-Pulido; Garcia Lopez RJ; Heras

1998-10-16

The Trifid nebula is a young (10(5) years) galactic HII region where several protostellar sources have been detected with the infrared space observatory. The sources are massive (17 to 60 solar masses) and are associated with molecular gas condensations at the edges or inside the nebula. They appear to be in an early evolutionary stage and may represent the most recent generation of stars in the Trifid. These sources range from dense, apparently still inactive cores to more evolved sources, undergoing violent mass ejection episodes, including a source that powers an optical jet. These observations suggest that the protostellar sources may have evolved by induced star formation in the Trifid nebula.

Trapping Planetary Noble Gases During the Fischer-Tropsch-Type Synthesis of Organic Materials

NASA Technical Reports Server (NTRS)

Nuth, Joseph A.; Johnson, N. M.; Meshik, A.

2010-01-01

When hydrogen, nitrogen and CO arc exposed to amorphous iron silicate surfaces at temperatures between 500 - 900K, a carbonaceous coating forms via Fischer-Tropsch type reactions!, Under normal circumstances such a catalytic coating would impede or stop further reaction. However, we find that this coating is a better catalyst than the amorphous iron silicates that initiate these rcactions:u . The formation of a self-perpetuating catalytic coating on grain surfaces could explain the rich deposits of macromolecular carbon found in primitive meteorites and would imply that protostellar nebulae should be rich in organic materiaL Many more experiments are needed to understand this chemical system and its application to protostellar nebulae.

Classifying Structures in the ISM with Machine Learning Techniques

NASA Astrophysics Data System (ADS)

Beaumont, Christopher; Goodman, A. A.; Williams, J. P.

2011-01-01

The processes which govern molecular cloud evolution and star formation often sculpt structures in the ISM: filaments, pillars, shells, outflows, etc. Because of their morphological complexity, these objects are often identified manually. Manual classification has several disadvantages; the process is subjective, not easily reproducible, and does not scale well to handle increasingly large datasets. We have explored to what extent machine learning algorithms can be trained to autonomously identify specific morphological features in molecular cloud datasets. We show that the Support Vector Machine algorithm can successfully locate filaments and outflows blended with other emission structures. When the objects of interest are morphologically distinct from the surrounding emission, this autonomous classification achieves >90% accuracy. We have developed a set of IDL-based tools to apply this technique to other datasets.

Post-merger evolution of a neutron star-black hole binary with neutrino transport

NASA Astrophysics Data System (ADS)

Foucart, Francois; O'Connor, Evan; Roberts, Luke; Duez, Matthew D.; Haas, Roland; Kidder, Lawrence E.; Ott, Christian D.; Pfeiffer, Harald P.; Scheel, Mark A.; Szilagyi, Bela

2015-06-01

We present a first simulation of the post-merger evolution of a black hole-neutron star binary in full general relativity using an energy-integrated general-relativistic truncated moment formalism for neutrino transport. We describe our implementation of the moment formalism and important tests of our code, before studying the formation phase of an accretion disk after a black hole-neutron star merger. We use as initial data an existing general-relativistic simulation of the merger of a neutron star of mass 1.4 M⊙ with a black hole of mass 7 M⊙ and dimensionless spin χBH=0.8 . Comparing with a simpler leakage scheme for the treatment of the neutrinos, we find noticeable differences in the neutron-to-proton ratio in and around the disk, and in the neutrino luminosity. We find that the electron neutrino luminosity is much lower in the transport simulations, and that both the disk and the disk outflows are less neutron rich. The spatial distribution of the neutrinos is significantly affected by relativistic effects, due to large velocities and curvature in the regions of strongest emission. Over the short time scale evolved, we do not observe purely neutrino-driven outflows. However, a small amount of material (3 ×10-4M⊙ ) is ejected in the polar region during the circularization of the disk. Most of that material is ejected early in the formation of the disk, and is fairly neutron rich (electron fraction Ye˜0.15 - 0.25 ). Through r-process nucleosynthesis, that material should produce high-opacity lanthanides in the polar region, and could thus affect the light curve of radioactively powered electromagnetic transients. We also show that by the end of the simulation, while the bulk of the disk remains neutron rich (Ye˜0.15 - 0.2 and decreasing), its outer layers have a higher electron fraction: 10% of the remaining mass has Ye>0.3 . As that material would be the first to be unbound by disk outflows on longer time scales, and as composition evolution is slower at later times, the changes in Ye experienced during the formation phase of the disk could have an impact on nucleosynthesis outputs from neutrino-driven and viscously driven outflows. Finally, we find that the effective viscosity due to momentum transport by neutrinos is unlikely to have a strong effect on the growth of the magnetorotational instability in the post-merger accretion disk.

Three-Dimensional General-Relativistic Magnetohydrodynamic Simulations of Remnant Accretion Disks from Neutron Star Mergers: Outflows and r -Process Nucleosynthesis

NASA Astrophysics Data System (ADS)

Siegel, Daniel M.; Metzger, Brian D.

2017-12-01

The merger of binary neutron stars, or of a neutron star and a stellar-mass black hole, can result in the formation of a massive rotating torus around a spinning black hole. In addition to providing collimating media for γ -ray burst jets, unbound outflows from these disks are an important source of mass ejection and rapid neutron capture (r -process) nucleosynthesis. We present the first three-dimensional general-relativistic magnetohydrodynamic (GRMHD) simulations of neutrino-cooled accretion disks in neutron star mergers, including a realistic equation of state valid at low densities and temperatures, self-consistent evolution of the electron fraction, and neutrino cooling through an approximate leakage scheme. After initial magnetic field amplification by magnetic winding, we witness the vigorous onset of turbulence driven by the magnetorotational instability (MRI). The disk quickly reaches a balance between heating from MRI-driven turbulence and neutrino cooling, which regulates the midplane electron fraction to a low equilibrium value Ye≈0.1 . Over the 380-ms duration of the simulation, we find that a fraction ≈20 % of the initial torus mass is unbound in powerful outflows with asymptotic velocities v ≈0.1 c and electron fractions Ye≈0.1 - 0.25 . Postprocessing the outflows through a nuclear reaction network shows the production of a robust second- and third-peak r process. Though broadly consistent with the results of previous axisymmetric hydrodynamical simulations, extrapolation of our results to late times suggests that the total ejecta mass from GRMHD disks is significantly higher. Our results provide strong evidence that postmerger disk outflows are an important site for the r process.

Numerical Simulations of Multiphase Winds and Fountains from Star-forming Galactic Disks. I. Solar Neighborhood TIGRESS Model

NASA Astrophysics Data System (ADS)

Kim, Chang-Goo; Ostriker, Eve C.

2018-02-01

Gas blown away from galactic disks by supernova (SN) feedback plays a key role in galaxy evolution. We investigate outflows utilizing the solar neighborhood model of our high-resolution, local galactic disk simulation suite, TIGRESS. In our numerical implementation, star formation and SN feedback are self-consistently treated and well resolved in the multiphase, turbulent, magnetized interstellar medium. Bursts of star formation produce spatially and temporally correlated SNe that drive strong outflows, consisting of hot (T> 5× {10}5 {{K}}) winds and warm (5050 {{K}}< T< 2× {10}4 {{K}}) fountains. The hot gas at distance d> 1 {kpc} from the midplane has mass and energy fluxes nearly constant with d. The hot flow escapes our local Cartesian box barely affected by gravity, and is expected to accelerate up to terminal velocity of {v}{wind}∼ 350{--}500 {km} {{{s}}}-1. The mean mass and energy loading factors of the hot wind are 0.1 and 0.02, respectively. For warm gas, the mean outward mass flux through d=1 {kpc} is comparable to the mean star formation rate, but only a small fraction of this gas is at velocity > 50 {km} {{{s}}}-1. Thus, the warm outflows eventually fall back as inflows. The warm fountain flows are created by expanding hot superbubbles at d< 1 {kpc}; at larger d neither ram pressure acceleration nor cooling transfers significant momentum or energy flux from the hot wind to the warm outflow. The velocity distribution at launching near d∼ 1 {kpc} is a better representation of warm outflows than a single mass loading factor, potentially enabling development of subgrid models for warm galactic winds in arbitrary large-scale galactic potentials.

Three-Dimensional General-Relativistic Magnetohydrodynamic Simulations of Remnant Accretion Disks from Neutron Star Mergers: Outflows and r-Process Nucleosynthesis.

PubMed

Siegel, Daniel M; Metzger, Brian D

2017-12-08

The merger of binary neutron stars, or of a neutron star and a stellar-mass black hole, can result in the formation of a massive rotating torus around a spinning black hole. In addition to providing collimating media for γ-ray burst jets, unbound outflows from these disks are an important source of mass ejection and rapid neutron capture (r-process) nucleosynthesis. We present the first three-dimensional general-relativistic magnetohydrodynamic (GRMHD) simulations of neutrino-cooled accretion disks in neutron star mergers, including a realistic equation of state valid at low densities and temperatures, self-consistent evolution of the electron fraction, and neutrino cooling through an approximate leakage scheme. After initial magnetic field amplification by magnetic winding, we witness the vigorous onset of turbulence driven by the magnetorotational instability (MRI). The disk quickly reaches a balance between heating from MRI-driven turbulence and neutrino cooling, which regulates the midplane electron fraction to a low equilibrium value Y_{e}≈0.1. Over the 380-ms duration of the simulation, we find that a fraction ≈20% of the initial torus mass is unbound in powerful outflows with asymptotic velocities v≈0.1c and electron fractions Y_{e}≈0.1-0.25. Postprocessing the outflows through a nuclear reaction network shows the production of a robust second- and third-peak r process. Though broadly consistent with the results of previous axisymmetric hydrodynamical simulations, extrapolation of our results to late times suggests that the total ejecta mass from GRMHD disks is significantly higher. Our results provide strong evidence that postmerger disk outflows are an important site for the r process.

The Cosmological Impact of AGN Outflows: Measuring Absolute Abundances and Kinetic Luminosities

NASA Astrophysics Data System (ADS)

Arav, Nahum

2009-07-01

AGN outflows are increasingly invoked as a major contributor to the formation and evolution of supermassive black holes, their host galaxies, the surrounding IGM, and cluster cooling flows. Our HST/COS proposal will determine reliable absolute chemical abundances in six AGN outflows, which influences several of the processes mentioned above. To date there is only one such determination, done by our team on Mrk 279 using 16 HST/STIS orbits and 100 ksec of FUSE time. The advent of COS and its high sensitivity allows us to choose among fainter objects at redshifts high enough to preclude the need for FUSE. This will allow us to determine the absolute abundances for six AGN {all fainter than Mrk 279} using only 40 HST COS orbits. This will put abundances studies in AGN on a firm footing, an elusive goal for the past four decades. In addition, prior FUSE observations of four of these targets indicate that it is probable that the COS observations will detect troughs from excited levels of C III. These will allow us to measure the distances of the outflows and thereby determine their kinetic luminosity, a major goal in AGN feedback research. We will use our state of the art column density extraction methods and velocity-dependent photoionization models to determine the abundances and kinetic luminosity. Previous AGN outflow projects suffered from the constraints of deciding what science we could do using ONE of the handful of bright targets that were observable. With COS we can choose the best sample for our experiment. As an added bonus, most of the spectral range of our targets has not been observed previously, greatly increasing the discovery phase space.

The dark nemesis of galaxy formation: why hot haloes trigger black hole growth and bring star formation to an end

NASA Astrophysics Data System (ADS)

Bower, Richard G.; Schaye, Joop; Frenk, Carlos S.; Theuns, Tom; Schaller, Matthieu; Crain, Robert A.; McAlpine, Stuart

2017-02-01

Galaxies fall into two clearly distinct types: `blue-sequence' galaxies which are rapidly forming young stars, and `red-sequence' galaxies in which star formation has almost completely ceased. Most galaxies more massive than 3 × 1010 M⊙ follow the red sequence, while less massive central galaxies lie on the blue sequence. We show that these sequences are created by a competition between star formation-driven outflows and gas accretion on to the supermassive black hole at the galaxy's centre. We develop a simple analytic model for this interaction. In galaxies less massive than 3 × 1010 M⊙, young stars and supernovae drive a high-entropy outflow which is more buoyant than any tenuous corona. The outflow balances the rate of gas inflow, preventing high gas densities building up in the central regions. More massive galaxies, however, are surrounded by an increasingly hot corona. Above a halo mass of ˜1012 M⊙, the outflow ceases to be buoyant and star formation is unable to prevent the build-up of gas in the central regions. This triggers a strongly non-linear response from the black hole. Its accretion rate rises rapidly, heating the galaxy's corona, disrupting the incoming supply of cool gas and starving the galaxy of the fuel for star formation. The host galaxy makes a transition to the red sequence, and further growth predominantly occurs through galaxy mergers. We show that the analytic model provides a good description of galaxy evolution in the EAGLE hydrodynamic simulations. So long as star formation-driven outflows are present, the transition mass scale is almost independent of subgrid parameter choice.

The Class 0 Protostar BHR71: Herschel Observations and Dust Continuum Models

NASA Astrophysics Data System (ADS)

Yang, Yao-Lun; Evans, Neal J., II; Green, Joel D.; Dunham, Michael M.; Jørgensen, Jes K.

2017-02-01

We use Herschel spectrophotometry of BHR71, an embedded Class 0 protostar, to provide new constraints on its physical properties. We detect 645 (non-unique) spectral lines among all spatial pixels. At least 61 different spectral lines originate from the central region. A CO rotational diagram analysis shows four excitation temperature components, 43, 197, 397, and 1057 K. Low-J CO lines trace the outflow while the high-J CO lines are centered on the infrared source. The low-excitation emission lines of {{{H}}}2{{O}} trace the large-scale outflow, while the high-excitation emission lines trace a small-scale distribution around the equatorial plane. We model the envelope structure using the dust radiative transfer code, hyperion, incorporating rotational collapse, an outer static envelope, outflow cavity, and disk. The evolution of a rotating collapsing envelope can be constrained by the far-infrared/millimeter spectral energy distribution along with the azimuthally averaged radial intensity profile, and the structure of the outflow cavity plays a critical role at shorter wavelengths. Emission at 20-40 μm requires a cavity with a constant-density inner region and a power-law density outer region. The best-fit model has an envelope mass of 19 {M}⊙ inside a radius of 0.315 pc and a central luminosity of 18.8 {L}⊙ . The time since collapse began is 24,630-44,000 years, most likely around 36,000 years. The corresponding mass infall rate in the envelope (1.2 × 10-5 {M}⊙ {{yr}}-1) is comparable to the stellar mass accretion rate, while the mass-loss rate estimated from the CO outflow is 20% of the stellar mass accretion rate. We find no evidence for episodic accretion.

Stellar feedback as the origin of an extended molecular outflow in a starburst galaxy.

PubMed

Geach, J E; Hickox, R C; Diamond-Stanic, A M; Krips, M; Rudnick, G H; Tremonti, C A; Sell, P H; Coil, A L; Moustakas, J

2014-12-04

Recent observations have revealed that starburst galaxies can drive molecular gas outflows through stellar radiation pressure. Molecular gas is the phase of the interstellar medium from which stars form, so these outflows curtail stellar mass growth in galaxies. Previously known outflows, however, involve small fractions of the total molecular gas content and have typical scales of less than a kiloparsec. In at least some cases, input from active galactic nuclei is dynamically important, so pure stellar feedback (the momentum return into the interstellar medium) has been considered incapable of rapidly terminating star formation on galactic scales. Molecular gas has been detected outside the galactic plane of the archetypal starburst galaxy M82 (refs 4 and 5), but so far there has been no evidence that starbursts can propel substantial quantities of cold molecular gas to the same galactocentric radius (about 10 kiloparsecs) as the warmer gas that has been traced by metal ion absorbers in the circumgalactic medium. Here we report observations of molecular gas in a compact (effective radius 100 parsecs) massive starburst galaxy at redshift 0.7, which is known to drive a fast outflow of ionized gas. We find that 35 per cent of the total molecular gas extends approximately 10 kiloparsecs, and one-third of this extended gas has a velocity of up to 1,000 kilometres per second. The kinetic energy associated with this high-velocity component is consistent with the momentum flux available from stellar radiation pressure. This demonstrates that nuclear bursts of star formation are capable of ejecting large amounts of cold gas from the central regions of galaxies, thereby strongly affecting their evolution by truncating star formation and redistributing matter.

The chemistry of planet-forming regions is not interstellar.

PubMed

Pontoppidan, Klaus M; Blevins, Sandra M

2014-01-01

Advances in infrared and submillimeter technology have allowed for detailed observations of the molecular content of the planet-forming regions of protoplanetary disks. In particular, disks around solar-type stars now have growing molecular inventories that can be directly compared with both prestellar chemistry and that inferred for the early solar nebula. The data directly address the old question of whether the chemistry of planet-forming matter is similar or different and unique relative to the chemistry of dense clouds and protostellar envelopes. The answer to this question may have profound consequences for the structure and composition of planetary systems. The practical challenge is that observations of emission lines from disks do not easily translate into chemical concentrations. Here, we present a two-dimensional radiative transfer model of RNO 90, a classical protoplanetary disk around a solar-mass star, and retrieve the concentrations of dominant molecular carriers of carbon, oxygen and nitrogen in the terrestrial region around 1 AU. We compare our results to the chemical inventory of dense clouds and protostellar envelopes, and argue that inner disk chemistry is, as expected, fundamentally different from prestellar chemistry. We find that the clearest discriminant may be the concentration of CO2, which is extremely low in disks, but one of the most abundant constituents of dense clouds and protostellar envelopes.

Embedded Star Formation in the Eagle Nebula with Spitzer GLIMPSE

NASA Astrophysics Data System (ADS)

Indebetouw, R.; Robitaille, T. P.; Whitney, B. A.; Churchwell, E.; Babler, B.; Meade, M.; Watson, C.; Wolfire, M.

2007-09-01

We present new Spitzer photometry of the Eagle Nebula (M16, containing the optical cluster NGC 6611) combined with near-infrared photometry from 2MASS. We use dust radiative transfer models, mid-infrared and near-infrared color-color analysis, and mid-infrared spectral indices to analyze point-source spectral energy distributions, select candidate YSOs, and constrain their mass and evolutionary state. Comparison of the different protostellar selection methods shows that mid-infrared methods are consistent, but as has been known for some time, near-infrared-only analysis misses some young objects. We reveal more than 400 protostellar candidates, including one massive YSO that has not been previously highlighted. The YSO distribution supports a picture of distributed low-level star formation, with no strong evidence of triggered star formation in the ``pillars.'' We confirm the youth of NGC 6611 by a large fraction of infrared excess sources and reveal a younger cluster of YSOs in the nearby molecular cloud. Analysis of the YSO clustering properties shows a possible imprint of the molecular cloud's Jeans length. Multiwavelength mid-IR imaging thus allows us to analyze the protostellar population, to measure the dust temperature and column density, and to relate these in a consistent picture of star formation in M16.

Multiple outflows in the bipolar planetary nebula M1-16: A molecular line study

NASA Technical Reports Server (NTRS)

Sahai, Raghvendra; Wootten, Alwyn; Schwarz, Hugo E.; Wild, W.

1994-01-01

Extensive observations of the molecular gas in the young, compact planetary nebula M1-16 have been made, using the Swedish-ESO-Submillimeter Telescope. A map of the CO J = 2-1 emission shows that the molecular envelope contains both a slow and a fast outflow with expansion velocities of 19 km/s and greater than 34 km/s, respectively. The slow outflow is mildly elliptical, while the fast molecular outflow is bipolar. This fast outflow is roughly aligned with the very fast outflows recently found in the optical, while the long axis of the slow elliptical outflow is roughly orthogonal to the optical outflow axis. The kinematic timescales for the CO fast outflow and the optical very fast outflow agree closely, supporting the view that the former represents material in the slow outflow accelerated by the very fast outflow. The kinematic signature of a disk expanding with about 15.5 km/s can also be seen in the CO J = 2-1 data. The mass-loss rate (a) for the slow outflow is greater than or equal to 2.8 x 10(exp -5) solar mass/yr and possibly as large as 9 x 10(exp -5) solar mass/yr, (b) for the fast outflow is greater than or equal to 5 x 10(exp -6) solar mass/yr, and (c) for the very fast optically visible outflow is approximately equal 5 x 10(exp -7) solar mass/yr. The disk mass is approximately equal 6 x 10(exp -3) solar mass. Grain photoelectric heating results in temperatures of 20-70 K in molecular gas of the slow outflow. The (13)C/(12)C abundance ratio in M1-16 is found to be 0.33, quite possibly the highest found for any evolved object. Upper limits for the (18)O/(16)O and (17)O/(16)O ratios were found to be consistent with the values found in AGB stars. A search for other molecular species in M1-16 resulted in the detection of the high-excitation species HCN, CN, (13)CN, HCO(+), and H(13)CO(+) and possibly N2H(+). Both the HCO(+)/HCN and CN/HCN line-intensity ratios are enhanced, the former by a very large factor, over the values found in the envelopes of AGB stars, probably as a result of enhancement of the CN and HCO(+) abundances due to photochemistry induced by the stellar UV. The CS J = 2-1, SiO J = 2-1 (v = 0), and SiS J = 6-5 lines were not detected to low levels. For the high-excitation molecules, adequate collisional excitation of rotational levels and survival against photodissociation by the UV radiation requires significant clumping of the molecular gas into clumps with H2 densities approximately 10(exp 5)/cu cm. The IRAS fluxes of M1-16, assuming negligible contribution from line emission, imply the presence of about (1.7-0.4) x 10(exp -3) solar mass of cool dust (temperature around 50 K) and a smaller quantity, (2.7-3.1) x 10(exp -6) solar mass, of warmer dust (temperature around 125 K) for a power-law emissivity index p = 1-2. The evolutionary nature of M1-16 cannot be explained by existing single-star models of post-AGB evolution. The very high (13)C/(12)C abundance ratio in M1-16 suggests a possible evolutionary connection between M1-16 and the rare class of J-type silicate-carbon stars which also have high (13)C/(12)C ratios and are thought to be binary systems with accretion disks.

Multiple outflows in the bipolar planetary nebula M1-16: A molecular line study

NASA Astrophysics Data System (ADS)

Sahai, Raghvendra; Wootten, Alwyn; Schwarz, Hugo E.; Wild, W.

1994-06-01

Extensive observations of the molecular gas in the young, compact planetary nebula M1-16 have been made, using the Swedish-ESO-Submillimeter Telescope. A map of the CO J = 2-1 emission shows that the molecular envelope contains both a slow and a fast outflow with expansion velocities of 19 km/s and greater than 34 km/s, respectively. The slow outflow is mildly elliptical, while the fast molecular outflow is bipolar. This fast outflow is roughly aligned with the very fast outflows recently found in the optical, while the long axis of the slow elliptical outflow is roughly orthogonal to the optical outflow axis. The kinematic timescales for the CO fast outflow and the optical very fast outflow agree closely, supporting the view that the former represents material in the slow outflow accelerated by the very fast outflow. The kinematic signature of a disk expanding with about 15.5 km/s can also be seen in the CO J = 2-1 data. The mass-loss rate (a) for the slow outflow is greater than or equal to 2.8 x 10-5 solar mass/yr and possibly as large as 9 x 10-5 solar mass/yr, (b) for the fast outflow is greater than or equal to 5 x 10-6 solar mass/yr, and (c) for the very fast optically visible outflow is approximately equal 5 x 10-7 solar mass/yr. The disk mass is approximately equal 6 x 10-3 solar mass. Grain photoelectric heating results in temperatures of 20-70 K in molecular gas of the slow outflow. The (13)C/(12)C abundance ratio in M1-16 is found to be 0.33, quite possibly the highest found for any evolved object. Upper limits for the (18)O/(16)O and (17)O/(16)O ratios were found to be consistent with the values found in AGB stars. A search for other molecular species in M1-16 resulted in the detection of the high-excitation species HCN, CN, (13)CN, HCO(+), and H(13)CO(+) and possibly N2H(+). Both the HCO(+)/HCN and CN/HCN line-intensity ratios are enhanced, the former by a very large factor, over the values found in the envelopes of AGB stars, probably as a result of enhancement of the CN and HCO(+) abundances due to photochemistry induced by the stellar UV. The CS J = 2-1, SiO J = 2-1 (v = 0), and SiS J = 6-5 lines were not detected to low levels. For the high-excitation molecules, adequate collisional excitation of rotational levels and survival against photodissociation by the UV radiation requires significant clumping of the molecular gas into clumps with H2 densities approximately 105/cu cm. The IRAS fluxes of M1-16, assuming negligible contribution from line emission, imply the presence of about (1.7-0.4) x 10-3 solar mass of cool dust (temperature around 50 K) and a smaller quantity, (2.7-3.1) x 10-6 solar mass, of warmer dust (temperature around 125 K) for a power-law emissivity index p = 1-2. The evolutionary nature of M1-16 cannot be explained by existing single-star models of post-AGB evolution. The very high (13)C/(12)C abundance ratio in M1-16 suggests a possible evolutionary connection between M1-16 and the rare class of J-type silicate-carbon stars which also have high (13)C/(12)C ratios and are thought to be binary systems with accretion disks.

Jet multiplicity in the proto-binary system NGC 1333-IRAS4A. The detailed CALYPSO IRAM-PdBI view

NASA Astrophysics Data System (ADS)

Santangelo, G.; Codella, C.; Cabrit, S.; Maury, A. J.; Gueth, F.; Maret, S.; Lefloch, B.; Belloche, A.; André, Ph.; Hennebelle, P.; Anderl, S.; Podio, L.; Testi, L.

2015-12-01

Context. Owing to the paucity of sub-arcsecond (sub)mm observations required to probe the innermost regions of newly forming protostars, several fundamental questions are still being debated, such as the existence and coevality of close multiple systems. Aims: We study the physical and chemical properties of the jets and protostellar sources in the NGC 1333-IRAS4A proto-binary system using continuum emission and molecular tracers of shocked gas. Methods: We observed NGC 1333-IRAS4A in the SiO(6-5), SO(65-54), and CO(2-1) lines and the continuum emission at 1.3, 1.4, and 3 mm using the IRAM Plateau de Bure Interferometer in the framework of the CALYPSO large program. Results: We clearly disentangle for the first time the outflow emission from the two sources A1 and A2. The two protostellar jets have very different properties: the A1 jet is faster, has a short dynamical timescale (≲103 yr), and is associated with H2 shocked emission, whereas the A2 jet, which dominates the large-scale emission, is associated with diffuse emission, bends, and emits at slower velocities. The observed bending of the A2 jet is consistent with the change of propagation direction observed at large scale and suggests jet precession on very short timescales (~200-600 yr). In addition, a chemically rich spectrum with emission from several complex organic molecules (e.g. HCOOH, CH3OCHO, CH3OCH3) is only detected towards A2. Finally, very high-velocity shocked emission (~50 km s-1) is observed along the A1 jet. An LTE analysis shows that SiO, SO, and H2CO abundances in the gas phase are enhanced up to (3-4)×10-7, (1.4-1.7)×10-6, and (3-7.9)×10-7, respectively. Conclusions: The intrinsic different properties of the jets and driving sources in NGC 1333-IRAS4A suggest different evolutionary stages for the two protostars, with A1 being younger than A2, in a very early stage of star formation previous to the hot-corino phase. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).Appendices are available in electronic form at http://www.aanda.org

Mass Ejection from Old and Young Stars and the Sun

NASA Astrophysics Data System (ADS)

Jatenco-Pereira, V.; Opher, R.

1990-11-01

RESUMEN. Para poder explicar: 1) la enorme cantidad de perdida de masa y la baja velocidad asint5tica de las estrellas gigantes de o, y 2) los flujos de masa observados en protoestrellas, se sugiere un modelo para Ia perdida de masa, en donde se usa un flujo de ondas de Alfvencomo un mecanismo de aceleraci6n para los vientos de estrellas de tipo y vientos en protoestrellas. Se estudian los mecanismos de disipaci5n de las ondas de Alfven: los amortiguamientos no lineal, de superficie reso- nante y turbulento. En nuestro modelo se usa una divergente A(r) = A(R0) (r/r0)5 (donde A(r) es el area a una distancia radial r, y (A(r)/r2)max/(A(ro)/r02 - 10). Tambien se sugiere un modelo para una de hoyo coronal en el Sol. Se muestra que para satisfacer los datos observacionales en el Sol, tomando en cuenta la deposici6n del momento de las ondas de Alfven sobre el viento, se necesita: (a) una divergencia lenta en un hoyo coronal hasta una altura de 0.01 - 0.1 R seguido de (b) una divergencia rap ida de hasta una altura aproximada de 1 R . ABSTRACT: In order to explain (1) a large mass-loss rate and a small asymptotic flow speed of late-type giant stars and (2) the observed protostellar mass outflows, we suggest a model for mass loss, where we use a flux of Alfven waves as a mechanism of acceleration for late-type giant star winds and protostellar winds. We study the Alfven wave dissipation mechanisms: nonlinear damping, resonant surface damping, and turbulent damping. In our model we use a diverging geometry A(r) = A(r0) (r I r )S (where A(r) is the cross sectional area of the geometry at a radial distance r, and(A(r) I r2)max/(A(r0)/r02) = 10). We also suggest a model for a coronal hole geometry in the sun. We show that in order to satisfy the observational data of the sun, taking into account Alfven wave momentum deposition in the wind, we need: (a) a slow divergence in a coronal hole up t6 a height of 0.01 - 0.1 followed by (b) a rapid divergence up to a height of approximately 1 Re Key : '? #TICS - STARS-LATE TYPE - STARS- LOSS

Correlation Analysis of Prompt Emission from Gamma Ray Bursts

NASA Astrophysics Data System (ADS)

Pothapragada, Sriharsha

Prompt emission from gamma-ray bursts (GRBs) exhibits very rapid, complicated temporal and spectral evolution. This diverse variability in the light-curves reflects the complicated nature of the underlying physics, in which inter-penetrating relativistic shells in the outflow are believed to generate strong magnetic fields that vary over very small scales. We use the theory of jitter radiation to model the emission from such regions and the resulting overall prompt gamma ray emission from a series of relativistic collisionless shocks. We present simulated GRB light-curves developed as a series of "pulses" corresponding to instantaneously illuminated "thin-shell" regions emitting via the jitter radiation mechanism. The effects of various geometries, viewing angles, and bulk Lorentz factor profiles of the radiating outflow jets on the spectral features and evolution of these light-curves are explored. Our results demonstrate how an anisotropic jitter radiation pattern, in conjunction with relativistic shock kinematics, can produce certain features observed in the GRB prompt emission spectra, such as the occurrence of hard, synchrotron violating spectra, the "tracking" of observed flux with spectral parameters, and spectral softening below peak energy within individual episodes of the light curve. We highlight predictions in the light of recent advances in the observational sphere of GRBs.

Rainfall Morphology in Semi-Tropical Convergence Zones

NASA Technical Reports Server (NTRS)

Shepherd, J. Marshall; Ferrier, Brad S.; Ray, Peter S.

2000-01-01

Central Florida is the ideal test laboratory for studying convergence zone-induced convection. The region regularly experiences sea breeze fronts and rainfall-induced outflow boundaries. The focus of this study is the common yet poorly-studied convergence zone established by the interaction of the sea breeze front and an outflow boundary. Previous studies have investigated mechanisms primarily affecting storm initiation by such convergence zones. Few have focused on rainfall morphology yet these storms contribute a significant amount precipitation to the annual rainfall budget. Low-level convergence and mid-tropospheric moisture have both been shown to correlate with rainfall amounts in Florida. Using 2D and 3D numerical simulations, the roles of low-level convergence and mid-tropospheric moisture in rainfall evolution are examined. The results indicate that time-averaged, vertical moisture flux (VMF) at the sea breeze front/outflow convergence zone is directly and linearly proportional to initial condensation rates. This proportionality establishes a similar relationship between VMF and initial rainfall. Vertical moisture flux, which encompasses depth and magnitude of convergence, is better correlated to initial rainfall production than surface moisture convergence. This extends early observational studies which linked rainfall in Florida to surface moisture convergence. The amount and distribution of mid-tropospheric moisture determines how rainfall associated with secondary cells develop. Rainfall amount and efficiency varied significantly over an observable range of relative humidities in the 850- 500 mb layer even though rainfall evolution was similar during the initial or "first-cell" period. Rainfall variability was attributed to drier mid-tropospheric environments inhibiting secondary cell development through entrainment effects. Observationally, 850-500 mb moisture structure exhibits wider variability than lower level moisture, which is virtually always present in Florida. A likely consequence of the variability in 850-500 moisture is a stronger statistical correlation to rainfall, which observational studies have noted. The study indicates that vertical moisture flux forcing at convergence zones is critical in determining rainfall in the initial stage of development but plays a decreasing role in rainfall evolution as the system matures. The mid-tropospheric moisture (e.g. environment) plays an increasing role in rainfall evolution as the system matures. This suggests the need to improve measurements of magnitude/depth of convergence and mid-tropospheric moisture distribution. It also highlights the need for better parameterization of entrainment and vertical moisture distribution in larger-scale models.

The CHESS survey of the L1157-B1 bow-shock: high and low excitation water vapor

NASA Astrophysics Data System (ADS)

Busquet, G.; Lefloch, B.; Benedettini, M.; Ceccarelli, C.; Codella, C.; Cabrit, S.; Nisini, B.; Viti, S.; Gómez-Ruiz, A. I.; Gusdorf, A.; di Giorgio, A. M.; Wiesenfeld, L.

2014-01-01

Context. Molecular outflows powered by young protostars strongly affect the kinematics and chemistry of the natal molecular cloud through strong shocks. This results in substantial modifications of the abundance of several species. In particular, water is a powerful tracer of shocked material because of its sensitivity to both physical conditions and chemical processes. Aims: As part of the Chemical HErschel Surveys of Star-forming regions (CHESS) guaranteed time key program, we aim at investigating the physical and chemical conditions of H2O in the brightest shock region B1 of the L1157 molecular outflow. Methods: We observed several ortho- and para-H2O transitions using the HIFI and PACS instruments on board Herschel toward L1157-B1, providing a detailed picture of the kinematics and spatial distribution of the gas. We performed a large velocity gradient (LVG) analysis to derive the physical conditions of H2O shocked material, and ultimately obtain its abundance. Results: We detected 13 H2O lines with both instruments probing a wide range of excitation conditions. This is the largest data set of water lines observed in a protostellar shock and it provides both the kinematics and the spatial information of the emitting gas. The PACS maps reveal that H2O traces weak and extended emission associated with the outflow identified also with HIFI in the o-H2O line at 556.9 GHz, and a compact (~10'') bright, higher excitation region. The LVG analysis of H2O lines in the bow-shock show the presence of two gas components with different excitation conditions: a warm (Tkin ≃ 200-300 K) and dense (n(H2) ≃ (1-3) × 106 cm-3) component with an assumed extent of 10'', and a compact (~2''-5'') and hot, tenuous (Tkin ≃ 900-1400 K, n(H2) ≃ 103-4 cm-3) gas component that is needed to account for the line fluxes of high Eu transitions. The fractional abundance of the warm and hot H2O gas components is estimated to be (0.7-2) × 10-6 and (1-3) × 10-4, respectively. Finally, we identified an additional component in absorption in the HIFI spectra of H2O lines that connect with the ground state level. This absorption probably arises from the photodesorption of icy mantles of a water-enriched layer at the edges of the cloud, driven by the external UV illumination of the interstellar radiation field. Based on Herschel HIFI and PACS observations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

The dusty silhouette jet HH 1019 in the Carina Nebula

NASA Astrophysics Data System (ADS)

Reiter, Megan; Kiminki, Megan M.; Smith, Nathan; Bally, John

2017-06-01

We report the discovery in Hubble Space Telescope (HST) images of the new Herbig-Haro jet, HH 1019, located near the Tr 14 cluster in the Carina Nebula. Like other HH jets in the region, this bipolar collimated flow emerges from the head of a dark dust pillar. However, HH 1019 is unique because - unlike all other HH jets known to date - it is identified by a linear chain of dark, dusty knots that are seen primarily in silhouette against the background screen of the H II region. Proper motions confirm that these dark condensations move along the jet axis at high speed. [S II] emission traces a highly collimated jet that is spatially coincident with these dust knots. The high extinction in the body of the jet suggests that this outflow has lifted a large amount of dust directly from the disc, although it is possible that it has entrained dust from its surrounding protostellar envelope before exiting the dust pillar. If dust in HH 1019 originates from the circumstellar disc, this provides further evidence for a jet launched from a range of radii in the disc, including those outside the dust sublimation radius. HH 1019 may be the prototype for a new subclass of dusty HH objects seen primarily in extinction against the background screen of a bright H II region. Such jets may be common, but difficult to observe because they require the special condition of a very bright background in order to be seen in silhouette.

Search for massive protostellar candidates in the southern hemisphere. I. Association with dense gas

NASA Astrophysics Data System (ADS)

Fontani, F.; Beltrán, M. T.; Brand, J.; Cesaroni, R.; Testi, L.; Molinari, S.; Walmsley, C. M.

2005-03-01

We have observed two rotational transitions of both CS and C17O, and the 1.2 mm continuum emission towards a sample of 130 high-mass protostellar candidates with δ < -30°. This work represents the first step of the extension to the southern hemisphere of a project started more than a decade ago aimed at the identification of massive protostellar candidates. Following the same approach adopted for sources with δ ≥ -30°, we have selected from the IRAS Point Source Catalogue 429 sources which potentially are compact molecular clouds on the basis of their IR colours. The sample has then been divided into two groups according to the colour indices [25 12] and [60 12]: the 298 sources with [25 12] ≥ 0.57 and [60 12] ≥ 1.30 have been called High sources, the remaining 131 have been called Low sources. In this paper, we check the association with dense gas and dust in 130 Low sources. We have obtained a detection rate of ~85% in CS, demonstrating a tight association of the sources with dense molecular clumps. Among the sources detected in CS, ~76% have also been detected in C17O and ~93% in the 1.2 mm continuum. Millimeter-continuum maps show the presence of clumps with diameters in the range 0.2-2 pc and masses from a few M⊙ to 105 M⊙; H2 volume densities computed from CS line ratios lie between ~104.5 and 105.5 cm-3. The bolometric luminosities of the sources, derived from IRAS data, are in the range 103-106 L⊙, consistent with embedded high-mass objects. Based on our results and those found in the literature for other samples of high-mass young stellar objects, we conclude that our sources are massive objects in a very early evolutionary stage, probably prior to the formation of an Hii region. We propose a scenario in which High and Low sources are both made of a massive clump hosting a high-mass protostellar candidate and a nearby stellar cluster. The difference might be due to the fact that the 12 μm IRAS flux, the best discriminant between the two groups, is dominated by the emission from the cluster in Lows and from the massive protostellar object in Highs. Based on results collected at the European Southern Observatory (ESO), La Silla, Chile. Tables [see full text]-[see full text] are only available in electronic form at http://www.edpsciences.org

Complex organics in IRAS 4A revisited with ALMA and PdBI: Striking contrast between two neighbouring protostellar cores

NASA Astrophysics Data System (ADS)

López-Sepulcre, A.; Sakai, N.; Neri, R.; Imai, M.; Oya, Y.; Ceccarelli, C.; Higuchi, A. E.; Aikawa, Y.; Bottinelli, S.; Caux, E.; Hirota, T.; Kahane, C.; Lefloch, B.; Vastel, C.; Watanabe, Y.; Yamamoto, S.

2017-10-01

Context. Hot corinos are extremely rich in complex organic molecules (COMs). Accurate abundance measurements of COMs in such objects are crucial to constrain astrochemical models. In the particular case of close binary systems this can only be achieved through high angular resolution imaging. Aims: We aim to perform an interferometric study of multiple COMs in NGC 1333 IRAS 4A, which is a protostellar binary hosting hot corino activity, at an angular resolution that is sufficient to distinguish easily the emission from the two cores separated by 1.8''. Methods: We used the Atacama Large (sub-)Millimeter Array (ALMA) in its 1.2 mm band and the IRAM Plateau de Bure Interferometer (PdBI) at 2.7 mm to image, with an angular resolution of 0.5'' (120 au) and 1'' (235 au), respectively, the emission from 11 different organic molecules in IRAS 4A. This allowed us to clearly disentangle A1 and A2, the two protostellar cores. For the first time, we were able to derive the column densities and fractional abundances simultaneously for the two objects, allowing us to analyse the chemical differences between them. Results: Molecular emission from organic molecules is concentrated exclusively in A2, while A1 appears completely devoid of COMs or even simpler organic molecules, such as HNCO, even though A1 is the strongest continuum emitter. The protostellar core A2 displays typical hot corino abundances and its deconvolved size is 70 au. In contrast, the upper limits we placed on COM abundances for A1 are extremely low, lying about one order of magnitude below prestellar values. The difference in the amount of COMs present in A1 and A2 ranges between one and two orders of magnitude. Our results suggest that the optical depth of dust emission at these wavelengths is unlikely to be sufficiently high to completely hide a hot corino in A1 similar in size to that in A2. Thus, the significant contrast in molecular richness found between the two sources is most probably real. We estimate that the size of a hypothetical hot corino in A1 should be less than 12 au. Conclusions: Our results favour a scenario in which the protostar in A2 is either more massive and/or subject to a higher accretion rate than A1, as a result of inhomogeneous fragmentation of the parental molecular clump. This naturally explains the smaller current envelope mass in A2 with respect to A1 along with its molecular richness. The extremely low abundances of organic molecules in A1 with respect to those in A2 demonstrate that the dense inner regions of a young protostellar core lacking hot corino activity may be poorer in COMs than the outer protostellar envelope. The reduced datacube is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/A121

Lagrangian Photochemical Box-Model Calculations of Asian Pacific Rim Outflow During TRACE-P

NASA Astrophysics Data System (ADS)

Hamlin, A.; Crawford, J.; Olson, J.; Avery, M.; Sachse, G.; Barrick, J.; Blake, D.; Tan, D.; Sandholm, S.; Kondo, Y.; Singh, H.; Eisele, F.; Zondlo, M.; Flocke, F.; Talbot, R.

2006-12-01

NASA's TRACE-P (TRAnsport and Chemical Evolution over the Pacific) mission was conducted over the northwestern Pacific February-April, 2001. During two transit flights across the Pacific, extensive pollution was observed from an Asian outflow event that split into two branches over the central Pacific, one subsiding and moving southward over the central Pacific and the other continuing eastward in the upper troposphere. The subsiding branch was observed as a widespread stagnant pollution layer between 2 and 4 km over the central Pacific during transit flights from Kona, HI to Guam. In this region, high levels of O3 (70 ppbv), CO (217 ppbv), and NOx (114 pptv) were well in excess of typical values observed during TRACE-P along the Asian coast. Evidence suggests that the subsiding branch experienced extensive photochemical processing compared to the branch that remained at altitude. To examine the processes controlling the chemical evolution of ozone and its precursors in this outflow event, data collected during the TRACE-P mission have been combined with lagrangian photochemical box model calculations. One of the largest sources of uncertainty in these calculations was associated with predicted water vapor levels along the transport trajectories calculated using the HYSPLIT model. Water vapor levels predicted by HYSPLIT trajectory calculations in the subsiding layer ranged from 3390 to 4880 ppm, while the median level observed in the pollution layer was only 637 ppm. Simulations of ozone production and associated radical chemistry differed dramatically when using water vapor levels based on trajectory calculations versus observed water vapor levels. Levels of PAN and HO2NO2, NOx reservoir species, are also influenced by uncertainties in temperature along the trajectories. These results highlight the importance of accurately representing the humidification and warming of subsiding air masses in 3-D chemical- transport models.

GREEN BANK TELESCOPE DETECTION OF POLARIZATION-DEPENDENT H I ABSORPTION AND H I OUTFLOWS IN LOCAL ULIRGs AND QUASARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teng, Stacy H.; Veilleux, Sylvain; Baker, Andrew J., E-mail: stacy.h.teng@nasa.gov

2013-03-10

We present the results of a 21 cm H I survey of 27 local massive gas-rich late-stage mergers and merger remnants with the Robert C. Byrd Green Bank Telescope. These remnants were selected from the Quasar/ULIRG Evolution Study sample of ultraluminous infrared galaxies (ULIRGs; L{sub 8{sub -{sub 1000{sub {mu}m}}}} > 10{sup 12} L{sub Sun }) and quasars; our targets are all bolometrically dominated by active galactic nuclei (AGNs) and sample the later phases of the proposed ULIRG-to-quasar evolutionary sequence. We find the prevalence of H I absorption (emission) to be 100% (29%) in ULIRGs with H I detections, 100% (88%)more » in FIR-strong quasars, and 63% (100%) in FIR-weak quasars. The absorption features are associated with powerful neutral outflows that change from being mainly driven by star formation in ULIRGs to being driven by the AGN in the quasars. These outflows have velocities that exceed 1500 km s{sup -1} in some cases. Unexpectedly, we find polarization-dependent H I absorption in 57% of our spectra (88% and 63% of the FIR-strong and FIR-weak quasars, respectively). We attribute this result to absorption of polarized continuum emission from these sources by foreground H I clouds. About 60% of the quasars displaying polarized spectra are radio-loud, far higher than the {approx}10% observed in the general AGN population. This discrepancy suggests that radio jets play an important role in shaping the environments in these galaxies. These systems may represent a transition phase in the evolution of gas-rich mergers into ''mature'' radio galaxies.« less

Observations of the impact of starbursts on the interstellar medium in dwarf galaxies

NASA Astrophysics Data System (ADS)

Marlowe, Amanda T.; Heckman, Timothy M.; Wyse, Rosemary F. G.; Schommer, Robert

1995-01-01

Dwarf galaxies play a crucial role in our understanding of the formation and evolution of galaxies, and the concept of supernova-driven mass outflows is a vital ingredient in theories of the structure and evolution of dwarf galaxies. Despite the theoretical importance of these outflows, there is a very limited amount of direct observational evidence for their existence. We have therefore begun a detailed multi-wave-band search for outflows in dwarf (MB greater than or = -18) galaxies with extensive recent or ongoing centrally concentrated star formation. We report the first results of this search in the present paper. Observations of the ionized gas in dwarf amorphous galaxies with centrally concentrated populations of massive stars provide evidence for the large-scale expansion of their expansion of their ionized interstellar media. Fabry-Perot H alpha images reveal the presence of kiloparsec-scale 'superbubbles' and filaments which tend to be oriented along the galaxy minor axis. These structures are comparable in size to the chracteristic optical sizes of the galaxies, and dominate the morphology of the galaxies at low surface brightness in H alpha. Since expanding structure of this size and velocity are not observed in all low-mass galaxies with recent or ongoing star formation, we suggest that we are witnessing transient events that likely have a relatively low 'duty cycle' in such galaxies. That is, we argue that the particular galaxies in the present paper have had significantly elevated star formation rates over the past 107-108 yr (i.e., these are starburst or young poststarburst systems). This interpretation is consistent with the optical colors and emission-line properties of these galaxies.

Observations of the impact of starbursts on the interstellar medium in dwarf galaxies

NASA Technical Reports Server (NTRS)

Marlowe, Amanda T.; Heckman, Timothy M.; Wyse, Rosemary F. G.; Schommer, Robert

1995-01-01

Dwarf galaxies play a crucial role in our understanding of the formation and evolution of galaxies, and the concept of supernova-driven mass outflows is a vital ingredient in theories of the structure and evolution of dwarf galaxies. Despite the theoretical importance of these outflows, there is a very limited amount of direct observational evidence for their existence. We have therefore begun a detailed multi-wave-band search for outflows in dwarf (M(sub B) greater than or = -18) galaxies with extensive recent or ongoing centrally concentrated star formation. We report the first results of this search in the present paper. Observations of the ionized gas in dwarf amorphous galaxies with centrally concentrated populations of massive stars provide evidence for the large-scale expansion of their expansion of their ionized interstellar media. Fabry-Perot H alpha images reveal the presence of kiloparsec-scale 'superbubbles' and filaments which tend to be oriented along the galaxy minor axis. These structures are comparable in size to the chracteristic optical sizes of the galaxies, and dominate the morphology of the galaxies at low surface brightness in H alpha. Since expanding structure of this size and velocity are not observed in all low-mass galaxies with recent or ongoing star formation, we suggest that we are witnessing transient events that likely have a relatively low 'duty cycle' in such galaxies. That is, we argue that the particular galaxies in the present paper have had significantly elevated star formation rates over the past 10(exp 7)-10(exp 8) yr (i.e., these are starburst or young poststarburst systems). This interpretation is consistent with the optical colors and emission-line properties of these galaxies.

Far-infrared image restoration analysis of the protostellar cluster in S140

NASA Technical Reports Server (NTRS)

Lester, D. F.; Harvey, P. M.; Joy, M.; Ellis, H. B., Jr.

1986-01-01

Image restoration techniques are applied to one-dimensional scans at 50 and 100 microns of the protostellar cluster in S140. These measurements resolve the surrounding nebula clearly, and Fourier methods are used to match the effective beam profiles at these wavelengths. This allows the radial distribution of temperature and dust column density to be derived at a diffraction limited spatial resolution of 23 arcsec (0.1 pc). Evidence for heating of the S140 molecular cloud by a nearby ionization front is established, and the dissociation of molecules inside the ionization front is spatially well correlated with the heating of the dust. The far-infrared spectral distribution of the three near-infrared sources within 10 arcsesc of the cluster center is presented.

Production of Organic Grain Coatings by Surface-Mediated Reactions and the Consequences of This Process for Meteoritic Constituents

NASA Technical Reports Server (NTRS)

Nuth, Joseph A., III; Johnson, Natasha M.

2011-01-01

When hydrogen, nitrogen and CO are exposed to amorphous iron silicate surfaces at temperatures between 500 - 900K, a carbonaceous coating forms via Fischer-Tropsch type reactions. Under normal circumstances such a catalytic coating would impede or stop further reaction. However, we find that this coating is a better catalyst than the amorphous iron silicates that initiate these reactions. The formation of a self-perpetuating catalytic coating on grain surfaces could explain the rich deposits of macromolecular carbon found in primitive meteorites and would imply that protostellar nebulae should be rich in organic material. Many more experiments are needed to understand this chemical system and its application to protostellar nebulae.

Jets from Young Stars in Cygnus-X

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-03-01

How do you spot very young, newly formed stars? One giveaway is the presence of jets and outflows that interact with the stars environments. In a new study, scientists have now discovered an unprecedented number of these outflows in a nearby star-forming region of our galaxy.Young Stars Hard at WorkCO map of the Cygnus-X region of the galactic plane, with the grid showing the UWISH2 coverage and the black triangles showing the positions of the detected outflows. [Makin Froebrich 2018]The birth and evolution of young stars is a dynamic, energetic process. As new stars form, material falls inward from the accretion disks surrounding young stellar objects, or YSOs. This material can power collimated streams of gas and dust that flow out along the stars rotation axes, plowing through the surrounding material. Where the outflows collide with the outside environment, shocks form that can be spotted in near-infrared hydrogen emission.Though weve learned a lot about these outflows, there remain a number of open questions. What factors govern their properties, such as their lengths, luminosities, and orientations? What is the origin of the emission features we see within the jets, known as knots? What roles do the driving sources and the environments play in the behavior and appearance of the jets?A selection of previously unknown outflows discovered as a result of this survey. Click for a closer look. [Makin Froebrich 2018]To answer these questions, we need to build a large, unbiased statistical sample of YSOs from across the galactic plane. Now, a large infrared survey known as the UKIRT Widefield Infrared Survey for H2 (UWISH2) is working toward that goal.Jackpot in Cygnus-XIn a recent publication, Sally Makin and Dirk Froebrich (University of Kent, UK), present results from UWISH2s latest release: a survey segment targeting a 42-square-degree region in the galactic plane known as the Cygnus-X star-forming region.The teams search for shock-excited emission in Cygnus-X yielded spectacular results. They found a treasure trove of outflows a remarkable 572 in total, representing a huge increase over the 107 known previously.Makin and Froebrich then measured properties of the outflows themselves such as length, orientation, and flux as well as properties of the sources that appear to drive them.Pinning Down PropertiesThis low-mass bright-rimmed cloud near IRAS 20294+4255 contains a number of stellar outflows. It may warrant further study as a classical example of triggered star formation. [Makin Froebrich 2018]Of the 572 outflows, the authors found that 27% are one-sided jets and 46% are bipolar. The bipolar outflows are typically 1.5 light-years in total length, and they are frequently asymmetric, with the shorter jet lobe averaging only 70% the length of the longer one. The flux from the two sides of bipolar jets is also often asymmetric: typically one side is brighter by about 50%.Exploring the knots of bright emission within the outflows, the authors found that they are typically closely spaced, suggesting that the material generating them is ejected every 9001,400 years. This rapid production faster than what has been found in YSO outflows in other regions rules out some models of how these knots are produced.Based on the fraction of UWISH2 data analyzed so far, the authors estimate that the entire UWISH2 survey will uncover a total of 2,000 jets and outflows from YSOs. This large, unbiased new sample is finally allowing astronomers to build out the statistics of YSO outflows to better understand them.CitationS. V. Makin and D. Froebrich 2018 ApJS 234 8. doi:10.3847/1538-4365/aa8862

MULTIPLE OUTFLOWS IN THE GIANT ERUPTION OF A MASSIVE STAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Humphreys, Roberta M.; Gordon, Michael S.; Jones, Terry J.

The supernova impostor PSN J09132750+7627410 in NGC 2748 reached a maximum luminosity of ≈−14 mag. It was quickly realized that it was not a true supernova, but another example of a nonterminal giant eruption. PSN J09132750+7627410 is distinguished by multiple P Cygni absorption minima in the Balmer emission lines that correspond to outflow velocities of −400, −1100, and −1600 km s{sup −1}. Multiple outflows have been observed in only a few other objects. In this paper we describe the evolution of the spectrum and the P Cygni profiles for 3 months past maximum, the post-maximum formation of a cool, densemore » wind, and the identification of a possible progenitor. One of the possible progenitors is an infrared source. Its pre-eruption spectral energy distribution suggests a bolometric luminosity of −8.3 mag and a dust temperature of 780 K. If it is the progenitor, it is above the AGB limit, unlike the intermediate-luminosity red transients. The three P Cygni profiles could be due to ejecta from the current eruption, the wind of the progenitor, or previous mass-loss events. We suggest that they were all formed as part of the same high-mass-loss event and are due to material ejected at different velocities or energies. We also suggest that multiple outflows during giant eruptions may be more common than reported.« less

Precipitation-generated oscillations in open cellular cloud fields.

PubMed

Feingold, Graham; Koren, Ilan; Wang, Hailong; Xue, Huiwen; Brewer, Wm Alan

2010-08-12

Cloud fields adopt many different patterns that can have a profound effect on the amount of sunlight reflected back to space, with important implications for the Earth's climate. These cloud patterns can be observed in satellite images of the Earth and often exhibit distinct cell-like structures associated with organized convection at scales of tens of kilometres. Recent evidence has shown that atmospheric aerosol particles-through their influence on precipitation formation-help to determine whether cloud fields take on closed (more reflective) or open (less reflective) cellular patterns. The physical mechanisms controlling the formation and evolution of these cells, however, are still poorly understood, limiting our ability to simulate realistically the effects of clouds on global reflectance. Here we use satellite imagery and numerical models to show how precipitating clouds produce an open cellular cloud pattern that oscillates between different, weakly stable states. The oscillations are a result of precipitation causing downward motion and outflow from clouds that were previously positively buoyant. The evaporating precipitation drives air down to the Earth's surface, where it diverges and collides with the outflows of neighbouring precipitating cells. These colliding outflows form surface convergence zones and new cloud formation. In turn, the newly formed clouds produce precipitation and new colliding outflow patterns that are displaced from the previous ones. As successive cycles of this kind unfold, convergence zones alternate with divergence zones and new cloud patterns emerge to replace old ones. The result is an oscillating, self-organized system with a characteristic cell size and precipitation frequency.

A Compton-thick Wind in the High Luminosity Quasar, PDS 456

NASA Technical Reports Server (NTRS)

Reeves, J. N.; O'Brien, P. T.; Behar, E.; Miller, L.; Turner, T. J.; Braito, V.; Fabian, A. C.; Kaspi, S.; Mushotzky, R.; Ward, M.

2009-01-01

PDS 456 is a nearby (z=0.184), luminous (L(sub bol) approximately equal to 10(exp 47) ergs(exp -1) type I quasar. A deep 190 ks Suzaku observation in February 2007 revealed the complex, broad band X-ray spectrum of PDS 456. The Suzaku spectrum exhibits highly statistically significant absorption features near 9 keV in the quasar rest-frame. We show that the most plausible origin of the absorption is from blue-shifted resonance (1s-2p) transitions of hydrogen-like iron (at 6.97 keV in the rest frame). This indicates that a highly ionized outflow may be present moving at near relativistic velocities (0.26-0.31c). A possible hard X-ray excess is detected above 15 keV with HXD (at 99.8% confidence), which may arise from high column density gas (N(sub H) greater than 10(exp 24)cm(exp -2) partially covering the X-ray emission, or through strong Compton reflection. Here we propose that the iron K-shell absorption in PDS 456 is associated with a thick, possibly clumpy outflow, covering about 20% of 4(pi) steradian solid angle. The outflow is likely launched from the inner accretion disk, within 15-100 gravitational radii of the black hole. The kinetic power of the outflow may be similar to the bolometric luminosity of PDS 456. Such a powerful wind could have a significant effect on the co-evolution of the host galaxy and its supermassive black hole, through feedback.

Hydrodynamic simulations of viscous accretion flows around black holes

NASA Astrophysics Data System (ADS)

Giri, Kinsuk; Chakrabarti, Sandip K.

2012-03-01

We study the time evolution of a rotating, axisymmetric, viscous accretion flow around black holes using a grid-based finite difference method. We use the Shakura-Sunyaev viscosity prescription. However, we compare with the results obtained when all the three independent components of the viscous stress are kept. We show that the centrifugal pressure supported shocks became weaker with the inclusion of viscosity. The shock is formed farther out when the viscosity is increased. When the viscosity is above a critical value, the shock disappears altogether and the flow becomes subsonic and Keplerian everywhere except in a region close to the horizon, where it remains supersonic. We also find that as the viscosity is increased, the amount of outflowing matter in the wind is decreased to less than a percentage of the inflow matter. Since the post-shock region could act as a reservoir of hot electrons or the so-called 'Compton cloud', the size of which changes with viscosity, the spectral properties are expected to depend on viscosity strongly: the harder states are dominated by low angular momentum and the low-viscosity flow with significant outflows while the softer states are dominated by the high-viscosity Keplerian flow having very few outflows.

Bipolar Molecular Outflows within 1pc of Sgr A*:Evidence for Low-mass Star Formation Activity

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, Farhad; Wardle, Mark; Kunneriath, Devaky; Royster, Marc; Wootten, Al; Roberts, Douglas

2018-01-01

The 4 million solar mass black hole, Sgr A*, is expected to suppress star formation because the measured density of the cloud is insufficient for self-gravity to overcome tidal disruption by the black hole's gravitational field. Nevertheless, objects resembling dust-enshrouded young stars and photo-evaporative flows from their disks have been identified within 2pc of Sgr A*. Clear identification of the nature of these objects has been hampered by the Galactic center's distance, 30 magnitudes of foreground extinction, and stellar crowding. Here, we report the discovery of 11 bipolar molecular outflows using ALMA within a projected distance of one pc from Sgr A*. These unambiguous signatures of young protostars manifest as approaching and receding lobes of dense gas swept up by the jets created during the formation and early evolution of low-mass stars. The mean dynamical age of the outflow sources and the rate of star formation are estimated to be ~6500 years and ~5x10^{-4} solar mass per year, respectively. These measurements suggest that star formation could take place in the immediate vicinity of supermassive black holes in the nuclei of external galaxies.

Molecular clumps photoevaporation in ionized regions

NASA Astrophysics Data System (ADS)

Decataldo, D.; Ferrara, A.; Pallottini, A.; Gallerani, S.; Vallini, L.

2017-11-01

We study the photoevaporation of molecular clumps exposed to a UV radiation field including hydrogen-ionizing photons (hν > 13.6 eV) produced by massive stars or quasars. We follow the propagation and collision of shock waves inside clumps and take into account self-shielding effects, determining the evolution of clump size and density with time. The structure of the ionization-photodissociation region is obtained for different initial clump masses (M = 0.01-104 M⊙) and impinging fluxes (G0 = 102-105 in units of the Habing flux). The cases of molecular clumps engulfed in the H II region of an OB star and clumps carried within quasar outflows are treated separately. We find that the clump undergoes in both cases an initial shock-contraction phase and a following expansion phase, which lets the radiation penetrate in until the clump is completely evaporated. Typical evaporation time-scales are ≃0.01 Myr in the stellar case and 0.1 Myr in the quasar case, where the clump mass is 0.1 M⊙ and 103 M⊙, respectively. We find that clump lifetimes in quasar outflows are compatible with their observed extension, suggesting that photoevaporation is the main mechanism regulating the size of molecular outflows.

The Red Sea outflow regulated by the Indian monsoon

NASA Astrophysics Data System (ADS)

Aiki, Hidenori; Takahashi, Keiko; Yamagata, Toshio

2006-08-01

To investigate why the Red Sea water overflows less in summer and more in winter, we have developed a locally high-resolution global OGCM with transposed poles in the Arabian peninsula and India. Based on a series of sensitivity experiments with different sets of idealized atmospheric forcing, the present study shows that the summer cessation of the strait outflow is remotely induced by the monsoonal wind over the Indian Ocean, in particular that over the western Arabian Sea. During the southwest monsoon (May-September), thermocline in the Gulf of Aden shoals as a result of coastal Ekman upwelling induced by the predominantly northeastward wind in the Gulf of Aden and the Arabian Sea. Because this shoaling is maximum during the southwest summer monsoon, the Red Sea water is blocked at the Bab el Mandeb Strait by upwelling of the intermediate water of the Gulf of Aden in late summer. The simulation also shows the three-dimensional evolution of the Red Sea water tongue at the mid-depths in the Gulf of Aden. While the tongue meanders, the discharged Red Sea outflow water (RSOW) (incoming Indian Ocean intermediate water (IOIW)) is always characterized by anticyclonic (cyclonic) vorticity, as suggested from the potential vorticity difference.

Super-Eddington Mechanical Power of an Accreting Black Hole in M83

NASA Technical Reports Server (NTRS)

Soria, R.; Long, K. S.; Blair, W. P.; Godfrey, L.; Kuntz, K. D.; Lenc, E.; Stockdale, C.; Winkler, P. F.

2014-01-01

Mass accretion onto black holes releases energy in the form of radiation and outflows. Although the radiative flux cannot substantially exceed the Eddington limit, at which the outgoing radiation pressure impedes the inflow of matter, it remains unclear whether the kinetic energy flux is bounded by this same limit. Here, we present the detection of a radio-optical structure, powered by outflows from a non-nuclear black hole. Its accretion disk properties indicate that this black hole is less than 100 solar masses. The optical-infrared line emission implies an average kinetic power of 3 × 10(exp 40) erg second(exp -1), higher than the Eddington luminosity of the black hole. These results demonstrate kinetic power exceeding the Eddington limit over a sustained period, which implies greater ability to influence the evolution of the black hole's environment.

Super-Eddington mechanical power of an accreting black hole in M83.

PubMed

Soria, R; Long, K S; Blair, W P; Godfrey, L; Kuntz, K D; Lenc, E; Stockdale, C; Winkler, P F

2014-03-21

Mass accretion onto black holes releases energy in the form of radiation and outflows. Although the radiative flux cannot substantially exceed the Eddington limit, at which the outgoing radiation pressure impedes the inflow of matter, it remains unclear whether the kinetic energy flux is bounded by this same limit. Here, we present the detection of a radio-optical structure, powered by outflows from a non-nuclear black hole. Its accretion disk properties indicate that this black hole is less than 100 solar masses. The optical-infrared line emission implies an average kinetic power of 3 × 10(40) erg second(-1), higher than the Eddington luminosity of the black hole. These results demonstrate kinetic power exceeding the Eddington limit over a sustained period, which implies greater ability to influence the evolution of the black hole's environment.

Accretion Disk Outflows from Compact Object Mergers

NASA Astrophysics Data System (ADS)

Metzger, Brian

Nuclear reactions play a key role in the accretion disks and outflows associated with the merger of binary compact objects and the central engines of gamma-ray bursts and supernovae. The proposed research program will investigate the impact of nucleosynthesis on these events and their observable signatures by means of analytic calculations and numerical simulations. One focus of this research is rapid accretion following the tidal disruption of a white dwarf (WD) by a neutron star (NS) or black hole (BH) binary companion. Tidal disruption shreds the WD into a massive torus composed of C, O, and/or He, which undergoes nuclear reactions and burns to increasingly heavier elements as it flows to smaller radii towards the central compact object. The nuclear energy so released is comparable to that released gravitationally, suggesting that burning could drastically alter the structure and stability of the accretion flow. Axisymmetric hydrodynamic simulations of the evolution of the torus including nuclear burning will be performed to explore issues such as the mass budget of the flow (accretion vs. outflows) and its thermal stability (steady burning and accretion vs. runaway explosion). The mass, velocity, and composition of outflows from the disk will be used in separate radiative transfer calculations to predict the lightcurves and spectra of the 56Ni-decay powered optical transients from WD-NS/WD-BH mergers. The possible connection of such events to recently discovered classes of sub-luminous Type I supernovae will be assessed. The coalescence of NS-NS/NS-BH binaries also results in the formation of a massive torus surrounding a central compact object. Three-dimensional magnetohydrodynamic simulations of the long-term evolution of such accretion disks will be performed, which for the first time follow the effects of weak interactions and the nuclear energy released by Helium recombination. The nucleosynthetic yield of disk outflows will be calculated using a detailed nuclear reaction network along characteristic Lagrangian trajectories. Results of these calculations will be used to (1) reassess NS-NS/NS-BH mergers as an astrophysical source of heavy r-process nuclei; and (2) calculate the light curves of the optical transients (`kilonovae') powered by the radioactive decay. Separate work will assess the effects that neutrino irradiation from a long-lived neutron star remnant has on the electron fraction of the disk outflows. The strong contrast between the opacities of proton- and neutron-rich matter imply that the presence and lifetime of such a remnant could be imprinted on the kilonova emission. Our investigation sheds light on the central engines of GRBs and other high-energy transients and hence is relevant to NASA's Swift, MAXI, and Fermi missions. Our results will also impact the interpretation of future observations of supernovae and their galactic environments with the Hubble Space Telescope (HST). Our results will also impact follow-up observations of kilonovae, maximizing the impact of HST to constrain the key open questions such as the progenitors of gamma-ray bursts and the origin of r-process nuclei.

The Feedback of Star Formation Based on Large-scale Spectroscopic Mapping Technology

NASA Astrophysics Data System (ADS)

Li, H. X.

2017-05-01

Star Formation is a fundamental topic in astrophysics. Although there is a popular model of low-mass star formation, every step of the process is full of physical and chemical complexity. One of the key questions is the dynamical feedback during the process of star formation. The answer of this question will help us to understand the star formation and the evolution of molecular clouds. We have identified outflows and bubbles in the Taurus molecular cloud based on the ˜ 100 deg2 Five College Radio Astronomy Observatory 12CO(1-0) and 13CO(1-0) maps and the Spitzer young stellar object (YSO) catalog. In the main 44 deg2 area of Taurus, we found 55 outflows, of which 31 were previously unknown. We also found 37 bubbles in the entire 100 deg2 area of Taurus, all of which had not been identified before. After visual inspection, we developed an interactive IDL pipeline to confirm the outflows and bubbles. This sample covers a contiguous region with a linear spatial dynamic range of ˜ 1000. Among the 55 outflows, we found that bipolar, monopolar redshifted, and monopolar blueshifted outflows account for 45%, 44%, and 11%, respectively. There are more red lobes than blue ones. The occurrence of more red lobes may result from the fact that Taurus is thin. Red lobes tend to be smaller and younger. The total mass and energy of red lobes are similar to blue lobes on average. There are 3 expanding bubbles and 34 broken bubbles among all the bubbles in Taurus. There are more outflow-driving YSOs in Class I, Flat, and Class II while few outflow-driving YSOs in Class III, which indicates that outflows more likely appear in the earlier stage (Class I) than in the later phase (Class III) of star formation. There are more bubble-driving YSOs of Class II and Class III while there are few bubble-driving YSOs of Class I and Flat, implying that the bubble structures are more likely to occur in the later stage of star formation. The total kinetic energy of the identified outflows is estimated to be ˜ 3.9 × 1045 erg, which is 1% of the cloud turbulent energy. The total kinetic energy of the detected bubbles is estimated to be ˜ 9.2 × 1046 erg, which is 29% of the turbulent energy of Taurus. The energy injection rate from the outflows is ˜ 1.3 × 1033 erg s-1, 0.4-2 times the turbulent dissipation rate of the cloud. The energy injection rate from bubbles is ˜ 6.4 × 1033 erg s-1, 2-10 times the turbulent dissipation rate of the cloud. The gravitational binding energy of the cloud is ˜ 1.5 × 1048 erg, 385 and 16 times the energy of outflows and bubbles, respectively. We conclude that neither outflows nor bubbles can provide sufficient energy to balance the overall gravitational binding energy and the turbulent energy of Taurus. However, in the current epoch, stellar feedback is sufficient to maintain the observed turbulence in Taurus. We studied the methods of spectral data processing for large-scale surveys, which is helpful in developing the data-processing software of FAST (Five-hundred-meter Aperture Spherical radio Telescope).

Generating large misalignments in gapped and binary discs

NASA Astrophysics Data System (ADS)

Owen, James E.; Lai, Dong

2017-08-01

Many protostellar gapped and binary discs show misalignments between their inner and outer discs; in some cases, ˜70° misalignments have been observed. Here, we show that these misalignments can be generated through a secular resonance between the nodal precession of the inner disc and the precession of the gap-opening (stellar or massive planetary) companion. An evolving protostellar system may naturally cross this resonance during its lifetime due to disc dissipation and/or companion migration. If resonance crossing occurs on the right time-scale, of the order of a few million years, characteristic for young protostellar systems, the inner and outer discs can become highly misaligned, with misalignments ≳ 60° typical. When the primary star has a mass of order a solar mass, generating a significant misalignment typically requires the companion to have a mass of ˜0.01-0.1 M⊙ and an orbital separation of tens of astronomical units. The recently observed companion in the cavity of the gapped, highly misaligned system HD 142527 satisfies these requirements, indicating that a previous resonance crossing event misaligned the inner and outer discs. Our scenario for HD 142527's misaligned discs predicts that the companion's orbital plane is aligned with the outer disc's; this prediction should be testable with future observations as the companion's orbit is mapped out. Misalignments observed in several other gapped disc systems could be generated by the same secular resonance mechanism.

Common Envelope Evolution: Implications for Post-AGB Stars and Planetary Nebulae

NASA Astrophysics Data System (ADS)

Nordhaus, J.

2017-10-01

Common envelopes (CE) are of broad interest as they represent one method by which binaries with initially long-period orbits of a few years can be converted into short-period orbits of a few hours. Despite their importance, the brief lifetimes of CE phases make them difficult to directly observe. Nevertheless, CE interactions are potentially common, can produce a diverse array of nebular shapes, and can accommodate current post-AGB and planetary nebula outflow constraints. Here, I discuss ongoing theoretical and computational work on CEs and speculate on what lies ahead for determining accurate outcomes of this elusive phase of evolution.

The response of filamentary and spherical clouds to the turbulence and magnetic field

NASA Astrophysics Data System (ADS)

Gholipour, Mahmoud

2018-05-01

Recent observations have revealed that there is a power-law relation between magnetic field and density in molecular clouds. Furthermore, turbulence has been observed in some regions of molecular clouds and the velocity dispersion resulting from the turbulence is found to correlate with to the cloud density. Relating to these observations, in this study, we model filamentary and spherical clouds in magnetohydrostatic equilibrium in two quiescent and turbulent regions. The proposed equations are expected to represent the impact of magnetic field and turbulence on the cloud structure and the relation of cloud mass with shape. The Virial theorem is applied to consider the cloud evolution leading to important conditions for equilibrium of the cloud over its lifetime. The obtained results indicate that under the same conditions of the magnetic field and turbulence, each shape presents different responses. The possible ways for the formation of massive cores or coreless clouds in some regions as well as the formation of massive stars or low-mass stars can be discussed based on the results of this study. It should be mentioned that the shape of the clouds plays an important role in the formation of the protostellar clouds as well as their structure and evolution. This role is due to the effects of magnetic fields and turbulence.

Role of Massive Stars in the Evolution of Primitive Galaxies

NASA Technical Reports Server (NTRS)

Heap, Sara

2012-01-01

An important factor controlling galaxy evolution is feedback from massive stars. It is believed that the nature and intensity of stellar feedback changes as a function of galaxy mass and metallicity. At low mass and metallicity, feedback from massive stars is mainly in the form of photoionizing radiation. At higher mass and metallicity, it is in stellar winds. IZw 18 is a local blue, compact dwarf galaxy that meets the requirements for a primitive galaxy: low halo mass greater than 10(exp 9)Msun, strong photoionizing radiation, no galactic outflow, and very low metallicity,log(O/H)+12=7.2. We will describe the properties of massive stars and their role in the evolution of IZw 18, based on analysis of ultraviolet images and spectra obtained with HST.

Chemical complexity induced by efficient ice evaporation in the Barnard 5 molecular cloud

NASA Astrophysics Data System (ADS)

Taquet, V.; Wirström, E. S.; Charnley, S. B.; Faure, A.; López-Sepulcre, A.; Persson, C. M.

2017-10-01

Cold gas-phase water has recently been detected in a cold dark cloud, Barnard 5 located in the Perseus complex, by targeting methanol peaks as signposts for ice mantle evaporation. Observed morphology and abundances of methanol and water are consistent with a transient non-thermal evaporation process only affecting the outermost ice mantle layers, possibly triggering a more complex chemistry. Here we present the detection of the complex organic molecules (COMs) acetaldehyde (CH3CHO) and methyl formate (CH3OCHO), as well as formic acid (HCOOH) and ketene (CH2CO), and the tentative detection of di-methyl ether (CH3OCH3) towards the "methanol hotspot" of Barnard 5 located between two dense cores using the single dish OSO 20 m, IRAM 30 m, and NRO 45 m telescopes. The high energy cis-conformer of formic acid is detected, suggesting that formic acid is mostly formed at the surface of interstellar grains and then evaporated. The detection of multiple transitions for each species allows us to constrain their abundances through LTE and non-LTE methods. All the considered COMs show similar abundances between 1 and 10% relative to methanol depending on the assumed excitation temperature. The non-detection of glycolaldehyde, an isomer of methyl formate, with a [glycolaldehyde]/[methyl formate] abundance ratio lower than 6%, favours gas phase formation pathways triggered by methanol evaporation. According to their excitation temperatures derived in massive hot cores, formic acid, ketene, and acetaldehyde have been designated as "lukewarm" COMs whereas methyl formate and di-methyl ether were defined as "warm" species. Comparison with previous observations of other types of sources confirms that lukewarm and warm COMs show similar abundances in low-density cold gas whereas the warm COMs tend to be more abundant than the lukewarm species in warm protostellar cores. This abundance evolution suggests either that warm COMs are indeed mostly formed in protostellar environments and/or that lukewarm COMs are efficiently depleted by increased hydrogenation efficiency around protostars.

Study of Outflow and Molecular Lines from the Observations of BHR71 by The Herschel Key Program,``Dust, Ice, and Gas In Time" (DIGIT)

NASA Astrophysics Data System (ADS)

Yang, Yao-Lun; Green, Joel D.

2014-07-01

The infall and outflow processes initiated by the collapse a dense core are widely observed in Class 0 protostars, and significantly change the density and temperature structure of the prestellar core as well as the following disk and envelope evolution. Since the Class 0 protostars are usually embedded in the cold molecular envelope preventing them from being observed at visible or near-IR wavelengths, the spectral analyses of the far-IR spectra provide us a window to look through the envelope and constrain the physical properties of the envelope and the core. BHR71, a Class 0 embedded protostar, is located in an isolated neighborhood with a collimated bipolar outflow and shows a rich far-IR spectrum as observed in the DIGIT program (PI: Neal Evans) with Herschel. It has numerous molecular and atomic features that can constrain its physical properties and the density structure well. In this research, we developed a robust data reduction (Green et al. 2013a, b) and automatic line fitting package that ensures all of the molecular and atomic lines are extracted to the same standard and it can be easily used for any other protostars observed by Herschel as well. We found 44 and 28 emission lines in the central spaxel in the PACS and the SPIRE bands respectively, including CO, 13CO, OH, and H2O. The extended feature observed at low-J CO and several H2O lines are consistent to the outflow direction but less collimated and a heterogeneous environment is concluded from the rotational diagram analysis. A dust Monte Carlo radiative transfer simulation using RADMC-3D will reveal the embedded structure with a dust density profile of a flared disk and a spherical envelope with bipolar outflow cavity. We will use a line radiative transfer simulation for multiple species to constrain the chemical abundance distributions and their temperature profiles.With high sensitivity spatial resolved spectra and simulated internal structure analysis of BHR71 will provide a good test of theoretical models of the infall and outflow.

Magnetic Topology and Ion Outflow in Mars' Magnetotail

NASA Astrophysics Data System (ADS)

Mitchell, D. L.; Xu, S.; McFadden, J. P.; Hara, T.; Luhmann, J. G.; Mazelle, C. X.; Andersson, L.; DiBraccio, G. A.; Connerney, J. E. P.

2017-12-01

Planetary ion outflow down the Martian magnetotail could be an important atmospheric loss mechanism. This process depends on magnetic connectivity to the day-side ionosphere and on acceleration of ions to escape velocity. The Mars Atmosphere and Volatile Evolution (MAVEN) mission has obtained comprehensive ion, electron, and magnetic field data in Mars' magnetotail. The spacecraft is in a 75°-inclination, elliptical orbit that samples altitudes from 150 to 6200 km. As the orbit precesses, it sweeps through the tail at a variety of altitudes in this range. Data from the Solar Wind Electron Analyzer (SWEA) and Magnetometer (MAG) are used to determine the magnetic field topology in the tail at high cadence (every 2-4 seconds), and in particular whether field lines are open, closed, or draped, and if open whether they have access to the day-side or night-side ionosphere. Simultaneous observations by the Supra-Thermal and Thermal Ion Composition (STATIC) instrument and the Langmuir Probe and Waves (LPW) experiment are used to measure the density, composition, and velocity of planetary plasma on these field lines. We find that magnetic topology in the tail is complex and variable, and is influenced by the IMF polarity and the orientation of Mars' crustal magnetic fields with respect to the Sun. We find that planetary ion outflow occurs on both open and draped field lines. On open field lines, outflow tends to occur parallel to the field line, with colder, denser, and slower outflow on field lines connected to the day-side ionosphere (Fig. 1). On these same field lines (after correction for the spacecraft potential) a shift in the position of the He-II photoelectron feature indicates a 1-Volt parallel electric potential directed away from the planet. Except for H+ and occasionally O+, this potential is insufficient by itself to accelerate planetary ions to escape velocity. Outflow is warmer, less dense, and faster moving on draped field lines. In this case, the ion bulk velocity can be at large angles to the magnetic field, suggesting JxB acceleration. This indicates that more than one mechanism is responsible for accelerating ions into the tail.

Warm Absorber Diagnostics of AGN Dynamics

NASA Astrophysics Data System (ADS)

Kallman, Timothy

Warm absorbers and related phenomena are observable manifestations of outflows or winds from active galactic nuclei (AGN) that have great potential value. Understanding AGN outflows is important for explaining the mass budgets of the central accreting black hole, and also for understanding feedback and the apparent co-evolution of black holes and their host galaxies. In the X-ray band warm absorbers are observed as photoelectric absorption and resonance line scattering features in the 0.5-10 keV energy band; the UV band also shows resonance line absorption. Warm absorbers are common in low luminosity AGN and they have been extensively studied observationally. They may play an important role in AGN feedback, regulating the net accretion onto the black hole and providing mechanical energy to the surroundings. However, fundamental properties of the warm absorbers are not known: What is the mechanism which drives the outflow?; what is the gas density in the flow and the geometrical distribution of the outflow?; what is the explanation for the apparent relation between warm absorbers and the surprising quasi-relativistic 'ultrafast outflows' (UFOs)? We propose a focused set of model calculations that are aimed at synthesizing observable properties of warm absorber flows and associated quantities. These will be used to explore various scenarios for warm absorber dynamics in order to answer the questions in the previous paragraph. The guiding principle will be to examine as wide a range as possible of warm absorber driving mechanisms, geometry and other properties, but with as careful consideration as possible to physical consistency. We will build on our previous work, which was a systematic campaign for testing important class of scenarios for driving the outflows. We have developed a set of tools that are unique and well suited for dynamical calculations including radiation in this context. We also have state-of-the-art tools for generating synthetic spectra, which are key for validating and testing models. New in this work is treatment of magnetically driven models, self-consistent calculation of the physical properties of the accretion flow and winds and their spectra. This will allow us to test the range of plausible physical origins for warm absorbers.

HO-CHUNK: Radiation Transfer code

NASA Astrophysics Data System (ADS)

Whitney, Barbara A.; Wood, Kenneth; Bjorkman, J. E.; Cohen, Martin; Wolff, Michael J.

2017-11-01

HO-CHUNK calculates radiative equilibrium temperature solution, thermal and PAH/vsg emission, scattering and polarization in protostellar geometries. It is useful for computing spectral energy distributions (SEDs), polarization spectra, and images.

The role of magnetic fields in the collapse of protostellar gas clouds

NASA Technical Reports Server (NTRS)

Scott, E. H.; Black, D. C.

1980-01-01

The paper presents the results of a numerical calculation of the collapse of an idealized protostellar gas cloud including the effects of a 'frozen-in' magnetic field. The 'traditional' picture of magnetic effects on gas clouds and recent observational and theoretical work on the subject are summarized. Attention is given to the method of calculation and the results are interpreted. It is found that the central magnetic field in the collapsing cloud model follows a rho to the 1/2 power relation, and the discussion implies that this is a general result which should hold true for some range of initial conditions around those chosen. In addition, it is found that the outer envelope of the cloud will be held up by tension in the field lines.

Polarization Science with the ngVLA: magnetic fields and dust properties in cores, disks and on larger scales

NASA Astrophysics Data System (ADS)

Matthews, Brenda; Hull, Chat

2018-01-01

Polarization capabilities of the ngVLA will enable exploration of a wide range of phenomena including: (1) magnetic fields in protostellar cores and protoplanetary disks via polarized emission from magnetically aligned dust grains and spectral lines, including in regions optically thick at ALMA wavelengths; (2) polarization from dust scattering in disks, (3) spectral-line polarization from the Zeeman and Goldreich-Kylafis effects, and (4) magnetic fields in protostellar jets and OB-star-forming cores via synchrotron emission.We will discuss each of these science drivers in turn, with a particular emphasis on why the ngVLA provides a unique means of probing dust properties in the midplane of protoplanetary disks and hence the building blocks of planets in the innermost regions of disks.

Dynamo magnetic field-induced angular momentum transport in protostellar nebulae - The 'minimum mass' protosolar nebula

NASA Technical Reports Server (NTRS)

Stepinski, T. F.; Levy, E. H.

1990-01-01

Magnetic torques can produce angular momentum redistribution in protostellar nebulas. Dynamo magnetic fields can be generated in differentially rotating and turbulent nebulas and can be the source of magnetic torques that transfer angular momentum from a protostar to a disk, as well as redistribute angular momentum within a disk. A magnetic field strength of 100-1000 G is needed to transport the major part of a protostar's angular momentum into a surrounding disk in a time characteristic of star formation, thus allowing formation of a solar-system size protoplanetary nebula in the usual 'minimum-mass' model of the protosolar nebula. This paper examines the possibility that a dynamo magnetic field could have induced the needed angular momentum transport from the proto-Sun to the protoplanetary nebula.

The ALMA Protostellar Interferometric Line Survey (PILS). First results from an unbiased submillimeter wavelength line survey of the Class 0 protostellar binary IRAS 16293-2422 with ALMA

NASA Astrophysics Data System (ADS)

Jørgensen, J. K.; van der Wiel, M. H. D.; Coutens, A.; Lykke, J. M.; Müller, H. S. P.; van Dishoeck, E. F.; Calcutt, H.; Bjerkeli, P.; Bourke, T. L.; Drozdovskaya, M. N.; Favre, C.; Fayolle, E. C.; Garrod, R. T.; Jacobsen, S. K.; Öberg, K. I.; Persson, M. V.; Wampfler, S. F.

2016-11-01

Context. The inner regions of the envelopes surrounding young protostars are characterized by a complex chemistry, with prebiotic molecules present on the scales where protoplanetary disks eventually may form. The Atacama Large Millimeter/submillimeter Array (ALMA) provides an unprecedented view of these regions zooming in on solar system scales of nearby protostars and mapping the emission from rare species. Aims: The goal is to introduce a systematic survey, the Protostellar Interferometric Line Survey (PILS), of the chemical complexity of one of the nearby astrochemical templates, the Class 0 protostellar binary IRAS 16293-2422, using ALMA in order to understand the origin of the complex molecules formed in its vicinity. In addition to presenting the overall survey, the analysis in this paper focuses on new results for the prebiotic molecule glycolaldehyde, its isomers, and rarer isotopologues and other related molecules. Methods: An unbiased spectral survey of IRAS 16293-2422 covering the full frequency range from 329 to 363 GHz (0.8 mm) has been obtained with ALMA, in addition to a few targeted observations at 3.0 and 1.3 mm. The data consist of full maps of the protostellar binary system with an angular resolution of 0.5'' (60 AU diameter), a spectral resolution of 0.2 km s-1, and a sensitivity of 4-5 mJy beam-1 km s-1, which is approximately two orders of magnitude better than any previous studies. Results: More than 10 000 features are detected toward one component in the protostellar binary, corresponding to an average line density of approximately one line per 3 km s-1. Glycolaldehyde; its isomers, methyl formate and acetic acid; and its reduced alcohol, ethylene glycol, are clearly detected and their emission well-modeled with an excitation temperature of 300 K. For ethylene glycol both lowest state conformers, aGg' and gGg', are detected, the latter for the first time in the interstellar medium (ISM). The abundance of glycolaldehyde is comparable to or slightly larger than that of ethylene glycol. In comparison to the Galactic Center these two species are over-abundant relative to methanol, possibly an indication of formation of the species at low temperatures in CO-rich ices during the infall of the material toward the central protostar. Both 13C and the deuterated isotopologues of glycolaldehyde are detected, also for the first time ever in the ISM. For the deuterated species, a D/H ratio of ≈5% is found with no differences between the deuteration in the different functional groups of glycolaldehyde, in contrast to previous estimates for methanol and recent suggestions of significant equilibration between water and -OH functional groups at high temperatures. Measurements of the 13C-species lead to a 12C:13C ratio of ≈30, lower than the typical ISM value. This low ratio may reflect an enhancement of 13CO in the ice due to either ion-molecule reactions in the gas before freeze-out or to differences in the temperatures where 12CO and 13CO ices sublimate. Conclusions: The results reinforce the importance of low-temperature grain surface chemistry for the formation of prebiotic molecules seen here in the gas after sublimation of the entire ice mantle. Systematic surveys of the molecules thought to be chemically related, as well as the accurate measurements of their isotopic composition, hold strong promise for understanding the origin of prebiotic molecules in the earliest stages of young stars.

Mathematical and physical model of gravity-fed infusion outflow: application to soft-bag-packed solutions.

PubMed

Simon, N; Décaudin, B; Lannoy, D; Barthélémy, C; Lemdani, M; Odou, P

2011-12-01

Gravity-fed infusion (GFI) systems are acknowledged as being unable to keep their flow-rate constant. This may affect drug plasma levels such as aminoglycosides. Numerous factors have previously been cited, but their relative importance has never been quantified so far. The objective of this work is to identify the main factors that influence GFI in vitro outflow and to propose a mathematical model of flow-rate evolution as a function of time. In this model, pressure loss and infusion device creep have been considered as the main variation factors. Concomitantly, two experiments were undertaken. Firstly, the flow-rate evolution of an in vitro infusion of 250 mL of dextrose 5% was assessed. Secondly, the creep occurring on an infusion device was measured through a stress relaxation experiment. The experimental infusion flow-rate decreased by as much as 28.5% over 1 h. Simulated and experimental data are well correlated (r = 0.987; P < 0.0001). The maximum creep effect happens during the first 15 min of infusion. In this work, height of the liquid in the bag and tube creep were found to be the main variation factors in GFI flow-rate. This new mathematical model should help to explain the differences observed in drug plasma levels with gravity-fed devices.

A guide to the use of theoretical models of the solar nebula for the interpretation of the meteoritic record

NASA Technical Reports Server (NTRS)

Cassen, Pat

1991-01-01

Attempts to derive a theoretical framework for the interpretation of the meteoritic record have been frustrated by our incomplete understanding of the fundamental processes that controlled the evolution of the primitive solar nebula. Nevertheless, it is possible to develop qualitative models of the nebula that illuminate its dynamic character, as well as the roles of some key parameters. These models draw on the growing body of observational data on the properties of disks around young, solar-type stars, and are constructed by applying the results of known solutions of protostellar collapse problems; making simple assumptions about the radial variations of nebular variables; and imposing the integral constraints demanded by conservation of mass, angular momentum, and energy. The models so constructed are heuristic, rather than predictive; they are intended to help us think about the nebula in realistic ways, but they cannot provide a definitive description of conditions in the nebula.

Hydrodynamical Modeling of Large Circumstellar Disks

NASA Astrophysics Data System (ADS)

Kurfürst, P.; Krtǐcka, J.

2016-11-01

Direct centrifugal ejection from a critically or near-critically rotating surface forms a gaseous equatorial decretion disk. Anomalous viscosity provides the efficient mechanism for transporting the angular momentum outwards. The outer part of the disk can extend up to a very large distance from the parent star. We study the evolution of density, radial and azimuthal velocity, and angular momentum loss rate of equatorial decretion disks out to very distant regions. We investigate how the physical characteristics of the disk depend on the distribution of temperature and viscosity. We also study the magnetorotational instability, which is considered to be the origin of anomalous viscosity in outflowing disks. We use analytical calculations to study the stability of outflowing disks submerged to the magnetic field. At large radii the instability disappears in the region where the disk orbital velocity is roughly equal to the sound speed. Therefore, the disk sonic radius can be roughly considered as an outer disk radius.

Nonlinear internal waves and plumes generated in response to sea-loch outflow, AUV, and time-lapse photography observations

NASA Astrophysics Data System (ADS)

Toberman, Matthew; Inall, Mark; Boyd, Tim; Dumount, Estelle; Griffiths, Colin

2017-07-01

The tidally modulated outflow of brackish water from a sea loch forms a thin surface layer that propagates into the coastal ocean as a buoyant gravity current, transporting nutrients and sediments, as well as fresh water, heat and momentum. The fresh intrusion both propagates into and generates a strongly stratified environment which supports trains of nonlinear internal waves (NLIWs). NLIWs are shown to propagate ahead of this buoyancy input in response to propagation of the outflow water into the stratified environment generated by the previous release as well as in the opposing direction after the reflection from steep bathymetry. Oblique aerial photographs were taken and photogrammetric rectification led to the identification of the buoyant intrusion and the subsequent generation of NLIWs. An autonomous underwater vehicle (AUV) was deployed on repeated reciprocal transects in order to make simultaneous CTD, ADCP, and microstructure shear measurements of the evolution of these phenomena in conjunction with conventional mooring measurements. AUV-based temperature and salinity signals of NLIWs of depression were observed together with increased turbulent kinetic energy dissipation rates of over 2 orders of magnitude within and in the wake of the NLIWs. Repeated measurements allow a unique opportunity to investigate the horizontal structure of these phenomena. Simple metric scaling demonstrates that these processes are likely to be feature of many fjordic systems located on the west coast of Scotland but may also play a key role in the assimilation of the outflow from many tidally dominated fjordic systems throughout the world.

Outflow-driven Transients from the Birth of Binary Black Holes. I. Tidally Locked Secondary Supernovae

NASA Astrophysics Data System (ADS)

Kimura, Shigeo S.; Murase, Kohta; Mészáros, Peter

2017-12-01

We propose a new type of electromagnetic transient associated with the birth of binary black holes (BBHs), which may lead to merger events accompanied by gravitational waves in ∼ 0.1{--}1 {Gyr}. We consider the newborn BBHs formed through the evolution of isolated massive stellar binaries. For a close massive binary, consisting of a primary black hole (BH) and a secondary Wolf–Rayet (WR) star that are orbiting around each other, the spin period of the WR star can be tidally synchronized to its orbital period. Then the angular momentum of the outer material of the WR star is large enough to form an accretion disk around a newborn, secondary BH, following its core-collapse. This disk may produce an energetic outflow with a kinetic energy of ∼ {10}50{--}{10}52 {erg} and an outflow velocity of ∼ {10}10 {cm} {{{s}}}-1, resulting in an optical transient with an absolute magnitude from approximately ‑14 to approximatley ‑17 with a duration of around a day. This type of transient also produces detectable radio signals ∼ 1{--}10 years after the birth of BBHs, via synchrotron emission from nonthermal electrons accelerated at external shocks. The predicted optical transients have a shorter duration than ordinary core-collapse supernovae. Dedicated optical transient surveys can detect them and distinguish them from ordinary SNe using the different features of its light curve and late-time spectrum. In this paper (Paper I), we investigate disk-driven outflows from the secondary BH, whereas possible signals from the primary BH will be discussed in Paper II.

SDSS-IV MaNGA: modelling the metallicity gradients of gas and stars - radially dependent metal outflow versus IMF

NASA Astrophysics Data System (ADS)

Lian, Jianhui; Thomas, Daniel; Maraston, Claudia; Goddard, Daniel; Parikh, Taniya; Fernández-Trincado, J. G.; Roman-Lopes, Alexandre; Rong, Yu; Tang, Baitian; Yan, Renbin

2018-05-01

In our previous work, we found that only two scenarios are capable of reproducing the observed integrated mass-metallicity relations for the gas and stellar components of local star-forming galaxies simultaneously. One scenario invokes a time-dependent metal outflow loading factor with stronger outflows at early times. The other scenario uses a time-dependent initial mass function (IMF) slope with a steeper IMF at early times. In this work, we extend our study to investigate the radial profile of gas and stellar metallicity in local star-forming galaxies using spatially resolved spectroscopic data from the SDSS-IV MaNGA survey. We find that most galaxies show negative gradients in both gas and stellar metallicity with steeper gradients in stellar metallicity. The stellar metallicity gradients tend to be mass dependent with steeper gradients in more massive galaxies while no clear mass dependence is found for the gas metallicity gradient. Then we compare the observations with the predictions from a chemical evolution model of the radial profiles of gas and stellar metallicities. We confirm that the two scenarios proposed in our previous work are also required to explain the metallicity gradients. Based on these two scenarios, we successfully reproduce the radial profiles of gas metallicity, stellar metallicity, stellar mass surface density, and star formation rate surface density simultaneously. The origin of the negative gradient in stellar metallicity turns out to be driven by either radially dependent metal outflow or IMF slope. In contrast, the radial dependence of the gas metallicity is less constrained because of the degeneracy in model parameters.

The SAMI Galaxy Survey: understanding observations of large-scale outflows at low redshift with EAGLE simulations

NASA Astrophysics Data System (ADS)

Tescari, E.; Cortese, L.; Power, C.; Wyithe, J. S. B.; Ho, I.-T.; Crain, R. A.; Bland-Hawthorn, J.; Croom, S. M.; Kewley, L. J.; Schaye, J.; Bower, R. G.; Theuns, T.; Schaller, M.; Barnes, L.; Brough, S.; Bryant, J. J.; Goodwin, M.; Gunawardhana, M. L. P.; Lawrence, J. S.; Leslie, S. K.; López-Sánchez, Á. R.; Lorente, N. P. F.; Medling, A. M.; Richards, S. N.; Sweet, S. M.; Tonini, C.

2018-01-01

This work presents a study of galactic outflows driven by stellar feedback. We extract main-sequence disc galaxies with stellar mass 109 ≤ M⋆/ M⊙ ≤ 5.7 × 1010 at redshift z = 0 from the highest resolution cosmological simulation of the Evolution and Assembly of GaLaxies and their Environments (EAGLE) set. Synthetic gas rotation velocity and velocity dispersion (σ) maps are created and compared to observations of disc galaxies obtained with the Sydney-AAO (Australian Astronomical Observatory) Multi-object Integral field spectrograph (SAMI), where σ-values greater than 150 km s-1 are most naturally explained by bipolar outflows powered by starburst activity. We find that the extension of the simulated edge-on (pixelated) velocity dispersion probability distribution depends on stellar mass and star formation rate surface density (ΣSFR), with low-M⋆/low-ΣSFR galaxies showing a narrow peak at low σ (∼30 km s-1) and more active, high-M⋆/high-ΣSFR galaxies reaching σ > 150 km s-1. Although supernova-driven galactic winds in the EAGLE simulations may not entrain enough gas with T <105 K compared to observed galaxies, we find that gas temperature is a good proxy for the presence of outflows. There is a direct correlation between the thermal state of the gas and its state of motion as described by the σ-distribution. The following equivalence relations hold in EAGLE: (i) low-σ peak ⇔ disc of the galaxy ⇔ gas with T <105 K; (ii) high-σ tail ⇔ galactic winds ⇔ gas with T ≥105 K.

Turbulent Collapse of Gravitationally Bound Clouds

NASA Astrophysics Data System (ADS)

Murray, Daniel W.

In this dissertation, I explore the time-variable rate of star formation, using both numerical and analytic techniques. I discuss the dynamics of collapsing regions, the effect of protostellar jets, and development of software for use in the hydrodynamic code RAMSES. I perform high-resolution adaptive mesh refinement simulations of star formation in self-gravitating turbulently driven gas. I have run simulations including hydrodynamics (HD), and HD with protostellar jet feedback. Accretion begins when the turbulent fluctuations on largescales, near the driving scale, produce a converging flow. I find that the character of the collapse changes at two radii, the disk radius rd, and the radius r* where the enclosed gas mass exceeds the stellar mass. This is the first numerical work to show that the density evolves to a fixed attractor, rho(r, t) → rho( r), for rd < r < r*; mass flows through this structure onto a sporadically gravitationally unstable disk, and from thence onto the star. The total stellar mass M*(t) (t - t*)2, where (t - t *)2 is the time elapsed since the formation of the first star. This is in agreement with previous numerical and analytic work that suggests a linear rate of star formation. I show that protostellar jets change the normalization of the stellar mass accretion rate, but do not strongly affect the dynamics of star formation in hydrodynamics runs. In particular, M*(t) infinity (1 - f jet)2(t - t*) 2 is the fraction of mass accreted onto the protostar, where fjet is the fraction ejected by the jet. For typical values of fjet 0.1 - 0.3 the accretion rate onto the star can be reduced by a factor of two or three. However, I find that jets have only a small effect (of order 25%) on the accretion rate onto the protostellar disk (the "raw" accretion rate). In other words, jets do not affect the dynamics of the infall, but rather simply eject mass before it reaches the star. Finally, I show that the small scale structure--the radial density, velocity, and mass accretion profiles--are very similar in the jet and no-jet cases.

The Chemistry of Protostellar Jet-Disk Systems

NASA Astrophysics Data System (ADS)

Codella, Claudio

2017-11-01

The birth of a Sun-like star is a complex game played by several participants whose respective roles are not yet entirely clear. On the one hand, the star-to-be accretes matter from a collapsing envelope. The gravitational energy released in the process heats up the material surrounding the protostar, creating warm regions enriched by interstellar complex organic molecules (iCOMs, at least 6 atoms) called hot-corinos. On the other hand, the presence of angular momentum and magnetic fields leads to two consequences: (i) the formation of circumstellar disks; and (ii) substantial episodes of matter ejection, as e.g. collimated jets. Thanks to the combination of the high-sensitivities and high-angular resolu- tions provided by the advent of new telescopes such as ALMA and NOEMA, it is now possible to image in details the earliest stages of the Sun-like star formation, thus inspecting the inner ( < 50 AU from the protostar) jet. at these spatial scales a proper study of jets has to take into account also the effects connected with the accreting disk. In other words, it is time to study the protostellar jet-disk system as a whole. Several still unanswered questions can be addressed. What is the origin of the chemically enriched hot corinos: are they jet-driven shocked regions? What is the origin of the ejections: are they due to disk or stellar winds? Shocks are precious tool to attack these questions, given they enrich the gas phase with the species deposited onto the dust mantles and/or locked in the refractory dust cores. Basically, we have to deal with two kind of shocks: (i) high-velocity shocks produced by protostellar jets, and (ii) slow accretion shocks located close to the centrifugal barrier of the accretion disks. Both shocks are factories of iCOMs, which can be then efficiently used to follow both the kinematics and the chemistry of the inner protostellar systems. With this in mind, we will discuss recent results obtained in the framework of different observational campaigns at mm and sub-mm wavelengths.

Non-conservative evolution in Algols: where is the matter?

NASA Astrophysics Data System (ADS)

Deschamps, R.; Braun, K.; Jorissen, A.; Siess, L.; Baes, M.; Camps, P.

2015-05-01

Context. There is indirect evidence of non-conservative evolutions in Algols. However, the systemic mass-loss rate is poorly constrained by observations and generally set as a free parameter in binary-star evolution simulations. Moreover, systemic mass loss may lead to observational signatures that still need to be found. Aims: Within the "hotspot" ejection mechanism, some of the material that is initially transferred from the companion star via an accretion stream is expelled from the system due to the radiative energy released on the gainer's surface by the impacting material. The objective of this paper is to retrieve observable quantities from this process and to compare them with observations. Methods: We investigate the impact of the outflowing gas and the possible presence of dust grains on the spectral energy distribution (SED). We used the 1D plasma code Cloudy and compared the results with the 3D Monte-Carlo radiative transfer code Skirt for dusty simulations. The circumbinary mass-distribution and binary parameters were computed with state-of-the-art binary calculations done with the Binstar evolution code. Results: The outflowing material reduces the continuum flux level of the stellar SED in the optical and UV. Because of the time-dependence of this effect, it may help to distinguish between different ejection mechanisms. If present, dust leads to observable infrared excesses, even with low dust-to-gas ratios, and traces the cold material at large distances from the star. By searching for this dust emission in the WISE catalogue, we found a small number of Algols showing infrared excesses, among which the two rather surprising objects SX Aur and CZ Vel. We find that some binary B[e] stars show the same strong Balmer continuum as we predict with our models. However, direct evidence of systemic mass loss is probably not observable in genuine Algols, since these systems no longer eject mass through the hotspot mechanism. Furthermore, owing to its high velocity, the outflowing material dissipates in a few hundred years. If hot enough, the hotspot may produce highly ionised species, such as Si iv, and observable characteristics that are typical of W Ser systems. Conclusions: If present, systemic mass loss leads to clear observational imprints. These signatures are not to be found in genuine Algols but in the closely related β Lyraes, W Serpentis stars, double periodic variables, symbiotic Algols, and binary B[e] stars. We emphasise the need for further observations of such objects where systemic mass loss is most likely to occur. Appendices are available in electronic form at http://www.aanda.org

Modern shelf ice, equatorial Aeolis Quadrangle, Mars

NASA Technical Reports Server (NTRS)

Brakenridge, G. R.

1993-01-01

As part of a detailed study of the geological and geomorphological evolution of Aeolis Quadrangle, I have encountered evidence suggesting that near surface ice exists at low latitudes and was formed by partial or complete freezing of an inland sea. The area of interest is centered at approximately -2 deg, 196 deg. As seen in a suite of Viking Orbiter frames obtained at a range of approximately 600 km, the plains surface at this location is very lightly cratered or uncratered, and it is thus of late Amazonian age. Extant topographic data indicate that the Amazonian plains at this location occupy a trough whose surface lies at least 1000 m below the Mars datum. A reasonable hypothesis is that quite recent surface water releases, perhaps associated with final evolution of large 'outflow chasms' to the south, but possibly from other source areas, filled this trough, that ice floes formed almost immediately, and that either grounded ice or an ice-covered sea still persists. A reasonable hypothesis is that quite recent surface water releases, perhaps associated with final evolution of large 'outflow chasms' to the south, but possibly from other source areas, filled this trough, that ice floes formed almost immediately, and that either grounded ice or an ice-covered sea still persists. In either case, the thin (a few meters at most) high albedo, low thermal inertia cover of aeolian materials was instrumental in allowing ice preservation, and at least the lower portions of this dust cover may be cemented by water ice. Detailed mapping using Viking stereopairs and quantitative comparisons to terrestrial shelf ice geometries are underway.

Bipolar Jets Launched by a Mean-field Accretion Disk Dynamo

NASA Astrophysics Data System (ADS)

Fendt, Christian; Gaßmann, Dennis

2018-03-01

By applying magnetohydrodynamic simulations, we investigate the launching of jets driven by a disk magnetic field generated by a mean-field disk dynamo. Extending our earlier studies, we explore the bipolar evolution of the disk α 2Ω-dynamo and the outflow. We confirm that a negative dynamo-α leads to a dipolar field geometry, whereas positive values generate quadrupolar fields. The latter remain mainly confined to the disk and cannot launch outflows. We investigate a parameter range for the dynamo-α ranging from a critical value below which field generation is negligible, {α }0,{crit}=-0.0005, to α 0 = ‑1.0. For weak | {α }0| ≤slant 0.07, two magnetic loop structures with opposite polarity may arise, which leads to reconnection and disturbs the field evolution and accretion-ejection process. For a strong dynamo-α, a higher poloidal magnetic energy is reached, roughly scaling with {E}mag}∼ | {α }0| , which also leads to higher accretion and ejection rates. The terminal jet speed is governed by the available magnetic energy and increases with the dynamo-α. We find jet velocities on the order of the inner disk Keplerian velocity. For a strong dynamo-α, oscillating dynamo modes may occur that can lead to a pulsed ejection. This is triggered by an oscillating mode in the toroidal field component. The oscillation period is comparable to the Keplerian timescale in the launching region, thus too short to be associated with the knots in observed jets. We find a hemispherically asymmetric evolution for the jet and counter-jet in the mass flux and field structure.

Molecular outflow and feedback in the obscured quasar XID2028 revealed by ALMA

NASA Astrophysics Data System (ADS)

Brusa, M.; Cresci, G.; Daddi, E.; Paladino, R.; Perna, M.; Bongiorno, A.; Lusso, E.; Sargent, M. T.; Casasola, V.; Feruglio, C.; Fraternali, F.; Georgiev, I.; Mainieri, V.; Carniani, S.; Comastri, A.; Duras, F.; Fiore, F.; Mannucci, F.; Marconi, A.; Piconcelli, E.; Zamorani, G.; Gilli, R.; La Franca, F.; Lanzuisi, G.; Lutz, D.; Santini, P.; Scoville, N. Z.; Vignali, C.; Vito, F.; Rabien, S.; Busoni, L.; Bonaglia, M.

2018-04-01

We imaged, with ALMA and ARGOS/LUCI, the molecular gas and dust and stellar continuum in XID2028, which is an obscured quasi-stellar object (QSO) at z = 1.593, where the presence of a massive outflow in the ionised gas component traced by the [OIII]5007 emission has been resolved up to 10 kpc. This target represents a unique test case to study QSO feedback in action at the peak epoch of AGN-galaxy co-evolution. The QSO was detected in the CO(5 - 4) transition and in the 1.3 mm continuum at 30 and 20σ significance, respectively; both emissions are confined in the central (<2 kpc) radius area. Our analysis suggests the presence of a fast rotating molecular disc (v 400 km s-1) on very compact scales well inside the galaxy extent seen in the rest-frame optical light ( 10 kpc, as inferred from the LUCI data). Adding available measurements in additional two CO transitions, CO(2 - 1) and CO(3 - 2), we could derive a total gas mass of 1010 M⊙, thanks to a critical assessment of CO excitation and the comparison with the Rayleigh-Jeans continuum estimate. This translates into a very low gas fraction (<5%) and depletion timescales of 40-75 Myr, reinforcing the result of atypical gas consumption conditions in XID2028, possibly because of feedback effects on the host galaxy. Finally, we also detect the presence of high velocity CO gas at 5σ, which we interpret as a signature of galaxy-scale molecular outflow that is spatially coincident with the ionised gas outflow. XID2028 therefore represents a unique case in which the measurement of total outflowing mass, of 500-800 M⊙ yr-1 including the molecular and atomic components in both the ionised and neutral phases, was attempted for a high-z QSO.

Binary stellar mergers with marginally bound ejecta: excretion discs, inflated envelopes, outflows, and their luminous transients

NASA Astrophysics Data System (ADS)

Pejcha, Ondřej; Metzger, Brian D.; Tomida, Kengo

2016-09-01

We study mass-loss from the outer Lagrange point (L2) in binary stellar mergers and their luminous transients by means of radiative hydrodynamical simulations. Previously, we showed that for binary mass ratios 0.06 ≲ q ≲ 0.8, synchronous L2 mass-loss results in a radiatively inefficient, dust-forming unbound equatorial outflow. A similar outflow exists irrespective of q if the ratio of the sound speed to the orbital speed at the injection point is sufficiently large, ε ≡ cT/vorb ≳ 0.15. By contrast, for cold L2 mass-loss (ε ≲ 0.15) from binaries with q ≲ 0.06 or q ≳ 0.8, the equatorial outflow instead remains marginally bound and falls back to the binary over tens to hundreds of binary orbits, where it experiences additional tidal torquing and shocking. As the bound gas becomes virialized with the binary, the luminosity of the system increases slowly at approximately constant photosphere radius, causing the temperature to rise. Subsequent evolution depends on the efficiency of radiative cooling. If the bound atmosphere is able to cool efficiently, as quantified by radiative diffusion time being shorter than the advection time (tdiff/tadv ≪ 1), then the virialized gas collapses to an excretion disc, while for tdiff/tadv ≳ 1 an isotropic wind is formed. Between these two extremes, an inflated envelope transports the heat generated near the binary to the surface by meridional flows. In all cases, the radiated luminosity reaches a fraction ˜10-2 to 10-1 of dot{M}v_orb^2/2, where dot{M} is the mass outflow rate. We discuss the implications of our results for transients in the luminosity gap between classical novae and supernovae, such as V1309 Sco and V838 Mon.

Chemical Evolution of Ozone and Its Precursors in Asian Pacific Rim Outflow During TRACE-P

NASA Astrophysics Data System (ADS)

Hamlin, A.; Crawford, J.; Olson, J.; Pippin, M.; Avery, M.; Sachse, G.; Barrick, J.; Blake, D.; Tan, D.; Sandholm, S.; Kondo, Y.; Singh, H.; Eisele, F.; Zondlo, M.; Flocke, F.; Talbot, R.

2002-12-01

During NASA's GTE/TRACE-P (Transport and Chemical Evolution over the Pacific) mission, a widespread stagnant pollution layer was observed between 2 and 4 km over the central Pacific. In this region, high levels of O3 (70~ppbv), CO (210~ppbv), and NOx (130~pptv) were observed. Back trajectories suggest this airmass had been rapidly transported from the Asian coast near the Yellow Sea to the central Pacific where it underwent subsidence. The chemical evolution of ozone and its precursors for this airmass is examined using lagrangian photochemical box model calculations. Simulations are conducted along trajectories which intersect the flight path where predicted mixing ratios are compared to measurements. An analysis of the photochemical processes controlling the cycling of nitrogen oxides and ozone production and destruction during transport will be presented.

X-Raying the Beating Heart of a Newborn Star: Rotational Modulation of High-Energy Radiation from V1647 Ori

NASA Technical Reports Server (NTRS)

Hamaguchi, Kenji; Grosso, Nicolas; Kastner, Joel H.; Weintraub, David A.; Richmond, Michael; Petre, Robert; Teets, William K.; Principe, David

2012-01-01

We report a periodicity of approx.1 day in the highly elevated X-ray emission from the protostar V1647 Ori during its two recent multiple-year outbursts of mass accretion. This periodicity is indicative of protostellar rotation at near-breakup speed. Modeling of the phased X-ray light curve indicates the high-temperature ( 50 MK), X-ray-emitting plasma, which is most likely heated by accretion-induced magnetic reconnection, resides in dense ( 5 1010 cm.3), pancake-shaped magnetic footprints where the accretion stream feeds the newborn star. The sustained X-ray periodicity of V1647 Ori demonstrates that such protostellar magnetospheric accretion configurations can be stable over timescales of years. Subject headings: stars: formation stars: individual (V1647 Ori) stars: pre-main sequence X-rays: stars

Flares, Magnetic Reconnections and Accretion Disk Viscosity

NASA Astrophysics Data System (ADS)

Welsh, William

2001-07-01

Accretion disks are invoked to explain a host of astrophysical phenomena, from protostellar objects to AGN. And yet the mechanism allowing accretion disks to operate are completely unknown. This proposal seeks to observe the ``smoking gun'' signature of magnetically-driven viscosity in accretion disks. Magnetically-induced viscosity is a plausible and generally accepted hypothesis {for esthetic reasons}, but it is completely untested. Determining the cause of accretion disk viscosity is of major significance to all accretion-disk powered systems {e.g. CVs, X-ray binaries, AGN and protostellar disks}. These data will also firmly establish the importance of magnetic fields in accretion disks. Because of its known flaring properites, we will observe the accretion disk in EM Cyg simulataneously with STIS/FUV and CHANDRA. The simultaneous X-rays are absolutely necessary for the unambiguous detection of accretion disk magnetic reconnection flares.

Change in the chemical composition of infalling gas forming a disk around a protostar.

PubMed

Sakai, Nami; Sakai, Takeshi; Hirota, Tomoya; Watanabe, Yoshimasa; Ceccarelli, Cecilia; Kahane, Claudine; Bottinelli, Sandrine; Caux, Emmanuel; Demyk, Karine; Vastel, Charlotte; Coutens, Audrey; Taquet, Vianney; Ohashi, Nagayoshi; Takakuwa, Shigehisa; Yen, Hsi-Wei; Aikawa, Yuri; Yamamoto, Satoshi

2014-03-06

IRAS 04368+2557 is a solar-type (low-mass) protostar embedded in a protostellar core (L1527) in the Taurus molecular cloud, which is only 140 parsecs away from Earth, making it the closest large star-forming region. The protostellar envelope has a flattened shape with a diameter of a thousand astronomical units (1 AU is the distance from Earth to the Sun), and is infalling and rotating. It also has a protostellar disk with a radius of 90 AU (ref. 6), from which a planetary system is expected to form. The interstellar gas, mainly consisting of hydrogen molecules, undergoes a change in density of about three orders of magnitude as it collapses from the envelope into the disk, while being heated from 10 kelvin to over 100 kelvin in the mid-plane, but it has hitherto not been possible to explore changes in chemical composition associated with this collapse. Here we report that the unsaturated hydrocarbon molecule cyclic-C3H2 resides in the infalling rotating envelope, whereas sulphur monoxide (SO) is enhanced in the transition zone at the radius of the centrifugal barrier (100 ± 20 AU), which is the radius at which the kinetic energy of the infalling gas is converted to rotational energy. Such a drastic change in chemistry at the centrifugal barrier was not anticipated, but is probably caused by the discontinuous infalling motion at the centrifugal barrier and local heating processes there.

The JCMT Gould Belt Survey: A First Look at the Auriga–California Molecular Cloud with SCUBA-2

NASA Astrophysics Data System (ADS)

Broekhoven-Fiene, H.; Matthews, B. C.; Harvey, P.; Kirk, H.; Chen, M.; Currie, M. J.; Pattle, K.; Lane, J.; Buckle, J.; Di Francesco, J.; Drabek-Maunder, E.; Johnstone, D.; Berry, D. S.; Fich, M.; Hatchell, J.; Jenness, T.; Mottram, J. C.; Nutter, D.; Pineda, J. E.; Quinn, C.; Salji, C.; Tisi, S.; Hogerheijde, M. R.; Ward-Thompson, D.; Bastien, P.; Bresnahan, D.; Butner, H.; Chrysostomou, A.; Coude, S.; Davis, C. J.; Duarte-Cabral, A.; Fiege, J.; Friberg, P.; Friesen, R.; Fuller, G. A.; Graves, S.; Greaves, J.; Gregson, J.; Holland, W.; Joncas, G.; Kirk, J. M.; Knee, L. B. G.; Mairs, S.; Marsh, K.; Moriarty-Schieven, G.; Mowat, C.; Rawlings, J.; Richer, J.; Robertson, D.; Rosolowsky, E.; Rumble, D.; Sadavoy, S.; Thomas, H.; Tothill, N.; Viti, S.; White, G. J.; Wilson, C. D.; Wouterloot, J.; Yates, J.; Zhu, M.

2018-01-01

We present 850 and 450 μm observations of the dense regions within the Auriga–California molecular cloud using SCUBA-2 as part of the JCMT Gould Belt Legacy Survey to identify candidate protostellar objects, measure the masses of their circumstellar material (disk and envelope), and compare the star formation to that in the Orion A molecular cloud. We identify 59 candidate protostars based on the presence of compact submillimeter emission, complementing these observations with existing Herschel/SPIRE maps. Of our candidate protostars, 24 are associated with young stellar objects (YSOs) in the Spitzer and Herschel/PACS catalogs of 166 and 60 YSOs, respectively (177 unique), confirming their protostellar nature. The remaining 35 candidate protostars are in regions, particularly around LkHα 101, where the background cloud emission is too bright to verify or rule out the presence of the compact 70 μm emission that is expected for a protostellar source. We keep these candidate protostars in our sample but note that they may indeed be prestellar in nature. Our observations are sensitive to the high end of the mass distribution in Auriga–Cal. We find that the disparity between the richness of infrared star-forming objects in Orion A and the sparsity in Auriga–Cal extends to the submillimeter, suggesting that the relative star formation rates have not varied over the Class II lifetime and that Auriga–Cal will maintain a lower star formation efficiency.

Driven and decaying turbulence simulations of low–mass star formation: From clumps to cores to protostars

DOE PAGES

Offner, Stella S. R.; Klein, Richard I.; McKee, Christopher F.

2008-10-20

Molecular clouds are observed to be turbulent, but the origin of this turbulence is not well understood. As a result, there are two different approaches to simulating molecular clouds, one in which the turbulence is allowed to decay after it is initialized, and one in which it is driven. We use the adaptive mesh refinement (AMR) code, Orion, to perform high-resolution simulations of molecular cloud cores and protostars in environments with both driven and decaying turbulence. We include self-gravity, use a barotropic equation of state, and represent regions exceeding the maximum grid resolution with sink particles. We analyze the propertiesmore » of bound cores such as size, shape, line width, and rotational energy, and we find reasonable agreement with observation. At high resolution the different rates of core accretion in the two cases have a significant effect on protostellar system development. Clumps forming in a decaying turbulence environment produce high-multiplicity protostellar systems with Toomre Q unstable disks that exhibit characteristics of the competitive accretion model for star formation. In contrast, cores forming in the context of continuously driven turbulence and virial equilibrium form smaller protostellar systems with fewer low-mass members. Furthermore, our simulations of driven and decaying turbulence show some statistically significant differences, particularly in the production of brown dwarfs and core rotation, but the uncertainties are large enough that we are not able to conclude whether observations favor one or the other.« less

Stochastic Forecasting of Algae Blooms in Lakes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Peng; Tartakovsky, Daniel M.; Tartakovsky, Alexandre M.

We consider the development of harmful algae blooms (HABs) in a lake with uncertain nutrients inflow. Two general frameworks, Fokker-Planck equation and the PDF methods, are developed to quantify the resultant concentration uncertainty of various algae groups, via deriving a deterministic equation of their joint probability density function (PDF). A computational example is examined to study the evolution of cyanobacteria (the blue-green algae) and the impacts of initial concentration and inflow-outflow ratio.

VLT near- to mid-IR imaging and spectroscopy of the M 17 UC1 - IRS5 region

NASA Astrophysics Data System (ADS)

Chen, Zhiwei; Nürnberger, Dieter E. A.; Chini, Rolf; Jiang, Zhibo; Fang, Min

2015-06-01

Aims: We investigate the surroundings of the hypercompact H ii region M 17 UC1 to probe the physical properties of the associated young stellar objects and the environment of massive star formation. Methods: We use diffraction-limited near-IR (VLT/NACO) and mid-IR (VLT/VISIR) images to reveal the different morphologies at various wavelengths. Likewise, we investigate the stellar and nebular content of the region with VLT/SINFONI integral field spectroscopy with a resolution R ˜ 1500 at H + K bands. Results: Five of the seven point sources in this region show L-band excess emission. A geometric match is found between the H2 emission and near-IR polarized light in the vicinity of IRS5A, and between the diffuse mid-IR emission and near-IR polarization north of UC1. The H2 emission is typical for dense photodissociation regions (PDRs), which are initially far-ultraviolet pumped and repopulated by collisional de-excitation. The spectral types of IRS5A and B273A are B3-B7 V/III and G4-G5 III, respectively. The observed infrared luminosity LIR in the range 1-20 μm is derived for three objects; we obtain 2.0 × 103 L⊙ for IRS5A, 13 L⊙ for IRS5C, and 10 L⊙ for B273A. Conclusions: IRS5 might be a young quadruple system. Its primary star IRS5A is confirmed to be a high-mass protostellar object (˜9 M⊙, ˜1 × 105 yrs); it might have terminated accretion due to the feedback from stellar activities (radiation pressure, outflow) and the expanding H ii region of M 17. The object UC1 might also have terminated accretion because of the expanding hypercompact H ii region, which it ionizes. The disk clearing process of the low-mass young stellar objects in this region might be accelerated by the expanding H ii region. The outflows driven by UC1 are running south-north with its northeastern side suppressed by the expanding ionization front of M 17; the blue-shifted outflow lobe of IRS5A is seen in two types of tracers along the same line of sight in the form of H2 emission filament and mid-emission. The H2 line ratios probe the properties of M 17 SW PDR, which is confirmed to have a clumpy structure with two temperature distributions: warm, dense molecular clumps with nH> 105 cm-3 and T ≈ 575 K and cooler atomic gas with nH ˜ 3.7 × 103-1.5 × 104 cm-3 and T ˜ 50 - 200 K. Based on observations by the European Southern Observatory Very Large Telescope on Cerro Paranal, Chile (ESO program IDs: 281.C-5027(A), 281.C-5051(A, B)).

Characterising the physical and chemical properties of a young Class 0 protostellar core embedded in the Orion B9 filament

NASA Astrophysics Data System (ADS)

Miettinen, O.

2016-08-01

Deeply embedded low-mass protostars can be used as testbeds to study the early formation stages of solar-type stars, and the prevailing chemistry before the formation of a planetary system. The present study aims to characterise further the physical and chemical properties of the protostellar core Orion B9-SMM3. The Atacama Pathfinder EXperiment (APEX) telescope was used to perform a follow-up molecular line survey of SMM3. The observations were done using the single pointing (frequency range 218.2-222.2 GHz) and on-the-fly mapping methods (215.1-219.1 GHz). These new data were used in conjunction with our previous data taken by the APEX and Effelsberg 100 m telescopes. The following species were identified from the frequency range 218.2-222.2 GHz: ^{13}CO, C^{18}O, SO, para-H2CO, and E1-type CH3OH. The mapping observations revealed that SMM3 is associated with a dense gas core as traced by DCO+ and p-H2CO. Altogether three different p-H2CO transitions were detected with clearly broadened linewidths (Δ v˜8.2-11 km s^{-1} in FWHM). The derived p-H2CO rotational temperature, 64±15 K, indicates the presence of warm gas. We also detected a narrow p-H2CO line (Δ v=0.42 km s^{-1}) at the systemic velocity. The p-H2CO abundance for the broad component appears to be enhanced by two orders of magnitude with respect to the narrow line value ({˜}3×10^{-9} versus {˜}2×10^{-11}). The detected methanol line shows a linewidth similar to those of the broad p-H2CO lines, which indicates their coexistence. The CO isotopologue data suggest that the CO depletion factor decreases from {˜}27±2 towards the core centre to a value of {˜}8±1 towards the core edge. In the latter position, the N2D+/N2H+ ratio is revised down to 0.14±0.06. The origin of the subfragments inside the SMM3 core we found previously can be understood in terms of the Jeans instability if non-thermal motions are taken into account. The estimated fragmentation timescale, and the derived chemical abundances suggest that SMM3 is a few times 105 yr old, in good agreement with its Class 0 classification inferred from the spectral energy distribution analysis. The broad p-H2CO and CH3OH lines, and the associated warm gas provide the first clear evidence of a molecular outflow driven by SMM3.

Cold gas and the disruptive effect of a young radio jet

NASA Astrophysics Data System (ADS)

Morganti, R.; Oosterloo, T.; Maccagni, F. M.; Geréb, K.; Oonk, J. B. R.; Tadhunter, C. N.

2016-02-01

Newly born and young radio sources are in a delicate phase of their life. Their jets are fighting their way through the surrounding gaseous medium, strongly experiencing this interaction while, at the same time, impacting and affecting the interstellar medium (ISM). Quantifying this interplay has far reaching implications: the rate of occurrence and the magnitude of the interaction between radio jets and ISM can have consequences for the evolution of the host galaxy. Despite the hostile conditions, cold gas - neutral atomic hydrogen and molecular - has been often found in these objects and can be also associated to fast outflows. Here we present the results from two studies of H I and molecular gas illustrating what can be learned from these phases of the gas. We first describe a statistical study of the occurrence and kinematics of H I observed in absorption with the Westerbork Synthesis Radio telescope. This allows a comparison between the properties of the gas in extended and in compact/young radio sources. The study shows that the young radio sources not only have an higher detection rate of H I, but also systematically broader and more asymmetric H I profiles, most of them blueshifted. This supports the idea that we are looking at young radio jets making their way through the surrounding ISM, which also appears to be, on average, richer in gas than in evolved radio sources. Signatures of the impact of the jet are seen in the kinematics of the gas, but the resulting outflows may be characteristic of only the initial phase of the radio source evolution. However, even among the young sources, we identify a population that remains undetected in H I even after stacking their profiles. Orientation effects can only partly explain the result. These objects either are genuinely gas-poor or have different conditions of the medium, e.g. higher spin temperature. The upcoming blind H I surveys which are about to start with large-field-of-view radio facilities (i.e. Apertif at the WSRT and ASKAP) will allow us to expand the statistics and reach even higher sensitivity with stacking techniques. We further present the case of the radio source IC 5063 where we have used the molecular gas observed with ALMA to trace in detail the jet impacting the ISM. The kinematics of the cold, molecular gas co-spatial with the radio plasma shows this process in action. The ALMA data reveal a fast outflow of molecular gas extending along the entire radio jet (˜1 kpc), with the highest outflow velocities at the location of the brighter hot-spot. The results can be described by a scenario of a radio plasma jet expanding into a clumpy medium, interacting directly with the clouds and inflating a cocoon that drives a lateral outflow into the ISM. This is consistent with the scenario proposed by numerical simulations for the expansion of a young radio jet, confirming the disruptive effect the radio plasma jet can have. Following this case, more ALMA observations of nearby young radio sources will be able to confirm if this process is common, as expected, in the initial phase of the evolution of the radio source.

Probing Radiation Pressure and Hot Gas Feedback through Spectral Simulation of Mid-IR to Submillimeter Fine-Structure Lines in Ultraluminous Infrared Galaxies

NASA Astrophysics Data System (ADS)

Fischer, Jacqueline

Recent observational studies have shown that the deeply buried phase found in local ultraluminous infrared galaxies (ULIRGs) is often characterized by powerful feedback thought to be an important mechanism involved in the transformation of gas-rich mergers into gas-poor red and dead galaxies. Based on Herschel studies of multilevel OH transitions in ULIRGs, we have shown that many of the molecular outflows are driven by a combination of an active galactic nucleus (AGN) and a nuclear starburst, as a result of radiation pressure, winds, and supernova remnants. In some sources, however, powerful AGN feedback is required in which the pressure supplied by radiation alone appears insufficient to supply the large outflow momentum fluxes. These outflows appear to be stochastic, strong AGN feedback events that occur throughout the merging process and may involve forces due to hot gas pressure in order to supply the needed momentum fluxes. Numerous theoretical studies have shown that the ratio of the ionizing photon number density to the particle density, commonly denoted as the ionization parameter, is an important diagnostic of the relative dynamical importance of radiation pressure and hot gas pressure in quasar and starburst feedback in galaxies. In optically selected quasars, measured ionization parameters indicate that the current average hot gas pressures are insufficient to power the observed outflows, and optical depths of the AGN radiation are not expected to be high enough to provide the necessary momentum boosts. It has been suggested, however, that during the buried stage of quasar and host galaxy evolution exemplified by ULIRGs, the hot gas pressures could be higher, prior to the development of leaky paths from which the gas can escape, and that infrared fine-structure lines can be used to probe and test this mechanism. The goal of this work is to further our understanding of this phase of galactic evolution by assembling and analyzing the highest quality observations from Spitzer IRS, Herschel PACS, and Herschel SPIRE that heretofore have never been analyzed together in a comprehensive fashion. The publically available Cloudy spectral synthesis code includes photoionization physics, as well as the physics of the transition regions between HII regions and molecular clouds (photodissociation regions (PDRs) and X-ray dominated regions (XDRs) existing beyond the hot ionized centers of AGNs and the cold conditions in molecular clouds. In previous work using Cloudy, we modeled the far-infrared spectra in a sample of the 10 brightest galaxies at 60 microns with infrared luminosities greater than 10^10 Lsol. We showed that both high ionization parameters and high far-infrared optical depths are necessary to explain the far-infrared line deficits found in the only ULIRG in that sample. Here we propose to further develop these models and to apply them for the first time to the full set of available mid-IR, far-IR, and submillimeter spectroscopic observations of 20 ULIRGs and a small comparison sample of LIRGs in the Spitzer and Herschel Archives with multilevel OH observations. With the constraints provided by the numerous mid-IR through submillimeter fine-structure line diagnostics for each galaxy we will evaluate the relative dynamical importance of radiation pressure and hot gas pressure during this pivotal stage of galaxy evolution, and will determine which of these mechanisms is responsible for the momentum fluxes we derived from the multilevel OH Herschel observations of galaxies with powerful molecular outflows.

Ion- and dust-acoustic instabilities in dusty plasmas

NASA Technical Reports Server (NTRS)

Rosenberg, M.

1993-01-01

Dust ion-acoustic and dust-acoustic instabilities in dusty plasmas are investigated using a standard Vlasov approach. Possible applications of these instabilities to various cosmic environments, including protostellar clouds and planetary rings, are briefly discussed.

Afterglow model for the radio emission from the jetted tidal disruption candidate Swift J1644+57

NASA Astrophysics Data System (ADS)

Metzger, Brian D.; Giannios, Dimitrios; Mimica, Petar

2012-03-01

The recent transient event Swift J1644+57 has been interpreted as emission from a collimated relativistic jet, powered by the sudden onset of accretion on to a supermassive black hole following the tidal disruption of a star. Here we model the radio-microwave emission as synchrotron radiation produced by the shock interaction between the jet and the gaseous circumnuclear medium (CNM). At early times after the onset of the jet (t≲ 5-10 d) a reverse shock propagates through and decelerates the ejecta, while at later times the outflow approaches the Blandford-McKee self-similar evolution (possibly modified by additional late energy injection). The achromatic break in the radio light curve of Swift J1644+57 is naturally explained as the transition between these phases. We show that the temporal indices of the pre- and post-break light curve are consistent with those predicted if the CNM has a wind-type radial density profile n∝r-2. The observed synchrotron frequencies and self-absorbed flux constrain the fraction of the post-shock thermal energy in relativistic electrons ɛe≈ 0.03-0.1, the CNM density at 1018 cm n18≈ 1-10 cm-3 and the initial Lorentz factor Γj≈ 10-20 and opening angle ? of the jet. Radio modelling thus provides robust independent evidence for a narrowly collimated outflow. Extending our model to the future evolution of Swift J1644+57, we predict that the radio flux at low frequencies (ν≲ few GHz) will begin to brighten more rapidly once the characteristic frequency νm crosses below the radio band after it decreases below the self-absorption frequency on a time-scale of months (indeed, such a transition may already have begun). Our results demonstrate that relativistic outflows from tidal disruption events provide a unique probe of the conditions in distant, previously inactive galactic nuclei, complementing studies of normal active galactic nuclei.

Investigations of infiltration processes from flooded areas by column experiments

NASA Astrophysics Data System (ADS)

Mohrlok, U.; Bethge, E.; Golalipour, A.

2009-04-01

In case of inundation of flood plains during flood events there is an increased risk of groundwater contamination due to infiltration of increasingly polluted river water. Specifically in densely populated regions, this groundwater may be used as source for drinking water supply. For the evaluation of this a detailed quantitative understanding of the infiltration processes under such conditions is required. In this context the infiltration related to a flood event can be described by three phases. The first phase is defined by the saturation of the unsaturated soils. Within the second phase infiltration takes place under almost saturated conditions determined by the hydraulic load of the flood water level. The drainage of the soils due to falling groundwater table is characterizing the third phase. Investigations by soil columns gave a detailed insight into the infiltration processes caused by flooding. Inflow at the soil top was established by a fixed water table fed by a Mariotte bottle. Free outflow and a groundwater table were used as lower boundary condition. Inflow and outflow volume were monitored. The evolution of the matrix pressure was observed by micro-tensiometers installed at several depths within the soil column. The flow processes during phase one and two were characterized by a tracer test. Some of the experiments were repeated in order to study the influence of preliminary events. Main results were a difference in infiltration due to the lower boundary condition with regard to inflow rate, outflow dynamics and matrix pressure evolution which is directly related to the water content evolution. Further, the influence of preliminary events was different for the different boundary conditions. A replacement of pre-event water could be observed which was confirmed by volume balances calculated for the infiltration experiments. Although these water balances were almost closed significant dynamics of the matrix pressure remained in soil column in the drainage phase. The detailed analysis of the hydraulic conditions and the flow rates provided an estimate of the unsaturated hydraulic conductivity that could be related to the degree of saturation. Numerical simulations were not able to reproduce these conditions. These results could be used to estimate time scales of flow and solute transport in soils caused by flood events.

CGM Evolution of a Simulated Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Sheehan-Klenk, Patrick; Christensen, Charlotte

2018-06-01

The circumgalactic medium (CGM), which is fed by galactic outflows, is intrinsically connected to star formation and galactic evolution. We followed the evolution of the CGM of a simulated dwarf galaxy of mass 4.75 × 1010 solar masses., through five timesteps corresponding to z = 3, 2, 1, 0.5, 0.15. The simulation includes metal line cooling, metal diffusion, and supernova feedback, and the resulting galaxy has a realistic stellar mass and metallicity. We measured the surface densities of HI, CIV and OVI in the CGM gas composition and analyzed their trends in relation to the galaxy's evolution. Additionally, we created mock absorption line spectra, which we used to find the mean equivalent width for sight lines spaced 0.1R/Rvir apart. From this analysis, we saw there was high metallicity at large radii, and over time the CGM cooled and became more ordered. We note the impact of a merger with a smaller galaxy at z = 0.5. We compare these results to observations.

The star formation history of low-mass disk galaxies: A case study of NGC 300

NASA Astrophysics Data System (ADS)

Kang, Xiaoyu; Zhang, Fenghui; Chang, Ruixiang; Wang, Lang; Cheng, Liantao

2016-01-01

Context. Since NGC 300 is a bulgeless, isolated low-mass galaxy and it has not experienced radial migration during its evolution history, it can be treated as an ideal laboratory to test the simple galactic chemical evolution model. Aims: Our main aim is to investigate the main properties of the star formation history (SFH) of NGC 300 and compare its SFH with that of M 33 to explore the common properties and differences between these two nearby low-mass systems. Methods: We construct a simple chemical evolution model for NGC 300, assuming its disk forms gradually from continuous accretion of primordial gas and including the gas-outflow process. The model allows us to build a bridge between the SFH and observed data of NGC 300, in particular, the present-day radial profiles and global observed properties (e.g., cold gas mass, star formation rate, and metallicity). By means of comparing the model predictions with the corresponding observations, we adopt the classical χ2 methodology to find out the best combination of free parameters a, b, and bout. Results: Our results show that by assuming an inside-out formation scenario and an appropriate outflow rate, our model reproduces well most of the present-day observational values. The model not only reproduces well the radial profiles, but also the global observational data for the NGC 300 disk. Our results suggest that NGC 300 may experience a rapid growth of its disk. Through comparing the best-fitting, model-predicted SFH of NGC 300 with that of M 33, we find that the mean stellar age of NGC 300 is older than that of M 33 and there is a recent lack of primordial gas infall onto the disk of NGC 300. Our results also imply that the local environment may play a key role in the secular evolution of galaxy disks.

The Role of Small-Scale Processes in Solar Active Region Decay

NASA Astrophysics Data System (ADS)

Meyer, Karen; Mackay, Duncan

2017-08-01

Active regions are locations of intense magnetic activity on the Sun, whose evolution can result in highly energetic eruptive phenomena such as solar flares and coronal mass ejections (CMEs). Therefore, fast and accurate simulation of their evolution and decay is essential in the prediction of Space Weather events. In this talk we present initial results from our new model for the photospheric evolution of active region magnetic fields. Observations show that small-scale processes appear to play a role in the dispersal and decay of solar active regions, for example through cancellation at the boundary of sunspot outflows and erosion of flux by surrounding convective cells. Our active region model is coupled to our existing model for the evolution of small-scale photospheric magnetic features. Focusing first on the active region decay phase, we consider the evolution of its magnetic field due to both large-scale (e.g. differential rotation) and small-scale processes, such as its interaction with surrounding small-scale magnetic features and convective flows.This project is funded by The Carnegie Trust for the Universities of Scotland, through their Research Incentives Grant scheme.

The kinematics of the diffuse ionized gas in NGC 4666

NASA Astrophysics Data System (ADS)

Voigtländer, P.; Kamphuis, P.; Marcelin, M.; Bomans, D. J.; Dettmar, R.-J.

2013-06-01

Context. The global properties of the interstellar medium with processes such as infall and outflow of gas and a large scale circulation of matter and its consequences for star formation and chemical enrichment are important for the understanding of galaxy evolution. Aims: In this paper we studied the kinematics and morphology of the diffuse ionized gas (DIG) in the disk and in the halo of the star forming spiral galaxy NGC 4666 to derive information about its kinematical properties. Especially, we searched for infalling and outflowing ionized gas. Methods: We determined surface brightness, radial velocity, and velocity dispersion of the warm ionized gas via high spectral resolution (R ≈ 9000) Fabry-Pérot interferometry. This allows the determination of the global velocity field and the detection of local deviations from this velocity field. We calculated models of the DIG distribution and its kinematics for comparison with the measured data. In this way we determined fundamental parameters such as the inclination and the scale height of NGC 4666, and established the need for an additional gas component to fit our observed data. Results: We found individual areas, especially along the minor axis, with gas components reaching into the halo which we interpret as an outflowing component of the DIG. As the main result of our study, we were able to determine that the vertical structure of the DIG distribution in NGC 4666 is best modeled with two components of ionized gas, a thick and a thin disk with 0.8 kpc and 0.2 kpc scale height, respectively. Therefore, the enhanced star formation in NGC 4666 drives an outflow and also maintains a thick ionized gas layer reminiscent of the Reynold's layer in the Milky Way.

Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers

NASA Astrophysics Data System (ADS)

Lippuner, Jonas; Fernández, Rodrigo; Roberts, Luke F.; Foucart, Francois; Kasen, Daniel; Metzger, Brian D.; Ott, Christian D.

2017-11-01

We investigate the nucleosynthesis of heavy elements in the winds ejected by accretion discs formed in neutron star mergers. We compute the element formation in disc outflows from hypermassive neutron star (HMNS) remnants of variable lifetime, including the effect of angular momentum transport in the disc evolution. We employ long-term axisymmetric hydrodynamic disc simulations to model the ejecta, and compute r-process nucleosynthesis with tracer particles using a nuclear reaction network containing ∼8000 species. We find that the previously known strong correlation between HMNS lifetime, ejected mass and average electron fraction in the outflow is directly related to the amount of neutrino irradiation on the disc, which dominates mass ejection at early times in the form of a neutrino-driven wind. Production of lanthanides and actinides saturates at short HMNS lifetimes (≲10 ms), with additional ejecta contributing to a blue optical kilonova component for longer-lived HMNSs. We find good agreement between the abundances from the disc outflow alone and the solar r-process distribution only for short HMNS lifetimes (≲10 ms). For longer lifetimes, the rare-earth and third r-process peaks are significantly underproduced compared to the solar pattern, requiring additional contributions from the dynamical ejecta. The nucleosynthesis signature from a spinning black hole (BH) can only overlap with that from an HMNS of moderate lifetime (≲60 ms). Finally, we show that angular momentum transport not only contributes with a late-time outflow component, but that it also enhances the neutrino-driven component by moving material to shallower regions of the gravitational potential, in addition to providing additional heating.

The Evolution of Quasar C IV and Si IV Broad Absorption Lines over Multi-year Timescales

NASA Astrophysics Data System (ADS)

Gibson, Robert R.; Brandt, W. N.; Gallagher, S. C.; Hewett, Paul C.; Schneider, Donald P.

2010-04-01

We investigate the variability of C IV λ1549 broad absorption line (BAL) troughs over rest-frame timescales of up to ≈7 yr in 14 quasars at redshifts z >~ 2.1. For nine sources at sufficiently high redshift, we also compare the C IV and Si IV λ1400 absorption variation. We compare shorter and longer term variability using spectra from up to four different epochs per source and find complex patterns of variation in the sample overall. The scatter in the change of absorption equivalent width (EW), ΔEW, increases with the time between observations. BALs do not, in general, strengthen or weaken monotonically, and variation observed over shorter (lsimmonths) timescales is not predictive of multi-year variation. We find no evidence for asymmetry in the distribution of ΔEW that would indicate that BALs form and decay on different timescales, and we constrain the typical BAL lifetime to be gsim30 yr. The BAL absorption for one source, LBQS 0022+0150, has weakened and may now be classified as a mini-BAL. Another source, 1235+1453, shows evidence of variable, blue continuum emission that is relatively unabsorbed by the BAL outflow. C IV and Si IV BAL shape changes are related in at least some sources. Given their high velocities, BAL outflows apparently traverse large spatial regions and may interact with parsec-scale structures such as an obscuring torus. Assuming BAL outflows are launched from a rotating accretion disk, notable azimuthal symmetry is required in the outflow to explain the relatively small changes observed in velocity structure over times up to 7 yr.

Super-Eddington Accretion in the Ultraluminous X-Ray Source NGC 1313 X-2: An Ephemeral Feast

NASA Astrophysics Data System (ADS)

Weng, Shan-Shan; Zhang, Shuang-Nan; Zhao, Hai-Hui

2014-01-01

We investigate the X-ray spectrum, variability, and the surrounding ionized bubble of NGC 1313 X-2 to explore the physics of super-Eddington accretion. Beyond the Eddington luminosity, the accretion disk of NGC 1313 X-2 is truncated at a large radius (~50 times the innermost stable circular orbit), and displays the similar evolution track with both luminous Galactic black-hole and neutron star X-ray binaries (XRBs). In super-critical accretion, the speed of radiatively driven outflows from the inner disk is mildly relativistic. Such ultra-fast outflows would be overionized and might produce weak Fe K absorption lines, which may be detected by the coming X-ray mission Astro-H. If NGC 1313 X-2 is a massive stellar XRB, the high luminosity indicates that an ephemeral feast is held in the source. That is, the source must be accreting at a hyper-Eddington mass rate to give the super-Eddington emission over ~104-105 yr. The expansion of the surrounding bubble nebula with a velocity of ~100 km s-1 might indicate that it has existed over ~106 yr and is inflated by the radiatively driven outflows from the transient with a duty cycle of activity of ~ a few percent. Alternatively, if the surrounding bubble nebula is produced by line-driven winds, less energy is required than the radiatively driven outflow scenario, and the radius of the Strömgren radius agrees with the nebula size. Our results are in favor of the line-driven winds scenario, which can avoid the conflict between the short accretion age and the apparently much longer bubble age inferred from the expansion velocity in the nebula.

Quasars with P v broad absorption in BOSS data release 9

NASA Astrophysics Data System (ADS)

Capellupo, D. M.; Hamann, F.; Herbst, H.; Brandt, W. N.; Ge, J.; Pâris, I.; Petitjean, P.; Schneider, D. P.; Streblyanska, A.; York, D.

2017-07-01

Broad absorption lines (BALs) found in a significant fraction of quasar spectra identify high-velocity outflows that might be present in all quasars and could be a major factor in feedback to galaxy evolution. Understanding the nature of these flows requires further constraints on their physical properties, including their column densities, for which well-studied BALs, such as C IV λλ1548,1551, typically provide only a lower limit because of saturation effects. Low-abundance lines, such as P v λλ1118,1128, indicate large column densities, implying that outflows more powerful than measurements of C IV alone would indicate. We search through a sample of 2694 BAL quasars from the Sloan Digital Sky Survey III/Baryon Oscillation Spectroscopic Survey data release 9 quasar catalogue for such absorption, and we identify 81 'definite' and 86 'probable' detections of P v broad absorption, yielding a firm lower limit of 3.0-6.2 per cent for the incidence of such absorption among BAL quasars. The P v-detected quasars tend to have stronger C IV and Si IV absorption, as well as a higher incidence of LoBAL absorption, than the overall BAL quasar population. Many of the P v-detected quasars have C IV troughs that do not reach zero intensity (at velocities where P v is detected), confirming that the outflow gas only partially covers the UV continuum source. P v appears significantly in a composite spectrum of non-P v-detected BAL quasars, indicating that P v absorption (and large column densities) is much more common than indicated by our search results. Our sample of P v detections significantly increases the number of known P v detections, providing opportunities for follow-up studies to better understand BAL outflow energetics.

DOE Office of Scientific and Technical Information (OSTI.GOV)

El-Badry, Kareem; Geha, Marla; Wetzel, Andrew

We examine the effects of stellar feedback and bursty star formation on low-mass galaxies (M{sub star} = 2 × 10{sup 6} − 5 × 10{sup 10} M{sub ⊙}) using the Feedback in Realistic Environments (FIRE) simulations. While previous studies emphasized the impact of feedback on dark matter profiles, we investigate the impact on the stellar component: kinematics, radial migration, size evolution, and population gradients. Feedback-driven outflows/inflows drive significant radial stellar migration over both short and long timescales via two processes: (1) outflowing/infalling gas can remain star-forming, producing young stars that migrate ∼1 kpc within their first 100 Myr, and (2) gas outflows/inflows drive strong fluctuations in the globalmore » potential, transferring energy to all stars. These processes produce several dramatic effects. First, galaxies’ effective radii can fluctuate by factors of >2 over ∼200 Myr, and these rapid size fluctuations can account for much of the observed scatter in the radius at fixed M{sub star}. Second, the cumulative effects of many outflow/infall episodes steadily heat stellar orbits, causing old stars to migrate outward most strongly. This age-dependent radial migration mixes—and even inverts—intrinsic age and metallicity gradients. Thus, the galactic-archaeology approach of calculating radial star formation histories from stellar populations at z = 0 can be severely biased. These effects are strongest at M{sub star} ≈ 10{sup 7–9.6} M{sub ⊙}, the same regime where feedback most efficiently cores galaxies. Thus, detailed measurements of stellar kinematics in low-mass galaxies can strongly constrain feedback models and test baryonic solutions to small-scale problems in ΛCDM.« less

The Effects of Thermal Energetics on Three-dimensional Hydrodynamic Instabilities in Massive Protostellar Disks. II. High-Resolution and Adiabatic Evolutions

NASA Astrophysics Data System (ADS)

Pickett, Brian K.; Cassen, Patrick; Durisen, Richard H.; Link, Robert

2000-02-01

In this paper, the effects of thermal energetics on the evolution of gravitationally unstable protostellar disks are investigated by means of three-dimensional hydrodynamic calculations. The initial states for the simulations correspond to stars with equilibrium, self-gravitating disks that are formed early in the collapse of a uniformly rotating, singular isothermal sphere. In a previous paper (Pickett et al.), it was shown that the nonlinear development of locally isentropic disturbances can be radically different than that of locally isothermal disturbances, even though growth in the linear regime may be similar. When multiple low-order modes grew rapidly in the star and inner disk region and saturated at moderate nonlinear levels in the isentropic evolution, the same modes in the isothermal evolution led to shredding of the disk into dense arclets and ejection of material. In this paper, we (1) examine the fate of the shredded disk with calculations at higher spatial resolution than the previous simulations had and (2) follow the evolution of the same initial state using an internal energy equation rather than the assumption of locally isentropic or locally isothermal conditions. Despite the complex structure of the nonlinear features that developed in the violently unstable isothermal disk referred to above, our previous calculation produced no gravitationally independent, long-lived stellar or planetary companions. The higher resolution calculations presented here confirm this result. When the disk of this model is cooled further, prompting even more violent instabilities, the end result is qualitatively the same--a shredded disk. At least for the disks studied here, it is difficult to produce condensations of material that do not shear away into fragmented spirals. It is argued that the ultimate fate of such fragments depends on how readily local internal energy is lost. On the other hand, if a dynamically unstable disk is to survive for very long times without shredding, then some mechanism must mitigate and control any violent phenomena that do occur. The prior simulations demonstrated a marked difference in final outcome, depending upon the efficiency of disk cooling under two different, idealized thermal conditions. We have here incorporated an internal energy equation that allows for arbitrary heating and cooling. Simulations are presented for adiabatic models with and without artificial viscosity. The artificial viscosity accounts for dissipation and heating due to shocks in the code physics. The expected nonaxisymmetric instabilities occur and grow as before in these energy equation evolutions. When artificial viscosity is not present, the model protostar displays behavior between the locally isentropic and locally isothermal cases of the last paper; a strong two-armed spiral grows to nonlinear amplitudes and saturates at a level higher than in the locally isentropic case. Since the amplitude of the spiral disturbance is large, it is expected that continued transport of material and angular momentum will occur well after the end of the calculation at nearly four outer rotation periods. The spiral is not strong enough, however, to disrupt the disk as in the locally isothermal case. When artificial viscosity is present, the same disturbances reach moderate nonlinear amplitude, then heat the gas, which in turn greatly reduces their strength and effects on the disk. Additional heating in the low-density regions of the disk also leads to a gentle flow of material vertically off the computational grid. The energy equation and high-resolution isothermal calculations are used to discuss the importance and relevance of the different thermal regimes so far examined, with particular attention to applications to star and planet formation.

SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matt, Sean P.; Pinzon, Giovanni; Greene, Thomas P.

2012-01-20

We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effectmore » of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.« less

Spin Evolution of Accreting Young Stars. II. Effect of Accretion-powered Stellar Winds

NASA Astrophysics Data System (ADS)

Matt, Sean P.; Pinzón, Giovanni; Greene, Thomas P.; Pudritz, Ralph E.

2012-01-01

We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh & Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

Role of the ionosphere for the atmospheric evolution of planets.

PubMed

Yamauchi, Masatoshi; Wahlund, Jan-Erik

2007-10-01

We have synthesized current understanding, mainly observations, with regard to ion escape mechanisms to space from the ionosphere and exosphere of Titan and Earth-type planets, with the intent to provide an improved input for models of atmospheric evolution on early Earth and Earth-type planets and exoplanets. We focus on the role of the ionosphere and its non-linear response to solar parameters, all of which have been underestimated in current models of ancient atmospheric escape (4 billion years ago). Factors that have been overlooked include the following: (1) Much larger variation of O(+) outflow than H(+) outflow from the terrestrial ionosphere, depending on solar and geomagnetic activities (an important consideration when attempting to determine the oxidized state of the atmosphere of early Earth); (2) magnetization of the ionopause, which keeps ionospheric ions from escaping and controls many other escape processes; (3) extra ionization by, for example, the critical ionization velocity mechanism, which expands the ionosphere to greater altitudes than current models predict; and (4) the large escape of cold ions from the dense, expanded ionosphere of Titan. Here we offer, as a guideline for quantitative simulations, a qualitative diagnosis of increases or decreases of non-thermal escape related to the ionosphere for magnetized and unmagnetized planets in response to changes in solar parameters (i.e., solar EUV/FUV flux, solar wind dynamic pressure, and interplanetary magnetic field).

Accretion flow dynamics during 1999 outburst of XTE J1859+226—modeling of broadband spectra and constraining the source mass

NASA Astrophysics Data System (ADS)

Nandi, Anuj; Mandal, S.; Sreehari, H.; Radhika, D.; Das, Santabrata; Chattopadhyay, I.; Iyer, N.; Agrawal, V. K.; Aktar, R.

2018-05-01

We examine the dynamical behavior of accretion flow around XTE J1859+226 during the 1999 outburst by analyzing the entire outburst data (˜166 days) from RXTE Satellite. Towards this, we study the hysteresis behavior in the hardness intensity diagram (HID) based on the broadband (3-150 keV) spectral modeling, spectral signature of jet ejection and the evolution of Quasi-periodic Oscillation (QPO) frequencies using the two-component advective flow model around a black hole. We compute the flow parameters, namely Keplerian accretion rate (\\dot{m}d), sub-Keplerian accretion rate (\\dot{m}h), shock location (rs) and black hole mass (M_{bh}) from the spectral modeling and study their evolution along the q-diagram. Subsequently, the kinetic jet power is computed as L^{obs}_{jet} ˜3-6 ×10^{37} erg s^{-1} during one of the observed radio flares which indicates that jet power corresponds to 8-16% mass outflow rate from the disc. This estimate of mass outflow rate is in close agreement with the change in total accretion rate (˜14%) required for spectral modeling before and during the flare. Finally, we provide a mass estimate of the source XTE J1859+226 based on the spectral modeling that lies in the range of 5.2-7.9 M_{⊙} with 90% confidence.

Unification of X-ray Winds in Seyfert Galaxies: From Ultra-fast Outflows to Warm Absorbers

NASA Technical Reports Server (NTRS)

Tombesi, F.; Cappi, M.; Reeves, J. N.; Nemmen, R. S.; Braito, V.; Gaspari, M.; Reynolds, C. S.

2013-01-01

The existence of ionized X-ray absorbing layers of gas along the line of sight to the nuclei of Seyfert galaxies is a well established observational fact. This material is systematically outflowing and shows a large range in parameters. However, its actual nature and dynamics are still not clear. In order to gain insights into these important issues we performed a literature search for papers reporting the parameters of the soft X-ray warm absorbers (WAs) in 35 type 1 Seyferts and compared their properties to those of the ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources with WAs is >60 per cent, consistent with previous studies. The fraction of sources with UFOs is >34 per cent, >67 per cent of which also show WAs. The large dynamic range obtained when considering all the absorbers together, spanning several orders of magnitude in ionization, column, velocity and distance allows us, for the first time, to investigate general relations among them. In particular, we find significant correlations indicating that the closer the absorber is to the central black hole, the higher the ionization, column, outflow velocity and consequently the mechanical power. In all the cases, the absorbers continuously populate the whole parameter space, with the WAs and the UFOs lying always at the two ends of the distribution. These evidence strongly suggest that these absorbers, often considered of different types, could actually represent parts of a single large-scale stratified outflow observed at different locations from the black hole. The UFOs are likely launched from the inner accretion disc and the WAs at larger distances, such as the outer disc and/or torus. We argue that the observed parameters and correlations are, to date, consistent with both radiation pressure through Compton scattering and magnetohydrodynamic processes contributing to the outflow acceleration, the latter playing a major role. Most of the absorbers, especially the UFOs, show a sufficiently high mechanical power (at least approx 0.5 per cent of the bolometric luminosity) to provide a significant contribution to active galactic nuclei (AGN) feedback and thus to the evolution of the host galaxy. In this regard, we find possible evidence for the interaction of the AGN wind with the surrounding environment on large scales.

An Extreme Metallicity, Large-scale Outflow from a Star-forming Galaxy at z ~ 0.4

NASA Astrophysics Data System (ADS)

Muzahid, Sowgat; Kacprzak, Glenn G.; Churchill, Christopher W.; Charlton, Jane C.; Nielsen, Nikole M.; Mathes, Nigel L.; Trujillo-Gomez, Sebastian

2015-10-01

We present a detailed analysis of a large-scale galactic outflow in the circumgalactic medium of a massive ({M}{{h}}˜ {10}12.5 {M}⊙ ), star-forming (˜ 6.9 {M}⊙ yr-1), sub-L* (˜ 0.5{L}B*) galaxy at z = 0.39853 that exhibits a wealth of metal-line absorption in the spectra of the background quasar Q 0122-003 at an impact parameter of 163 kpc. The galaxy inclination angle (i=63^\\circ ) and the azimuthal angle ({{Φ }}=73^\\circ ) imply that the QSO sightline is passing through the projected minor-axis of the galaxy. The absorption system shows a multiphase, multicomponent structure with ultra-strong, wide velocity spread {{O}} {{VI}} ({log}N=15.16+/- 0.04, {{Δ }}{v}90 = 419 km s-1) and {{N}} {{V}} ({log}N=14.69+/- 0.07, {{Δ }}{v}90 = 285 km s-1) lines that are extremely rare in the literature. The highly ionized absorption components are well explained as arising in a low density (˜ {10}-4.2 cm-3), diffuse (˜10 kpc), cool (˜104 K) photoionized gas with a super-solar metallicity ([{{X}}/{{H}}]≳ 0.3). From the observed narrowness of the Lyβ profile, the non-detection of {{S}} {{IV}} absorption, and the presence of strong {{C}} {{IV}} absorption in the low-resolution FOS spectrum, we rule out equilibrium/non-equilibrium collisional ionization models. The low-ionization photoionized gas with a density of ˜ {10}-2.5 cm-3 and a metallicity of [{{X}}/{{H}}]≳ -1.4 is possibly tracing recycled halo gas. We estimate an outflow mass of ˜ 2× {10}10 {M}⊙ , a mass-flow rate of ˜ 54 {M}⊙ {{yr}}-1, a kinetic luminosity of ˜ 9× {10}41 erg s-1, and a mass loading factor of ˜8 for the outflowing high-ionization gas. These are consistent with the properties of “down-the-barrel” outflows from infrared-luminous starbursts as studied by Rupke et al. Such powerful, large-scale, metal-rich outflows are the primary means of sufficient mechanical and chemical feedback as invoked in theoretical models of galaxy formation and evolution.

Unification of X-ray winds in Seyfert galaxies: from ultra-fast outflows to warm absorbers

NASA Astrophysics Data System (ADS)

Tombesi, F.; Cappi, M.; Reeves, J. N.; Nemmen, R. S.; Braito, V.; Gaspari, M.; Reynolds, C. S.

2013-04-01

The existence of ionized X-ray absorbing layers of gas along the line of sight to the nuclei of Seyfert galaxies is a well established observational fact. This material is systematically outflowing and shows a large range in parameters. However, its actual nature and dynamics are still not clear. In order to gain insights into these important issues we performed a literature search for papers reporting the parameters of the soft X-ray warm absorbers (WAs) in 35 type 1 Seyferts and compared their properties to those of the ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources with WAs is >60 per cent, consistent with previous studies. The fraction of sources with UFOs is >34 per cent, >67 per cent of which also show WAs. The large dynamic range obtained when considering all the absorbers together, spanning several orders of magnitude in ionization, column, velocity and distance allows us, for the first time, to investigate general relations among them. In particular, we find significant correlations indicating that the closer the absorber is to the central black hole, the higher the ionization, column, outflow velocity and consequently the mechanical power. In all the cases, the absorbers continuously populate the whole parameter space, with the WAs and the UFOs lying always at the two ends of the distribution. These evidence strongly suggest that these absorbers, often considered of different types, could actually represent parts of a single large-scale stratified outflow observed at different locations from the black hole. The UFOs are likely launched from the inner accretion disc and the WAs at larger distances, such as the outer disc and/or torus. We argue that the observed parameters and correlations are, to date, consistent with both radiation pressure through Compton scattering and magnetohydrodynamic processes contributing to the outflow acceleration, the latter playing a major role. Most of the absorbers, especially the UFOs, show a sufficiently high mechanical power (at least ˜0.5 per cent of the bolometric luminosity) to provide a significant contribution to active galactic nuclei (AGN) feedback and thus to the evolution of the host galaxy. In this regard, we find possible evidence for the interaction of the AGN wind with the surrounding environment on large scales.

Dead Zone Accretion Flows in Protostellar Disks

NASA Technical Reports Server (NTRS)

Turner, Neal; Sano, T.

2008-01-01

Planets form inside protostellar disks in a dead zone where the electrical resistivity of the gas is too high for magnetic forces to drive turbulence. We show that much of the dead zone nevertheless is active and flows toward the star while smooth, large-scale magnetic fields transfer the orbital angular momentum radially outward. Stellar X-ray and radionuclide ionization sustain a weak coupling of the dead zone gas to the magnetic fields, despite the rapid recombination of free charges on dust grains. Net radial magnetic fields are generated in the magnetorotational turbulence in the electrically conducting top and bottom surface layers of the disk, and reach the midplane by ohmic diffusion. A toroidal component to the fields is produced near the midplane by the orbital shear. The process is similar to the magnetization of the solar tachocline. The result is a laminar, magnetically driven accretion flow in the region where the planets form.

VizieR Online Data Catalog: MYStIX candidate protostars (Romine+, 2016)

NASA Astrophysics Data System (ADS)

Romine, G.; Feigelson, E. D.; Getman, K. V.; Kuhn, M. A.; Povich, M. S.

2017-04-01

The present study seeks protostars from the Massive Young Star-forming complex in Infrared and X-ray (MYStIX) survey catalogs. We combine objects with protostellar infrared SEDs and 4.5um excesses with X-ray sources exhibiting ultrahard spectra denoting very heavy obscuration. These criteria filter away nearly all of the older Class II-III stars and contaminant populations, but give very incomplete samples. The result is a list of 1109 protostellar candidates in 14 star-forming regions. See sections 1 and 2 for further explanations. The reliability of the catalog is strengthened because a large majority (86%) are found to be associated with dense cores seen in Herschel 500um maps that trace cold dust emission. However, the candidate list requires more detailed study for confirmation and cannot be viewed as an unbiased view of star formation in the clouds. (3 data files).

Cosmic evolution of stellar quenching by AGN feedback: clues from the Horizon-AGN simulation

NASA Astrophysics Data System (ADS)

Beckmann, R. S.; Devriendt, J.; Slyz, A.; Peirani, S.; Richardson, M. L. A.; Dubois, Y.; Pichon, C.; Chisari, N. E.; Kaviraj, S.; Laigle, C.; Volonteri, M.

2017-11-01

The observed massive end of the galaxy stellar mass function is steeper than its predicted dark matter halo counterpart in the standard Λ cold dark matter paradigm. In this paper, we investigate the impact of active galactic nuclei (AGN) feedback on star formation in massive galaxies. We isolate the impact of AGN by comparing two simulations from the HORIZON suite, which are identical except that one also includes supermassive black holes (SMBHs) and related feedback models. This allows us to cross-identify individual galaxies between simulations and quantify the effect of AGN feedback on their properties, including stellar mass and gas outflows. We find that massive galaxies (M* ≥ 1011 M⊙) are quenched by AGN feedback to the extent that their stellar masses decrease by up to 80 per cent at z = 0. SMBHs affect their host halo through a combination of outflows that reduce their baryonic mass, particularly for galaxies in the mass range 109 M⊙ ≤ M* ≤ 1011 M⊙, and a disruption of central gas inflows, which limits in situ star formation. As a result, net gas inflows on to massive galaxies, M* ≥ 1011 M⊙, drop by up to 70 per cent. We measure a redshift evolution in the stellar mass ratio of twin galaxies with and without AGN feedback, with galaxies of a given stellar mass showing stronger signs of quenching earlier on. This evolution is driven by a progressive flattening of the MSMBH-M* relation with redshift, particularly for galaxies with M* ≤ 1010 M⊙. MSMBH/M* ratios decrease over time, as falling average gas densities in galaxies curb SMBH growth.

Shocks and metallicity gradients in normal star-forming galaxies

NASA Astrophysics Data System (ADS)

Ho, I.-Ting

Gas flow is one of the most fundamental processes driving galaxy evolution. This thesis explores gas flows in local galaxies by studying metallicity gradients and galactic-scale outflows in normal star-forming galaxies. This is made possible by new integral field spectroscopy data that provide simultaneously spatial and spectral information of galaxies. First, I measure metallicity gradients in isolated disk galaxies and show that their metallicity gradients are remarkably simple and universal. When the metallicity gradients are normalized to galaxy sizes, all the 49 galaxies studied have virtually the same metallicity gradient. I model the common metallicity gradient using a simple chemical evolution model to understand its origin. The common metallicity gradient is a direct result of the coevolution of gas and stellar disk while galactic disks build up their masses from inside-out. Tight constraints on the mass outflow rates and inflow rates can be placed by the chemical evolution model. Second, I investigate galactic winds in normal star-forming galaxies using data from an integral field spectroscopy survey. I demonstrate how to search for galactic winds by probing emission line ratios, shocks, and gas kinematics. Galactic winds are found to be common even in normal star-forming galaxies that were not expected to host winds. By comparing galaxies with and without hosting winds, I show that galaxies with high star formation rate surface densities and bursty star formation histories are more likely to drive large-scale galactic winds. Finally, lzifu, a toolkit for fitting multiple emission lines simultaneously in integral field spectroscopy data, is developed in this thesis. I describe in detail the structure of the toolkit and demonstrate the capabilities of lzifu.

MAGNETIZED ACCRETION AND DEAD ZONES IN PROTOSTELLAR DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dzyurkevich, Natalia; Henning, Thomas; Turner, Neal J.

The edges of magnetically dead zones in protostellar disks have been proposed as locations where density bumps may arise, trapping planetesimals and helping form planets. Magneto-rotational turbulence in magnetically active zones provides both accretion of gas on the star and transport of mass to the dead zone. We investigate the location of the magnetically active regions in a protostellar disk around a solar-type star, varying the disk temperature, surface density profile, and dust-to-gas ratio. We also consider stellar masses between 0.4 and 2 M{sub Sun }, with corresponding adjustments in the disk mass and temperature. The dead zone's size andmore » shape are found using the Elsasser number criterion with conductivities including the contributions from ions, electrons, and charged fractal dust aggregates. The charged species' abundances are found using the approach proposed by Okuzumi. The dead zone is in most cases defined by the ambipolar diffusion. In our maps, the dead zone takes a variety of shapes, including a fish tail pointing away from the star and islands located on and off the midplane. The corresponding accretion rates vary with radius, indicating locations where the surface density will increase over time, and others where it will decrease. We show that density bumps do not readily grow near the dead zone's outer edge, independently of the disk parameters and the dust properties. Instead, the accretion rate peaks at the radius where the gas-phase metals freeze out. This could lead to clearing a valley in the surface density, and to a trap for pebbles located just outside the metal freezeout line.« less

ALMA Dust Polarization Observations of Two Young Edge-on Protostellar Disks

NASA Astrophysics Data System (ADS)

Lee, Chin-Fei; Li, Zhi-Yun; Ching, Tao-Chung; Lai, Shih-Ping; Yang, Haifeng

2018-02-01

Polarized emission is detected in two young nearly edge-on protostellar disks in 343 GHz continuum at ∼50 au (∼0.″12) resolution with Atacama Large Millimeter/submillimeter Array. One disk is in HH 212 (Class 0) and the other in the HH 111 (early Class I) protostellar system. The polarization fraction is ∼1%. The disk in HH 212 has a radius of ∼60 au. The emission is mainly detected from the nearside of the disk. The polarization orientations are almost perpendicular to the disk major axis, consistent with either self-scattering or emission by grains aligned with a poloidal field around the outer edge of the disk because of the optical depth effect and temperature gradient; the presence of a poloidal field would facilitate the launching of a disk wind, for which there is already tentative evidence in the same source. The disk of HH 111 VLA 1 has a larger radius of ∼220 au and is thus more resolved. The polarization orientations are almost perpendicular to the disk major axis in the nearside, but more along the major axis in the farside, forming roughly half of an elliptical pattern there. It appears that toroidal and poloidal magnetic field may explain the polarization on the near and far sides of the disk, respectively. However, it is also possible that the polarization is due to self-scattering. In addition, alignment of dust grains by radiation flux may play a role in the farside. Our observations reveal a diversity of disk polarization patterns that should be taken into account in future modeling efforts.

Signatures of Young Planets in the Continuum Emission from Protostellar Disks

NASA Astrophysics Data System (ADS)

Isella, Andrea; Turner, Neal J.

2018-06-01

Many protostellar disks show central cavities, rings, or spiral arms likely caused by low-mass stellar or planetary companions, yet few such features are conclusively tied to bodies embedded in the disks. We note that even small features on the disk surface cast shadows, because the starlight grazes the surface. We therefore focus on accurately computing the disk thickness, which depends on its temperature. We present models with temperatures set by the balance between starlight heating and radiative cooling, which are also in vertical hydrostatic equilibrium. The planet has 20, 100, or 1000 M ⊕, ranging from barely enough to perturb the disk significantly, to clearing a deep tidal gap. The hydrostatic balance strikingly alters the appearance of the model disk. The outer walls of the planet-carved gap puff up under starlight heating, throwing a shadow across the disk beyond. The shadow appears in scattered light as a dark ring that could be mistaken for a gap opened by another more distant planet. The surface brightness contrast between outer wall and shadow for the 1000 M ⊕ planet is an order of magnitude greater than a model neglecting the temperature disturbances. The shadow is so deep that it largely hides the planet-launched outer arm of the spiral wave. Temperature gradients are such that outer low-mass planets undergoing orbital migration will converge within the shadow. Furthermore, the temperature perturbations affect the shape, size, and contrast of features at millimeter and centimeter wavelengths. Thus radiative heating and cooling are key to the appearance of protostellar disks with embedded planets.

SIGNATURES OF GRAVITATIONAL INSTABILITY IN RESOLVED IMAGES OF PROTOSTELLAR DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Ruobing; Vorobyov, Eduard; Pavlyuchenkov, Yaroslav

2016-06-01

Protostellar (class 0/I) disks, which have masses comparable to those of their nascent host stars and are fed continuously from their natal infalling envelopes, are prone to gravitational instability (GI). Motivated by advances in near-infrared (NIR) adaptive optics imaging and millimeter-wave interferometry, we explore the observational signatures of GI in disks using hydrodynamical and Monte Carlo radiative transfer simulations to synthesize NIR scattered light images and millimeter dust continuum maps. Spiral arms induced by GI, located at disk radii of hundreds of astronomical units, are local overdensities and have their photospheres displaced to higher altitudes above the disk midplane; therefore,more » arms scatter more NIR light from their central stars than inter-arm regions, and are detectable at distances up to 1 kpc by Gemini/GPI, VLT/SPHERE, and Subaru/HiCIAO/SCExAO. In contrast, collapsed clumps formed by disk fragmentation have such strong local gravitational fields that their scattering photospheres are at lower altitudes; such fragments appear fainter than their surroundings in NIR scattered light. Spiral arms and streamers recently imaged in four FU Ori systems at NIR wavelengths resemble GI-induced structures and support the interpretation that FUors are gravitationally unstable protostellar disks. At millimeter wavelengths, both spirals and clumps appear brighter in thermal emission than the ambient disk and can be detected by ALMA at distances up to 0.4 kpc with one hour integration times at ∼0.″1 resolution. Collapsed fragments having masses ≳1 M {sub J} can be detected by ALMA within ∼10 minutes.« less

Embedded Protostellar Disks Around (Sub-)Solar Stars. II. Disk Masses, Sizes, Densities, Temperatures, and the Planet Formation Perspective

NASA Astrophysics Data System (ADS)

Vorobyov, Eduard I.

2011-03-01

We present basic properties of protostellar disks in the embedded phase of star formation (EPSF), which is difficult to probe observationally using available observational facilities. We use numerical hydrodynamics simulations of cloud core collapse and focus on disks formed around stars in the 0.03-1.0 M sun mass range. Our obtained disk masses scale near-linearly with the stellar mass. The mean and median disk masses in the Class 0 and I phases (M mean d,C0 = 0.12 M sun, M mdn d,C0 = 0.09 M sun and M mean d,CI = 0.18 M sun, M mdn d,CI = 0.15 M sun, respectively) are greater than those inferred from observations by (at least) a factor of 2-3. We demonstrate that this disagreement may (in part) be caused by the optically thick inner regions of protostellar disks, which do not contribute to millimeter dust flux. We find that disk masses and surface densities start to systematically exceed that of the minimum mass solar nebular for objects with stellar mass as low as M * = 0.05-0.1 M sun. Concurrently, disk radii start to grow beyond 100 AU, making gravitational fragmentation in the disk outer regions possible. Large disk masses, surface densities, and sizes suggest that giant planets may start forming as early as in the EPSF, either by means of core accretion (inner disk regions) or direct gravitational instability (outer disk regions), thus breaking a longstanding stereotype that the planet formation process begins in the Class II phase.

The Physical Constraints on a New LoBAL QSO at z = 4.82

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yi, Weimin; Bai, Jin-Ming; Green, Richard

Very few low-ionization broad absorption line (LoBAL) QSOs have been found at high redshifts, to date. One high-redshift LoBAL QSO, J0122+1216, was recently discovered by the Lijiang 2.4 m Telescope, with an initial redshift determination of 4.76. Aiming to investigate its physical properties, we carried out follow-up observations in the optical and near-IR spectroscopy. Near-IR spectra from UKIRT and P200 confirm that it is a LoBAL, with a new redshift determination of 4.82 ± 0.01 based on the Mg ii emission-line. The new Mg ii redshift determination reveals strong blueshifts and asymmetry of the high-ionization emission lines. We estimate amore » black hole mass of ∼2.3 × 10{sup 9} M {sub ⊙} and Eddington ratio of ∼1.0 according to the empirical Mg ii-based single-epoch relation and bolometric correction factor. It is possible that strong outflows are the result of an extreme quasar environment driven by the high Eddington ratio. A lower limit on the outflowing kinetic power (>0.9% L {sub Edd}) is derived from both emission and absorption lines, indicating that these outflows play a significant role in the feedback process that regulates the growth of its black hole, as well as host galaxy evolution.« less

Ionized and Molecular Gas in IC 860: Evidence for an Outflow

NASA Astrophysics Data System (ADS)

Adams, Carson; Alatalo, Katherine; Medling, Anne M.

2018-01-01

Galaxies at present-day fall predominantly in two distinct populations, as either blue, star-forming spirals or red, quiescent early-type galaxies. Blue galaxies appear to evolve onto the red sequence as star formation is quenched. The absence of a significant population falling in the intermediate ‘green valley’ implies that these transitions must occur rapidly. Identifying the initial properties of and pathways taken by these ‘dying galaxies’ is essential to building a complete understanding of galactic evolution. In this work, we investigate these phenomena in action within IC860 — a nearby, early-type spiral in the initial stages of undergoing a rapid transition in the presence of a powerful AGN-driven molecular outflow. As a shocked, post-starburst galaxy with an intermediate-age stellar population which lies on the blue end of the green valley, IC860 provides a window into the early stages of galaxy transition and AGN feedback. We present Hubble Space Telescope imaging of IC860 showing a violent, dusty outflow originating from a compact core. We find that the mean velocity map of the CO(1-0) from CARMA suggests a dynamically excited bar funneling molecular gas into the galactic center. Finally, we present kinematic maps of ionized gas emission lines as well as sodium D absorption tracing neutral winds obtained by the Wide-Field Spectrograph.

High Resolution Studies of Mass Loss from Massive Binary Stars

NASA Astrophysics Data System (ADS)

Corcoran, Michael F.; Gull, Theodore R.; Hamaguchi, Kenji; Richardson, Noel; Madura, Thomas; Post Russell, Christopher Michael; Teodoro, Mairan; Nichols, Joy S.; Moffat, Anthony F. J.; Shenar, Tomer; Pablo, Herbert

2017-01-01

Mass loss from hot luminous single and binary stars has a significant, perhaps decisive, effect on their evolution. The combination of X-ray observations of hot shocked gas embedded in the stellar winds and high-resolution optical/UV spectra of the cooler mass in the outflow provides unique ways to study the unstable process by which massive stars lose mass both through continuous stellar winds and rare, impulsive, large-scale mass ejections. The ability to obtain coordinated observations with the Hubble Space Telescope Imaging Spectrograph (HST/STIS) and the Chandra High-Energy Transmission Grating Spectrometer (HETGS) and other X-ray observatories has allowed, for the first time, studies of resolved line emisssion over the temperature range of 104- 108K, and has provided observations to confront numerical dynamical models in three dimensions. Such observations advance our knowledge of mass-loss asymmetries, spatial and temporal variabilities, and the fundamental underlying physics of the hot shocked outflow, providing more realistic constraints on the amount of mass lost by different luminous stars in a variety of evolutionary stages. We discuss the impact that these joint observational studies have had on our understanding of dynamical mass outflows from massive stars, with particular emphasis on two important massive binaries, Delta Ori Aa, a linchpin of the mass luminosity relation for upper HRD main sequence stars, and the supermassive colliding wind binary Eta Carinae.

A High Definition View of AGN Feedback: Chandra Imaging of Nearby Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Wang, Junfeng; Fabbiano, G.; Risaliti, G.; Elvis, M.; Karovska, M.; Zezas, A.; Mundell, C. G.

2010-03-01

To improve the physics of AGN feedback, it is crucial to evaluate the true role of outflows on galaxy evolution observationally. I will present new results from Chandra spectral imaging of nearby Seyfert galaxies, which offer unique opportunities to examine feedback in action in much greater detail than at high redshift. Exploiting Chandra's highest possible resolution, we are able to study structures in NGC 4151 on spatial scales of 0.5 arcsec (30 pc), showing an extended X-ray morphology overall consistent with the optical NLR. We find that most of the NLR clouds in NGC 4151 have [OIII] to soft X-ray ratio consistent with the values observed in NLRs of some Seyfert 2 galaxies, which indicates a uniform ionization parameter even at large radii. We examine various X-ray emission mechanisms of the radio jet and consider thermal emission from interaction between radio outflow and the NLR clouds the most probable origin for the X-ray emission associated with the jet.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fujibayashi, Sho; Sekiguchi, Yuichiro; Kiuchi, Kenta

We performed general relativistic, long-term, axisymmetric neutrino radiation hydrodynamics simulations for the remnant formed after a binary neutron star merger, which consists of a massive neutron star and a torus surrounding it. As an initial condition, we employ the result derived in a three-dimensional, numerical relativity simulation for the binary neutron star merger. We investigate the properties of neutrino-driven ejecta. Due to the pair-annihilation heating, the dynamics of the neutrino-driven ejecta are significantly modified. The kinetic energy of the ejecta is about two times larger than that in the absence of pair-annihilation heating. This suggests that the pair-annihilation heating playsmore » an important role in the evolution of merger remnants. The relativistic outflow, which is required for driving gamma-ray bursts, is not observed because the specific heating rate around the rotational axis is not sufficiently high, due to the baryon loading caused by the neutrino-driven ejecta from the massive neutron star. We discuss the condition for launching the relativistic outflow and the nucleosynthesis in the ejecta.« less

Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC4RS) Field Campaign Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmid, B.; Flynn, C.

Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS), a National Aeronautics and Space Administration (NASA) field campaign, was based out of Ellington Field in Houston, Texas, during August and September 2013. The study focused on pollution emissions and the evolution of gases and aerosols in deep convective outflow, and the influences and feedbacks of aerosol particles from anthropogenic pollution and biomass burning on meteorology, clouds, and climate. The project required three aircraft to accomplish these goals. The NASA DC-8 provided observations from near the surface to 12 km, while the NASA ER-2 provided high-altitudemore » observations reaching into the lower stratosphere as well as important remote-sensing observations connecting satellites with observations from lower-flying aircraft and surface sites. The SPEC, Inc. Learjet obtained aerosol and cloud microphysical measurement in convective clouds and convective outflow.« less

Driving ionospheric outflows and magnetospheric O + energy density with Alfvén waves

DOE PAGES

Chaston, C. C.; Bonnell, J. W.; Reeves, Geoffrey D.; ...

2016-05-11

We show how dispersive Alfvén waves observed in the inner magnetosphere during geomagnetic storms can extract O + ions from the topside ionosphere and accelerate these ions to energies exceeding 50 keV in the equatorial plane. This occurs through wave trapping, a variant of “shock” surfing, and stochastic ion acceleration. These processes in combination with the mirror force drive field-aligned beams of outflowing ionospheric ions into the equatorial plane that evolve to provide energetic O + distributions trapped near the equator. These waves also accelerate preexisting/injected ion populations on the same field lines. We show that the action of dispersivemore » Alfvén waves over several minutes may drive order of magnitude increases in O + ion pressure to make substantial contributions to magnetospheric ion energy density. These wave accelerated ions will enhance the ring current and play a role in the storm time evolution of the magnetosphere.« less

Chemical Evolution and Star Formation History of the Disks of Spirals in Local Group

NASA Astrophysics Data System (ADS)

Yin, J.

2011-05-01

Milky Way (MW), M31 and M33 are the only three spiral galaxies in our Local group. MW and M31 have similar mass, luminosity and morphology, while M33 is only about one tenth of MW in terms of its baryonic mass. Detailed theoretical researches on these three spirals will help us to understand the formation and evolution history of both spiral galaxies and Local group. Referring to the phenomenological chemical evolution model adopted in MW disk, a similar model is established to investigate the star formation and chemical enrichment history of these three local spirals. Firstly, the properties of M31 disk are studied by building a similar chemical evolution model which is able to successfully describe the MW disk. It is expected that a simple unified phenomenological chemical evolution model could successfully describe the radial and global properties of both disks. Comparing with the former work, we adopt an extensive data set as model constraints, including the star formation profile of M31 disk derived from the recent UV data of GALEX. The comparison among the observed properties of these two disks displays very interesting similarities in their radial profiles when the distance from the galactic center is expressed in terms of the corresponding scale length. This implies some common processes in their formation and evolution history. Based on the observed data of the gas mass surface density and SFR surface density, the SFR radial profile of MW can be well described by Kennicutt-Schmidt star formation law (K-S law) or modified K-S law (SFR is inversely proportional to the distance from the galactic center), but this is not applicable to the M31 disk. Detailed calculations show that our unified model describes fairly well all the main properties of the MW disk and most properties of M31 disk, provided that the star formation efficiency of M31 disk is adjusted to be twice as large as that of MW disk (as anticipated from the lower gas fraction of M31). However, the model fails to match the present SFR in M31 disk by predicting too much SFR in the outer disk. We attribute this disagreement to the fact that M31 has been perturbed recently by a violent encounter. The observed SFR profile of M31 caused by this encounter does not seem to follow any form of the K-S law. On the other hand, the stellar metallicity distribution functions (MDFs) measured along the disk of M31 indicate the integrated star formation during the whole disk history and should not be affected by recent events. Our model reproduces rather well those distributions from 6 kpc to 21 kpc (except the region at 16 kpc). Basically, the disks of MW and M31 are formed "inside-out" with similar infall timescale. If M31 is closer to a typical disk galaxy, it would be the best that the researches on the models of this disk galaxy are carried out within the cosmological framework. Simple models, like the one adopted in this thesis, could be used to describe the quiescent galaxy, like the MW. Secondly, the similar model is applied to investigate the formation history of M33 disk. We calculate the radial profiles of gas surface density and SFR surface density, gas fraction, abundances, the surface brightness of FUV and K bands, FUV-K color gradient and so on. All those properties are compared with observations if available. Two different infall histories, namely collapse model and accretion model, are adopted respectively. The effects of free parameters (infall timescale, infall delay time and efficiency of outflow) on the model results are discussed in detail. It is found that the disk of M33 can not be formed by fast collapse process. Observations show that M33 is much smaller and less massive than MW, but has larger gas fraction and lower metallicity. This implies that it should be formed by slow accretion process and is consistent with the slow accretion model. We study the abundance gradients of different elements in M33 disk and find that outflow should play an important role in the evolution of abundance gradients. The present abundances will be much higher than the observation if without outflow. When the disk undergoes an outflow with a similar strength to the local SFR, the abundance within the radius of 6 kpc will be reduced dramatically, but no noticeable change occurs in outer regions, resulting in a flatter abundance gradient. This is consistent with the observed features. Our model predicts a slightly flatter FUV-K color gradient when the long infall timescale and proper outflow are adopted. Considering the uncertainty of the extinction correction, the results are acceptable.

Stochastic 2-D galaxy disk evolution models. Resolved stellar populations in the galaxy M33

NASA Astrophysics Data System (ADS)

Mineikis, T.; Vansevičius, V.

We improved the stochastic 2-D galaxy disk models (Mineikis & Vansevičius 2014a) by introducing enriched gas outflows from galaxies and synthetic color-magnitude diagrams of stellar populations. To test the models, we use the HST/ACS stellar photometry data in four fields located along the major axis of the galaxy M33 (Williams et al. 2009) and demonstrate the potential of the models to derive 2-D star formation histories in the resolved disk galaxies.

Geomorphic and landform survey of Northern Appennine Range (NAR)

NASA Technical Reports Server (NTRS)

Marino, C. M. (Principal Investigator); Zilioli, E.

1977-01-01

The author has identified the following significant results. An approach to landslide hazard detection was developed through the analysis of satellite imagery (LANDSAT 2) showing many landslide areas that occur on marine silts and clays in northern Appennine Range in Italy. A landslide risk score was given for large areas by narrowing and extending well defined areas, whose behavior and reflectivity variation was due to upper surface changes. Results show that this methodology allows evolution pattern of clay outflows to be distinguished.

Chemical Composition of Asian Continental Outflow over the Western Pacific: Results from Transport and Chemical Evolution over the Pacific (TRACE-P)

NASA Technical Reports Server (NTRS)

Russo, R. S.; Talbot, R. W.; Dibb, J. E.; Scheuer, E.; Seid, G.; Jordan, C. E.; Fuelberg, H. E.; Sachse, G. W.; Avery, M. A.; Vay, S. A.

2003-01-01

We characterize the chemical composition of Asian continental outflow observed during the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) mission during February-April 2001 in the western Pacific using data collected on the NASA DC-8 aircraft. A significant anthropogenic impact was present in the free troposphere and as far east as 150degE longitude reflecting rapid uplift and transport of continental emissions. Five-day backward trajectories were utilized to identify five principal Asian source regions of outflow: central, coastal, north-northwest(NNW), southeast (SE), and west-southwest (WSW). The maximum mixing ratios for several species, such as CO, C2Cl4, CH3Cl, and hydrocarbons, were more than a factor of 2 larger in the boundary layer of the central and coastal regions due to industrial activity in East Asia. CO was well correlated with C2H2, C2H6, C2Cl4, and CH3Cl at low altitudes in these two regions (r(sup 2) approx. 0.77-0.97). The NNW, WSW, and SE regions were impacted by anthropogenic sources above the boundary layer presumably due to the longer transport distances of air masses to the western Pacific. Frontal and convective lifting of continental emissions was most likely responsible for the high altitude outflow in these three regions. Photochemical processing was influential in each source region resulting in enhanced mixing ratios of O3, PAN, HNO3, H2O2, and CH3OOH. The air masses encountered in all five regions were composed of a complex mixture of photcrchemically aged air with more recent emissions mixed into the outflow as indicated by enhanced hydrocarbon ratios (C2H2/CO greater than or equal to 3 and C3H8/C2H6 greater than or equal to 0.2). Combustion, industrial activities, and the burning of biofuels and biomass all contributed to the chemical composition of air masses from each source region as demonstrated by the H6, SO2, and C2Cl4 were compared for the TRACE-P and PEM-West B missions. In the more northern regions, O3, CO, and SO2 were higher at low altitudes during TRACE-P. In general, mixing ratios were fairly similar between the two missions in the southern regions. A comparison between CO/CO2, CO/CH4, C2H6/C3H8, NO(x)/SO2, and NO(y)/(SO2 + nss-SO4) ratios for the five source regions and for the 2000 Asian emissions summary showed vay close agreement indicating that Asian emissions were well represented by the TRACE-P data and tbe emissions inventory.

The Prevalence of Ionized Gas Outflow Signatures in SDSS-IV MaNGA Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Flores, Anthony M.; Wylezalek, Dominika; Zakamska, Nadia

2018-01-01

Actively accreting supermassive black holes (AGN) can have a variety of effects on their host galaxies, from generating large regions of hot, photoionized gas, to driving AGN feedback in the form of galaxy wide outflows that may affect the evolution of the galaxy over time by quenching their star formation and by thus setting limits to the total mass of their host galaxy. The focus of this work is to assess the prevalence of AGN-driven outflows in low-redshift AGN of moderate power using IFU observations of 2778 galaxies available through SDSS-IV MaNGA.SDSS-IV MaNGA is an optical spectroscopic IFU survey which will have obtained spatially resolved spectroscopic observations of ~10,000 galaxies at z ≤ 0.1 and with stellar masses >10^9 solar masses over the next three years, allowing us to describe the kinematic properties of a large galaxy sample across different spatial regions.We have re-mapped the kinematics of the [O III] emission line to account for asymmetries and secondary kinematic components in the emission line brought on by potential AGN-driven outflows. Using all galaxies currently in the MaNGA survey, we implement a new fitting procedure to help determine the prevalence of these secondary components. Specifically, we use the non-parametric W80 value as a proxy for velocity dispersion, which we expect to be affected especially in the case of asymmetries and broadening of the emission lines. Separating these galaxies into two samples of independently identified AGN candidates and non-AGN, I will show that broad secondary components are twice as common in MaNGA-selected AGN compared to galaxies in MaNGA not classified as AGN. Moreover, when the underlying distribution of W80 values are compared between samples, I will show that the differences in these distributions are statistically significant. This demonstrates that large IFU survey like SDSS-IV MaNGA will uncover many previously unknown AGN and AGN feedback signatures. Outflows and feedback from low- and intermediate-luminosity AGN might have been underestimated in the past but can potentially significantly contribute to the AGN/host-galaxy self-regulation.

Long-range pollution transport during the MILAGRO-2006 campaign: a case study of a major Mexico City outflow event using free-floating altitude-controlled balloons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voss, Paul B.; Zaveri, Rahul A.; Flocke, Frank M.

2010-08-04

One of the major objectives of the Megacities Initiative: Local And Global Research 3 Observations (MILAGRO 2006) campaign was to investigate the long-range transport of 4 Mexico City Metropolitan Area (MCMA) pollution outflow and its downwind impacts on air 5 quality and climate. Four aircraft (DOE G-1, NSF/NCAR C-130, NASA-J31, and NASA 6 DC-8) made extensive chemical, aerosol, and radiation measurements above MCMA and over 7 1000 km downwind in order to characterize the evolution of MCMA pollution as it aged and 8 dispersed over the central Mexican plateau and the Gulf of Mexico. As part of this effort, 9more » free-floating Controlled-Meteorological (CMET) balloons, capable of changing altitude on 10 command via satellite, characterized the MCMA outflow by performing repeated soundings 11 during the transit. In this paper, we present an analysis based on the data from two CMET 12 balloons that were launched near Mexico City on the afternoon of 18 March 2006 and floated 13 downwind with the outflow for nearly 30 hours. Continuous profile measurements made by 14 the balloons show the evolving structure of the MCMA outflow in considerable detail: its 15 stability and stratification, interaction with other air masses, mixing episodes, and dispersion 16 into the regional background. Air parcel trajectories, computed directly from the balloon 17 wind profiles, show three different transport pathways for Mexico City outflow on 18-19 18 March: (a) high-altitude advection of the top of the MCMA mixed layer, (b) low-altitude flow 19 over the Sierra Madre Oriental followed by decoupling and isolated transport over the Gulf, 20 and (c) the same decoupling scenario with entrainment into a cleaner westerly jet below the 21 plateau. The C-130 intercepted the balloon-based trajectories three times on 19 March, once 22 along each transport pathway. In all three cases, distinct peaks in the urban tracer signature 23 and LIDAR backscatter imagery provided evidence for Mexico City air. The coherence of the 24 high-altitude outflow was well preserved after 25 hours whereas that lower in the atmosphere 25 was more widely dispersed over the same time period. Other C-130 intercepts, previously 26 thought to be from Mexico City, are shown to have likely originated elsewhere. These 27 findings address key questions about the long-range transport of Mexico City pollution and its 28 impact on the regional background. The particular intercepts identified should prove useful in 29 answering a wide range scientific questions pertaining to the transport, transformation, and 30 downwind impacts of megacity air pollution. 31 32« less

Towards Forming a Primordial Protostar in a Cosmological AMR Simulation

NASA Astrophysics Data System (ADS)

Turk, Matthew J.; Abel, Tom; O'Shea, Brian W.

2008-03-01

Modeling the formation of the first stars in the universe is a well-posed problem and ideally suited for computational investigation.We have conducted high-resolution numerical studies of the formation of primordial stars. Beginning with primordial initial conditions appropriate for a ΛCDM model, we used the Eulerian adaptive mesh refinement code (Enzo) to achieve unprecedented numerical resolution, resolving cosmological scales as well as sub-stellar scales simultaneously. Building on the work of Abel, Bryan and Norman (2002), we followed the evolution of the first collapsing cloud until molecular hydrogen is optically thick to cooling radiation. In addition, the calculations account for the process of collision-induced emission (CIE) and add approximations to the optical depth in both molecular hydrogen roto-vibrational cooling and CIE. Also considered are the effects of chemical heating/cooling from the formation/destruction of molecular hydrogen. We present the results of these simulations, showing the formation of a 10 Jupiter-mass protostellar core bounded by a strongly aspherical accretion shock. Accretion rates are found to be as high as one solar mass per year.

Chemistry and Evolution of Interstellar Clouds

NASA Technical Reports Server (NTRS)

Wooden, D. H.; Charnley, S. B.; Ehrenfreund, P.

2003-01-01

In this chapter we describe how elements have been and are still being formed in the galaxy and how they are transformed into the reservoir of materials present at the time of formation of our protosolar nebula. We discuss the global cycle of matter, beginning at its formation site in stars, where it is ejected through winds and explosions into the diffuse interstellar medium. In the next stage of the global cycle occurs in cold, dense molecular clouds, where the complexity of molecules and ices increases relative to the diffuse ISM.. When a protostar forms in a dense core within a molecular cloud, it heats the surrounding infalling matter warms and releases molecules from the solid phase into the gas phase in a warm, dense core, sponsoring a rich gas-phase chemistry. Some material from the cold and warm regions within molecular clouds probably survives as interstellar matter in the protostellar disk. For the diffuse ISM, for cold, dense clouds, and for dense-warm cores, the physio-chemical processes that occur within the gas and solid phases are discussed in detail.

SELF-GRAVITATIONAL FORCE CALCULATION OF SECOND-ORDER ACCURACY FOR INFINITESIMALLY THIN GASEOUS DISKS IN POLAR COORDINATES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hsiang-Hsu; Taam, Ronald E.; Yen, David C. C., E-mail: yen@math.fju.edu.tw

Investigating the evolution of disk galaxies and the dynamics of proto-stellar disks can involve the use of both a hydrodynamical and a Poisson solver. These systems are usually approximated as infinitesimally thin disks using two-dimensional Cartesian or polar coordinates. In Cartesian coordinates, the calculations of the hydrodynamics and self-gravitational forces are relatively straightforward for attaining second-order accuracy. However, in polar coordinates, a second-order calculation of self-gravitational forces is required for matching the second-order accuracy of hydrodynamical schemes. We present a direct algorithm for calculating self-gravitational forces with second-order accuracy without artificial boundary conditions. The Poisson integral in polar coordinates ismore » expressed in a convolution form and the corresponding numerical complexity is nearly linear using a fast Fourier transform. Examples with analytic solutions are used to verify that the truncated error of this algorithm is of second order. The kernel integral around the singularity is applied to modify the particle method. The use of a softening length is avoided and the accuracy of the particle method is significantly improved.« less

Constraining planetary migration and tidal dissipation with coeval hot Jupiters

NASA Astrophysics Data System (ADS)

O'Connor, Christopher E.; Hansen, Bradley M. S.

2018-06-01

We investigate the constraints on the formation of, and tidal dissipation processes in, hot Jupiters (HJs) that can be inferred based on reliable knowledge of the age of a system or population. Particular attention is paid to the role of young systems (such as those in open clusters or star-forming regions) in such studies. For an ensemble of coeval HJ (or proto-HJ) systems, we quantify the effect of age on the distribution of orbital eccentricities with respect to orbital periods as well as the location of the observed `pile-up' feature. We expect the effects of pre-main-sequence stellar evolution to be important only if a substantial fraction of HJs approach their current orbits early in protostellar contraction (ages ≲ 10 Myr). Application to the HJs presently known in the cluster M 67 yields constraints on the dissipation roughly consistent with those gleaned from planets in the field; for those in the Hyades and Praesepe, our results suggest a higher degree of dissipation at early times than that inferred from other populations.

A search for cyanopolyynes in L1157-B1

NASA Astrophysics Data System (ADS)

Mendoza, Edgar; Lefloch, B.; Ceccarelli, C.; Kahane, C.; Jaber, A. A.; Podio, L.; Benedettini, M.; Codella, C.; Viti, S.; Jimenez-Serra, I.; Lepine, J. R. D.; Boechat-Roberty, H. M.; Bachiller, R.

2018-04-01

We present here a systematic search for cyanopolyynes in the shock region L1157-B1 and its associated protostar L1157-mm in the framework of the Large Program`Astrochemical Surveys At IRAM' (ASAI), dedicated to chemical surveys of solar-type star-forming regions with the IRAM 30-m telescope. Observations of the millimeter windows between 72 and 272 GHz permitted the detection of HC3N and its 13C isotopologues, and HC5N (for the first time in a protostellar shock region). In the shock, the analysis of the line profiles shows that the emission arises from the outflow cavities associated with L1157-B1 and L1157-B2. Molecular abundances and excitation conditions were obtained from the analysis of the Spectral Line Energy Distributions under the assumption of Local Thermodynamical Equilibrium or using a radiative transfer code in the Large Velocity Gradient approximation. Towards L1157 mm, the HC3N emission arises from the cold envelope (T_rot=10K) and a higher-excitation region (Trot = 31K) of smaller extent around the protostar. We did not find any evidence of 13C or D fractionation enrichment towards L1157-B1. We obtain a relative abundance ratio HC3N/HC5N of 3.3 in the shocked gas. We find an increase by a factor of 30 of the HC3N abundance between the envelope of L1157-mm and the shock region itself. Altogether, these results are consistent with a scenario in which the bulk of HC3N was produced by means of gas phase reactions in the passage of the shock. This scenario is supported by the predictions of a parametric shock code coupled with the chemical model UCL_CHEM.

A Detached Protostellar Disk around a ˜0.2 M ⊙ Protostar in a Possible Site of a Multiple Star Formation in a Dynamical Environment in Taurus

NASA Astrophysics Data System (ADS)

Tokuda, Kazuki; Onishi, Toshikazu; Saigo, Kazuya; Hosokawa, Takashi; Matsumoto, Tomoaki; Inutsuka, Shu-ichiro; Machida, Masahiro N.; Tomida, Kengo; Kunitomo, Masanobu; Kawamura, Akiko; Fukui, Yasuo; Tachihara, Kengo

2017-11-01

We report ALMA observations in 0.87 mm continuum and 12CO (J = 3-2) toward a very low-luminosity (<0.1 L ⊙) protostar, which is deeply embedded in one of the densest cores, MC27/L1521F, in Taurus with an indication of multiple star formation in a highly dynamical environment. The beam size corresponds to ˜20 au, and we have clearly detected blueshifted/redshifted gas in 12CO associated with the protostar. The spatial/velocity distributions of the gas show there is a rotating disk with a size scale of ˜10 au, a disk mass of ˜10-4 M ⊙, and a central stellar mass of ˜0.2 M ⊙. The observed disk seems to be detached from the surrounding dense gas, although it is still embedded at the center of the core whose density is ˜106 cm-3. The current low-outflow activity and the very low luminosity indicate that the mass accretion rate onto the protostar is extremely low in spite of a very early stage of star formation. We may be witnessing the final stage of the formation of ˜0.2 M ⊙ protostar. However, we cannot explain the observed low luminosity with the standard pre-main-sequence evolutionary track unless we assume cold accretion with an extremely small initial radius of the protostar (˜0.65 {R}⊙ ). These facts may challenge our current understanding of the low mass star formation, in particular the mass accretion process onto the protostar and the circumstellar disk.

On the nature of the deeply embedded protostar OMC-2 FIR 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furlan, E.; Megeath, S. T.; Fischer, W. J.

We use mid-infrared to submillimeter data from the Spitzer, Herschel, and Atacama Pathfinder Experiment telescopes to study the bright submillimeter source OMC-2 FIR 4. We find a point source at 8, 24, and 70 μm, and a compact, but extended source at 160, 350, and 870 μm. The peak of the emission from 8 to 70 μm, attributed to the protostar associated with FIR 4, is displaced relative to the peak of the extended emission; the latter represents the large molecular core the protostar is embedded within. We determine that the protostar has a bolometric luminosity of 37 L {submore » ☉}, although including more extended emission surrounding the point source raises this value to 86 L {sub ☉}. Radiative transfer models of the protostellar system fit the observed spectral energy distribution well and yield a total luminosity of most likely less than 100 L {sub ☉}. Our models suggest that the bolometric luminosity of the protostar could be as low as 12-14 L {sub ☉}, while the luminosity of the colder (∼20 K) extended core could be around 100 L {sub ☉}, with a mass of about 27 M {sub ☉}. Our derived luminosities for the protostar OMC-2 FIR 4 are in direct contradiction with previous claims of a total luminosity of 1000 L {sub ☉}. Furthermore, we find evidence from far-infrared molecular spectra and 3.6 cm emission that FIR 4 drives an outflow. The final stellar mass the protostar will ultimately achieve is uncertain due to its association with the large reservoir of mass found in the cold core.« less

Ionospheric Outflow in the Magnetosphere: Circulation and Consequences

NASA Astrophysics Data System (ADS)

Welling, D. T.; Liemohn, M. W.

2017-12-01

Including ionospheric outflow in global magnetohydrodynamic models of near-Earth outer space has become an important step towards understanding the role of this plasma source in the magnetosphere. Such simulations have revealed the importance of outflow in populating the plasma sheet and inner magnetosphere as a function of outflow source characteristics. More importantly, these experiments have shown how outflow can control global dynamics, including tail dynamics and dayside reconnection rate. The broad impact of light and heavy ion outflow can create non-linear feedback loops between outflow and the magnetosphere. This paper reviews some of the most important revelations from global magnetospheric modeling that includes ionospheric outflow of light and heavy ions. It also introduces new advances in outflow modeling and coupling outflow to the magnetosphere.

The JCMT Transient Survey: Stochastic and Secular Variability of Protostars and Disks In the Submillimeter Region Observed over 18 Months

NASA Astrophysics Data System (ADS)

Johnstone, Doug; Herczeg, Gregory J.; Mairs, Steve; Hatchell, Jennifer; Bower, Geoffrey C.; Kirk, Helen; Lane, James; Bell, Graham S.; Graves, Sarah; Aikawa, Yuri; Chen, Huei-Ru Vivien; Chen, Wen-Ping; Kang, Miju; Kang, Sung-Ju; Lee, Jeong-Eun; Morata, Oscar; Pon, Andy; Scicluna, Peter; Scholz, Aleks; Takahashi, Satoko; Yoo, Hyunju; The JCMT Transient Team

2018-02-01

We analyze results from the first 18 months of monthly submillimeter monitoring of eight star-forming regions in the JCMT Transient Survey. In our search for stochastic variability in 1643 bright peaks, only the previously identified source, EC 53, shows behavior well above the expected measurement uncertainty. Another four sources—two disks and two protostars—show moderately enhanced standard deviations in brightness, as expected for stochastic variables. For the two protostars, this apparent variability is the result of single epochs that are much brighter than the mean. In our search for secular brightness variations that are linear in time, we measure the fractional brightness change per year for 150 bright peaks, 50 of which are protostellar. The ensemble distribution of slopes is well fit by a normal distribution with σ ∼ 0.023. Most sources are not rapidly brightening or fading at submillimeter wavelengths. Comparison against time-randomized realizations shows that the width of the distribution is dominated by the uncertainty in the individual brightness measurements of the sources. A toy model for secular variability reveals that an underlying Gaussian distribution of linear fractional brightness change σ = 0.005 would be unobservable in the present sample, whereas an underlying distribution with σ = 0.02 is ruled out. Five protostellar sources, 10% of the protostellar sample, are found to have robust secular measures deviating from a constant flux. The sensitivity to secular brightness variations will improve significantly with a sample over a longer time duration, with an improvement by factor of two expected by the conclusion of our 36 month survey.

The Hall effect in star formation

NASA Astrophysics Data System (ADS)

Braiding, C. R.; Wardle, M.

2012-05-01

Magnetic fields play an important role in star formation by regulating the removal of angular momentum from collapsing molecular cloud cores. Hall diffusion is known to be important to the magnetic field behaviour at many of the intermediate densities and field strengths encountered during the gravitational collapse of molecular cloud cores into protostars, and yet its role in the star formation process is not well studied. We present a semianalytic self-similar model of the collapse of rotating isothermal molecular cloud cores with both Hall and ambipolar diffusion, and similarity solutions that demonstrate the profound influence of the Hall effect on the dynamics of collapse. The solutions show that the size and sign of the Hall parameter can change the size of the protostellar disc by up to an order of magnitude and the protostellar accretion rate by 50 per cent when the ratio of the Hall to ambipolar diffusivities is varied between -0.5 ≤ηH/ηA≤ 0.2. These changes depend upon the orientation of the magnetic field with respect to the axis of rotation and create a preferred handedness to the solutions that could be observed in protostellar cores using next-generation instruments such as ALMA. Hall diffusion also determines the strength and position of the shocks that bound the pseudo and rotationally supported discs, and can introduce subshocks that further slow accretion on to the protostar. In cores that are not initially rotating (not examined here), Hall diffusion can even induce rotation, which could give rise to disc formation and resolve the magnetic braking catastrophe. The Hall effect clearly influences the dynamics of gravitational collapse and its role in controlling the magnetic braking and radial diffusion of the field merits further exploration in numerical simulations of star formation.

IRAS 16293-2422: Evidence for Infall onto a Counter-Rotating Protostellar Accretion Disk

NASA Technical Reports Server (NTRS)

Remijan, Anthony J.; Hollis, J. M.

2005-01-01

We report high spatial resolution VLA observations of the low-mass star-forming region IRAS 16293-2422 using four molecular probes: ethyl cyanide (CH3CH2CN)) methyl formate (CH3OCHO), formic acid (HCOOH), and the ground vibrational state of silicon monoxide (SiO). Ethyl cyanide emission has a spatial scale of approx. 20" and encompasses binary cores A and B as determined by continuum emission peaks. Surrounded by formic acid emission, methyl formate emission has a spatial scale of approx. 6" and is confined to core B. SiO emission shows two velocity components with spatial scales less than 2" that map approx. 2" northeast of the A and B symmetry axis. The redshifted SiO is approx. 2" northwest of blueshifted SiO along a position angle of approx. 135deg which is approximately parallel to the A and B symmetry axis. We interpret the spatial position offset in red and blueshifted SiO emission as due to rotation of a protostellar accretion disk and we derive approx. 1.4 Solar Mass, interior to the SiO emission. In the same vicinity, Mundy et al. (1986) also concluded rotation of a nearly edge-on disk from OVRO observations of much stronger and ubiquitous CO-13 emission but the direction of rotation is opposite to the SiO emission findings. Taken together, SiO and CO-13 data suggest evidence for a counter-rotating disk. Moreover, archival BIMA array CO-12C data show an inverse P Cygni profile with the strongest absorption in close proximity to the SiO emission, indicating unambiguous material infall toward the counter-rotating protostellar disk at a new source location within the IRAS 16293-2422 complex. The details of these observations and our interpretations are discussed.

The JCMT Gould Belt Survey: A First Look at SCUBA-2 Observations of the Lupus I Molecular Cloud

NASA Astrophysics Data System (ADS)

Mowat, C.; Hatchell, J.; Rumble, D.; Kirk, H.; Buckle, J.; Berry, D. S.; Broekhoven-Fiene, H.; Currie, M. J.; Jenness, T.; Johnstone, D.; Mottram, J. C.; Pattle, K.; Tisi, S.; Di Francesco, J.; Hogerheijde, M. R.; Ward-Thompson, D.; Bastien, P.; Bresnahan, D.; Butner, H.; Chen, M.; Chrysostomou, A.; Coudé, S.; Davis, C. J.; Drabek-Maunder, E.; Duarte-Cabral, A.; Fich, M.; Fiege, J.; Friberg, P.; Friesen, R.; Fuller, G. A.; Graves, S.; Greaves, J.; Holland, W.; Joncas, G.; Kirk, J. M.; Knee, L. B. G.; Mairs, S.; Marsh, K.; Matthews, B. C.; Moriarty-Schieven, G.; Rawlings, J.; Retter, B.; Richer, J.; Robertson, D.; Rosolowsky, E.; Sadavoy, S.; Thomas, H.; Tothill, N.; Viti, S.; White, G. J.; Wouterloot, J.; Yates, J.; Zhu, M.

2017-05-01

This paper presents observations of the Lupus I molecular cloud at 450 and 850 μm with Submillimetre Common User Bolometer Array (SCUBA-2) as part of the James Clerk Maxwell Telescope Gould Belt Survey (JCMT GBS). Nine compact sources, assumed to be the discs of young stellar objects (YSOs), 12 extended protostellar, pre-stellar and starless cores, and one isolated, low-luminosity protostar, are detected in the region. Spectral energy distributions, including submillimetre fluxes, are produced for 15 YSOs, and each is fitted with the models of Robitaille et al. The proportion of Class 0/I protostars is higher than that seen in other Gould Belt regions such as Ophiuchus and Serpens. Circumstellar disc masses are calculated for more evolved sources, while protostellar envelope masses are calculated for protostars. Up to four very low luminosity objects are found; a large fraction when compared to other Spitzer c2d regions. One YSO has a disc mass greater than the minimum mass solar nebula. 12 starless/protostellar cores are detected by SCUBA-2 and their masses are calculated. The stability of these cores is examined using both the thermal Jeans mass and a turbulent virial mass when possible. Two cores in Lupus I are super-Jeans and contain no known YSOs. One of these cores has a virial parameter of 1.1 ± 0.4, and could therefore be pre-stellar. The high ratio of Class 0/I to Class III YSOs (1:1), and the presence of a pre-stellar core candidate, provides support for the hypothesis that a shock recently triggered star formation in Lupus I.

DOES MAGNETIC-FIELD-ROTATION MISALIGNMENT SOLVE THE MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Zhiyun; Krasnopolsky, Ruben; Shang, Hsien

2013-09-01

Stars form in dense cores of molecular clouds that are observed to be significantly magnetized. In the simplest case of a laminar (non-turbulent) core with the magnetic field aligned with the rotation axis, both analytic considerations and numerical simulations have shown that the formation of a large, 10{sup 2} AU scale, rotationally supported protostellar disk is suppressed by magnetic braking in the ideal MHD limit for a realistic level of core magnetization. This theoretical difficulty in forming protostellar disks is termed the ''magnetic braking catastrophe''. A possible resolution to this problem, proposed by Hennebelle and Ciardi and Joos et al.,more » is that misalignment between the magnetic field and rotation axis may weaken the magnetic braking enough to enable disk formation. We evaluate this possibility quantitatively through numerical simulations. We confirm the basic result of Joos et al. that the misalignment is indeed conducive to disk formation. In relatively weakly magnetized cores with dimensionless mass-to-flux ratio {approx}> 4, it enabled the formation of rotationally supported disks that would otherwise be suppressed if the magnetic field and rotation axis are aligned. For more strongly magnetized cores, disk formation remains suppressed, however, even for the maximum tilt angle of 90 Degree-Sign . If dense cores are as strongly magnetized as indicated by OH Zeeman observations (with a mean dimensionless mass-to-flux ratio {approx}2), it would be difficult for the misalignment alone to enable disk formation in the majority of them. We conclude that, while beneficial to disk formation, especially for the relatively weak field case, misalignment does not completely solve the problem of catastrophic magnetic braking in general.« less

Models of Interacting Stellar Winds

NASA Astrophysics Data System (ADS)

Wilkin, Francis Patrick

Stars drive supersonic winds which interact violently with their surroundings. Analytic and numerical models of hypersonic, interacting circumstellar flows are presented for several important astrophysical problems. A new solution method for steady-state, axisymmetric, wind collision problems is applied to radiative bow shocks from moving stars and to the collision of two spherical winds in a binary star system. The solutions obtained describe the shape of the geometrically thin, shocked shell of matter, as well as its mass surface density and the tangential velocity within it. Analytic solutions are also obtained for non-axisymmetric bow shocks, where the asymmetry arises due to either a transverse gradient in the ambient medium, or a misaligned, axisymmetric stellar wind. While the solutions are all easily scaled in terms of their relevant dimensional parameters, the important assumption of radiative shocks implies that the models are most applicable towards systems with dense environments and low preshock velocities. The bow shock model has previously been applied to cometary, ultracompact HII regions by Van Buren et al. (1990), who discussed extensively the applicability of the thin shell approximation. I next model the collision between a protostellar wind and supersonic infall from a rotating cloud, employing a quasi-steady, thin-shell formulation. The spherical wind is initially crushed to the protostellar surface by nearly spherical infall. The centrifugal distortion of infalling matter eventually permits a wind-supported, trapped bubble to slowly expand on an evolutionary (~ 105 yr) time. The shell becomes progressively more extended along the rotational axis, due to the asymmetry of the infall. When the quasi-steady assumption breaks down, the shell has become a needle-like, bipolar configuration that may represent a precursor to protostellar jets. I stress, however, the likelihood of instability for the shell, and the possibility of oscillatory behavior in a fully time-dependent model.

The Hi-GAL compact source catalogue - I. The physical properties of the clumps in the inner Galaxy (-71.0° < ℓ < 67.0°)

NASA Astrophysics Data System (ADS)

Elia, Davide; Molinari, S.; Schisano, E.; Pestalozzi, M.; Pezzuto, S.; Merello, M.; Noriega-Crespo, A.; Moore, T. J. T.; Russeil, D.; Mottram, J. C.; Paladini, R.; Strafella, F.; Benedettini, M.; Bernard, J. P.; Di Giorgio, A.; Eden, D. J.; Fukui, Y.; Plume, R.; Bally, J.; Martin, P. G.; Ragan, S. E.; Jaffa, S. E.; Motte, F.; Olmi, L.; Schneider, N.; Testi, L.; Wyrowski, F.; Zavagno, A.; Calzoletti, L.; Faustini, F.; Natoli, P.; Palmeirim, P.; Piacentini, F.; Piazzo, L.; Pilbratt, G. L.; Polychroni, D.; Baldeschi, A.; Beltrán, M. T.; Billot, N.; Cambrésy, L.; Cesaroni, R.; García-Lario, P.; Hoare, M. G.; Huang, M.; Joncas, G.; Liu, S. J.; Maiolo, B. M. T.; Marsh, K. A.; Maruccia, Y.; Mège, P.; Peretto, N.; Rygl, K. L. J.; Schilke, P.; Thompson, M. A.; Traficante, A.; Umana, G.; Veneziani, M.; Ward-Thompson, D.; Whitworth, A. P.; Arab, H.; Bandieramonte, M.; Becciani, U.; Brescia, M.; Buemi, C.; Bufano, F.; Butora, R.; Cavuoti, S.; Costa, A.; Fiorellino, E.; Hajnal, A.; Hayakawa, T.; Kacsuk, P.; Leto, P.; Li Causi, G.; Marchili, N.; Martinavarro-Armengol, S.; Mercurio, A.; Molinaro, M.; Riccio, G.; Sano, H.; Sciacca, E.; Tachihara, K.; Torii, K.; Trigilio, C.; Vitello, F.; Yamamoto, H.

2017-10-01

Hi-GAL (Herschel InfraRed Galactic Plane Survey) is a large-scale survey of the Galactic plane, performed with Herschel in five infrared continuum bands between 70 and 500 μm. We present a band-merged catalogue of spatially matched sources and their properties derived from fits to the spectral energy distributions (SEDs) and heliocentric distances, based on the photometric catalogues presented in Molinari et al., covering the portion of Galactic plane -71.0° < ℓ < 67.0°. The band-merged catalogue contains 100 922 sources with a regular SED, 24 584 of which show a 70-μm counterpart and are thus considered protostellar, while the remainder are considered starless. Thanks to this huge number of sources, we are able to carry out a preliminary analysis of early stages of star formation, identifying the conditions that characterize different evolutionary phases on a statistically significant basis. We calculate surface densities to investigate the gravitational stability of clumps and their potential to form massive stars. We also explore evolutionary status metrics such as the dust temperature, luminosity and bolometric temperature, finding that these are higher in protostellar sources compared to pre-stellar ones. The surface density of sources follows an increasing trend as they evolve from pre-stellar to protostellar, but then it is found to decrease again in the majority of the most evolved clumps. Finally, we study the physical parameters of sources with respect to Galactic longitude and the association with spiral arms, finding only minor or no differences between the average evolutionary status of sources in the fourth and first Galactic quadrants, or between 'on-arm' and 'interarm' positions.

Metallicity Distribution of Disk Stars and the Formation History of the Milky Way

NASA Astrophysics Data System (ADS)

Toyouchi, Daisuke; Chiba, Masashi

2018-03-01

We investigate the formation history of the stellar disk component in the Milky Way (MW) based on our new chemical evolution model. Our model considers several fundamental baryonic processes, including gas infall, reaccretion of outflowing gas, and radial migration of disk stars. Each of these baryonic processes in the disk evolution is characterized by model parameters that are determined by fitting to various observational data of the stellar disk in the MW, including the radial dependence of the metallicity distribution function (MDF) of the disk stars, which has recently been derived in the APOGEE survey. We succeeded to obtain the best set of model parameters that well reproduces the observed radial dependences of the mean, standard deviation, skewness, and kurtosis of the MDFs for the disk stars. We analyze the basic properties of our model results in detail to gain new insights into the important baryonic processes in the formation history of the MW. One of the remarkable findings is that outflowing gas, containing many heavy elements, preferentially reaccretes onto the outer disk parts, and this recycling process of metal-enriched gas is a key ingredient for reproducing the observed narrower MDFs at larger radii. Moreover, important implications for the radial dependence of gas infall and the influence of radial migration on the MDFs are also inferred from our model calculation. Thus, the MDF of disk stars is a useful clue for studying the formation history of the MW.

Interstellar/Precometary Organic Material and the Photochemical Evolution of Complex Organics

NASA Technical Reports Server (NTRS)

Allamandola, Lou J.; Bernstein, Max; Sandford, Scott; Witteborn, Fred (Technical Monitor)

1996-01-01

During the past two decades ground-, air-, and space-based infrared spectroscopic observations, combined with realistic laboratory simulations, have revolutionized our understanding of interstellar ice and dust, the raw materials from which planets, comets and stars form. Most interstellar material is concentrated in Large molecular clouds where simple molecules are formed by dust grain and gas phase reactions. Gaseous species striking the cold (10 K) dust will stick, forming an icy grain mantle. This accretion, coupled with energetic particle bombardment and UV photolysis, will produce a complex chemical mixture containing volatile, non-volatile, and isotopically fractionated species. Ices in molecular clouds contain the very simple molecules H2O, CH3OH, CO, CO2, H2, and perhaps some NH3 and H2CO, as well as more complex species including nitriles and ketones or esters. The evidence for these compounds as well as carbon rich materials such as polycyclic aromatic hydrocarbons (PAHs), microdiamonds, and amorphous carbon will be reviewed and the possible connections with comets and meteorites will be presented in the first part of the talk. The second part of the presentation will focus on interstellar/precometary ice photochemical evolution. The chemical composition and photochemical evolution of realistic interstellar/pre-cometary ice analogs containing methanol will be discussed. ultraviolet photolysis of these ices produces H2, H2CO, CO2, CO, CH4, HCO, and more complex molecules. Infrared spectroscopy, H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography-mass spectrometry demonstrate that when ices representative of interstellar grains and comets are exposed to UV radiation at low temperature a series of moderately complex organic molecules are formed in the ice including: CH3CH2OH (ethanol), HC(=O)NH2 (formamide), CH3C(=O)NH2 (acetamide), and R-C(integral)N (nitriles). Several of these are already known to be in the interstellar medium, and their presence indicates the importance of grain processing. After warming to room temperature what remains is an organic residue composed primarily of Hexamethylenetetramine (HMT, C6H12N4), with lesser amounts of polyoxymethylene related species (POMs), amides, and ketones. This is in sharp contrast to the organic residues produced by irradiating ices which do not contain methanol (unrealistic interstellar ice analogs) or thermally promoted polymerization-type reactions in unirradiated realistic ice mixtures. Here HMT is only a minor product in a residue dominated by a mixture of polyoxymethylene related species. The implications, for infrared astronomy and astrochemistry, of high concentrations of HMT in interstellar and cometary ices may be profound. The ultraviolet photolysis of HMT frozen in H20 ice produces the "XCN" band observed in the spectra of protostellar objects and laboratory ices, as well as carbon oxides and other nitriles. Thus, HMT may be a precursor of XCN in protostellar objects and a source of CN and CO in the tail of comets. Also, HMT is known to hydrolyze under acidic conditions to yield ammonia and formaldehyde as well as amino acids. Thus, HMT may have been a source of organic material delivered to the early earth by comets.

The Confinement and Breakout of Protostellar Winds: Time-Dependent Solution

NASA Technical Reports Server (NTRS)

Wilkin, F.; Stahler, S.

2000-01-01

Jets from embedded young stars may be collimated by the anisotropic infall of their cloud envelopes. To model this effect, we have followed numerically the motion of the shocked shell created by the impact of a spherical wind and a rotating, collapsing cloud.

WIND-DRIVEN ACCRETION IN TRANSITIONAL PROTOSTELLAR DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Lile; Goodman, Jeremy J.

Transitional protostellar disks have inner cavities that are heavily depleted in dust and gas, yet most of them show signs of ongoing accretion, often at rates comparable to full disks. We show that recent constraints on the gas surface density in a few well-studied disk cavities suggest that the accretion speed is at least transsonic. We propose that this is the natural result of accretion driven by magnetized winds. Typical physical conditions of the gas inside these cavities are estimated for plausible X-ray and FUV radiation fields. The gas near the midplane is molecular and predominantly neutral, with a dimensionlessmore » ambipolar parameter in the right general range for wind solutions of the type developed by Königl, Wardle, and others. That is to say, the density of ions and electrons is sufficient for moderately good coupling to the magnetic field, but it is not so good that the magnetic flux needs to be dragged inward by the accreting neutrals.« less

Theoretical Models of Protostellar Binary and Multiple Systems with AMR Simulations

NASA Astrophysics Data System (ADS)

Matsumoto, Tomoaki; Tokuda, Kazuki; Onishi, Toshikazu; Inutsuka, Shu-ichiro; Saigo, Kazuya; Takakuwa, Shigehisa

2017-05-01

We present theoretical models for protostellar binary and multiple systems based on the high-resolution numerical simulation with an adaptive mesh refinement (AMR) code, SFUMATO. The recent ALMA observations have revealed early phases of the binary and multiple star formation with high spatial resolutions. These observations should be compared with theoretical models with high spatial resolutions. We present two theoretical models for (1) a high density molecular cloud core, MC27/L1521F, and (2) a protobinary system, L1551 NE. For the model for MC27, we performed numerical simulations for gravitational collapse of a turbulent cloud core. The cloud core exhibits fragmentation during the collapse, and dynamical interaction between the fragments produces an arc-like structure, which is one of the prominent structures observed by ALMA. For the model for L1551 NE, we performed numerical simulations of gas accretion onto protobinary. The simulations exhibit asymmetry of a circumbinary disk. Such asymmetry has been also observed by ALMA in the circumbinary disk of L1551 NE.