Constraining high-energy neutrino emission from choked jets in stripped-envelope supernovae

NASA Astrophysics Data System (ADS)

Senno, Nicholas; Murase, Kohta; Mészáros, Peter

2018-01-01

There are indications that γ-ray dark objects such as supernovae (SNe) with choked jets, and the cores of active galactic nuclei may contribute to the diffuse flux of astrophysical neutrinos measured by the IceCube observatory. In particular, stripped-envelope SNe have received much attention since they are capable of producing relativistic jets and could explain the diversity in observations of collapsar explosions (e.g., gamma-ray bursts (GRBs), low-luminosity GRBs, and Type Ibc SNe). We use an unbinned maximum likelihood method to search for spatial and temporal coincidences between Type Ibc core-collapse SNe, which may harbor a choked jet, and muon neutrinos from a sample of IceCube up-going track-like events measured from May 2011–May 2012. In this stacking analysis, we find no significant deviation from a background-only hypothesis using one year of data, and are able to place upper limits on the total amount of isotropic equivalent energy that choked jet core-collapse SNe deposit in cosmic rays Script Ecr and the fraction of core-collapse SNe which have a jet pointed towards Earth fjet. This analysis can be extended with yet to be made public IceCube data, and the increased amount of optically detected core-collapse SNe discovered by wide field-of-view surveys such as the Palomar Transient Factory and All-Sky Automated Survey for Supernovae. The choked jet SNe/high-energy cosmic neutrino connection can be more tightly constrained in the near future.

Galaxy and the solar system

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

Smoluchowski, R.; Bahcall, J.M.; Matthews, M.S.

1986-01-01

The solar-Galactic neighborhood, massive interstellar clouds and other Galactic features, the Oort cloud, perturbations of the solar system, and the existence and stability of a solar companion star are examined in chapters based on contributions to a conference held in Tucson, AZ during January 1985. The individual topics addressed include: the Galactic environment of the solar system; stars within 25 pc of the sun; the path of the sun in 100 million years; the local velocity field in the last billion years; interstellar clouds near the sun; and evidence for a local recent supernova. Also considered are: dynamic influence ofmore » Galactic tides and molecular clouds on the Oort cloud; cometary evidence for a solar companion; dynamical interactions between the Oort cloud and the Galaxy; geological periodicities and the Galaxy; giant comets and the Galaxy; dynamical evidence for Planet X; evolution of the solar system in the presence of a solar companion star; mass extinctions, crater ages, and comet showers; evidence for Nemesis, a solar companion star.« less

The Energetic Gamma-Ray Experiment Telescope (EGRET) Science Symposium

NASA Technical Reports Server (NTRS)

Fichtel, Carl E. (Editor); Hunter, Stanley D. (Editor); Sreekumar, Parameswaran (Editor); Stecker, Floyd W. (Editor)

1990-01-01

The principle purpose of this symposium is to provide the EGRET (Energetic Gamma-Ray Experiment Telescope) scientists with an opportunity to study and improve their understanding of high energy gamma ray astronomy. The Symposium began with the galactic diffusion radiation both because of its importance in studying galactic cosmic rays, galactic structure, and dynamic balance, and because an understanding of its characteristics is important in the study of galactic sources. The galactic objects to be reviewed included pulsars, bursts, solar flares, and other galactic sources of several types. The symposium papers then proceeded outward from the Milky Way to normal galaxies, active galaxies, and the extragalactic diffuse radiation.

Intense electromagnetic outbursts from collapsing hypermassive neutron stars

NASA Astrophysics Data System (ADS)

Lehner, Luis; Palenzuela, Carlos; Liebling, Steven L.; Thompson, Christopher; Hanna, Chad

2012-11-01

We study the gravitational collapse of a magnetized neutron star using a novel numerical approach able to capture both the dynamics of the star and the behavior of the surrounding plasma. In this approach, a fully general relativistic magnetohydrodynamics implementation models the collapse of the star and provides appropriate boundary conditions to a force-free model which describes the stellar exterior. We validate this strategy by comparing with known results for the rotating monopole and aligned rotator solutions and then apply it to study both rotating and nonrotating stellar collapse scenarios and contrast the behavior with what is obtained when employing the electrovacuum approximation outside the star. The nonrotating electrovacuum collapse is shown to agree qualitatively with a Newtonian model of the electromagnetic field outside a collapsing star. We illustrate and discuss a fundamental difference between the force-free and electrovacuum solutions, involving the appearance of large zones of electric-dominated field in the vacuum case. This provides a clear demonstration of how dissipative singularities appear generically in the nonlinear time evolution of force-free fluids. In both the rotating and nonrotating cases, our simulations indicate that the collapse induces a strong electromagnetic transient, which leaves behind an uncharged, unmagnetized Kerr black hole. In the case of submillisecond rotation, the magnetic field experiences strong winding, and the transient carries much more energy. This result has important implications for models of gamma-ray bursts. Even when the neutron star is surrounded by an accretion torus (as in binary merger and collapsar scenarios), a magnetosphere may emerge through a dynamo process operating in a surface shear layer. When this rapidly rotating magnetar collapses to a black hole, the electromagnetic energy released can compete with the later output in a Blandford-Znajek jet. Much less electromagnetic energy is released by a massive magnetar that is (initially) gravitationally stable: its rotational energy is dissipated mainly by internal torques. A distinct plasmoid structure is seen in our nonrotating simulations, which will generate a radio transient with subluminal expansion and greater synchrotron efficiency than is expected in shock models. Closely related phenomena appear to be at work in the giant flares of Galactic magnetars.

The distribution of cosmic rays in the galaxy and their dynamics as deduced from recent gamma-ray observations. [X-ray intensity variations with galactocentric distance

NASA Technical Reports Server (NTRS)

Puget, J. L.; Stecker, F. W.

1974-01-01

Recent data from SAS-2 on the galactic gamma ray line flux as a function of longitude reveal a broad maximum in the gamma ray intensity in the region absolute value of l approximately smaller than 30 deg. These data imply that the low energy galactic cosmic ray flux varies with galactocentric distance and is about an order of magnitude higher than the local value in a toroidal region between 4 and 5 kpc from the galactic center. This enhancement can be plausibly accounted for by first order Fermi acceleration, compression and trapping of cosmic rays consistent with present ideas of galactic dynamics and galactic structure theory. Calculations indicate that cosmic rays in the 4 to 5 kpc region are trapped and accelerated over a mean time of the order of a few million years or about 2 to 4 times the assumed trapping time in the solar region of the galaxy.

Galactic evolution. I - Single-zone models. [encompassing stellar evolution and gas-star dynamic theories

NASA Technical Reports Server (NTRS)

Thuan, T. X.; Hart, M. H.; Ostriker, J. P.

1975-01-01

The two basic approaches of physical theory required to calculate the evolution of a galactic system are considered, taking into account stellar evolution theory and the dynamics of a gas-star system. Attention is given to intrinsic (stellar) physics, extrinsic (dynamical) physics, and computations concerning the fractionation of an initial mass of gas into stars. The characteristics of a 'standard' model and its variants are discussed along with the results obtained with the aid of these models.

A new gamma-ray burst classification scheme from GRB 060614.

PubMed

Gehrels, N; Norris, J P; Barthelmy, S D; Granot, J; Kaneko, Y; Kouveliotou, C; Markwardt, C B; Mészáros, P; Nakar, E; Nousek, J A; O'Brien, P T; Page, M; Palmer, D M; Parsons, A M; Roming, P W A; Sakamoto, T; Sarazin, C L; Schady, P; Stamatikos, M; Woosley, S E

2006-12-21

Gamma-ray bursts (GRBs) are known to come in two duration classes, separated at approximately 2 s. Long-duration bursts originate from star-forming regions in galaxies, have accompanying supernovae when these are near enough to observe and are probably caused by massive-star collapsars. Recent observations show that short-duration bursts originate in regions within their host galaxies that have lower star-formation rates, consistent with binary neutron star or neutron star-black hole mergers. Moreover, although their hosts are predominantly nearby galaxies, no supernovae have been so far associated with short-duration GRBs. Here we report that the bright, nearby GRB 060614 does not fit into either class. Its approximately 102-s duration groups it with long-duration GRBs, while its temporal lag and peak luminosity fall entirely within the short-duration GRB subclass. Moreover, very deep optical observations exclude an accompanying supernova, similar to short-duration GRBs. This combination of a long-duration event without an accompanying supernova poses a challenge to both the collapsar and the merging-neutron-star interpretations and opens the door to a new GRB classification scheme that straddles both long- and short-duration bursts.

Hyper-Eddington accretion in GRB

NASA Astrophysics Data System (ADS)

Janiuk, A.; Czerny, B.; Perna, R.; Di Matteo, T.

2005-05-01

Popular models of the GRB origin associate this event with a cosmic explosion, birth of a stellar mass black hole and jet ejection. Due to the shock collisions that happen in the jet, the gamma rays are produced and we detect a burst of duration up to several tens of seconds. This burst duration is determined by the lifetime of the central engine, which may be different in various scenarios. Characteristically, the observed bursts have a bimodal distribution and constitute the two classes: short (t < 2s) and long bursts. Theoretical models invoke the mergers of two neutron stars or a neutron star with a black hole, or, on the other hand, a massive star explosion (collapsar). In any of these models we have a phase of disc accretion onto a newly born black hole: the disc is formed from the disrupted neutron star or fed by the material fallback from the ejected collapsar envelope. The disc is extremely hot and dense, and the accretion rate is orders of magnitude higher than the Eddington rate. In such physical conditions the main cooling mechanism is neutrino emission, and one of possible ways of energy extraction from the accretion disc is the neutrino-antineutrino annihilation.

Protomagnetar and black hole formation in high-mass stars

NASA Astrophysics Data System (ADS)

Obergaulinger, M.; Aloy, M. Á.

2017-07-01

Using axisymmetric simulations coupling special relativistic magnetohydrodynamics (MHD), an approximate post-Newtonian gravitational potential and two-moment neutrino transport, we show different paths for the formation of either protomagnetars or stellar mass black holes. The fraction of prototypical stellar cores which should result in collapsars depends on a combination of several factors, among which the structure of the progenitor star and the profile of specific angular momentum are probably the foremost. Along with the implosion of the stellar core, we also obtain supernova-like explosions driven by neutrino heating and hydrodynamic instabilities or by magneto-rotational effects in cores of high-mass stars. In the latter case, highly collimated, mildly relativistic outflows are generated. We find that after a rather long post-collapse phase (lasting ≳1 s) black holes may form in cases both of successful and failed supernova-like explosions. A basic trend is that cores with a specific angular momentum smaller than that obtained by standard, one-dimensional stellar evolution calculations form black holes (and eventually collapsars). Complementary, protomagnetars result from stellar cores with the standard distribution of specific angular momentum obtained from prototypical stellar evolution calculations including magnetic torques and moderate to large mass-loss rates.

Anisotropy and corotation of galactic cosmic rays.

PubMed

Amenomori, M; Ayabe, S; Bi, X J; Chen, D; Cui, S W; Danzengluobu; Ding, L K; Ding, X H; Feng, C F; Feng, Zhaoyang; Feng, Z Y; Gao, X Y; Geng, Q X; Guo, H W; He, H H; He, M; Hibino, K; Hotta, N; Hu, Haibing; Hu, H B; Huang, J; Huang, Q; Jia, H Y; Kajino, F; Kasahara, K; Katayose, Y; Kato, C; Kawata, K; Labaciren; Le, G M; Li, A F; Li, J Y; Lou, Y-Q; Lu, H; Lu, S L; Meng, X R; Mizutani, K; Mu, J; Munakata, K; Nagai, A; Nanjo, H; Nishizawa, M; Ohnishi, M; Ohta, I; Onuma, H; Ouchi, T; Ozawa, S; Ren, J R; Saito, T; Saito, T Y; Sakata, M; Sako, T K; Sasaki, T; Shibata, M; Shiomi, A; Shirai, T; Sugimoto, H; Takita, M; Tan, Y H; Tateyama, N; Torii, S; Tsuchiya, H; Udo, S; Wang, B; Wang, H; Wang, X; Wang, Y G; Wu, H R; Xue, L; Yamamoto, Y; Yan, C T; Yang, X C; Yasue, S; Ye, Z H; Yu, G C; Yuan, A F; Yuda, T; Zhang, H M; Zhang, J L; Zhang, N J; Zhang, X Y; Zhang, Y; Zhang, Yi; Zhaxisangzhu; Zhou, X X

2006-10-20

The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments.

Dynamical equivalence, the origin of the Galactic field stellar and binary population, and the initial radius-mass relation of embedded clusters

NASA Astrophysics Data System (ADS)

Belloni, Diogo; Kroupa, Pavel; Rocha-Pinto, Helio J.; Giersz, Mirek

2018-03-01

In order to allow a better understanding of the origin of Galactic field populations, dynamical equivalence of stellar-dynamical systems has been postulated by Kroupa and Belloni et al. to allow mapping of solutions of the initial conditions of embedded clusters such that they yield, after a period of dynamical processing, the Galactic field population. Dynamically equivalent systems are defined to initially and finally have the same distribution functions of periods, mass ratios and eccentricities of binary stars. Here, we search for dynamically equivalent clusters using the MOCCA code. The simulations confirm that dynamically equivalent solutions indeed exist. The result is that the solution space is next to identical to the radius-mass relation of Marks & Kroupa, ( r_h/pc )= 0.1^{+0.07}_{-0.04} ( M_ecl/M_{⊙} )^{0.13± 0.04}. This relation is in good agreement with the oIMF. This is achieved by applying a similar procedurebserved density of molecular cloud clumps. According to the solutions, the time-scale to reach dynamical equivalence is about 0.5 Myr which is, interestingly, consistent with the lifetime of ultra-compact H II regions and the time-scale needed for gas expulsion to be active in observed very young clusters as based on their dynamical modelling.

Orbits of Selected Globular Clusters in the Galactic Bulge

NASA Astrophysics Data System (ADS)

Pérez-Villegas, A.; Rossi, L.; Ortolani, S.; Casotto, S.; Barbuy, B.; Bica, E.

2018-05-01

We present orbit analysis for a sample of eight inner bulge globular clusters, together with one reference halo object. We used proper motion values derived from long time base CCD data. Orbits are integrated in both an axisymmetric model and a model including the Galactic bar potential. The inclusion of the bar proved to be essential for the description of the dynamical behaviour of the clusters. We use the Monte Carlo scheme to construct the initial conditions for each cluster, taking into account the uncertainties in the kinematical data and distances. The sample clusters show typically maximum height to the Galactic plane below 1.5 kpc, and develop rather eccentric orbits. Seven of the bulge sample clusters share the orbital properties of the bar/bulge, having perigalactic and apogalatic distances, and maximum vertical excursion from the Galactic plane inside the bar region. NGC 6540 instead shows a completely different orbital behaviour, having a dynamical signature of the thick disc. Both prograde and prograde-retrograde orbits with respect to the direction of the Galactic rotation were revealed, which might characterise a chaotic behaviour.

Special Features of Galactic Dynamics

NASA Astrophysics Data System (ADS)

Efthymiopoulos, Christos; Voglis, Nikos; Kalapotharakos, Constantinos

This is an introductory article to some basic notions and currently open problems of galactic dynamics. The focus is on topics mostly relevant to the so-called `new methods' of celestial mechanics or Hamiltonian dynamics, as applied to the ellipsoidal components of galaxies, i.e., to the elliptical galaxies and to the dark halos and bulges of disk galaxies. Traditional topics such as Jeans theorem, the role of a `third integral' of motion, Nekhoroshev theory, violent relaxation, and the statistical mechanics of collisionless stellar systems are first discussed. The emphasis is on modern extrapolations of these old topics. Recent results from orbital and global dynamical studies of galaxies are then shortly reviewed. The role of various families of orbits in supporting self-consistency, as well as the role of chaos in galaxies, are stressed. A description is then given of the main numerical techniques of integration of the N-body problem in the framework of stellar dynamics and of the results obtained via N-Body experiments. A final topic is the secular evolution and self-organization of galactic systems.

Understanding the Current Dynamical States of Globular Clusters

NASA Astrophysics Data System (ADS)

Pooley, David

2008-09-01

We appear to be on the verge of a major paradigm shift in our understanding of the current dynamical states of Galactic globular clusters. Fregeau (2008) brought together two recent theoretical breakthroughs as well as an observational breakthrough made possible by Chandra -- that a globular cluster's X-ray source population scales with its dynamical encounter frequency -- to persuasively argue that we have misunderstood the dynamical states of Galactic globular clusters. The observational evidence hinges on Chandra results from clusters which are classified as "core collapsed," of which there are only a handful of observations. I propose a nearly complete census with Chandra of the rest of the "core collapsed" globular clusters.

Gamma-ray bursts: The central engine

NASA Astrophysics Data System (ADS)

Woosley, S. E.

2000-09-01

A variety of arguments suggest that the most common form of gamma-ray bursts (GRBs), those longer than a few seconds, involve the formation of black holes in supernova-like events. Two kinds of ``collapsar'' models are discussed, those in which the black hole forms promptly-a second or so after iron core collapse-and those in which formation occurs later, following ``fallback'' over a period of minutes to hours. In most cases, extraction of energy from a rapidly accreting disk (and a rapidly rotating black hole) is achieved by magnetohydrodynamical processes, although neutrino-powered models remain viable in cases where the accretion rate is >~0.05Msolar s-1. GRBs are but one observable phenomenon accompanying black hole birth and other possibilities are discussed, some of which (long, faint GRBs and soft x-ray transients) may await discovery. Since they all involve black holes of similar mass accreting one to several Msolar, collapsars have a nearly standard total energy, around 1052 erg, but both the fraction of that energy ejected as highly relativistic matter and the distribution of that energy with angle can be highly variable. An explanation is presented why inferred GRB luminosity might correlate inversely with time scales and arguments are given against the production of ordinary GRBs by supergiant stars. .

Ideal engine durations for gamma-ray-burst-jet launch

NASA Astrophysics Data System (ADS)

Hamidani, Hamid; Takahashi, Koh; Umeda, Hideyuki; Okita, Shinpei

2017-08-01

Aiming to study gamma-ray-burst (GRB) engine duration, we present numerical simulations to investigate collapsar jets. We consider typical explosion energy (1052 erg) but different engine durations, in the widest domain to date from 0.1 to 100 s. We employ an adaptive mesh refinement 2D hydrodynamical code. Our results show that engine duration strongly influences jet nature. We show that the efficiency of launching and collimating relativistic outflow increases with engine duration, until the intermediate engine range where it is the highest, past this point to long engine range, the trend is slightly reversed; we call this point where acceleration and collimation are the highest 'sweet spot' (˜10-30 s). Moreover, jet energy flux shows that variability is also high in this duration domain. We argue that not all engine durations can produce the collimated, relativistic and variable long GRB jets. Considering a typical progenitor and engine energy, we conclude that the ideal engine duration to reproduce a long GRB is ˜10-30 s, where the launch of relativistic, collimated and variable jets is favoured. We note that this duration domain makes a good link with a previous study suggesting that the bulk of Burst and Transient Source Experiment's long GRBs is powered by ˜10-20 s collapsar engines.

The distribution of cosmic rays in the galaxy and their dynamics as deduced from recent gamma ray observations. [noting maximum in toroidal region between 4 and 5 kpc from galactic center

NASA Technical Reports Server (NTRS)

Puget, J. L.; Stecker, F. W.

1974-01-01

Data from SAS-2 on the galactic gamma ray line flux as a function of longitude is examined. It is shown that the gamma ray emissivity varies with galactocentric distance and is about an order of magnitude higher than the local value in a toroidal region between 4 and 5 kpc from the galactic center. This enhancement is accounted for in part by first-order Fermi acceleration, compression, and trapping of cosmic rays consistent with present ideas of galactic dynamics and galactic structure theory. Calculations indicate that cosmic rays in the 4 to 5 kpc region are trapped and accelerated over a mean time of the order of a few million years or about 2 to 4 times the assumed trapping time in the solar region of the galaxy on the assumption that only an increased cosmic ray flux is responsible for the observed emission. Cosmic ray nucleons, cosmic ray electrons, and ionized hydrogen gas were found to have a strikingly similar distribution in the galaxy according to both the observational data and the theoretical model discussed.

Cosmic cannibals

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

Tucker, W.

1980-06-01

The collision and subsequent assimilation of small galaxies by larger ones are examined in connection with cD galaxy radio sources. The dynamic-friction galactic-cannibalism theory is reviewed. It is noted that galactic cannibalism accounts for the relative absence of bright galaxies other than cD galaxies in rich clusters.

Milgromian dynamics and dwarf galaxies in galactic voids

NASA Astrophysics Data System (ADS)

Khadem, Mahdi; Haghi, Hosein

2018-05-01

We use kinematic data of 103 dwarf galaxies, obtained from the Sloan Digital Sky Survey catalog, to test the Milgromian dynamics (MOND) inside a galactic void. From this data, we compute the line-of-sight velocity dispersions of the dwarf galaxies in the frameworks of MOND and Newtonian dynamics without invoking any dark matter. The prediction for the line-of-sight velocity dispersions from MOND of 53 selected dwarf galaxies is compared with their measured values. For appropriate mass-to-light ratios in the range 1 to 5 for each individual dwarf galaxy, our results for the line-of-sight velocity dispersions predicted by MOND are more compatible with observations than those predicted by Newtonian dynamics.

Ordinary Dark Matter versus Mysterious Dark Matter in Galactic Rotation

NASA Astrophysics Data System (ADS)

Gallo, C. F.; Feng, James

2008-04-01

To theoretically describe the measured rotational velocity curves of spiral galaxies, there are two different approaches and conclusions. (1) ORDINARY DARK MATTER. We assume Newtonian gravity/dynamics and successfully find (via computer) mass distributions in bulge/disk configurations that duplicate the measured rotational velocities. There is ordinary dark matter within the galactic disk towards the cooler periphery which has lower emissivity/opacity. There are no mysteries in this scenario based on verified physics. (2) MYSTERIOUS DARK MATTER. Others INaccurately assume the galactic mass distributions follow the measured light distributions, and then the measured rotational velocity curves are NOT duplicated. To alleviate this discrepancy, speculations are invoked re ``Massive Peripheral Spherical Halos of Mysterious Dark Matter.'' But NO matter has been detected in this UNtenable Halo configuration. Many UNverified ``Mysteries'' are invoked as necessary and convenient. CONCLUSION. The first approach utilizing Newtonian gravity/dynamics and searching for the ordinary mass distributions within the galactic disk simulates reality and agrees with data.

OT2_wlanger_7: Dynamics of Giant Magnetic Gas Loops and Their Connection to the CMZ in the Galactic Center

NASA Astrophysics Data System (ADS)

Langer, W.

2011-09-01

Understanding the mass transfer and dynamics among the Galactic Center, the disk, and the halo of the Milky Way is fundamental to the study of the evolution of galaxies and star formation. Recently several giant loops of molecular gas (GML) have been found in the Galactic Center from CO maps, which are likely the result of the magnetic Parker instability. There is new evidence of a possible connection between these loops and the Central Molecular Zone as shown in a sparse [CII] sampling made by the Herschel Key Project GOT C+. Here we propose to map various features of the GMLs and the interface region in [CII] with HIFI. We will also map the foot points of the loop, which are thought to be highly shocked regions, in the ortho 110-101 line of water, which is a known shock tracer. With this data we will characterize different ISM components and their flow among these Galactic Center features.

Alternative Gravity Rotation Curves for the LITTLE THINGS Survey

NASA Astrophysics Data System (ADS)

O’Brien, James G.; Chiarelli, Thomas L.; Dentico, Jeremy; Stulge, Modestas; Stefanski, Brian; Moss, Robert; Chaykov, Spasen

2018-01-01

Galactic rotation curves have proven to be the testing ground for dark matter bounds in spiral galaxies of all morphologies. Dwarf galaxies serve as an increasingly interesting case of rotation curve dynamics due to their typically rising rotation curve as opposed to the flattening curve of large spirals. Dwarf galaxies usually vary in galactic structure and mostly terminate at small radial distances. This, coupled with the fact that Cold Dark Matter theories struggle with the universality of galactic rotation curves, allow for exclusive features of alternative gravitational models to be analyzed. Recently, The H I Nearby Galactic Survey (THINGS) has been extended to include a sample of 25 dwarf galaxies now known as the LITTLE THINGS Survey. Here, we show an application of alternative gravitational models to the LITTLE THINGS survey, specifically focusing on conformal gravity (CG) and Modified Newtonian Dynamics (MOND). In this work, we provide an analysis and discussion of the rotation curve predictions of each theory to the sample. Furthermore, we show how these two alternative gravitational models account for the recently observed universal trends in centripetal accelerations in spiral galaxies. This work highlights the similarities and differences of the predictions of the two theories in dwarf galaxies. The sample is not large or diverse enough to strongly favor a single theory, but we posit that both CG and MOND can provide an accurate description of the galactic dynamics in the LITTLE THINGS sample without the need for dark matter.

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) and its successor, APOGEE-2

NASA Astrophysics Data System (ADS)

Majewski, S. R.; APOGEE Team; APOGEE-2 Team

2016-09-01

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) of Sloan Digital Sky Survey III (SDSS-III) has produced a large catalog of high resolution ({R = 22 500}), high quality (S/N > 100), infrared (H-band) spectra for stars throughout all stellar populations of the Milky Way, including in regions veiled by significant dust opacity. APOGEE's half million spectra collected on > 163 000 unique stars, with time series information via repeat visits to each star, are being applied to numerous problems in stellar populations, Galactic astronomy, and stellar astrophysics. From among the early results of the APOGEE project - which span from measurements of Galactic dynamics, to multi-element chemical maps of the disk and bulge, new views of the interstellar medium, explorations of stellar companions, the chemistry of star clusters, and the discovery of rare stellar species - I highlight a few results that demonstrate APOGEE's unique ability to sample and characterize the Galactic disk and bulge. Plans are now under way for an even more ambitious successor to APOGEE: the six-year, dual-hemisphere APOGEE-2 project. Both phases of APOGEE feature a strong focus on targets having asteroseismological measurements from either Kepler or {CoRoT}, from which it is possible to derive relatively precise stellar ages. The combined APOGEE and APOGEE-2 databases of stellar chemistry, dynamics and ages constitute an unusually comprehensive, systematic and homogeneous resource for constraining models of Galactic evolution.

Theoretical Astrophysics - Volume 3, Galaxies and Cosmology

NASA Astrophysics Data System (ADS)

Padmanabhan, T.

2002-12-01

1. Overview: galaxies and cosmology; 2. Galactic structure and dynamics; 3. Friedmann model of the universe; 4. Thermal history of the universe; 5. Structure formation; 6. Cosmic microwave background radiation; 7. Formation of baryonic structures; 8. Active galactic nuclei; 9. Intergalactic medium and absorption systems; 10. Cosmological observations.

Tully-Fisher relation, galactic rotation curves and dissipative mirror dark matter

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

Foot, R., E-mail: rfoot@unimelb.edu.au

2014-12-01

If dark matter is dissipative then the distribution of dark matter within galactic halos can be governed by dissipation, heating and hydrostatic equilibrium. Previous work has shown that a specific model, in the framework of mirror dark matter, can explain several empirical galactic scaling relations. It is shown here that this dynamical halo model implies a quasi-isothermal dark matter density, ρ(r) ≅ ρ{sub 0}r{sub 0}{sup 2}/(r{sup 2}+r{sub 0}{sup 2}), where the core radius, r{sub 0}, scales with disk scale length, r{sub D}, via r{sub 0}/kpc ≈ 1.4(r{sub D}/kpc). Additionally, the product ρ{sub 0}r{sub 0} is roughly constant, i.e. independent ofmore » galaxy size (the constant is set by the parameters of the model). The derived dark matter density profile implies that the galactic rotation velocity satisfies the Tully-Fisher relation, L{sub B}∝v{sup 3}{sub max}, where v{sub max} is the maximal rotational velocity. Examples of rotation curves resulting from this dynamics are given.« less

Galactic civilizations - Population dynamics and interstellar diffusion

NASA Technical Reports Server (NTRS)

Newman, W. I.; Sagan, C.

1981-01-01

A model is developed of the interstellar diffusion of galactic civilizations which takes into account the population dynamics of such civilizations. The problem is formulated in terms of potential theory, with a family of nonlinear partial differential and difference equations specifying population growth and diffusion for an organism with advantageous genes that undergoes random dispersal while increasing in population locally, and a population at zero population growth. In the case of nonlinear diffusion with growth and saturation, it is found that the colonization wavefront from the nearest independently arisen galactic civilization can have reached the earth only if its lifetime exceeds 2.6 million years, or 20 million years if discretization can be neglected. For zero population growth, the corresponding lifetime is 13 billion years. It is concluded that the earth is uncolonized not because interstellar spacefaring civilizations are rare, but because there are too many worlds to be colonized in the plausible colonization lifetime of nearby civilizations, and that there exist no very old galactic civilizations with a consistent policy of the conquest of inhabited worlds.

ARE ULTRA-LONG GAMMA-RAY BURSTS CAUSED BY BLUE SUPERGIANT COLLAPSARS, NEWBORN MAGNETARS, OR WHITE DWARF TIDAL DISRUPTION EVENTS?

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

Ioka, Kunihito; Hotokezaka, Kenta; Piran, Tsvi, E-mail: kunihito.ioka@yukawa.kyoto-u.ac.jp

Ultra-long gamma-ray bursts (ulGRBs) are a new population of GRBs with extreme durations of ∼10{sup 4} s. Leading candidates for their origin are blue supergiant collapsars, magnetars, and white dwarf tidal disruption events (WD-TDEs) caused by massive black holes (BHs). Recent observations of supernova-like (SN-like) bumps associated with ulGRBs challenged both the WD-TDE and the blue supergiant models because of the detection of SNe and the absence of hydrogen lines, respectively. We propose that WD-TDEs can accommodate the observed SN-like bumps if the fallback WD matter releases energy into the unbound WD ejecta. The observed ejecta energy, luminosity, and velocitymore » are explained by the gravitational energy, Eddington luminosity, and escape velocity of the formed accretion disk, respectively. We also show that the observed X-rays can ionize the ejecta, eliminating lines. The SN-like light curves (SN 2011kl) for the ulGRB 111209A are consistent with all three models, although a magnetar model is unnatural because the spin-down time required to power the SN-like bump is a hundred times longer than the GRB. Our results imply that TDEs are a possible energy source for SN-like events in general and for ulGRBs in particular.« less

ON THE ORIGIN OF THE HIGHEST REDSHIFT GAMMA-RAY BURSTS

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

Belczynski, Krzysztof; Holz, Daniel E.; Fryer, Chris L.

2010-01-01

GRB 080913 and GRB 090423 are the most distant gamma-ray bursts (GRBs) known to date, with spectroscopically determined redshifts of z = 6.7 and z = 8.1, respectively. The detection of bursts at this early epoch of the universe significantly constrains the nature of GRBs and their progenitors. We perform population synthesis studies of the formation and evolution of early stars, and calculate the resulting formation rates of short- and long-duration GRBs at high redshift. The peak of the GRB rate from Population II stars occurs at z approx 7 for a model with efficient/fast mixing of metals, while itmore » is found at z approx 3 for an inefficient/slow metallicity evolution model. We show that in the redshift range 6 approx< z approx< 10, essentially all GRBs originate from Population II stars, regardless of the metallicity evolution model. These stars (having small, but non-zero metallicity) are the most likely progenitors for both long GRBs (collapsars) and short GRBs (neutron star-neutron star or blackhole-neutron star mergers) at this epoch. Although the predicted intrinsic rates of long and short GRBs are similar at these high redshifts, observational selection effects lead to higher (a factor of approx10) observed rates for long GRBs. We conclude that the two recently observed high-z GRB events are most likely long GRBs originating from Population II collapsars.« less

Galactic gamma-ray observations and galactic structure

NASA Technical Reports Server (NTRS)

Stecker, F. W.

1975-01-01

Recent observations of gamma-rays originating in the galactic disk together with radio observations, support an emerging picture of the overall structure of our galaxy with higher interstellar gas densities and star formation rates in a region which corresponds to that of the inner arms. The emerging picture is one where molecular clouds make up the dominant constituent of the interstellar gas in the inner galaxy and play a key role in accounting for the gamma-rays and phenomena associated with the production of young stars and other population 1 objects. In this picture, cosmic rays are associated with supernovae and are primarily of galactic origin. These newly observed phenomena can be understood as consequences of the density wave theories of spiral structure. Based on these new developments, the suggestion is made that a new galactic population class, Population O, be added to the standard Populations 1 and 2 in order to recognize important differences in dynamics and distribution between diffuse galactic H1 and interstellar molecular clouds.

Thousands of Stellar SiO masers in the Galactic center: The Bulge Asymmetries and Dynamic Evolution (BAaDE) survey

NASA Astrophysics Data System (ADS)

Sjouwerman, Loránt O.; Pihlström, Ylva M.; Rich, R. Michael; Morris, Mark R.; Claussen, Mark J.

2017-01-01

A radio survey of red giant SiO sources in the inner Galaxy and bulge is not hindered by extinction. Accurate stellar velocities (<1 km/s) are obtained with minimal observing time (<1 min) per source. Detecting over 20,000 SiO maser sources yields data comparable to optical surveys with the additional strength of a much more thorough coverage of the highly obscured inner Galaxy. Modeling of such a large sample would reveal dynamical structures and minority populations; the velocity structure can be compared to kinematic structures seen in molecular gas, complex orbit structure in the bar, or stellar streams resulting from recently infallen systems. Our Bulge Asymmetries and Dynamic Evolution (BAaDE) survey yields bright SiO masers suitable for follow-up Galactic orbit and parallax determination using VLBI. Here we outline our early VLA observations at 43 GHz in the northern bulge and Galactic plane (0

Necessity of dark matter in modified Newtonian dynamics within galactic scales.

PubMed

Ferreras, Ignacio; Sakellariadou, Mairi; Yusaf, Muhammad Furqaan

2008-01-25

To test modified Newtonian dynamics (MOND) on galactic scales, we study six strong gravitational lensing early-type galaxies from the CASTLES sample. Comparing the total mass (from lensing) with the stellar mass content (from a comparison of photometry and stellar population synthesis), we conclude that strong gravitational lensing on galactic scales requires a significant amount of dark matter, even within MOND. On such scales a 2 eV neutrino cannot explain the excess of matter in contrast with recent claims to explain the lensing data of the bullet cluster. The presence of dark matter is detected in regions with a higher acceleration than the characteristic MOND scale of approximately 10(-10) m/s(2). This is a serious challenge to MOND unless lensing is qualitatively different [possibly to be developed within a covariant, such as Tensor-Vector-Scalar (TeVeS), theory].

Masses, luminosities and dynamics of galactic molecular clouds

NASA Technical Reports Server (NTRS)

Solomon, P. M.; Rivolo, A. R.; Mooney, T. J.; Barrett, J. W.; Sage, L. J.

1987-01-01

Star formation in galaxies takes place in molecular clouds and the Milky Way is the only galaxy in which it is possible to resolve and study the physical properties and star formation activity of individual clouds. The masses, luminosities, dynamics, and distribution of molecular clouds, primarily giant molecular clouds in the Milky Way are described and analyzed. The observational data sets are the Massachusetts-Stony Brook CO Galactic Plane Survey and the IRAS far IR images. The molecular mass and infrared luminosities of glactic clouds are then compared with the molecular mass and infrared luminosities of external galaxies.

Division H Commission 33: Structure & Dynamics of the Galactic System

NASA Astrophysics Data System (ADS)

Nordström, Birgitta; Bland-Hawthorn, Joss; Wyse, Rosemary; Athanassoula, Lia; Feltzing, Sofia; Jog, Chanda; Lockman, Jay; Minniti, Dante; Robin, Annie

2016-04-01

Research on the structure and dynamics of the Galactic System covers a large field of research, from formation scenarios to long-term evolution and secular processes. Today we speak of near-field cosmology where the oldest parts of the Galaxy are used to probe back to early times, e.g. studying the chemical signatures of the oldest star clusters and dwarf galaxies to learn about the byproducts of the first stars. Some of the most detailed work relates to the structure of the dark matter and baryons in order to compare with expectation from N-body models. Secular processes have been identified (e.g. stellar migration) where material within the Galaxy is being reorganized by dynamical resonances and feedback processes.

Resonance Trapping in the Galactic Disc and Halo and its Relation with Moving Groups

NASA Astrophysics Data System (ADS)

Pichardo, Barbara; Moreno, Edmundo; william, schuster B.

2015-08-01

With the use of a detailed Milky Way nonaxisymmetric potential, observationally and dynamically constrained, the eects of the bar and the spiral arms in the Galaxy are studied in the disc and in the stellar halo. Especially the trapping of stars in the disk and Galactic halo by resonances on the Galactic plane created by the Galactic bar has been analysed in detail. To this purpose, a new method is presented to delineate the trapping regions using empirical diagrams of some orbital properties obtained in the Galactic potential. In these diagrams we plot in the inertial Galactic frame a characteristic orbital energy versus a characteristic orbital angular momentum, or versus the orbital Jacobi constant in the reference frame of the bar, when this is the only nonaxisymmetric component in the Galactic potential. With these diagrams some trapping regions are obtained in the disc and halo using a sample of disc stars and halo stars in the solar neighborhood. We compute several families of periodic orbits on the Galactic plane, some associated with this resonant trapping. In particular, we nd that the trapping eect of these resonances on the Galactic plane can extend some kpc from this plane, trapping stars in the Galactic halo. The purpose of our analysis is to investigate if the trapping regions contain some known moving groups in our Galaxy. We have applied our method to the Kapteyn group, a moving group in the halo, and we have found that this group appears not to be associated with a particular resonance on the Galactic plane.

The Formation of Galactic Bulges

NASA Astrophysics Data System (ADS)

Carollo, C. Marcella; Ferguson, Henry C.; Wyse, Rosemary F. G.

2000-03-01

Part I. Introduction: What are galactic bulges?; Part II. The Epoch of Bulge Formation: Origin of bulges; Deep sub-mm surveys: High-z ULIRGs and the formation of spheroids; Ages and metallicities for stars in the galactic bulge; Integrated stellar populations of bulges: First results; HST-NICMOS observations of galactic bulges: Ages and dust; Inside-out bulge formation and the origin of the Hubble sequence; Part III. The Timescales of Bulge Formation: Constraints on the bulge formation timescale from stellar populations; Bulge building with mergers and winds; Role of winds, starbursts, and activity in bulge formation; Dynamical timescales of bulge formation; Part IV. Physical Processes in Bulge Formation: the role of bars for secular bulge formation; Bars and boxy/peanut-shaped bulges: an observational point of view; Boxy- and peanut-shaped bulges; A new class of bulges; The role of secondary bars in bulge formation; Radial transport of molecular gas to the nuclei of spiral galaxies; Dynamical evolution of bulge shapes; Two-component stellar systems: Phase-space constraints; Central NGC 2146 - a firehose-type bending instability?; Bulge formation: the role of the multi-phase ISM; Global evolution of a self-gravitating multi-phase ISM in the central kpc region of galaxies; Part V. Bulge Phenomenology: Bulge-disk decomposition of spiral galaxies in the near-infrared; The triaxial bulge of NGC 1371; The bulge-disk orthogonal decoupling in galaxies: NGC 4698 and NGC 4672; The kinematics and the origin of the ionized gas in NGC 4036; Optically thin thermal plasma in the galactic bulge; X-ray properties of bulges; The host galaxies of radio-loud AGN; The centers of radio-loud early-type galaxies with HST; Central UV spikes in two galactic spheroids; Conference summary: where do we stand?

The early dynamical evolution of star clusters near the Galactic Centre

NASA Astrophysics Data System (ADS)

Park, So-Myoung; Goodwin, Simon P.; Kim, Sungsoo S.

2018-07-01

We examine the dynamical evolution of both Plummer sphere and substructured (fractal) star-forming regions in Galactic Centre (GC) strong tidal fields to see what initial conditions could give rise to an Arches-like massive star cluster by ˜2 Myr. We find that any initial distribution has to be contained within its initial tidal radius to survive, which sets a lower limit of the initial density of the Arches of ˜600 M⊙ pc-3 if the Arches is at 30 pc from the GC, or ˜200 M⊙ pc-3 if the Arches is at 100 pc from the GC. Plummer spheres that survive change little other than to dynamically mass segregate, but initially fractal distributions rapidly erase substructure, dynamically mass segregate and by 2 Myr look extremely similar to initial Plummer spheres, therefore it is almost impossible to determine the initial conditions of clusters in strong tidal fields.

The early dynamical evolution of star clusters near the Galactic Centre

NASA Astrophysics Data System (ADS)

Park, So-Myoung; Goodwin, Simon P.; Kim, Sungsoo S.

2018-04-01

We examine the dynamical evolution of both Plummer sphere and substructured (fractal) star forming regions in Galactic Centre (GC) strong tidal fields to see what initial conditions could give rise to an Arches-like massive star cluster by ˜2 Myr. We find that any initial distribution has to be contained within its initial tidal radius to survive, which sets a lower limit of the initial density of the Arches of ˜ 600 M⊙ pc-3 if the Arches is at 30 pc from the GC, or ˜ 200 M⊙ pc-3 if the Arches is at 100 pc from the GC. Plummer spheres that survive change little other than to dynamically mass segregate, but initially fractal distributions rapidly erase substructure, dynamically mass segregate and by 2 Myr look extremely similar to initial Plummer spheres, therefore it is almost impossible to determine the initial conditions of clusters in strong tidal fields.

Parameters of Six Selected Galactic Potential Models

NASA Astrophysics Data System (ADS)

Bajkova, Anisa; Bobylev, Vadim

2017-11-01

This paper is devoted to the refinement of the parameters of the six three-component (bulge, disk, halo) axisymmetric Galactic gravitational potential models on the basis of modern data on circular velocities of Galactic objects located at distances up to 200 kpc from the Galactic center. In all models the bulge and disk are described by the Miyamoto-Nagai expressions. To describe the halo, the models of Allen-Santillán (I), Wilkinson-Evans (II), Navarro- Frenk-White (III), Binney (IV), Plummer (V), and Hernquist (VI) are used. The sought-for parameters of potential models are determined by fitting the model rotation curves to the measured velocities, taking into account restrictions on the local dynamical matter density p⊙ - 0.1M⊙ pc-3 and the vertical force |Kz=1.1|/2πG = 77M⊙ pc-2. A comparative analysis of the refined potential models is made and for each of the models the estimates of a number of the Galactic characteristics are presented.

Fast dynamos, cosmic rays, and the Galactic magnetic field

NASA Technical Reports Server (NTRS)

Parker, E. N.

1992-01-01

It is suggested here that the dynamo believed to be responsible for the magnetic field of the Galaxy is a fast dynamo due to the dynamical reconnection of the azimuthal field of the Galaxy as the field is deformed by the instability of the gaseous disk and the rapid inflation of magnetic lobes by the cosmic-ray gas to form the Galactic halo. The reconnection of adjacent lobes carries out both the alpha effect and field dissipation essential for the existence of the Galactic alpha-omega dynamo. The azimuthal field is generated primarily in the gaseous disk, while the alpha effect is carried out in the halo.

The fueling of active galaxies

NASA Technical Reports Server (NTRS)

Hernquist, Lars

1991-01-01

Collisions of galaxies are often invoked to explain violent phenomena in the universe. The dynamics of interacting galaxies is intrinsically three-dimensional and involves both gas and stellar dynamics. In general, a computational approach is needed to model galactic collisions. Galaxy encounters are studied using a hybrid N-body/hydrodynamics code, capable of integrating systems of stars, gas, and dark matter in a fully self-consistent manner. These experiments demonstrate that gravitational coupling between gas and stars in galactic interactions can drive most of the gas throughout a galaxy into the nucleus of a merger remnant. The high densities in these gas concentrations are likely to result in strong bursts of star formation. Hence, this process may explain the nuclear starbursts in some systems of interacting galaxies. Further collapse of these gas concentrations can trigger even more intense activity if some gas is eventually accreted by a supermassive black hole. Such an evolutionary sequence may account for some quasars and active galactic nuclei.

The effect of the solar motion on the flux of long-period comets

NASA Astrophysics Data System (ADS)

Gardner, E.; Nurmi, P.; Flynn, C.; Mikkola, S.

2011-02-01

The long-term dynamics of Oort cloud comets are studied under the influence of both the radial and the vertical components of the Galactic tidal field. Sporadic dynamical perturbation processes, such as passing stars, are ignored since we aim to study the influence of just the axisymmetric Galactic tidal field on the cometary motion and how it changes in time. We use a model of the Galaxy with a disc, bulge and dark halo, and a local disc density and disc scalelength constrained to fit the best available observational constraints. By integrating a few million of cometary orbits over 1 Gyr, we calculate the time variable flux of Oort cloud comets that enter the inner Solar system for the cases of a constant Galactic tidal field and a realistically varying tidal field, which is a function of the Sun's orbit. The applied method calculates the evolution of the comets by using first-order averaged mean elements. We find that the periodicity in the cometary flux is complicated and quasi-periodic. The amplitude of the variations in the flux is of the order of 30 per cent. The radial motion of the Sun is the chief cause of this behaviour, and should be taken into account when the Galactic influence on the Oort cloud comets is studied.

Road to MOND: A novel perspective

NASA Astrophysics Data System (ADS)

Milgrom, Mordehai

2015-08-01

Accepting that galactic mass discrepancies are due to modified dynamics, I show why it is specifically the Modified Newtonian dynamics (MOND) paradigm that is pointed to cogently. MOND is thus discussed here as a special case of a larger class of modified dynamics theories whereby galactic systems with large mass discrepancies are described by scale-invariant dynamics. This is a novel presentation that uses more recent, after-the-fact insights and data (largely predicted beforehand by MOND). Starting from a purist set of tenets, I follow the path that leads specifically to the MOND basic tenets. The main signposts are as follows: (i) Space-time scale invariance underlies the dynamics of systems with large mass discrepancies. (ii) In these dynamics, G must be replaced by a single "scale-invariant" gravitational constant, Q0 (in MOND, Q0=A0=G a0, where a0 is MOND's acceleration constant). (iii) Universality of free fall points to the constant q0≡Q0/G as the boundary between the G -controlled, standard dynamics, and the Q0-controlled, scale-invariant dynamics (in MOND, q0=a0). (iv) Data clinch the case for q0 being an acceleration (MOND).

Galactic and stellar dynamics in the era of high resolution surveys

NASA Astrophysics Data System (ADS)

Boily, C. M.; Combes, F.; Hensler, G.; Spurzem, R.

2008-12-01

The conference Galactic and Stellar Dynamics in the Era of High Resolution Surveys took place at the European Doctoral College (EDC) in Strasbourg from 2008 March 16 to 20. The event was co-sponsored by the Astronomische Gesellschaft (AG) and the Société Fran\\c{c}aise d'Astronomie et d'Astrophysique (SF2A), a joint venture aiming to set a new trend of regular thematic meetings in specific areas of research. This special issue of the Astronomische Nachrichten is a compilation of the papers presented at the meeting. We give an outline of the meeting together with a short history of the relations of the two societies.

Finding evolved stars in the inner Galactic disk with Gaia

NASA Astrophysics Data System (ADS)

Quiroga-Nuñez, L. H.; van Langevelde, H. J.; Pihlström, Y. M.; Sjouwerman, L. O.; Brown, A. G. A.

2018-04-01

The Bulge Asymmetries and Dynamical Evolution (BAaDE) survey will provide positions and line-of-sight velocities of ~20, 000 evolved, maser bearing stars in the Galactic plane. Although this Galactic region is affected by optical extinction, BAaDE targets may have Gaia cross-matches, eventually providing additional stellar information. In an initial attempt to cross-match BAaDE targets with Gaia, we have found more than 5,000 candidates. Of these, we may expect half to show SiO emission, which will allow us to obtain velocity information. The cross-match is being refined to avoid false positives using different criteria based on distance analysis, flux variability, and color assessment in the mid- and near-IR. Once the cross-matches can be confirmed, we will have a unique sample to characterize the stellar population of evolved stars in the Galactic bulge, which can be considered fossils of the Milky Way formation.

Rates of collapse and evaporation of globular clusters

NASA Technical Reports Server (NTRS)

Hut, Piet; Djorgovski, S.

1992-01-01

Observational estimates of the dynamical relaxation times of Galactic globular clusters are used here to estimate the present rate at which core collapse and evaporation are occurring in them. A core collapse rate of 2 +/- 1 per Gyr is found, which for a Galactic age of about 12 Gyr agrees well with the fact that 27 clusters have surface brightness profiles with the morphology expected for the postcollapse phase. A destruction and evaporation rate of 5 +/- 3 per Gyr is found, suggesting that a significant fraction of the Galaxy's original complement of globular clusters have perished through the combined effects of mechanisms such as relaxation-driven evaporation and shocking due to interaction with the Galactic disk and bulge.

The Planar Satellite Distributions around Andromeda, the Milky Way and Other Galaxies, and Their Implications for Fundamental Physics

NASA Astrophysics Data System (ADS)

Kroupa, P.

2014-05-01

The existence of dark matter particles is a key hypothesis in present-day cosmology and galactic dynamics. The validity of this hypothesis is challenged significantly by two independent arguments. 1) The dual dwarf galaxy theorem must be true in any realistic cosmological model. But it is found to be falsified when the dark-matter-based model is applied to the observational data. A consistency check of this conclusion comes from the observed significantly disk-like distributions of satellite populations which orbit in the same direction around their hosting galaxy and which cannot be derived from dark-matter models. 2) The action of dynamical friction due to expansive and massive dark matter halos must be evident in the galaxy population. The evidence however for dynamical friction is void or meagre at best. The M81 group fo galaxies already appears to rule out the existence of dynamical friction through dark matter halos, and the Milky Way satellite galaxies have been shown to challenge dark-matter-induced dynamical friction. The implication of this deduction for fundamental physics would be that exotic dark matter particles do not exist and that consequently gravitational physics on the scales of galaxies and beyond ought to be non-Newtonian/Einsteinian. An analysis of the kinematical data in galaxies shows them to be described excellently by scale-invariant dynamics, as discovered by Milgrom. This leads to a natural emergence of laws that galaxies are observed to obey. Such success has not been forthcoming in the dark-matter-based models. A consequence of this novel understanding of galactic astrophysics is that most dwarf satellite galaxies are formed as tidal dwarf galaxies in galaxy-galaxy encounters and that galactic mergers are rare.

Hibernating black holes revealed by photometric mass functions

NASA Astrophysics Data System (ADS)

Casares, Jorge

2018-02-01

We present a novel strategy to uncover the Galactic population of quiescent black holes (BHs). This is based on a new concept, the photometric mass function (PMF), which opens up the possibility of an efficient identification of dynamical BHs in large fields-of-view. This exploits the width of the disc H α emission line, combined with orbital period information. We here show that H α widths can be recovered using a combination of customized H α filters. By setting a width cut-off at 2200 km s-1 we are able to cleanly remove other Galactic populations of H α emitters, including ∼99.9 per cent of cataclysmic variables (CVs). Only short-period (Porb <2.1 h) eclipsing CVs and AGNs will contaminate the sample but these can be easily flagged through photometric variability and, in the latter case, also mid-IR colours. We also describe the strategy of a deep (r = 22) Galactic plane survey based on the concept of PMFs: HAWKs, the HAlpha-Width Kilo-deg Survey. We estimate that ∼800 deg2 are required to unveil ∼50 new dynamical BHs, a three-fold improvement over the known population. For comparison, a century would be needed to produce an enlarged sample of 50 dynamical BHs from X-ray transients at the current discovery rate.

Galactic cannibalism. IV. The evidence-correlations between dynamical time scales and Bautz-Morgan type

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

McGlynn, T.A.; Ostriker, J.P.

1980-11-01

If the luminosity of supergiant cD galaxies in particular, and the Bautz-Morgan sequence of galaxy types in general, is produced by dynamical evolutionary processes, then one expects to find a correlation between dynamical times and ..delta..M/sub 12/, the magnitude difference between first and second brightest cluster members.

Storage Rings in the Sky: Gamma Ray Bursts and Galactic Gravitational Collapse Stored Energy

NASA Astrophysics Data System (ADS)

Greyber, H. D.

2004-05-01

The recent discovery of almost 100% polarization of the prompt gamma ray emission from GRB021206, (1), confirms my 44 year old ``Strong" Magnetic Field" model (SMF) for galactic dynamics. In SMF, Storage Ring particles were accelerated long ago during the original gravitational collapse of the pregalactic/prequasar plasma cloud that is permeated by an almost uniform primordial magnetic field (2,3) The enormous, intense, slender, relativistic, stable, completely coherent Storage Ring stores a very small fraction of the huge galactic gravitational collapse energy in an almost radiationless state, unless disturbed. The concept of an Astrophysical Storage Ring was introduced by me in l961. At first it was to explain galactic structure, but soon it proved useful to explain active galactic nuclei (AGN) and the dynamics of quasar/AGN jets. AGN and galactic morphology, energetics and dynamics vary as the ratio of magnetic energy to rotational energy in the particular object. Gamma ray bursts (GRB) are due simply to a ``rock". i.e. a white dwarf, ordinary star, neutron sstar, asteroid, planet, etc. falling rapidly through the Storage Ring and being almost instantly vaporized into a hot plasma fireball, causing an electromagnetic shower (2) Then the fireball speeds into the huge organized magnetic field surrounding the current ring, thus generating very highly polarized prompt gamma ray emission (as seen in GRB021206) from the synchrotron radiation process. The timing fits the GRB observations nicely. For instance, a ``rock" racing at 1000 kilometers per second across a 20,000 km. path in the beam would produce a twenty second burst. Other times, a target might track across a short chord for a short burst. Space missions have shown that often typical currents in space plasmas are made up of slender filaments. Thus the puzzling less than one millisecond spikes observed in some GRB are simply describing the structure of that particular ring current at that particular time. 1. W. Coburn and S.E. Boggs, Nature, 423, 415, (2003) 2. H. D. Greyber in a book, After the Dark Ages: When Galaxies Were Young, eds. S.S. Holt and E. P. Smith, AIP Conference Proceedings 470, 388-396. (1998) 3. H. D. Greyber in a Space Telescope Science Institute Report: Poster Papers from their 2001 Spring Symposium, ``The Dark Universe: Matter, Energy and Gravity," ed. Mario Livio, published March 2003, (34-39)

The Fossil Nuclear Outflow in the Central 30 pc of the Galactic Center

NASA Astrophysics Data System (ADS)

Hsieh, Pei-Ying; Ho, Paul T. P.; Hwang, Chorng-Yuan; Shimajiri, Yoshito; Matsushita, Satoki; Koch, Patrick M.; Iono, Daisuke

2016-11-01

We report a new 1 pc (30″) resolution CS(J=2-1) line map of the central 30 pc of the Galactic center (GC), made with the Nobeyama 45 m telescope. We revisit our previous study of an extraplanar feature called the polar arc (PA), which is a molecular cloud located above SgrA*, with a velocity gradient perpendicular to the galactic plane. We find that the PA can be traced back to the galactic disk. This provides clues to the launching point of the PA, roughly 6 × 106 years ago. Implications of the dynamical timescale of the PA might be related to the Galactic center lobe at parsec scale. Our results suggest that, in the central 30 pc of the GC, the feedback from past explosions could alter the orbital path of molecular gas down to the central tenth of a parsec. In the follow-up work of our new CS(J=2-1) map, we also find that, near systemic velocity, the molecular gas shows an extraplanar hourglass-shaped feature (HG-feature) with a size of ˜13 pc. The latitude-velocity diagrams show that the eastern edge of the HG-feature is associated with an expanding bubble B1, ˜7 pc away from SgrA*. The dynamical timescale of this bubble is ˜3 × 105 years. This bubble is interacting with the 50 km s-1 cloud. Part of the molecular gas from the 50 km s-1 cloud was swept away by the bubble to b=-0\\buildrel{\\circ}\\over{.} 2. The western edge of the HG-feature seems to be molecular gas entrained from the 20 km s-1 cloud toward the north of the galactic disk. Our results suggest a fossil explosion in the central 30 pc of the GC, a few 105 years ago.

Taking Measure of the Milky Way

NASA Technical Reports Server (NTRS)

Majewski, Steven R.; Bahcall, John N.; Geisler, Douglas; Gieren, Wolfgang; Grebel, Eva; Grillmair, Carl; Irwin, Michael; Johnston, Kathryn V.; Patterson, Richard J.; Reid, Neill I.

2004-01-01

We intend to use SIM to make definitive measurements of fundamental structural and dynamical parameters of the Milky Way. The important niche in dynamical parameter space afforded by SIM can be exploited to resolve, with unprecedented precision, a number of classical problems of Galactic astronomy. In addition, we have developed new tests of the Galactic mass distribution specifically designed for data with the special properties of SIM products. Our proposed suite of experiments will utilize the SIM Astrometric Grid as well as complementary observations of star clusters and other strategically-selected, distant "test particles" for a definitive characterization of the major components (bulge, disk, halo, satellite system) of the Milky Way. Specifically, our goals will be: 1) The determination of two fundamental parameters that play a central role in virtually every problem in Galactic astronomy, namely (a) the solar distance to the center of the Milky Way, R(sub 0); (b) the solar angular velocity around the Galactic: center, omega(sub 0). 2) The measurement of fundamental dynamical properties of the Milky Way, among them (a) the pattern speed of the central bar (b) the rotation field and velocity-dispersion tensor in the disk (c) the kinematics (mean rotational velocity and velocity dispersion tensor) of the halo as a function of position 3. The definition of the mass distribution of the Galaxy, which is dominated by the presence of dark matter. We intend to measure (a) the relative contribution of the disk and halo to the gravitational potential (b) the local volume and surface mass density of the disk (c) the shape, mass and extent of the dark halo of the Milky Way out to 250 kpc.

Some Dynamical Effects of the Cosmological Constant

NASA Astrophysics Data System (ADS)

Axenides, M.; Floratos, E. G.; Perivolaropoulos, L.

Newton's law gets modified in the presence of a cosmological constant by a small repulsive term (antigravity) that is proportional to the distance. Assuming a value of the cosmological constant consistent with the recent SnIa data (Λ~=10-52 m-2), we investigate the significance of this term on various astrophysical scales. We find that on galactic scales or smaller (less than a few tens of kpc), the dynamical effects of the vacuum energy are negligible by several orders of magnitude. On scales of 1 Mpc or larger however we find that the vacuum energy can significantly affect the dynamics. For example we show that the velocity data in the local group of galaxies correspond to galactic masses increased by 35% in the presence of vacuum energy. The effect is even more important on larger low density systems like clusters of galaxies or superclusters.

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

Bettoni, Dario; Nusser, Adi; Blas, Diego

We develop the framework for testing Lorentz invariance in the dark matter sector using galactic dynamics. We consider a Lorentz violating (LV) vector field acting on the dark matter component of a satellite galaxy orbiting in a host halo. We introduce a numerical model for the dynamics of satellites in a galactic halo and for a galaxy in a rich cluster to explore observational consequences of such an LV field. The orbital motion of a satellite excites a time dependent LV force which greatly affects its internal dynamics. Our analysis points out key observational signatures which serve as probes ofmore » LV forces. These include modifications to the line of sight velocity dispersion, mass profiles and shapes of satellites. With future data and a more detailed modeling these signatures can be exploited to constrain a new region of the parameter space describing the LV in the dark matter sector.« less

The Barred Inner Region of the Milky Way

NASA Astrophysics Data System (ADS)

Gerhard, Ortwin

2018-04-01

The central few kpc of our Galaxy, the Milky Way, are dominated by thegravitational field of the Galactic bar. This talk describes dynamicalmodels of the bar and box/peanut bulge, and what we have learnt fromthem about the dynamical structure, the distribution of stellar anddark matter mass, and the spatial and orbital distributions of theGalactic stellar populations. Finally I discuss models for theformation of galaxies like ours, and how Milky Way studies enlightengalaxy formation theories in general.

The ACS Survey of Galactic Globular Clusters. VIII. Effects of Environment on Globular Cluster Global Mass Functions

NASA Astrophysics Data System (ADS)

Paust, Nathaniel E. Q.; Reid, I. Neill; Piotto, Giampaolo; Aparicio, Antonio; Anderson, Jay; Sarajedini, Ata; Bedin, Luigi R.; Chaboyer, Brian; Dotter, Aaron; Hempel, Maren; Majewski, Steven; Marín-Franch, A.; Milone, Antonino; Rosenberg, Alfred; Siegel, Michael

2010-02-01

We have used observations obtained as part of the Hubble Space Telescope/ACS Survey of Galactic Globular Clusters to construct global present-day mass functions for 17 globular clusters utilizing multi-mass King models to extrapolate from our observations to the global cluster behavior. The global present-day mass functions for these clusters are well matched by power laws from the turnoff, ≈0.8 M sun, to 0.2-0.3 M sun on the lower main sequence. The slopes of those power-law fits, α, have been correlated with an extensive set of intrinsic and extrinsic cluster properties to investigate which parameters may influence the form of the present-day mass function. We do not confirm previous suggestions of correlations between α and either metallicity or Galactic location. However, we do find a strong statistical correlation with the related parameters central surface brightness, μ V , and inferred central density, ρ0. The correlation is such that clusters with denser cores (stronger binding energy) tend to have steeper mass functions (a higher proportion of low-mass stars), suggesting that dynamical evolution due to external interactions may have played a key role in determining α. Thus, the present-day mass function may owe more to nurture than to nature. Detailed modeling of external dynamical effects is therefore a requisite for determining the initial mass function for Galactic globular clusters.

The Formation and Evolution of Galactic Disks with APOGEE and the Gaia Survey

NASA Astrophysics Data System (ADS)

Li, Chengdong; Zhao, Gang; Zhai, Meng; Jia, Yunpeng

2018-06-01

We explore the structure and evolutionary history of Galactic disks with Apache Point Observatory Galactic Evolution Experiment data release 13 (DR13 hereafter) and Gaia Tycho-Gaia Astrometric Solution data. We use the [α/M] ratio to allocate stars into particular Galactic components to elucidate the chemical and dynamical properties of the thin and thick disks. The spatial motions of the sample stars are obtained in Galactic Cartesian and cylindrical coordinates. We analyze the abundance trends and metallicity and [α/M] gradients of the thick and thin disks. We confirm the existence of metal-weak thick-disk stars in Galactic disks. A kinematical method is used to select the thin- and thick-disk stars for comparison. We calculate the scale length and scale height of the kinematically and chemically selected thick and thin disks based on the axisymmetric Jeans equation. We conclude that the scale length of the thick disk is approximately equal to that of the thin disk via a kinematical approach. For the chemical selection, this disparity is about 1 kpc. Finally, we get the stellar orbital parameters and try to unveil the formation scenario of the thick disk. We conclude that the gas-rich merger and radial migration are more reasonable formation scenarios for the thick disk.

Kinematic imprints from the bar and spiral structures in the galatic disk

NASA Astrophysics Data System (ADS)

Figueras, F.; Antoja, T.; Valenzuela, O.; Romero-Gómez, M.; Pichardo, B.; Moreno, E.

2011-12-01

At 140 years of the discovery of the moving groups, these stellar streams are emerging as powerful tools to constrain the models for the spiral arms and the Galactic bar in the Gaia era. From the kinematic-age-metallicity analysis in the solar neighbourhood it is now well established that some of these kinematic structures have a dynamical origin, different from the classical cluster disruption hypothesis. Test particle simulations allow us to definitively establish that these local structures can be created by the dynamical resonances of material spiral arms and not exclusively by the Galactic bar. First studies to evaluate the capabilities of the future Gaia data to detect and characterize moving groups at 2-6 kpc from the solar neighborhood are discussed.

Dynamics of supernova remnants in the Galactic centre.

NASA Astrophysics Data System (ADS)

Bortolas, E.; Mapelli, M.; Spera, M.

The Galactic centre (GC) is a unique place to study the extreme dynamical processes occurring near a super-massive black hole (SMBH). Here we simulate a large set of binaries orbiting the SMBH while the primary member undergoes a supernova (SN) explosion, in order to study the impact of SN kicks on the orbits of stars and dark remnants in the GC. We find that SN explosions are efficient in scattering neutron stars and other light stars on new (mostly eccentric) orbits, while black holes (BHs) tend to retain memory of the orbit of their progenitor star. SN kicks are thus unable to eject BHs from the GC: a cusp of dark remnants may be lurking in the central parsec of our Galaxy.

A RECIPE TO PROBE ALTERNATIVE THEORIES OF GRAVITATION VIA N-BODY NUMERICAL SIMULATIONS. I. SPIRAL GALAXIES

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

Brandao, C. S. S.; De Araujo, J. C. N., E-mail: claudiosoriano.uesc@gmail.com, E-mail: jcarlos.dearaujo@inpe.br

2012-05-01

A way to probe alternative theories of gravitation is to study if they could account for the structures of the universe. We therefore modified the well-known Gadget-2 code to probe alternative theories of gravitation through galactic dynamics. As an application, we simulate the evolution of spiral galaxies to probe alternative theories of gravitation whose weak field limits have a Yukawa-like gravitational potential. These simulations show that galactic dynamics can be used to constrain the parameters associated with alternative theories of gravitation. It is worth stressing that the recipe given in this study can be applied to any other alternative theorymore » of gravitation in which the superposition principle is valid.« less

The Evolution of the Globular Cluster System in a Triaxial Galaxy: Can a Galactic Nucleus Form by Globular Cluster Capture?

NASA Astrophysics Data System (ADS)

Capuzzo-Dolcetta, Roberto

1993-10-01

Among the possible phenomena inducing evolution of the globular cluster system in an elliptical galaxy, dynamical friction due to field stars and tidal disruption caused by a central nucleus is of crucial importance. The aim of this paper is the study of the evolution of the globular cluster system in a triaxial galaxy in the presence of these phenomena. In particular, the possibility is examined that some galactic nuclei have been formed by frictionally decayed globular clusters moving in a triaxial potential. We find that the initial rapid growth of the nucleus, due mainly to massive clusters on box orbits falling in a short time scale into the galactic center, is later slowed by tidal disruption induced by the nucleus itself on less massive clusters in the way described by Ostriker, Binney, and Saha. The efficiency of dynamical friction is such to carry to the center of the galaxy enough globular cluster mass available to form a compact nucleus, but the actual modes and results of cluster-cluster encounters in the central potential well are complicated phenomena which remains to be investigated. The mass of the resulting nucleus is determined by the mutual feedback of the described processes, together with the initial spatial, velocity, and mass distributions of the globular cluster family. The effect on the system mass function is studied, showing the development of a low- and high-mass turnover even with an initially flat mass function. Moreover, in this paper is discussed the possibility that the globular cluster fall to the galactic center has been a cause of primordial violent galactic activity. An application of the model to M31 is presented.

Theoretical implications of the galactic radial acceleration relation of McGaugh, Lelli, and Schombert

NASA Astrophysics Data System (ADS)

Nesbet, Robert K.

2018-05-01

Velocities in stable circular orbits about galaxies, a measure of centripetal gravitation, exceed the expected Kepler/Newton velocity as orbital radius increases. Standard Λ cold dark matter (ΛCDM) attributes this anomaly to galactic dark matter. McGaugh et al. have recently shown for 153 disc galaxies that observed radial acceleration is an apparently universal function of classical acceleration computed for observed galactic baryonic mass density. This is consistent with the empirical modified Newtonian dynamics (MOND) model, not requiring dark matter. It is shown here that suitably constrained ΛCDM and conformal gravity (CG) also produce such a universal correlation function. ΛCDM requires a very specific dark matter distribution, while the implied CG non-classical acceleration must be independent of galactic mass. All three constrained radial acceleration functions agree with the empirical baryonic v4 Tully-Fisher relation. Accurate rotation data in the nominally flat velocity range could distinguish between MOND, ΛCDM, and CG.

Dynamical Processes Near the Super Massive Black Hole at the Galactic Center

NASA Astrophysics Data System (ADS)

Antonini, Fabio

2011-01-01

Observations of the stellar environment near the Galactic center provide the strongest empirical evidence for the existence of massive black holes in the Universe. Theoretical models of the Milky Way nuclear star cluster fail to explain numerous properties of such environment, including the presence of very young stars close to the super massive black hole (SMBH) and the more recent discovery of a parsec-scale core in the central distribution of the bright late-type (old) stars. In this thesis we present a theoretical study of dynamical processes near the Galactic center, strongly related to these issues. Using different numerical techniques we explore the close environment of a SMBH as catalyst for stellar collisions and mergers. We study binary stars that remain bound for several revolutions around the SMBH, finding that in the case of highly inclined binaries the Kozai resonance can lead to large periodic oscillations in the internal binary eccentricity and inclination. Collisions and mergers of the binary elements are found to increase significantly for multiple orbits around the SMBH. In collisions involving a low-mass and a high-mass star, the merger product acquires a high core hydrogen abundance from the smaller star, effectively resetting the nuclear evolution clock to a younger age. This process could serve as an important source of young stars at the Galactic center. We then show that a core in the old stars can be naturally explained in a scenario in which the Milky Way nuclear star cluster (NSC) is formed via repeated inspiral of globular clusters into the Galactic center. We present results from a set of N -body simulations of this process, which show that the fundamental properties of the NSC, including its mass, outer density profile and velocity structure, are also reproduced. Chandrasekhar's dynamical friction formula predicts no frictional force on a test body in a low-density core, regardless of its density, due to the absence of stars moving more slowly than the local circular velocity. We have tested this prediction using large-scale N -body experiments. The rate of orbital decay never drops precisely to zero, because stars moving faster than the test body also contribute to the frictional force. When the contribution from the fast-moving stars is included in the expression for the dynamical friction force, and the changes induced by the massive body on the stellar distribution are taken into account, Chandrasekhar's theory is found to reproduce the rate of orbital decay remarkably well. However, this rate is still substantially smaller than the rate predicted by Chandrasekhar's formula in its most widely-used forms, implying longer time scales for inspiral. Motivated by recent observations that suggest a parsec-scale core around the Galactic center SMBH, we investigated the evolution of a population of stellar-mass black holes (BHs) as they spiral in to the center of the Galaxy. After ˜ 10 Gyr, we find that the density of BHs can remain substantially less than the density in stars at all radii; we conclude that it would be unjustified to assume that the spatial distribution of BHs at the Galactic center is well described by steady-state models.

Evolution of the Oort Cloud under Galactic Perturbations

NASA Astrophysics Data System (ADS)

Higuchi, A.; Kokubo, E.; Mukai, T.

2005-08-01

The Oort cloud is a spherical comet reservoir surrounding the solar system. There is general agreement that the Oort cloud comets are the residual planetesimals of planet formation. The standard scenario of the Oort cloud formation consists of two dynamical stages: (1) giant planets raise the aphelia of planetesimals to the outer region of the solar system and (2) the galactic tide, passing stars, and giant molecular clouds pull up their perihelia out of the planetary region and randomize their inclinations. Here we show the orbital evolution of planetesimals due to the galactic tide. Planetesimals with large aphelion distances change their perihelion distances toward the outside of the planetary region by the galactic tide and become members of the Oort cloud. We consider only the vertical component of the galactic tide because it is dominant compared to other components. Then, under such an axi-symmetric assumption, some planetesimals may show the librations around ω (argument of perihelion)=π /2 or 3π /2 (the Kozai mechanism). The alternate increases of eccentricity and inclination of the Kozai mechanism are effective to form the Oort cloud. Using the secular perturbation theory, we can understand the motion of the planetesimals analytically. We applied the Kozai mechanism to the galactic tide and found that the galactic tide raise perihelia and randomize inclinations of planetesimals with semimajor axes larger than ˜ 103 AU in 5Gyr. We take into account time evolution of the local galactic density, which is thought to be denser in the early stage of the sun than the current one. This work was supported by the 21st Century COE Program Origin and Evolution of Planetary Systems of the Ministry of Education, Culture, Sports, Science, and Technology, Japan, and JSPS Research Fellowship for Young Scientists.

Smoking Gun Found for Gamma-Ray Burst in Milky Way

NASA Astrophysics Data System (ADS)

2004-06-01

Combined data from NASA's Chandra X-ray Observatory and infrared observations with the Palomar 200-inch telescope have uncovered evidence that a gamma-ray burst, one of nature's most catastrophic explosions, occurred in our Galaxy a few thousand years ago. The supernova remnant, W49B, may also be the first remnant of a gamma-ray burst discovered in the Milky Way. W49B is a barrel-shaped nebula located about 35,000 light years from Earth. The new data reveal bright infrared rings, like hoops around a barrel, and intense X-radiation from iron and nickel along the axis of the barrel. "These results provide intriguing evidence that an extremely massive star exploded in two powerful, oppositely directed jets that were rich in iron," said Jonathan Keohane of NASA's Jet Propulsion Laboratory at a press conference at the American Astronomical Society meeting in Denver. "This makes W49B a prime candidate for being the remnant of a gamma ray burst involving a black hole collapsar." "The nearest known gamma-ray burst to Earth is several million light years away - most are billions of light years distant - so the detection of the remnant of one in our galaxy would be a major breakthrough," said William Reach, one of Keohane's collaborators from the California Institute of Technology. According to the collapsar theory, gamma-ray bursts are produced when a massive star runs out of nuclear fuel and the star's core collapses to form a black hole surrounded by a disk of extremely hot, rapidly rotating, magnetized gas. Much of this gas is pulled into the black hole, but some is flung away in oppositely directed jets of gas traveling at near the speed of light. An observer aligned with one these jets would see a gamma-ray burst, a blinding flash in which the concentrated power equals that of ten quadrillion Suns for a minute or so. The view perpendicular to the jets is a less astonishing, although nonetheless spectacular supernova explosion. For W49B, the jet is tilted out of the plane of the sky by about 20 degrees. W49B Chandra Fe K-line Image of W49B Four rings about 25 light years in diameter can be identified in the infrared image. These rings, which are due to warm gas, were presumably flung out by the rapid rotation of the massive star a few hundred thousand years before the star exploded. The rings were pushed outward by a hot wind from the star a few thousand years before it exploded. Chandra's image and spectral data show that the jets of multimillion-degree-Celsius gas extending along the axis of the barrel are rich in iron and nickel ions, consistent with their being ejected from the center of the star. This distinguishes the explosion from a conventional type II supernova in which most of the Fe and Ni goes into making the neutron star, and the outer part of the star is what is flung out. In contrast, in the collapsar model of gamma ray bursts iron and nickel from the center is ejected along the jet. At the ends of the barrel, the X-ray emission flares out to make a hot cap. The X-ray cap is surrounded by a flattened cloud of hydrogen molecules detected in the infrared. These features indicate that the shock wave produced by the explosion has encountered a large, dense cloud of gas and dust. The scenario that emerges is one in which a massive star formed from a dense cloud of dust, shone brightly for a few million years while spinning off rings of gas and pushing them away, forming a nearly empty cavity around the star. The star then underwent a collapsar-type supernova explosion that resulted in a gamma-ray burst. The observations of W49B may help to resolve a problem that has bedeviled the collapsar model for gamma-ray bursts. On the one hand, the model is based on the collapse of a massive star, which is normally formed from a dense cloud. On the other hand, observations of the afterglow of many gamma-ray bursts indicate that the explosion occurred in a low-density gas. Based on the W49B data, the resolution proposed by Keohane and colleagues is that the star had carved out an extensive low-density cavity in which the explosion subsequently occurred. "This star appears to have exploded inside a bubble it had created," said Keohane. "In a sense, it dug its own grave." NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. The image and additional information are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

GLOBAL SIMULATIONS OF GALACTIC WINDS INCLUDING COSMIC-RAY STREAMING

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

Ruszkowski, Mateusz; Yang, H.-Y. Karen; Zweibel, Ellen, E-mail: mateuszr@umich.edu, E-mail: hsyang@astro.umd.edu, E-mail: zweibel@astro.wisc.edu

2017-01-10

Galactic outflows play an important role in galactic evolution. Despite their importance, a detailed understanding of the physical mechanisms responsible for the driving of these winds is lacking. In an effort to gain more insight into the nature of these flows, we perform global three-dimensional magnetohydrodynamical simulations of an isolated Milky Way-size starburst galaxy. We focus on the dynamical role of cosmic rays (CRs) injected by supernovae, and specifically on the impact of the streaming and anisotropic diffusion of CRs along the magnetic fields. We find that these microphysical effects can have a significant effect on the wind launching andmore » mass loading factors, depending on the details of the plasma physics. Due to the CR streaming instability, CRs propagating in the interstellar medium scatter on self-excited Alfvén waves and couple to the gas. When the wave growth due to the streaming instability is inhibited by some damping process, such as turbulent damping, the coupling of CRs to the gas is weaker and their effective propagation speed faster than the Alfvén speed. Alternatively, CRs could scatter from “extrinsic turbulence” that is driven by another mechanism. We demonstrate that the presence of moderately super-Alfvénic CR streaming enhances the efficiency of galactic wind driving. Cosmic rays stream away from denser regions near the galactic disk along partially ordered magnetic fields and in the process accelerate more tenuous gas away from the galaxy. For CR acceleration efficiencies broadly consistent with the observational constraints, CRs reduce the galactic star formation rates and significantly aid in launching galactic winds.« less

Foreword

NASA Astrophysics Data System (ADS)

Boulanger, François; Miville-Deschênes, Marc-Antoine

Scientific awareness of the galactic magnetic field arose in the late 40's with Fermi's work on cosmic rays, the discovery of the polarization of dust reddened starlight by Hiltner and Hall, and its interpretation in terms of magnetically aligned dust grains by Spitzer and Tukey and Davis and Greenstein. It was soon clear that the magnetic field and the cosmic ray are tied to the interstellar gas and form together an active dynamical system. Its importance for star formation and interstellar matter energetics was also quickly recognized but more than 50 years after most questions remain quantitatively open due to the paucity of data on the small scale structure of the field. In the last decade, interferometric surveys have revealed striking patterns in the diffuse polarized emission, imposed by Faraday rotation, that give a way to study the field structure in the intervening ionized medium. The advent of high sensitivity measurements of polarized emission at sub-millimeter wavelengths promise to further open our perspective on the Galactic field. The dust observations will soon extend from high resolution observations from star forming regions with ground based telescopes and the ALMA interferometer to the continuous mapping of the diffuse interstellar medium with Planck. A few months after the discovery of optical interstellar polarization, the Galactic magnetic field was an unexpected highlight of the first symposium on Cosmical Gas Dynamics held in Paris in august 1949. The Polarization 2005 meeting held at the University of Orsay was also a premiere. For the first time, two communities with disconnected backgrounds but common interests in polarization observations were given the opportunity to meet and learn from each other's research. The measurement of the polarization of the Cosmic Microwave Background has become a major Physics challenge of the decade(s) to come. The numerous experiments designed to achieve this goal have started providing data with unprecedented sensitivity on the Galactic polarization from sub-millimeter to centimetric wavelengths. Detailed modeling of the Galactic contribution to the observed polarization is a required key to the success of their endeavor. This book gathers invited lectures presented at the meeting. It gives an in depth account of our present knowledge of the Galactic magnetic field from measurements of its structure and intensity to its role in the physics of interstellar matter and star formation. The Galactic part of the book is complemented by three papers that introduce the Cosmic Microwave Background polarization and describe the experiments being built to observe it, with special attention to the Planck ESA mission. Few years after the Paris Cosmical Gas Dynamics symposium, the discovery of polarized synchrotron emission in the Crab was a new highlight in magnetic field research. Quoting a review by van de Hulst: “From that time on, measuring the polarization and thus mapping the magnetic field became a prime desideratum in galactic radio astronomy”. We hope that observations to come will stimulate similar enthusiasm and bring more and more scientists to the field for whom this book will be a useful and lasting reference. The editors would like to thank the IAS staff that took care of the organization with a special mention for Catherine Cougrand.

What we learn from eclipsing binaries in the ultraviolet

NASA Technical Reports Server (NTRS)

Guinan, Edward F.

1990-01-01

Recent results on stars and stellar physics from IUE (International Ultraviolet Explorer) observations of eclipsing binaries are discussed. Several case studies are presented, including V 444 Cyg, Aur stars, V 471 Tau and AR Lac. Topics include stellar winds and mass loss, stellar atmospheres, stellar dynamos, and surface activity. Studies of binary star dynamics and evolution are discussed. The progress made with IUE in understanding the complex dynamical and evolutionary processes taking place in W UMa-type binaries and Algol systems is highlighted. The initial results of intensive studies of the W UMa star VW Cep and three representative Algol-type binaries (in different stages of evolution) focused on gas flows and accretion, are included. The future prospects of eclipsing binary research are explored. Remaining problems are surveyed and the next challenges are presented. The roles that eclipsing binaries could play in studies of stellar evolution, cluster dynamics, galactic structure, mass luminosity relations for extra galactic systems, cosmology, and even possible detection of extra solar system planets using eclipsing binaries are discussed.

The Modified Dynamics is Conducive to Galactic Warp Formation

NASA Astrophysics Data System (ADS)

Brada, Rafael; Milgrom, Mordehai

2000-03-01

There is an effect in the modified dynamics that is conducive to the formation of warps. Because of the nonlinearity of the theory, the internal dynamics of a galaxy is affected by a perturber over and above possible tidal effects. For example, a relatively distant and light companion or the mean influence of a parent cluster, with negligible tidal effects, could still produce a significant warp in the outer part of a galactic disk. We present results of numerical calculations for simplified models that show, for instance, that a satellite with the (baryonic) mass and distance of the Magellanic Clouds can distort the axisymmetric field of the Milky Way enough to produce a warp of the magnitude (and position) observed. Details of the warp geometry remain to be explained; we use a static configuration that can produce only warps with a straight line of nodes. In more realistic simulations, one must reckon with the motion of the perturbing body, which sometimes occurs on timescales not much longer than the response time of the disk.

Probing Black Holes With Gravitational Radiation

NASA Astrophysics Data System (ADS)

Cornish, Neil J.

2006-09-01

Gravitational radiation can provide unique insights into the dynamics and evolution of black holes. Gravitational waveforms encode detailed information about the spacetime geometry, much as the sounds made by a musical instrument reflect the geometry of the instrument. The LISA gravitational wave observatory will be able to record black holes colliding out to the edge of the visible Universe, with an expected event rate of tens to thousands per year. LISA has unmatched capabilities for studying the role of black holes in galactic evolution, in particular, by studying the mergers of seed black holes at very high redshift, z > 5. Merger events at lower redshift will be detected at extremely high signal-to-noise, allowing for precision tests of the black hole paradigm. Below z=1 LISA will be able to record stellar remnants falling into supermassive black holes. These extreme mass ratio inspiral events will yield insights into the dynamics of galactic cusps, and the brighter events will provide incredibly precise tests of strong field, dynamical gravity.

Gravitational Wave Signatures in Black Hole Forming Core Collapse

NASA Astrophysics Data System (ADS)

Cerdá-Durán, Pablo; DeBrye, Nicolas; Aloy, Miguel A.; Font, José A.; Obergaulinger, Martin

2013-12-01

We present general relativistic numerical simulations of collapsing stellar cores. Our initial model consists of a low metallicity rapidly-rotating progenitor which is evolved in axisymmetry with the latest version of our general relativistic code CoCoNuT, which allows for black hole formation and includes the effects of a microphysical equation of state (LS220) and a neutrino leakage scheme to account for radiative losses. The motivation of our study is to analyze in detail the emission of gravitational waves in the collapsar scenario of long gamma-ray bursts. Our simulations show that the phase during which the proto-neutron star (PNS) survives before ultimately collapsing to a black hole is particularly optimal for gravitational wave emission. The high-amplitude waves last for several seconds and show a remarkable quasi-periodicity associated with the violent PNS dynamics, namely during the episodes of convection and the subsequent nonlinear development of the standing-accretion shock instability (SASI). By analyzing the spectrogram of our simulations we are able to identify the frequencies associated with the presence of g-modes and with the SASI motions at the PNS surface. We note that the gravitational waves emitted reach large enough amplitudes to be detected with third-generation detectors such as the Einstein Telescope within a Virgo Cluster volume at rates <~ 0.1 yr-1.

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

Cerdá-Durán, Pablo; DeBrye, Nicolas; Aloy, Miguel A.

We present general relativistic numerical simulations of collapsing stellar cores. Our initial model consists of a low metallicity rapidly-rotating progenitor which is evolved in axisymmetry with the latest version of our general relativistic code CoCoNuT, which allows for black hole formation and includes the effects of a microphysical equation of state (LS220) and a neutrino leakage scheme to account for radiative losses. The motivation of our study is to analyze in detail the emission of gravitational waves in the collapsar scenario of long gamma-ray bursts. Our simulations show that the phase during which the proto-neutron star (PNS) survives before ultimatelymore » collapsing to a black hole is particularly optimal for gravitational wave emission. The high-amplitude waves last for several seconds and show a remarkable quasi-periodicity associated with the violent PNS dynamics, namely during the episodes of convection and the subsequent nonlinear development of the standing-accretion shock instability (SASI). By analyzing the spectrogram of our simulations we are able to identify the frequencies associated with the presence of g-modes and with the SASI motions at the PNS surface. We note that the gravitational waves emitted reach large enough amplitudes to be detected with third-generation detectors such as the Einstein Telescope within a Virgo Cluster volume at rates ≲ 0.1 yr{sup –1}.« less

The Interstellar Medium in External Galaxies: Summaries of contributed papers

NASA Technical Reports Server (NTRS)

Hollenbach, David J. (Editor); Thronson, Harley A., Jr. (Editor)

1990-01-01

The Second Wyoming Conference entitled, The Interstellar Medium in External Galaxies, was held on July 3 to 7, 1989, to discuss the current understanding of the interstellar medium in external galaxies and to analyze the basic physical processes underlying interstellar phenomena. The papers covered a broad range of research on the gas and dust in external galaxies and focused on such topics as the distribution and morphology of the atomic, molecular, and dust components; the dynamics of the gas and the role of the magnetic field in the dynamics; elemental abundances and gas depletions in the atomic and ionized components; cooling flows; star formation; the correlation of the nonthermal radio continuum with the cool component of the interstellar medium; the origin and effect of hot galactic halos; the absorption line systems seen in distant quasars; and the effect of galactic collisions.

Gamma-ray and X-ray emission from the Galactic centre: hints on the nuclear star cluster formation history

NASA Astrophysics Data System (ADS)

Arca-Sedda, Manuel; Kocsis, Bence; Brandt, Timothy D.

2018-06-01

The Milky Way centre exhibits an intense flux in the gamma and X-ray bands, whose origin is partly ascribed to the possible presence of a large population of millisecond pulsars (MSPs) and cataclysmic variables (CVs), respectively. However, the number of sources required to generate such an excess is much larger than what is expected from in situ star formation and evolution, opening a series of questions about the formation history of the Galactic nucleus. In this paper we make use of direct N-body simulations to investigate whether these sources could have been brought to the Galactic centre by a population of star clusters that underwent orbital decay and formed the Galactic nuclear star cluster (NSC). Our results suggest that the gamma ray emission is compatible with a population of MSPs that were mass segregated in their parent clusters, while the X-ray emission is consistent with a population of CVs born via dynamical interactions in dense star clusters. Combining observations with our modelling, we explore how the observed γ ray flux can be related to different NSC formation scenarios. Finally, we show that the high-energy emission coming from the galactic central regions can be used to detect black holes heavier than 105M⊙ in nearby dwarf galaxies.

Galactic Forces Rule the Dynamics of Milky Way Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Hammer, Francois; Yang, Yanbin; Arenou, Frederic; Babusiaux, Carine; Wang, Jianling; Puech, Mathieu; Flores, Hector

2018-06-01

Dwarf galaxies populating the Galactic halo are assumed to host the largest fractions of dark matter, as calculated from their velocity dispersions. Their major axes are preferentially aligned with the Vast Polar Structure (VPOS) that is perpendicular to the Galactic disk, and we find their velocity gradients aligned as well. This finding results in a probability of random occurrence for the VPOS as low as ∼10‑5. It suggests that tidal forces exerted by the Milky Way are distorting dwarf galaxies. Here we demonstrate on the basis of the impulse approximation that the Galactic gravitational acceleration induces the dwarf line-of-sight velocity dispersion, which is also evidenced by strong dependences between both quantities. Since this result is valid for any dwarf mass value, it implies that dark matter estimates in Milky Way dwarfs cannot be deduced from the product of their radius to the square of their line-of-sight velocity dispersion. This questions the high dark matter fractions reported for these evanescent systems, and the universally adopted total-to-stellar mass relationship in the dwarf regime. It suggests that many dwarfs are at their first passage and are dissolving into the Galactic halo. This gives rise to a promising method to estimate the Milky Way total mass profile at large distances.

The end of the MACHO era, revisited: New limits on MACHO masses from halo wide binaries

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

Monroy-Rodríguez, Miguel A.; Allen, Christine, E-mail: chris@astro.unam.mx

2014-08-01

In order to determine an upper bound for the mass of the massive compact halo objects (MACHOs), we use the halo binaries contained in a recent catalog by Allen and Monroy-Rodríguez. To dynamically model their interactions with massive perturbers, a Monte Carlo simulation is conducted, using an impulsive approximation method and assuming a galactic halo constituted by massive particles of a characteristic mass. The results of such simulations are compared with several subsamples of our improved catalog of candidate halo wide binaries. In accordance with Quinn et al., we also find our results to be very sensitive to the widestmore » binaries. However, our larger sample, together with the fact that we can obtain galactic orbits for 150 of our systems, allows a more reliable estimate of the maximum MACHO mass than that obtained previously. If we employ the entire sample of 211 candidate halo stars we, obtain an upper limit of 112 M{sub ☉}. However, using the 150 binaries in our catalog with computed galactic orbits, we are able to refine our fitting criteria. Thus, for the 100 most halo-like binaries we obtain a maximum MACHO mass of 21-68 M{sub ☉}. Furthermore, we can estimate the dynamical effects of the galactic disk using binary samples that spend progressively shorter times within the disk. By extrapolating the limits obtained for our most reliable—albeit smallest—sample, we find that as the time spent within the disk tends to zero, the upper bound of the MACHO mass tends to less than 5 M{sub ☉}. The non-uniform density of the halo has also been taken into account, but the limit obtained, less than 5 M{sub ☉}, does not differ much from the previous one. Together with microlensing studies that provide lower limits on the MACHO mass, our results essentially exclude the existence of such objects in the galactic halo.« less

SPENDING TOO MUCH TIME AT THE GALACTIC BAR: CHAOTIC FANNING OF THE OPHIUCHUS STREAM

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

Price-Whelan, Adrian M.; Johnston, Kathryn V.; Sesar, Branimir

2016-06-20

The Ophiuchus stellar stream is peculiar: (1) its length is short given the age of its constituent stars, and (2) several probable member stars have dispersions in sky position and velocity that far exceed those seen within the stream. The stream’s proximity to the Galactic center suggests that its dynamical history is significantly influenced by the Galactic bar. We explore this hypothesis with models of stream formation along orbits consistent with Ophiuchus’ properties in a Milky Way potential model that includes a rotating bar. In all choices for the rotation parameters of the bar, orbits fit to the stream aremore » strongly chaotic. Mock streams generated along these orbits qualitatively match the observed properties of the stream: because of chaos, stars stripped early generally form low-density, high-dispersion “fans” leaving only the most recently disrupted material detectable as a strong over-density. Our models predict that there should be a significant amount of low-surface-brightness tidal debris around the stream with a complex phase-space morphology. The existence of or lack of these features could provide interesting constraints on the Milky Way bar and would rule out formation scenarios for the stream. This is the first time that chaos has been used to explain the properties of a stellar stream and is the first demonstration of the dynamical importance of chaos in the Galactic halo. The existence of long, thin streams around the Milky Way, presumably formed along non- or weakly chaotic orbits, may represent only a subset of the total population of disrupted satellites.« less

Tidal stripping stellar substructures around four metal-poor globular clusters in the galactic bulge

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

Chun, Sang-Hyun; Kang, Minhee; Jung, DooSeok

2015-01-01

We investigate the spatial density configuration of stars around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642, and NGC 6723) in the Galactic bulge region using wide-field deep J, H, and K imaging data obtained with the Wide Field Camera near-infrared array on the United Kingdom Infrared Telescope. A statistical weighted filtering algorithm for the stars on the color–magnitude diagram is applied in order to sort cluster member candidates from the field star contamination. In two-dimensional isodensity contour maps of the clusters, we find that all four of the globular clusters exhibit strong evidence of tidally stripped stellarmore » features beyond the tidal radius in the form of tidal tails or small density lobes/chunks. The orientations of the extended stellar substructures are likely to be associated with the effect of dynamic interaction with the Galaxy and the cluster's space motion. The observed radial density profiles of the four globular clusters also describe the extended substructures; they depart from theoretical King and Wilson models and have an overdensity feature with a break in the slope of the profile at the outer region of clusters. The observed results could imply that four globular clusters in the Galactic bulge region have experienced strong environmental effects such as tidal forces or bulge/disk shocks of the Galaxy during the dynamical evolution of globular clusters. These observational results provide further details which add to our understanding of the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.« less

Orbital Evolution of Planetesimals by the Galactic Tide

NASA Astrophysics Data System (ADS)

Higuchi, A.; Kokubo, E.; Mukai, T.

2005-05-01

The Oort cloud is a spherical comet reservoir surrounding the solar system. There is general agreement that the Oort cloud comets are the residual planetesimals of planet formation. The standard scenario of the Oort cloud formation consists of two dynamical stages: (1) giant planets raise the aphelia of planetesimals to the outer region of the solar system and (2) the galactic tide, passing stars, and giant molecular clouds pull up their perihelia out of the planetary region. Here we show the orbital evolution of planetesimals by the galactic tide. Planetesimals with large aphelion distances change their perihelion distances toward the outside of the planetary region by the galactic tide and become members of the Oort cloud. The effect of the galactic tide on the planetesimals with semimajor axes of ˜ 104AU is about 10-3 of the solar gravity. The timescale of the orbital evolution is ˜ 108 years. We consider only the vertical component of the galactic tide. Under the axisymmetric potential, some planetesimals may show the librations around ω (argument of perihelion)=π /2 and 3π /2 (the Kozai mechanism). The alternate increases of eccentricity and inclination of the Kozai mechanism are effective to form the Oort cloud. The secular perturbation theory demonstrates the Kozai mechanism and we can understand the motion of the planetesimals analytically. We apply the Kozai mechanism to the galactic tide and discuss the property of the Oort cloud formed by the Kozai mechanizm. This work was supported by the 21st Century COE Program Origin and Evolution of Planetary Systems of the Ministry of Education, Culture, Sports, Science, and Technology, Japan, and JSPS Research Fellowship for Young Scientists.

Starburst clusters in the Galactic center

NASA Astrophysics Data System (ADS)

Habibi, Maryam

2014-09-01

The central region of the Galaxy is the most active site of star formation in the Milky Way, where massive stars have formed very recently and are still forming today. The rich population of massive stars in the Galactic center provide a unique opportunity to study massive stars in their birth environment and probe their initial mass function, which is the spectrum of stellar masses at their birth. The Arches cluster is the youngest among the three massive clusters in the Galactic center, providing a collection of high-mass stars and a very dense core which makes this cluster an excellent site to address questions about massive star formation, the stellar mass function and the dynamical evolution of massive clusters in the Galactic center. In this thesis, I perform an observational study of the Arches cluster using K_{s}-band imaging obtained with NAOS/CONICA at the VLT combined with Subaru/Cisco J-band data to gain a full understanding of the cluster mass distribution out to its tidal radius for the first time. Since the light from the Galactic center reaches us through the Galactic disc, the extinction correction is crucial when studying this region. I use a Bayesian method to construct a realistic extinction map of the cluster. It is shown in this study that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, I show that the difference can reach up to 30% for individually derived stellar masses and Δ A_{Ks}˜ 1 magnitude in acquired K_{s}-band extinction, while the present-day mass function slope changes by ˜ 0.17 dex. The present-day mass function slope derived assuming the more recent extinction law, which suggests a steeper wavelength dependence for the infrared extinction law, reveals an overpopulation of massive stars in the core (r<0.2 pc) with a flat slope of α_{Nishi}=-1.50 ±0.35 in comparison to the Salpeter slope of α=-2.3. The slope of the mass function increases to α_{Nishi}=-2.21 ±0.27 in the intermediate annulus (0.2

Thermomagnetic torques in polyatomic gases

NASA Technical Reports Server (NTRS)

Hildebrandt, A. F.; Wood, C. T.

1972-01-01

The application of the Scott effect to the dynamics of galactic and stellar rotation is investigated. Efforts were also made to improve the sensitivity and stability of torque measurements and understand the microscopic mechanism that causes the Scott effect.

The chemical evolution of Dwarf Galaxies with galactic winds - the role of mass and gas distribution

NASA Astrophysics Data System (ADS)

Hensler, Gerhard; Recchi, Simone

2015-08-01

Energetic feedback from Supernovae and stellar winds can drive galactic winds. Dwarf galaxies (DGs), due to their shallower potential wells, are assumed to be more vulnera-ble to these energetic processes. Metal loss through galactic winds is also commonly invoked to explain the low metal content of DGs.Our main aim in this presentation is to show that galactic mass cannot be the only pa-rameter determining the fraction of metals lost by a galaxy. In particular, the distribution of gas must play an equally important role. We perform 2-D chemo-dynamical simula-tions of galaxies characterized by different gas distributions, masses and gas fractions. The gas distribution can change the fraction of lost metals through galactic winds by up to one order of magnitude. In particular, disk-like galaxies tend to lose metals more easily than roundish ones. Consequently, also the final element abundances attained by models with the same mass but with different gas distributions can vary by up to one dex. Confirming previous studies, we also show that the fate of gas and freshly pro-duced metals strongly depends on the mass of the galaxy. Smaller galaxies (with shal-lower potential wells) more easily develop large-scale outflows; therefore, the fraction of lost metals tends to be higher.Another important issue is that the invoked mechanism to transform central cusps to cored dark-matter distributions by baryon loss due to strong galactic winds cannot work in general, must be critically tested, and should be clearly discernible by the chemical evolution of DGs.

Moving Groups in the Milky Way Halo and Disk Induced by the Bar and Spiral Arms

NASA Astrophysics Data System (ADS)

Schuster, William John

2015-08-01

In a previous study (Moreno et al. 2015), the use of a detailed Milky Way potential (observationally and dynamically constrained) has shown that the Galactic bar is able to efficiently concentrate stars of the stellar halo and disk into several main resonances. With the tools introduced here, the Galactic bar is shown to produce significant phase-space structure attracting stars to several main resonances. This new study is dedicated to the study of known groups of the Galactic halo and disk, and their relation to these resonances. Stars belonging to some known halo and disk moving groups have settled down along these bar resonant families, showing, in some cases, a likely Galactic secular origin. In general, the 2D resonant orbits of the disk produced by the bar, seem to dominate at large scale-heights (several kiloparsecs) into the Galactic halo. In particular, provisionally six of the members of the Kapteyn halo moving group seem to be associated with one of these resonances, and also the Groombridge 1830 (Eggen 1996a; Eggen & Sandage 1959) and especially the newer halo moving groups G21-22 and G18-39 (Silva et al. 2012) show some correlation with these resonances suggesting possible secular origins, while the halo moving group Ross 451 (Eggen 1996b) does not show any such correlation, indicating a more probable cosmological (non-secular) ancestry. All Galactic disk moving groups (such as Arcturus, Hercules, Castor, IC 2391, Hyades, Pleiades, and Ursa Major) show considerable association with these resonances.

Oscillatory patterns in the light curves of five long-term monitored type 1 active galactic nuclei

NASA Astrophysics Data System (ADS)

Kovačević, Andjelka B.; Pérez-Hernández, Ernesto; Popović, Luka Č.; Shapovalova, Alla I.; Kollatschny, Wolfram; Ilić, Dragana

2018-04-01

New combined data of five well-known type 1 active galactic nuclei (AGNs) are probed with a novel hybrid method in a search for oscillatory behaviour. Additional analysis of artificial light curves obtained from the coupled oscillatory models gives confirmation for detected periods that could have a physical background. We find periodic variations in the long-term light curves of 3C 390.3, NGC 4151 and NGC 5548, and E1821 + 643, with correlation coefficients larger than 0.6. We show that the oscillatory patterns of two binary black hole candidates, NGC 5548 and E1821 + 643, correspond to qualitatively different dynamical regimes of chaos and stability, respectively. We demonstrate that the absence of oscillatory patterns in Arp 102B could be the result of a weak coupling between oscillatory mechanisms. This is the first good evidence that 3C 390.3 and Arp 102B, categorized as double-peaked Balmer line objects, have qualitative different dynamics. Our analysis shows a novelty in the oscillatory dynamical patterns of the light curves of these type 1 AGNs.

Galactic disk dynamical tracers: Open clusters and the local Milky Way rotation curve and velocity field

NASA Astrophysics Data System (ADS)

Frinchaboy, Peter Michael, III

Establishing the rotation curve of the Milky Way is one of the fundamental contributions needed to understand the Galaxy and its mass distribution. We have undertaken a systematic spectroscopic survey of open star clusters which can serve as tracers of Galactic disk dynamics. We report on our initial sample of 67 clusters for which the Hydra multi-fiber spectrographs on the WIYN and Blanco telescopes have delivered ~1-2 km s -1 radial velocities (RVs) of many dozens of stars in the fields of each cluster, which are used to derive cluster membership and bulk cluster kinematics when combined with Tycho-2 proper motions. The clusters selected for study have a broad spatial distribution in order to be sensitive to the disk velocity field in all Galactic quadrants and across a Galactocentric radius range as much as 3.0 kpc from the solar circle. Through analysis of the cluster sample, we find (1) the rotation velocity of the Local Standard of Rest (LSR) is [Special characters omitted.] km s -1 , (2 ) the local rotation curve is declining with radius having a slope of -9.1 km s -1 kpc -1 , (3) we find (using R 0 = 8.5 kpc) the following Galactic parameters: A = 17.0 km s -1 kpc -1 and B = -8.9 km s -1 kpc -1 , which using a flat rotation curve and our determined values for the rotation velocity of the LSR yields a Galaxy mass within 1.5 R 0 of M = 1.4 ± 0.2 × 10 11 [Spe cial characters omitted.] and a M/L of 9 [Special characters omitted.] . We also explore the distribution of the local velocity field and find evidence for non- circular motion due to the spiral arms. Additionally, a number of outer disk ( R gc > 12 kpc) open clusters, including Be29 and Sa1, are studied that have potentially critical leverage on radial, age and metallicity gradients in the outer Galactic disk. We find that the measured kinematics of Sa1 and Be29 are consistent with being associated with the Galactic anticenter stellar structure (GASS; or Monoceros stream), which points to a possible "accretion" origin for these and possibly other outer disk open clusters, if one believes that GASS represents an accreting dwarf galaxy system.

The local stellar velocity distribution of the Galaxy. Galactic structure and potential

NASA Astrophysics Data System (ADS)

Bienaymé, O.

1999-01-01

The velocity distribution of neighbouring stars is deduced from the Hipparcos proper motions. We have used a classical Schwarzschild decomposition and also developed a dynamical model for quasi-exponential stellar discs. This model is a 3-D derivation of Shu's model in the framework of Stäckel potentials with three integrals of motion. We determine the solar motion relative to the local standard of rest (LSR) (U_sun=9.7+/-0.3kms , V_sun=5.2+/-1.0kms and W_sun=6.7+/-0.2kms ), the density and kinematic radial gradients, as well as the local slope of the velocity curve. We find out that the scale density length of the Galaxy is 1.8+/-0.2kpc . We measure a large kinematic scale length for blue (young) stars, R_{sigma_r }=17+/-4kpc , while for red stars (predominantly old) we find R_{sigma_r }=9.7+/-0.8kpc (or R_{sigma_r (2}=4.8+/-0.4kpc ) ). From the stellar disc dynamical model, we determine explicitly the link between the tangential-vertical velocity (v_theta , v_z) coupling and the local shape of the potential. Using a restricted sample of 3-D velocity data, we measure z_o, the focus of the spheroidal coordinate system defining the best fitted Stäckel potential. The parameter z_o is related to the tilt of the velocity ellipsoid and more fundamentally to the mass gradient in the galactic disc. This parameter is found to be 5.7+/-1.4kpc . This implies that the galactic potential is not extremely flat and that the dark matter component is not confined in the galactic plane. Based on data from the Hipparcos astrometry satellite.

A magnetic torsional wave near the Galactic Centre traced by a 'double helix' nebula.

PubMed

Morris, Mark; Uchida, Keven; Do, Tuan

2006-03-16

The magnetic field in the central few hundred parsecs of the Milky Way has a dipolar geometry and is substantially stronger than elsewhere in the Galaxy, with estimates ranging up to a milligauss (refs 1-6). Characterization of the magnetic field at the Galactic Centre is important because it can affect the orbits of molecular clouds by exerting a drag on them, inhibit star formation, and could guide a wind of hot gas or cosmic rays away from the central region. Here we report observations of an infrared nebula having the morphology of an intertwined double helix about 100 parsecs from the Galaxy's dynamical centre, with its axis oriented perpendicular to the Galactic plane. The observed segment is about 25 parsecs in length, and contains about 1.25 full turns of each of the two continuous, helically wound strands. We interpret this feature as a torsional Alfvén wave propagating vertically away from the Galactic disk, driven by rotation of the magnetized circumnuclear gas disk. The direct connection between the circumnuclear disk and the double helix is ambiguous, but the images show a possible meandering channel that warrants further investigation.

Seeing the Forest Through the Trees: The Distribution and Properties of Dense Molecular Gas in the Milky Way Galaxy

NASA Astrophysics Data System (ADS)

Ellsworth-Bowers, Timothy P.

The Milky Way Galaxy serves as a vast laboratory for studying the dynamics and evolution of the dense interstellar medium and the processes of and surrounding massive star formation. From our vantage point within the Galactic plane, however, it has been extremely difficult to construct a coherent picture of Galactic structure; we cannot see the forest for the trees. The principal difficulties in studying the structure of the Galactic disk have been obscuration by the ubiquitous dust and molecular gas and confusion between objects along a line of sight. Recent technological advances have led to large-scale blind surveys of the Galactic plane at (sub-)millimeter wavelengths, where Galactic dust is generally optically thin, and have opened a new avenue for studying the forest. The Bolocam Galactic Plane Survey (BGPS) observed over 190 deg 2 of the Galactic plane in dust continuum emission near lambda = 1.1 mm, producing a catalog of over 8,000 dense molecular cloud structures across a wide swath of the Galactic disk. Deriving the spatial distribution and physical properties of these objects requires knowledge of distance, a component lacking in the data themselves. This thesis presents a generalized Bayesian probabilistic distance estimation method for dense molecular cloud structures, and demonstrates it with the BGPS data set. Distance probability density functions (DPDFs) are computed from kinematic distance likelihoods (which may be double- peaked for objects in the inner Galaxy) and an expandable suite of prior information to produce a comprehensive tally of our knowledge (and ignorance) of the distances to dense molecular cloud structures. As part of the DPDF formalism, this thesis derives several prior DPDFs for resolving the kinematic distance ambiguity in the inner Galaxy. From the collection of posterior DPDFs, a set of objects with well-constrained distance estimates is produced for deriving Galactic structure and the physical properties of dense molecular cloud structures. This distance catalog of 1,802 objects across the Galactic plane represents the first large-scale analysis of clump-scale objects in a variety of Galactic environments. The Galactocentric positions of these objects begin to trace out the spiral structure of the Milky Way, and suggest that dense molecular gas settles nearer the Galactic midplane than tracers of less-dense gas such as CO. Physical properties computed from the DPDFs reveal that BGPS objects trace a continuum of scales within giant molecular clouds, and extend the scaling relationships known as Larson's Laws to lower-mass substructures. The results presented here represent the first step on the road to seeing the molecular content of the Milky Way as a forest rather than individual nearby trees.

The Astronomical Low Frequency Array: A Proposed Explorer Mission for Radio Astronomy

NASA Technical Reports Server (NTRS)

Jones, D.; Allen, R.; Basart, J.; Bastian, T.; Bougeret, J. L.; Dennison, B.; Desch, M.; Dwarakanath, K.; Erickson, W.; Finley, D.;

Echo Mapping of Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Peterson, B. M.; Horne, K.

2004-01-01

Echo mapping makes use of the intrinsic variability of the continuum source in active galactic nuclei to map out the distribution and kinematics of line-emitting gas from its light travel time-delayed response to continuum changes. Echo mapping experiments have yielded sizes for the broad line-emitting region in about three dozen AGNs. The dynamics of the line-emitting gas seem to be dominated by the gravity of the central black hole, enabling measurement of the black-hole masses in AGNs. We discuss requirements for future echo-mapping experiments that will yield the high quality velocity-delay maps of the broad-line region that are needed to determine its physical nature.

Exploring Black Hole Accretion in Active Galactic Nuclei with Simbol-X

NASA Astrophysics Data System (ADS)

Goosmann, R. W.; Dovčiak, M.; Mouchet, M.; Czerny, B.; Karas, V.; Gonçalves, A.

2009-05-01

A major goal of the Simbol-X mission is to improve our knowledge about black hole accretion. By opening up the X-ray window above 10 keV with unprecedented sensitivity and resolution we obtain new constraints on the X-ray spectral and variability properties of active galactic nuclei. To interpret the future data, detailed X-ray modeling of the dynamics and radiation processes in the black hole vicinity is required. Relativistic effects must be taken into account, which then allow to constrain the fundamental black hole parameters and the emission pattern of the accretion disk from the spectra that will be obtained with Simbol-X.

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XV. The Dynamical Clock: Reading Cluster Dynamical Evolution from the Segregation Level of Blue Straggler Stars

NASA Astrophysics Data System (ADS)

Ferraro, F. R.; Lanzoni, B.; Raso, S.; Nardiello, D.; Dalessandro, E.; Vesperini, E.; Piotto, G.; Pallanca, C.; Beccari, G.; Bellini, A.; Libralato, M.; Anderson, J.; Aparicio, A.; Bedin, L. R.; Cassisi, S.; Milone, A. P.; Ortolani, S.; Renzini, A.; Salaris, M.; van der Marel, R. P.

2018-06-01

The parameter A +, defined as the area enclosed between the cumulative radial distribution of blue straggler stars (BSSs) and that of a reference population, is a powerful indicator of the level of BSS central segregation. As part of the Hubble Space Telescope UV Legacy Survey of Galactic globular clusters (GCs), here we present the BSS population and the determination of A + in 27 GCs observed out to about one half-mass radius. In combination with 21 additional clusters discussed in a previous paper, this provides us with a global sample of 48 systems (corresponding to ∼32% of the Milky Way GC population), for which we find a strong correlation between A + and the ratio of cluster age to the current central relaxation time. Tight relations have also been found with the core radius and the central luminosity density, which are expected to change with the long-term cluster dynamical evolution. An interesting relation is emerging between A + and the ratio of the BSS velocity dispersion relative to that of main sequence turn-off stars, which measures the degree of energy equipartition experienced by BSSs in the cluster. These results provide further confirmation that BSSs are invaluable probes of GC internal dynamics and that A + is a powerful dynamical clock.

Secular Dynamical Anti-friction in Galactic Nuclei

NASA Astrophysics Data System (ADS)

Madigan, Ann-Marie; Levin, Yuri

2012-07-01

We identify a gravitational-dynamical process in near-Keplerian potentials of galactic nuclei that occurs when an intermediate-mass black hole (IMBH) is migrating on an eccentric orbit through the stellar cluster towards the central supermassive black hole. We find that, apart from conventional dynamical friction, the IMBH experiences an often much stronger systematic torque due to the secular (i.e., orbit-averaged) interactions with the cluster's stars. The force which results in this torque is applied, counterintuitively, in the same direction as the IMBH's precession and we refer to its action as "secular dynamical anti-friction" (SDAF). We argue that SDAF, and not the gravitational ejection of stars, is responsible for the IMBH's eccentricity increase seen in the initial stages of previous N-body simulations. Our numerical experiments, supported by qualitative arguments, demonstrate that (1) when the IMBH's precession direction is artificially reversed, the torque changes sign as well, which decreases the orbital eccentricity; (2) the rate of eccentricity growth is sensitive to the IMBH migration rate, with zero systematic eccentricity growth for an IMBH whose orbit is artificially prevented from inward migration; and (3) SDAF is the strongest when the central star cluster is rapidly rotating. This leads to eccentricity growth/decrease for the clusters rotating in the opposite/same direction relative to the IMBH's orbital motion.

Anomalous Galactic Dynamics by Collusion of Rindler and Cosmological Horizons

NASA Astrophysics Data System (ADS)

van Putten, Maurice H. P. M.

2017-03-01

In holography, the dimensional reduction of phase space to two dimensions defines a dynamical dark energy of {{Λ }}=(1-q){H}2, associated with the cosmological horizon at a Hubble radius of {R}H=c/H, and inertia m of baryonic matter at acceleration α in terms of a thermodynamic potential U={{mc}}2 of Rindler horizons at ξ ={c}2/α . Here, H is the Hubble parameter with deceleration q and c is the velocity of light. In weak gravity, m drops below Newton’s value m 0 as α < {a}H, when Rindler horizons fall beyond the cosmological horizon. The onset to weak gravity across α ={a}H is sharp by causality. Striking evidence is found in galaxy rotation curves, whose asymptotic dynamics is parameterized by Milgrom’s scale of acceleration {a}0=({cH}/2π )\\sqrt{1-q}. This onset presents a new challenge for canonical dark matter distributions on galactic scales in ΛCDM. Instead, future galaxy surveys may determine {Q}0={{dq}(z)/{dz}| }z=0, to provide a direct test of dynamical dark energy ({Q}0> 2.5) versus ΛCDM ({Q}0< 1) and establish a bound of {10}-30 {{eV}} on the mass of the putative dark matter particle with clustering limited to galaxy clusters.

Dynamics with a Nonstandard Inertia-Acceleration Relation: An Alternative to Dark Matter in Galactic Systems

NASA Astrophysics Data System (ADS)

Milgrom, M.

1994-02-01

We investigate particle dynamics that is governed by a nonstandard kinetic action of a special form. We are guided by a phenomenological scheme-the modified dynamics (MOND)-that imputes the mass discrepancy, observed in galactic systems, not to the presence of dark matter, but to a departure from Newtonian dynamics below a certain scale of accelerations, a0. The particle's equation of motion in a potential φ is derived from an action, S, of the form S ~ Sk[r(t), a0] - ∫ φ dt. The limit a0 --> 0 corresponds to Newtonian dynamics, and there the kinetic action Sk must take the standard form. In the opposite limit, a0 --> ∞ we require Sk --> 0-and more specifically, for circular orbits Sk ~ a-10-in order to attain the phenomenological success of MOND. Galilei-invariant such theories must be strongly nonlocal. This is a blessing, as such theories need not suffer from the illnesses that are endemic to higher-derivative theories. We comment on the possibility that such a modified law of motion is an effective theory resulting from the elimination of degrees of freedom pertaining to the universe at large (the near equality a0 ≍ cH0 being a trace of that connection). We derive a general virial relation for bounded trajectories. Exact solutions are obtained for circular orbits, which pertain to rotation curves of disk galaxies. We also explore, in passing, theories that depart from the conventional Newtonian dynamics for very low frequencies.

Habitability in Different Milky Way Stellar Environments: A Stellar Interaction Dynamical Approach

PubMed Central

Pichardo, Bárbara; Lake, George; Segura, Antígona

2013-01-01

Abstract Every Galactic environment is characterized by a stellar density and a velocity dispersion. With this information from literature, we simulated flyby encounters for several Galactic regions, numerically calculating stellar trajectories as well as orbits for particles in disks; our aim was to understand the effect of typical stellar flybys on planetary (debris) disks in the Milky Way Galaxy. For the solar neighborhood, we examined nearby stars with known distance, proper motions, and radial velocities. We found occurrence of a disturbing impact to the solar planetary disk within the next 8 Myr to be highly unlikely; perturbations to the Oort cloud seem unlikely as well. Current knowledge of the full phase space of stars in the solar neighborhood, however, is rather poor; thus we cannot rule out the existence of a star that is more likely to approach than those for which we have complete kinematic information. We studied the effect of stellar encounters on planetary orbits within the habitable zones of stars in more crowded stellar environments, such as stellar clusters. We found that in open clusters habitable zones are not readily disrupted; this is true if they evaporate in less than 108 yr. For older clusters the results may not be the same. We specifically studied the case of Messier 67, one of the oldest open clusters known, and show the effect of this environment on debris disks. We also considered the conditions in globular clusters, the Galactic nucleus, and the Galactic bulge-bar. We calculated the probability of whether Oort clouds exist in these Galactic environments. Key Words: Stellar interactions—Galactic habitable zone—Oort cloud. Astrobiology 13, 491–509. PMID:23659647

Cosmic-ray Induced Destruction of CO in Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Bisbas, Thomas G.; van Dishoeck, Ewine F.; Papadopoulos, Padelis P.; Szűcs, László; Bialy, Shmuel; Zhang, Zhi-Yu

2017-04-01

We explore the effects of the expected higher cosmic ray (CR) ionization rates {\\zeta }{CR} on the abundances of carbon monoxide (CO), atomic carbon (C), and ionized carbon (C+) in the H2 clouds of star-forming galaxies. The study of Bisbas et al. is expanded by (a) using realistic inhomogeneous giant molecular cloud (GMC) structures, (b) a detailed chemical analysis behind the CR-induced destruction of CO, and (c) exploring the thermal state of CR-irradiated molecular gas. CRs permeating the interstellar medium with {\\zeta }{CR}≳ 10× ({Galactic}) are found to significantly reduce the [CO]/[H2] abundance ratios throughout the mass of a GMC. CO rotational line imaging will then show much clumpier structures than the actual ones. For {\\zeta }{CR}≳ 100 × (Galactic) this bias becomes severe, limiting the usefulness of CO lines for recovering structural and dynamical characteristics of H2-rich galaxies throughout the universe, including many of the so-called main-sequence galaxies where the bulk of cosmic star formation occurs. Both C+ and C abundances increase with rising {\\zeta }{CR}, with C remaining the most abundant of the two throughout H2 clouds, when {\\zeta }{CR}˜ (1-100) × (Galactic). C+ starts to dominate for {\\zeta }{CR}≳ {10}3 × (Galactic). The thermal state of the gas in the inner and denser regions of GMCs is invariant with {T}{gas}˜ 10 {{K}} for {\\zeta }{CR}˜ (1-10) × (Galactic). For {\\zeta }{CR}˜ {10}3 × (Galactic) this is no longer the case and {T}{gas}˜ 30{--}50 {{K}} are reached. Finally, we identify OH as the key species whose T gas-sensitive abundance could mitigate the destruction of CO at high temperatures.

Black-hole binaries as relics of gamma-ray burst/hypernova explosions

NASA Astrophysics Data System (ADS)

Moreno Mendez, Enrique

The Collapsar model, in which a fast-spinning massive star collapses into a Kerr black hole, has become the standard model to explain long-soft gamma-ray bursts and hypernova explosions (GRB/HN). However, stars massive enough (those with ZAMS mass ≳ (18--20) M⊙ ) to produce these events evolve through a path that loses too much angular momentum to produce a central engine capable of delivering the necessary energy. In this work I suggest that the soft X-ray transient sources are the remnants of GRBs/HNe. Binaries in which the massive primary star evolves a carbon-oxygen burning core, then start to transfer material to the secondary star (Case C mass transfer), causing the orbit to decay until a common-envelope phase sets in. The secondary spirals in, further narrowing the orbit of the binary and removing the hydrogen envelope of the primary star. Eventually the primary star becomes tidally locked and spins up, acquiring enough rotational energy to power up a GRB/HN explosion. The central engine producing the GRB/HN event is the Kerr black hole acting through the Blandford-Znajek mechanism. This model can explain not only the long-soft GRBs, but also the subluminous bursts (which comprise ˜ 97% of the total), the long-soft bursts and the short-hard bursts (in a neutron star, black hole merger). Because of our binary evolution through Case C mass transfer, it turns out that for the subluminous and cosmological bursts, the angular momentum O is proportional to m3/2D , where mD is the mass of the donor (secondary star). This binary evolution model has a great advantage over the Woosley Collapsar model; one can "dial" the donor mass in order to obtain whatever angular momentum is needed to drive the explosion. Population syntheses show that there are enough binaries to account for the progenitors of all known classes of GRBs.

A Reconnection Switch to Trigger gamma-Ray Burst Jet Dissipation

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

McKinney, Jonathan C.; Uzdensky, Dmitri A.

2012-03-14

Prompt gamma-ray burst (GRB) emission requires some mechanism to dissipate an ultrarelativistic jet. Internal shocks or some form of electromagnetic dissipation are candidate mechanisms. Any mechanism needs to answer basic questions, such as what is the origin of variability, what radius does dissipation occur at, and how does efficient prompt emission occur. These mechanisms also need to be consistent with how ultrarelativistic jets form and stay baryon pure despite turbulence and electromagnetic reconnection near the compact object and despite stellar entrainment within the collapsar model. We use the latest magnetohydrodynamical models of ultrarelativistic jets to explore some of these questionsmore » in the context of electromagnetic dissipation due to the slow collisional and fast collisionless reconnection mechanisms, as often associated with Sweet-Parker and Petschek reconnection, respectively. For a highly magnetized ultrarelativistic jet and typical collapsar parameters, we find that significant electromagnetic dissipation may be avoided until it proceeds catastrophically near the jet photosphere at large radii (r {approx} 10{sup 13}-10{sup 14}cm), by which the jet obtains a high Lorentz factor ({gamma} {approx} 100-1000), has a luminosity of L{sub j} {approx} 10{sup 50}-10{sup 51} erg s{sup -1}, has observer variability timescales of order 1s (ranging from 0.001-10s), achieves {gamma}{theta}{sub j} {approx} 10-20 (for opening half-angle {theta}{sub j}) and so is able to produce jet breaks, and has comparable energy available for both prompt and afterglow emission. A range of model parameters are investigated and simplified scaling laws are derived. This reconnection switch mechanism allows for highly efficient conversion of electromagnetic energy into prompt emission and associates the observed prompt GRB pulse temporal structure with dissipation timescales of some number of reconnecting current sheets embedded in the jet. We hope this work helps motivate the development of self-consistent radiative compressible relativistic reconnection models.« less

Stellar streams as gravitational experiments. I. The case of Sagittarius

NASA Astrophysics Data System (ADS)

Thomas, Guillaume F.; Famaey, Benoit; Ibata, Rodrigo; Lüghausen, Fabian; Kroupa, Pavel

2017-07-01

Tidal streams of disrupting dwarf galaxies orbiting around their host galaxy offer a unique way to constrain the shape of galactic gravitational potentials. Such streams can be used as "leaning tower" gravitational experiments on galactic scales. The most well-motivated modification of gravity proposed as an alternative to dark matter on galactic scales is Milgromian dynamics (MOND), and we present here the first ever N-body simulations of the dynamical evolution of the disrupting Sagittarius dwarf galaxy in this framework. Using a realistic baryonic mass model for the Milky Way, we attempt to reproduce the present-day spatial and kinematic structure of the Sagittarius dwarf and its immense tidal stream that wraps around the Milky Way. With very little freedom on the original structure of the progenitor, constrained by the total luminosity of the Sagittarius structure and by the observed stellar mass-size relation for isolated dwarf galaxies, we find reasonable agreement between our simulations and observations of this system. The observed stellar velocities in the leading arm can be reproduced if we include a massive hot gas corona around the Milky Way that is flattened in the direction of the principal plane of its satellites. This is the first time that tidal dissolution in MOND has been tested rigorously at these mass and acceleration scales. The movie associated to Fig. 6 is available at http://www.aanda.org

Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars

NASA Astrophysics Data System (ADS)

Abbate, F.; Mastrobuono-Battisti, A.; Colpi, M.; Possenti, A.; Sippel, A. C.; Dotti, M.

2018-01-01

The origin of the nuclear star cluster in the centre of our Galaxy is still unknown. One possibility is that it formed after the disruption of stellar clusters that spiralled into the Galactic Centre due to dynamical friction. We trace the formation of the nuclear star cluster around the central black hole, using state-of-the-art N-body simulations, and follow the dynamics of the neutron stars born in the clusters. We then estimate the number of millisecond pulsars (MSPs) that are released in the nuclear star cluster during its formation. The assembly and tidal dismemberment of globular clusters lead to a population of MSPs distributed over a radius of about 20 pc, with a peak near 3 pc. No clustering is found on the subparsec scale. We simulate the detectability of this population with future radio telescopes like the MeerKAT radio telescope and SKA1, and find that about an order of 10 MSPs can be observed over this large volume, with a paucity of MSPs within the central parsec. This helps discriminating this scenario from the in situ formation model for the nuclear star cluster that would predict an overabundance of MSPs closer to the black hole. We then discuss the potential contribution of our MSP population to the gamma-ray excess at the Galactic Centre.

Role of Turbulent Damping in Cosmic Ray Galactic Winds

NASA Astrophysics Data System (ADS)

Holguin, Francisco; Ruszkowski, Mateusz; Lazarian, Alex; Yang, H. Y. Karen

2018-06-01

Large-scale galactic winds driven by stellar feedback are one phenomenon that influences the dynamical and chemical evolution of a galaxy, pushing and redistributing material throughout the interstellar medium (ISM) and galactic halo. A detailed understanding of the exact physical mechanisms responsible for these winds is lacking. Non-thermal feedback from galactic cosmic rays (CR), high-energy charged particles accelerated in supernovae and young stars, can impact the efficiency in accelerating the wind. In the self-confinement model, CR stream along magnetic field lines at the Alfven speed due to scattering off self-excited Aflv{é}n waves. However, magneto-hydrodynamic (MHD) turbulence stirred up by stellar feedback dissipates these confining waves, allowing CR to be super Aflvenic. Previous simulations relying on a simplified model of transport have shown that super-Alfv{é}nic streaming of CRs can launch a stronger wind. We perform three-dimensional MHD simulations of a section of a galactic disk, including CR streaming dependent on the local environment, using a realistic model of turbulent dissipation of Alfven waves presented in Lazarian (2016). In this implementation, the CR streaming speed can be super Alfv{é}nic depending on local conditions. We compare results for Alfv{é}nic and locally determined streaming, and find that gas/CR distributions and instantaneous mass loading factor of the wind are different depending on the level of turbulence.Lazarian, A. “Damping of Alfven waves by turbulence and its consequences: from cosmic-ray streaming to launching winds.” ApJ. Vol. 833, Num. 2. (2016).

On the rate of black hole binary mergers in galactic nuclei due to dynamical hardening

NASA Astrophysics Data System (ADS)

Leigh, N. W. C.; Geller, A. M.; McKernan, B.; Ford, K. E. S.; Mac Low, M.-M.; Bellovary, J.; Haiman, Z.; Lyra, W.; Samsing, J.; O'Dowd, M.; Kocsis, B.; Endlich, S.

2018-03-01

We assess the contribution of dynamical hardening by direct three-body scattering interactions to the rate of stellar-mass black hole binary (BHB) mergers in galactic nuclei. We derive an analytic model for the single-binary encounter rate in a nucleus with spherical and disc components hosting a super-massive black hole (SMBH). We determine the total number of encounters NGW needed to harden a BHB to the point that inspiral due to gravitational wave emission occurs before the next three-body scattering event. This is done independently for both the spherical and disc components. Using a Monte Carlo approach, we refine our calculations for NGW to include gravitational wave emission between scattering events. For astrophysically plausible models, we find that typically NGW ≲ 10. We find two separate regimes for the efficient dynamical hardening of BHBs: (1) spherical star clusters with high central densities, low-velocity dispersions, and no significant Keplerian component and (2) migration traps in discs around SMBHs lacking any significant spherical stellar component in the vicinity of the migration trap, which is expected due to effective orbital inclination reduction of any spherical population by the disc. We also find a weak correlation between the ratio of the second-order velocity moment to velocity dispersion in galactic nuclei and the rate of BHB mergers, where this ratio is a proxy for the ratio between the rotation- and dispersion-supported components. Because discs enforce planar interactions that are efficient in hardening BHBs, particularly in migration traps, they have high merger rates that can contribute significantly to the rate of BHB mergers detected by the advanced Laser Interferometer Gravitational-Wave Observatory.

The mond external field effect on the dynamics of the globular clusters: general considerations and application to NGC 2419

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

Derakhshani, Kamran, E-mail: kderakhshani@iasbs.ac.ir

2014-03-01

In this paper, we investigate the external field effect in the context of the MOdified Newtonian Dynamics (MOND) on the surface brightness and velocity dispersion profiles of globular clusters (GCs). Using N-MODY, which is an N-body simulation code with a MOND potential solver, we show that the general effect of the external field for diffuse clusters, which obey MOND in most of their parts, is that it pushes the dynamics toward the Newtonian regime. On the other hand, for more compact clusters, which are essentially Newtonian in their inner parts, the external field is effective mainly in the outer partsmore » of compact clusters. As a case study, we then choose the remote Galactic GC NGC 2419. By varying the cluster mass, half-light radius, and mass-to-light ratio, we aim to find a model that will reproduce the observational data most effectively, using N-MODY. We find that even if we take the Galactic external field into account, a Newtonian Plummer sphere represents the observational data better than MOND to an order of magnitude in terms of the total χ{sup 2} of surface brightness and velocity dispersion.« less

The MOND External Field Effect on the Dynamics of the Globular Clusters: General Considerations and Application to NGC 2419

NASA Astrophysics Data System (ADS)

Derakhshani, Kamran

2014-03-01

In this paper, we investigate the external field effect in the context of the MOdified Newtonian Dynamics (MOND) on the surface brightness and velocity dispersion profiles of globular clusters (GCs). Using N-MODY, which is an N-body simulation code with a MOND potential solver, we show that the general effect of the external field for diffuse clusters, which obey MOND in most of their parts, is that it pushes the dynamics toward the Newtonian regime. On the other hand, for more compact clusters, which are essentially Newtonian in their inner parts, the external field is effective mainly in the outer parts of compact clusters. As a case study, we then choose the remote Galactic GC NGC 2419. By varying the cluster mass, half-light radius, and mass-to-light ratio, we aim to find a model that will reproduce the observational data most effectively, using N-MODY. We find that even if we take the Galactic external field into account, a Newtonian Plummer sphere represents the observational data better than MOND to an order of magnitude in terms of the total χ2 of surface brightness and velocity dispersion.

A Speeding Binary in the Galactic Halo

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-04-01

The recent discovery of a hyper-velocity binary star system in the halo of the Milky Way poses a mystery: how was this system accelerated to its high speed?Accelerating StarsUnlike the uniform motion in the Galactic disk, stars in the Milky Ways halo exhibit a huge diversity of orbits that are usually tilted relative to the disk and have a variety of speeds. One type of halo star, so-called hyper-velocity stars, travel with speeds that can approach the escape velocity of the Galaxy.How do these hyper-velocity stars come about? Assuming they form in the Galactic disk, there are multiple proposed scenarios through which they could be accelerated and injected into the halo, such as:Ejection after a close encounter with the supermassive black hole at the Galactic centerEjection due to a nearby supernova explosionEjection as the result of a dynamical interaction in a dense stellar population.Further observations of hyper-velocity stars are necessary to identify the mechanism responsible for their acceleration.J1211s SurpriseModels of J1211s orbit show it did not originate from the Galactic center (black dot). The solar symbol shows the position of the Sun and the star shows the current position of J1211. The bottom two panels show two depictions(x-y plane and r-z plane) of estimated orbits of J1211 over the past 10 Gyr. [Nmeth et al. 2016]To this end, a team of scientists led by Pter Nmeth (Friedrich Alexander University, Erlangen-Nrnberg) recently studied the candidate halo hyper-velocity star SDSS J121150.27+143716.2. The scientists obtained spectroscopy of J1211 using spectrographs at the Keck Telescope in Hawaii and ESOs Very Large Telescope in Chile. To their surprise, they discovered the signature of a companion in the spectra: J1211 is actually a binary!Nmeth and collaborators found that J1211, located roughly 18,000 light-years away, is moving at a rapid ~570 km/s relative to the galactic rest frame. The binary system consists of a hot (30,600 K) subdwarf and a cool (4,800 K) companion star in a wide orbit, likely separated by several AU.An Unknown Past and FutureWhy are these new observations of J1211 such a big deal? Because all the acceleration scenarios for a star originating in the Galactic disk fail in the case of J1211. The authors find by modeling J1211s motion that the system cant have originated in the Galactic center, so interactions with the supermassive black hole are out. And supernova explosions or dynamical interactions would tear the wide binary apart in the process of accelerating it. Nmeth and collaborators suggest instead that J1211 was either born in the halo population or accreted later from the debris of a destroyed satellite galaxy.J1211s speed is so extreme that its orbit could be either bound or unbound. Interestingly, when the authors model the binarys orbit, they find that the assumed mass of the Milky Ways dark-matter halo determines whether J1211s orbit is bound. This means that future observations of J1211 may provide a new way to probe the Galactic potential and determine the mass of the dark matter halo, in addition to revealing unexpected origins of high-velocity halo stars.CitationPter Nmeth et al 2016 ApJ 821 L13. doi:10.3847/2041-8205/821/1/L13

The role of self-interacting right-handed neutrinos in galactic structure

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

Argüelles, C.R.; Rueda, J.A.; Ruffini, R.

2016-04-01

It has been shown previously that the DM in galactic halos can be explained by a self-gravitating system of massive keV fermions ('inos') in thermodynamic equilibrium, and predicted the existence of a denser quantum core of inos towards the center of galaxies. In this article we show that the inclusion of self-interactions among the inos, modeled within a relativistic mean-field-theory approach, allows the quantum core to become massive and compact enough to explain the dynamics of the S-cluster stars closest to the Milky Way's galactic center. The application of this model to other galaxies such as large elliptical harboring massivemore » central dark objects of ∼ 10{sup 9} M {sub ⊙} is also investigated. We identify these interacting inos with sterile right-handed neutrinos pertaining to minimal extensions of the Standard Model, and calculate the corresponding total cross-section σ within an electroweak-like formalism to be compared with other observationally inferred cross-section estimates. The coincidence of an ino mass range of few tens of keV derived here only from the galactic structure, with the range obtained independently from other astrophysical and cosmological constraints, points towards an important role of the right-handed neutrinos in the cosmic structure.« less

Mapping photometric metallicities in the Galactic halo using broadband photometry

NASA Astrophysics Data System (ADS)

Hebenstreit, Samuel David; Nidever, David L.; Munn, Jeffrey A.; Majewski, Steven R.

2018-06-01

An important objective of modern Astrophysics is to trace the history of galaxies and the dynamics of their formations. The outer regions of the Milky Way, including the Galactic halo, could potentially elucidate the evolutionary history of our galaxy. In this study, we make use of extensive DDO51 photometry combined with SDSS broadband photometry to select giant stars reaching to 90 kpc. Photometric metallicities, calibrated by overlapping spectroscopic data (SDSS, APOGEE and LAMOST), and distances are calculated for all giant stars. Using these metallicities and distances, we construct metallicity distribution functions (MDFs) from these stars. We study the MDFs for information pertaining to the accretion history of the Milky Way.

Análisis de la evolución química de los cúmulos abiertos de la Galaxia a través de simulaciones dinámicas con procesos de destrucción

NASA Astrophysics Data System (ADS)

Bignone, L. A.; Pellizza, L. J.; Piatti, A. E.; Tecce, T. E.

It is well known that open clusters are excellent tracers (in time and space) of the metallicity of the Galactic disk. We analyze the history of stellar for- mation of the Galactic disk using numerical simulations of the dynamical evolution of the open cluster system. We have included the effects of clus- ter disruption caused by stellar evolution, tidal fields, and the interaction with the spiral arms. We model the present astrophysical properties of open clusters from initial hypothesis regarding their formation history. FULL TEXT IN SPANISH

AMI-CL J0300+2613: a Galactic anomalous-microwave-emission ring masquerading as a galaxy cluster

NASA Astrophysics Data System (ADS)

Perrott, Yvette C.; Cantwell, Therese M.; Carey, Steve H.; Elwood, Patrick J.; Feroz, Farhan; Grainge, Keith J. B.; Green, David A.; Hobson, Michael P.; Javid, Kamran; Jin, Terry Z.; Pooley, Guy G.; Razavi-Ghods, Nima; Rumsey, Clare; Saunders, Richard D. E.; Scaife, Anna M. M.; Schammel, Michel P.; Scott, Paul F.; Shimwell, Timothy W.; Titterington, David J.; Waldram, Elizabeth M.

2018-01-01

The Arcminute Microkelvin Imager (AMI) carried out a blind survey for galaxy clusters via their Sunyaev-Zel'dovich effect decrements between 2008 and 2011. The first detection, known as AMI-CL J0300+2613, has been reobserved with AMI equipped with a new digital correlator with high dynamic range. The combination of the new AMI data and more recent high-resolution sub-mm and infrared maps now shows the feature in fact to be a ring of positive dust-correlated Galactic emission, which is likely to be anomalous microwave emission (AME). If so, this is the first completely blind detection of AME at arcminute scales.

Galactic civilizations: Population dynamics and interstellar diffusion

NASA Technical Reports Server (NTRS)

Newman, W. I.; Sagan, C.

1978-01-01

The interstellar diffusion of galactic civilizations is reexamined by potential theory; both numerical and analytical solutions are derived for the nonlinear partial differential equations which specify a range of relevant models, drawn from blast wave physics, soil science, and, especially, population biology. An essential feature of these models is that, for all civilizations, population growth must be limited by the carrying capacity of the environment. Dispersal is fundamentally a diffusion process; a density-dependent diffusivity describes interstellar emigration. Two models are considered: the first describing zero population growth (ZPG), and the second which also includes local growth and saturation of a planetary population, and for which an asymptotic traveling wave solution is found.

Habitability in different Milky Way stellar environments: a stellar interaction dynamical approach.

PubMed

Jiménez-Torres, Juan J; Pichardo, Bárbara; Lake, George; Segura, Antígona

2013-05-01

Every Galactic environment is characterized by a stellar density and a velocity dispersion. With this information from literature, we simulated flyby encounters for several Galactic regions, numerically calculating stellar trajectories as well as orbits for particles in disks; our aim was to understand the effect of typical stellar flybys on planetary (debris) disks in the Milky Way Galaxy. For the solar neighborhood, we examined nearby stars with known distance, proper motions, and radial velocities. We found occurrence of a disturbing impact to the solar planetary disk within the next 8 Myr to be highly unlikely; perturbations to the Oort cloud seem unlikely as well. Current knowledge of the full phase space of stars in the solar neighborhood, however, is rather poor; thus we cannot rule out the existence of a star that is more likely to approach than those for which we have complete kinematic information. We studied the effect of stellar encounters on planetary orbits within the habitable zones of stars in more crowded stellar environments, such as stellar clusters. We found that in open clusters habitable zones are not readily disrupted; this is true if they evaporate in less than 10(8) yr. For older clusters the results may not be the same. We specifically studied the case of Messier 67, one of the oldest open clusters known, and show the effect of this environment on debris disks. We also considered the conditions in globular clusters, the Galactic nucleus, and the Galactic bulge-bar. We calculated the probability of whether Oort clouds exist in these Galactic environments.

Dynamical evolution of galaxies in dense cluster environment.

NASA Astrophysics Data System (ADS)

Gnedin, O. Y.

1997-12-01

I present the results of study of the dynamics of galaxies in clusters of galaxies. The effects of the galaxy environment could be quite dramatic. The time-varying gravitational potential of the cluster subjects the galaxies to strong tidal effects. The tidal density cutoff effectively strips the dark matter halos and leads to highly concentrated structures in the galactic centers. The fast gravitational tidal shocks raise the random motion of stars in the galaxies, transforming the thin disks into the kinematically hot thick configurations. The tidal shocks also cause relaxation of stellar energies that enhances the rate of accretion onto the galactic centers. These effects of the time-varying cluster potential have not been consistently taken into account before. I present numerical N-body simulations of galaxies using the Self-Consistent Field code with 10(7) - 10(8) particles. The code is coupled with the PM code that provides a fully dynamic simulation of the cluster potential. The tidal field of the cluster along the galaxy trajectories is imposed as an external perturbation on the galaxies in the SCF scheme. Recent HST observations show that the high-redshift (z > 0.4) clusters contain numerous bright blue spirals, often with distorted profiles, whereas the nearby clusters are mostly populated by featureless ellipticals. The goal of my study is to understand whether dynamics is responsible for the observed strong evolution of galaxies in clusters.

THE PROPERTIES OF HYPERVELOCITY STARS AND S-STARS ORIGINATING FROM AN ECCENTRIC DISK AROUND A SUPERMASSIVE BLACK HOLE

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

Šubr, Ladislav; Haas, Jaroslav, E-mail: subr@sirrah.troja.mff.cuni.cz, E-mail: haas@sirrah.troja.mff.cuni.cz

2016-09-01

Hypervelocity stars (HVSs), which are observed in the Galactic halo, are believed to be accelerated to large velocities by a process of tidal disruption of binary stars passing close to the supermassive black hole (SMBH) which resides in the center of the Galaxy. It is, however, still unclear where these relatively young stars were born and what dynamical process pushed them to nearly radial orbits around the SMBH. In this paper we investigate the possibility that the young binaries originated from a thin eccentric disk, similar to the one currently observed in the Galactic center. By means of direct Nmore » -body simulations, we follow the dynamical evolution of an initially thin and eccentric disk of stars with a 100% binary fraction orbiting around the SMBH. Such a configuration leads to Kozai–Lidov oscillations of orbital elements, bringing a considerable number of binaries to the close vicinity of the black hole. Subsequent tidal disruption of these binaries accelerates one of their components to velocities well above the escape velocity from the SMBH, while the second component becomes tightly bound to the SMBH. We describe the main kinematic properties of the escaping and tightly bound stars within our model, and compare them qualitatively to the properties of the observed HVSs and S-stars, respectively. The most prominent feature is strong anisotropy in the directions of the escaping stars, which is observed for Galactic HVSs but has not yet been explained.« less

Catching Galactic open clusters in advanced stages of dynamical evolution

NASA Astrophysics Data System (ADS)

Angelo, M. S.; Piatti, A. E.; Dias, W. S.; Maia, F. F. S.

2018-04-01

During their dynamical evolution, Galactic open clusters (OCs) gradually lose their stellar content mainly because of internal relaxation and tidal forces. In this context, the study of dynamically evolved OCs is necessary to properly understand such processes. We present a comprehensive Washington CT1 photometric analysis of six sparse OCs, namely: ESO 518-3, Ruprecht 121, ESO 134-12, NGC 6573, ESO 260-7 and ESO 065-7. We employed Markov chain Monte-Carlo simulations to robustly determine the central coordinates and the structural parameters and T1 × (C - T1) colour-magnitude diagrams (CMDs) cleaned from field contamination were used to derive the fundamental parameters. ESO 518-03, Ruprecht 121, ESO 134-12 and NGC 6573 resulted to be of nearly the same young age (8.2 ≤log(t yr-1) ≤ 8.3); ESO 260-7 and ESO065-7 are of intermediate age (9.2 ≤log(t yr-1) ≤ 9.4). All studied OCs are located at similar Galactocentric distances (RG ˜ 6 - 6.9 kpc), considering uncertainties, except for ESO 260-7 (RG = 8.9 kpc). These OCs are in a tidally filled regime and are dynamically evolved, since they are much older than their half-mass relaxation times (t/trh ≳ 30) and present signals of low-mass star depletion. We distinguished two groups: those dynamically evolving towards final disruptions and those in an advanced dynamical evolutionary stage. Although we do not rule out that the Milky Way potential could have made differentially faster their dynamical evolutions, we speculate here with the possibility that they have been mainly driven by initial formation conditions.

Catching Galactic open clusters in advanced stages of dynamical evolution

NASA Astrophysics Data System (ADS)

Angelo, M. S.; Piatti, A. E.; Dias, W. S.; Maia, F. F. S.

2018-07-01

During their dynamical evolution, Galactic open clusters (OCs) gradually lose their stellar content mainly because of internal relaxation and tidal forces. In this context, the study of dynamically evolved OCs is necessary to properly understand such processes. We present a comprehensive Washington CT1 photometric analysis of six sparse OCs, namely ESO 518-3, Ruprecht 121, ESO 134-12, NGC 6573, ESO 260-7, and ESO 065-7. We employed Markov chain Monte Carlo simulations to robustly determine the central coordinates and the structural parameters and T1 × (C - T1) colour-magnitude diagrams cleaned from field contamination were used to derive the fundamental parameters. ESO 518-03, Ruprecht 121, ESO 134-12, and NGC 6573 resulted to be of nearly the same young age [8.2 ≤log(t yr-1) ≤ 8.3]; ESO 260-7 and ESO065-7 are of intermediate age [9.2 ≤log(t yr-1) ≤ 9.4]. All studied OCs are located at similar Galactocentric distances (RG ˜6-6.9 kpc), considering uncertainties, except for ESO 260-7 (RG = 8.9 kpc). These OCs are in a tidally filled regime and are dynamically evolved, since they are much older than their half-mass relaxation times (t/trh ≳ 30) and present signals of low-mass star depletion. We distinguished two groups: those dynamically evolving towards final disruptions and those in an advanced dynamical evolutionary stage. Although we do not rule out that the Milky Way potential could have made differentially faster their dynamical evolutions, we speculate here with the possibility that they have been mainly driven by initial formation conditions.

KPOT_wlanger_1: State of the Diffuse ISM: Galactic Observations of the Terahertz CII Line (GOT CPlus)

NASA Astrophysics Data System (ADS)

Langer, W.

2007-10-01

Star formation activity throughout the Galactic disk depends on the thermal and dynamical state of the interstellar gas, which in turn depends on heating and cooling rates, modulated by the gravitational potential and shock and turbulent pressures. Molecular cloud formation, and thus the star formation, may be regulated by pressures in the interstellar medium (ISM). To understand these processes we need information about the properties of the diffuse atomic and diffuse molecular gas clouds, and Photon Dominated Regions (PDR). An important tracer of these regions is the CII line at 158 microns (1900.5 GHz). We propose a "pencil-beam" survey of CII with HIFI band 7b, based on deep integrations and systematic sparse sampling of the Galactic disk plus selected targets, totaling over 900 lines of sight. We will detect both emission and, against the bright inner Galaxy and selected continuum sources, absorption lines. These spectra will provide the astronomical community with a large rich statistical database of the diffuse cloud properties throughout the Galaxy for understanding the Milky Way ISM and, by extension, other galaxies. It will be extremely valuable for determining the properties of the atomic gas, the role of barometric pressure and turbulence in cloud evolution, and the properties of the interface between the atomic and molecular clouds. The CII line is one of the major ISM cooling lines and is present throughout the Galactic plane. It is the strongest far-IR emission line in the Galaxy, with a total luminosity about a 1000 times that of the CO J=1-0 line. Combined with other data, it can be used to determine density, pressure, and radiation environment in gas clouds, and PDRs, and their dynamics via velocity fields. HSO is the best opportunity over the next several years to probe the ISM in this tracer and will provide a template for large-scale surveys with dedicated small telescopes and future surveys of other important ISM tracers.

SDP_wlanger_3: State of the Diffuse ISM: Galactic Observations of the Terahertz CII Line (GOT CPlus)

NASA Astrophysics Data System (ADS)

Langer, W.

2011-09-01

Star formation activity throughout the Galactic disk depends on the thermal and dynamical state of the interstellar gas, which in turn depends on heating and cooling rates, modulated by the gravitational potential and shock and turbulent pressures. Molecular cloud formation, and thus the star formation, may be regulated by pressures in the interstellar medium (ISM). To understand these processes we need information about the properties of the diffuse atomic and diffuse molecular gas clouds, and Photon Dominated Regions (PDR). An important tracer of these regions is the CII line at 158 microns (1900.5 GHz). We propose a "pencil-beam" survey of CII with HIFI band 7b, based on deep integrations and systematic sparse sampling of the Galactic disk plus selected targets, totaling over 900 lines of sight. We will detect both emission and, against the bright inner Galaxy and selected continuum sources, absorption lines. These spectra will provide the astronomical community with a large rich statistical database of the diffuse cloud properties throughout the Galaxy for understanding the Milky Way ISM and, by extension, other galaxies. It will be extremely valuable for determining the properties of the atomic gas, the role of barometric pressure and turbulence in cloud evolution, and the properties of the interface between the atomic and molecular clouds. The CII line is one of the major ISM cooling lines and is present throughout the Galactic plane. It is the strongest far-IR emission line in the Galaxy, with a total luminosity about a 1000 times that of the CO J=1-0 line. Combined with other data, it can be used to determine density, pressure, and radiation environment in gas clouds, and PDRs, and their dynamics via velocity fields. HSO is the best opportunity over the next several years to probe the ISM in this tracer and will provide a template for large-scale surveys with dedicated small telescopes and future surveys of other important ISM tracers.

Observing the Super-Massive Black Hole of the Galactic center with Simbol-X .

NASA Astrophysics Data System (ADS)

Goldwurm, A.

The Center of our Galaxy is one of the prime objective of the Simbol-X mission. This region of several square degrees around the dynamical center of the galaxy hosts a large variety of high energy sources and violent phenomena that involve different non-thermal processes contributing to the hard X-ray emission from the region. Here we present in detail the case for the observation of Sgr A*, the super-massive black hole of the galactic nucleus, with Simbol-X, stressing on the presently open questions and on the crucial measurements that will be performed in the hard X-ray domain with this formation-flying hard X-ray focussing telescope expected to flight in the next decade.

On the Origin of Hyperfast Neutron Stars

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Gualandris, A.; Portegies Zwart, S.

2008-05-01

We propose an explanation for the origin of hyperfast neutron stars (e.g. PSR B1508+55, PSR B2224+65, RX J0822 4300) based on the hypothesis that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star (or its helium core) which attained its peculiar velocity (similar to that of the neutron star) in the course of a strong three- or four-body dynamical encounter in the core of a young massive star cluster. This hypothesis implies that the dense cores of star clusters (located either in the Galactic disk or near the Galactic centre) could also produce the so-called hypervelocity stars ordinary stars moving with a speed of ~ 1 000 km s-1.

Massive black holes in galactic halos?

NASA Technical Reports Server (NTRS)

Lacey, C. G.; Ostriker, J. P.

1985-01-01

In the present attempt to resolve the problems posed by the composition of dark halos and the heating of stellar disks, under the assumption that galaxy halos are composed of massive black holes, it is noted that the black holes must have masses of the order of one million solar masses. The heating mechanism proposed yields predictions for the dependence of the velocity dispersion on time, and for the shape of the velocity ellipsoid, which are in good agreement with observations. Attention is given to the constraints set by dynamical friction causing black holes to spiral to the Galactic center, by the possible presence of dark matter in dwarf spheroidal galaxies, and by the accretion of interstellar gas by the black holes that produce luminous objects in the Galaxy.

Star-disc interaction in galactic nuclei: formation of a central stellar disc

NASA Astrophysics Data System (ADS)

Panamarev, Taras; Shukirgaliyev, Bekdaulet; Meiron, Yohai; Berczik, Peter; Just, Andreas; Spurzem, Rainer; Omarov, Chingis; Vilkoviskij, Emmanuil

2018-05-01

We perform high-resolution direct N-body simulations to study the effect of an accretion disc on stellar dynamics in an active galactic nucleus (AGN). We show that the interaction of the nuclear stellar cluster (NSC) with the gaseous accretion disc (AD) leads to formation of a stellar disc in the central part of the NSC. The accretion of stars from the stellar disc on to the super-massive black hole is balanced by the capture of stars from the NSC into the stellar disc, yielding a stationary density profile. We derive the migration time through the AD to be 3 per cent of the half-mass relaxation time of the NSC. The mass and size of the stellar disc are 0.7 per cent of the mass and 5 per cent of the influence radius of the super-massive black hole. An AD lifetime shorter than the migration time would result in a less massive nuclear stellar disc. The detection of such a stellar disc could point to past activity of the hosting galactic nucleus.

Galactic cosmic-ray mediation of a spherical solar wind flow. 1: The steady state cold gas hydrodynamical approximation

NASA Technical Reports Server (NTRS)

Le Roux, J. A.; Ptuskin, V. S.

1995-01-01

Realistic models of the outer heliosphere should consider that the interstellar cosmic-ray pressure becomes comparable to pressures in the solar wind at distances more than 100 AU from the Sun. The cosmic-ray pressure dynamically affects solar wind flow through deceleration. This effect, which occurs over a scale length of the order of the effective diffusion length at large radial distances, has important implications for cosmic-ray modulation and acceleration. As a first step toward solution of this nonlinear problem, a steady state numerical model was developed for a relatively cold spherical solar wind flow which encounters the confining isotropic pressure of the surrounding Galactic medium. This pressure is assumed to be dominated by energetic particles (Galactic cosmic rays). The system of equations, which are solved self-consistently, includes the relevant hydrodynamical equations for the solar wind flow and the spherical cosmic-ray transport equation. To avoid the closure parameter problem of the two-fluid model, the latter equation is solved for the energy-dependent cosmic-ray distribution function.

Galactic disks, infall, and the global value of Omega

NASA Technical Reports Server (NTRS)

Toth, G.; Ostriker, J. P.

1992-01-01

Stringent limits on the current rate of infall of satellite systems onto spiral galaxies are set on the basis of the thinness and coldness of Galactic disks. For infalling satellites on isotropically oriented circular orbits, it is shown that, due to scattering, the thermal energy gain of the disk exceeds the satellite energy loss from dynamical friction by a factor of 1.6, with 25 percent deposited in z motion and 75 percent in planar motions. It is found that no more than 4 percent of the Galactic mass inside the solar radius can have accreted within the last 5 billion years, or else its scale and its Toomre Q-parameter would exceed observed values. In standard cold-dark-matter-dominated models for the growth of structure with Omega sub tot of 1, the mass accreted in dark matter lumps rises faster than t exp 2/3 and would exceed 28 percent in the last 5 Gyr. It is proposed that heating from satellite infall accounts for a substantial fraction of the increase of velocity dispersion and scale height with age that is observed in the Galaxy.

The Galactic Distribution of Massive Star Formation from the Red MSX Source Survey

NASA Astrophysics Data System (ADS)

Figura, Charles C.; Urquhart, J. S.

2013-01-01

Massive stars inject enormous amounts of energy into their environments in the form of UV radiation and molecular outflows, creating HII regions and enriching local chemistry. These effects provide feedback mechanisms that aid in regulating star formation in the region, and may trigger the formation of subsequent generations of stars. Understanding the mechanics of massive star formation presents an important key to understanding this process and its role in shaping the dynamics of galactic structure. The Red MSX Source (RMS) survey is a multi-wavelength investigation of ~1200 massive young stellar objects (MYSO) and ultra-compact HII (UCHII) regions identified from a sample of colour-selected sources from the Midcourse Space Experiment (MSX) point source catalog and Two Micron All Sky Survey. We present a study of over 900 MYSO and UCHII regions investigated by the RMS survey. We review the methods used to determine distances, and investigate the radial galactocentric distribution of these sources in context with the observed structure of the galaxy. The distribution of MYSO and UCHII regions is found to be spatially correlated with the spiral arms and galactic bar. We examine the radial distribution of MYSOs and UCHII regions and find variations in the star formation rate between the inner and outer Galaxy and discuss the implications for star formation throughout the galactic disc.

Active galactic nucleus outflows in galaxy discs

NASA Astrophysics Data System (ADS)

Hartwig, Tilman; Volonteri, Marta; Dashyan, Gohar

2018-05-01

Galactic outflows, driven by active galactic nuclei (AGNs), play a crucial role in galaxy formation and in the self-regulated growth of supermassive black holes (BHs). AGN feedback couples to and affects gas, rather than stars, and in many, if not most, gas-rich galaxies cold gas is rotationally supported and settles in a disc. We present a 2D analytical model for AGN-driven outflows in a gaseous disc and demonstrate the main improvements, compared to existing 1D solutions. We find significant differences for the outflow dynamics and wind efficiency. The outflow is energy-driven due to inefficient cooling up to a certain AGN luminosity (˜1043 erg s-1 in our fiducial model), above which the outflow remains momentum-driven in the disc up to galactic scales. We reproduce results of 3D simulations that gas is preferentially ejected perpendicular to the disc and find that the fraction of ejected interstellar medium is lower than in 1D models. The recovery time of gas in the disc, defined as the free-fall time from the radius to which the AGN pushes the ISM at most, is remarkably short, of the order 1 Myr. This indicates that AGN-driven winds cannot suppress BH growth for long. Without the inclusion of supernova feedback, we find a scaling of the BH mass with the halo velocity dispersion of MBH ∝ σ4.8.

Interstellar Matters: Neutral Hydrogen and the Galactic Magnetic Field

NASA Astrophysics Data System (ADS)

Verschuur, Gerrit; Schmelz, Joan T.; Asgari-Targhi asgari-Targhi, M.

2018-01-01

The physics of the interstellar medium was revolutionized by the observations of the Galactic Arecibo L-Band Feed Array (GALFA) HI survey done at the Arecibo Observatory. The high-resolution, high-sensitivity, high-dynamic- range images show complex, tangled, extended filaments, and reveal that the fabric of the neutral interstellar medium is deeply tied to the structure of the ambient magnetic field. This discovery prompts an obvious question – how exactly is the interstellar {\\it neutral} hydrogen being affected by the galactic magnetic field? We look into this question by examining a set of GALFA-HI data in great detail. We have chosen a long, straight filament in the southern galactic sky. This structure is both close by and isolated in velocity space. Gaussian analysis of profiles both along and across the filament reveal internal structure – braided strands that can be traced through the simplest part, but become tangled in more complex segments. These braids do not resemble in any way the old spherical HI clouds and rudimentary pressure balance models that were used to explain the pre-GALFA- HI interstellar medium. It is clear that these structures are created, constrained, and dominated by magnetic fields. Like many subfields of astronomy before it, e.g., physics of the solar coronal, extragalactic radio jets, and pulsar environment, scientists are confronted with observations that simply cannot be explained by simple hydrodynamics and are forced to consider magneto-hydrodynamics.

Dynamical origin of non-thermal states in galactic filaments

NASA Astrophysics Data System (ADS)

Di Cintio, Pierfrancesco; Gupta, Shamik; Casetti, Lapo

2018-03-01

Observations strongly suggest that filaments in galactic molecular clouds are in a non-thermal state. As a simple model of a filament, we study a two-dimensional system of self-gravitating point particles by means of numerical simulations of the dynamics, with various methods: direct N-body integration of the equations of motion, particle-in-cell simulations, and a recently developed numerical scheme that includes multiparticle collisions in a particle-in-cell approach. Studying the collapse of Gaussian overdensities, we find that after the damping of virial oscillations the system settles in a non-thermal steady state whose radial density profile is similar to the observed ones, thus suggesting a dynamical origin of the non-thermal states observed in real filaments. Moreover, for sufficiently cold collapses, the density profiles are anticorrelated with the kinetic temperature, i.e. exhibit temperature inversion, again a feature that has been found in some observations of filaments. The same happens in the state reached after a strong perturbation of an initially isothermal cylinder. Finally, we discuss our results in the light of recent findings in other contexts (including non-astrophysical ones) and argue that the same kind of non-thermal states may be observed in any physical system with long-range interactions.

Evidence for the interaction of the IRS 16 wind with the ionized and molecular gas at the Galactic center

NASA Technical Reports Server (NTRS)

Yusef-Zadeh, Farhad; Wardle, Mark

1993-01-01

We present a number of high-resolution radio images showing evidence for the dynamical interaction of the outflow arising from the IRS 16 complex with the ionized gas associated with the Northern Arm of Sgr A West, and with the northwestern segment of the circumnuclear molecular disk which engulfs the inner few parsecs of the Galactic center. We suggest that the wind disturbs the dynamics of the Northern Arm within 0.1 pc of the center, is responsible for the waviness of the arm at larger distances, and is collimated by Sgr A West and the circumnuclear disk. The waviness is discussed in terms of the Rayleigh-Taylor instability induced by the ram pressure of the wind incident on the surface of the Northern Arm. Another consequence of this interaction is the strong mid-IR polarization of the Northern Arm in the vicinity of the IRS 16 complex which is explained as a result of the ram pressure of the wind compressing the gas and the magnetic field.

Our cometary environment

NASA Astrophysics Data System (ADS)

Napier, W. M.; Clube, S. V. M.

1997-03-01

The encounter of a small armada of spacecraft with Halley's Comet in 1986, the disintegration and multiple impact of Comet Shoemaker - Levy 9 on Jupiter in 1994, and the application of new technologies to the detection of distant solar system bodies, have led to great revisions in the understanding of comets. Further, rapid improvements in computing power and numerical techniques have permitted the dynamical evolution of comets and asteroids to be followed far into the future and past, and the relationships between families of small interplanetary bodies to be explored. The small body environment is now generally recognized as strongly interacting with the terrestrial one, and may be hazardous on timescales of human as well as geological interest. We review our current understanding of the cometary environment, with particular regard to the hazard it presents. It appears that many comets are handed down from the Oort - Öpik cloud, which is dynamically sensitive to the galactic environment, through the planetary system into Earth-crossing orbits. Thus, the terrestrial environment is subject to stresses which vary cyclically on a number of timescales from planetary to galactic.

COSMIC-LAB: unveling the true nature of Terzan 5, a pristine fragment of the Galactic bulge

NASA Astrophysics Data System (ADS)

Ferraro, Francesco

2012-10-01

We have discovered that Terzan5, a stellar system in the Galactic bulge, harbors two stellar populations with different iron content {Delta[Fe/H] 0.5 dex} and possibly different ages {Ferraro et al. 2009, Nature 462, 483}. Moreover, the observed chemical patterns {Origlia et al. 2011, ApJ 726, L20} significantly differ from those observed in any known genuine GC. These evidences demonstrate that, similarly to omega Centauri in the halo, Terzan5 is NOT a genuine globular cluster {GC}, but a stellar system that was able to retain the gas ejected by violent supernova {SN} explosions.Indeed the striking chemical similarity with the bulge stars suggests that Terzan5 and the Galactic bulge shared the same star formation and chemical enrichment processes, driven by an exceptional amount of SNeII explosions {this is also the key to understand the origin of the extraordinary population of millisecond pulsars in Terzan5}. A quite intriguing scenario is emerging from these observations: Terzan5 could be the relic of one of the massive clumps that contributed {through strong dynamical interactions with other pre-formed and internally-evolved sub-structures} to the formation of the Galactic bulge.Here we propose to use the WFC3 to accurately measure the age of the two populations directly from the main sequence turn-off luminosities. Precisely dating the first and second burst of star formation is a crucial step for the correct reconstruction of the evolutionary history of Terzan5, with a significant impact on our comprehension of the formation processes of the Milky Way bulge and, more in general, of galactic spheroids.

HST/COS OBSERVATIONS OF GALACTIC HIGH-VELOCITY CLOUDS: FOUR ACTIVE GALACTIC NUCLEUS SIGHT LINES THROUGH COMPLEX C

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

Shull, J. Michael; Stevans, Matthew; Danforth, Charles

2011-10-01

We report ultraviolet spectra of Galactic high-velocity clouds (HVCs) in Complex C, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), together with new 21 cm spectra from the Green Bank Telescope. The wide spectral coverage and higher signal-to-noise ratio, compared to previous HST spectra, provide better velocity definition of the HVC absorption, additional ionization species (including high ions), and improved abundances in this halo gas. Complex C has a metallicity of 10%-30% solar and a wide range of ions, suggesting dynamical and thermal interactions with hot gas in the Galactic halo. Spectra in the COSmore » medium-resolution G130M (1133-1468 A) and G160M (1383-1796 A) gratings detect ultraviolet absorption lines from eight elements in low-ionization states (O I, N I, C II, S II, Si II, Al II, Fe II, P II) and three elements in intermediate- and high-ionization states (Si III, Si IV, C IV, N V). Our four active galactic nucleus sight lines toward Mrk 817, Mrk 290, Mrk 876, and PG 1259+593 have high-velocity H I and O VI column densities, log N{sub Hi}= 19.39-20.05 and log N{sub Ovi}= 13.58-14.10, with substantial amounts of kinematically associated photoionized gas. The high-ion abundance ratios are consistent with cooling interfaces between photoionized and collisionally ionized gas: N(C IV)/N(O VI) {approx} 0.3-0.5, N(Si IV)/N(O VI) {approx} 0.05-0.11, N(N V)/N(O VI) {approx} 0.07-0.13, and N(Si IV)/N(Si III) {approx}0.2.« less

Disruption of the Globular Cluster Pal 5

NASA Technical Reports Server (NTRS)

Miller, R. H.; Smith, B. F.; Cuzzi, Jeffrey N. (Technical Monitor)

1995-01-01

Orbit calculations suggest that the sparse globular cluster, Pal 5, will pass within 7 kpc of the Galactic center the next time it crosses the plane, where it might be destroyed by tidal stresses. We study this problem, treating Pal 5 as a self-consistent dynamical system orbiting through an external potential that represents the Galaxy. The first part of the problem is to find suitable analytic approximations to the Galactic potential. They must be valid in all regions the cluster is likely to explore. Observed velocity and positional data for Pal 5 are used as initial conditions to determine the orbit. Methods we used for a different problem some 12 years ago have been adapted to this problem. Three experiments have been run, with M/L= 1, 3, and 10, for the cluster model. The cluster blew up shortly after passing through the Galactic plane (about 130 Myrs after the beginning of the run) with M/L=1. At M/L = 3 and 10 the cluster survived, although it got quite a kick in the fundamental mode on passing through the plane. But the fundamental mode oscillation died out in a couple of oscillation cycles at M/L=10. Pal 5 will probably be destroyed on its next crossing of the Galactic plane if M/L=1, but it can survive (albeit with fairly heavy damage) if NI/L=3. We haven't tried to trap the mass limits more closely than that. Pal 5 comes through pretty well unscathed at M/L=10. An interesting follow-up experiment would be to back the cluster up along its orbit to look at its previous passage through the Galactic plane, to see what kind of object it might have been at earlier times.

Influence of galactic arm scale dynamics on the molecular composition of the cold and dense ISM. I. Observed abundance gradients in dense clouds

NASA Astrophysics Data System (ADS)

Ruaud, M.; Wakelam, V.; Gratier, P.; Bonnell, I. A.

2018-04-01

Aim. We study the effect of large scale dynamics on the molecular composition of the dense interstellar medium during the transition between diffuse to dense clouds. Methods: We followed the formation of dense clouds (on sub-parsec scales) through the dynamics of the interstellar medium at galactic scales. We used results from smoothed particle hydrodynamics (SPH) simulations from which we extracted physical parameters that are used as inputs for our full gas-grain chemical model. In these simulations, the evolution of the interstellar matter is followed for 50 Myr. The warm low-density interstellar medium gas flows into spiral arms where orbit crowding produces the shock formation of dense clouds, which are held together temporarily by the external pressure. Results: We show that depending on the physical history of each SPH particle, the molecular composition of the modeled dense clouds presents a high dispersion in the computed abundances even if the local physical properties are similar. We find that carbon chains are the most affected species and show that these differences are directly connected to differences in (1) the electronic fraction, (2) the C/O ratio, and (3) the local physical conditions. We argue that differences in the dynamical evolution of the gas that formed dense clouds could account for the molecular diversity observed between and within these clouds. Conclusions: This study shows the importance of past physical conditions in establishing the chemical composition of the dense medium.

A Kinematic Survey in the Perseus Molecular Cloud: Results from the APOGEE Infrared Survey of Young Nebulous Clusters (IN-SYNC)

NASA Astrophysics Data System (ADS)

Covey, Kevin R.; Cottaar, M.; Foster, J. B.; Nidever, D. L.; Meyer, M.; Tan, J.; Da Rio, N.; Flaherty, K. M.; Stassun, K.; Frinchaboy, P. M.; Majewski, S.; APOGEE IN-SYNC Team

2014-01-01

Demographic studies of stellar clusters indicate that relatively few persist as bound structures for 100 Myrs or longer. If cluster dispersal is a 'violent' process, it could strongly influence the formation and early evolution of stellar binaries and planetary systems. Unfortunately, measuring the dynamical state of 'typical' (i.e., ~300-1000 member) young star clusters has been difficult, particularly for clusters still embedded within their parental molecular cloud. The near-infrared spectrograph for the Apache Point Observatory Galactic Evolution Experiment (APOGEE), which can measure precise radial velocities for 230 cluster stars simultaneously, is uniquely suited to diagnosing the dynamics of Galactic star formation regions. We give an overview of the INfrared Survey of Young Nebulous Clusters (IN-SYNC), an APOGEE ancillary science program that is carrying out a comparative study of young clusters in the Perseus molecular cloud: NGC 1333, a heavily embedded cluster, and IC 348, which has begun to disperse its surrounding molecular gas. These observations appear to rule out a significantly super-virial velocity dispersion in IC 348, contrary to predictions of models where a cluster's dynamics is strongly influenced by the dispersal of its primordial gas. We also summarize the properties of two newly identified spectroscopic binaries; binary systems such as these play a key role in the dynamical evolution of young clusters, and introduce velocity offsets that must be accounted for in measuring cluster velocity dispersions.

Star Formation and Gas Dynamics in Galactic Disks: Physical Processes and Numerical Models

NASA Astrophysics Data System (ADS)

Ostriker, Eve C.

2011-04-01

Star formation depends on the available gaseous ``fuel'' as well as galactic environment, with higher specific star formation rates where gas is predominantly molecular and where stellar (and dark matter) densities are higher. The partition of gas into different thermal components must itself depend on the star formation rate, since a steady state distribution requires a balance between heating (largely from stellar UV for the atomic component) and cooling. In this presentation, I discuss a simple thermal and dynamical equilibrium model for the star formation rate in disk galaxies, where the basic inputs are the total surface density of gas and the volume density of stars and dark matter, averaged over ~kpc scales. Galactic environment is important because the vertical gravity of the stars and dark matter compress gas toward the midplane, helping to establish the pressure, and hence the cooling rate. In equilibrium, the star formation rate must evolve until the gas heating rate is high enough to balance this cooling rate and maintain the pressure imposed by the local gravitational field. In addition to discussing the formulation of this equilibrium model, I review the current status of numerical simulations of multiphase disks, focusing on measurements of quantities that characterize the mean properties of the diffuse ISM. Based on simulations, turbulence levels in the diffuse ISM appear relatively insensitive to local disk conditions and energetic driving rates, consistent with observations. It remains to be determined, both from observations and simulations, how mass exchange processes control the ratio of cold-to-warm gas in the atomic ISM.

Dynamical constraints on the dark matter distribution in the Milky Way

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

Pato, Miguel; Iocco, Fabio; Bertone, Gianfranco, E-mail: migpato@gmail.com, E-mail: fabio.iocco.astro@gmail.com, E-mail: g.bertone@uva.nl

2015-12-01

An accurate knowledge of the dark matter distribution in the Milky Way is of crucial importance for galaxy formation studies and current searches for particle dark matter. In this paper we set new dynamical constraints on the Galactic dark matter profile by comparing the observed rotation curve, updated with a comprehensive compilation of kinematic tracers, with that inferred from a wide range of observation-based morphologies of the bulge, disc and gas. The generalised Navarro-Frenk-White (NFW) and Einasto dark matter profiles are fitted to the data in order to determine the favoured ranges of local density, slope and scale radius. Formore » a representative baryonic model, a typical local circular velocity v{sub 0}=230 km/s and a distance of the Sun to the Galactic centre R{sub 0}=8 kpc, we find a local dark matter density ρ{sub 0} = 0.420{sup +0.021}{sub −0.018} (2σ) ± 0.025 GeV/cm{sup 3} (ρ{sub 0} = 0.420{sup +0.019}{sub −0.021} (2σ) ± 0.026 GeV/cm{sup 3}) for NFW (Einasto), where the second error is an estimate of the systematic due to baryonic modelling. Apart from the Galactic parameters, the main sources of uncertainty inside and outside the solar circle are baryonic modelling and rotation curve measurements, respectively. Upcoming astronomical observations are expected to reduce all these uncertainties substantially over the coming years.« less

A dynamical model for gas flows, star formation and nuclear winds in galactic centres

NASA Astrophysics Data System (ADS)

Krumholz, Mark R.; Kruijssen, J. M. Diederik; Crocker, Roland M.

2017-04-01

We present a dynamical model for gas transport, star formation and winds in the nuclear regions of galaxies, focusing on the Milky Way's Central Molecular Zone (CMZ). In our model angular momentum and mass are transported by a combination of gravitational and bar-driven acoustic instabilities. In gravitationally unstable regions the gas can form stars, and the resulting feedback drives both turbulence and a wind that ejects mass from the CMZ. We show that the CMZ is in a quasi-steady state where mass deposited at large radii by the bar is transported inwards to a star-forming, ring-shaped region at ˜100 pc from the Galactic Centre, where the shear reaches a minimum. This ring undergoes episodic starbursts, with bursts lasting ˜5-10 Myr occurring at ˜20-40 Myr intervals. During quiescence the gas in the ring is not fully cleared, but is driven out of a self-gravitating state by the momentum injected by expanding supernova remnants. Starbursts also drive a wind off the star-forming ring, with a time-averaged mass flux comparable to the star formation rate. We show that our model agrees well with the observed properties of the CMZ, and places it near a star formation minimum within the evolutionary cycle. We argue that such cycles of bursty star formation and winds should be ubiquitous in the nuclei of barred spiral galaxies, and show that the resulting distribution of galactic nuclei on the Kennicutt-Schmidt relation is in good agreement with that observed in nearby galaxies.

New Observational Constraints to Milky Way Chemodynamical Models

NASA Astrophysics Data System (ADS)

Chiappini, Cristina; Minchev, Ivan; Anders, Friedrich; Brauer, Dorothee; Boeche, Corrado; Martig, Marie

Galactic Archaeology, i.e. the use of chemo-dynamical information for stellar samples covering large portions of the Milky Way to infer the dominant processes involved in its formation and evolution, is now a powerful method thanks to the large recently completed and ongoing spectroscopic surveys. It is now important to ask the right questions when analyzing and interpreting the information contained in these rich datasets. To this aim, we have developed a chemodynamical model for the Milky Way that provides quantitative predictions to be compared with the chemo-kinematical properties extracted from the stellar spectra. Three key parameters are needed to make the comparison between data and model predictions useful in order to advance in the field, namely: precise proper-motions, distances and ages. The uncertainties involved in the estimate of ages and distances for field stars are currently the main obstacles in the Galactic Archaeology method. Two important developments might change this situation in the near future: asteroseismology and the now launched Gaia. When combined with the large datasets from surveys like RAVE, SEGUE, LAMOST, Gaia-ESO, APOGEE, HERMES and the future 4MOST we will have the basic ingredients for the reconstruction of the MW history in hands. In the light of these observational advances, the development of detailed chemo-dynamical models tailored to the Milky Way is urgently needed in the field. Here we show the steps we have taken, both in terms of data analysis and modelling. The examples shown here illustrate how powerful can the Galactic Archaeology method become once ages and distances are known with better precision than what is currently feasible.

Dynamical evolution of globular-cluster systems in clusters of galaxies

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

Muzzio, J.C.

1987-04-01

The dynamical processes that affect globular-cluster systems in clusters of galaxies are analyzed. Two-body and impulsive approximations are utilized to study dynamical friction, drag force, tidal stripping, tidal radii, globular-cluster swapping, tidal accretion, and galactic cannibalism. The evolution of galaxies and the collision of galaxies are simulated numerically; the steps involved in the simulation are described. The simulated data are compared with observations. Consideration is given to the number of galaxies, halo extension, location of the galaxies, distribution of the missing mass, nonequilibrium initial conditions, mass dependence, massive central galaxies, globular-cluster distribution, and lost globular clusters. 116 references.

On the dynamical basis of the classification of normal galaxies

PubMed Central

Haass, J.; Bertin, G.; Lin, C. C.

1982-01-01

Some realistic galaxy models have been found to support discrete unstable spiral modes. Here, through the study of the relevant physical mechanisms and an extensive numerical investigation of the properties of the dominant modes in a wide class of galactic equilibria, we show how spiral structures are excited with different morphological features, depending on the properties of the equilibrium model. We identify the basic dynamical parameters and mechanisms and compare the resulting morphology of spiral modes with the actual classification of galaxies. The present study suggests a dynamical basis for the transition among various types and subclasses of normal and barred spiral galaxies. Images PMID:16593200

Resolving Star Formation, Multiphase ISM Structure, and Wind Driving with MHD and RHD Models of Galactic Disks

NASA Astrophysics Data System (ADS)

Ostriker, Eve

Current studies of star and galaxy formation have concluded that energetic feedback from young stars and supernovae (SNe) is crucial, both for controlling observed interstellar medium (ISM) properties and star formation rates in the Milky Way and other galaxies, and for driving galactic winds that govern the baryon abundance in dark matter halos. However, in many numerical studies of the ISM, energy inputs have not been implemented self-consistently with the evolving rate of gravitational collapse to make stars, or have considered only isolated star-forming clouds without a realistic galactic environment (including sheared rotation and externally-originating SNe), or have not directly incorporated radiation, magnetic, and chemical effects that are important or even dominant. In models of galaxy formation and evolution in the cosmic context, galactic winds are indispensable but highly uncertain as the physics of superbubble evolution and radiation-gas interactions cannot be resolved. Our central objectives are (1) to address the above limitations of current models, developing self-consistent simulations of the multiphase ISM in disk galaxies that resolve both star formation and stellar feedback, covering the range of scales needed to connect star cluster formation to galactic superwind ejection, and the range of environments from dwarfs to ULIRGs; and (2) to analyze the detailed properties of the gas, magnetic field, radiation field, and star formation/SNe in our simulations, including dependencies on local galactic disk environment, and to connect intrinsic properties with observable diagnostics. The proposed project will employ the Athena code for numerical magneto-hydrodynamic (MHD) and radiation-hydrodynamic (RHD) simulations, using comprehensive physics modules that have been developed, tested, and demonstrated in sample simulations. We will consider local ``shearing box'' disk models with gas surface density Sigma = 2 - 10,000 Msun/pc^2, and a range of stellar potentials and galactic rotation rates. Our simulations follow all thermal phases of the gas, the driving of turbulence, and the expulsion of material in high-velocity galactic winds as well as the circulation of lowervelocity material in galactic ``fountains.'' We resolve gravitational collapse and apply stellar population modeling to determine radiation emitted by star cluster particles, and both in situ and runaway O-star SN events. With time-dependent chemistry, we will be able to follow C+/C/CO transitions and assess the relationship between the observed molecular component and self-gravitating or diffuse clouds in varying galactic environments, also determining how cloud properties (e.g. distributions of mass, size, virial parameter, internal/external pressure, magnetization) and lifetimes depend on environment. We will also investigate the dependence on local galactic environment of: * mass and volume fractions, and turbulent and magnetic state, of each thermal and chemical ISM phase * star formation rate, and galactic wind mass loss rate in each ISM phase * metrics of ISM energy gain/loss, large-scale force balance, wind acceleration * roles of SN and radiation feedback in setting cloud SFEs, overall SFRs, and wind massloss rates Our models will be valuable for interpreting a wide range of observations with Chandra, Hubble, Spitzer, Herschel, Planck, and ground-based telescopes. Obtaining self-consistent solutions for the dynamical, thermal, magnetic, chemical, and radiative state of the star-forming ISM is a long-sought goal of galactic theory. Understanding why ISM and star formation properties vary among and within galaxies is essential for interpreting new multiwavelength extragalactic surveys. Connecting galactic winds to star formation via resolved physical mechanisms will provide a missing link in contemporary galaxy formation models. With our planned research program, we are in a position to achieve all of these advances.

The Of?p stars of the Magellanic Clouds: Are they strongly magnetic?

NASA Astrophysics Data System (ADS)

Munoz, M.; Wade, G. A.; Nazé, Y.; Bagnulo, S.; Puls, J.

2018-01-01

All known Galactic Of?p stars have been shown to host strong, organized, magnetic fields. Recently, five Of?p stars have been discovered in the Magellanic Clouds. They posses photometric (Nazé et al., 2015) and spectroscopic (Walborn et al., 2015) variability compatible with the Oblique Rotator Model (ORM). However, their magnetic fields have yet to be directly detected. We have developed an algorithm allowing for the synthesis of photometric observables based on the Analytic Dynamical Magnetosphere (ADM) model by Owocki et al. (2016). We apply our model to OGLE photometry in order to constrain their magnetic geometries and surface dipole strengths. We predict that the field strengths for some of theses candidate extra-Galactic magnetic stars may be within the detection limits of the FORS2 instrument

Galactic neutral hydrogen and the magnetic ISM foreground

NASA Astrophysics Data System (ADS)

Clark, S. E.

2018-05-01

The interstellar medium is suffused with magnetic fields, which inform the shape of structures in the diffuse gas. Recent high-dynamic range observations of Galactic neutral hydrogen, combined with novel data analysis techniques, have revealed a deep link between the morphology of neutral gas and the ambient magnetic field. At the same time, an observational revolution is underway in low-frequency radio polarimetry, driven in part by the need to characterize foregrounds to the cosmological 21-cm signal. A new generation of experiments, capable of high angular and Faraday depth resolution, are revealing complex filamentary structures in diffuse polarization. The relationship between filamentary structures observed in radio-polarimetric data and those observed in atomic hydrogen is not yet well understood. Multiwavelength observations will enable new insights into the magnetic interstellar medium across phases.

Tracing the evolution of the Galactic bulge with chemodynamical modelling of alpha-elements

NASA Astrophysics Data System (ADS)

Friaça, A. C. S.; Barbuy, B.

2017-02-01

Context. Galactic bulge abundances can be best understood as indicators of bulge formation and nucleosynthesis processes by comparing them with chemo-dynamical evolution models. Aims: The aim of this work is to study the abundances of alpha-elements in the Galactic bulge, including a revision of the oxygen abundance in a sample of 56 bulge red giants. Methods: Literature abundances for O, Mg, Si, Ca and Ti in Galactic bulge stars are compared with chemical evolution models. For oxygen in particular, we reanalysed high-resolution spectra obtained using FLAMES+UVES on the Very Large Telescope, now taking each star's carbon abundances, derived from CI and C2 lines, into account simultaneously. Results: We present a chemical evolution model of alpha-element enrichment in a massive spheroid that represents a typical classical bulge evolution. The code includes multi-zone chemical evolution coupled with hydrodynamics of the gas. Comparisons between the model predictions and the abundance data suggest a typical bulge formation timescale of 1-2 Gyr. The main constraint on the bulge evolution is provided by the O data from analyses that have taken the C abundance and dissociative equilibrium into account. Mg, Si, Ca and Ti trends are well reproduced, whereas the level of overabundance critically depends on the adopted nucleosynthesis prescriptions. Observations collected both at the European Southern Observatory, Paranal, Chile (ESO programmes 71.B-0617A, 73.B0074A, and GTO 71.B-0196)

The supernova-gamma-ray burst-jet connection.

PubMed

Hjorth, Jens

2013-06-13

The observed association between supernovae and gamma-ray bursts represents a cornerstone in our understanding of the nature of gamma-ray bursts. The collapsar model provides a theoretical framework for this connection. A key element is the launch of a bipolar jet (seen as a gamma-ray burst). The resulting hot cocoon disrupts the star, whereas the (56)Ni produced gives rise to radioactive heating of the ejecta, seen as a supernova. In this discussion paper, I summarize the observational status of the supernova-gamma-ray burst connection in the context of the 'engine' picture of jet-driven supernovae and highlight SN 2012bz/GRB 120422A--with its luminous supernova but intermediate high-energy luminosity--as a possible transition object between low-luminosity and jet gamma-ray bursts. The jet channel for supernova explosions may provide new insights into supernova explosions in general.

Gamma-ray burst theory after Swift.

PubMed

Piran, Tsvi; Fan, Yi-Zhong

2007-05-15

Afterglow observations in the pre-Swift era confirmed to a large extend the relativistic blast wave model for gamma-ray bursts (GRBs). Together with the observations of properties of host galaxies and the association with (type Ic) SNe, this has led to the generally accepted collapsar origin of long GRBs. However, most of the afterglow data was collected hours after the burst. The X-ray telescope and the UV/optical telescope onboard Swift are able to slew to the direction of a burst in real time and record the early broadband afterglow light curves. These observations, and in particular the X-ray observations, resulted in many surprises. While we have anticipated a smooth transition from the prompt emission to the afterglow, many observed that early light curves are drastically different. We review here how these observations are changing our understanding of GRBs.

Simulating galactic dust grain evolution on a moving mesh

NASA Astrophysics Data System (ADS)

McKinnon, Ryan; Vogelsberger, Mark; Torrey, Paul; Marinacci, Federico; Kannan, Rahul

2018-05-01

Interstellar dust is an important component of the galactic ecosystem, playing a key role in multiple galaxy formation processes. We present a novel numerical framework for the dynamics and size evolution of dust grains implemented in the moving-mesh hydrodynamics code AREPO suited for cosmological galaxy formation simulations. We employ a particle-based method for dust subject to dynamical forces including drag and gravity. The drag force is implemented using a second-order semi-implicit integrator and validated using several dust-hydrodynamical test problems. Each dust particle has a grain size distribution, describing the local abundance of grains of different sizes. The grain size distribution is discretised with a second-order piecewise linear method and evolves in time according to various dust physical processes, including accretion, sputtering, shattering, and coagulation. We present a novel scheme for stochastically forming dust during stellar evolution and new methods for sub-cycling of dust physics time-steps. Using this model, we simulate an isolated disc galaxy to study the impact of dust physical processes that shape the interstellar grain size distribution. We demonstrate, for example, how dust shattering shifts the grain size distribution to smaller sizes resulting in a significant rise of radiation extinction from optical to near-ultraviolet wavelengths. Our framework for simulating dust and gas mixtures can readily be extended to account for other dynamical processes relevant in galaxy formation, like magnetohydrodynamics, radiation pressure, and thermo-chemical processes.

A Statistical Study of the Southern Fermi Bubble in UV Absorption Spectra

NASA Astrophysics Data System (ADS)

Karim, Md. Tanveer; Fox, Andrew; Jenkins, Edward; Bordoloi, Rongmon; Wakker, Bart; Savage, Blair D.; Lockman, Felix; Crawford, Steve; Bland-Hawthorn, Joss; Jorgenson, Regina A.

2018-01-01

The Fermi Bubbles are two giant lobes of plasma situated at the center of the Milky Way, extending 55° above and below the Galactic Midplane. Although the Bubbles have been widely studied in multiple wavelengths, few studies have been done in UV absorption. Here we present a statistical study of the Southern Fermi Bubble using 17 QSO sightlines — 6 inside the Bubble, 11 outside — using UV absorption spectra from the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS). We searched for high-velocity clouds (HVCs) in 11 metal lines from ions of Aluminium, Carbon and Silicon. We detected HVCs in 83% of the sightlines inside the Bubble and 64% outside the Bubble, showing an enhancement in the covering fraction of HVCs in the Southern Bubble region. We also observed a decrease in vLSR of the HVCs as a function of the galactic latitude, consistent with a scenario where the identified HVCs trace the Galactic nuclear outflow, as sightlines closer to the central engine are expected to show a higher velocity. Combined with previous studies, our analysis indicates that the Southern Fermi Bubble is a dynamic environment giving rise to complex absorption features.

The Galactic fountain as an origin for the Smith Cloud

NASA Astrophysics Data System (ADS)

Marasco, A.; Fraternali, F.

2017-01-01

The recent discovery of an enriched metallicity for the Smith high-velocity H I Cloud (SC) lends support to a Galactic origin for this system. We use a dynamical model of the galactic fountain to reproduce the observed properties of the SC. In our model, fountain clouds are ejected from the region of the disc spiral arms and move through the halo interacting with a pre-existing hot corona. We find that a simple model where cold gas outflows vertically from the Perseus spiral arm reproduces the kinematics and the distance of the SC, but is in disagreement with the cloud's cometary morphology, if this is produced by ram-pressure stripping by the ambient gas. To explain the cloud morphology, we explore two scenarios: (I) the outflow is inclined with respect to the vertical direction and (II) the cloud is entrained by a fast wind that escapes an underlying superbubble. Solutions in agreement with all observational constraints can be found for both cases, the former requires outflow angles >40° while the latter requires ≳1000 km s-1 winds. All scenarios predict that the SC is in the ascending phase of its trajectory and has large - but not implausible - energy requirements.

Peanuts, brezels and bananas: food for thought on the orbital structure of the Galactic bulge

NASA Astrophysics Data System (ADS)

Portail, Matthieu; Wegg, Christopher; Gerhard, Ortwin

2015-06-01

Recent observations have discovered the presence of a box/peanut or X-shape structure in the Galactic bulge. Such box/peanut structures are common in external disc galaxies, and are well known in N-body simulations where they form following the buckling instability of a bar. From studies of analytical potentials and N-body models, it has been claimed in the past that box/peanut bulges are supported by `bananas', or x1v1 orbits. We present here a set of N-body models where instead the peanut bulge is mainly supported by brezel-like orbits, allowing strong peanuts to form with short extent relative to the bar length. This shows that stars in the X-shape do not necessarily stream along banana orbits which follow the arms of the X-shape. The brezel orbits are also found to be the main orbital component supporting the peanut shape in our recent made-to-measure dynamical models of the Galactic bulge. We also show that in these models the fraction of stellar orbits that contribute to the X-structure account for 40-45 per cent of the stellar mass.

The great escape - III. Placing post-main-sequence evolution of planetary and binary systems in a Galactic context

NASA Astrophysics Data System (ADS)

Veras, Dimitri; Evans, N. Wyn; Wyatt, Mark C.; Tout, Christopher A.

2014-01-01

Our improving understanding of the life cycle of planetary systems prompts investigations of the role of the Galenvironment before, during and after asymptotic giant branch (AGB) stellar evolution. Here, we investigate the interplay between stellar mass-loss, Galactic tidal perturbations and stellar flybys for evolving stars which host one planet, smaller body or stellar binary companion and reside in the Milky Way's bulge or disc. We find that the potential evolutionary pathways from a main sequence (MS) to a white dwarf (WD) planetary system are a strong function of Galactocentric distance only with respect to the prevalence of stellar flybys. Planetary ejection and collision with the parent star should be more common towards the bulge. At a given location anywhere in the Galaxy, if the mass-loss is adiabatic, then the secondary is likely to avoid close flybys during AGB evolution, and cannot eventually escape the resulting WD because of Galactic tides alone. Partly because AGB mass-loss will shrink a planetary system's Hill ellipsoid axes by about 20 to 40 per cent, Oort clouds orbiting WDs are likely to be more depleted and dynamically excited than on the MS.

Testing General Relativity with Stellar Orbits around the Supermassive Black Hole in Our Galactic Center.

PubMed

Hees, A; Do, T; Ghez, A M; Martinez, G D; Naoz, S; Becklin, E E; Boehle, A; Chappell, S; Chu, D; Dehghanfar, A; Kosmo, K; Lu, J R; Matthews, K; Morris, M R; Sakai, S; Schödel, R; Witzel, G

2017-05-26

We demonstrate that short-period stars orbiting around the supermassive black hole in our Galactic center can successfully be used to probe the gravitational theory in a strong regime. We use 19 years of observations of the two best measured short-period stars orbiting our Galactic center to constrain a hypothetical fifth force that arises in various scenarios motivated by the development of a unification theory or in some models of dark matter and dark energy. No deviation from general relativity is reported and the fifth force strength is restricted to an upper 95% confidence limit of |α|<0.016 at a length scale of λ=150 astronomical units. We also derive a 95% confidence upper limit on a linear drift of the argument of periastron of the short-period star S0-2 of |ω[over ˙]_{S0-2}|<1.6×10^{-3}  rad/yr, which can be used to constrain various gravitational and astrophysical theories. This analysis provides the first fully self-consistent test of the gravitational theory using orbital dynamic in a strong gravitational regime, that of a supermassive black hole. A sensitivity analysis for future measurements is also presented.

Tidal Effects on the Oort Cloud Comets and Dynamics of the Sun in the Spiral Arms of the Galaxy

NASA Astrophysics Data System (ADS)

De Biasi, Alice

2014-01-01

The Solar System presents a complex dynamical structure and is not isolated from the Galaxy. In particular the comet reservoir of our planetary system, the Oort cloud, is extremely sensitive to the the galactic environment due to its peripheral collocation inside the Solar System. In this framework, the growing evidences about a possible migration of the Sun open new research scenarios relative to the effects that such kind of migration might induce on the cometary motion. Following several previous studied, we identified the spiral arm structure as the main perturbation that is able to produce an efficient solar migration through the disk. Widening the classical model for the spiral arms, provided by Lin& Shu to a 3D formalism, we verified the compatibility between the presence of the spiral perturbation and a significant solar motion for an inner Galactic position to the current one, in agreement with the constrains in position, velocity and metallicity due to the present conditions of our star. The main perturbers of the Oort cloud, the close stellar passages and the tidal field of the Galaxy, might be both affected by the variation of Galactic environment that the solar migration entails. Despite that, in order to isolate the effects to the two different perturbators, we decided to focus our attention only on the Galactic tide. The perturbation due to the spiral structure was included in the study on the cometary motion, introducing the solar migration and adding the direct presence of the non-axisymmetric component in the Galactic potential of the tidal field. The results show a significant influence of the spiral arm in particular on cometary objects belonged to the outer shell of the Oort cloud, for which provides an injection rate three times bigger than the integration performed without the spiral arms. The introduction of the spiral perturbation seems to bolster the planar component of the tide, indeed it produces the most significant variation of the perihelion distance for moderate inclination orbits with respect to the plane. The peak for the cometary injections has been registered between 6 and 7 kpc. If this evidence will be confirmed by more realistic cometary sample, it might involve a redefinition of the habitability edges in the Galaxy (GHZ). In particular regions not precluded to the formation of life, may compromise the development of the life with a high cometary impact risk

On the Distribution of Orbital Poles of Milky Way Satellites

NASA Astrophysics Data System (ADS)

Palma, Christopher; Majewski, Steven R.; Johnston, Kathryn V.

2002-01-01

In numerous studies of the outer Galactic halo some evidence for accretion has been found. If the outer halo did form in part or wholly through merger events, we might expect to find coherent streams of stars and globular clusters following orbits similar to those of their parent objects, which are assumed to be present or former Milky Way dwarf satellite galaxies. We present a study of this phenomenon by assessing the likelihood of potential descendant ``dynamical families'' in the outer halo. We conduct two analyses: one that involves a statistical analysis of the spatial distribution of all known Galactic dwarf satellite galaxies (DSGs) and globular clusters, and a second, more specific analysis of those globular clusters and DSGs for which full phase space dynamical data exist. In both cases our methodology is appropriate only to members of descendant dynamical families that retain nearly aligned orbital poles today. Since the Sagittarius dwarf (Sgr) is considered a paradigm for the type of merger/tidal interaction event for which we are searching, we also undertake a case study of the Sgr system and identify several globular clusters that may be members of its extended dynamical family. In our first analysis, the distribution of possible orbital poles for the entire sample of outer (Rgc>8 kpc) halo globular clusters is tested for statistically significant associations among globular clusters and DSGs. Our methodology for identifying possible associations is similar to that used by Lynden-Bell & Lynden-Bell, but we put the associations on a more statistical foundation. Moreover, we study the degree of possible dynamical clustering among various interesting ensembles of globular clusters and satellite galaxies. Among the ensembles studied, we find the globular cluster subpopulation with the highest statistical likelihood of association with one or more of the Galactic DSGs to be the distant, outer halo (Rgc>25 kpc), second-parameter globular clusters. The results of our orbital pole analysis are supported by the great circle cell count methodology of Johnston, Hernquist, & Bolte. The space motions of the clusters Pal 4, NGC 6229, NGC 7006, and Pyxis are predicted to be among those most likely to show the clusters to be following stream orbits, since these clusters are responsible for the majority of the statistical significance of the association between outer halo, second-parameter globular clusters and the Milky Way DSGs. In our second analysis, we study the orbits of the 41 globular clusters and six Milky Way-bound DSGs having measured proper motions to look for objects with both coplanar orbits and similar angular momenta. Unfortunately, the majority of globular clusters with measured proper motions are inner halo clusters that are less likely to retain memory of their original orbit. Although four potential globular cluster/DSG associations are found, we believe three of these associations involving inner halo clusters to be coincidental. While the present sample of objects with complete dynamical data is small and does not include many of the globular clusters that are more likely to have been captured by the Milky Way, the methodology we adopt will become increasingly powerful as more proper motions are measured for distant Galactic satellites and globular clusters, and especially as results from the Space Interferometry Mission (SIM) become available.

The Prolate Dark Matter Halo of the Andromeda Galaxy

NASA Astrophysics Data System (ADS)

Hayashi, Kohei; Chiba, Masashi

2014-07-01

We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi & Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for its dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.

Dynamics and stellar population of the Galactic Center (French Title: Étude de la cinématique et de la population stellaire du Centre Galactique)

NASA Astrophysics Data System (ADS)

Paumard, Thibaut

2003-09-01

The central parsec of the Galaxy has been observed using BEAR spectroimagery at high spectral resolution (up to 21 km/s) and medium spatial resolution (0.5"), in Bracket gamma (2.16 microns) and He I (2.06 microns), and high resolution imaging. These data were used to study the young, massive stars of the central parsec, and the structure and dynamics of ionized gas in Sgr A West. The stellar population has been separated into two groups: the IRS 16 complex of 6 LBVs, and at least 20 Wolf-Rayets. The IRS 13E complex has been identified as a cluster of at least 6 massive stars. All this is consistent with the young stars being born in a massive cluster a few tens of parsecs from the Galactic Centre. Providing a deep insight into the morphology of Sgr A West, our data allowed us to derive a kinematic model for the Northern Arm. Our results are in agreement with the idea that the Minispiral is made of ionisation fronts of wider neutral clouds, gravitationally stretched, coming from the CND.

The prolate dark matter halo of the Andromeda galaxy

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

Hayashi, Kohei; Chiba, Masashi, E-mail: k.hayasi@astr.tohoku.ac.jp, E-mail: chiba@astr.tohoku.ac.jp

We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi and Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for itsmore » dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.« less

HD271791: dynamical versus binary-supernova ejection scenario

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.

2009-05-01

The atmosphere of the extremely high-velocity (530-920kms-1) early B-type star HD271791 is enriched in α-process elements, which suggests that this star is a former secondary component of a massive tight binary system and that its surface was polluted by the nucleosynthetic products after the primary star exploded in a supernova. It was proposed that the (asymmetric) supernova explosion unbind the system and that the secondary star (HD271791) was released at its orbital velocity in the direction of Galactic rotation. In this Letter, we show that to explain the Galactic rest-frame velocity of HD271791 within the framework of the binary-supernova scenario, the stellar remnant of the supernova explosion (a <~10Msolar black hole) should receive an unrealistically large kick velocity of >=750-1200kms-1. We therefore consider the binary-supernova scenario as highly unlikely and instead propose that HD271791 attained its peculiar velocity in the course of a strong dynamical three- or four-body encounter in the dense core of the parent star cluster. Our proposal implies that by the moment of encounter HD271791 was a member of a massive post-supernova binary.

A strong magnetic field around the supermassive black hole at the centre of the Galaxy.

PubMed

Eatough, R P; Falcke, H; Karuppusamy, R; Lee, K J; Champion, D J; Keane, E F; Desvignes, G; Schnitzeler, D H F M; Spitler, L G; Kramer, M; Klein, B; Bassa, C; Bower, G C; Brunthaler, A; Cognard, I; Deller, A T; Demorest, P B; Freire, P C C; Kraus, A; Lyne, A G; Noutsos, A; Stappers, B; Wex, N

2013-09-19

Earth's nearest candidate supermassive black hole lies at the centre of the Milky Way. Its electromagnetic emission is thought to be powered by radiatively inefficient accretion of gas from its environment, which is a standard mode of energy supply for most galactic nuclei. X-ray measurements have already resolved a tenuous hot gas component from which the black hole can be fed. The magnetization of the gas, however, which is a crucial parameter determining the structure of the accretion flow, remains unknown. Strong magnetic fields can influence the dynamics of accretion, remove angular momentum from the infalling gas, expel matter through relativistic jets and lead to synchrotron emission such as that previously observed. Here we report multi-frequency radio measurements of a newly discovered pulsar close to the Galactic Centre and show that the pulsar's unusually large Faraday rotation (the rotation of the plane of polarization of the emission in the presence of an external magnetic field) indicates that there is a dynamically important magnetic field near the black hole. If this field is accreted down to the event horizon it provides enough magnetic flux to explain the observed emission--from radio to X-ray wavelengths--from the black hole.

A strong magnetic field around the supermassive black hole at the centre of the Galaxy

NASA Astrophysics Data System (ADS)

Eatough, R. P.; Falcke, H.; Karuppusamy, R.; Lee, K. J.; Champion, D. J.; Keane, E. F.; Desvignes, G.; Schnitzeler, D. H. F. M.; Spitler, L. G.; Kramer, M.; Klein, B.; Bassa, C.; Bower, G. C.; Brunthaler, A.; Cognard, I.; Deller, A. T.; Demorest, P. B.; Freire, P. C. C.; Kraus, A.; Lyne, A. G.; Noutsos, A.; Stappers, B.; Wex, N.

2013-09-01

Earth's nearest candidate supermassive black hole lies at the centre of the Milky Way. Its electromagnetic emission is thought to be powered by radiatively inefficient accretion of gas from its environment, which is a standard mode of energy supply for most galactic nuclei. X-ray measurements have already resolved a tenuous hot gas component from which the black hole can be fed. The magnetization of the gas, however, which is a crucial parameter determining the structure of the accretion flow, remains unknown. Strong magnetic fields can influence the dynamics of accretion, remove angular momentum from the infalling gas, expel matter through relativistic jets and lead to synchrotron emission such as that previously observed. Here we report multi-frequency radio measurements of a newly discovered pulsar close to the Galactic Centre and show that the pulsar's unusually large Faraday rotation (the rotation of the plane of polarization of the emission in the presence of an external magnetic field) indicates that there is a dynamically important magnetic field near the black hole. If this field is accreted down to the event horizon it provides enough magnetic flux to explain the observed emission--from radio to X-ray wavelengths--from the black hole.

Merging Black Hole Binaries in Galactic Nuclei: Implications for Advanced-LIGO Detections

NASA Astrophysics Data System (ADS)

Antonini, Fabio; Rasio, Frederic A.

2016-11-01

Motivated by the recent detection of gravitational waves from the black hole binary merger GW150914, we study the dynamical evolution of (stellar-mass) black holes in galactic nuclei, where massive star clusters reside. With masses of ˜ {10}7 {M}⊙ and sizes of only a few parsecs, nuclear star clusters (NSCs) are the densest stellar systems observed in the local universe and represent a robust environment where black hole binaries can dynamically form, harden, and merge. We show that due to their large escape speeds, NSCs can retain a large fraction of their merger remnants. Successive mergers can then lead to significant growth and produce black hole mergers of several tens of solar masses similar to GW150914 and up to a few hundreds of solar masses, without the need to invoke extremely low metallicity environments. We use a semi-analytical approach to describe the dynamics of black holes in massive star clusters. Our models give a black hole binary merger rate of ≈ 1.5 {{Gpc}}-3 {{yr}}-1 from NSCs, implying up to a few tens of possible detections per year with Advanced LIGO. Moreover, we find a local merger rate of ˜ 1 {{Gpc}}-3 {{yr}}-1 for high mass black hole binaries similar to GW150914; a merger rate comparable to or higher than that of similar binaries assembled dynamically in globular clusters (GCs). Finally, we show that if all black holes receive high natal kicks, ≳ 50 {km} {{{s}}}-1, then NSCs will dominate the local merger rate of binary black holes compared to either GCs or isolated binary evolution.

Post-Newtonian Dynamical Modeling of Supermassive Black Holes in Galactic-scale Simulations

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

Rantala, Antti; Pihajoki, Pauli; Johansson, Peter H.

We present KETJU, a new extension of the widely used smoothed particle hydrodynamics simulation code GADGET-3. The key feature of the code is the inclusion of algorithmically regularized regions around every supermassive black hole (SMBH). This allows for simultaneously following global galactic-scale dynamical and astrophysical processes, while solving the dynamics of SMBHs, SMBH binaries, and surrounding stellar systems at subparsec scales. The KETJU code includes post-Newtonian terms in the equations of motions of the SMBHs, which enables a new SMBH merger criterion based on the gravitational wave coalescence timescale, pushing the merger separation of SMBHs down to ∼0.005 pc. Wemore » test the performance of our code by comparison to NBODY7 and rVINE. We set up dynamically stable multicomponent merger progenitor galaxies to study the SMBH binary evolution during galaxy mergers. In our simulation sample the SMBH binaries do not suffer from the final-parsec problem, which we attribute to the nonspherical shape of the merger remnants. For bulge-only models, the hardening rate decreases with increasing resolution, whereas for models that in addition include massive dark matter halos, the SMBH binary hardening rate becomes practically independent of the mass resolution of the stellar bulge. The SMBHs coalesce on average 200 Myr after the formation of the SMBH binary. However, small differences in the initial SMBH binary eccentricities can result in large differences in the SMBH coalescence times. Finally, we discuss the future prospects of KETJU, which allows for a straightforward inclusion of gas physics in the simulations.« less

A cloud/particle model of the interstellar medium - Galactic spiral structure

NASA Technical Reports Server (NTRS)

Levinson, F. H.; Roberts, W. W., Jr.

1981-01-01

A cloud/particle model for gas flow in galaxies is developed that incorporates cloud-cloud collisions and supernovae as dominant local processes. Cloud-cloud collisions are the main means of dissipation. To counter this dissipation and maintain local dispersion, supernova explosions in the medium administer radial snowplow pushes to all nearby clouds. The causal link between these processes is that cloud-cloud collisions will form stars and that these stars will rapidly become supernovae. The cloud/particle model is tested and used to investigate the gas dynamics and spiral structures in galaxies where these assumptions may be reasonable. Particular attention is given to whether large-scale galactic shock waves, which are thought to underlie the regular well-delineated spiral structure in some galaxies, form and persist in a cloud-supernova dominated interstellar medium; this question is answered in the affirmative.

WHITE DWARFS IN LOCAL STAR STREAMS

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

Fuchs, Burkhard; Dettbarn, Christian

2011-01-15

We have studied the fine structure of the phase space distribution of white dwarfs in the solar neighborhood. White dwarfs have kinematics that are typical for the stellar population of the old thin disk of the Milky Way. Using a projection of the space velocities of stars onto vertical angular momentum components and eccentricities of the stellar orbits we demonstrate that stellar streams can be identified in the phase space distribution of the white dwarfs. These correspond to the well-known Sirius, Pleiades, and Hercules star streams. Membership of white dwarfs, which represent the oldest population in the Galaxy, in thesemore » streams lends support to the interpretation that the streams owe their existence to dynamical resonance effects of the stars with Galactic spiral arms or the Galactic bar, because these indiscriminately affect all stellar populations.« less

Through thick and thin: Structure of the Galactic thick disc from extragalactic surveys

NASA Astrophysics Data System (ADS)

Kordopatis, G.; Hill, V.; Irwin, M.; Gilmore, G.; Wyse, R. F. G.; Tolstoy, E.; de Laverny, P.; Recio-Blanco, A.; Battaglia, G.; Starkenburg, E.

2013-07-01

Context. We aim to understand the accretion history of the Milky Way by exploring the vertical and radial properties of the Galactic thick disc. Aims: We study the chemical and kinematic properties of roughly a thousand spectra of faint magnitude foreground Galactic stars observed serendipitously during extra-galactic surveys in four lines-of-sight: three in the southern Galactic hemisphere (surveys of the Carina, Fornax and Sculptor dwarf spheroidal galaxies) and one in the northern Galactic hemisphere (a survey of the Sextans dwarf spheroidal galaxy). The foreground stars span distances up to ~3 kpc from the Galactic plane and Galactocentric radii up to 11 kpc. Methods: The stellar atmospheric parameters (effective temperature, surface gravity, metallicity) are obtained by an automated parameterisation pipeline and the distances of the stars are then derived by a projection of the atmospheric parameters on a set of theoretical isochrones using a Bayesian approach. The metallicity gradients are estimated for each line-of-sight and compared with predictions from the Besançon model of the Galaxy, in order to test the chemical structure of the thick disc. Finally, we use the radial velocities in each line-of-sight to derive a proxy for either the azimuthal or the vertical component of the orbital velocity of the stars. Results: Only three lines-of-sight have a sufficient number of foreground stars for a robust analysis. Towards Sextans in the Northern Galactic hemisphere and Sculptor in the South, we measure a consistent decrease in mean metallicity with height from the Galactic plane, suggesting a chemically symmetric thick disc. This decrease can either be due to an intrinsic thick disc metallicity gradient, or simply due to a change in the thin disc/thick disc population ratio and no intrinsic metallicity gradients for the thick disc. We favour the latter explanation. In contrast, we find evidence of an unpredicted metal-poor population in the direction of Carina. This population was earlier detected, but our more detailed analysis provides robust estimates of its location (|Z| < 1 kpc), metallicity (-2 < [M/H] < -1 dex) and azimuthal orbital velocity (Vφ ~ 120 km s-1). Conclusions: Given the chemo-dynamical properties of the over-density towards the Carina line-of-sight, we suggest that it represents the metal-poor tail of the canonical thick disc. In spite of the small number of stars available, we suggest that this metal-weak thick disc follows the often suggested canonical thick disc velocity-metallicity correlation of ∂Vφ/∂ [M/H] ~ 40-50 km s-1 dex-1. Based on observations collected at the European Southern Observatory at Paranal, Chile, ESO Large Programme 171.B-0588 (DART) and 171.B-0520(A).Full Tables 2 and 4 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/555/A12

Dynamics of massive black holes as a possible candidate of Galactic dark matter

NASA Technical Reports Server (NTRS)

Xu, Guohong; Ostriker, Jeremiah P.

1994-01-01

If the dark halo of the Galaxy is comprised of massive black holes (MBHs), then those within approximately 1 kpc will spiral to the center, where they will interact with one another, forming binaries which contract, owing to further dynamical friction, and then possibly merge to become more massive objects by emission of gravitational radiation. If successive mergers would invariably lead, as has been proposed by various authors, to the formation of a very massive nucleus of 10(exp 8) solar mass, then the idea of MBHs as a dark matter candidate could be excluded on observational grounds, since the observed limit (or value) for a Galactic central black hole is approximately 10(exp 6.5) solar mass. But, if successive mergers are delayed or prevented by other processes, such as the gravitational slingshot or rocket effect of gravitational radiation, then a large mass accumulation will not occur. In order to resolve this issue, we perform detailed N-body simulations using a modfied Aarseth code to explore the dynamical behavior of the MBHs, and we find that for a 'best estimate' model of the Galaxy a runaway does not occur. The code treates the MBHs as subject to the primary gravitational forces of one another and to the smooth stellar distribution, as well as the secondary perturbations in their orbits due to another and to the smooth stellar distribution, as well as the secondary perturbations in their orbits due to dynamical friction and gravitational radiation. Instead of a runaway, three-body interactions between hard binaries and single MBHs eject massive objects before accumulation of more than a few units, so that typically the center will contain zero, one, or two MBHs. We study how the situation depends in detail on the mass per MBH, the rotation of the halo, the mass distribution within the Galaxy, and other parameters. A runaway will most sensitively depend on the ratio of initial (spheroid/halo) central mass densities and secondarily on the typical values for the mass per MBH, with the rough dividing line, using Galactic parameters, being M(sub BH) less than or = 10(exp 6.5) solar mass. Using parameters from Lacey & Ostriker (1985) and our most accurate model for Galaxy, no runaway occurs.

Keck Observations of the Gas Dynamics at the Galactic Center

NASA Astrophysics Data System (ADS)

Campbell, Randall; Ciurlo, Anna; Morris, Mark; Sitarski, Breann N.; Ghez, Andrea M.; Do, Tuan

2018-06-01

In the central parsec of the Milky Way Galaxy the environment of the super-massive black hole (SMBH) presents a complicated mixture of stars, gas, and dust. These inner few tens of arcseconds of the GC have been observed at high resolution with Keck for 20 years with the primary goal of monitoring stars orbiting the SMBH. However, the gas features and their dynamics can also be closely examined using this unique baseline of data. In particular, observations with the Keck OSIRIS integral field spectrometer allow us to examine of the dynamical properties of the gas and to possibly identify new “G-type” objects, or dusty stellar objects. We present a study of morphology and orbital dynamics of sub-parsec scale gas features in the central region.

THE CONTRIBUTION OF SPIRAL ARMS TO THE THICK DISK ALONG THE HUBBLE SEQUENCE

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

Martinez-Medina, L. A.; Pichardo, B.; Moreno, E.

2015-04-01

The first mechanism invoked to explain the existence of the thick disk in the Milky Way Galaxy was the spiral arms. Up-to-date work summons several other possibilities that together seem to better explain this component of our Galaxy. All these processes must affect distinct types of galaxies differently, but the contribution of each one has not been straightforward to quantify. In this work, we present the first comprehensive study of the effect of the spiral arms on the formation of thick disks, looking at early- to late-type disk galaxies in an attempt to characterize and quantify this specific mechanism in galactic potentials. To this purpose,more » we perform test particle numerical simulations in a three-dimensional spiral galactic potential (for early- to late-types spiral galaxies). By varying the parameters of the spiral arms we found that the vertical heating of the stellar disk becomes very important in some cases and strongly depends on the galactic morphology, pitch angle, arm mass, and the arm pattern speed. The later the galaxy type, the larger is the effect on the disk heating. This study shows that the physical mechanism causing the vertical heating is different from simple resonant excitation. The spiral pattern induces chaotic behavior not linked necessarily to resonances but to direct scattering of disk stars, which leads to an increase of the velocity dispersion. We applied this study to the specific example of the Milky Way Galaxy, for which we have also added an experiment that includes the Galactic bar. From this study we deduce that the effect of spiral arms of a Milky-Way-like potential on the dynamical vertical heating of the disk is negligible, unlike later galactic potentials for disks.« less

THE DEARTH OF NEUTRAL HYDROGEN IN GALACTIC DWARF SPHEROIDAL GALAXIES

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

Spekkens, Kristine; Urbancic, Natasha; Mason, Brian S.

We present new upper limits on the neutral hydrogen (H I) content within the stellar half-light ellipses of 15 Galactic dwarf spheroidal galaxies (dSphs), derived from pointed observations with the Green Bank Telescope (GBT) as well as Arecibo L-band Fast ALFA survey and Galactic All-Sky Survey data. All of the limits M{sub H} {sub I}{sup lim} are more stringent than previously reported values, and those from the GBT improve upon constraints in the literature by a median factor of 23. Normalizing by V-band luminosity L{sub V} and dynamical mass M {sub dyn}, we find M{sub H} {sub I}{sup lim}/L{sub V}∼10{supmore » −3} M{sub ⊙}/L{sub ⊙} and M{sub H} {sub I}{sup lim}/M{sub dyn}∼5×10{sup −5}, irrespective of location in the Galactic halo. Comparing these relative H I contents to those of the Local Group and nearby neighbor dwarfs compiled by McConnachie, we find that the Galactic dSphs are extremely gas-poor. Our H I upper limits therefore provide the clearest picture yet of the environmental dependence of the H I content in Local Volume dwarfs. If ram pressure stripping explains the dearth of H I in these systems, then orbits in a relatively massive Milky Way are favored for the outer halo dSph Leo I, while Leo II and Canes Venatici I have had a pericentric passage in the past. For Draco and Ursa Minor, the interstellar medium mass that should accumulate through stellar mass loss in between pericentric passages exceeds M{sub H} {sub I}{sup lim} by a factor of ∼30. In Ursa Minor, this implies that either this material is not in the atomic phase, or that another mechanism clears the recycled gas on shorter timescales.« less

Interstellar Medium, Young Stars, and Astrometric Binaries in Galactic Archaeology Spectroscopic Surveys

NASA Astrophysics Data System (ADS)

Zwitter, T.; Kos, J.; Žerjal, M.; Traven, G.

2016-10-01

Current ongoing stellar spectroscopic surveys (RAVE, GALAH, Gaia-ESO, LAMOST, APOGEE, Gaia) are mostly devoted to studying Galactic archaeology and the structure of the Galaxy. But they allow also for important auxiliary science: (i) the Galactic interstellar medium can be studied in four dimensions (position in space plus radial velocity) through weak but numerous diffuse interstellar bands and atomic absorptions seen in spectra of background stars, (ii) emission spectra which are quite frequent even in field stars can serve as a good indicator of their youth, pointing e.g. to stars recently ejected from young stellar environments, (iii) an astrometric solution of the photocenter of a binary to be obtained by Gaia can yield accurate masses when joined by spectroscopic information obtained serendipitously during a survey. These points are illustrated by first results from the first three surveys mentioned above. These hint at the near future: spectroscopic studies of the dynamics of the interstellar medium can identify and quantify Galactic fountains which may sustain star formation in the disk by entraining fresh gas from the halo; RAVE already provided a list of ˜ 14,000 field stars with chromospheric emission in Ca II lines, to be supplemented by many more observations by Gaia in the same band, and by GALAH and Gaia-ESO observations of Balmer lines; several millions of astrometric binaries with periods up to a few years which are being observed by Gaia can yield accurate masses when supplemented with measurements from only a few high-quality ground based spectra.

Star formation induced by cloud-cloud collisions and galactic giant molecular cloud evolution

NASA Astrophysics Data System (ADS)

Kobayashi, Masato I. N.; Kobayashi, Hiroshi; Inutsuka, Shu-ichiro; Fukui, Yasuo

2018-05-01

Recent millimeter/submillimeter observations towards nearby galaxies have started to map the whole disk and to identify giant molecular clouds (GMCs) even in the regions between galactic spiral structures. Observed variations of GMC mass functions in different galactic environments indicates that massive GMCs preferentially reside along galactic spiral structures whereas inter-arm regions have many small GMCs. Based on the phase transition dynamics from magnetized warm neutral medium to molecular clouds, Kobayashi et al. (2017, ApJ, 836, 175) proposes a semi-analytical evolutionary description for GMC mass functions including a cloud-cloud collision (CCC) process. Their results show that CCC is less dominant in shaping the mass function of GMCs than the accretion of dense H I gas driven by the propagation of supersonic shock waves. However, their formulation does not take into account the possible enhancement of star formation by CCC. Millimeter/submillimeter observations within the Milky Way indicate the importance of CCC in the formation of star clusters and massive stars. In this article, we reformulate the time-evolution equation largely modified from Kobayashi et al. (2017, ApJ, 836, 175) so that we additionally compute star formation subsequently taking place in CCC clouds. Our results suggest that, although CCC events between smaller clouds are more frequent than the ones between massive GMCs, CCC-driven star formation is mostly driven by massive GMCs ≳ 10^{5.5} M_{⊙} (where M⊙ is the solar mass). The resultant cumulative CCC-driven star formation may amount to a few 10 percent of the total star formation in the Milky Way and nearby galaxies.

A model for the origin of bursty star formation in galaxies

NASA Astrophysics Data System (ADS)

Faucher-Giguère, Claude-André

2018-01-01

We propose a simple analytic model to understand when star formation is time steady versus bursty in galaxies. Recent models explain the observed Kennicutt-Schmidt relation between star formation rate and gas surface densities in galaxies as resulting from a balance between stellar feedback and gravity. We argue that bursty star formation occurs when such an equilibrium cannot be stably sustained, and identify two regimes in which galaxy-scale star formation should be bursty: (i) at high redshift (z ≳ 1) for galaxies of all masses, and (ii) at low masses (depending on gas fraction) for galaxies at any redshift. At high redshift, characteristic galactic dynamical time-scales become too short for supernova feedback to effectively respond to gravitational collapse in galactic discs (an effect recently identified for galactic nuclei), whereas in dwarf galaxies star formation occurs in too few bright star-forming regions to effectively average out. Burstiness is also enhanced at high redshift owing to elevated gas fractions in the early Universe. Our model can thus explain the bursty star formation rates predicted in these regimes by recent high-resolution galaxy formation simulations, as well as the bursty star formation histories observationally inferred in both local dwarf and high-redshift galaxies. In our model, bursty star formation is associated with particularly strong spatiotemporal clustering of supernovae. Such clustering can promote the formation of galactic winds and our model may thus also explain the much higher wind mass loading factors inferred in high-redshift massive galaxies relative to their z ∼ 0 counterparts.

The Galactic Bulge Radial Velocity/Abundance Assay

NASA Astrophysics Data System (ADS)

Rich, R. M.

2012-08-01

The Bulge Radial Velocity Assay (BRAVA) measured radial velocities for ˜ 9500 late-type giants in the Galactic bulge, predominantly from -10° < l < +10° and -2° < b < -10°. The project has discovered that the bulge exhibits cylindrical rotation characteristic of bars, and two studies of dynamics (Shen et al. 2010; Wang et al. 2012 MNRAS sub.) find that bar models- either N-body formed from an instability in a preexisting disk, or a self-consistent model- can account for the observed kinematics. Studies of the Plaut field at (l,b) = 0°, -8° show that alpha enhancement is found in bulge giants even 1 kpc from the nucleus. New infrared studies extending to within 0.25° = 35 pc of the Galactic Center find no iron or alpha gradient from Baade's Window (l,b) = 0.9°, -3.9° to our innermost field, in contrast to the marked gradient observed in the outer bulge. We consider the case of the remarkable globular cluster Terzan 5, which has a strongly bimodal iron and rm [α/Fe] within its members, and we consider evidence pro and con that the bulge was assembled from dissolved clusters. The Subaru telescope has the potential to contribute to study of the Galactic bulge, especially using the Hyper Superime-Cam and planned spectroscopic modes, as well as the high resolution spectrograph. The planned Jasmine satellite series may deliver a comprehensive survey of distances and proper motions of bulge stars, and insight into the origin and importance of the X-shaped bulge.

Chemical Compositions of Young Stars in the Leading Arm of the Magellanic System

NASA Astrophysics Data System (ADS)

Zhang, L.; Moni Bidin, C.; Casetti-Dinescu, D. I.; Mendez, R. A.; Girard, T. M.; Korchagin, V. I.; Vieira, K.; van Altena, W. F.; Zhao, G.

2017-07-01

Seven element abundances (He, C, N, O, Mg, Si, and S) and kinematics were determined for eight O-/B- type stars, based on high resolution spectra taken with the MIKE instrument on the Magellan 6.5m Clay telescope (program ID: CN2014A-057). The sample is selected from 42 candidates Casetti-Dinescu et al.(2014, ApJL, 784, L37) of membership in the Leading Arm (LA) of the Magellanic System. After investigating the relationship between abundances and kinematics parameters, we found that five stars have kinematics compatible with LA membership, i.e. RV>100kms-1. For the five possible LA member stars, Mg abundance is significantly lower than that of the remaining two that are kinematical members of the Galactic disk, and is more close to the LMC values. Distances to the LA members indicate that they are at the edge of the Galactic disk, while ages are of the order of ˜ 50-70 Myr, lower than the dynamical age of the LA, suggesting a single star-forming episode in the LA. VLSR of the LA members decreases with decreasing Magellanic longitude, confirming the results of previous LA gas studies (McClure-Griffiths et al.2008, ApJ, 673, L143). Our abundance and kinematic results for the LA member stars demonstrate that parts of the LA are hydrodynamically interacting with the gaseous Galactic disk, forming young stars that are chemically distinct from those in the Galactic disk. These results can provide constraints to future models for the Magellanic leading material.

A GLIMPSE of Star Formation in the Outer Galaxy

NASA Astrophysics Data System (ADS)

Winston, Elaine; Hora, Joseph L.; Tolls, Volker

2018-01-01

The wealth of infrared data provided by recent infrared missions such as Spitzer, Herschel, and WISE has yet to be fully mined in the study of star formation in the outer galaxy. The nearby galaxy and massive star forming regions towards the galactic center have been extensively studied. However the outer regions of the Milky Way, where the metallicity is intermediate in value between the inner galactic disk and the Magellanic Clouds, has not been systematically studied. We are using Spitzer/IRAC’s GLIMPSE (Galactic Legacy Infrared Mid-plane Survey Extraordinaire) observations of the galactic plane at 3.6, 4.5, 5.8, and 8.0 microns to identify young stellar objects (YSOs) via their disk emission in the mid-infrared. A tiered clustering analysis is then performed: preliminary large scale clustering is identified across the field using a Density-Based Spatial Clustering of Applications with Noise (DBSCAN) technique. Smaller scale sub clustering within these regions is performed using an implementation of the Minimum Spanning Tree (MST) technique. The YSOs are then compared to known objects in the SIMBAD catalogue and their photometry and cluster membership is augmented using available Herschel and WISE photometry. We compare our results to those in the inner galaxy to determine how dynamical processes and environmental factors affect the star formation efficiency. These results will have applications to the study of star formation in other galaxies, where only global properties can be determined. We will present here the results of our initial investigation into star formation in the outer galaxy using the Spitzer/GLIMPSE observations of the SMOG field.

The life cycle of starbursting circumnuclear gas discs

NASA Astrophysics Data System (ADS)

Schartmann, M.; Mould, J.; Wada, K.; Burkert, A.; Durré, M.; Behrendt, M.; Davies, R. I.; Burtscher, L.

2018-01-01

High-resolution observations from the submm to the optical wavelength regime resolve the central few 100 pc region of nearby galaxies in great detail. They reveal a large diversity of features: thick gas and stellar discs, nuclear starbursts, inflows and outflows, central activity, jet interaction, etc. Concentrating on the role circumnuclear discs play in the life cycles of galactic nuclei, we employ 3D adaptive mesh refinement hydrodynamical simulations with the RAMSES code to self-consistently trace the evolution from a quasi-stable gas disc, undergoing gravitational (Toomre) instability, the formation of clumps and stars and the disc's subsequent, partial dispersal via stellar feedback. Our approach builds upon the observational finding that many nearby Seyfert galaxies have undergone intense nuclear starbursts in their recent past and in many nearby sources star formation is concentrated in a handful of clumps on a few 100 pc distant from the galactic centre. We show that such observations can be understood as the result of gravitational instabilities in dense circumnuclear discs. By comparing these simulations to available integral field unit observations of a sample of nearby galactic nuclei, we find consistent gas and stellar masses, kinematics, star formation and outflow properties. Important ingredients in the simulations are the self-consistent treatment of star formation and the dynamical evolution of the stellar distribution as well as the modelling of a delay time distribution for the supernova feedback. The knowledge of the resulting simulated density structure and kinematics on pc scale is vital for understanding inflow and feedback processes towards galactic scales.

The Arches Cluster Out to its Tidal Radius: Dynamical Mass Segregation and the Effect of the Extinction Law on the - Lar Mass Function

NASA Astrophysics Data System (ADS)

Habibi, Maryam; Stolte, Andrea; Brandner, Wolfgang; Hussman, Benjamin

2013-07-01

The Galactic Center is the most active site of star formation in the Milky Way Galaxy, where particularly high-mass stars have formed very recently and are still forming today. However, since we are looking at the Galactic Center through the Galactic disk, knowledge of extinction is crucial to study this region. The Arches cluster is a young, massive starburst cluster near the Galactic Center. We observed the Arches cluster out to its tidal radius using Ks-band imaging obtained with NAOS/CONICA at the VLT combined with Subaro/Cisco J-band data to gain a full understanding of the cluster mass distribution. We show that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper-mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, we show that the difference can reach up to 30% for individually derived stellar masses and ∆AKs˜1 magnitude in acquired Ks-band extinction, while the present mass function slope changes by ˜0.17 dex. The present-day mass function slope derived assuming the Nishiyama et al. (2009) extinction law increases from a flat slope of α-Nishi = 1.50 ± 0.35 in the core (r<0.2 pc) to α-Nishi = 2.21±0.27 in the intermediate annulus (0.2

On the origin of the warm-hot absorbers in the Milky Way's halo

NASA Astrophysics Data System (ADS)

Marasco, A.; Marinacci, F.; Fraternali, F.

2013-08-01

Disc galaxies like the Milky Way are expected to be surrounded by massive coronae of hot plasma that may contain a significant fraction of the so-called missing baryons. We investigate whether the local (|vLSR| < 400 km s-1) warm-hot absorption features observed towards extra-Galactic sources or halo stars are consistent with being produced by the cooling of the Milky Way's corona. In our scheme, cooling occurs at the interface between the disc and the corona and it is triggered by positive supernova feedback. We combine hydrodynamical simulations with a dynamical 3D model of the galactic fountain to predict the all-sky distribution of this cooling material, and we compare it with the observed distribution of detections for different `warm' (Si III, Si IV, C II, C IV) and `hot' (O VI) ionized species. The model reproduces the position-velocity distribution and the column densities of the vast majority of warm absorbers and about half of O VI absorbers. We conclude that the warm-hot gas responsible for most of the detections lies within a few kiloparsec from the Galactic plane, where high-metallicity material from the disc mixes efficiently with the hot corona. This process provides an accretion of a few M⊙ yr- 1 of fresh gas that can easily feed the star formation in the disc of the Galaxy. The remaining O VI detections are likely to be a different population of absorbers, located in the outskirts of the Galactic corona and/or in the circumgalactic medium of nearby galaxies.

Addressing the missing matter problem in galaxies through a new fundamental gravitational radius

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

Capozziello, S.; Jovanović, P.; Jovanović, V. Borka

We demonstrate that the existence of a Noether symmetry in f ( R ) theories of gravity gives rise to a further gravitational radius, besides the standard Schwarzschild one, determining the dynamics at galactic scales. By this feature, it is possible to explain the baryonic Tully-Fisher relation and the rotation curve of gas-rich galaxies without the dark matter hypothesis.

Interstellar Magnetic Fields and Polarimetry of Dust Emission

NASA Technical Reports Server (NTRS)

Dowell, Darren

2010-01-01

Magnetic fields are an important ingredient in the stormy cosmos. Magnetic fields: (1) are intimately involved with winds from Active Galactic Nuclei (AGN) and stars (2) create at least some of the structures observed in the ISM (3) modulate the formation of clouds, cores, and stars within a turbulent medium (4) may be dynamically important in protostellar accretion disks (5) smooth weak shocks (C-shocks).

A self-consistent field method for galactic dynamics

NASA Technical Reports Server (NTRS)

Hernquist, Lars; Ostriker, Jeremiah P.

1992-01-01

The present study describes an algorithm for evolving collisionless stellar systems in order to investigate the evolution of systems with density profiles like the R exp 1/4 law, using only a few terms in the expansions. A good fit is obtained for a truncated isothermal distribution, which renders the method appropriate for galaxies with flat rotation curves. Calculations employing N of about 10 exp 6-7 are straightforward on existing supercomputers, making possible simulations having significantly smoother fields than with direct methods such as tree-codes. Orbits are found in a given static or time-dependent gravitational field; the potential, phi(r, t) is revised from the resultant density, rho(r, t). Possible scientific uses of this technique are discussed, including tidal perturbations of dwarf galaxies, the adiabatic growth of central masses in spheroidal galaxies, instabilities in realistic galaxy models, and secular processes in galactic evolution.

Significance of medium energy gamma ray astronomy in the study of cosmic rays

NASA Technical Reports Server (NTRS)

Fichtel, C. E.; Kniffen, D. A.; Thompson, D. J.; Bignami, G. F.; Cheung, C. Y.

1975-01-01

Medium energy (about 10 to 30 MeV) gamma ray astronomy provides information on the product of the galactic electron cosmic ray intensity and the galactic matter to which the electrons are dynamically coupled by the magnetic field. Because high energy (greater than 100 MeV) gamma ray astronomy provides analogous information for the nucleonic cosmic rays and the relevant matter, a comparison between high energy and medium energy gamma ray intensities provides a direct ratio of the cosmic ray electrons and nucleons throughout the galaxy. A calculation of gamma ray production by electron bremsstrahlung shows that: bremsstrahlung energy loss is probably not negligible over the lifetime of the electrons in the galaxy; and the approximate bremsstrahlung calculation often used previously overestimates the gamma ray intensity by about a factor of two. As a specific example, expected medium energy gamma ray intensities are calculated for the speral arm model.

Constraints on baryonic dark matter in the Galactic halo and Local Group

NASA Technical Reports Server (NTRS)

Richstone, Douglas; Gould, Andrew; Guhathakurta, Puragra; Flynn, Chris

1992-01-01

A four-color method and deep CCD data are used to search for very faint metal-poor stars in the direction of the south Galactic pole. The results make it possible to limit the contribution of ordinary old, metal-poor stars to the dynamical halo of the Galaxy or to the Local Group. The ratio of the mass of the halo to its ordinary starlight must be more than about 2000, unless the halo is very small. For the Local Group, this ratio is greater than about 400. If this local dark matter is baryonic, the process of compact-object formation must produce very few 'impurities' in the form of stars similar to those found in globular clusters. The expected number of unbound stars with MV not greater than 6 within 100 pc of the sun is less than 1 based on the present 90-percent upper limit to the Local Group starlight.

On the effects of cluster density and concentration on the horizontal branch morphology - The origin of the blue tails

NASA Technical Reports Server (NTRS)

Fusi Pecci, F.; Ferraro, F. R.; Bellazzini, M.; Djorgovski, S.; Piotto, G.; Buonanno, R.

1993-01-01

Possible relationships between horizontal branch (HB) morphology in Galactic globular clusters and the cluster structure and dynamical evolution are investigated. New HB observables are defined and determined using a theoretical framework deduced from HB models. Data for 53 Galactic globular clusters are used to obtain correlations between the observables. It is found that the net length of the HB and the presence and extent of blue tails in particular are correlated with the cluster density and concentrations, in the sense of more concentrated or denser clusters having bluer and longer HB morphologies. This effect is especially strong for the intermediate metallicity clusters. Thus, the cluster environment can affect the stellar evolution leading to the HB and therefore the HB morphology. This result is interpreted in terms of an enhanced mass removal from the HB progenitors.

PRIMA: study for a dual-beam instrument for the VLT Interferometer

NASA Astrophysics Data System (ADS)

Quirrenbach, Andreas; Coudé du Foresto, Vincent; Daigne, Gerard; Hofmann, Karl H.; Hofmann, Reiner; Lattanzi, Mario; Osterbart, R.; Le Poole, Rudolf S.; Queloz, Didier; Vakili, Farrokh

1998-07-01

PRIMA is a conceptual study for a single-baseline dual-feed instrument for the very large telescope interferometer, which is under construction by the European Southern Observatory on Cerro Paranal in Chile. The goals of PRIMA include narrow-angle astrometry with a precision of 10 (mu) as over an arc of 10 inches, and imaging of faint sources with the full sensitivity of the 8m telescopes in the VLT array. Key scientific programs that can be carried out with PRIMA in imaging mode include observations of active galactic nuclei, the Galactic Center, stars, and circumstellar matter. Scientific drivers for the astrometry are searches for planets and low-mass stellar companions, binary stars, dynamics of clusters, and parallaxes. We list the main performance requirements for PRIMA, present system architectures for the dual-beam system, and discuss limitations of the interferometric field-of-view.

Adaptive Optics Images of the Galactic Center: Using Empirical Noise-maps to Optimize Image Analysis

NASA Astrophysics Data System (ADS)

Albers, Saundra; Witzel, Gunther; Meyer, Leo; Sitarski, Breann; Boehle, Anna; Ghez, Andrea M.

2015-01-01

Adaptive Optics images are one of the most important tools in studying our Galactic Center. In-depth knowledge of the noise characteristics is crucial to optimally analyze this data. Empirical noise estimates - often represented by a constant value for the entire image - can be greatly improved by computing the local detector properties and photon noise contributions pixel by pixel. To comprehensively determine the noise, we create a noise model for each image using the three main contributors—photon noise of stellar sources, sky noise, and dark noise. We propagate the uncertainties through all reduction steps and analyze the resulting map using Starfinder. The estimation of local noise properties helps to eliminate fake detections while improving the detection limit of fainter sources. We predict that a rigorous understanding of noise allows a more robust investigation of the stellar dynamics in the center of our Galaxy.

The Open Cluster Chemical Abundances and Mapping (OCCAM) Survey: Current Status

NASA Astrophysics Data System (ADS)

Frinchaboy, Peter; O'Connell, Julia; Donor, John; Cunha, Katia; Thompson, Benjamin; Melendez, Matthew; Shetrone, Matthew; Zasowski, Gail; Majewski, Steven R.; APOGEE TEAM

2018-01-01

The Open Cluster Chemical Analysis and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based data set forhundreds of open clusters, and constrain key Galactic dynamical and chemical parameters using the SDSS/APOGEE survey and follow-up from the McDonald Observatory Otto Struve 2.1-m telescope and Sandiford Cass Echelle Spectrograph (R ~ 60,000). We report on multi-element radial abundance gradients obtained from a sample of over 30 disk open clusters. The APOGEE chemical abundances were derived automatically by the ASPCAP pipeline and these are part of the SDSS IV Data Release 14, optical follow-up were analyzed using equivalent width analysis and spectral synthesis. We present the current open cluster sample that spans a significant range in age allowing exploration of the evolution of the Galactic abundance gradients. This work is supported by an NSF AAG grants AST-1311835 & AST-1715662.

Review: Magnetic Fields of O-Type Stars

NASA Astrophysics Data System (ADS)

Wade, G. A.; MiMeS Collaboration

2015-04-01

Since 2002, strong, organized magnetic fields have been firmly detected at the surfaces of about 10 Galactic O-type stars. In this paper I will review the characteristics of the inferred fields of individual stars as well as the overall population. I will discuss the extension of the “magnetic desert,” first inferred among the A-type stars, to O stars up to 60 M⊙. I will discuss the interaction of the winds of the magnetic stars with the fields above their surfaces, generating complex “dynamical magnetosphere” structures detected in optical and UV lines, and in X-ray lines and continuum. Finally, I will discuss the detection of a small number of variable O stars in the LMC and SMC that exhibit spectral characteristics analogous to the known Galactic magnetic stars, and that almost certainly represent the first known examples of extragalactic magnetic stars.

Oscillation effects and time variation of the supernova neutrino signal

NASA Astrophysics Data System (ADS)

Kneller, James P.; McLaughlin, Gail C.; Brockman, Justin

2008-02-01

The neutrinos detected from the next galactic core-collapse supernova will contain valuable information on the internal dynamics of the explosion. One mechanism leading to a temporal evolution of the neutrino signal is the variation of the induced neutrino flavor mixing driven by changes in the density profile. With one and two-dimensional hydrodynamical simulations we identify the behavior and properties of prominent features of the explosion. Using these results we demonstrate the time variation of the neutrino crossing probabilities due to changes in the Mikheyev-Smirnov-Wolfenstein (MSW) neutrino transformations as the star explodes by using the S-matrix—Monte Carlo—approach to neutrino propagation. After adopting spectra for the neutrinos emitted from the proto-neutron star we calculate for a galactic supernova the evolution of the positron spectra within a water Cerenkov detector and find that this signal allows us to probe of a number of explosion features.

The line-emitting gas in active galaxies - A probe of the nuclear engine

NASA Technical Reports Server (NTRS)

Veilleux, Sylvain

1993-01-01

This paper reviews some of the basic questions regarding the structure of the engine powering active galactic nuclei (AGN), the nature of the interaction between the AGN and the host galaxy, and the origin and evolution of AGN. The study of the dynamics and physical characteristics of the line-emitting gas in these objects has proven fruitful in addressing many of these issues. Recent advances in optical and infrared detector technology combined with the development of superior ground-based instruments have produced efficient new tools for the study of the line-emitting gas on nuclear and Galactic scales. Programs which take advantage of two of these new techniques, Fabry-Perot imaging spectroscopy and infrared spectroscopy, are described in this paper. The origin of nuclear activity in galaxies is also addressed in a third project which aims at determining the nature of luminous infrared galaxies.

Using photometrically selected metal-poor stars to study dwarf galaxies and the Galactic stellar halo

NASA Astrophysics Data System (ADS)

Youakim, Kris; Starkenburg, Else; Martin, Nicolas; Pristine Team

2018-06-01

The Pristine survey is a narrow-band photometric survey designed to efficiently search for extremely metal-poor (EMP) stars. In the first three years of the survey, it has demonstrated great efficiency at finding EMP stars, and also great promise for increasing the current, small sample of the most metal-poor stars. The present sky coverage is ~2500 square degrees in the Northern Galactic Halo, including several individual fields targeting dwarf galaxies. By efficiently identifying member stars in the outskirts of known faint dwarf galaxies, the dynamical histories and chemical abundance patterns of these systems can be understood in greater detail. Additionally, with reliable photometric metallicities over a large sky coverage it is possible to perform a large scale clustering analysis in the Milky Way halo, and investigate the characteristic scale of substructure at different metallicities. This can reveal important details about the process of building up the halo through dwarf galaxy accretion, and offer insight into the connection between dwarf galaxies and the Milky Way halo. In this talk I will outline our results on the search for the most pristine stars, with a focus on how we are using this information to advance our understanding of dwarf galaxies and their contribution to the formation of the Galactic stellar halo.

GALACTIC ANGULAR MOMENTUM IN THE ILLUSTRIS SIMULATION: FEEDBACK AND THE HUBBLE SEQUENCE

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

Genel, Shy; Fall, S. Michael; Snyder, Gregory F.

We study the stellar angular momentum of thousands of galaxies in the Illustris cosmological simulation, which captures gravitational and gas dynamics within galaxies, as well as feedback from stars and black holes. We find that the angular momentum of the simulated galaxies matches observations well, and in particular two distinct relations are found for late-type versus early-type galaxies. The relation for late-type galaxies corresponds to the value expected from full conservation of the specific angular momentum generated by cosmological tidal torques. The relation for early-type galaxies corresponds to retention of only ∼30% of that, but we find that those early-typemore » galaxies with low angular momentum at z = 0 nevertheless reside at high redshift on the late-type relation. Some of them abruptly lose angular momentum during major mergers. To gain further insight, we explore the scaling relations in simulations where the galaxy formation physics is modified with respect to the fiducial model. We find that galactic winds with high mass-loading factors are essential for obtaining the high angular momentum relation typical for late-type galaxies, while active galactic nucleus feedback largely operates in the opposite direction. Hence, feedback controls the stellar angular momentum of galaxies, and appears to be instrumental for establishing the Hubble sequence.« less

Effect of the cosmological constant on halo size

NASA Astrophysics Data System (ADS)

Kulchoakrungsun, Ekapob; Lam, Adrian; Lowe, David A.

2018-04-01

In this work, we consider the effect of the cosmological constant on galactic halo size. As a model, we study the general relativistic derivation of orbits in the Schwarzschild-de Sitter metric. We find that there exists a length scale rΛ corresponding to a maximum size of a circular orbit of a test mass in a gravitationally bound system, which is the geometric mean of the cosmological horizon size squared and the Schwarzschild radius. This agrees well with the size of a galactic halo when the effects of dark matter are included. The size of larger structures such as galactic clusters and superclusters are also well-approximated by this scale. This model provides a simplified approach to computing the size of such structures without the usual detailed dynamical models. Some of the more detailed approaches that appear in the literature are reviewed, and we find the length scales agree to within a factor of order one. Finally, we note the length scale associated with the effects of MOND or Verlinde’s emergent gravity, which offer explanations of the flattening of galaxy rotation curves without invoking dark matter, may be expressed as the geometric mean of the cosmological horizon size and the Schwarzschild radius, which is typically 100 times smaller than rΛ.

Relativistically Skewed Iron Emission and Disk Reflection in Galactic Microquasar XTE J1748-288

NASA Technical Reports Server (NTRS)

Miller, J. M.; Fox, D. W.; DiMatteo, T.; Wijnands, R.; Belloni, T.; Kouveliotou, C.; Lewin, W. H. G.

2000-01-01

We report evidence for an Fe K-alpha fluorescence line feature in the Very High, High, and Low state X-ray spectra of the galactic microquasar XTE JI748-288 during its June 1998 outburst. Spectral analyses were made on observations spread across the outburst, gathered with the Rossi X-ray Timing Explorer. Gaussian line. disk emission line, relativistic disk emission line, and disk reflection models are fit to the data. In the Very High State, the line profile is strongly redshifted and consistent with emission from the innermost radius of a maximally rotating Kerr black hole, 1.235 R(sub g). The line profile is less redshifted in the High State, but increasingly prominent. In the Low State, the line profile is very strong and centered af approx. 6.7 keV; disk line emission models constrain the inner edge of the disk to fluctuate between approx.20 and approx.59 R(sub g). We trace the disk reflection fraction across the full outburst of this source, and find well-constrained fractions below those observed in AGN in the Very High and High States, but consistent with other galactic sources in the Low State. We discuss the possible implications for black hole X-ray binary system dynamics and accretion flow geometry.

Magnetic activity in the Galactic Centre region - fast downflows along rising magnetic loops

NASA Astrophysics Data System (ADS)

Kakiuchi, Kensuke; Suzuki, Takeru K.; Fukui, Yasuo; Torii, Kazufumi; Enokiya, Rei; Machida, Mami; Matsumoto, Ryoji

2018-06-01

We studied roles of the magnetic field on the gas dynamics in the Galactic bulge by a three-dimensional global magnetohydrodynamical simulation data, particularly focusing on vertical flows that are ubiquitously excited by magnetic activity. In local regions where the magnetic field is stronger, it is frequently seen that fast downflows slide along inclined magnetic field lines that are associated with buoyantly rising magnetic loops. The vertical velocity of these downflows reaches ˜100 km s-1 near the footpoint of the loops by the gravitational acceleration towards the Galactic plane. The two footpoints of rising magnetic loops are generally located at different radial locations and the field lines are deformed by the differential rotation. The angular momentum is transported along the field lines, and the radial force balance breaks down. As a result, a fast downflow is often observed only at the one footpoint located at the inner radial position. The fast downflow compresses the gas to form a dense region near the footpoint, which will be important in star formation afterwards. Furthermore, the horizontal components of the velocity are also fast near the footpoint because the downflow is accelerated along the magnetic sliding slope. As a result, the high-velocity flow creates various characteristic features in a simulated position-velocity diagram, depending on the viewing angle.

Dynamical lifetime of the new Oort Cloud comets under planetary perturbations

NASA Astrophysics Data System (ADS)

Ito, T.; Higuchi, A.

2014-07-01

Nearly-isotropic comets with very long orbital period are supposed to come from the Oort Cloud. Recent observational and theoretical studies have greatly revealed the dynamical nature of this cloud and its evolutional history, but many issues are yet to be known. Our goal is to trace the dynamical evolution of the Oort Cloud new comets (OCNCs) produced by an evolving comet cloud, hopefully estimating the fraction of OCNCs embedded in the current populations of the solar system small bodies. We combine two models to follow the dynamical evolution of OCNCs beginning from their production until their ejection out of the solar system, obtaining statistics of the dynamical lifetime of OCNCs: The first model is a semi-analytical one about the OCNC production in an evolving comet cloud under the perturbation of the galactic tide and stellar encounters. The second model numerically deals with planetary perturbation over OCNCs' dynamics in planetary region. The main results of the present study are: (1) Typical dynamical lifetime of OCNCs in our models turned out to be O(10^7) years. Once entering into the planetary region, most OCNCs stay there just for this timespan, then get ejected out of the solar system on hyperbolic orbits. (2) While average orbital inclination of OCNCs is small, the so-called ''planet barrier'' works rather effectively, preventing some OCNCs from penetrating into the terrestrial planetary region. Models. Recently a series of detailed dynamical studies with similar scientific objects to ours are published [1-3]. Our present study is an extension of our own independent project [4], using a pair of dynamical models. The first model is for the evolving Oort Cloud that produces OCNCs along its evolution [5,6]. The model initially starts from a planar planetesimal disk, which evolves into a three- dimensional, nearly isotropic shape over a timespan of Gyr under the perturbation by the galactic tide and stellar encounters. This model is largely analytical in order to reduce the amount of computation. The second one is a numerical model for incorporating planetary perturbation from the major seven planets except Mercury, similar to the framework of our previous studies [7,8]. It receives OCNCs from the first model, and traces the orbital evolution of the comets up to 500 Myr until they get ejected out of the solar system by being scattered away. The second model does not include the galactic tide or stellar perturbation. For further reduction of computation amount, we assume that OCNCs go along their Keplerian orbits beyond r = 800 au without any perturbations. The effect of the galactic tide that OCNCs would have during this period is separately evaluated using a perturbation function that includes the galactic tide used in the first model. Results. We selected two different eras among the Oort Cloud history: (a) the initial 1 Gyr while the comet cloud is still nearly planar with a high OCNC production rate, and (b) the period t =4-5 Gyr when the comet cloud is almost in an isotropic shape with nearly constant supply of OCNCs. It turned out that most of the OCNCs got scattered away by the four giant planets (i.e being ejected out of the system with r > 800 au and e > 1, or aphelion distance becoming larger than Q >2 × 10^5 au) with a typical timespan of O(10^7) years in the planetary region. This timescale is roughly consistent with an analytical estimate in [9]. Also, this timescale does not strongly dependent on which era we choose, as the range of OCNC's semimajor axis is similar to each other. To get an estimate as to which planet has the largest dynamical influence on the fate of OCNCs, we calculated the number of planetary encounters defined by OCNC's close approaches within 500 × scatter radius of planets, r_{s} (r_{s} is a typical distance when a massless body's orbit gets bent 90 degrees by scattering. It is proportional to (relative velocity){}^{-2}). A simple analysis shows that Jupiter and Saturn play a dominant role on scattering OCNCs away from the system. There has been a concept called the ''Jupiter barrier'' where giant planets such as Jupiter protect the Earth from cometary bombardments (e.g. [10,11]). Our study partially validates this hypothesis, showing that the planetary barrier actually works when the incoming OCNC flux is nearly planar as in the era (a). The main barrier is composed by Saturn with an aid by Jupiter, making OCNCs' perihelia stick around Saturn's orbit. Once the comet cloud has become isotropic as in the era (b), OCNCs come from almost any directions, and the barrier no longer works. This is just the situation in the current solar system.

Revealing the Character of Orbits in a Binary System Consisting of a Primary Galaxy and a Satellite Companion

NASA Astrophysics Data System (ADS)

Zotos, Euaggelos E.

2013-02-01

In this article, we present a galactic gravitational model of three degrees of freedom (3D), in order to study and reveal the character of the orbits of the stars, in a binary stellar system composed of a primary quiet or active galaxy and a small satellite companion galaxy. Our main dynamical analysis will be focused on the behaviour of the primary galaxy. We investigate in detail the regular or chaotic nature of motion, in two different cases: (i) the time-independent model in both 2D and 3D dynamical systems and (ii) the time-evolving 3D model. For the description of the structure of the 2D system, we use the classical method of the Poincaré (x, px ), y = 0, py < 0 phase plane. In order to study the structure of the phase space of the 3D system, we take sections in the plane y = 0 of the 3D orbits, whose initial conditions differ from the plane parent periodic orbits, only by the z component. The set of the four-dimensional points in the (x, px , z, pz ) phase space is projected on the (z, pz ) plane. The maximum Lyapunov characteristic exponent is used in order to make an estimation of the chaoticity of our galactic system, in both 2D and 3D dynamical models. Our numerical calculations indicate that the percentage of the chaotic orbits increases when the primary galaxy has a dense and massive nucleus. The presence of the dense galactic core also increases the stellar velocities near the center of the galaxy. Moreover, for small values of the distance R between the two bodies, low-energy stars display chaotic motion, near the central region of the galaxy, while for larger values of the distance R, the motion in active galaxies is entirely regular for low-energy stars. Our simulations suggest that in galaxies with a satellite companion, the chaotic nature of motion is not only a result of the galactic interaction between the primary galaxy and its companion, but also a result caused by the presence of the dense nucleus in the core of the primary galaxy. Theoretical arguments are presented in order to support and interpret the numerically derived outcomes. Furthermore, we follow the 3D evolution of the primary galaxy, when mass is transported adiabatically from the disk to the nucleus. Our numerical results are in satisfactory agreement with observational data obtained from the M51-type binary stellar systems. A comparison between the present research and similar and earlier work is also made.

Globular cluster systems - Comparative evolution of Galactic halos

NASA Astrophysics Data System (ADS)

Harris, William E.

Space distributions, metallicity/age distributions, and kinematics are considered for the Milky Way halo system. Comparisons are made with other systems, and time scales for dynamical evolution are considered. It is noted that the globular cluster subsystems of halos resemble each other more closely than their parent galaxies do; this forms a reasonable basis for supposing that they represent a kind of underlying unity in the protogalaxy formation process.

Perchlorate Detection at Nanomolar Concentrations by Surface-Enhanced Raman Scattering

DTIC Science & Technology

2009-01-01

grooves/mm grating light path controlled by Renishaw WiRE software and analyzed by Galactic GRAMS software. RESULTS AND DISCUSSION Quantitative... Federal Rights License 14. ABSTRACT Perchlorate (ClO4 ) has emerged as a widespread environmental contaminant and has been detected in various food...by means of dynamic light scattering using a ZetaPlus particle size analyzer (Brookhaven Instruments, Holtsville, NY). Data were collected for every

A dynamical model for the formation of gas rings and episodic starbursts near galactic centres

NASA Astrophysics Data System (ADS)

Krumholz, Mark R.; Kruijssen, J. M. Diederik

2015-10-01

We develop a simple dynamical model for the evolution of gas in the centres of barred spiral galaxies, using the Milky Way's Central Molecular Zone (CMZ, i.e. the central few hundred pc) as a case study. We show that, in the presence of a galactic bar, gas in a disc in the central regions of a galaxy will be driven inwards by angular momentum transport induced by acoustic instabilities within the bar's inner Lindblad resonance. This transport process drives turbulence within the gas that temporarily keeps it strongly gravitationally stable and prevents the onset of rapid star formation. However, at some point the rotation curve must transition from approximately flat to approximately solid body, and the resulting reduction in shear reduces the transport rates and causes gas to build up, eventually producing a gravitationally unstable region that is subject to rapid and violent star formation. For the observed rotation curve of the Milky Way, the accumulation happens ˜100 pc from the centre of the Galaxy, in good agreement with the observed location of gas clouds and young star clusters in the CMZ. The characteristic time-scale for gas accumulation and star formation is of the order of 10-20 Myr. We argue that similar phenomena should be ubiquitous in other barred spiral galaxies.

Search for OB stars running away from young star clusters. I. NGC 6611

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Bomans, D. J.

2008-11-01

N-body simulations have shown that the dynamical decay of the young (~1 Myr) Orion Nebula cluster could be responsible for the loss of at least half of its initial content of OB stars. This result suggests that other young stellar systems could also lose a significant fraction of their massive stars at the very beginning of their evolution. To confirm this expectation, we used the Mid-Infrared Galactic Plane Survey (completed by the Midcourse Space Experiment satellite) to search for bow shocks around a number of young (⪉several Myr) clusters and OB associations. We discovered dozens of bow shocks generated by OB stars running away from these stellar systems, supporting the idea of significant dynamical loss of OB stars. In this paper, we report the discovery of three bow shocks produced by O-type stars ejected from the open cluster NGC 6611 (M16). One of the bow shocks is associated with the O9.5Iab star HD165319, which was suggested to be one of “the best examples for isolated Galactic high-mass star formation” (de Wit et al. 2005, A&A, 437, 247). Possible implications of our results for the origin of field OB stars are discussed.

Test-particle dynamics in general spherically symmetric black hole spacetimes

NASA Astrophysics Data System (ADS)

De Laurentis, Mariafelicia; Younsi, Ziri; Porth, Oliver; Mizuno, Yosuke; Rezzolla, Luciano

2018-05-01

To date, the most precise tests of general relativity have been achieved through pulsar timing, albeit in the weak-field regime. Since pulsars are some of the most precise and stable "clocks" in the Universe, present observational efforts are focused on detecting pulsars in the vicinity of supermassive black holes (most notably in the Galactic Centre), enabling pulsar timing to be used as an extremely precise probe of strong-field gravity. In this paper, a mathematical framework to describe test-particle dynamics in general black-hole spacetimes is presented and subsequently used to study a binary system comprising a pulsar orbiting a black hole. In particular, taking into account the parameterization of a general spherically symmetric black-hole metric, general analytic expressions for both the advance of the periastron and for the orbital period of a massive test particle are derived. Furthermore, these expressions are applied to four representative cases of solutions arising in both general relativity and in alternative theories of gravity. Finally, this framework is applied to the Galactic center S -stars and four distinct pulsar toy models. It is shown that by adopting a fully general-relativistic description of test-particle motion which is independent of any particular theory of gravity, observations of pulsars can help impose better constraints on alternative theories of gravity than is presently possible.

Galactic Spiral Shocks with Thermal Instability in Vertically Stratified Disks

NASA Astrophysics Data System (ADS)

Kim, Chang-Goo; Kim, W.; Ostriker, E. C.

2010-01-01

Galactic spiral shocks are dominant morphological features and believed to be responsible for substructure formation of spiral arms in disk galaxies. They can also provide a large amount of kinetic energy for the interstellar gas by tapping the rotational energy. We use numerical hydrodynamic simulations to investigate dynamics and structure of spiral shocks with thermal instability in vertically stratified galactic disks. We initially consider an isothermal disk in vertical hydrostatic equilibrium and let it evolve under interstellar cooling and heating. Due to cooling and heating, the disk rapidly turns to a dense slab near the midplane surrounded by rarefied gas at high-altitude regions. The imposed stellar spiral potential develops a vertically curved shock that exhibits strong flapping motions along the direction perpendicular to the arm. The flows across the spiral shock are characterized by transitions from rarefied to dense phases at the shock and from dense to rarefied phases at the postshock expansion zone. The shock flapping motions stirs the disk, supplying the gas with random kinetic energy. For a model resembling the galactic disk near the solar neighborhood, the density-weighted vertical velocity dispersions are 2 km/s for the rarefied gas and 1 km/s for the dense gas. The shock compression in this model reduces an amount of the rarefied gas from 29% to 19% by mass. Despite the flapping motions, the time-averaged profiles of surface density are similar to those of the one-dimensional counterparts, and the vertical density distribution is overall consistent with effective hydrostatic equilibrium. When self-gravity is included, the shock compression forms large gravitationally bound condensations with virial ratio of about 2 and typical masses of 0.5 to one million solar masses, comparable to the Jeans mass.

Characterizing the Norma Overdensity

NASA Astrophysics Data System (ADS)

Sargent, Benjamin; Chakrabarti, Sukanya; Boyer, Martha; Angeloni, Rodolfo; Sarajedini, Ata; Guhathakurta, Raja

2018-05-01

We recently discovered receding, clustered Cepheid candidates towards the Norma constellation that may mark a new dwarf galaxy of the Milky Way. If this dwarf galaxy is confirmed, this would be a breakthrough in near-field cosmology, as it would represent the first dwarf galaxy that was predicted by a dynamical analysis to be subsequently discovered. Underlying the search for this dwarf galaxy is the hope that one could characterize dark-matter dominated dwarf galaxies from analysis of disturbances in Galactic disks, i.e., Galactoseismology. At b 1, it would also be the closest dwarf galaxy to the Galactic plane. Aside from its expected distinct kinematics, another signature of a dwarf galaxy is an excess of stars in the CMD. When we correct for extinction the VVV photometry of the area where we saw the Cepheid candidates and subtract out a control field (i.e. a Galactic background field), we see an excess of stars that may correspond to red-clump stars at a distance of 80 kpc. However, we used the Bonifacio et al. (2000) extinction prescription that is known to be inaccurate close to the Galactic plane. Majewski et al. (2011) have shown that the combination of NIR and MIR colors, namely H-4.5 micron or K_s - 3.6 micron, can produce a far better extinction correction than prior extinction maps. To extinction correct the VVV data, we need Spitzer data that is complete down to 17 mag in 4.5 um. Deep MIR data are crucial for us to do the extinction correction properly, and Spitzer is the only instrument that can enable this effort. By appropriately correcting the VVV and F2 photometry for extinction following Majewski et al. (2011), we should be able to separate the stellar populations of the expected dwarf galaxy candidate.

Spherical accretion in giant elliptical galaxies: multi-transonicity, shocks, and implications on AGN feedback

NASA Astrophysics Data System (ADS)

Raychaudhuri, Sananda; Ghosh, Shubhrangshu; Joarder, Partha S.

2018-06-01

Isolated massive elliptical galaxies, or that are present at the center of cool-core clusters, are believed to be powered by hot gas accretion directly from their surrounding hot X-ray emitting gaseous medium. This leads to a giant Bondi-type spherical/quasi-spherical accretion flow onto their host SMBHs, with the accretion flow region extending well beyond the Bondi radius. In this work, we present a detailed study of Bondi-type spherical flow in the context of these massive ellipticals by incorporating the effect of entire gravitational potential of the host galaxy in the presence of cosmological constant Λ, considering a five-component galactic system (SMBH + stellar + dark matter + hot gas + Λ). The current work is an extension of Ghosh & Banik (2015), who studied only the cosmological aspect of the problem. The galactic contribution to the potential renders the (adiabatic) spherical flow to become multi-transonic in nature, with the flow topology and flow structure significantly deviating from that of classical Bondi solution. More notably, corresponding to moderate to higher values of galactic mass-to-light ratios, we obtain Rankine-Hugoniot shocks in spherical wind flows. Galactic potential enhances the Bondi accretion rate. Our study reveals that there is a strict lower limit of ambient temperature below which no Bondi accretion can be triggered; which is as high as ˜9 × 106 K for flows from hot ISM-phase, indicating that the hot phase tightly regulates the fueling of host nucleus. Our findings may have wider implications, particularly in the context of outflow/jet dynamics, and radio-AGN feedback, associated with these massive galaxies in the contemporary Universe.

The Masses and Accretion Rates of White Dwarfs in Classical and Recurrent Novae

NASA Astrophysics Data System (ADS)

Shara, Michael M.; Prialnik, Dina; Hillman, Yael; Kovetz, Attay

2018-06-01

Models have long predicted that the frequency-averaged masses of white dwarfs (WDs) in Galactic classical novae are twice as large as those of field WDs. Only a handful of dynamically well-determined nova WDs masses have been published, leaving the theoretical predictions poorly tested. The recurrence time distributions and mass accretion rate distributions of novae are even more poorly known. To address these deficiencies, we have combined our extensive simulations of nova eruptions with the Strope et al. and Schaefer databases of outburst characteristics of Galactic classical and recurrent novae (RNe) to determine the masses of 92 WDs in novae. We find that the mean mass (frequency-averaged mean mass) of 82 Galactic classical novae is 1.06 (1.13) M ⊙, while the mean mass of 10 RNe is 1.31 M ⊙. These masses, and the observed nova outburst amplitude and decline time distributions allow us to determine the long-term mass accretion rate distribution of classical novae. Remarkably, that value is just 1.3 × 10‑10 M ⊙ yr‑1, which is an order of magnitude smaller than that of cataclysmic binaries in the decades before and after classical nova eruptions. This predicts that old novae become low-mass transfer rate systems, and hence dwarf novae, for most of the time between nova eruptions. We determine the mass accretion rates of each of the 10 known Galactic recurrent nova, finding them to be in the range of 10‑7–10‑8 M ⊙ yr‑1. We are able to predict the recurrence time distribution of novae and compare it with the predictions of population synthesis models.

The Galactic Center S-stars and the Hypervelocity Stars in the Galactic Halo: Two Faces of the Tidal Breakup of Stellar Binaries by the Central Massive Black Hole?

NASA Astrophysics Data System (ADS)

Zhang, Fupeng; Lu, Youjun; Yu, Qingjuan

2013-05-01

In this paper, we investigate the link between the hypervelocity stars (HVSs) discovered in the Galactic halo and the Galactic center (GC) S-stars, under the hypothesis that they are both the products of the tidal breakup of the same population of stellar binaries by the central massive black hole (MBH). By adopting several hypothetical models for binaries to be injected into the vicinity of the MBH and doing numerical simulations, we realize the tidal breakup processes of the binaries and their follow-up dynamical evolution. We find that many statistical properties of the detected HVSs and GC S-stars could be reproduced under some binary injecting models, and their number ratio can be reproduced if the stellar initial mass function is top-heavy (e.g., with slope ~ - 1.6). The total number of the captured companions is ~50 that have masses in the range ~3-7 M ⊙ and semimajor axes <~ 4000 AU and survive to the present within their main-sequence lifetime. The innermost one is expected to have a semimajor axis ~300-1500 AU and a pericenter distance ~10-200 AU, with a significant probability of being closer to the MBH than S2. Future detection of such a close star would offer an important test to general relativity. The majority of the surviving ejected companions of the GC S-stars are expected to be located at Galactocentric distances <~ 20 kpc, and have heliocentric radial velocities ~ - 500-1500 km s-1 and proper motions up to ~5-20 mas yr-1. Future detection of these HVSs may provide evidence for the tidal breakup formation mechanism of the GC S-stars.

The Smith Cloud: surviving a high-speed transit of the Galactic disc

NASA Astrophysics Data System (ADS)

Tepper-García, Thor; Bland-Hawthorn, Joss

2018-02-01

The origin and survival of the Smith high-velocity H I cloud has so far defied explanation. This object has several remarkable properties: (i) its prograde orbit is ≈100 km s-1 faster than the underlying Galactic rotation; (ii) its total gas mass (≳ 4 × 106 M⊙) exceeds the mass of all other high-velocity clouds (HVCs) outside of the Magellanic Stream; (iii) its head-tail morphology extends to the Galactic H I disc, indicating some sort of interaction. The Smith Cloud's kinetic energy rules out models based on ejection from the disc. We construct a dynamically self-consistent, multi-phase model of the Galaxy with a view to exploring whether the Smith Cloud can be understood in terms of an infalling, compact HVC that has transited the Galactic disc. We show that while a dark-matter (DM) free HVC of sufficient mass and density can reach the disc, it does not survive the transit. The most important ingredient to survival during a transit is a confining DM subhalo around the cloud; radiative gas cooling and high spatial resolution (≲ 10pc) are also essential. In our model, the cloud develops a head-tail morphology within ∼10 Myr before and after its first disc crossing; after the event, the tail is left behind and accretes on to the disc within ∼400 Myr. In our interpretation, the Smith Cloud corresponds to a gas 'streamer' that detaches, falls back and fades after the DM subhalo, distorted by the disc passage, has moved on. We conclude that subhaloes with MDM ≲ 109 M⊙ have accreted ∼109 M⊙ of gas into the Galaxy over cosmic time - a small fraction of the total baryon budget.

Search for EeV protons of galactic origin

NASA Astrophysics Data System (ADS)

Abbasi, R. U.; Abe, M.; Abu-Zayyad, T.; Allen, M.; Azuma, R.; Barcikowski, E.; Belz, J. W.; Bergman, D. R.; Blake, S. A.; Cady, R.; Cheon, B. G.; Chiba, J.; Chikawa, M.; Fujii, T.; Fukushima, M.; Goto, T.; Hanlon, W.; Hayashi, Y.; Hayashi, M.; Hayashida, N.; Hibino, K.; Honda, K.; Ikeda, D.; Inoue, N.; Ishii, T.; Ishimori, R.; Ito, H.; Ivanov, D.; Jui, C. C. H.; Kadota, K.; Kakimoto, F.; Kalashev, O.; Kasahara, K.; Kawai, H.; Kawakami, S.; Kawana, S.; Kawata, K.; Kido, E.; Kim, H. B.; Kim, J. H.; Kim, J. H.; Kishigami, S.; Kitamura, S.; Kitamura, Y.; Kuzmin, V.; Kwon, Y. J.; Lan, J.; Lubsandorzhiev, B.; Lundquist, J. P.; Machida, K.; Martens, K.; Matsuda, T.; Matsuyama, T.; Matthews, J. N.; Minamino, M.; Mukai, K.; Myers, I.; Nagasawa, K.; Nagataki, S.; Nakamura, T.; Nonaka, T.; Nozato, A.; Ogio, S.; Ogura, J.; Ohnishi, M.; Ohoka, H.; Oki, K.; Okuda, T.; Ono, M.; Onogi, R.; Oshima, A.; Ozawa, S.; Park, I. H.; Pshirkov, M. S.; Rodriguez, D. C.; Rubtsov, G.; Ryu, D.; Sagawa, H.; Saito, K.; Saito, Y.; Sakaki, N.; Sakurai, N.; Scott, L. M.; Sekino, K.; Shah, P. D.; Shibata, T.; Shibata, F.; Shimodaira, H.; Shin, B. K.; Shin, H. S.; Smith, J. D.; Sokolsky, P.; Stokes, B. T.; Stratton, S. R.; Stroman, T. A.; Suzawa, T.; Takahashi, Y.; Takamura, M.; Takeda, M.; Takeishi, R.; Taketa, A.; Takita, M.; Tameda, Y.; Tanaka, M.; Tanaka, K.; Tanaka, H.; Thomas, S. B.; Thomson, G. B.; Tinyakov, P.; Tirone, A. H.; Tkachev, I.; Tokuno, H.; Tomida, T.; Troitsky, S.; Tsunesada, Y.; Tsutsumi, K.; Uchihori, Y.; Udo, S.; Urban, F.; Wong, T.; Yamane, R.; Yamaoka, H.; Yamazaki, K.; Yang, J.; Yashiro, K.; Yoneda, Y.; Yoshida, S.; Yoshii, H.; Zollinger, R.; Zundel, Z.

2017-01-01

Cosmic rays in the energy range 1018.0-1018.5 eV are thought to have a light, probably protonic, composition. To study their origin one can search for anisotropy in their arrival directions. Extragalactic cosmic rays should be isotropic, but galactic cosmic rays of this type should be seen mostly along the galactic plane, and there should be a shortage of events coming from directions near the galactic anticenter. This is due to the fact that, under the influence of the galactic magnetic field, the transition from ballistic to diffusive behavior is well advanced, and this qualitative picture persists over the whole energy range. Guided by models of the galactic magnetic field that indicate that the enhancement along the galactic plane should have a standard deviation of about 20° in galactic latitude, and the deficit in the galactic anticenter direction should have a standard deviation of about 50° in galactic longitude, we use the data of the Telescope Array surface detector in 1018.0 to 1018.5 eV energy range to search for these effects. The data are isotropic. Neither an enhancement along the galactic plane nor a deficit in the galactic anticenter direction is found. Using these data we place an upper limit on the fraction of EeV cosmic rays of galactic origin at 1.3% at 95% confidence level.

Chemo-dynamical signatures in simulated Milky Way-like galaxies

NASA Astrophysics Data System (ADS)

Spagna, Alessandro; Curir, Anna; Giammaria, Marco; Lattanzi, Mario G.; Murante, Giuseppe; Re Fiorentin, Paola

2018-04-01

We have investigated the chemo-dynamical evolution of a Milky Way-like disk galaxy, AqC4, produced by a cosmological simulation integrating a sub-resolution ISM model. We evidence a global inside-out and upside-down disk evolution, that is consistent with a scenario where the ``thin disk'' stars are formed from the accreted gas close to the galactic plane, while the older ``thick disk'' stars are originated in situ at higher heights. Also, the bar appears the most effective heating mechanism in the inner disk. Finally, no significant metallicity-rotation correlation has been observed, in spite of the presence of a negative [Fe/H] radial gradient.

The influence of cosmic rays on the stability and large-scale dynamics of the interstellar medium

NASA Astrophysics Data System (ADS)

Kuznetsov, V. D.

1986-06-01

The diffusion-convection formulation is used to study the influence of galactic cosmic rays on the stability and dynamics of the interstellar medium which is supposedly kept in equilibrium by the gravitational field of stars. It is shown that the influence of cosmic rays on the growth rate of MHD instability depends largely on a dimensionless parameter expressing the ratio of the characteristic acoustic time scale to the cosmic-ray diffusion time. If this parameter is small, the cosmic rays will decelerate the build-up of instabilities, thereby stabilizing the system; in contrast, if the parameter is large, the system will be destabilized.

A Modern Picture of Barred Galaxy Dynamics

NASA Astrophysics Data System (ADS)

Petersen, Michael; Weinberg, Martin; Katz, Neal

2018-01-01

Observations of disk galaxies suggest that bars are responsible for altering global galaxy parameters (e.g. structures, gas fraction, star formation rate). The canonical understanding of the mechanisms underpinning bar-driven secular dynamics in disk galaxies has been largely built upon the analysis of linear theory, despite galactic bars being clearly demonstrated to be nonlinear phenomena in n-body simulations. We present simulations of barred Milky Way-like galaxy models designed to elucidate nonlinear barred galaxy dynamics. We have developed two new methodologies for analyzing n-body simulations that give the best of both powerful analytic linear theory and brute force simulation analysis: orbit family identification and multicomponent torque analysis. The software will be offered publicly to the community for their own simulation analysis.The orbit classifier reveals that the details of kinematic components in galactic disks (e.g. the bar, bulge, thin disk, and thick disk components) are powerful discriminators of evolutionary paradigms (i.e. violent instabilities and secular evolution) as well as the basic parameters of the dark matter halo (mass distribution, angular momentum distribution). Multicomponent torque analysis provides a thorough accounting of the transfer of angular momentum between orbits, global patterns, and distinct components in order to better explain the underlying physics which govern the secular evolution of barred disk galaxies.Using these methodologies, we are able to identify the successes and failures of linear theory and traditional n-body simulations en route to a detailed understanding of the control bars exhibit over secular evolution in galaxies. We present explanations for observed physical and velocity structures in observations of barred galaxies alongside predictions for how structures will vary with dynamical properties from galaxy to galaxy as well as over the lifetime of a galaxy, finding that the transfer of angular momentum through previously unidentified channels can more fully explain the observed dynamics.

Proper Motion of the Compact, Nonthermal Radio Source in the Galactic Center, Sagittarius A*

NASA Astrophysics Data System (ADS)

Backer, D. C.; Sramek, R. A.

1999-10-01

Proper motions and radial velocities of luminous infrared stars in the Galactic center have provided strong evidence for a dark mass of 2.5×106 Msolar in the central 0.05 pc of the Galaxy. The leading hypothesis for this mass is a black hole. High angular resolution measurements at radio wavelengths find a compact radio source, Sagittarius (Sgr) A*, that is either the faint glow from a small amount of material accreting onto the hole with low radiative efficiency or a miniature active galactic nucleus (AGN) core-jet system. This paper provides a full report on the first program that has measured the apparent proper motion of Sgr A* with respect to background extragalactic reference frame. Our current result isμl,*=[-6.18+/-0.19] mas yr-1 μb,*=[-0.65+/-0.17] mas yr-1 . The observations were obtained with the NRAO Very Large Array at 4.9 GHz over 16 yr. The proper motion of Sgr A* provides an estimate of its mass based on equipartition of kinetic energy between the hole and the surrounding stars. The measured motion is largest in galactic longitude. This component of the motion is consistent with the secular parallax that results from the rotation of the solar system about the center, which is a global measure of the difference between Oort's constants (A-B), with no additional peculiar motion of Sgr A*. The current uncertainty in Oort's galactic rotation constants limits the use of this component of the proper motion for a mass inference. In latitude, we find a small, and weakly significant, peculiar motion of Sgr A*, -19+/-7 km s-1 after correction for the motion of the solar system with respect to the local standard of rest. We consider sources of peculiar motion of Sgr A* ranging from unstable radio wave propagation through intervening turbulent plasma to the effects of asymmetric masses in the center. These fail to account for a significant peculiar motion. One can appeal to an m=1 dynamical instability that numerical simulations have revealed. However, the measurement of a latitude peculiar proper motion of comparable magnitude and error but with opposite sign in the companion paper by Reid leads us to conclude at the present time that our errors may be underestimated and that the actual peculiar motion might therefore be closer to zero. Improvement of these measurements with further observations and resolving the differences between independent experiments will provide the accuracies of a few km s-1 in both coordinates that will provide both a black hole mass estimate and a definitive determination of Oort's galactic rotation constants on a global Galactic scale.

Open Cluster Dynamics via Fundamental Plane

NASA Astrophysics Data System (ADS)

Lin, Chien-Cheng; Pang, Xiao-Ying

2018-04-01

Open clusters (OCs) are important objects for stellar dynamics studies. The short survival timescale of OCs makes them closely related to the formation of Galactic field stars. We motivate to investigate the dynamical evolution of OCs on the aspect of internal effect and the external influence. Firstly, we make use of the known OC catalog to obtain OCs masses, effective radii. Additionally, we estimate OCs kinematics properties by OC members cross-matched with radial velocity and metallicity from SDSSIV/APOGEE2. We then establish the fundamental plane of OCs based on the radial velocity dispersion, the effective radius, and average surface brightness. The deviation of the fundamental plane from the Virial Plane, so called the tilt, and the r.m.s. dispersion of OCs around the average plane are used to indicate the dynamical status of OCs. Parameters of the fitted plane will vary with cluster age and distance.

Effect of tidal fields on star clusters

NASA Technical Reports Server (NTRS)

Chernoff, David; Weinberg, Martin

1991-01-01

We follow the dynamical evolution of a star cluster in a galactic tidal field using a restricted N-body code. We find large asymmetric distortions in the outer profile of the cluster in the first 10 or so crossing times as material is lost. Prograde stars escape preferentially and establish a potentially observable retrograde rotation in the halo. We present the rate of particle loss and compare with the prescription proposed by Lee and Ostriker (1987).

S2 like Star Orbits near the Galactic Center in Rn and Yukawa Gravity

NASA Astrophysics Data System (ADS)

Borka, Dusko; Jovanović, Predrag; Jovanović Vesna Borka; Zakharov, Alexander F.

2015-01-01

In this chapter we investigate the possibility to provide theoretical explanation for the observed deviations of S2 star orbit around the Galactic Center using gravitational potentials derived from extended gravity models, but in absence of dark matter. Extended Theories of Gravity are alternative theories of gravitational interaction developed from the exact starting points investigated first by Einstein and Hilbert and aimed from one side to extend the positive results of General Relativity and, on the other hand, to cure its shortcomings. One of the aims of these theories is to explain galactic and extragalactic dynamics without introduction of dark matter. They are based on straightforward generalizations of the Einstein theory where the gravitational action (the Hilbert-Einstein action) is assumed to be linear in the Ricci curvature scalar R. The f(R) gravity is a type of modified gravity which generalizes Einstein's General Relativity, i.e. the simplest case is just the General Relativity. It is actually a family of models, each one defined by a different function of the Ricci scalar. Here, we consider Rn (power-law fourth-order theories of gravity) and Yukawa-like modified gravities in the weak field limit and discuss the constrains on these theories. For that purpose we simulate the orbit of S2 star around the Galactic Center in Rn and Yukawa-like gravity potentials and compare it with New Technology Telescope/Very Large Telescope (NTT/VLT) as well as by Keck telescope observations. Our simulations result in strong constraints on the range of gravity interaction and showed that both Rn and Yukawa gravity could satisfactorily explain the observed orbits of S2 star. However, we concluded that parameters of Rn and Yukawa gravity theories must be very close to those corresponding to the Newtonian limit of the theory. Besides, in contrast to Newtonian gravity, these two modified theories induce orbital precession, even in the case of point-like central mass. The approach we are proposing seems to be sufficiently reliable to constrain the modified gravity models from stellar orbits around Galactic Center.

OT2_tvelusam_4: Probing Galactic Spiral Arm Tangencies with [CII

NASA Astrophysics Data System (ADS)

Velusamy, T.

2011-09-01

We propose to use the unique viewing geometry of the Galactic spiral arm tangents , which provide an ideal environment for studying the effects of density waves on spiral structure. We propose a well-sampled map of the[C II] 1.9 THz line emission along a 15-degree longitude region across the Norma-3kpc arm tangential, which includes the edge of the Perseus Arm. The COBE-FIRAS instrument observed the strongest [C II] and [N II] emission along these spiral arm tangencies.. The Herschel Open Time Key Project Galactic Observations of Terahertz C+ (GOT C+), also detects the strongest [CII] emission near these spiral arm tangential directions in its sparsely sampled HIFI survey of [CII] in the Galactic plane survey. The [C II] 158-micron line is the strongest infrared line emitted by the ISM and is an excellent tracer and probe of both the diffuse gases in the cold neutral medium (CNM) and the warm ionized medium (WIM). Furthermore, as demonstrated in the GOTC+ results, [C II] is an efficient tracer of the dark H2 gas in the ISM that is not traced by CO or HI observations. Thus, taking advantage of the long path lengths through the spiral arm across the tangencies, we can use the [C II] emission to trace and characterize the diffuse atomic and ionized gas as well as the diffuse H2 molecular gas in cloud transitions from HI to H2 and C+ to C and CO, throughout the ISM. The main goal of our proposal is to use the well sampled (at arcmin scale) [C II] to study these gas components of the ISM in the spiral-arm, and inter-arm regions, to constrain models of the spiral structure and to understand the influence of spiral density waves on the Galactic gas and the dynamical interaction between the different components. The proposed HIFI observations will consist of OTF 15 degree longitude scans and one 2-degree latitude scan sampled every 40arcsec across the Norma- 3kpc Perseus Spiral tangency.

A starburst region at the tip of the Galactic bar around l=347-350

NASA Astrophysics Data System (ADS)

Marco, Amparo; Negueruela, Ignacio; González-Fernández, Carlos; Maíz-Apellániz, Jesús; Dorda, Ricardo; Clark, J. Simon

2015-08-01

In the past few years, several clusters of red supergiants have been discovered in a small region of the Milky Way, close to the base of the Scutum-Crux Arm and the tip of the Long Bar, between l=24º and l=29º. According to the number of observed red supergiants and using population synthesis models, they must contain very large stellar populations to harbour so many RSGs, some of them being candidates to the most massive young clusters in the Galaxy. These massive open clusters are part of a huge structure most likely containing hundreds of red supergiants. These results suggest that the Scutum complex represents a giant star formation region triggered by dynamical excitation by the Galactic bar, whose tip is believed to intersect the Scutum-Crux Arm close to this region. If this scenario is correct, a similar structure would be expected close to the opposite end of the Galactic long bar. We must find in an area between l=347º-350º (these sight lines include the expected location of the far tip of the Galactic bar in the model of González-Fernández et al. (2012)) likely candidates to very massive open clusters.We are carrying out a comprehensive optical and infrared photometric and spectroscopic study of this region containing the open clusters VdBH 222, Teutsch 85 and their surroundings. We have analyzed the population of VdBH 222 and we have found a large population of luminous supergiants and OB stars. The cluster lies behind ~7.5 mag of extinction and has a probable distance of ~ 10 kpc and an age of ~12 Ma. VdBH 222 is a young massive cluster with a likely mass > 20000 Msolar. Now, we are analyzing the population of the open cluster Teutsch 85 and surroundings, finding a numerous population of supergiants.In this work, we will discuss the possible role of the Galactic bar in triggering the formation of starburst clusters.

Deformation of the Galactic Centre stellar cusp due to the gravity of a growing gas disc

NASA Astrophysics Data System (ADS)

Kaur, Karamveer; Sridhar, S.

2018-06-01

The nuclear star cluster surrounding the massive black hole at the Galactic Centre consists of young and old stars, with most of the stellar mass in an extended, cuspy distribution of old stars. The compact cluster of young stars was probably born in situ in a massive accretion disc around the black hole. We investigate the effect of the growing gravity of the disc on the orbits of the old stars, using an integrable model of the deformation of a spherical star cluster with anisotropic velocity dispersions. A formula for the perturbed phase-space distribution function is derived using linear theory, and new density and surface density profiles are computed. The cusp undergoes a spheroidal deformation with the flattening increasing strongly at smaller distances from the black hole; the intrinsic axis ratio ˜0.8 at ˜0.15 pc. Stellar orbits are deformed such that they spend more time near the disc plane and sample the dense inner parts of the disc; this could result in enhanced stripping of the envelopes of red giant stars. Linear theory accounts only for orbits whose apsides circulate. The non-linear theory of adiabatic capture into resonance is needed to understand orbits whose apsides librate. The mechanism is a generic dynamical process, and it may be common in galactic nuclei.

3D Asymmetrical motions of the Galactic outer disc with LAMOST K giant stars

NASA Astrophysics Data System (ADS)

Wang, Haifeng; López-Corredoira, Martín; Carlin, Jeffrey L.; Deng, Licai

2018-07-01

We present a three dimensional velocity analysis of Milky Way disc kinematics using LAMOST K giant stars and the GPS1 proper motion catalogue. We find that Galactic disc stars near the anticentre direction (in the range of Galactocentric distance between R = 8 and 13 kpc and vertical position between Z = -2 and 2 kpc) exhibit asymmetrical motions in the Galactocentric radial, azimuthal, and vertical components. Radial motions are not zero, thus departing from circularity in the orbits; they increase outwards within R ≲ 12 kpc, show some oscillation in the northern (0 < Z < 2 kpc) stars, and have north-south asymmetry in the region corresponding to a well-known nearby northern structure in the velocity field. There is a clear vertical gradient in azimuthal velocity, and also an asymmetry that shifts from a larger azimuthal velocity above the plane near the solar radius to faster rotation below the plane at radii of 11-12 kpc. Stars both above and below the plane at R ≳ 9 kpc exhibit net upward vertical motions. We discuss some possible mechanisms that might create the asymmetrical motions, such as external perturbations due to dwarf galaxy minor mergers or dark matter sub-haloes, warp dynamics, internal processes due to spiral arms or the Galactic bar, and (most likely) a combination of some or all of these components.

The structure and content of the galaxy and galactic gamma rays. [conferences

NASA Technical Reports Server (NTRS)

Fichtel, C. E.; Stecker, F. W.

1976-01-01

Papers are presented dealing with galactic structure drawing on all branches of galactic astronomy with emphasis on the implications of the new gamma ray observations. Topics discussed include: (1) results from the COS-B gamma ray satellite; (2) results from SAS-2 on gamma ray pulsar, Cygnus X-3, and maps of the galactic diffuse flux; (3) recent data from CO surveys of the galaxy; (4) high resolution radio surveys of external galaxies; (5) results on the galactic distribution of pulsars; and (6) theoretical work on galactic gamma ray emission.

Astrophysical targets of the Fresnel diffractive imager

NASA Astrophysics Data System (ADS)

Koechlin, L.; Deba, P.; Raksasataya, T.

2017-11-01

The Fresnel Diffractive imager is an innovative concept of distributed space telescope, for high resolution (milli arc-seconds) spectro-imaging in the IR, visible and UV domains. This paper presents its optical principle and the science that can be done on potential astrophysical targets. The novelty lies in the primary optics: a binary Fresnel array, akin to a binary Fresnel zone plate. The main interest of this approach is the relaxed manufacturing and positioning constraints. While having the resolution and imaging capabilities of lens or mirrors of equivalent size, no optical material is involved in the focusing process: just vacuum. A Fresnel array consists of millions void subapertures punched into a large and thin opaque membrane, that focus light by diffraction into a compact and highly contrasted image. The positioning law of the aperture edges drives the image quality and contrast. This optical concept allows larger and lighter apertures than solid state optics, aiming to high angular resolution and high dynamic range imaging, in particular for UV applications. Diffraction focusing implies very long focal distances, up to dozens of kilometers, which requires at least a two-vessel formation flying in space. The first spacecraft, "the Fresnel Array spacecraft", holds the large punched foil: the Fresnel Array. The second, the "Receiver spacecraft" holds the field optics and focal instrumentation. A chromatism correction feature enables moderately large (20%) relative wavebands, and fields of a few to a dozen arc seconds. This Fresnel imager is adapted to high contrast stellar environments: dust disks, close companions and (we hope) exoplanets. Specific to the particular grid-like pattern of the primary focusing zone plate, is the very high dynamic range achieved in the images, in the case of compact objects. Large stellar photospheres may also be mapped with Fresnel arrays of a few meters opertaing in the UV. Larger and more complex fields can be imaged with a lesser dynamic range: galactic or extragalactic, or at the opposite distance scale: small solar system bodies. This paper will briefly address the optical principle, and in more detail the astrophysical missions and targets proposed for a 4-meter class demonstrator: - Exoplanet imaging, Exoplanet spectroscopic analysis in the visible and UV, - Stellar environments, young stellar systems, disks, - Galactic clouds, astrochemistry, - IR observation of the galactic center, - Small objects of our solar system.

New results and techniques in space radio astronomy.

NASA Technical Reports Server (NTRS)

Alexander, J. K.

1971-01-01

The methods and results of early space radioastronomy experiments are reviewed, with emphasis on the RAE 1 spacecraft which was designed specifically and exclusively for radio astronomical studies. The RAE 1 carries two gravity-gradient-stabilized 229-m traveling-wave V-antennas, a 37-m dipole antenna, and a number of radiometer systems to provide measurements over the 0.2 to 9.2 MHz frequency range with a time resolution of 0.5 sec and an absolute accuracy of plus or minus 25%. Observations of solar bursts at frequencies down to 0.2 MHz provide new information on the density, plasma velocity, and dynamics of coronal streamers out to distances greater than 50 solar radii. New information on the distribution of the ionized component of the interstellar medium is being obtained from galactic continuum background maps at frequencies around 4 MHz. Cosmic noise background spectra measured down to 0.5 MHz produce new estimates on the interstellar flux of cosmic rays, on magnetic fields in the galactic halo, and on distant extragalactic radio sources.

A Multi-Wavelength Survey of Intermediate-Mass Star-Forming Regions

NASA Astrophysics Data System (ADS)

Lundquist, Michael J.; Kobulnicky, Henry A.; Kerton, Charles R.

2015-01-01

Current research into Galactic star formation has focused on either massive star-forming regions or nearby low-mass regions. We present results from a survey of Galactic intermediate-mass star-forming regions (IM SFRs). These regions were selected from IRAS colors that specify cool dust and large PAH contribution, suggesting that they produce stars up to but not exceeding about 8 solar masses. Using WISE data we have classified 984 candidate IM SFRs as star-like objects, galaxies, filamentary structures, or blobs/shells based on their mid-infrared morphologies. Focusing on the blobs/shells, we combined follow-up observations of deep near-infrared (NIR) imaging with optical and NIR spectroscopy to study the stellar content, confirming the intermediate-mass nature of these regions. We also gathered CO data from OSO and APEX to study the molecular content and dynamics of these regions. We compare these results to those of high-mass star formation in order to better understand their role in the star-formation paradigm.

ARMAS and NAIRAS Comparisons of Radiation at Aviation Altitudes

NASA Astrophysics Data System (ADS)

Bell, L. D.

2015-12-01

Space Environment Technologies and the Space Weather Center (SWC) at Utah State University are deploying and obtaining effective dose rate radiation data from dosimeters flown on research aircraft. This project is called Automated Radiation Measurements for Aerospace Safety (ARMAS). Through several dozen flights since 2013 the ARMAS project has successfully demonstrated the operation of a micro-dosimeter on commercial aviation altitude aircraft that captures the real-time radiation environment resulting from galactic cosmic rays (GCR's) and solar energetic particles (SEP's). Space weather effects upon the near Earth environment are to dynamic changes in the energy transfer process from the Sun's photons, particles, and fields. The coupling between the solar and galactic high-energy particles, and atmospheric regions can significantly affect human tissue and the aircrafts technology as a result of radiation exposure. We describe and compare the types of radiation we have been measuring with the NAIRAS global climatological model as it relates to human tissue susceptibility and as a source at different altitude regions.

Synoptic GNIRS XD Spectra ToO Novae

NASA Astrophysics Data System (ADS)

Woodward, Chick; Helton, Andrew; Spitzer/Chandra Team

2007-02-01

Novae are important contributors to galactic chemical enrichment on local scales. NIR spectroscopy of novae provides information about the elemental abundances of the gas and dust in the ejecta dispersing into the ISM as well as kinematic information related to the outburst. We propose to obtain synoptic GNIRS spectra of select Target of Opportunity (ToO) novae in the Magellanic Clouds (MC) and the galaxy to study the dynamics of the ejecta, to determine the temporal evolution of coronal lines and recombination lines (measuring their strength and velocity profiles), and to determine abundances. Being all equidistant, MC nova permit a more robust analysis of distant-dependent physical parameters of outburst than is generally possible for Galactic novae. The GNIRS data will provide critical spectral coverage and synoptic data to complement extant Spitzer and Chandra nova programs. Triggering of the GNIRS program will occur when a nova becomes brighter than V=12 mag, (assuming that adequate PWFS guide stars exist) as reported in the IAUC or CBET.

Galactic Halo Stars in Phase Space: A Hint of Satellite Accretion?

NASA Astrophysics Data System (ADS)

Brook, Chris B.; Kawata, Daisuke; Gibson, Brad K.; Flynn, Chris

2003-03-01

The present-day chemical and dynamical properties of the Milky Way bear the imprint of the Galaxy's formation and evolutionary history. One of the most enduring and critical debates surrounding Galactic evolution is that regarding the competition between ``satellite accretion'' and ``monolithic collapse'' the apparent strong correlation between orbital eccentricity and metallicity of halo stars was originally used as supporting evidence for the latter. While modern-day unbiased samples no longer support the claims for a significant correlation, recent evidence has been presented by Chiba & Beers for the existence of a minor population of high-eccentricity metal-deficient halo stars. It has been suggested that these stars represent the signature of a rapid (if minor) collapse phase in the Galaxy's history. Employing velocity and integrals of motion phase-space projections of these stars, coupled with a series of N-body/smoothed particle hydrodynamic chemodynamical simulations, we suggest that an alternative mechanism for creating such stars may be the recent accretion of a polar orbit dwarf galaxy.

Clarification of the formation process of the super massive black hole by Infrared astrometric satellite, Small-JASMINE

NASA Astrophysics Data System (ADS)

Yano, Taihei; JASMINE-WG

2018-04-01

Small-JASMINE (hearafter SJ), infrared astrometric satellite, will measure the positions and the proper motions which are located around the Galactic center, by operating at near infrared wave-lengths. SJ will clarify the formation process of the super massive black hole (hearafter SMBH) at the Galactic center. In particular, SJ will determine whether the SMBH was formed by a sequential merging of multiple black holes. The clarification of this formation process of the SMBH will contribute to a better understanding of merging process of satellite galaxies into the Galaxy, which is suggested by the standard galaxy formation scenario. A numerical simulation (Tanikawa and Umemura, 2014) suggests that if the SMBH was formed by the merging process, then the dynamical friction caused by the black holes have influenced the phase space distribution of stars. The phase space distribution measured by SJ will make it possible to determine the occurrences of the merging process.

STREAMFINDER - I. A new algorithm for detecting stellar streams

NASA Astrophysics Data System (ADS)

Malhan, Khyati; Ibata, Rodrigo A.

2018-07-01

We have designed a powerful new algorithm to detect stellar streams in an automated and systematic way. The algorithm, which we call the STREAMFINDER, is well suited for finding dynamically cold and thin stream structures that may lie along any simple or complex orbits in Galactic stellar surveys containing any combination of positional and kinematic information. In the present contribution, we introduce the algorithm, lay out the ideas behind it, explain the methodology adopted to detect streams, and detail its workings by running it on a suite of simulations of mock Galactic survey data of similar quality to that expected from the European Space Agency/Gaia mission. We show that our algorithm is able to detect even ultra-faint stream features lying well below previous detection limits. Tests show that our algorithm will be able to detect distant halo stream structures >10° long containing as few as ˜15 members (ΣG ˜ 33.6 mag arcsec-2) in the Gaia data set.

The Role of Feedback in Galaxy Formation

NASA Astrophysics Data System (ADS)

Martin, C. L.

2004-12-01

Our understanding of galaxy formation is founded on the well-understood principle of gravitational amplification of structure but lacks the astrophysical knowledge needed to predict the properties of galaxies and small scale properties of the intergalactic medium. While gas cooling and galaxy merging are now modeled with reasonable accuracy, the complex process of gas reheating by massive stars and active nuclei is described by simple empirical "feedback" recipes. Chandra and XMM-Newton observations now provide direct imaging of this hot gas in nearby starburst galaxies; and outflow speeds -- of cooler gas entrained in hot galactic winds -- have been measured over a large range of galaxy masses and formation epochs. My talk will describe how these empirical studies help us understand the dynamics of galactic winds and discuss the consequences for the shape of the galaxy luminosity function and the enrichment of the intergalactic medium with metals. Funding from NASA, the Alfred P. Sloan Foundation, and the David and Lucile Packard Foundation made much of this work possible.

A setup for Gaia-DR1: the star formation history of our thin disc environment

NASA Astrophysics Data System (ADS)

Miret-Roig, N.; Romero-Gómez, M.; Figueras, F.; Mor, R.

2017-03-01

The first Gaia Data Release (Gaia-DR1, 14 September 2016) primes the pump and paves the way for a new golden age of the galactic astronomy. Gaia-DR1 will provide new parallaxes and proper motions for about two million well-behaved Tycho-2 stars placed in the solar neighborhood. This TGAS (Tycho-Gaia Astrometric Solution) catalogue is being obtained through the combination of the Gaia observations with the positions of the stars obtained by Hipparcos (ESA 1997) when available, or Tycho-2. The aim of the work presented here has been to evaluate the capabilities of Gaia and future on-ground spectroscopic surveys to derive the dynamical age and place of birth of the Young Local Associations (YLAs). Test particle simulations in realistic galactic potentials and different scenarios for the accuracy on astrometric and spectroscopic data allow us to quantify our future capabilities to trace back in time the star formation history of our thin disc environment.

Imprints to the terrestrial environment at galactic arm crossings of the solar system

NASA Astrophysics Data System (ADS)

Fahr, H. J.; Fichtner, H.; Scherer, K.; Stawicki, O.

At its itinerary through our milky way galaxy the solar system moves through highly variable interstellar environments. Due to its orbital revolution around the galactic center, the solar system also crosses periodically the spiral arms of our galactic plane and thereby expe riences pronounced enviromental changes. Gas densities, magnetic fields and galactic cosmic ray intensities are substantially higher there compared to interarm conditions. Here we present theoretical calculations describing the SN-averaged galactic cosmic ray spectrum for regions inside and outside of galactic arms which then allow to predict how periodic passages of the solar system through galactic arms should be reflected by enhanced particle irradiations of the earth`s atmosphere and by correlated terrestrial Be-10 production rates.

Modeling mergers of known galactic systems of binary neutron stars

NASA Astrophysics Data System (ADS)

Feo, Alessandra; De Pietri, Roberto; Maione, Francesco; Löffler, Frank

2017-02-01

We present a study of the merger of six different known galactic systems of binary neutron stars (BNS) of unequal mass with a mass ratio between 0.75 and 0.99. Specifically, these systems are J1756-2251, J0737-3039A, J1906  +  0746, B1534  +  12, J0453  +  1559 and B1913  +  16. We follow the dynamics of the merger from the late stage of the inspiral process up to  ∼20ms after the system has merged, either to form a hyper-massive neutron star (NS) or a rotating black hole (BH), using a semi-realistic equation of state (EOS), namely the seven-segment piece-wise polytropic SLy with a thermal component. For the most extreme of these systems (q  =  0.75, J0453  +  1559), we also investigate the effects of different EOSs: APR4, H4, and MS1. Our numerical simulations are performed using only publicly available open source code such as, the Einstein toolkit code deployed for the dynamical evolution and the LORENE code for the generation of the initial models. We show results on the gravitational wave signals, spectrogram and frequencies of the BNS after the merger and the BH properties in the two cases in which the system collapses within the simulated time.

DEMOGRAPHICS OF THE GALAXIES HOSTING SHORT-DURATION GAMMA-RAY BURSTS

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

Fong, W.; Berger, E.; Chornock, R.

We present observations of the afterglows and host galaxies of three short-duration gamma-ray bursts (GRBs): 100625A, 101219A, and 110112A. We find that GRB 100625A occurred in a z = 0.452 early-type galaxy with a stellar mass of Almost-Equal-To 4.6 Multiplication-Sign 10{sup 9} M{sub Sun} and a stellar population age of Almost-Equal-To 0.7 Gyr, and GRB 101219A originated in a star-forming galaxy at z = 0.718 with a stellar mass of Almost-Equal-To 1.4 Multiplication-Sign 10{sup 9} M{sub Sun }, a star formation rate of Almost-Equal-To 16 M{sub Sun} yr{sup -1}, and a stellar population age of Almost-Equal-To 50 Myr. We alsomore » report the discovery of the optical afterglow of GRB 110112A, which lacks a coincident host galaxy to i {approx}> 26 mag, and we cannot conclusively identify any field galaxy as a possible host. From afterglow modeling, the bursts have inferred circumburst densities of Almost-Equal-To 10{sup -4}-1 cm{sup -3} and isotropic-equivalent gamma-ray and kinetic energies of Almost-Equal-To 10{sup 50}-10{sup 51} erg. These three events highlight the diversity of galactic environments that host short GRBs. To quantify this diversity, we use the sample of 36 Swift short GRBs with robust associations to an environment ({approx}1/2 of 68 short bursts detected by Swift to 2012 May) and classify bursts originating from four types of environments: late-type ( Almost-Equal-To 50%), early-type ( Almost-Equal-To 15%), inconclusive ( Almost-Equal-To 20%), and ''host-less'' (lacking a coincident host galaxy to limits of {approx}> 26 mag; Almost-Equal-To 15%). To find likely ranges for the true late- and early-type fractions, we assign each of the host-less bursts to either the late- or early-type category using probabilistic arguments and consider the scenario that all hosts in the inconclusive category are early-type galaxies to set an upper bound on the early-type fraction. We calculate most likely ranges for the late- and early-type fractions of Almost-Equal-To 60%-80% and Almost-Equal-To 20%-40%, respectively. We find no clear trend between gamma-ray duration and host type. We also find no change to the fractions when excluding events recently claimed as possible contaminants from the long GRB/collapsar population. Our reported demographics are consistent with a short GRB rate driven by both stellar mass and star formation.« less

THE BLACK HOLE CENTRAL ENGINE FOR ULTRA-LONG GAMMA-RAY BURST 111209A AND ITS ASSOCIATED SUPERNOVA 2011KL

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

Gao, He; You, Zhi-Qiang; Lei, Wei-Hua

Recently, the first association between an ultra-long gamma-ray burst (GRB) and a supernova was reported, i.e., GRB 111209A/SN 2011kl, enabling us to investigate the physics of central engines or even progenitors for ultra-long GRBs. In this paper, we inspect the broadband data of GRB 111209A/SN 2011kl. The late-time X-ray light curve exhibits a GRB 121027A-like fallback bump, suggesting a black hole (BH) central engine. We thus propose a collapsar model with fallback accretion for GRB 111209A/SN 2011kl. The required model parameters, such as the total mass and radius of the progenitor star, suggest that the progenitor of GRB 111209A ismore » more likely a Wolf–Rayet star instead of a blue supergiant, and the central engine of this ultra-long burst is a BH. The implications of our results are discussed.« less

HIREGS observations of the Galactic center and Galactic plane: Separation of the diffuse Galactic hard X-ray continuum from the point source spectra

NASA Technical Reports Server (NTRS)

Boggs, S. E.; Lin, R. P.; Coburn, W.; Feffer, P.; Pelling, R. M.; Schroeder, P.; Slassi-Sennou, S.

1997-01-01

The balloon-borne high resolution gamma ray and X-ray germanium spectrometer (HIREGS) was used to observe the Galactic center and two positions along the Galactic plane from Antarctica in January 1995. For its flight, the collimators were configured to measure the Galactic diffuse hard X-ray continuum between 20 and 200 keV by directly measuring the point source contributions to the wide field of view flux for subtraction. The hard X-ray spectra of GX 1+4 and GRO J1655-40 were measured with the diffuse continuum subtracted off. The analysis technique for source separation is discussed and the preliminary separated spectra for these point sources and the Galactic diffuse emission are presented.

Kinematics of symmetric Galactic longitudes to probe the spiral arms of the Milky Way with Gaia

NASA Astrophysics Data System (ADS)

Antoja, T.; Roca-Fàbrega, S.; de Bruijne, J.; Prusti, T.

2016-05-01

Aims: We model the effects of the spiral arms of the Milky Way on the disk stellar kinematics in the Gaia observable space. We also estimate the Gaia capabilities of detecting the predicted signatures. Methods: We use both controlled orbital integrations in analytic potentials and self-consistent simulations. We introduce a new strategy to investigate the effects of spiral arms, which consists of comparing the stellar kinematics of symmetric Galactic longitudes (+l and -l), in particular the median transverse velocity as determined from parallaxes and proper motions. This approach does not require the assumption of an axisymmetric model because it involves an internal comparison of the data. Results: The typical differences between the transverse velocity in symmetric longitudes in the models are of the order of ~2 km s-1, but can be larger than 10 km s-1 for certain longitudes and distances. The longitudes close to the Galactic centre and to the anti-centre are those with larger and smaller differences, respectively. The differences between the kinematics for +l and -l show clear trends that depend strongly on the properties of spiral arms. Thus, this method can be used to quantify the importance of the effects of spiral arms on the orbits of stars in the different regions of the disk, and to constrain the location of the arms, main resonances and, thus, pattern speed. Moreover, the method allows us to test different origin scenarios of spiral arms and the dynamical nature of the spiral structure (e.g. grand design versus transient multiple arms). We estimate the number of stars of each spectral type that Gaia will observe in certain representative Galactic longitudes, their characteristic errors in distance and transverse velocity, and the error in computing the median velocity as a function of distance. We will be able to measure the median transverse velocity exclusively with Gaia data, with precision smaller than ~1 km s-1 up to distances of ~4-6 kpc for certain giant stars, and up to ~2-4 kpc and better kinematic precision (≲0.5 km s-1) for certain sub-giants and dwarfs. These are enough to measure the typical signatures seen in the models. Conclusions: The Gaia catalogue will allow us to use the presented approach successfully and improve significantly upon current studies of the dynamics of the spiral arms of our Galaxy. We also show that a similar strategy can be used with line-of-sight velocities, which could be applied to Gaia data and to upcoming spectroscopic surveys.

The Arches cluster out to its tidal radius: dynamical mass segregation and the effect of the extinction law on the stellar mass function

NASA Astrophysics Data System (ADS)

Habibi, M.; Stolte, A.; Brandner, W.; Hußmann, B.; Motohara, K.

2013-08-01

The Galactic center is the most active site of star formation in the Milky Way, where particularly high-mass stars have formed very recently and are still forming today. However, since we are looking at the Galactic center through the Galactic disk, knowledge of extinction is crucial when studying this region. The Arches cluster is a young, massive starburst cluster near the Galactic center. We observed the Arches cluster out to its tidal radius using Ks-band imaging obtained with NAOS/CONICA at the VLT combined with Subaru/CISCO J-band data to gain a full understanding of the cluster mass distribution. We show that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, we show that the difference can reach up to 30% for individually derived stellar masses and ΔAKs ~ 1 magnitude in acquired Ks-band extinction, while the present-day mass function slope changes by ~ 0.17 dex. The present-day mass function slope derived assuming the more recent extinction law increases from a flat slope of αNishi = -1.50 ± 0.35 in the core (r < 0.2 pc) to αNishi = -2.21 ± 0.27 in the intermediate annulus (0.2 < r < 0.4 pc), where the Salpeter slope is -2.3. The mass function steepens to αNishi = -3.21 ± 0.30 in the outer annulus (0.4 < r < 1.5 pc), indicating that the outer cluster region is depleted of high-mass stars. This picture is consistent with mass segregation owing to the dynamical evolution of the cluster. Based on observations collected at the ESO/VLT under Program ID 081.D-0572(B) (PI: Brandner) and ID 71.C-0344(A) (PI: Eisenhauer, retrieved from the ESO archive). Also based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.Full Table 5 is 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/556/A26

Galactic bulge preferred over dark matter for the Galactic centre gamma-ray excess

NASA Astrophysics Data System (ADS)

Macias, Oscar; Gordon, Chris; Crocker, Roland M.; Coleman, Brendan; Paterson, Dylan; Horiuchi, Shunsaku; Pohl, Martin

2018-05-01

An anomalous gamma-ray excess emission has been found in the Fermi Large Area Telescope data1 covering the centre of the Galaxy2,3. Several theories have been proposed for this `Galactic centre excess'. They include self-annihilation of dark-matter particles4, an unresolved population of millisecond pulsars5, an unresolved population of young pulsars6, or a series of burst events7. Here, we report on an analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. We find evidence that the Galactic centre excess gamma rays are statistically better described by the stellar over-density in the Galactic bulge and the nuclear stellar bulge, rather than a spherical excess. Given its non-spherical nature, we argue that the Galactic centre excess is not a dark-matter phenomenon but rather associated with the stellar population of the Galactic bulge and the nuclear bulge.

The Dynamics of Truncated Black Hole Accretion Disks. I. Viscous Hydrodynamic Case

NASA Astrophysics Data System (ADS)

Hogg, J. Drew; Reynolds, Christopher S.

2017-07-01

Truncated accretion disks are commonly invoked to explain the spectro-temporal variability in accreting black holes in both small systems, I.e., state transitions in galactic black hole binaries (GBHBs), and large systems, I.e., low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the dynamics of truncated disks is lacking. We present a well-resolved viscous, hydrodynamic simulation that uses an ad hoc cooling prescription to drive a thermal instability and, hence, produce the first sustained truncated accretion disk. With this simulation, we perform a study of the dynamics, angular momentum transport, and energetics of a truncated disk. We find that the time variability introduced by the quasi-periodic transition of gas from efficient cooling to inefficient cooling impacts the evolution of the simulated disk. A consequence of the thermal instability is that an outflow is launched from the hot/cold gas interface, which drives large, sub-Keplerian convective cells into the disk atmosphere. The convective cells introduce a viscous θ - ϕ stress that is less than the generic r - ϕ viscous stress component, but greatly influences the evolution of the disk. In the truncated disk, we find that the bulk of the accreted gas is in the hot phase.

Radiation pressure in galactic discs: stability, turbulence, and winds in the single-scattering limit

NASA Astrophysics Data System (ADS)

Wibking, Benjamin D.; Thompson, Todd A.; Krumholz, Mark R.

2018-07-01

The radiation force on dust grains may be dynamically important in driving turbulence and outflows in rapidly star-forming galaxies. Recent studies focus on the highly optically thick limit relevant to the densest ultraluminous galaxies and super star clusters, where reprocessed infrared photons provide the dominant source of electromagnetic momentum. However, even among starburst galaxies, the great majority instead lie in the so-called `single-scattering' limit, where the system is optically thick to the incident starlight, but optically thin to the reradiated infrared. In this paper, we present a stability analysis and multidimensional radiation-hydrodynamic simulations exploring the stability and dynamics of isothermal dusty gas columns in this regime. We describe our algorithm for full angle-dependent radiation transport based on the discontinuous Galerkin finite element method. For a range of near-Eddington fluxes, we show that the medium is unstable, producing convective-like motions in a turbulent atmosphere with a scale height significantly inflated compared to the gas pressure scale height and mass-weighted turbulent energy densities of ˜0.01-0.1 of the mid-plane radiation energy density, corresponding to mass-weighted velocity dispersions of Mach number ˜0.5-2. Extrapolation of our results to optical depths of 103 implies maximum turbulent Mach numbers of ˜20. Comparing our results to galaxy-averaged observations, and subject to the approximations of our calculations, we find that radiation pressure does not contribute significantly to the effective supersonic pressure support in star-forming discs, which in general are substantially sub-Eddington. We further examine the time-averaged vertical density profiles in dynamical equilibrium and comment on implications for radiation-pressure-driven galactic winds.

The angular momentum of disc galaxies: implications for gas accretion, outflows, and dynamical friction

NASA Astrophysics Data System (ADS)

Dutton, Aaron A.; van den Bosch, Frank C.

2012-03-01

We combine constraints on the galaxy-dark matter connection with structural and dynamical scaling relations to investigate the angular momentum content of disc galaxies. For haloes with masses in the interval 1011.3 M⊙≲Mvir≲ 1012.7 M⊙ we find that the galaxy spin parameters are basically independent of halo mass with ?. This is significantly lower than for relaxed Λcold dark matter (ΛCDM) haloes, which have an average spin parameter ?. The average ratio between the specific angular momentum of disc galaxies and their host dark matter haloes is therefore ?. This calls into question a standard assumption made in the majority of all (semi-analytical) models for (disc) galaxy formation, namely that ?. Using simple disc formation models we show that it is particularly challenging to understand why ? is independent of halo mass, while the galaxy formation efficiency (ɛGF; proportional to the ratio of galaxy mass to halo mass) reveals a strong halo mass dependence. We argue that the empirical scaling relations between ɛGF, ? and halo mass require both feedback (i.e. galactic outflows) and angular momentum transfer from the baryons to the dark matter (i.e. dynamical friction). Most importantly, the efficiency of angular momentum loss needs to decrease with increasing halo mass. Such a mass dependence may reflect a bias against forming stable discs in high-mass, low-spin haloes or a transition from cold-mode accretion in low-mass haloes to hot-mode accretion at the massive end. However, current hydrodynamical simulations of galaxy formation, which should include these processes, seem unable to reproduce the empirical relation between ɛGF and ?. We conclude that the angular momentum build-up of galactic discs remains poorly understood.

The Dynamics of Truncated Black Hole Accretion Disks. I. Viscous Hydrodynamic Case

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

Hogg, J. Drew; Reynolds, Christopher S.

Truncated accretion disks are commonly invoked to explain the spectro-temporal variability in accreting black holes in both small systems, i.e., state transitions in galactic black hole binaries (GBHBs), and large systems, i.e., low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to supportmore » this phenomenological model, but a detailed understanding of the dynamics of truncated disks is lacking. We present a well-resolved viscous, hydrodynamic simulation that uses an ad hoc cooling prescription to drive a thermal instability and, hence, produce the first sustained truncated accretion disk. With this simulation, we perform a study of the dynamics, angular momentum transport, and energetics of a truncated disk. We find that the time variability introduced by the quasi-periodic transition of gas from efficient cooling to inefficient cooling impacts the evolution of the simulated disk. A consequence of the thermal instability is that an outflow is launched from the hot/cold gas interface, which drives large, sub-Keplerian convective cells into the disk atmosphere. The convective cells introduce a viscous θ − ϕ stress that is less than the generic r − ϕ viscous stress component, but greatly influences the evolution of the disk. In the truncated disk, we find that the bulk of the accreted gas is in the hot phase.« less

Radiation pressure in galactic disks: stability, turbulence, and winds in the single-scattering limit

NASA Astrophysics Data System (ADS)

Wibking, Benjamin D.; Thompson, Todd A.; Krumholz, Mark R.

2018-04-01

The radiation force on dust grains may be dynamically important in driving turbulence and outflows in rapidly star-forming galaxies. Recent studies focus on the highly optically-thick limit relevant to the densest ultra-luminous galaxies and super star clusters, where reprocessed infrared photons provide the dominant source of electromagnetic momentum. However, even among starburst galaxies, the great majority instead lie in the so-called "single-scattering" limit, where the system is optically-thick to the incident starlight, but optically-thin to the re-radiated infrared. In this paper we present a stability analysis and multidimensional radiation-hydrodynamic simulations exploring the stability and dynamics of isothermal dusty gas columns in this regime. We describe our algorithm for full angle-dependent radiation transport based on the discontinuous Galerkin finite element method. For a range of near-Eddington fluxes, we show that the medium is unstable, producing convective-like motions in a turbulent atmosphere with a scale height significantly inflated compared to the gas pressure scale height and mass-weighted turbulent energy densities of ˜0.01 - 0.1 of the midplane radiation energy density, corresponding to mass-weighted velocity dispersions of Mach number ˜0.5 - 2. Extrapolation of our results to optical depths of 103 implies maximum turbulent Mach numbers of ˜20. Comparing our results to galaxy-averaged observations, and subject to the approximations of our calculations, we find that radiation pressure does not contribute significantly to the effective supersonic pressure support in star-forming disks, which in general are substantially sub-Eddington. We further examine the time-averaged vertical density profiles in dynamical equilibrium and comment on implications for radiation-pressure-driven galactic winds.

Quantum foam, gravitational thermodynamics, and the dark sector

NASA Astrophysics Data System (ADS)

Ng, Y. Jack

2017-05-01

Is it possible that the dark sector (dark energy in the form of an effective dynamical cosmological constant, and dark matter) has its origin in quantum gravity? This talk sketches a positive response. Here specifically quantum gravity refers to the combined effect of quantum foam (or spacetime foam due to quantum fluctuations of spacetime) and gravitational thermodynamics. We use two simple independent gedankan experiments to show that the holographic principle can be understood intuitively as having its origin in the quantum fluctuations of spacetime. Applied to cosmology, this consideration leads to a dynamical cosmological constant of the observed magnitude, a result that can also be obtained for the present and recent cosmic eras by using unimodular gravity and causal set theory. Next we generalize the concept of gravitational thermodynamics to a spacetime with positive cosmological constant (like ours) to reveal the natural emergence, in galactic dynamics, of a critical acceleration parameter related to the cosmological constant. We are then led to construct a phenomenological model of dark matter which we call “modified dark matter” (MDM) in which the dark matter density profile depends on both the cosmological constant and ordinary matter. We provide observational tests of MDM by fitting the rotation curves to a sample of 30 local spiral galaxies with a single free parameter and by showing that the dynamical and observed masses agree in a sample of 93 galactic clusters. We also give a brief discussion of the possibility that quanta of both dark energy and dark matter are non-local, obeying quantum Boltzmann statistics (also called infinite statistics) as described by a curious average of the bosonic and fermionic algebras. If such a scenario is correct, we can expect some novel particle phenomenology involving dark matter interactions. This may explain why so far no dark matter detection experiments have been able to claim convincingly to have detected dark matter.

A NEW ELECTRON-DENSITY MODEL FOR ESTIMATION OF PULSAR AND FRB DISTANCES

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

Yao, J. M.; Wang, N.; Manchester, R. N.

2017-01-20

We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H ii regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offsetmore » of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.« less

Evolution of Hot Gas in Elliptical Galaxies

NASA Technical Reports Server (NTRS)

Mathews, William G.

2004-01-01

This theory grant was awarded to study the curious nature, origin and evolution of hot gas in elliptical galaxies and their surrounding groups. Understanding the properties of this X-ray emitting gas has profound implications over the broad landscape of modern astrophysics: cosmology, galaxy formation, star formation, cosmic metal enrichment, galactic structure and dynamics, and the physics of hot gases containing dust and magnetic fields. One of our principal specific objectives was to interpret the marvelous new observations from the XMM and Chandru satellite X-ray telescopes.

Near-earth radiation environment including time variations and secondary radiation; Meetings F2.6 and F2.7, COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994

NASA Technical Reports Server (NTRS)

Shea, M. A. (Editor); Heinrich, W. (Editor); Badhwar, G. D. (Editor)

1996-01-01

Both man and technological equipment must survive the near-earth space radiation environment, which can, under specific conditions, be extremely severe. This conference produced 17 papers on the dynamic space radiation environment covering: galactic, solar and trapped particles; nuclear fragmentation; nuclear interactions and transport theory; solar proton events; radiation shielding; and heavy ion fluences. Several papers present results from the recent SAMPEX mission.

Gamma ray constraints on the Galactic supernova rate

NASA Technical Reports Server (NTRS)

Hartmann, D.; The, L.-S.; Clayton, Donald D.; Leising, M.; Mathews, G.; Woosley, S. E.

1991-01-01

We perform Monte Carlo simulations of the expected gamma ray signatures of Galactic supernovae of all types to estimate the significance of the lack of a gamma ray signal due to supernovae occurring during the last millenium. Using recent estimates of the nuclear yields, we determine mean Galactic supernova rates consistent with the historic supernova record and the gamma ray limits. Another objective of these calculations of Galactic supernova histories is their application to surveys of diffuse Galactic gamma ray line emission.

Gamma ray constraints on the galactic supernova rate

NASA Technical Reports Server (NTRS)

Hartmann, D.; The, L.-S.; Clayton, D. D.; Leising, M.; Mathews, G.; Woosley, S. E.

1992-01-01

Monte Carlo simulations of the expected gamma-ray signatures of galactic supernovae of all types are performed in order to estimate the significance of the lack of a gamma-ray signal due to supernovae occurring during the last millenium. Using recent estimates of nuclear yields, we determine galactic supernova rates consistent with the historic supernova record and the gamma-ray limits. Another objective of these calculations of galactic supernova histories is their application to surveys of diffuse galactic gamma-ray line emission.

Quantitative chemical tagging, stellar ages and the chemo-dynamical evolution of the Galactic disc

NASA Astrophysics Data System (ADS)

Mitschang, A. W.; De Silva, G.; Zucker, D. B.; Anguiano, B.; Bensby, T.; Feltzing, S.

2014-03-01

The early science results from the new generation of high-resolution stellar spectroscopic surveys, such as Galactic Archaeology with HERMES (GALAH) and the Gaia European Southern Observatory survey (Gaia-ESO), will represent major milestones in the quest to chemically tag the Galaxy. Yet this technique to reconstruct dispersed coeval stellar groups has remained largely untested until recently. We build on previous work that developed an empirical chemical tagging probability function, which describes the likelihood that two field stars are conatal, that is, they were formed in the same cluster environment. In this work, we perform the first ever blind chemical tagging experiment, i.e. tagging stars with no known or otherwise discernible associations, on a sample of 714 disc field stars with a number of high-quality high-resolution homogeneous metal abundance measurements. We present evidence that chemical tagging of field stars does identify coeval groups of stars, yet these groups may not represent distinct formation sites, e.g. as in dissolved open clusters, as previously thought. Our results point to several important conclusions, among them that group finding will be limited strictly to chemical abundance space, e.g. stellar ages, kinematics, colours, temperature and surface gravity do not enhance the detectability of groups. We also demonstrate that in addition to its role in probing the chemical enrichment and kinematic history of the Galactic disc, chemical tagging represents a powerful new stellar age determination technique.

Nuclear Physics in Space: What We Can Learn From Cosmic Rays

NASA Technical Reports Server (NTRS)

Moskalenko, Igor V.

2004-01-01

Studies and discoveries in cosmic-ray physics and generally in Astrophysics provide a fertile ground for research in many areas of Particle Physics and Cosmology, such as the search for dark matter, antimatter, new particles, and exotic physics, studies of the nucleosynthesis, origin of Galactic and extragalactic gamma-ray diffuse emission, formation of the large scale structure of the universe etc. In several years new missions are planned for cosmic-ray experiments, which will tremendously increase the quality and accuracy of cosmic-ray data. On the other hand, direct measurements of cosmic rays are possible in only one location on the outskirts of the Milky Way galaxy and present only a snapshot of very dynamic processes. It has been recently realized that direct information about the fluxes and spectra of cosmic rays in distant locations is provided by the Galactic diffuse gamma-rays, therefore, complementing the local cosmic-ray studies. A wealth of information is also contained in the isotopic abundances of cosmic rays, therefore, accurate evaluation of the isotopic production cross sections is of primary importance for Astrophysics of cosmic rays, studies of the galactic chemical evolution, and Cosmology. In this talk, I will show new results obtained with GALPROP, the most advanced numerical model for cosmic-ray propagation, which includes in a self-consistent way all cosmic-ray species (stable and long-lived radioactive isotopes from H to Ni, antiprotons, positrons and electrons, gamma rays and synchrotron radiation), and all relevant processes and reactions.

Shrinking of Binaries in a WIMPY Background at the Galactic Center

NASA Astrophysics Data System (ADS)

Hills, J. G.

2001-12-01

The nature of the dark matter in the Galactic Halo is still not clear. Constraints can be placed on it; e.g., it cannot be in baryons less massive than about 1022 grams (Hills, 1986, Astron. J. 92, 595). It may be in elementary weakly interacting massive particles, WIMPS. Apart from providing most of the mass of the Galaxy, the only known significant dynamical effect of WIMPS is to cause a gradual shrinking of tightly bound binaries (Hills 1983, Astron. J. 88, 1269) as they interact with the background soup of WIMPS. This effect may be observable in binaries close to the Galactic Center if a significant fraction of the mass density near the central black hole is from WIMPS. The requisite binaries would have to have orbital velocities greater than the local velocity dispersion of the WIMPS relative to the binary. The velocity dispersion increases near the black hole. The binary cannot be too close to the black hole or its tidal field will breakup the binary. If the local WIMP density is 107 g/cm3, the fractional rate of reduction in the binary orbital period is about 5 x 10-10/yr for a binary having a semimajor axis equal to 3 solar radii in a soup of WIMPS having a velocity dispersion of 200 km/s relative to the binary. This gradual erosion of the binary period may be detectable, particularly, if one of the binary components is a pulsar.

Effect of dark matter halo on global spiral modes in a collisionless galactic disk

NASA Astrophysics Data System (ADS)

Ghosh, Soumavo; Saini, Tarun Deep; Jog, Chanda J.

2017-07-01

Low surface brightness (LSB) galaxies are dominated by dark matter halo from the innermost radii; hence they are ideal candidates to investigate the influence of dark matter on different dynamical aspects of spiral galaxies. Here, we study the effect of dark matter halo on grand-design, m = 2 , spiral modes in a galactic disk, treated as a collisionless system, by carrying out a global modal analysis within the WKB approximation. First, we study a superthin, LSB galaxy UGC 7321 and show that it does not support discrete global spiral modes when modeled as a disk-alone system or as a disk plus dark matter system. Even a moderate increase in the stellar central surface density does not yield any global spiral modes. This naturally explains the observed lack of strong large-scale spiral structure in LSBs. An earlier work (Ghosh et al., 2016) where the galactic disk was treated as a fluid system for simplicity had shown that the dominant halo could not arrest global modes. We found that this difference arises due to the different dispersion relation used in the two cases and which plays a crucial role in the search for global spiral modes. Thus the correct treatment of stars as a collisionless system as done here results in the suppression of global spiral modes, in agreement with the observations. We performed a similar modal analysis for the Galaxy, and found that the dark matter halo has a negligible effect on large-scale spiral structure.

The Impact Of Galactic Environment On Star Formation

NASA Astrophysics Data System (ADS)

Kreckel, Kathryn

2016-09-01

While spiral arms are the most prominent sites for star formation in disk galaxies, interarm star formation contributes significantly to the overall star formation budget. However, it is still an open question if the star formation proceeds differently in the arm and inter-arm environment. We use deep VLT/MUSE optical IFU spectroscopy to resolve and fully characterize the physical properties of 428 interarm and arm HII regions in the nearby grand design spiral galaxy NGC 628. Unlike molecular clouds (the fuel for star formation) which exhibit a clear dependence on galactic environment, we find that most HII region properties (luminosity, size, metallicity, ionization parameter) are independent of environment. One clear exception is the diffuse ionized gas (DIG) contribution to the arm and interarm flux (traced via the temperature sensitive [SII]/Halpha line ratio inside and outside of the HII region boundaries). We find a systematically higher DIG background within HII regions, particularly on the spiral arms. Correcting for this DIG contamination can result in significant (70%) changes to the star formation rate measured. We also show preliminary results comparing well@corrected star formation rates from our MUSE HII regions to ALMA CO(2-1) molecular gas observations at matched 1"=35pc resolution, tracing the Kennicutt-Schmidt star formation law at the scales relevant to the physics of star formation. We estimate the timescales relevant for GMC evolution using distance from the spiral arm as a proxy for age, and test whether star formation feedback or galactic@scale dynamical processes dominate GMC disruption.

The impact of galactic environment on star formation

NASA Astrophysics Data System (ADS)

Kreckel, Kathryn; Blanc, Guillermo A.; Schinnerer, Eva; Groves, Brent; Adamo, Angela; Hughes, Annie; Meidt, Sharon; SFNG Collaboration

2017-01-01

While spiral arms are the most prominent sites for star formation in disk galaxies, interarm star formation contributes significantly to the overall star formation budget. However, it is still an open question if the star formation proceeds differently in the arm and inter-arm environment. We use deep VLT/MUSE optical IFU spectroscopy to resolve and fully characterize the physical properties of 428 interarm and arm HII regions in the nearby grand design spiral galaxy NGC 628. Unlike molecular clouds (the fuel for star formation) which exhibit a clear dependence on galactic environment, we find that most HII region properties (luminosity, size, metallicity, ionization parameter) are independent of environment. One clear exception is the diffuse ionized gas (DIG) contribution to the arm and interarm flux (traced via the temperature sensitive [SII]/Halpha line ratio inside and outside of the HII region boundaries). We find a systematically higher DIG background within HII regions, particularly on the spiral arms. Correcting for this DIG contamination can result in significant (70%) changes to the star formation rate measured. We also show preliminary results comparing well-corrected star formation rates from our MUSE HII regions to ALMA CO(2-1) molecular gas observations at matched 1"=50pc resolution, tracing the Kennicutt-Schmidt star formation law at the scales relevant to the physics of star formation. We estimate the timescales relevant for GMC evolution using distance from the spiral arm as a proxy for age, and test whether star formation feedback or galactic-scale dynamical processes dominate GMC disruption.

X-raying galaxies: a Chandra legacy.

PubMed

Wang, Q Daniel

2010-04-20

This presentation reviews Chandra's major contribution to the understanding of nearby galaxies. After a brief summary on significant advances in characterizing various types of discrete x-ray sources, the presentation focuses on the global hot gas in and around galaxies, especially normal ones like our own. The hot gas is a product of stellar and active galactic nuclear feedback--the least understood part in theories of galaxy formation and evolution. Chandra observations have led to the first characterization of the spatial, thermal, chemical, and kinetic properties of the gas in our galaxy. The gas is concentrated around the galactic bulge and disk on scales of a few kiloparsec. The column density of chemically enriched hot gas on larger scales is at least an order magnitude smaller, indicating that it may not account for the bulk of the missing baryon matter predicted for the galactic halo according to the standard cosmology. Similar results have also been obtained for other nearby galaxies. The x-ray emission from hot gas is well correlated with the star formation rate and stellar mass, indicating that the heating is primarily due to the stellar feedback. However, the observed x-ray luminosity of the gas is typically less than a few percent of the feedback energy. Thus the bulk of the feedback (including injected heavy elements) is likely lost in galaxy-wide outflows. The results are compared with simulations of the feedback to infer its dynamics and interplay with the circumgalactic medium, hence the evolution of galaxies.

X-raying galaxies: A Chandra legacy

PubMed Central

Wang, Q. Daniel

2010-01-01

This presentation reviews Chandra’s major contribution to the understanding of nearby galaxies. After a brief summary on significant advances in characterizing various types of discrete x-ray sources, the presentation focuses on the global hot gas in and around galaxies, especially normal ones like our own. The hot gas is a product of stellar and active galactic nuclear feedback—the least understood part in theories of galaxy formation and evolution. Chandra observations have led to the first characterization of the spatial, thermal, chemical, and kinetic properties of the gas in our galaxy. The gas is concentrated around the galactic bulge and disk on scales of a few kiloparsec. The column density of chemically enriched hot gas on larger scales is at least an order magnitude smaller, indicating that it may not account for the bulk of the missing baryon matter predicted for the galactic halo according to the standard cosmology. Similar results have also been obtained for other nearby galaxies. The x-ray emission from hot gas is well correlated with the star formation rate and stellar mass, indicating that the heating is primarily due to the stellar feedback. However, the observed x-ray luminosity of the gas is typically less than a few percent of the feedback energy. Thus the bulk of the feedback (including injected heavy elements) is likely lost in galaxy-wide outflows. The results are compared with simulations of the feedback to infer its dynamics and interplay with the circumgalactic medium, hence the evolution of galaxies. PMID:20212160

Stellar streams as gravitational experiments. II. Asymmetric tails of globular cluster streams

NASA Astrophysics Data System (ADS)

Thomas, G. F.; Famaey, B.; Ibata, R.; Renaud, F.; Martin, N. F.; Kroupa, P.

2018-01-01

Kinematically cold tidal streams of globular clusters (GC) are excellent tracers of the Galactic gravitational potential at moderate Galactocentric distances, and can also be used as probes of the law of gravity on Galactic scales. Here, we compare for the first time the generation of such streams in Newtonian and Milgromian gravity (MOND). We first computed analytical results to investigate the expected shape of the GC gravitational potential in both frameworks, and we then ran N-body simulations with the Phantom of Ramses code. We find that the GCs tend to become lopsided in MOND. This is a consequence of the external field effect which breaks the strong equivalence principle. When the GC is filling its tidal radius the lopsidedness generates a strongly asymmetric tidal stream. In Newtonian dynamics, such markedly asymmetric streams can in general only be the consequence of interactions with dark matter subhalos, giant molecular clouds, or interaction with the Galactic bar. In these Newtonian cases, the asymmetry is the consequence of a very large gap in the stream, whilst in MOND it is a true asymmetry. This should thus allow us in the future to distinguish these different scenarios by making deep observations of the environment of the asymmetric stellar stream of Palomar 5. Moreover, our simulations indicate that the high internal velocity dispersion of Palomar 5 for its small stellar mass would be natural in MOND. The movie is available in electronic form at http://www.aanda.org

Photoionization of the diffuse interstellar medium and galactic halo by OB associtations

NASA Technical Reports Server (NTRS)

Dove, James B.; Shull, J. Michael

1994-01-01

Assuming smoothly varying H I distributions in te Galactic disk, we have calculated the geometry of diffuse II regions due to OB associations in the Galactic plane. Near the solar circle, OB associations with a Lyman continuum (Lyc) photon luminosity Psi(sub Lyc) = 3.3 x 10(exp 7) cm(exp -2) s(exp -1), produce H II regions that are density bounded in the vertical direction (H II chimneys) allowing Lyc to escape the gaseous disk and penetrate into the Galactic halo. We provide analytic formulae for the Lyc escape fraction as functions of S(sub 0) O-star catalog of Garmany and a new Lyc stellar stellar Lyc stellar flux calibration, we find a production rate of Lyc photons by OB associations within 2.5 kpc of Psi(sub Lyc) = 3.3 x 10(exp 7) cm(exp -2) s(exp -1). Integrating the fraction of Lyc photons that escape the disk over our adopted luminosity function of OB associations, we estimate that approximately 7% of the ionizing photons, or Phi(sub Lyc) = 2.3 x 10(exp 6) cm(exp -2) s(exp -1), escape each side of the H I disk layer and penetrate the diffuse ionized medium ('Reynolds layer'). This flux is sufficient to explain the potoionization of this, although we have not constructed a model for the observed H-alpha emission and pulsar dispersion measures that is fully consistent with the absorption rate of Lyc in the H II layer. Since our quiescent model does not account for the effects of dynamic chimneys and superbubbles, which should enhance Lyc escape, we conclude the O stars are the probable source of ionizing radiation for the Reynolds layer. For a random distribution of OB associations throughout the disk, the Lyc flux is nearly uniform for heights Z is greater than approximately 0.8 kpc above the midplane.

THE STELLAR INITIAL MASS FUNCTION OF ULTRA-FAINT DWARF GALAXIES: EVIDENCE FOR IMF VARIATIONS WITH GALACTIC ENVIRONMENT

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

Geha, Marla; Brown, Thomas M.; Tumlinson, Jason

2013-07-01

We present constraints on the stellar initial mass function (IMF) in two ultra-faint dwarf (UFD) galaxies, Hercules and Leo IV, based on deep Hubble Space Telescope Advanced Camera for Surveys imaging. The Hercules and Leo IV galaxies are extremely low luminosity (M{sub V} = -6.2, -5.5), metal-poor (([Fe/H]) = -2.4, -2.5) systems that have old stellar populations (>11 Gyr). Because they have long relaxation times, we can directly measure the low-mass stellar IMF by counting stars below the main-sequence turnoff without correcting for dynamical evolution. Over the stellar mass range probed by our data, 0.52-0.77 M{sub Sun }, the IMFmore » is best fit by a power-law slope of {alpha}= 1.2{sub -0.5}{sup +0.4} for Hercules and {alpha} = 1.3 {+-} 0.8 for Leo IV. For Hercules, the IMF slope is more shallow than a Salpeter ({alpha} = 2.35) IMF at the 5.8{sigma} level, and a Kroupa ({alpha} = 2.3 above 0.5 M{sub Sun }) IMF slope at 5.4{sigma} level. We simultaneously fit for the binary fraction, f{sub binary}, finding f{sub binary}= 0.47{sup +0.16}{sub -0.14} for Hercules, and 0.47{sup +0.37}{sub -0.17} for Leo IV. The UFD binary fractions are consistent with that inferred for Milky Way stars in the same mass range, despite very different metallicities. In contrast, the IMF slopes in the UFDs are shallower than other galactic environments. In the mass range 0.5-0.8 M{sub Sun }, we see a trend across the handful of galaxies with directly measured IMFs such that the power-law slopes become shallower (more bottom-light) with decreasing galactic velocity dispersion and metallicity. This trend is qualitatively consistent with results in elliptical galaxies inferred via indirect methods and is direct evidence for IMF variations with galactic environment.« less

Galactic Winds and the Role Played by Massive Stars

NASA Astrophysics Data System (ADS)

Heckman, Timothy M.; Thompson, Todd A.

Galactic winds from star-forming galaxies play at key role in the evolution of galaxies and the intergalactic medium. They transport metals out of galaxies, chemically enriching the intergalactic medium and modifying the chemical evolution of galaxies. They affect the surrounding interstellar and circumgalactic media, thereby influencing the growth of galaxies though gas accretion and star formation. In this contribution we first summarize the physical mechanisms by which the momentum and energy output from a population of massive stars and associated supernovae can drive galactic winds. We use the prototypical example of M 82 to illustrate the multiphase nature of galactic winds. We then describe how the basic properties of galactic winds are derived from the data, and summarize how the properties of galactic winds vary systematically with the properties of the galaxies that launch them. We conclude with a brief discussion of the broad implications of galactic winds.

The galactic contribution to IceCube's astrophysical neutrino flux

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

Denton, Peter B.; Marfatia, Danny; Weiler, Thomas J., E-mail: peterbd1@gmail.com, E-mail: dmarf8@hawaii.edu, E-mail: tom.weiler@vanderbilt.edu

2017-08-01

High energy neutrinos have been detected by IceCube, but their origin remains a mystery. Determining the sources of this flux is a crucial first step towards multi-messenger studies. In this work we systematically compare two classes of sources with the data: galactic and extragalactic. We assume that the neutrino sources are distributed according to a class of Galactic models. We build a likelihood function on an event by event basis including energy, event topology, absorption, and direction information. We present the probability that each high energy event with deposited energy E {sub dep}>60 TeV in the HESE sample is Galactic,more » extragalactic, or background. For Galactic models considered the Galactic fraction of the astrophysical flux has a best fit value of 1.3% and is <9.5% at 90% CL. A zero Galactic flux is allowed at <1σ.« less

Galactic plane gamma-radiation

NASA Technical Reports Server (NTRS)

Hartman, R. C.; Kniffen, D. A.; Thompson, D. J.; Fichtel, C. E.; Ogelman, H. B.; Tumer, T.; Ozel, M. E.

1979-01-01

Analysis of the SAS 2 data together with the COS B results shows that the distribution of galactic gamma-radiation has several similarities to that of other large-scale tracers of galactic structure. The radiation is primarily confined to a thin disc which exhibits offsets from b = 0 degrees similar to warping at radio frequencies. The principal distinction of the gamma-radiation is a stronger contrast in intensity between the region from 310 to 45 degrees in longitude and the regions away from the center that can be attributed to a variation in cosmic-ray density as a function of position in Galaxy. The diffuse galactic gamma-ray energy spectrum shows no significant variation in direction, and the spectrum seen along the plane is the same as that for the galactic component of the gamma-radiation at high altitudes. The uniformity of the galactic gamma-ray spectrum, the smooth decrease in intensity as a function of altitude, and the absence of any galactic gamma-ray sources at high altitudes indicate a diffuse origin for bulk of the galactic gamma-radiation rather than a collection of localized sources.

Chandrasekhar's dynamical friction and non-extensive statistics

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

Silva, J.M.; Lima, J.A.S.; De Souza, R.E.

2016-05-01

The motion of a point like object of mass M passing through the background potential of massive collisionless particles ( m || M ) suffers a steady deceleration named dynamical friction. In his classical work, Chandrasekhar assumed a Maxwellian velocity distribution in the halo and neglected the self gravity of the wake induced by the gravitational focusing of the mass M . In this paper, by relaxing the validity of the Maxwellian distribution due to the presence of long range forces, we derive an analytical formula for the dynamical friction in the context of the q -nonextensive kinetic theory. Inmore » the extensive limiting case ( q = 1), the classical Gaussian Chandrasekhar result is recovered. As an application, the dynamical friction timescale for Globular Clusters spiraling to the galactic center is explicitly obtained. Our results suggest that the problem concerning the large timescale as derived by numerical N -body simulations or semi-analytical models can be understood as a departure from the standard extensive Maxwellian regime as measured by the Tsallis nonextensive q -parameter.« less

Local Stellar Kinematics from RAVE data - V. Kinematic Investigation of the Galaxy with Red Clump Stars

NASA Astrophysics Data System (ADS)

Karaali, S.; Bilir, S.; Ak, S.; Gökçe, E. Yaz; Önal, Ö.; Ak, T.

2014-02-01

We investigated the space velocity components of 6 610 red clump (RC) stars in terms of vertical distance, Galactocentric radial distance and Galactic longitude. Stellar velocity vectors are corrected for differential rotation of the Galaxy which is taken into account using photometric distances of RC stars. The space velocity components estimated for the sample stars above and below the Galactic plane are compatible only for the space velocity component in the direction to the Galactic rotation of the thin disc stars. The space velocity component in the direction to the Galactic rotation (V lsr) shows a smooth variation relative to the mean Galactocentric radial distance (Rm ), while it attains its maximum at the Galactic plane. The space velocity components in the direction to the Galactic centre (U lsr) and in the vertical direction (W lsr) show almost flat distributions relative to Rm , with small changes in their trends at Rm ~ 7.5 kpc. U lsr values estimated for the RC stars in quadrant 180° < l ⩽ 270° are larger than the ones in quadrants 0° < l ⩽ 90° and 270° < l ⩽ 360°. The smooth distribution of the space velocity dispersions reveals that the thin and thick discs are kinematically continuous components of the Galaxy. Based on the W lsr space velocity components estimated in the quadrants 0° < l ⩽ 90° and 270° < l ⩽ 360°, in the inward direction relative to the Sun, we showed that RC stars above the Galactic plane move towards the North Galactic Pole, whereas those below the Galactic plane move in the opposite direction. In the case of quadrant 180° < l ⩽ 270°, their behaviour is different, i.e. the RC stars above and below the Galactic plane move towards the Galactic plane. We stated that the Galactic long bar is the probable origin of many, but not all, of the detected features.

Galactic Spiral Shocks with Thermal Instability in Vertically Stratified Galactic Disks

NASA Astrophysics Data System (ADS)

Kim, Chang-Goo; Kim, Woong-Tae; Ostriker, Eve C.

2010-09-01

Galactic spiral shocks are dominant morphological features and believed to be responsible for substructure formation within spiral arms in disk galaxies. They can also contribute a substantial amount of kinetic energy to the interstellar gas by tapping the (differential) rotational motion. We use numerical hydrodynamic simulations to investigate dynamics and structure of spiral shocks with thermal instability (TI) in vertically stratified galactic disks, focusing on environmental conditions (of heating and the galactic potential) similar to the Solar neighborhood. We initially consider an isothermal disk in vertical hydrostatic equilibrium and let it evolve subject to interstellar cooling and heating as well as a stellar spiral potential. Due to TI, a disk with surface density Σ0 >= 6.7 M sun pc-2 rapidly turns to a thin dense slab near the midplane sandwiched between layers of rarefied gas. The imposed spiral potential leads to a vertically curved shock that exhibits strong flapping motions in the plane perpendicular to the arm. The overall flow structure at saturation is comprised of the arm, postshock expansion zone, and interarm regions that occupy typically 10%, 20%, and 70% of the arm-to-arm distance, in which the gas resides for 15%, 30%, and 55% of the arm-to-arm crossing time, respectively. The flows are characterized by transitions from rarefied to dense phases at the shock and from dense to rarefied phases in the postshock expansion zone, although gas with too-large postshock-density does not undergo this return phase transition, instead forming dense condensations. If self-gravity is omitted, the shock flapping drives random motions in the gas, but only up to ~2-3 km s-1 in the in-plane direction and less than 2 km s-1 in the vertical direction. Time-averaged shock profiles show that the spiral arms in stratified disks are broader and less dense compared to those in unstratified models, and that the vertical density distribution is overall consistent with local effective hydrostatic equilibrium. Inclusion of self-gravity increases the dense gas fraction by a factor of ~2 and raises the in-plane velocity dispersion to ~5-7 km s-1. When the disks are massive enough, with Σ0 >= 5 M sun pc-2, self-gravity promotes formation of bound clouds that repeatedly collide with each other in the arm and break up in the postshock expansion zone.

Galactic-scale Feedback Observed in the 3C 298 Quasar Host Galaxy

NASA Astrophysics Data System (ADS)

Vayner, Andrey; Wright, Shelley A.; Murray, Norman; Armus, Lee; Larkin, James E.; Mieda, Etsuko

2017-12-01

We present high angular resolution multiwavelength data of the 3C 298 radio-loud quasar host galaxy (z = 1.439) taken using the W.M. Keck Observatory OSIRIS integral field spectrograph (IFS) with adaptive optics, the Atacama Large Millimeter/submillimeter Array (ALMA), the Hubble Space Telescope (HST) WFC3, and the Very Large Array (VLA). Extended emission is detected in the rest-frame optical nebular emission lines Hβ, [O III], Hα, [N II], and [S II], as well as in the molecular lines CO (J = 3‑2) and (J = 5‑4). Along the path of the relativistic jets of 3C 298, we detect conical outflows in ionized gas emission with velocities of up to 1700 {km} {{{s}}}-1 and an outflow rate of 450–1500 {M}ȯ {{yr}}-1 extended over 12 kpc. Near the spatial center of the conical outflow, CO (J = 3‑2) emission shows a molecular gas disk with a rotational velocity of ±150 {km} {{{s}}}-1 and total molecular mass ({M}{{{H}}2}) of 6.6+/- 0.36× {10}9 {M}ȯ . On the blueshifted side of the molecular disk, we observe broad extended emission that is due to a molecular outflow with a rate of 2300 {M}ȯ {{yr}}-1 and depletion timescale of 3 Myr. We detect no narrow Hα emission in the outflow regions, suggesting a limit on star formation of 0.3 {M}ȯ {{yr}}-1 {{kpc}}-2. Quasar-driven winds are evacuating the molecular gas reservoir, thereby directly impacting star formation in the host galaxy. The observed mass of the supermassive black hole is {10}9.37{--9.56} {M}ȯ , and we determine a dynamical bulge mass of {M}{bulge}=1{--}1.7× {10}10\\tfrac{R}{1.6 {kpc}} {M}ȯ . The bulge mass of 3C 298 lies 2–2.5 orders of magnitude below the expected value from the local galactic bulge—supermassive black hole mass ({M}{bulge}{--}{M}{BH}) relationship. A second galactic disk observed in nebular emission is offset from the quasar by 9 kpc, suggesting that the system is an intermediate-stage merger. These results show that galactic-scale negative feedback is occurring early in the merger phase of 3C 298, well before the coalescence of the galactic nuclei and assembly on the local {M}{bulge}{--}{M}{BH} relationship.

Formation and Evolution of X-ray Binaries

NASA Astrophysics Data System (ADS)

Fragkos, Anastasios

X-ray binaries - mass-transferring binary stellar systems with compact object accretors - are unique astrophysical laboratories. They carry information about many complex physical processes such as star formation, compact object formation, and evolution of interacting binaries. My thesis work involves the study of the formation and evolution of Galactic and extra-galacticX-ray binaries using both detailed and realistic simulation tools, and population synthesis techniques. I applied an innovative analysis method that allows the reconstruction of the full evolutionary history of known black hole X-ray binaries back to the time of compact object formation. This analysis takes into account all the available observationally determined properties of a system, and models in detail four of its evolutionary evolutionary phases: mass transfer through the ongoing X-ray phase, tidal evolution before the onset of Roche-lobe overflow, motion through the Galactic potential after the formation of the black hole, and binary orbital dynamics at the time of core collapse. Motivated by deep extra-galactic Chandra survey observations, I worked on population synthesis models of low-mass X-ray binaries in the two elliptical galaxies NGC3379 and NGC4278. These simulations were targeted at understanding the origin of the shape and normalization of the observed X-ray luminosity functions. In a follow up study, I proposed a physically motivated prescription for the modeling of transient neutron star low-mass X-ray binary properties, such as duty cycle, outburst duration and recurrence time. This prescription enabled the direct comparison of transient low-mass X-ray binary population synthesis models to the Chandra X-ray survey of the two ellipticals NGC3379 and NGC4278. Finally, I worked on population synthesismodels of black holeX-ray binaries in the MilkyWay. This work was motivated by recent developments in observational techniques for the measurement of black hole spin magnitudes in black hole X-ray binaries. The accuracy of these techniques depend on misalignment of the black hole spin with respect to the orbital angular momentum. In black hole X-ray binaries, this misalignment can occur during the supernova explosion that forms the compact object. In this study, I presented population synthesis models of Galactic black hole X-ray binaries, and examined the distribution of misalignment angles, and its dependence on the model parameters.

On the fundamental properties of dynamically hot galaxies

NASA Astrophysics Data System (ADS)

Kritsuk, Alexei G.

1997-01-01

A two-component isothermal equilibrium model is applied to reproduce basic structural properties of dynamically hot stellar systems immersed in their massive dark haloes. The origin of the fundamental plane relation for giant ellipticals is naturally explained as a consequence of dynamical equilibrium in the context of the model. The existence of two galactic families displaying different behaviour in the luminosity-surface-brightness diagram is shown to be a result of a smooth transition from dwarfs, dominated by dark matter near the centre, to giants dominated by the luminous stellar component. The comparison of empirical scaling relations with model predictions suggests that probably a unique dissipative process was operating during the violent stage of development of stellar systems in the dark haloes, and the depth of the potential well controlled the observed luminosity of the resulting galaxies. The interpretation also provides some restrictions on the properties of dark haloes implied by the fundamental scaling laws.

Particle tagging and its implications for stellar population dynamics

NASA Astrophysics Data System (ADS)

Le Bret, Theo; Pontzen, Andrew; Cooper, Andrew P.; Frenk, Carlos; Zolotov, Adi; Brooks, Alyson M.; Governato, Fabio; Parry, Owen H.

2017-07-01

We establish a controlled comparison between the properties of galactic stellar haloes obtained with hydrodynamical simulations and with 'particle tagging'. Tagging is a fast way to obtain stellar population dynamics: instead of tracking gas and star formation, it 'paints' stars directly on to a suitably defined subset of dark matter particles in a collisionless, dark-matter-only simulation. Our study shows that 'live' particle tagging schemes, where stellar masses are painted on to the dark matter particles dynamically throughout the simulation, can generate good fits to the hydrodynamical stellar density profiles of a central Milky Way-like galaxy and its most prominent substructure. Energy diffusion processes are crucial to reshaping the distribution of stars in infalling spheroidal systems and hence the final stellar halo. We conclude that the success of any particular tagging scheme hinges on this diffusion being taken into account, and discuss the role of different subgrid feedback prescriptions in driving this diffusion.

Dynamically important magnetic fields near accreting supermassive black holes.

PubMed

Zamaninasab, M; Clausen-Brown, E; Savolainen, T; Tchekhovskoy, A

2014-06-05

Accreting supermassive black holes at the centres of active galaxies often produce 'jets'--collimated bipolar outflows of relativistic particles. Magnetic fields probably play a critical role in jet formation and in accretion disk physics. A dynamically important magnetic field was recently found near the Galactic Centre black hole. If this is common and if the field continues to near the black hole event horizon, disk structures will be affected, invalidating assumptions made in standard models. Here we report that jet magnetic field and accretion disk luminosity are tightly correlated over seven orders of magnitude for a sample of 76 radio-loud active galaxies. We conclude that the jet-launching regions of these radio-loud galaxies are threaded by dynamically important fields, which will affect the disk properties. These fields obstruct gas infall, compress the accretion disk vertically, slow down the disk rotation by carrying away its angular momentum in an outflow and determine the directionality of jets.

Dark Matter or Modified Dynamics? Hints from Galaxy Kinematics

NASA Astrophysics Data System (ADS)

Gentile, G.

2010-12-01

I show two observational projects I am involved in, which are aimed at understanding better the existence and nature of dark matter, and also aimed at testing alternatives to galactic dark matter such as MOND (Modified Newtonian Dynamics). I present new HI observations of the nearby dwarf galaxy NGC 3741. This galaxy has an extremely extended HI disc (42 B-band exponential scalelengths). The distribution and kinematics are accurately derived by building model data cubes, which closely reproduce the observations. Mass modelling of the rotation curve shows that a cored dark matter halo or MOND provide very good fits, whereas Cold Dark Matter density profiles fail to fit the data. I also show new results about tidal dwarf galaxies, which within the CDM framework are expected to be dark matter-free but whose kinematics instead show a mass discrepancy, exactly of the magnitude that is expected in MOND (Modified Newtonian Dynamics).

The Optical Gravitational Lensing Experiment. BVI Maps of Dense Stellar Regions. III. The Galactic Bulge

NASA Astrophysics Data System (ADS)

Udalski, A.; Szymanski, M.; Kubiak, M.; Pietrzynski, G.; Soszynski, I.; Wozniak, P.; Zebrun, K.; Szewczyk, O.; Wyrzykowski, L.

2002-09-01

We present the VI photometric maps of the Galactic bulge. They contain VI photometry and astrometry of about 30 million stars from 49 fields of 0.225 square degree each in the Galactic center region. The data were collected during the second phase of the OGLE microlensing project. We discuss the accuracy of data and present color-magnitude diagrams of selected fields observed by OGLE in the Galactic bulge. The VI maps of the Galactic bulge are accessible electronically for the astronomical community from the OGLE Internet archive.

Intermittent behavior of galactic dynamo activities

NASA Technical Reports Server (NTRS)

Ko, C. M.; Parker, E. N.

1989-01-01

Recent observations by Beck and Golla of far-infrared and radio continuum emission from nearby spiral galaxies suggest that the galactic magnetic field strength is connected to the current star formation rate. The role of star formation on the generation of large-scale galactic magnetic field is studied in this paper. Using a simple galactic model, it is shown how the galactic dynamo depends strongly on the turbulent velocity of the interstellar medium. When the star formation efficiency is high, the ISM is churned which in turn amplifies the galactic magnetic field. Between active star formation epochs, the magnetic field is in dormant state and decays at a negligible rate. If density waves trigger star formation, then they also turn on the otherwise dormant dynamo.

Internal kinematics and dynamics of galaxies; Proceedings of the Symposium, Universitede Franche-Comte, Besancon, France, August 9-13, 1982

NASA Astrophysics Data System (ADS)

Athanassoula, E.

Various aspects of the internal kinematics and dynamics of galaxies are considered. The kinematics of the gas and the underlying mass distribution are discussed, including the systematics of H II rotation curves, H I velocity fields and rotation curves, the distribution of molecular clouds in spiral galaxies, gas at large radii, the implications for galactic mass models of vertical motion and the thickness of H I disks, and mass distribution and dark halos. The theory of spiral structure is addressed, along with conflicts and directions in spiral structure studies. Theories of warps are covered. Barred galaxies are treated, including their morphology, stellar kinematics, and dynamics, the stability of their disks, theoretical studies of their gas flows, and the formation of rings and lenses. Spheroidal systems are considered, including dynamics of early type galaxies, models of ellipticals and bulges, and interstellar matter in elliptical galaxies. Simulations and observational evidence for mergers are addressed, and the formation of galaxies and dynamics of globular cluster systems are examined. For individual items see A83-49202 to A83-49267

Chemodynamical modelling of the galactic bulge and bar

NASA Astrophysics Data System (ADS)

Portail, Matthieu; Wegg, Christopher; Gerhard, Ortwin; Ness, Melissa

2017-09-01

We present the first self-consistent chemodynamical model fitted to reproduce data for the galactic bulge, bar and inner disc. We extend the Made-to-Measure method to an augmented phase-space including the metallicity of stars, and show its first application to the bar region of the Milky Way. Using data from the ARGOS and APOGEE (DR12) surveys, we adapt the recent dynamical model from Portail et al. to reproduce the observed spatial and kinematic variations as a function of metallicity, thus allowing the detailed study of the 3D density distributions, kinematics and orbital structure of stars in different metallicity bins. We find that metal-rich stars with [Fe/H] ≥ -0.5 are strongly barred and have dynamical properties that are consistent with a common disc origin. Metal-poor stars with [Fe/H] ≤ -0.5 show strong kinematic variations with metallicity, indicating varying contributions from the underlying stellar populations. Outside the central kpc, metal-poor stars are found to have the density and kinematics of a thick disc while in the inner kpc, evidence for an extra concentration of metal-poor stars is found. Finally, the combined orbit distributions of all metallicities in the model naturally reproduce the observed vertex deviations in the bulge. This paper demonstrates the power of Made-to-Measure chemodynamical models, that when extended to other chemical dimensions will be very powerful tools to maximize the information obtained from large spectroscopic surveys such as APOGEE, GALAH and MOONS.

Dark catalysis

NASA Astrophysics Data System (ADS)

Agrawal, Prateek; Cyr-Racine, Francis-Yan; Randall, Lisa; Scholtz, Jakub

2017-08-01

Recently it was shown that dark matter with mass of order the weak scale can be charged under a new long-range force, decoupled from the Standard Model, with only weak constraints from early Universe cosmology. Here we consider the implications of an additional charged particle C that is light enough to lead to significant dissipative dynamics on galactic times scales. We highlight several novel features of this model, which can be relevant even when the C particle constitutes only a small fraction of the number density (and energy density). We assume a small asymmetric abundance of the C particle whose charge is compensated by a heavy X particle so that the relic abundance of dark matter consists mostly of symmetric X and bar X, with a small asymmetric component made up of X and C. As the universe cools, it undergoes asymmetric recombination binding the free Cs into (XC) dark atoms efficiently. Even with a tiny asymmetric component, the presence of C particles catalyzes tight coupling between the heavy dark matter X and the dark photon plasma that can lead to a significant suppression of the matter power spectrum on small scales and lead to some of the strongest bounds on such dark matter theories. We find a viable parameter space where structure formation constraints are satisfied and significant dissipative dynamics can occur in galactic haloes but show a large region is excluded. Our model shows that subdominant components in the dark sector can dramatically affect structure formation.

Dark catalysis

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

Agrawal, Prateek; Cyr-Racine, Francis-Yan; Randall, Lisa

Recently it was shown that dark matter with mass of order the weak scale can be charged under a new long-range force, decoupled from the Standard Model, with only weak constraints from early Universe cosmology. Here we consider the implications of an additional charged particle C that is light enough to lead to significant dissipative dynamics on galactic times scales. We highlight several novel features of this model, which can be relevant even when the C particle constitutes only a small fraction of the number density (and energy density). We assume a small asymmetric abundance of the C particle whosemore » charge is compensated by a heavy X particle so that the relic abundance of dark matter consists mostly of symmetric X and X-bar , with a small asymmetric component made up of X and C . As the universe cools, it undergoes asymmetric recombination binding the free C s into ( XC ) dark atoms efficiently. Even with a tiny asymmetric component, the presence of C particles catalyzes tight coupling between the heavy dark matter X and the dark photon plasma that can lead to a significant suppression of the matter power spectrum on small scales and lead to some of the strongest bounds on such dark matter theories. We find a viable parameter space where structure formation constraints are satisfied and significant dissipative dynamics can occur in galactic haloes but show a large region is excluded. Our model shows that subdominant components in the dark sector can dramatically affect structure formation.« less

A New Outer Galaxy Molecular Cloud Catalog: Applications to Galactic Structure

NASA Astrophysics Data System (ADS)

Kerton, C. R.; Brunt, C. M.; Pomerleau, C.

2001-12-01

We have generated a new molecular cloud catalog from a reprocessed version of the Five College Radio Astronomy (FCRAO) Observatory Outer Galaxy Survey (OGS) of 12CO (J=1--0) emission. The catalog has been used to develop a technique that uses the observed angular size-linewidth relation (ASLWR) as a distance indicator to molecular cloud ensembles. The new technique is a promising means to map out the large-scale structure of our Galaxy using the new high spatial dynamic range CO surveys currently available. The catalog was created using a two-stage object-identification algorithm. We first identified contiguous emission structures of a specified minimum number of pixels above a specified temperature threshold. Each structure so defined was then examined and localized emission enhancements within each structure were identified as separate objects. The resulting cloud catalog, contains basic data on 14595 objects. From the OGS we identified twenty-three cloud ensembles. For each, bisector fits to angular size vs. linewidth plots were made. The fits vary in a systematic way that allows a calibration of the fit parameters with distance to be made. Our derived distances to the ensembles are consistent with the distance to the Perseus Arm, and the accurate radial velocity measurements available from the same data are in accord with the known non-circular motions at the location of the Perseus Arm. The ASLWR method was also successfully applied to data from the Boston University/FCRAO Galactic Ring Survey (GRS) of 13CO(J=1--0) emission. Based upon our experience with the GRS and OGS, the ASLWR technique should be usable in any data set with sufficient spatial dynamic range to allow it to be properly calibrated. C.P. participated in this study through the Women in Engineering and Science (WES) program of NRC Canada. The Dominion Radio Astrophysical Observatory is a National Facility operated by the National Research Council. The Canadian Galactic Plane Survey is a Canadian project with international partners, and is supported by the Natural Sciences and Engineering Research Council (NSERC).

A simulation of high energy cosmic ray propagation 2

NASA Technical Reports Server (NTRS)

Honda, M.; Kamata, K.; Kifune, T.; Matsubara, Y.; Mori, M.; Nishijima, K.

1985-01-01

The cosmic ray propagation in the Galactic arm is simulated. The Galactic magnetic fields are known to go along with so called Galactic arms as a main structure with turbulences of the scale about 30pc. The distribution of cosmic ray in Galactic arm is studied. The escape time and the possible anisotropies caused by the arm structure are discussed.

VizieR Online Data Catalog: OGLE II. VI photometry of Galactic Bulge (Udalski+, 2002)

NASA Astrophysics Data System (ADS)

Udalski, A.; Szymanski, M.; Kubiak, M.; Pietrzynski, G.; Soszynski, I.; Wozniak, P.; Zebrun, K.; Szewczyk, O.; Wyrzykowski, L.

2003-09-01

We present the VI photometric maps of the Galactic bulge. They contain VI photometry and astrometry of about 30 million stars from 49 fields of 0.225 square degree each in the Galactic center region. The data were collected during the second phase of the OGLE microlensing project. We discuss the accuracy of data and present color-magnitude diagrams of selected fields observed by OGLE in the Galactic bulge. The VI maps of the Galactic bulge are accessible electronically for the astronomical community from the OGLE Internet archive (2 data files).

Scale-invariant scalar field dark matter through the Higgs portal

NASA Astrophysics Data System (ADS)

Cosme, Catarina; Rosa, João G.; Bertolami, O.

2018-05-01

We discuss the dynamics and phenomenology of an oscillating scalar field coupled to the Higgs boson that accounts for the dark matter in the Universe. The model assumes an underlying scale invariance such that the scalar field only acquires mass after the electroweak phase transition, behaving as dark radiation before the latter takes place. While for a positive coupling to the Higgs field the dark scalar is stable, for a negative coupling it acquires a vacuum expectation value after the electroweak phase transition and may decay into photon pairs, albeit with a mean lifetime much larger than the age of the Universe. We explore possible astrophysical and laboratory signatures of such a dark matter candidate in both cases, including annihilation and decay into photons, Higgs decay, photon-dark scalar oscillations and induced oscillations of fundamental constants. We find that dark matter within this scenario will be generically difficult to detect in the near future, except for the promising case of a 7 keV dark scalar decaying into photons, which naturally explains the observed galactic and extra-galactic 3.5 keV X-ray line.

Evolutionary Models of Cold, Magnetized, Interstellar Clouds

NASA Technical Reports Server (NTRS)

Gammie, Charles F.; Ostriker, Eve; Stone, James M.

2004-01-01

We modeled the long-term and small-scale evolution of molecular clouds using direct 2D and 3D magnetohydrodynamic (MHD) simulations. This work followed up on previous research by our group under auspices of the ATP in which we studied the energetics of turbulent, magnetized clouds and their internal structure on intermediate scales. Our new work focused on both global and smallscale aspects of the evolution of turbulent, magnetized clouds, and in particular studied the response of turbulent proto-cloud material to passage through the Galactic spiral potential, and the dynamical collapse of turbulent, magnetized (supercritical) clouds into fragments to initiate the formation of a stellar cluster. Technical advances under this program include developing an adaptive-mesh MHD code as a successor to ZEUS (ATHENA) in order to follow cloud fragmentation, developing a shearing-sheet MHD code which includes self-gravity and externally-imposed gravity to follow the evolution of clouds in the Galactic potential, and developing radiative transfer models to evaluate the internal ionization of clumpy clouds exposed to external photoionizing UV and CR radiation. Gammie's work at UIUC focused on the radiative transfer aspects of this program.

Recent Progress in Active Antenna Designs for the Long Wavelength Array (LWA)

NASA Astrophysics Data System (ADS)

Hicks, B. C.; Stewart, K. P.; Paravastu, N.; Bradley, R. F.; Parashare, C. R.; Erickson, W. C.; Gross, C.; Polisensky, E.; Crane, P. C.; Ray, P. S.; Kassim, N. E.; Weiler, K. W.

2005-12-01

We present new designs for active antenna systems optimized for HF/VHF radio astronomy, ionospheric science, space weather, and other radio science applications. Active antenna designs have been developed and tested which satisfy the need for high linearity and stability while achieving Galactic background dominated noise levels. The presence of very strong terrestrial radio-frequency interference (RFI), and world-wide propagation at these frequencies require that the preamplifiers have very high dynamic range. Distortion products must be below the Galactic background level for RFI mitigation techniques to be successful. Individual antennas should have broad response patterns to cover most of the sky without pointing mechanisms, but with decreased sensitivity at low elevations. Ideal designs would also be immune to environmental effects such as temperature variations and precipitation. For projects such as the LWA, where thousands of receptors will be needed, they must also be robust, inexpensive, and easy to manufacture and install. We discuss high-performance designs that are optimized for cost-sensitive applications such as the LWA. Basic research in astronomy is supported by the Office of Naval Research.

Recovering a MOND-like acceleration law in mimetic gravity

NASA Astrophysics Data System (ADS)

Vagnozzi, Sunny

2017-09-01

We reconsider the recently proposed mimetic gravity, focusing in particular on whether the theory is able to reproduce the inferred flat rotation curves of galaxies. We extend the theory by adding a non-minimal coupling between matter and mimetic field. Such coupling leads to the appearance of an extra force which renders the motion of test particles non-geodesic. By studying the weak field limit of the resulting equations of motion, we demonstrate that in the Newtonian limit the acceleration law induced by the non-minimal coupling reduces to a modified Newtonian dynamics (MOND)-like one. In this way, it is possible to reproduce the successes of MOND, namely the explanation for the flat galactic rotation curves and the Tully-Fisher relation, within the framework of mimetic gravity, without the need for particle dark matter. The scale-dependence of the recovered acceleration scale opens up the possibility of addressing the missing mass problem not only on galactic but also on cluster scales: we defer a full study of this issue, together with a complete analysis of fits to spiral galaxy rotation curves, to an upcoming companion paper.

Emergence of a dark force in corpuscular gravity

NASA Astrophysics Data System (ADS)

Cadoni, M.; Casadio, R.; Giusti, A.; Tuveri, M.

2018-02-01

We investigate the emergent laws of gravity when dark energy and the de Sitter space-time are modeled as a critical Bose-Einstein condensate of a large number of soft gravitons NG. We argue that this scenario requires the presence of various regimes of gravity in which NG scales in different ways. Moreover, the local gravitational interaction affecting baryonic matter can be naturally described in terms of gravitons pulled out from this dark energy condensate (DEC). We then explain the additional component of the acceleration at galactic scales, commonly attributed to dark matter, as the reaction of the DEC to the presence of baryonic matter. This additional dark force is also associated to gravitons pulled out from the DEC and correctly reproduces the modified Newtonian dynamics (MOND) acceleration. It also allows for an effective description in terms of general relativity sourced by an anisotropic fluid. We finally calculate the mass ratio between the contribution of the apparent dark matter and the baryonic matter in a region of size r at galactic scales and show that it is consistent with the Λ CDM predictions.

The standard model and some new directions. [for scientific theory of Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Blandford, R. D.; Rees, M. J.

1992-01-01

A 'standard' model of Active Galactic Nuclei (AGN), based upon a massive black hole surrounded by a thin accretion disk, is defined. It is argued that, although there is good evidence for the presence of black holes and orbiting gas, most of the details of this model are either inadequate or controversial. Magnetic field may be responsible for the confinement of continuum and line-emitting gas, for the dynamical evolution of accretion disks and for the formation of jets. It is further argued that gaseous fuel is supplied in molecular form and that this is responsible for thermal re-radiation, equatorial obscuration and, perhaps, the broad line gas clouds. Stars may also supply gas close to the black hole, especially in low power AGN and they may be observable in discrete orbits as probes of the gravitational field. Recent observations suggest that magnetic field, stars, dusty molecular gas and orientation effects must be essential components of a complete description of AGN. The discovery of quasars with redshifts approaching 5 is an important clue to the mechanism of galaxy formation.

Gravitational wave as probe of superfluid dark matter

NASA Astrophysics Data System (ADS)

Cai, Rong-Gen; Liu, Tong-Bo; Wang, Shao-Jiang

2018-02-01

In recent years, superfluid dark matter (SfDM) has become a competitive model of emergent modified Newtonian dynamics (MOND) scenario: MOND phenomenons naturally emerge as a derived concept due to an extra force mediated between baryons by phonons as a result of axionlike particles condensed as superfluid at galactic scales; Beyond galactic scales, these axionlike particles behave as normal fluid without phonon-mediated MOND-like force between baryons, therefore SfDM also maintains the usual success of Λ CDM at cosmological scales. In this paper, we use gravitational waves (GWs) to probe the relevant parameter space of SfDM. GWs through Bose-Einstein condensate (BEC) could propagate with a speed slightly deviation from the speed-of-light due to the change in the effective refractive index, which depends on the SfDM parameters and GW-source properties. We find that Five hundred meter Aperture Spherical Telescope (FAST), Square Kilometre Array (SKA) and International Pulsar Timing Array (IPTA) are the most promising means as GW probe of relevant parameter space of SfDM. Future space-based GW detectors are also capable of probing SfDM if a multimessenger approach is adopted.

RAVE-Gaia and the impact on Galactic archeology

NASA Astrophysics Data System (ADS)

Kunder, Andrea

2018-04-01

The new data release (DR5) of the RAdial Velocity Experiment (RAVE) includes radial velocities of 520,781 spectra of 457,588 individual stars, of which 215,590 individual stars are released in the Tycho-Gaia astrometric solution (TGAS) in Gaia DR1. Therefore, RAVE contains the largest TGAS overlap of the recent and ongoing Milky Way spectroscopic surveys. Most of the RAVE stars also contain stellar parameters (effective temperature, surface gravity, overall metallicity), as well as individual abundances for Mg, Al, Si, Ca, Ti, Fe, and Ni. Combining RAVE with TGAS brings the uncertainties in space velocities down by a factor of 2 for stars in the RAVE volume - 10 km s-1 uncertainties in space velocities are now able to be derived for the majority (70%) of the RAVE-TGAS sample, providing a powerful platform for chemo-dynamic analyses of the Milky Way. Here we discuss the RAVE-TGAS impact on Galactic archaeology as well as how the Gaia parallaxes can be used to break degeneracies within the RAVE spectral regime for an even better return in the derivation of stellar parameters and abundances.

A Census of Large-scale (≥10 PC), Velocity-coherent, Dense Filaments in the Northern Galactic Plane: Automated Identification Using Minimum Spanning Tree

NASA Astrophysics Data System (ADS)

Wang, Ke; Testi, Leonardo; Burkert, Andreas; Walmsley, C. Malcolm; Beuther, Henrik; Henning, Thomas

2016-09-01

Large-scale gaseous filaments with lengths up to the order of 100 pc are on the upper end of the filamentary hierarchy of the Galactic interstellar medium (ISM). Their association with respect to the Galactic structure and their role in Galactic star formation are of great interest from both an observational and theoretical point of view. Previous “by-eye” searches, combined together, have started to uncover the Galactic distribution of large filaments, yet inherent bias and small sample size limit conclusive statistical results from being drawn. Here, we present (1) a new, automated method for identifying large-scale velocity-coherent dense filaments, and (2) the first statistics and the Galactic distribution of these filaments. We use a customized minimum spanning tree algorithm to identify filaments by connecting voxels in the position-position-velocity space, using the Bolocam Galactic Plane Survey spectroscopic catalog. In the range of 7\\buildrel{\\circ}\\over{.} 5≤slant l≤slant 194^\\circ , we have identified 54 large-scale filaments and derived mass (˜ {10}3{--}{10}5 {M}⊙ ), length (10-276 pc), linear mass density (54-8625 {M}⊙ pc-1), aspect ratio, linearity, velocity gradient, temperature, fragmentation, Galactic location, and orientation angle. The filaments concentrate along major spiral arms. They are widely distributed across the Galactic disk, with 50% located within ±20 pc from the Galactic mid-plane and 27% run in the center of spiral arms. An order of 1% of the molecular ISM is confined in large filaments. Massive star formation is more favorable in large filaments compared to elsewhere. This is the first comprehensive catalog of large filaments that can be useful for a quantitative comparison with spiral structures and numerical simulations.

Black-hole model of galactic nuclei

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

Norman, C.A.; ter Haar, D.

1973-04-01

It is shown that the observed large infrared emission from some galactic nuclei finds a natural explanation, if one takes plasma turbulence into account in Lynden-Bell and Rees' blackhole model of galactic nuclei. (auth)

Star Formation in Galaxies

NASA Technical Reports Server (NTRS)

1987-01-01

Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

Acceleration of petaelectronvolt protons in the Galactic Centre

NASA Astrophysics Data System (ADS)

HESS Collaboration; Abramowski, A.; Aharonian, F.; Benkhali, F. Ait; Akhperjanian, A. G.; Angüner, E. O.; Backes, M.; Balzer, A.; Becherini, Y.; Tjus, J. Becker; Berge, D.; Bernhard, S.; Bernlöhr, K.; Birsin, E.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bordas, P.; Bregeon, J.; Brun, F.; Brun, P.; Bryan, M.; Bulik, T.; Carr, J.; Casanova, S.; Chakraborty, N.; Chalme-Calvet, R.; Chaves, R. C. G.; Chen, A.; Chrétien, M.; Colafrancesco, S.; Cologna, G.; Conrad, J.; Couturier, C.; Cui, Y.; Davids, I. D.; Degrange, B.; Deil, C.; Dewilt, P.; Djannati-Ataï, A.; Domainko, W.; Donath, A.; Drury, L. O'C.; Dubus, G.; Dutson, K.; Dyks, J.; Dyrda, M.; Edwards, T.; Egberts, K.; Eger, P.; Ernenwein, J.-P.; Espigat, P.; Farnier, C.; Fegan, S.; Feinstein, F.; Fernandes, M. V.; Fernandez, D.; Fiasson, A.; Fontaine, G.; Förster, A.; Füßling, M.; Gabici, S.; Gajdus, M.; Gallant, Y. A.; Garrigoux, T.; Giavitto, G.; Giebels, B.; Glicenstein, J. F.; Gottschall, D.; Goyal, A.; Grondin, M.-H.; Grudzińska, M.; Hadasch, D.; Häffner, S.; Hahn, J.; Hawkes, J.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hervet, O.; Hillert, A.; Hinton, J. A.; Hofmann, W.; Hofverberg, P.; Hoischen, C.; Holler, M.; Horns, D.; Ivascenko, A.; Jacholkowska, A.; Jamrozy, M.; Janiak, M.; Jankowsky, F.; Jung-Richardt, I.; Kastendieck, M. A.; Katarzyński, K.; Katz, U.; Kerszberg, D.; Khélifi, B.; Kieffer, M.; Klepser, S.; Klochkov, D.; Kluźniak, W.; Kolitzus, D.; Komin, Nu.; Kosack, K.; Krakau, S.; Krayzel, F.; Krüger, P. P.; Laffon, H.; Lamanna, G.; Lau, J.; Lefaucheur, J.; Lefranc, V.; Lemiére, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Lohse, T.; Lopatin, A.; Lu, C.-C.; Lui, R.; Marandon, V.; Marcowith, A.; Mariaud, C.; Marx, R.; Maurin, G.; Maxted, N.; Mayer, M.; Meintjes, P. J.; Menzler, U.; Meyer, M.; Mitchell, A. M. W.; Moderski, R.; Mohamed, M.; Morå, K.; Moulin, E.; Murach, T.; de Naurois, M.; Niemiec, J.; Oakes, L.; Odaka, H.; Öttl, S.; Ohm, S.; Opitz, B.; Ostrowski, M.; Oya, I.; Panter, M.; Parsons, R. D.; Arribas, M. Paz; Pekeur, N. W.; Pelletier, G.; Petrucci, P.-O.; Peyaud, B.; Pita, S.; Poon, H.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raab, S.; Reichardt, I.; Reimer, A.; Reimer, O.; Renaud, M.; de Los Reyes, R.; Rieger, F.; Romoli, C.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Rulten, C. B.; Sahakian, V.; Salek, D.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schlickeiser, R.; Schüssler, F.; Schulz, A.; Schwanke, U.; Schwemmer, S.; Seyffert, A. S.; Simoni, R.; Sol, H.; Spanier, F.; Spengler, G.; Spies, F.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Stinzing, F.; Stycz, K.; Sushch, I.; Tavernet, J.-P.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tluczykont, M.; Trichard, C.; Tuffs, R.; Valerius, K.; van der Walt, J.; van Eldik, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Viana, A.; Vincent, P.; Vink, J.; Voisin, F.; Völk, H. J.; Vuillaume, T.; Wagner, S. J.; Wagner, P.; Wagner, R. M.; Weidinger, M.; Weitzel, Q.; White, R.; Wierzcholska, A.; Willmann, P.; Wörnlein, A.; Wouters, D.; Yang, R.; Zabalza, V.; Zaborov, D.; Zacharias, M.; Zdziarski, A. A.; Zech, A.; Zefi, F.; Żywucka, N.

2016-03-01

Galactic cosmic rays reach energies of at least a few petaelectronvolts (of the order of 1015 electronvolts). This implies that our Galaxy contains petaelectronvolt accelerators (‘PeVatrons’), but all proposed models of Galactic cosmic-ray accelerators encounter difficulties at exactly these energies. Dozens of Galactic accelerators capable of accelerating particles to energies of tens of teraelectronvolts (of the order of 1013 electronvolts) were inferred from recent γ-ray observations. However, none of the currently known accelerators—not even the handful of shell-type supernova remnants commonly believed to supply most Galactic cosmic rays—has shown the characteristic tracers of petaelectronvolt particles, namely, power-law spectra of γ-rays extending without a cut-off or a spectral break to tens of teraelectronvolts. Here we report deep γ-ray observations with arcminute angular resolution of the region surrounding the Galactic Centre, which show the expected tracer of the presence of petaelectronvolt protons within the central 10 parsecs of the Galaxy. We propose that the supermassive black hole Sagittarius A* is linked to this PeVatron. Sagittarius A* went through active phases in the past, as demonstrated by X-ray outburstsand an outflow from the Galactic Centre. Although its current rate of particle acceleration is not sufficient to provide a substantial contribution to Galactic cosmic rays, Sagittarius A* could have plausibly been more active over the last 106-107 years, and therefore should be considered as a viable alternative to supernova remnants as a source of petaelectronvolt Galactic cosmic rays.

The Planck Catalogue of Galactic Cold Clumps : PGCC

NASA Astrophysics Data System (ADS)

Montier, L.

The Planck satellite has provided an unprecedented view of the submm sky, allowing us to search for the dust emission of Galactic cold sources. Combining Planck-HFI all-sky maps in the high frequency channels with the IRAS map at 100um, we built the Planck catalogue of Galactic Cold Clumps (PGCC, Planck 2015 results. XXVIII), counting 13188 sources distributed over the whole sky, and following mainly the Galactic structures at low and intermediate latitudes. This is the first all-sky catalogue of Galactic cold sources obtained with a single instrument at this resolution and sensitivity, which opens a new window on star-formation processes in our Galaxy.

The impact of star formation feedback on the circumgalactic medium

NASA Astrophysics Data System (ADS)

Fielding, Drummond; Quataert, Eliot; McCourt, Michael; Thompson, Todd A.

2017-04-01

We use idealized 3D hydrodynamic simulations to study the dynamics and thermal structure of the circumgalactic medium (CGM). Our simulations quantify the role of cooling, stellar feedback driven galactic winds and cosmological gas accretion in setting the properties of the CGM in dark matter haloes ranging from 1011 to 1012 M⊙. Our simulations support a conceptual picture in which the properties of the CGM, and the key physics governing it, change markedly near a critical halo mass of Mcrit ≈ 1011.5 M⊙. As in calculations without stellar feedback, above Mcrit halo gas is supported by thermal pressure created in the virial shock. The thermal properties at small radii are regulated by feedback triggered when tcool/tff ≲ 10 in the hot gas. Below Mcrit, however, there is no thermally supported halo and self-regulation at tcool/tff ˜ 10 does not apply. Instead, the gas is out of hydrostatic equilibrium and largely supported against gravity by bulk flows (turbulence and coherent inflow/outflow) arising from the interaction between cosmological gas inflow and outflowing galactic winds. In these lower mass haloes, the phase structure depends sensitively on the outflows' energy per unit mass and mass-loading, which may allow measurements of the CGM thermal state to constrain the nature of galactic winds. Our simulations account for some of the properties of the multiphase halo gas inferred from quasar absorption line observations, including the presence of significant mass at a wide range of temperatures, and the characteristic O VI and C IV column densities and kinematics. However, we underpredict the neutral hydrogen content of the z ˜ 0 CGM.

Signatures of the Galactic bar on stellar kinematics unveiled by APOGEE

NASA Astrophysics Data System (ADS)

Palicio, Pedro A.; Martinez-Valpuesta, Inma; Allende Prieto, Carlos; Dalla Vecchia, Claudio; Zamora, Olga; Zasowski, Gail; Fernandez-Trincado, J. G.; Masters, Karen L.; García-Hernández, D. A.; Roman-Lopes, Alexandre

2018-07-01

Bars are common galactic structures in the local universe that play an important role in the secular evolution of galaxies, including the Milky Way. In particular, the velocity distribution of individual stars in our galaxy is useful to shed light on stellar dynamics, and provides information complementary to that inferred from the integrated light of external galaxies. However, since a wide variety of models reproduce the distribution of velocity and the velocity dispersion observed in the Milky Way, we look for signatures of the bar on higher order moments of the line-of-sight velocity (V_{los}) distribution. We use two different numerical simulations - one that has developed a bar and one that remains nearly axisymmetric - to compare them with observations in the latest Apache Point Observatory Galactic Evolution Experiment data release (SDSS DR14). This comparison reveals three interesting structures that support the notion that the Milky Way is a barred galaxy. A high-skewness region found at positive longitudes constrains the orientation angle of the bar, and is incompatible with the orientation of the bar at ℓ = 0° proposed in previous studies. We also analyse the V_{los} distributions in three regions, and introduce the Hellinger distance to quantify the differences among them. Our results show a strong non-Gaussian distribution both in the data and in the barred model, confirming the qualitative conclusions drawn from the velocity maps. In contrast to earlier work, we conclude it is possible to infer the presence of the bar from the kurtosis distribution.

Black hole binaries in galactic nuclei and gravitational wave sources

NASA Astrophysics Data System (ADS)

Hong, Jongsuk; Lee, Hyung Mok

2015-03-01

Stellar black hole (BH) binaries are one of the most promising gravitational wave (GW) sources for GW detection by the ground-based detectors. Nuclear star clusters (NCs) located at the centre of galaxies are known to harbour massive black holes (MBHs) and to be bounded by a gravitational potential by other galactic components such as the galactic bulge. Such an environment of NCs provides a favourable conditions for the BH-BH binary formation by the gravitational radiation capture due to the high BH number density and velocity dispersion. We carried out detailed numerical study of the formation of BH binaries in the NCs using a series of N-body simulations for equal-mass cases. There is no mass segregation introduced. We have derived scaling relations of the binary formation rate with the velocity dispersion of the stellar system beyond the radius of influence and made estimates of the rate of formation of BH binaries per unit comoving volume and thus expected detection rate by integrating the binary formation rate over galaxy population within the detection distance of the advanced detectors. We find that the overall formation rates for BH-BH binaries per NC is ˜10-10 yr-1 for the Milky Way-like galaxies and weakly dependent on the mass of MBH as Γ ∝ M_MBH^{3/28}. We estimate the detection rate of 0.02-14 yr-1 for advanced LIGO/Virgo considering several factors such as the dynamical evolution of NCs, the variance of the number density of stars and the mass range of MBH giving uncertainties.

Calibration of the Tip of the Red Giant Branch Distance Method in IR

NASA Astrophysics Data System (ADS)

Sakai, Shoko

1999-02-01

We propose to investigate the feasibility of the tip of the red giant branch (TRGB) as a distance indicator in IR wavelength. The TRGB has been shown both observationally and theoretically to be an excellent distance indicator in I-band, mainly because of its insensitivity to both metallicity and age. Its accuracy is comparable to that of the Cepheid variable stars. The TRGB method in I-band is currently calibrated by Galactic globular clusters whose distances have been measured with RR Lyrae variables. The main objective of this proposal is to calibrate this method in IR by obtaining JHK photometry for a number of Galactic globular clusters. This is motivated by two related scientific goals: (1) It will be possible in the future to obtain direct distances to galaxies even in Coma cluster using the NGST, but only if the TRGB method has been calibrated accurately in IR filters. If the method is proven reliable, then it can be a powerful tool to map out the density and velocity fields of the local Universe in three dimensions. (2) A considerable amount of effort has been spent on obtaining accurate, direct distances to nearby galaxies. However, this has been difficult for a number of galaxies, including IC 342, because they are located at very low Galactic latitude. These galaxies could potentially have a tremendous effect on the dynamics of the Local Group, depending on their distances. Using the calibrated IR TRGB method, we could solve this uncertainty by measuring their distances directly.

Using Open Clusters to Trace the Local Milky Way Rotation Curve and Velocity Field

NASA Astrophysics Data System (ADS)

Frinchaboy, Peter M.; Majewski, S. R.

2006-12-01

Establishing the rotation curve of the Milky Way is one of the fundamental contributions needed to understand the Galaxy and its mass distribution. We have undertaken a systematic spectroscopic survey of open star clusters which can serve as tracers of Galactic disk dynamics. We report on our initial sample of 67 clusters for which the Hydra multi-fiber spectrographs on the WIYN and Blanco telescopes have delivered 1-2 km/s radial velocities (RVs) of many dozens of stars in the fields of each cluster, which are used to derive cluster membership and bulk cluster kinematics when combined with Tycho-2 proper motions. The clusters selected for study have a broad spatial distribution in order to be sensitive to the disk velocity field in all Galactic quadrants and across a Galactocentric radius range as much as 3.0 kpc from the solar circle. Through analysis of the cluster sample, we find (1) the rotation velocity of the LSR is 221 (+2,-4) km/s, (2) the local rotation curve is declining with radius having a slope of -9.0 km/s/kpc, (3) we find (using R_0 = 8.5 kpc) the following Galactic parameters: A = 17.0 km/s/kpc and B = -8.9 km/s/kpc, which yields a Galaxy mass within of 1.5 R_0 of M = 0.9 ± 0.2 x 10^11 solar masses and a M/L of 5.9 in solar units. We also explore the distribution of the local velocity field and find evidence for non-circular motion due to the sprial arms.

IRAS and the Boston University Arecibo Galactic H I Survey: A catalog of cloud properties

NASA Technical Reports Server (NTRS)

Bania, Thomas M.

1992-01-01

The Infrared Astronomy Satellite (IRAS) Galactic Plane Surface Brightness Images were used to identify infrared emission associated with cool, diffuse H I clouds detected by the Boston University-Arecibo Galactic H I Survey. These clouds are associated with galactic star clusters, H II regions, and molecular clouds. Using emission-absorption experiments toward galactic H II regions, we determined the H I properties of cool H I clouds seen in absorption against the thermal continuum, including their kinematic distances. Correlations were then made between IRAS sources and these H II regions, thus some of the spatial confusion associated with the IRAS fields near the galactic plane was resolved since the distances to these sources was known. Because we can also correlate the BU-Arecibo clouds with existing CO surveys, these results will allow us to determine the intrinsic properties of the gas (neutral and ionized atomic as well as molecular) and dust for interstellar clouds in the inner galaxy. For the IRAS-identified H II region sample, we have established the far infrared (FIR) luminosities and galactic distribution of these sources.

X-Ray Processing of ChaMPlane Fields: Methods and Initial Results for Selected Anti-Galactic Center Fields

NASA Astrophysics Data System (ADS)

Hong, JaeSub; van den Berg, Maureen; Schlegel, Eric M.; Grindlay, Jonathan E.; Koenig, Xavier; Laycock, Silas; Zhao, Ping

2005-12-01

We describe the X-ray analysis procedure of the ongoing Chandra Multiwavelength Plane (ChaMPlane) Survey and report the initial results from the analysis of 15 selected anti-Galactic center observations (90deg

Gaia I: the Mission - the adventure begins

NASA Astrophysics Data System (ADS)

Altmann, M.

2015-10-01

The ESA Gaia satellite mission, launched on Dec. 19, 2013, will undoubtedly leave a profound impact on Galactic dynamics, revolutionising many aspects of the trade. Nine months later, with the commissioning phase over and the regular five year measuring phase of Gaia starting, it is time to give an overview of the mission, what to expect after the potential of the spacecraft has been fully assessed in situ. Moreover this paper will give a brief description of the mission as a whole, to be followed by a second contribution by Figueras (2015) focussing on Gaia science.

Can we detect antimatter from other galaxies

NASA Technical Reports Server (NTRS)

Ahlen, S. P.; Price, P. B.; Salamon, M. H.; Tarle, G.

1982-01-01

A novel particle detection technique employing well established principles of high order quantum electrodynamics for searching for antimatter in cosmic rays is described, and shown to have both collecting power and resolution superior to conventional alternatives. By taking into account various estimates of the metagalactic cosmic-ray energy density, and the possible modulation of metagalactic cosmic rays by a galactic wind within the framework of the dynamical halo model, it is shown that the experiment proposed would be the first to be sensitive to the presence of extragalactic antimatter.

Wiggles and knots in radio jets

NASA Astrophysics Data System (ADS)

Trussoni, E.; Ferrari, A.; Zaninetti, L.

Dynamical effects in binary nuclei inside parent galactic cores, gravitational interactions with companion galaxies, and Kelvin-Helmholtz instabilities in the flow propagation have been proposed as mechanism responsible for the formation of the low amplitude morphologies, wiggles and knots, observed in radio jets. Here the basic characteristics and implications of these models are discussed with reference to the limited sample of existing data. In conclusion it will be shown that present observations cannot discriminate definitely these theories; conversely, different mechanisms may be at work together in any jet at the same time.

Fueling the AGN

NASA Astrophysics Data System (ADS)

Combes, F.

Active Galactic Nuclei are fueled from material (gas or stars) that are in general far away from the gravitational influence of the central black hole, the engine thought to be responsible for their activity. The required material has a lot of angular momentum that, a priori, is quite difficult to evacuate. The various dynamical mechanisms that may play a role in this game are reviewed, including m = 2 perturbations (bars and spirals), m = 1 perturbations (spirals, warps, lopsidedness), and tidal interactions between galaxies and mergers. In the latest stages of the merger, a binary black hole could be formed, and its influence on the dynamics and fueling is discussed. Starbursts are often associated with AGN, and the nature of their particular connection, and their role in the nuclear fueling is described. Evolution of the fueling efficiency with redshift is addressed.

Panel Discussion Vi: Cosmology

NASA Astrophysics Data System (ADS)

Anderson, E.; Dolgov, A.; Crothers, S.; Mitra, A.; Rubakov, V.; Zakharov, A.

2014-03-01

Questions to discuss: * To what extent are Dark Matter and Dark Energy necessary to explain the observed properties of the Universe? * Why are the Dark matter profiles so universal at the galactic scales? * Are there viable candidates of modified gravitational dynamics to exclude the dark components of Universe? * Do we have any perspectives to distinguish the Dark Energy from the cosmological constant? * Are there any certain indications for sterile neutrinos in the cosmos? * How does the Planck data change the view of inflation in the early Universe? What could be the origin of the inflaton plateau? So far, what else is interesting about the Planck data? * What are the nearest crucial points in cosmological observations? * Can we be more decisive discriminating between the anthropic principle, the superstringy landscape, fine tuning or dynamics as reasons for the cosmological coincidences?

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.

Galactic Haze seen by Planck and Galactic Bubbles seen by Fermi

NASA Image and Video Library

2012-02-13

This all-sky image shows the distribution of the galactic haze seen by ESA Planck mission at microwave frequencies superimposed over the high-energy sky, as seen by NASA Fermi Gamma-ray Space Telescope.

The structure and content of the galaxy and galactic gamma rays

NASA Technical Reports Server (NTRS)

Fichtel, C. E. (Editor); Stecker, F. W. (Editor)

1977-01-01

Gamma radiation investigations by COS-B and SAS-2 satellite are reported. Data from CO surveys of the galaxy and the galactic distribution of pulsars are analyzed. Theories of galactic gamma ray emission are explored.

Survey of the galactic disk from 1 = -150 deg to 1 = 82 deg in the submillimeter range

NASA Technical Reports Server (NTRS)

Caux, Emmanuel; Serra, Guy

1987-01-01

The first almost complete survey of the galactic disk from 1 = -150 deg to 1 = 82 deg in the submillimeter range (effective wavelength = 380 microns), performed with the AGLAE balloon-borne instrument modified to include a submillimeter channel, is reported. The instrumentation and observational procedures are described, as are the signal processing and calibration. The results are presented as a profile of the submillimeter brightness of the galactic disk displayed as a function of the galactic longitude. This profile exhibits diffuse emission all along the disk with bright peaks associated with resolved sources. The averaged galactic spectrum is in agreement with a temperature distribution of the interstellar cold dust.

Open star clusters and Galactic structure

NASA Astrophysics Data System (ADS)

Joshi, Yogesh C.

2018-04-01

In order to understand the Galactic structure, we perform a statistical analysis of the distribution of various cluster parameters based on an almost complete sample of Galactic open clusters yet available. The geometrical and physical characteristics of a large number of open clusters given in the MWSC catalogue are used to study the spatial distribution of clusters in the Galaxy and determine the scale height, solar offset, local mass density and distribution of reddening material in the solar neighbourhood. We also explored the mass-radius and mass-age relations in the Galactic open star clusters. We find that the estimated parameters of the Galactic disk are largely influenced by the choice of cluster sample.

The annihilation of galactic positrons

NASA Technical Reports Server (NTRS)

Bussard, R.; Rematy, R.

1978-01-01

The probabilities of various channels of galactic positron annihilation were evaluated and the spectrum of the resulting radiation was calculated. The narrow width (FWHM less than 3.2 keV) of the 0.511 MeV line observed from the galactic center implies that a large fraction of positrons should annihilate in a medium of temperature less than 100,000 K and ionization fraction greater than 0.05. HII regions at the galactic center could be possible sites of annihilation.

The afterglow of GRB 050709 and the nature of the short-hard gamma-ray bursts.

PubMed

Fox, D B; Frail, D A; Price, P A; Kulkarni, S R; Berger, E; Piran, T; Soderberg, A M; Cenko, S B; Cameron, P B; Gal-Yam, A; Kasliwal, M M; Moon, D-S; Harrison, F A; Nakar, E; Schmidt, B P; Penprase, B; Chevalier, R A; Kumar, P; Roth, K; Watson, D; Lee, B L; Shectman, S; Phillips, M M; Roth, M; McCarthy, P J; Rauch, M; Cowie, L; Peterson, B A; Rich, J; Kawai, N; Aoki, K; Kosugi, G; Totani, T; Park, H-S; MacFadyen, A; Hurley, K C

2005-10-06

The final chapter in the long-standing mystery of the gamma-ray bursts (GRBs) centres on the origin of the short-hard class of bursts, which are suspected on theoretical grounds to result from the coalescence of neutron-star or black-hole binary systems. Numerous searches for the afterglows of short-hard bursts have been made, galvanized by the revolution in our understanding of long-duration GRBs that followed the discovery in 1997 of their broadband (X-ray, optical and radio) afterglow emission. Here we present the discovery of the X-ray afterglow of a short-hard burst, GRB 050709, whose accurate position allows us to associate it unambiguously with a star-forming galaxy at redshift z = 0.160, and whose optical lightcurve definitively excludes a supernova association. Together with results from three other recent short-hard bursts, this suggests that short-hard bursts release much less energy than the long-duration GRBs. Models requiring young stellar populations, such as magnetars and collapsars, are ruled out, while coalescing degenerate binaries remain the most promising progenitor candidates.

A very energetic supernova associated with the gamma-ray burst of 29 March 2003.

PubMed

Hjorth, Jens; Sollerman, Jesper; Møller, Palle; Fynbo, Johan P U; Woosley, Stan E; Kouveliotou, Chryssa; Tanvir, Nial R; Greiner, Jochen; Andersen, Michael I; Castro-Tirado, Alberto J; Castro Cerón, José María; Fruchter, Andrew S; Gorosabel, Javier; Jakobsson, Páll; Kaper, Lex; Klose, Sylvio; Masetti, Nicola; Pedersen, Holger; Pedersen, Kristian; Pian, Elena; Palazzi, Eliana; Rhoads, James E; Rol, Evert; van den Heuvel, Edward P J; Vreeswijk, Paul M; Watson, Darach; Wijers, Ralph A M J

2003-06-19

Over the past five years evidence has mounted that long-duration (>2 s) gamma-ray bursts (GRBs)-the most luminous of all astronomical explosions-signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model.

Death or Survival? Determining the nature of SNe IIn-P explosions

NASA Astrophysics Data System (ADS)

Mauerhan, Jon

2016-10-01

An increasing number of transients classifiable as interacting supernovae of Type IIn have become the subject of intense debate, as the death or survival of the precursor star is unclear. This is because giant non-terminal eruptions from massive luminous blue variable (LBV) stars can spectroscopically resemble SNe IIn and achieve comparable luminosities via shock interaction with pre-existing circumstellar material (CSM). The stellar origin of the new SNe IIn-P class of explosions is particularly controversial. Competing interpretations predict stellar progenitors with very different initial masses and explosion outcomes: 1) non-terminal super-Eddington eruptions from LBVs; 2) collapsars from very massive stars that should die within their natal OB associations; and 3) electron-capture SNe from super-AGB stars with dense CSM envelopes. To resolve the uncertain origin of SNe IIn-P, we propose a simple and inexpensive optical imaging experiment to see if there is a luminous surviving star remaining at the site. UV imaging is also proposed to determine the nature of a UV source detected in pre-explosion GALEX images, and to survey the progenitor's environment for sibling O-type stars.

COMPACT GALACTIC PLANETARY NEBULAE: AN HST /WFC3 MORPHOLOGICAL CATALOG, AND A STUDY OF THEIR ROLE IN THE GALAXY

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

Stanghellini, Letizia; Shaw, Richard A.; Villaver, Eva

We present the images of a Hubble Space Telescope ( HST /WFC3) snapshot program of angularly compact Galactic planetary nebulae (PNe), acquired with the aim of studying their size, evolutionary status, and morphology. PNe that are smaller than ∼4″ are underrepresented in most morphological studies, and today they are less well studied than their immediate evolutionary predecessors, the pre-planetary nebulae. The images have been acquired in the light of [O iii] λ 5007, which is commonly used to classify the PN morphology, in the UV continuum with the aim of detecting the central star unambiguously, and in the I -bandmore » to detect a cool stellar companion, if present. The sample of 51 confirmed PNe exhibits nearly the full range of primary morphological classes, with the distribution more heavily weighted toward bipolar PNe, but with the total of aspherical PNe almost identical to that of the general Galactic sample. A large range of microstructures is evident in our sample as well, with many nebulae displaying attached shells, halos, ansae, and internal structure in the form of arcs, rings, and spirals. Various aspherical structures in a few PNe, including detached arcs, suggest an interaction with the ISM. We studied the observed sample of compact Galactic PNe in the context of the general Galactic PN population, and explore whether their physical size, spatial distribution, reddening, radial metallicity gradient, and possible progenitors are peculiar within the population of Galactic PNe. We found that these compact Galactic PNe, which have been selected based on apparent dimensions, constitute a diverse Galactic PN population that is relatively uniformly distributed across the Galactic disk, including the outskirts of our Galaxy. This unique sample will be used in the future to probe the old Galactic disk population.« less

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

Pu, Hung-Yi; Asada, Keiichi; Akiyama, Kazunori

A radiatively inefficient accretion flow (RIAF), which is commonly characterized by its sub-Keplerian nature, is a favored accretion model for the supermassive black hole at the Galactic center, Sagittarius A*. To investigate the observable features of an RIAF, we compare the modeled shadow images, visibilities, and spectra of three flow models with dynamics characterized by (i) a Keplerian shell that is rigidly rotating outside the innermost stable circular orbit (ISCO) and infalling with a constant angular momentum inside ISCO, (ii) a sub-Keplerian motion, and (iii) a free-falling motion with zero angular momentum at infinity. At near-millimeter wavelengths, the emission ismore » dominated by the flow within several Schwarzschild radii. The energy shift due to these flow dynamics becomes important and distinguishable, suggesting that the flow dynamics are an important model parameter for interpreting the millimeter/sub-millimeter very long baseline interferometric observations with the forthcoming, fully assembled Event Horizon Telescope (EHT). As an example, we demonstrate that structural variations of Sagittarius A* on event horizon-scales detected in previous EHT observations can be explained by the non-stationary dynamics of an RIAF.« less

Dynamics of the Triple-Star System Alpha Centauri and its Impact on Habitable Planets

NASA Astrophysics Data System (ADS)

Jayla Jones, Ayanna; Fabrycky, Daniel

2018-01-01

The Alpha Centauri system, our solar system's closest neighbor, has become a target in the search for habitable planets. The system is composed of three stars: Alpha Centauri A and Alpha Centauri B, stars forming an inner binary, and Proxima Centauri, an outer star that orbits around the inner binary. We computed 3-body models to follow the dynamics for the main-sequence lifetimes of the stars that are based on 100 realizations of the observed orbits. In the majority of cases, Proxima only modestly torques the A-B binary orbit, and so previous studies of planet formation and dynamics, which find the habitable zones to be stable, are somewhat justified in ignoring this effect. On the other hand, in ~16% of the observationally allowed orbits, fluctuations in the orbital eccentricity of the A-B orbit destabilize the middle of the habitable zone of both stars. This result calls for further theoretical work to quantify the effect of galactic tides, passing stars, and massive planets in the triple-system dynamics.

Implications of the IRAS data for galactic gamma ray astronomy and EGRET

NASA Technical Reports Server (NTRS)

Stecker, Floyd W.

1990-01-01

Using the results of gamma-ray, millimeter wave and far surveys of the galaxy, logically consistent picture of the large scale distribution of galactic gas and cosmic rays was derived, tied to the overall processes of stellar birth and destruction on a galactic scale. Using the results of the IRAS far-infrared survey of te galaxy, the large scale radial distributions of galactic far-infrared emission independently was obtained for both the Northern and Southern Hemisphere sides of the Galaxy. The dominant feature in these distributions was found to be a broad peak coincident with the 5 kpc molecular gas cloud ring. Evidence was found for spiral arm features. Strong correlations are evident between the large scale galactic distributions of far-infrared emission, gamma-ray emission and total CO emission. There is particularly tight correlation between the distribution of warm molecular clouds and far-infrared emission on a galactic scale. The 5 kpc ring was evident in existing galactic gamma-ray data. The extent to which the more detailed spiral arm features are evident in the more resolved EGRET (Energetic Gamma-Ray Experimental Telescope) data will help to determine more precisely the propagation characteristics of cosmic rays.

GSFC Contributions to the NATO X-ray Astronomy Institute, Erice, July 1979. [X-ray spectra of supernova remants, galactic X-ray sources, active galactic nuclei, and clusters of galaxies

NASA Technical Reports Server (NTRS)

Holt, S. S.; Mushotzky, R. F.

1979-01-01

An overview of X-ray astronomical spectroscopy in general is presented and results obtained by HEAO 1 and 2 as well as earlier spacecraft are examined. Particular emphasis is given to the spectra of supernova remnants; galactic binary X-ray sources, cataclysmic variables, bulges, pulsars, and stars; the active nuclei of Seyfert 1 galaxy, BL Lac, and quasars; the diffuse X-ray background; and galactic clusters.

Infrared Space Astrometry missions: JASMINE

NASA Astrophysics Data System (ADS)

Gouda, Naoteru

2015-08-01

JASMINE is an abbreviation for Japan Astrometry Satellite Mission for INfrared Exploration. We are now focusing on the development of two projects, those are Nano-JASMINE and Small-JASMINE. The Nano-JASMINE micro-satellite project, with a primary mirror aperture of 5-cm class, is currently underway to test part of the technologies used for Small-JASMINE and to produce scientific results based on the astrometric information of bright objects in the neighboring space. Despite its small aperture, the satellite is capable of a level of observational precision comparable to the Hipparcos satellite, and the combination of the observational data from Nano-JASMINE and the Hipparcos Catalogue is expected to produce more precise data on proper motions and annual parallaxes. The satellite is scheduled for launch in the near future. An additional plan is underway to launch a small-scale JASMINE satellite (Small-JASMINE), with a primary mirror aperture of 30-cm class, in around FY 2021. This satellite will engage in observations of only a limited area around the bulge and certain specific astronomical objects.. The main scientific objective of Small-JASMINE is to clarify the dynamical structure of the Galactic nuclear bulge and search for observational relics of a sequential merger of multiple black holes to form the supermassive black hole at the Galactic center. In particular, our main goal is that Small-JASMINE will provide an understanding of the past evolution processes of the supermassive black hole and a prediction of the future activities of our Galactic center through knowledge of the gravitational potential in the Galactic nuclear bulge, and that this understanding can contribute to a better understanding of the co-evolution of the supermassive black holes and bulges in external galaxies. Next to this primary goal, Small-JASMINE will have many other scientific targets. Small-JASMINE can measure the same target every 100 minutes, so it is useful to resolve phenomena with short periods such as X-ray binaries, extrasolar planetary systems and gravitational lens effects. For example, the orbital elements of the star accompanying Cygnus X-1 can be resolved by Small-JASMINE.

Giant Molecular Clouds with High Abundance of Atomic Carbon and Cyano Radical in the Milky Way's Central Molecular Zone

NASA Astrophysics Data System (ADS)

Tanaka, Kunihiko; Oka, Tomoharu; Nagai, Makoto; Kamegai, Kazuhisa

2015-08-01

The central 400 pc region of the Milky Way Galaxy is the closest galactic central region to us, providing a unique opportunity to detailedly investigate gas dynamics, star formation activity, and chemistry under the extreme environment of galactic centers, where the presence of bar, intense UV/cosmic-ray fluxes, high degree of turbulence may significantly affect those processes. We report the results of molecular line surveys toward the Milky Way's central molecular zone (CMZ) performed with the ASTE 10m telescope, the Mopra 22m telescope, and the Nobeyama 45 m telescope. With the observations of the 500 GHz [CI] fine structure line of atomic carbon (C0), we have found a molecular cloud structure with remarkably bright [CI] emission in the Sgr A comlex in the innermost 20 pc region. The [CI] cloud is more extended than the GMCs in the region, and appears to connect the northern part of the 50 kms-1 (M-0.02-0.07) and the circumnuclear disk (CND), though no corresponding structures are visible in other molecular lines. The [C0]/[CO] abundance ratio is measured to be 0.5-2, which is 2-10 times those measured to the clouds at larger Galactic radii. This high ratio is close to the values measured toward centers of galaxies with starburst and AGN, suggesting that the chemical state of the cloud is similar to that in those active galaxies. We have also found a large scale gradient of the cyano radical (CN) abundance toward the Galactic center in the innermost 100 pc radius, showing near the Sgr A complex. We suggest that the cloud with high C0 and CN abundance is a feature formed as a result of inward transfer of diffuse molecular gas by the bar potential in the inner Galaxy, in which PDR-like chemical composition remains preserved, and that thus the [CI] cloud could be deeply related to formation of the GMCs and star formation in the CMZ. We also discuss other possible mechanisms to enhance C0 and CN abundances, including the enhanced cosmic-ray dissociation ratio.

UNCOVERING THE NUCLEUS CANDIDATE FOR NGC 253

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

Günthardt, G. I.; Camperi, J. A.; Agüero, M. P.

2015-11-15

NGC 253 is the nearest spiral galaxy with a nuclear starburst that becomes the best candidate for studying the relationship between starburst and active galactic nucleus activity. However, this central region is veiled by large amounts of dust, and it has been so far unclear which is the true dynamical nucleus to the point that there is no strong evidence that the galaxy harbors a supermassive black hole co-evolving with the starburst as was supposed earlier. Near-infrared (NIR) spectroscopy, especially NIR emission line analysis, could be advantageous in shedding light on the true nucleus identity. Using Flamingos-2 at Gemini Southmore » we have taken deep K-band spectra along the major axis of the central structure and through the brightest infrared source. In this work, we present evidence showing that the brightest NIR and mid-infrared source in the central region, already known as radio source TH7 and so far considered just a large stellar supercluster, in fact presents various symptoms of a genuine galactic nucleus. Therefore, it should be considered a valid nucleus candidate. Mentioning some distinctive aspects, it is the most massive compact infrared object in the central region, located at 2.″0 of the symmetry center of the galactic bar, as measured in the K-band emission. Moreover, our data indicate that this object is surrounded by a large circumnuclear stellar disk and it is also located at the rotation center of the large molecular gas disk of NGC 253. Furthermore, a kinematic residual appears in the H{sub 2} rotation curve with a sinusoidal shape consistent with an outflow centered in the candidate nucleus position. The maximum outflow velocity is located about 14 pc from TH7, which is consistent with the radius of a shell detected around the nucleus candidate, observed at 18.3 μm (Qa) and 12.8 μm ([Ne ii]) with T-ReCS. Also, the Brγ emission line profile shows a pronounced blueshift and this emission line also has the highest equivalent width at this position. All this evidence points to TH7 as the best candidate for the galactic nucleus of NGC 253.« less

DISCOVERY OF CANDIDATE H{sub 2}O DISK MASERS IN ACTIVE GALACTIC NUCLEI AND ESTIMATIONS OF CENTRIPETAL ACCELERATIONS

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

Greenhill, Lincoln J.; Moran, James M.; Tilak, Avanti

2009-12-10

Based on spectroscopic signatures, about one-third of known H{sub 2}O maser sources in active galactic nuclei (AGNs) are believed to arise in highly inclined accretion disks around central engines. These 'disk maser candidates' are of interest primarily because angular structure and rotation curves can be resolved with interferometers, enabling dynamical study. We identify five new disk maser candidates in studies with the Green Bank Telescope, bringing the total number published to 30. We discovered two (NGC 1320, NGC 17) in a survey of 40 inclined active galaxies (v {sub sys} < 20, 000 km s{sup -1}). The remaining three diskmore » maser candidates were identified in monitoring of known sources: NGC 449, NGC 2979, and NGC 3735. We also confirm a previously marginal case in UGC 4203. For the disk maser candidates reported here, inferred rotation speeds are 130-500 km s{sup -1}. Monitoring of three more rapidly rotating candidate disks (CG 211, NGC 6264, VV 340A) has enabled measurement of likely orbital centripetal acceleration, and estimation of central masses ((2-7) x10{sup 7} M {sub sun}) and mean disk radii (0.2-0.4 pc). Accelerations may ultimately permit estimation of distances when combined with interferometer data. This is notable because the three AGNs are relatively distant (10,000 km s{sup -1}

New constraints on all flavor Galactic diffuse neutrino emission with the ANTARES telescope

NASA Astrophysics Data System (ADS)

Albert, A.; André, M.; Anghinolfi, M.; Anton, G.; Ardid, M.; Aubert, J.-J.; Avgitas, T.; Baret, B.; Barrios-Martí, J.; Basa, S.; Belhorma, B.; Bertin, V.; Biagi, S.; Bormuth, R.; Bourret, S.; Bouwhuis, M. C.; Bruijn, R.; Brunner, J.; Busto, J.; Capone, A.; Caramete, L.; Carr, J.; Celli, S.; Cherkaoui El Moursli, R.; Chiarusi, T.; Circella, M.; Coelho, J. A. B.; Coleiro, A.; Coniglione, R.; Costantini, H.; Coyle, P.; Creusot, A.; Díaz, A. F.; Deschamps, A.; de Bonis, G.; Distefano, C.; di Palma, I.; Domi, A.; Donzaud, C.; Dornic, D.; Drouhin, D.; Eberl, T.; El Bojaddaini, I.; El Khayati, N.; Elsässer, D.; Enzenhöfer, A.; Ettahiri, A.; Fassi, F.; Felis, I.; Fusco, L. A.; Galatà, S.; Gay, P.; Giordano, V.; Glotin, H.; Grégoire, T.; Gracia Ruiz, R.; Graf, K.; Hallmann, S.; van Haren, H.; Heijboer, A. J.; Hello, Y.; Hernández-Rey, J. J.; Hößl, J.; Hofestädt, J.; Hugon, C.; Illuminati, G.; James, C. W.; de Jong, M.; Jongen, M.; Kadler, M.; Kalekin, O.; Katz, U.; Kießling, D.; Kouchner, A.; Kreter, M.; Kreykenbohm, I.; Kulikovskiy, V.; Lachaud, C.; Lahmann, R.; Lefèvre, D.; Leonora, E.; Lotze, M.; Loucatos, S.; Marcelin, M.; Margiotta, A.; Marinelli, A.; Martínez-Mora, J. A.; Mele, R.; Melis, K.; Michael, T.; Migliozzi, P.; Moussa, A.; Navas, S.; Nezri, E.; Organokov, M.; Pǎvǎlaş, G. E.; Pellegrino, C.; Perrina, C.; Piattelli, P.; Popa, V.; Pradier, T.; Quinn, L.; Racca, C.; Riccobene, G.; Sánchez-Losa, A.; Saldaña, M.; Salvadori, I.; Samtleben, D. F. E.; Sanguineti, M.; Sapienza, P.; Schüssler, F.; Sieger, C.; Spurio, M.; Stolarczyk, Th.; Taiuti, M.; Tayalati, Y.; Trovato, A.; Turpin, D.; Tönnis, C.; Vallage, B.; van Elewyck, V.; Versari, F.; Vivolo, D.; Vizzoca, A.; Wilms, J.; Zornoza, J. D.; Zúñiga, J.; Gaggero, D.; Grasso, D.; ANTARES Collaboration

2017-09-01

The flux of very high-energy neutrinos produced in our Galaxy by the interaction of accelerated cosmic rays with the interstellar medium is not yet determined. The characterization of this flux will shed light on Galactic accelerator features, gas distribution morphology and Galactic cosmic ray transport. The central Galactic plane can be the site of an enhanced neutrino production, thus leading to anisotropies in the extraterrestrial neutrino signal as measured by the IceCube Collaboration. The ANTARES neutrino telescope, located in the Mediterranean Sea, offers a favorable view of this part of the sky, thereby allowing for a contribution to the determination of this flux. The expected diffuse Galactic neutrino emission can be obtained, linking a model of generation and propagation of cosmic rays with the morphology of the gas distribution in the Milky Way. In this paper, the so-called "gamma model" introduced recently to explain the high-energy gamma-ray diffuse Galactic emission is assumed as reference. The neutrino flux predicted by the "gamma model" depends on the assumed primary cosmic ray spectrum cutoff. Considering a radially dependent diffusion coefficient, this proposed scenario is able to account for the local cosmic ray measurements, as well as for the Galactic gamma-ray observations. Nine years of ANTARES data are used in this work to search for a possible Galactic contribution according to this scenario. All flavor neutrino interactions are considered. No excess of events is observed, and an upper limit is set on the neutrino flux of 1.1 (1.2) times the prediction of the "gamma model," assuming the primary cosmic ray spectrum cutoff at 5 (50) PeV. This limit excludes the diffuse Galactic neutrino emission as the major cause of the "spectral anomaly" between the two hemispheres measured by IceCube.

BATSE Observations of the Large-Scale Isotropy of Gamma-Ray Bursts

NASA Technical Reports Server (NTRS)

Briggs, Michael S.; Paciesas, William S.; Pendleton, Geoffrey N.; Meegan, Charles A.; Fishman, Gerald J.; Horack, John M.; Brock, Martin N.; Kouveliotou, Chryssa; Hartmann, Dieter H.; Hakkila, Jon

1996-01-01

We use dipole and quadrupole statistics to test the large-scale isotropy of the first 1005 gamma-ray bursts observed by the Burst and Transient Source Experiment (BATSE). In addition to the entire sample of 1005 gamma-ray bursts, many subsets are examined. We use a variety of dipole and quadrupole statistics to search for Galactic and other predicted anisotropies and for anisotropies in a coordinate-system independent manner. We find the gamma-ray burst locations to be consistent with isotropy, e.g., for the total sample the observed Galactic dipole moment (cos theta) differs from the value predicted for isotropy by 0.9 sigma and the observed Galactic quadrupole moment (sin(exp 2) b - 1/3) by 0.3 sigma. We estimate for various models the anisotropies that could have been detected. If one-half of the locations were within 86 deg of the Galactic center, or within 28 deg of the Galactic plane, the ensuing dipole or quadrupole moment would have typically been detected at the 99% confidence level. We compare the observations with the dipole and quadrupole moments of various Galactic models. Several Galactic gamma-ray bursts models have moments within 2 sigma of the observations; most of the Galactic models proposed to date are no longer in acceptable agreement with the data. Although a spherical dark matter halo distribution could be consistent with the data, the required core radius is larger than the core radius of the dark matter halo used to explain the Galaxy's rotation curve. Gamma-ray bursts are much more isotropic than any observed Galactic population, strongly favoring but not requiring an origin at cosmological distances.

Star Formation History In Merging Galaxies

NASA Astrophysics Data System (ADS)

Chien, Li-Hsin

2009-01-01

Interacting and merging galaxies are believed to play an important role in many aspects of galactic evolution. Their violent interactions can trigger starbursts, which lead to formation of young globular clusters. Therefore the ages of these young globular clusters can be interpreted to yield the timing of interaction-triggered events, and thus provide a key to reconstruct the star formation history in merging galaxies. The link between galaxy interaction and star formation is well established, but the triggers of star formation in interacting galaxies are still not understood. To date there are two competing formulas that describe the star formation mechanism--density-dependent and shock-induced rules. Numerical models implementing the two rules predict significantly different star formation histories in merging galaxies. My dissertation combines these two distinct areas of astrophysics, stellar evolution and galactic dynamics, to investigate the star formation history in galaxies at various merging stages. Begin with NGC 4676 as an example, I will briefly describe its model and illustrate the idea of using the ages of clusters to constrain the modeling. The ages of the clusters are derived from spectra that were taken with multi-object spectroscopy on Keck. Using NGC 7252 as a second example, I will present a state of the art dynamical model which predicts NGC7252's star formation history and other properties. I will then show a detailed comparison and analysis between the clusters and the modeling. In the end, I will address this important link as the key to answer the fundamental question of my thesis: what is the trigger of star formation in merging galaxies?

Relativistic dynamics and extreme mass ratio inspirals

NASA Astrophysics Data System (ADS)

Amaro-Seoane, Pau

2018-05-01

It is now well-established that a dark, compact object, very likely a massive black hole (MBH) of around four million solar masses is lurking at the centre of the Milky Way. While a consensus is emerging about the origin and growth of supermassive black holes (with masses larger than a billion solar masses), MBHs with smaller masses, such as the one in our galactic centre, remain understudied and enigmatic. The key to understanding these holes—how some of them grow by orders of magnitude in mass—lies in understanding the dynamics of the stars in the galactic neighbourhood. Stars interact with the central MBH primarily through their gradual inspiral due to the emission of gravitational radiation. Also stars produce gases which will subsequently be accreted by the MBH through collisions and disruptions brought about by the strong central tidal field. Such processes can contribute significantly to the mass of the MBH and progress in understanding them requires theoretical work in preparation for future gravitational radiation millihertz missions and X-ray observatories. In particular, a unique probe of these regions is the gravitational radiation that is emitted by some compact stars very close to the black holes and which could be surveyed by a millihertz gravitational-wave interferometer scrutinizing the range of masses fundamental to understanding the origin and growth of supermassive black holes. By extracting the information carried by the gravitational radiation, we can determine the mass and spin of the central MBH with unprecedented precision and we can determine how the holes "eat" stars that happen to be near them.

A Multi-Faceted Study of Three Forms of Galactic Formation in the Early Universe

NASA Astrophysics Data System (ADS)

Jones, Gareth Christopher

While observations of the early universe have focused on bright, highly starbursting galaxies, star formation activity in the early universe was dominated by main sequence galaxies. Observations of the former group have been accumulating for decades, but the latter are only recently observable using modern instruments. In this work, we apply the Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) to observe specific examples of each galactic class, in order to explore three modes of galaxy formation: smooth accretion, satellite accretion, and massive mergers. Using the molecular gas tracer CO and a broad set of continuum measurements, we characterize the gas mass and distribution, star formation, and dust temperature of the two archetypal massively merging Hyper-Luminous IR Galaxies (HyLIRGs) BRI1202-0725 & BRI1335-0417. We then examine the [C II] emission of the Lyman-Break Galaxy (LBG) WMH5, which shows two infalling gas clouds, implying ongoing formation via filamentary accretion. Finally, we apply a classical suite of dynamical characterization tools to [C II] observations of three MS galaxies and three starbursts, resulting in rotation curves and dynamical masses for each. By examining each of these sources in detail, we find that galaxies in the early (i.e., z > 4) universe formed via a broad range of interactions, ranging from cold-mode accretion to major mergers. As these instruments continue observing, and with the future advent of JWST and perhaps the ngVLA, stronger constraints may be placed on the behavior of the galaxies in the epoch of initial galaxy formation.

On Estimating the Mass of Keplerian Accretion Disks in H2O Maser Galaxies

NASA Astrophysics Data System (ADS)

Kuo, C. Y.; Reid, M. J.; Braatz, J. A.; Gao, F.; Impellizzeri, C. M. V.; Chien, W. T.

2018-06-01

H2O maser disks with Keplerian rotation in active galactic nuclei offer a clean way to determine accurate black hole mass and the Hubble constant. An important assumption made in using a Keplerian H2O maser disk for measuring black hole mass and the Hubble constant is that the disk mass is negligible compared to the black hole mass. A simple and useful model of Huré et al. can be used to test this assumption. In that work, the authors apply a linear disk model to a position–dynamical mass diagram and re-analyze position–velocity data from H2O maser disks associated with active galactic nuclei. They claim that a maser disk with nearly perfect Keplerian rotation could have a disk mass comparable to the black hole mass. This would imply that ignoring the effects of disk self-gravity can lead to large systematic errors in the measurement of black hole mass and the Hubble constant. We examine their methods and find that their large estimated disk masses of Keplerian disks are likely the result of their use of projected instead of three-dimensional position and velocity information. To place better constraints on the disk masses of Keplerian maser systems, we incorporate disk self-gravity into a three-dimensional Bayesian modeling program for maser disks and also evaluate constraints based on the physical conditions for disks that support water maser emission. We find that there is little evidence that disk masses are dynamically important at the ≲1% level compared to the black holes.

A Nonthermal Radio Filament Connected to the Galactic Black Hole?

NASA Astrophysics Data System (ADS)

Morris, Mark R.; Zhao, Jun-Hui; Goss, W. M.

2017-12-01

Using the Very Large Array, we have investigated a nonthermal radio filament (NTF) recently found very near the Galactic black hole and its radio counterpart, Sgr A*. While this NTF—the Sgr A West Filament (SgrAWF)—shares many characteristics with the population of NTFs occupying the central few hundred parsecs of the Galaxy, the SgrAWF has the distinction of having an orientation and sky location that suggest an intimate physical connection to Sgr A*. We present 3.3 and 5.5 cm images constructed using an innovative methodology that yields a very high dynamic range, providing an unprecedentedly clear picture of the SgrAWF. While the physical association of the SgrAWF with Sgr A* is not unambiguous, the images decidedly evoke this interesting possibility. Assuming that the SgrAWF bears a physical relationship to Sgr A*, we examine the potential implications. One is that Sgr A* is a source of relativistic particles constrained to diffuse along ordered local field lines. The relativistic particles could also be fed into the local field by a collimated outflow from Sgr A*, perhaps driven by the Poynting flux accompanying the black hole spin in the presence of a magnetic field threading the event horizon. Second, we consider the possibility that the SgrAWF is the manifestation of a low-mass-density cosmic string that has become anchored to the black hole. The simplest form of these hypotheses would predict that the filament be bi-directional, whereas the SgrAWF is only seen on one side of Sgr A*, perhaps because of the dynamics of the local medium.

Supernova kicks and dynamics of compact remnants in the Galactic Centre

NASA Astrophysics Data System (ADS)

Bortolas, Elisa; Mapelli, Michela; Spera, Mario

2017-08-01

The Galactic Centre (GC) is a unique place to study the extreme dynamical processes occurring near a supermassive black hole (SMBH). Here, we investigate the role of supernova (SN) explosions occurring in massive binary systems lying in a disc-like structure within the innermost parsec. We use a regularized algorithm to simulate 3 × 104 isolated three-body systems composed of a stellar binary orbiting the SMBH. We start the integration when the primary member undergoes an SN explosion and analyse the impact of SN kicks on the orbits of stars and compact remnants. We find that SN explosions scatter the lighter stars in the pair on completely different orbits, with higher eccentricity and inclination. In contrast, stellar-mass black holes (BHs) and massive stars retain memory of the orbit of their progenitor star. Our results suggest that SN kicks are not sufficient to eject BHs from the GC. We thus predict that all BHs that form in situ in the central parsec of our Galaxy remain in the GC, building up a cluster of dark remnants. In addition, the change of neutron star (NS) orbits induced by SNe may partially account for the observed dearth of NSs in the GC. About 40 per cent of remnants stay bound to the stellar companion after the kick; we expect up to 70 per cent of them might become X-ray binaries through Roche lobe filling. Finally, the eccentricity of some light stars becomes >0.7 as an effect of the SN kick, producing orbits similar to those of the G1 and G2 dusty objects.

Self-consistent Bulge/Disk/Halo Galaxy Dynamical Modeling Using Integral Field Kinematics

NASA Astrophysics Data System (ADS)

Taranu, D. S.; Obreschkow, D.; Dubinski, J. J.; Fogarty, L. M. R.; van de Sande, J.; Catinella, B.; Cortese, L.; Moffett, A.; Robotham, A. S. G.; Allen, J. T.; Bland-Hawthorn, J.; Bryant, J. J.; Colless, M.; Croom, S. M.; D'Eugenio, F.; Davies, R. L.; Drinkwater, M. J.; Driver, S. P.; Goodwin, M.; Konstantopoulos, I. S.; Lawrence, J. S.; López-Sánchez, Á. R.; Lorente, N. P. F.; Medling, A. M.; Mould, J. R.; Owers, M. S.; Power, C.; Richards, S. N.; Tonini, C.

2017-11-01

We introduce a method for modeling disk galaxies designed to take full advantage of data from integral field spectroscopy (IFS). The method fits equilibrium models to simultaneously reproduce the surface brightness, rotation, and velocity dispersion profiles of a galaxy. The models are fully self-consistent 6D distribution functions for a galaxy with a Sérsic profile stellar bulge, exponential disk, and parametric dark-matter halo, generated by an updated version of GalactICS. By creating realistic flux-weighted maps of the kinematic moments (flux, mean velocity, and dispersion), we simultaneously fit photometric and spectroscopic data using both maximum-likelihood and Bayesian (MCMC) techniques. We apply the method to a GAMA spiral galaxy (G79635) with kinematics from the SAMI Galaxy Survey and deep g- and r-band photometry from the VST-KiDS survey, comparing parameter constraints with those from traditional 2D bulge-disk decomposition. Our method returns broadly consistent results for shared parameters while constraining the mass-to-light ratios of stellar components and reproducing the H I-inferred circular velocity well beyond the limits of the SAMI data. Although the method is tailored for fitting integral field kinematic data, it can use other dynamical constraints like central fiber dispersions and H I circular velocities, and is well-suited for modeling galaxies with a combination of deep imaging and H I and/or optical spectra (resolved or otherwise). Our implementation (MagRite) is computationally efficient and can generate well-resolved models and kinematic maps in under a minute on modern processors.

Relativistic dynamics and extreme mass ratio inspirals.

PubMed

Amaro-Seoane, Pau

2018-01-01

It is now well-established that a dark, compact object, very likely a massive black hole (MBH) of around four million solar masses is lurking at the centre of the Milky Way. While a consensus is emerging about the origin and growth of supermassive black holes (with masses larger than a billion solar masses), MBHs with smaller masses, such as the one in our galactic centre, remain understudied and enigmatic. The key to understanding these holes-how some of them grow by orders of magnitude in mass-lies in understanding the dynamics of the stars in the galactic neighbourhood. Stars interact with the central MBH primarily through their gradual inspiral due to the emission of gravitational radiation. Also stars produce gases which will subsequently be accreted by the MBH through collisions and disruptions brought about by the strong central tidal field. Such processes can contribute significantly to the mass of the MBH and progress in understanding them requires theoretical work in preparation for future gravitational radiation millihertz missions and X-ray observatories. In particular, a unique probe of these regions is the gravitational radiation that is emitted by some compact stars very close to the black holes and which could be surveyed by a millihertz gravitational-wave interferometer scrutinizing the range of masses fundamental to understanding the origin and growth of supermassive black holes. By extracting the information carried by the gravitational radiation, we can determine the mass and spin of the central MBH with unprecedented precision and we can determine how the holes "eat" stars that happen to be near them.

Starburst Galaxies. III. Properties of a Radio-selected Sample

NASA Astrophysics Data System (ADS)

Smith, Denise A.; Herter, Terry; Haynes, Martha P.

1998-02-01

We have analyzed the properties of the 20 most radio-luminous UGC starburst galaxies from Condon, Frayer, & Broderick. Near-infrared images, spectra, and optical rotation curves were presented in Smith et al. In this paper, we use these data and published radio data to assess the stellar populations, dust contents, ionizing conditions, and dynamics of the starbursts. Certain properties of the star formation occurring in these galaxies differ from those observed locally. The infrared excesses (IREs) are lower than and span a narrower range of values than those of Galactic H II regions. The starbursts appear to produce a higher proportion of ionizing photons than most Galactic H II regions. Consequently, the initial mass functions (IMFs) of the starbursts may be more strongly biased toward high-mass star formation. The starbursts may also contain fewer old H II regions than the Milky Way. Furthermore, the starburst IRE is likely to be influenced by the presence of large reservoirs of gas that absorb a larger fraction of the Lyman continuum photons. The OB stellar and far-infrared luminosities imply that the upper mass range of the starburst IMF (M > 10 M⊙) is characterized by a slope of 2.7 +/- 0.2. The starburst IMF thus bears a strong similarity to that observed in Magellanic OB associations. Optical line ratios indicate that a range of excitation conditions are present. We conclude that the near-infrared light from many of the starbursts is dominated by a heavily obscured mixture of emission from evolved red stars and young blue stars with small contributions (~5%) from thermal gas and hot dust, under the assumptions that a Galactic or SMC extinction law can be applied to these systems and that the true reddening curve follows one of the models currently existing in the literature. In some cases, larger amounts of emission from blue stars or hot dust may be required to explain the observed near-infrared colors. The amount of dust emission exceeds that predicted from comparisons with Galactic H II regions. The near-infrared colors of some of the systems may also be influenced by the presence of a low-luminosity active galactic nucleus (AGN). Emission from blue stars and hot dust, if present, dilutes the observed CO index. The activity in the redder, more luminous systems is strongly peaked. The galaxies hosting the starbursts exhibit a wide range of morphological and star-forming properties. While all of the host galaxies are interacting systems, the nuclear separations of the interacting nuclei range from <1 kpc to >1 Mpc. The dynamical behavior ranges from relaxed to strongly perturbed. The off-nuclear regions of the galaxies are sites of active star formation and are characterized by a range of excitation conditions. Spatially extended LINER emission is consistent with shock excitation produced by superwinds or galaxy-galaxy collisions. Violent star formation activity occurs over a larger physical scale in the most active starbursts. Systems containing mergers and widely separated nuclei possess similar colors and luminosities. The burst properties are most likely regulated by the internal structures of the interacting galaxies and not the separations of the interacting galaxies. Observations at the Palomar Observatory were made as part of a continuing collaborative agreement between the California Institute of Technology and Cornell University.

Hi-GAL, the Herschel infrared Galactic Plane Survey: photometric maps and compact source catalogues. First data release for the inner Milky Way: +68° ≥ l ≥ -70°

NASA Astrophysics Data System (ADS)

Molinari, S.; Schisano, E.; Elia, D.; Pestalozzi, M.; Traficante, A.; Pezzuto, S.; Swinyard, B. M.; Noriega-Crespo, A.; Bally, J.; Moore, T. J. T.; Plume, R.; Zavagno, A.; di Giorgio, A. M.; Liu, S. J.; Pilbratt, G. L.; Mottram, J. C.; Russeil, D.; Piazzo, L.; Veneziani, M.; Benedettini, M.; Calzoletti, L.; Faustini, F.; Natoli, P.; Piacentini, F.; Merello, M.; Palmese, A.; Del Grande, R.; Polychroni, D.; Rygl, K. L. J.; Polenta, G.; Barlow, M. J.; Bernard, J.-P.; Martin, P. G.; Testi, L.; Ali, B.; André, P.; Beltrán, M. T.; Billot, N.; Carey, S.; Cesaroni, R.; Compiègne, M.; Eden, D.; Fukui, Y.; Garcia-Lario, P.; Hoare, M. G.; Huang, M.; Joncas, G.; Lim, T. L.; Lord, S. D.; Martinavarro-Armengol, S.; Motte, F.; Paladini, R.; Paradis, D.; Peretto, N.; Robitaille, T.; Schilke, P.; Schneider, N.; Schulz, B.; Sibthorpe, B.; Strafella, F.; Thompson, M. A.; Umana, G.; Ward-Thompson, D.; Wyrowski, F.

2016-07-01

Aims: We present the first public release of high-quality data products (DR1) from Hi-GAL, the Herschel infrared Galactic Plane Survey. Hi-GAL is the keystone of a suite of continuum Galactic plane surveys from the near-IR to the radio and covers five wavebands at 70, 160, 250, 350 and 500 μm, encompassing the peak of the spectral energy distribution of cold dust for 8 ≲ T ≲ 50 K. This first Hi-GAL data release covers the inner Milky Way in the longitude range 68° ≳ ℓ ≳ -70° in a | b | ≤ 1° latitude strip. Methods: Photometric maps have been produced with the ROMAGAL pipeline, which optimally capitalizes on the excellent sensitivity and stability of the bolometer arrays of the Herschel PACS and SPIRE photometric cameras. It delivers images of exquisite quality and dynamical range, absolutely calibrated with Planck and IRAS, and recovers extended emission at all wavelengths and all spatial scales, from the point-spread function to the size of an entire 2°× 2° "tile" that is the unit observing block of the survey. The compact source catalogues were generated with the CuTEx algorithm, which was specifically developed to optimise source detection and extraction in the extreme conditions of intense and spatially varying background that are found in the Galactic plane in the thermal infrared. Results: Hi-GAL DR1 images are cirrus noise limited and reach the 1σ-rms predicted by the Herschel Time Estimators for parallel-mode observations at 60'' s-1 scanning speed in relatively low cirrus emission regions. Hi-GAL DR1 images will be accessible through a dedicated web-based image cutout service. The DR1 Compact Source Catalogues are delivered as single-band photometric lists containing, in addition to source position, peak, and integrated flux and source sizes, a variety of parameters useful to assess the quality and reliability of the extracted sources. Caveats and hints to help in this assessment are provided. Flux completeness limits in all bands are determined from extensive synthetic source experiments and greatly depend on the specific line of sight along the Galactic plane because the background strongly varies as a function of Galactic longitude. Hi-GAL DR1 catalogues contain 123210, 308509, 280685, 160972, and 85460 compact sources in the five bands. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.The images and the catalogues 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/591/A149

Implications of the IRAS data for galactic gamma-ray astronomy and EGRET

NASA Technical Reports Server (NTRS)

Stecker, F. W.

1990-01-01

Using the results of gamma-ray, millimeter wave and far infrared surveys of the galaxy, one can derive a logically consistent picture of the large scale distribution of galactic gas and cosmic rays, one tied to the overall processes of stellar birth and destruction on a galactic scale. Using the results of the IRAS far-infrared survey of the galaxy, the large scale radial distribution of galactic far-infrared emission were obtained independently for both the Northern and Southern Hemisphere sides of the Galaxy. It was found that the dominant feature in these distributions to be a broad peak coincident with the 5 kpc molecular gas cloud ring. Also found was evidence of spiral arm features. Strong correlations are evident between the large scale galactic distributions of far infrared emission, gamma-ray emission and total CO emission. There is a particularly tight correlation between the distribution of warm molecular clouds and far-infrared emission on a galactic scale.

The Optical Gravitational Lensing Experiment Catalog of stellar proper motions in the OGLE-II Galactic bulge fields

NASA Astrophysics Data System (ADS)

Sumi, T.; Wu, X.; Udalski, A.; Szymański, M.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Woźniak, P.; Zebruń, K.; Szewczyk, O.; Wyrzykowski, L.

2003-12-01

We present proper motion (μ ) catalogue of 5,078,188 stars in 49 Optical Gravitational Lensing Experiment II (OGLE-II) Galactic bulge fields, with the total area close to 11 square degrees. The proper motion measurements are based on 138 - 555 I-band images taken during four observing seasons: 1997-2000. The catalogue stars are in the magnitude range 11 < I < 18 mag. In particular, the catalogue includes Red Clump Giants (RCGs) and Red Giants in the Galactic Bulge, and main sequence stars in the Galactic disc. The proper motions up to μ = 500 mas yr -1 were measured with the mean accuracy of 0.8 ˜ 3.5 mas yr-1, depending on the brightness of a star. This catalogue may be useful for studying the kinematic of stars in the Galactic Bulge and the Galactic disk with Extinction maps in these fields which are construncted by using two-band photometry of RCGs.

ILLUMINATING BLACK HOLE BINARY FORMATION CHANNELS WITH SPINS IN ADVANCED LIGO

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

Rodriguez, Carl L.; Zevin, Michael; Pankow, Chris

The recent detections of the binary black hole mergers GW150914 and GW151226 have inaugurated the field of gravitational-wave astronomy. For the two main formation channels that have been proposed for these sources, isolated binary evolution in galactic fields and dynamical formation in dense star clusters, the predicted masses and merger rates overlap significantly, complicating any astrophysical claims that rely on measured masses alone. Here, we examine the distribution of spin–orbit misalignments expected for binaries from the field and from dense star clusters. Under standard assumptions for black hole natal kicks, we find that black hole binaries similar to GW150914 couldmore » be formed with significant spin–orbit misalignment only through dynamical processes. In particular, these heavy-black hole binaries can only form with a significant spin–orbit anti -alignment in the dynamical channel. Our results suggest that future detections of merging black hole binaries with measurable spins will allow us to identify the main formation channel for these systems.« less

Nonlinear Dynamics, Artificial Cognition and Galactic Export

NASA Astrophysics Data System (ADS)

Rössler, Otto E.

2004-08-01

The field of nonlinear dynamics focuses on function rather than structure. Evolution and brain function are examples. An equation for a brain, described in 1973, is explained. Then, a principle of interactional function change between two coupled equations of this type is described. However, all of this is not done in an abstract manner but in close contact with the meaning of these equations in a biological context. Ethological motivation theory and Batesonian interaction theory are reencountered. So is a fairly unknown finding by van Hooff on the indistinguishability of smile and laughter in a single primate species. Personhood and evil, two human characteristics, are described abstractly. Therapies and the question of whether it is ethically allowed to export benevolence are discussed. The whole dynamic approach is couched in terms of the Cartesian narrative, invented in the 17th century and later called Enlightenment. Whether or not it is true that a "second Enlightenment" is around the corner is the main question raised in the present paper.

ARCADE 2 Observations of Galactic Radio Emission

NASA Technical Reports Server (NTRS)

Kogut, A.; Fixsen, D. J.; Levin, S. M.; Limon, M.; Lubin, P. M.; Mirel, P.; Seiffert, M.; Singal, J.; Villela, T.; Wollack, E.;

Badhwar-O'Neil 2007 Galactic Cosmic Ray (GCR) Model Using Advanced Composition Explorer (ACE) Measurements for Solar Cycle 23

NASA Technical Reports Server (NTRS)

ONeill, P. M.

2007-01-01

Advanced Composition Explorer (ACE) satellite measurements of the galactic cosmic ray flux and correlation with the Climax Neutron Monitor count over Solar Cycle 23 are used to update the Badhwar O'Neill Galactic Cosmic Ray (GCR) model.

Testing Galactic Cosmic Ray Models

NASA Technical Reports Server (NTRS)

Adams, James H., Jr.

2009-01-01

Models of the Galactic Cosmic Ray Environment are used for designing and planning space missions. The existing models will be reviewed. Spectral representations from these models will be compared with measurements of galactic cosmic ray spectra made on balloon flights and satellite flights over a period of more than 50 years.

Testing Galactic Cosmic Ray Models

NASA Technical Reports Server (NTRS)

Adams, James H., Jr.

2010-01-01

Models of the Galactic Cosmic Ray Environment are used for designing and planning space missions. The exising models will be reviewed. Spectral representations from these models will be compared with measurements of galactic cosmic ray spectra made on balloon flights and satellite flights over a period of more than 50 years.

Pondermotive acceleration of charged particles along the relativistic jets of an accreting blackhole

NASA Astrophysics Data System (ADS)

Ebisuzaki, T.; Tajima, T.

2014-05-01

Accreting blackholes such as miniquasars and active galactic nuclei can contribute to the highest energy components of intra- (˜1015 eV) galactic and extra-galactic components (˜1020 eV) of cosmic rays. Alfven wave pulses which are excited in the accretion disk around blackholes propagate in relativistic jets. Because of their highly non-linear nature of the waves, charged particles (protons, ions, and electrons) can be accelerated to high energies in relativistic jets in accreting blackhole systems, the central engine of miniquasars and active galactic nuclei.

Science Brought by JASMINE Data

NASA Astrophysics Data System (ADS)

Tsujimoto, T.

The planned astrometric space mission JASMINE will provide the exact positions, distances, and proper motions of the bulge stars. These data will certainly reveal the origin and evolution of the Galactic bulge. In fact, the formation process of the bulge is still veiled. It is generally believed that the Galactic bulge possesses a simple old population. On the other hand, the Galactic bulge has a bar with some kinematic implications for a secular evolution. Here we review some evidences for the recent star formation in the Galactic bulge, that will be verified by JASMINE.

Hubble Space Telescope Proper Motion (HSTPROMO) Catalogs of Galactic Globular Clusters. IV. Kinematic Profiles and Average Masses of Blue Straggler Stars

NASA Astrophysics Data System (ADS)

Baldwin, A. T.; Watkins, L. L.; van der Marel, R. P.; Bianchini, P.; Bellini, A.; Anderson, J.

2016-08-01

We make use of the Hubble Space Telescope proper-motion catalogs derived by Bellini et al. to produce the first radial velocity dispersion profiles σ (R) for blue straggler stars (BSSs) in Galactic globular clusters (GCs), as well as the first dynamical estimates for the average mass of the entire BSS population. We show that BSSs typically have lower velocity dispersions than stars with mass equal to the main-sequence turnoff mass, as one would expect for a more massive population of stars. Since GCs are expected to experience some degree of energy equipartition, we use the relation σ \\propto {M}-η , where η is related to the degree of energy equipartition, along with our velocity dispersion profiles to estimate BSS masses. We estimate η as a function of cluster relaxation from recent Monte Carlo cluster simulations by Bianchini et al. and then derive an average mass ratio {M}{BSS}/{M}{MSTO}=1.50+/- 0.14 and an average mass {M}{BSS}=1.22+/- 0.12 M ⊙ from 598 BSSs across 19 GCs. The final error bars include any systematic errors that are random between different clusters, but not any potential biases inherent to our methodology. Our results are in good agreement with the average mass of {M}{BSS}=1.22+/- 0.06 M ⊙ for the 35 BSSs in Galactic GCs in the literature with properties that have allowed individual mass determination. Based on proprietary and archival observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

Highlights of Commission 37 Science Results

NASA Astrophysics Data System (ADS)

Carraro, Giovanni; de Grijs, Richard; Elmegreen, Bruce; Stetson, Peter; Anthony-Twarog, Barbara; Goodwin, Simon; Geisler, Douglas; Minniti, Dante

2016-04-01

It is widely accepted that stars do not form in isolation but result from the fragmentation of molecular clouds, which in turn leads to star cluster formation. Over time, clusters dissolve or are destroyed by interactions with molecular clouds or tidal stripping, and their members become part of the general field population. Star clusters are thus among the basic building blocks of galaxies. In turn, star cluster populations, from young associations and open clusters to old globulars, are powerful tracers of the formation, assembly, and evolutionary history of their parent galaxies. Although their importance (e.g., in mapping out the Milky Way) had been recognised for decades, major progress in this area has only become possible in recent years, both for Galactic and extragalactic cluster populations. Star clusters are the observational foundation for stellar astrophysics and evolution, provide essential tracers of galactic structure, and are unique stellar dynamical environments. Star formation, stellar structure, stellar evolution, and stellar nucleosynthesis continue to benefit and improve tremendously from the study of these systems. Additionally, fundamental quantities such as the initial mass function can be successfully derived from modelling either the Hertzsprung-Russell diagrams or the integrated velocity structures of, respectively, resolved and unresolved clusters and cluster populations. Star cluster studies thus span the fields of Galactic and extragalactic astrophysics, while heavily affecting our detailed understanding of the process of star formation in dense environments. This report highlights science results of the last decade in the major fields covered by IAU Commission 37: Star clusters and associations. Instead of focusing on the business meeting - the out-going president presentation can be found here: http://www.sc.eso.org/gcarraro/splinter2015.pdf - this legacy report contains highlights of the most important scientific achievements in the Commission science area, compiled by 5 well expert members.

A JWST Study of the Starburst-AGN Connection in Merging LIRGs

NASA Astrophysics Data System (ADS)

Armus, Lee; Appleton, P.; Barcos-Munoz, L.; Charmandaris, V.; Diaz-Santos, T.; Evans, A.; Howell, J.; Inami, H.; Larson, K.; Linden, S.; Malkan, M.; Marshall, J.; Mazzarella, J.; Medling, A.; Murphy, E.; Privon, G.; Rich, J.; Sanders, D.; Stierwalt, S.; Surace, J.; U, V.

2017-11-01

Galaxies evolve through a combination of secular processes, such as cold gas accretion, and nonsecular processes, such as galactic mergers, which can trigger massive starbursts and powerful AGN. JWST will transform our understanding of galactic evolution, providing a detailed look at the physics of star formation and black hole growth in nearby and distant galaxies. By using NIRSPEC, NIRCAM and MIRI, we will create a rich dataset for understanding the dynamics and energetics of the ISM on scales of 50-100pc in the nuclei of local Luminous Infrared Galaxies (LIRGs). Our targets cover a range of starburst-to-AGN power and IR spectral properties, and are all visible to JWST over the first 5 months of Cycle-1. We will target each nucleus with the NIRSPEC and MIRI IFUs to cover the full spectral range from 0.96-29 microns, and obtain deep, wide-field NIRCAM and MIRI images in the F150W, F200W, F335M, F444W, F560W, F770W and F1500W filters. The total time for our proposal (NOI #80) is 30.97hrs. Our science-enabling products include multi-wavelength, ancillary datasets from Spitzer, ALMA, JVLA, AKARI and HST, valuable cross-calibration infrared data from Spitzer and AKARI, together with custom spectral fitting software which we will deliver and use to analyze the JWST spectral cubes. The proposed observations will be scientifically compelling in their own right, and they will also demonstrate to the community how to fully explore the power of JWST to unravel the complex galactic ecosystems in nearby active and starburst galaxies. This proposal will set the stage for more extensive studies of active and starburst galaxies at low and high-redshift in Cycle-2 and beyond.

The simulation of the outer Oort cloud formation. The first giga-year of the evolution

NASA Astrophysics Data System (ADS)

Dybczyński, P. A.; Leto, G.; Jakubík, M.; Paulech, T.; Neslušan, L.

2008-08-01

Aims: Considering a model of an initial disk of planetesimals that consists of 10 038 test particles, we simulate the formation of distant-comet reservoirs for the first 1 Gyr. Since only the outer part of the Oort cloud can be formed within this period, we analyse the efficiency of the formation process and describe approximately the structure of the part formed. Methods: The dynamical evolution of the particles is followed by numerical integration of their orbits. We consider the perturbations by four giant planets on their current orbits and with their current masses, in addition to perturbations by the Galactic tide and passing stars. Results: In our simulation, the population size of the outer Oort cloud reaches its maximum value at about 210 Myr. After a subsequent, rapid decrease, it becomes almost stable (with only a moderate decrease) from about 500 Myr. At 1 Gyr, the population size decreases to about 40% of its maximum value. The efficiency of the formation is low. Only about 0.3% of the particles studied still reside in the outer Oort cloud after 1 Gyr. The space density of particles in the comet cloud, beyond the heliocentric distance, r, of 25 000 AU is proportional to r-s, where s = 4.08 ± 0.34. From about 50 Myr to the end of the simulation, the orbits of the Oort cloud comets are not distributed randomly, but high galactic inclinations of the orbital planes are strongly dominant. Among all of the outer perturbers considered, this is most likely caused by the dominant, disk component of the Galactic tide. Movies (cf. caption to Fig. 1) are only available at http://www.aanda.org

Local stellar kinematics from RAVE data—VIII. Effects of the Galactic disc perturbations on stellar orbits of red clump stars

NASA Astrophysics Data System (ADS)

Önal Taş, Ö.; Bilir, S.; Plevne, O.

2018-02-01

We aim to probe the dynamic structure of the extended Solar neighborhood by calculating the radial metallicity gradients from orbit properties, which are obtained for axisymmetric and non-axisymmetric potential models, of red clump (RC) stars selected from the RAdial Velocity Experiment's Fourth Data Release. Distances are obtained by assuming a single absolute magnitude value in near-infrared, i.e. M_{Ks}=-1.54±0.04 mag, for each RC star. Stellar orbit parameters are calculated by using the potential functions: (i) for the MWPotential2014 potential, (ii) for the same potential with perturbation functions of the Galactic bar and transient spiral arms. The stellar age is calculated with a method based on Bayesian statistics. The radial metallicity gradients are evaluated based on the maximum vertical distance (z_{max}) from the Galactic plane and the planar eccentricity (ep) of RC stars for both of the potential models. The largest radial metallicity gradient in the 0< z_{max} ≤0.5 kpc distance interval is -0.065±0.005 dex kpc^{-1} for a subsample with ep≤0.1, while the lowest value is -0.014±0.006 dex kpc^{-1} for the subsample with ep≤0.5. We find that at z_{max}>1 kpc, the radial metallicity gradients have zero or positive values and they do not depend on ep subsamples. There is a large radial metallicity gradient for thin disc, but no radial gradient found for thick disc. Moreover, the largest radial metallicity gradients are obtained where the outer Lindblad resonance region is effective. We claim that this apparent change in radial metallicity gradients in the thin disc is a result of orbital perturbation originating from the existing resonance regions.

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 Spatially Uniform Spectrum of the Fermi Bubbles: The Leptonic Active Galactic Nucleus Jet Scenario

NASA Astrophysics Data System (ADS)

Yang, H.-Y. K.; Ruszkowski, M.

2017-11-01

The Fermi bubbles are among the most important findings of the Fermi Gamma-ray Space Telescope; however, their origin is still elusive. One of the unique features of the bubbles is that their gamma-ray spectrum, including a high-energy cutoff at ˜110 GeV and the overall shape of the spectrum, is nearly spatially uniform. The high-energy spectral cutoff is suggestive of a leptonic origin due to synchrotron and inverse-Compton cooling of cosmic-ray (CR) electrons; however, even for a leptonic model, it is not obvious why the spectrum should be spatially uniform. In this work, we investigate the bubble formation in the leptonic active galactic nucleus (AGN) jet scenario using a new CRSPEC module in FLASH that allows us to track the evolution of a CR spectrum during the simulations. We show that the high-energy cutoff is caused by fast electron cooling near the Galactic center (GC) when the jets were launched. Afterwards, the dynamical timescale becomes the shortest among all relevant timescales, and therefore the spectrum is essentially advected with only mild cooling losses. This could explain why the bubble spectrum is nearly spatially uniform: the CRs from different parts of the bubbles as seen today all share the same origin near the GC at an early stage of the bubble expansion. We find that the predicted CR spatial and spectral distribution can simultaneously match the normalization, spectral shape, and high-energy cutoff of the observed gamma-ray spectrum and their spatial uniformity, suggesting that past AGN jet activity is a likely mechanism for the formation of the Fermi bubbles.

Supernova Ejecta in the Youngest Galactic Supernova Remnant G1.9+0.3

NASA Technical Reports Server (NTRS)

Borkowski, Kazimierz J.; Reynolds, Stephen P.; Hwang, Una; Green, David A.; Petre, Robert; Krishnamurthy, Kalyani; Willett, Rebecca

2013-01-01

G1.9+0.3 is the youngest known Galactic supernova remnant (SNR), with an estimated supernova (SN) explosion date of approximately 1900, and most likely located near the Galactic Center. Only the outermost ejecta layers with free-expansion velocities (is) approximately greater than 18,000 km s-1 have been shocked so far in this dynamically young, likely Type Ia SNR. A long (980 ks) Chandra observation in 2011 allowed spatially-resolved spectroscopy of heavy-element ejecta. We denoised Chandra data with the spatio-spectral method of Krishnamurthy et al., and used a wavelet based technique to spatially localize thermal emission produced by intermediate-mass elements (IMEs: Si and S) and iron. The spatial distribution of both IMEs and Fe is extremely asymmetric, with the strongest ejecta emission in the northern rim. Fe K alpha emission is particularly prominent there, and fits with thermal models indicate strongly oversolar Fe abundances. In a localized, outlying region in the northern rim, IMEs are less abundant than Fe, indicating that undiluted Fe-group elements (including 56Ni) with velocities greater than 18,000 km s-1 were ejected by this SN. But in the inner west rim, we find Si- and S-rich ejecta without any traces of Fe, so high-velocity products of O-burning were also ejected. G1.9+0.3 appears similar to energetic Type Ia SNe such as SN 2010jn where iron-group elements at such high free-expansion velocities have been recently detected. The pronounced asymmetry in the ejecta distribution and abundance inhomogeneities are best explained by a strongly asymmetric SN explosion, similar to those produced in some recent 3D delayed-detonation Type Ia models.

Dynamical evidence for causality between galactic cosmic rays and interannual variation in global temperature

DOE PAGES

Tsonis, Anastasios A.; Deyle, Ethan R.; May, Robert M.; ...

2015-03-02

As early as 1959, it was hypothesized that an indirect link between solar activity and climate could be mediated by mechanisms controlling the flux of galactic cosmic rays (CR). Although the connection between CR and climate remains controversial, a significant body of laboratory evidence has emerged at the European Organization for Nuclear Research and elsewhere, demonstrating the theoretical mechanism of this link. In this article, we present an analysis based on convergent cross mapping, which uses observational time series data to directly examine the causal link between CR and year-to-year changes in global temperature. Despite a gross correlation, we findmore » no measurable evidence of a causal effect linking CR to the overall 20th-century warming trend. Furthermore, on short interannual timescales, we find a significant, although modest, causal effect between CR and short-term, year-to-year variability in global temperature that is consistent with the presence of nonlinearities internal to the system. Thus, although CR do not contribute measurably to the 20th-century global warming trend, they do appear as a nontraditional forcing in the climate system on short interannual timescales.« less

Stellar and Binary Evolution in Star Clusters

NASA Technical Reports Server (NTRS)

McMillan, Stephen L. W.

2001-01-01

This paper presents a final report on research activities covered on Stellar and Binary Evolution in Star Clusters. Substantial progress was made in the development and dissemination of the "Starlab" software environment. Significant improvements were made to "kira," an N-body simulation program tailored to the study of dense stellar systems such as star clusters and galactic nuclei. Key advances include (1) the inclusion of stellar and binary evolution in a self-consistent manner, (2) proper treatment of the anisotropic Galactic tidal field, (3) numerous technical enhancements in the treatment of binary dynamics and interactions, and (4) full support for the special-purpose GRAPE-4 hardware, boosting the program's performance by a factor of 10-100 over the accelerated version. The data-reduction and analysis tools in Starlab were also substantially expanded. A Starlab Web site (http://www.sns.ias.edu/-starlab) was created and developed. The site contains detailed information on the structure and function of the various tools that comprise the package, as well as download information, "how to" tips and examples of common operations, demonstration programs, animations, etc. All versions of the software are freely distributed to all interested users, along with detailed installation instructions.

You’re Cut Off: HD and MHD Simulations of Truncated Accretion Disks

NASA Astrophysics Data System (ADS)

Hogg, J. Drew; Reynolds, Christopher S.

2017-01-01

Truncated accretion disks are commonly invoked to explain the spectro-temporal variability from accreting black holes in both small systems, i.e. state transitions in galactic black hole binaries (GBHBs), and large systems, i.e. low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the disk behavior is lacking. We present well-resolved hydrodynamic (HD) and magnetohydrodynamic (MHD) numerical models that use a toy cooling prescription to produce the first sustained truncated accretion disks. Using these simulations, we study the dynamics, angular momentum transport, and energetics of a truncated disk in the two different regimes. We compare the behaviors of the HD and MHD disks and emphasize the need to incorporate a full MHD treatment in any discussion of truncated accretion disk evolution.

Spectroscopic confirmation of the low-latitude object FSR 1716 as an old globular cluster

NASA Astrophysics Data System (ADS)

Koch, Andreas; Kunder, Andrea; Wojno, Jennifer

2017-09-01

Star clusters are invaluable tracers of the Galactic components and the discovery and characterization of low-mass stellar systems can be used to appraise their prevailing disruption mechanisms and time scales. However, owing to significant foreground contamination, high extinction, and still uncharted interfaces of the underlying Milky Way components, objects at low Galactic latitudes are notoriously difficult to characterize. Here, we present the first spectroscopic campaign to identify the chemodynamical properties of the low-latitude star cluster FSR 1716. While its photometric age and distance are far from settled, the presence of RR Lyrae variables indicates a rather old cluster variety. Using medium-resolution (R 10 600) calcium triplet (CaT) spectroscopy obtained with the wide-field, multi-fiber AAOmega instrument, we identified six member candidates with a mean velocity of -30 km s-1 and a velocity dispersion of 2.5 ± 0.9 km s-1. The latter value implies a dynamic mass of 1.3 × 104M⊙, typical of a low-mass globular cluster. Combined with our derived CaT metallicity of -1.38 ± 0.20 dex, this object is finally confirmed as an old, metal-poor globular cluster.

On the Formation of Extended Galactic Disks by Tidally Disrupted Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Peñarrubia, Jorge; McConnachie, Alan; Babul, Arif

2006-10-01

We explore the possibility that extended disks, such as that recently discovered in M31, are the result of a single dwarf (109-1010 Msolar) satellite merger. We conduct N-body simulations of dwarf NFW halos with embedded spheroidal stellar components on coplanar, prograde orbits in an M31-like host galaxy. As the orbit decays due to dynamical friction and the system is disrupted, the stellar particles relax to form an extended, exponential-disk-like structure that spans the radial range 30-200 kpc. The disk scale length Rd correlates with the initial extent of the stellar component within the satellite halo: the more embedded the stars, the smaller the resulting disk scale length. If the progenitors start on circular orbits, the kinematics of the stars that make up the extended disk have an average rotational motion that is 30-50 km s-1 lower than the host's circular velocity. For dwarf galaxies moving on highly eccentric orbits (e~=0.7), the stellar debris exhibits a much lower rotational velocity. Our results imply that extended galactic disks might be a generic feature of the hierarchical formation of spiral galaxies such as M31 and the Milky Way.

The Generation Model of Particle Physics and Galactic Dark Matter

NASA Astrophysics Data System (ADS)

Robson, B. A.

2013-09-01

Galactic dark matter is matter hypothesized to account for the discrepancy of the mass of a galaxy determined from its gravitational effects, assuming the validity of Newton's law of universal gravitation, and the mass calculated from the "luminous matter", stars, gas, dust, etc. observed to be contained within the galaxy. The conclusive observation from the rotation curves of spiral galaxies that the mass discrepancy is greater, the larger the distance scales involved implies that either Newton's law of universal gravitation requires modification or considerably more mass (dark matter) is required to be present in each galaxy. Both the modification of Newton's law of gravitation and the hypothesis of the existence of considerable dark matter in a galaxy are discussed. It is shown that the Generation Model (GM) of particle physics, which leads to a modification of Newton's law of gravitation, is found to be essentially equivalent to that of Milgrom's modified Newtonian dynamics (MOND) theory, with the GM providing a physical understanding of the MOND theory. The continuing success of MOND theory in describing the extragalactic mass discrepancy problems constitutes a strong argument against the existence of undetected dark matter haloes, consisting of unknown nonbaryonic matter, surrounding spiral galaxies.

Dynamical evidence for causality between galactic cosmic rays and interannual variation in global temperature

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

Tsonis, Anastasios A.; Deyle, Ethan R.; May, Robert M.

As early as 1959, it was hypothesized that an indirect link between solar activity and climate could be mediated by mechanisms controlling the flux of galactic cosmic rays (CR). Although the connection between CR and climate remains controversial, a significant body of laboratory evidence has emerged at the European Organization for Nuclear Research and elsewhere, demonstrating the theoretical mechanism of this link. In this article, we present an analysis based on convergent cross mapping, which uses observational time series data to directly examine the causal link between CR and year-to-year changes in global temperature. Despite a gross correlation, we findmore » no measurable evidence of a causal effect linking CR to the overall 20th-century warming trend. Furthermore, on short interannual timescales, we find a significant, although modest, causal effect between CR and short-term, year-to-year variability in global temperature that is consistent with the presence of nonlinearities internal to the system. Thus, although CR do not contribute measurably to the 20th-century global warming trend, they do appear as a nontraditional forcing in the climate system on short interannual timescales.« less

An Extension of the EDGES Survey: Stellar Populations in Dark Matter Halos

NASA Astrophysics Data System (ADS)

van Zee, Liese

The formation and evolution of galactic disks is one of the key questions in extragalactic astronomy today. We plan to use archival data from GALEX, Spitzer, and WISE to investigate the growth and evolution of the stellar component in a statistical sample of nearby galaxies. Data covering a broad wavelength range are critical for measurement of current star formation activity, stellar populations, and stellar distributions in nearby galaxies. In order to investigate the timescales associated with the growth of galactic disks, we will (1) investigate the structure of the underlying stellar distribution, (2) measure the ratio of current-to-past star formation activity as a function of radius, and (3) investigate the growth of the stellar disk as a function of baryon fraction and total dynamical mass. The proposed projects leverage the existing deep wide field-of-view near infrared imaging observations obtained with the Spitzer Space Telescope as part of the EDGES Survey, a Cycle 8 Exploration Science Program. The proposed analysis of multiwavelength imaging observations of a well-defined statistical sample will place strong constraints on hierarchical models of galaxy formation and evolution and will further our understanding of the stellar component of nearby galaxies.

The Cosinusoidal Gravitational Potential, a Unique Alternative to Newton

NASA Astrophysics Data System (ADS)

Bartlett, D. F.

1997-04-01

Recently Bartlett & Su have shown that there are only three central potentials that allow a uniqueness theorem. (D.F. Bartlett & Y. Su, Am J. Phys. 62, 683 (1994)) Two of these, the newtonian and Yukawa, are familiar. The third, e^± ikr/r has hardly been studied at all. I consider the potential GM cos(kr)/r as an alternative to dark matter. The universal wavelength λ = 2π/k = 1800 lt-yrs comes from the only thoroughly catalogued system of galactic shells, those around the elliptical, NGC 3923. This λ is confirmed by the location of the gravitationally lensed images in the Einstein Cross. The potential can also explain several features of our Galaxy. The central bar is related dynamically to the spiral arms and, surprisingly, to the distant dwarf spheroidals. The radial oscillations of the potential provide the strong galactic tidal force that may be required to nudge distant comets into the inner solar system. The large, periodic oscillation of the sun within this radial pocket gives a unique mechanism for exposing the solar system to a periodic tidal force. The period of this oscillation and the period of cratering and mass extinctions agree, within errors.

MAPPING THE DYNAMICS OF COLD GAS AROUND SGR A* THROUGH 21 cm ABSORPTION

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

Christian, Pierre; Loeb, Abraham, E-mail: pchristian@cfa.harvard.edu

2015-11-20

The presence of a circumnuclear stellar disk around Sgr A* and megamaser systems near other black holes indicates that dense neutral disks can be found in galactic nuclei. We show that depending on their inclination angle, optical depth, and spin temperature, these disks could be observed spectroscopically through 21 cm absorption. Related spectroscopic observations of Sgr A* can determine its HI disk parameters and the possible presence of gaps in the disk. Clumps of dense gas similar to the G2 could could also be detected in 21 cm absorption against Sgr A* radio emission.

Beyond Pluto: The Search for the Edge of the Solar System

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

Funsten, Herb

In July, we finally visited the last major body of our solar system, Pluto. But what lies beyond? The stellar wind from our Sun forms an enormous bubble in interstellar space. This “sphere of our Sun,” or heliosphere, extends far beyond Pluto and forms a protective cocoon that shields us from cosmic radiation. In this talk, we will travel to the edge of the solar system, peer into the structure and dynamics of the outer heliosphere as it interacts with the interstellar medium and anticipate the future of the solar system as it moves through our galactic neighborhood.

Building black holes: supercomputer cinema.

PubMed

Shapiro, S L; Teukolsky, S A

1988-07-22

A new computer code can solve Einstein's equations of general relativity for the dynamical evolution of a relativistic star cluster. The cluster may contain a large number of stars that move in a strong gravitational field at speeds approaching the speed of light. Unstable star clusters undergo catastrophic collapse to black holes. The collapse of an unstable cluster to a supermassive black hole at the center of a galaxy may explain the origin of quasars and active galactic nuclei. By means of a supercomputer simulation and color graphics, the whole process can be viewed in real time on a movie screen.

Modelling Cosmic-Ray Effects in the Protosolar Disk

NASA Technical Reports Server (NTRS)

Wilson, Thomas L.

2010-01-01

The role that Galactic cosmic rays (GCRs) and solar energetic particles (SEPs) play in the dynamic evolution of protosolar disks and the origin of our Solar System is a fundamental one. The GCRs are an important component of the interstellar medium (ISM), and even play a role in correcting the age determinations of some irons versus CAIs (calcium-aluminum inclusions) in meteoroids . Because CRs also are one of the energy transport mechanisms in a planetary nebula, the question of modelling their effect upon this broad subject is a serious topic for planetary science. The problem is addressed here.

Initial Dynamical Evolution of Star Clusters with Tidal Field

NASA Astrophysics Data System (ADS)

Park, So-Myoung; Goodwin, Simon P.; Kim, Sungsoo S.

2017-03-01

Observations have been suggested that star clusters could form from the rapid collapse and violent relaxation of substructured distributions. We investigate the collapse of fractal stellar distributions in no, weak, and very strong tidal fields. We find that the rapid collapse of substructure into spherical clusters happens quickly with no or a weak tidal field, but very strong tidal fields prevent a cluster forming. However, we also find that dense Plummer spheres are also rapidly destroyed in strong tidal fields. We suggest that this is why the low-mass star clusters cannot survive near the galactic centre which has strong tidal field.

Chaos and noise in a truncated Toda potential

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

Habib, S.; Kandrup, H.E.; Mahon, M.E.

Results are reported from a numerical investigation of orbits in a truncated Toda potential that is perturbed by weak friction and noise. Aside from the perturbations displaying a simple scaling in the amplitude of the friction and noise, it is found that even very weak friction and noise can induce an extrinsic diffusion through cantori on a time scale that is much shorter than that associated with intrinsic diffusion in the unperturbed system. The results have applications in galactic dynamics and in the formation of a beam halo in charged particle beams. {copyright} {ital 1996 The American Physical Society.}

REVIEWS OF TOPICAL PROBLEMS: Birth and life of massive black holes

NASA Astrophysics Data System (ADS)

Dokuchaev, V. I.

1991-06-01

The problems of massive black holes in galactic nuclei of different types are reviewed. The dynamical evolution of compact star systems ends naturally in a gigantic concentrated mass of gas, containing an admixture of surviving stars, that unavoidably collapses into a black hole. The subsequent joint evolution of the remnant star system with a massive black hole at the center leads either to the phenomenon of a bright central source in the nuclei of active galaxies and quasars or to the opposite case of a "dead" frozen black hole in the nucleus of a normal galaxy.

Measuring the Symmetry of Supernova Remnants in the Radio

NASA Astrophysics Data System (ADS)

Stafford, Jennifer; Lopez, Laura A.

2017-01-01

Nearly 300 supernova remnants (SNRs) are known in the MIlky Way galaxy, and they offer an important means to study the explosions and interactions of supernovae at sub-pc scales. In this poster, we present analysis of the morphology of Galactic SNRs at radio wavelengths. Specifically, we measure the symmetry of several tens of SNRs in 6- and 20-cm Very Large Array images using a multipole expansion technique, the power-ratio method. We explore how the SNRs' morphology changes as a function of their size and estimated dynamical ages, with the aim of probing how SNR shapes evolve with time.

On Magnetic Dynamos in Thin Accretion Disks around Compact and Young Stars

NASA Technical Reports Server (NTRS)

Stepinski, T. F.

1993-01-01

A variety of geometrically thin accretion disks commonly associated with such astronomical objects as X-ray binaries, cataclysmic variables, and protostars are likely to be seats of MHD dynamo actions. Thin disk geometry and the particular physical environment make accretion disk dynamos different from stellar, planetary, or even galactic dynamos. We discuss those particular features of disk dynamos with emphasis on the difference between protoplanetary disk dynamos and those associated with compact stars. We then describe normal mode solutions for thin disk dynamos and discuss implications for the dynamical behavior of dynamo-magnetized accretion disks.

Taking the Measure of the Universe : Precision Astrometry with SIM PlanetQuest

NASA Technical Reports Server (NTRS)

Unwin, Stephen C.; Shao, Michael; Tanner, Angelle M.; Allen, Ronald J.; Beichman, Charles A.; Boboltz, David; Catanzarite, Joseph H.; Chaboyer, Brian C.; Ciardi, David R.; Edberg, Stephen J.;

Active galactic nuclei

PubMed Central

Fabian, Andrew C.

1999-01-01

Active galactic nuclei are the most powerful, long-lived objects in the Universe. Recent data confirm the theoretical idea that the power source is accretion into a massive black hole. The common occurrence of obscuration and outflows probably means that the contribution of active galactic nuclei to the power density of the Universe has been generally underestimated. PMID:10220363

Featured Image: Globular Cluster Orbits

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-04-01

This figure (click for the full view) shows the meridional galactic orbits of 12 globular clusters that orbit the Milky Way. The recent release of stellar parallax data from Gaia allowed a team of scientists at Dartmouth College to improve measurements of a number of galactic globular clusters very old clusters of stars that can either orbit within the galactic disk and bulge or more distantly in the galactic halo. In a recent publication led by Erin OMalley, the team presents their findings and combines their new measurements for the clusters with proper motions from past studies to calculate the orbits that these globulars take. These calculations show us whether the clusters reside in the galactic disk and bulge (as only NGC 104 does in the sample shown here, since its orbit is confined to 8 kpc radially and 4 kpc vertically of the galactic center), or if they are halo clusters. To learn more about the authors work, you can check out the paper below!CitationErin M. OMalley et al 2017 ApJ 838 162. doi:10.3847/1538-4357/aa6574

A study of ultraviolet absorption lines through the complete Galactic halo by the analysis of HST faint object spectrograph spectra of active Galactic nuclei, 1

NASA Technical Reports Server (NTRS)

Burks, Geoffrey S.; Bartko, Frank; Shull, J. Michael; Stocke, John T.; Sachs, Elise R.; Burbidge, E. Margaret; Cohen, Ross D.; Junkkarinen, Vesa T.; Harms, Richard J.; Massa, Derck

1994-01-01

The ultraviolet (1150 - 2850 A) spectra of a number of active galactic nuclei (AGNs) observed with the Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) have been used to study the properties of the Galactic halo. The objects that served as probes are 3C 273, PKS 0454-220, Pg 1211+143, CSO 251, Ton 951, and PG 1351+640. The equivalent widths of certain interstellar ions have been measured, with special attention paid to the C IV/C II and Si IV/Si II ratios. These ratios have been intercompared, and the highest values are found in the direction of 3C 273, where C IV/C II = 1.2 and Si IV/Si II greater than 1. These high ratios may be due to a nearby supernova remnant, rather than to ionized gas higher up in the Galactic halo. Our data give some support to the notion that QSO metal-line systems may arise from intervening galaxies which contain high supernova rates, galactic fountains, and turbulent mixing layers.

SMM detection of diffuse Galactic 511 keV annihilation radiation

NASA Technical Reports Server (NTRS)

Share, G. H.; Kinzer, R. L.; Kurfess, J. D.; Messina, D. C.; Purcell, W. R.

1988-01-01

Observations of the 511 keV annihilation line from the vicinity of the Galactic center from October to February for 1980/1981, 1981/1982, 1982/1983, 1984/1985, and 1985/1986 are presented. The measurements were made with the gamma-ray spectrometer on the SMM. The design of the instrument and some of its properties used in the analysis are described, and the methods used for accumulating, fitting, and analyzing the data are outlined. It is shown how the Galactic 511 keV line was separated from the intense and variable background observed in orbit. The SMM observations are compared with previous measurements of annihilation radiation from the Galactic center region, and the astrophysical implications are discussed. It is argued that most of the measurements made to date suggest the presence of an extended Galactic source of annihilation radiation.

High energy gamma ray results from the second small astronomy satellite

NASA Technical Reports Server (NTRS)

Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.; Thompson, D. J.; Bignami, G. F.; Oegelman, H.; Oezel, M. F.; Tuemer, T.

1974-01-01

A high energy (35 MeV) gamma ray telescope employing a thirty-two level magnetic core spark chamber system was flown on SAS 2. The high energy galactic gamma radiation is observed to dominate over the general diffuse radiation along the entire galactic plane, and when examined in detail, the longitudinal and latitudinal distribution seem generally correlated with galactic structural features, particularly with arm segments. The general high energy gamma radiation from the galactic plane, explained on the basis of its angular distribution and magnitude, probably results primarily from cosmic ray interactions with interstellar matter.

The age of the Galactic disk - Inflow, chemical evolution, astration, and radioactivity

NASA Technical Reports Server (NTRS)

Clayton, Donald D.

1989-01-01

Theoretical models of Galactic evolution and observational data on the age of the Galaxy are compared, with a focus on recent results. Topics addressed include the infall of material and its effects on the age-metallicity relation, the distribution of metallicity, the present gas fraction and metallicity, and the age spectrum of interstellar nuclei; the chemical evolution of the solar neighborhood; the key results of nuclear cosmochronology; and astration effects on Galactic age. It is found that both nuclear cosmochronology and detailed stellar and Galactic evolution models tend to support an age of 12-16 Gyr.

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

Balaji, Bhaskaran; Cholis, Ilias; Fox, Patrick J.

We analyze the gamma-ray sky at energies of 0.5 to 50 GeV using the undecimated wavelet transform on the sphere. Focusing on the innermore » $$60^{\\circ} \\times 60^{\\circ}$$ of the sky, we identify and characterize four separate residuals beyond the expected Milky Way diffuse emission. We detect the \\textit{Fermi} Bubbles, finding compelling evidence that they are diffuse in nature and contain very little small-scale structure. We detect the "cocoon" inside the Southern Bubble, and we also identify its northern counterpart above 2 GeV. The Northern Cocoon lies along the same axis but is $$\\sim 30 \\%$$ dimmer than the southern one. We characterize the Galactic center excess, which we find extends up to $$20^{\\circ}$$ in $|b|$. At latitudes $$|b| \\leq 5^{\\circ}$$ we find evidence for power in small angular scales that could be the result of point-source contributions, but for $$|b| \\geq 5^{\\circ}$$ the Galactic center excess is dominantly diffuse in its nature. Our findings show that either the Galactic center excess and {\\it Fermi} Bubbles connect smoothly or that the Bubbles brighten significantly below $$15^\\circ$$ in latitude. We find that the Galactic center excess appears off-center by a few degrees towards negative $$\\ell$$. Additionally, we find and characterize two emissions along the Galactic disk centered at $$\\ell \\simeq +25^{\\circ}$$ and $$-20^{\\circ}$$. These emissions are significantly more elongated along the Galactic disk than the Galactic center excess.« less

Testing Intermittence of the Galactic Star Formation History along with the Infall Model

NASA Astrophysics Data System (ADS)

Takeuchi, Tsutomu T.; Hirashita, Hiroyuki

2000-09-01

We analyze the star formation history (SFH) of the Galactic disk by using an infall model. Based on the observed SFH of the Galactic disk, we first determine the timescale of the gas infall into the Galactic disk (tin) and that of the gas consumption to form stars (tsf). Since each of the two timescales does not prove to be determined independently from the SFH, we first fix tsf. Then, tin is determined so that we minimize χ2. Consequently, we choose three parameter sets: [tsf (Gyr),tin (Gyr)]=(6.0, 23), (11, 12), and (15, 9.0), where we set the Galactic age as 15 Gyr. All of the three cases predict almost identical star formation history. Next, we test the intermittence (or variability) of the star formation rate (SFR) along with the smooth SFH suggested from the infall model. The large value of the χ2 statistic supports the violent time variation of the SFH. If we interpret the observed SFH with smooth and variable components, the amplitude of the variable component is comparable to the smooth component. Thus, intermittent SFH of the Galactic disk is strongly suggested. We also examined the metallicity distribution of G dwarfs. We found that the true parameter set lies between [tsf (Gyr),tin (Gyr)]=(6, 23) and (11, 12), though we need a more sophisticated model including the process of metal enrichment within the Galactic halo.

Finding Distant Galactic HII Regions

NASA Astrophysics Data System (ADS)

Anderson, L. D.; Armentrout, W. P.; Johnstone, B. M.; Bania, T. M.; Balser, Dana S.; Wenger, Trey V.; Cunningham, V.

2015-12-01

The WISE Catalog of Galactic H ii Regions contains ˜2000 H ii region candidates lacking ionized gas spectroscopic observations. All candidates have the characteristic H ii region mid-infrared morphology of WISE 12 μ {{m}} emission surrounding 22 μ {{m}} emission, and additionally have detected radio continuum emission. We here report Green Bank Telescope hydrogen radio recombination line and radio continuum detections in the X-band (9 GHz; 3 cm) of 302 WISE H ii region candidates (out of 324 targets observed) in the zone 225^\\circ ≥slant {\\ell }≥slant -20^\\circ , | {\\text{}}b| ≤slant 6^\\circ . Here we extend the sky coverage of our H ii region Discovery Survey, which now contains nearly 800 H ii regions distributed across the entire northern sky. We provide LSR velocities for the 302 detections and kinematic distances for 131 of these. Of the 302 new detections, 5 have ({\\ell },{\\text{}}b,v) coordinates consistent with the Outer Scutum-Centaurus Arm (OSC), the most distant molecular spiral arm of the Milky Way. Due to the Galactic warp, these nebulae are found at Galactic latitudes >1° in the first Galactic quadrant, and therefore were missed in previous surveys of the Galactic plane. One additional region has a longitude and velocity consistent with the OSC but lies at a negative Galactic latitude (G039.183-01.422 -54.9 {km} {{{s}}}-1). With Heliocentric distances >22 kpc and Galactocentric distances >16 kpc, the OSC H ii regions are the most distant known in the Galaxy. We detect an additional three H ii regions near {\\ell }≃ 150^\\circ whose LSR velocities place them at Galactocentric radii >19 kpc. If their distances are correct, these nebulae may represent the limit to Galactic massive star formation.

The K2 Galactic Archaeology Program Data Release. I. Asteroseismic Results from Campaign 1

NASA Astrophysics Data System (ADS)

Stello, Dennis; Zinn, Joel; Elsworth, Yvonne; Garcia, Rafael A.; Kallinger, Thomas; Mathur, Savita; Mosser, Benoit; Sharma, Sanjib; Chaplin, William J.; Davies, Guy; Huber, Daniel; Jones, Caitlin D.; Miglio, Andrea; Silva Aguirre, Victor

2017-01-01

NASA's K2 mission is observing tens of thousands of stars along the ecliptic, providing data suitable for large-scale asteroseismic analyses to inform galactic archaeology studies. Its first campaign covered a field near the north Galactic cap, a region never covered before by large asteroseismic-ensemble investigations, and was therefore of particular interest for exploring this part of our Galaxy. Here we report the asteroseismic analysis of all stars selected by the K2 Galactic Archaeology Program during the mission's “north Galactic cap” campaign 1. Our consolidated analysis uses six independent methods to measure the global seismic properties, in particular the large frequency separation and the frequency of maximum power. From the full target sample of 8630 stars we find about 1200 oscillating red giants, a number comparable with estimates from galactic synthesis modeling. Thus, as a valuable by-product we find roughly 7500 stars to be dwarfs, which provide a sample well suited for galactic exoplanet occurrence studies because they originate from our simple and easily reproducible selection function. In addition, to facilitate the full potential of the data set for galactic archaeology, we assess the detection completeness of our sample of oscillating red giants. We find that the sample is at least nearly complete for stars with 40 ≲ {ν }\\max /μHz ≲ 270 and {ν }\\max ,{detect}< 2.6× {10}6\\cdot {2}-{\\text{Kp}} μHz. There is a detection bias against helium core burning stars with {ν }\\max ˜ 30 μHz, affecting the number of measurements of {{Δ }}ν and possibly also {ν }\\max . Although we can detect oscillations down to {\\text{Kp}} = 15, our campaign 1 sample lacks enough faint giants to assess the detection completeness for stars fainter than {\\text{Kp}} ˜ 14.5.

The Planck Catalogue of Galactic Cold Clumps : Looking at the early stages of star-formation

NASA Astrophysics Data System (ADS)

Montier, Ludovic

2015-08-01

The Planck satellite has provided an unprecedented view of the submm sky, allowing us to search for the dust emission of Galactic cold sources. Combining Planck-HFI all-sky maps in the high frequency channels with the IRAS map at 100um, we built the Planck catalogue of Galactic Cold Clumps (PGCC, Planck 2015 results XXVIII 2015), counting 13188 sources distributed over the whole sky, and following mainly the Galactic structures at low and intermediate latitudes. This is the first all-sky catalogue of Galactic cold sources obtained with a single instrument at this resolution and sensitivity, which opens a new window on star-formation processes in our Galaxy.I will briefly describe the colour detection method used to extract the Galactic cold sources, i.e., the Cold Core Colour Detection Tool (CoCoCoDeT, Montier et al. 2010), and its application to the Planck data. I will discuss the statistical distribution of the properties of the PGCC sources (in terms of dust temperature, distance, mass, density and luminosity), which illustrates that the PGCC catalogue spans a large variety of environments and objects, from molecular clouds to cold cores, and covers various stages of evolution. The Planck catalogue is a very powerful tool to study the formation and the evolution of prestellar objects and star-forming regions.I will finally present an overview of the Herschel Key Program Galactic Cold Cores (PI. M.Juvela), which allowed us to follow-up about 350 Planck Galactic Cold Clumps, in various stages of evolution and environments. With this program, the nature and the composition of the 5' Planck sources have been revealed at a sub-arcmin resolution, showing very different configurations, such as starless cold cores or multiple Young Stellar objects still embedded in their cold envelope.

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

Gaggero, Daniele; Urbano, Alfredo; Valli, Mauro

We compute the γ-ray and neutrino diffuse emission of the Galaxy on the basis of a recently proposed phenomenological model characterized by radially dependent cosmic-ray (CR) transport properties. We show how this model, designed to reproduce both Fermi-LAT γ-ray data and local CR observables, naturally reproduces the anomalous TeV diffuse emission observed by Milagro in the inner Galactic plane. Above 100 TeV our picture predicts a neutrino flux that is about five (two) times larger than the neutrino flux computed with conventional models in the Galactic Center region (full-sky). Explaining in that way up to ∼25% of the flux measuredmore » by IceCube, we reproduce the full-sky IceCube spectrum adding an extra-Galactic component derived from the muonic neutrinos flux in the northern hemisphere. We also present precise predictions for the Galactic plane region where the flux is dominated by the Galactic emission.« less

The Extragalactic Radio Background

NASA Technical Reports Server (NTRS)

Kogut, A.; Fixsen, D. J.; Levin, S. M.; Limon, M.; Lubin, P. M.; Seiffert, M.; Singal, J.; Villela, T.; Wollack, E.; Wuensche, C. A.

2011-01-01

The existence of an isotropic component of the high-latitude radio sky has been recognized for nearly fifty years, but has typically been assumed to be Galactic in origin. We use recent radio observations to test whether the observed high-latitude component could originate within either an extended Galactic halo or a more local "bubble" structure. The lack of significant polarization from the isotropic component, combined with the lack of significant correlation with the Galactic far-infrared emission, rule out an origin within the Galaxy. We conclude that an extragalactic origin is the only viable alternative for the bulk of the isotropic high-latitude emission. The extragalactic component is 2-3 times brighter than local (Galactic) emission towards the Galactic poles and is consistent with a power law in frequency with amplitude T(sub r) = 24.1 plus or minus 2.1 K and spectral index beta = -2.599 plus or minus 0.036 evaluated at reference frequency 310 MHz.

HI Clouds Near the Galactic Center: Possible Tracers of the Nuclear Wind

NASA Astrophysics Data System (ADS)

Lockman, Felix J.; McClure-Griffiths, Naomi; DiTeodoro, Enrico

2017-01-01

We have used the Green Bank Telescope to discover more than one hundred neutral hydrogen clouds that appear to be embedded in the Fermi Bubble -- the Milky Way’s nuclear wind. With the other members of this population that were previously found with the Australia Telescope Compact Array, we now have a sample of about 200 such clouds. They are identified by their peculiar velocities. The cloud kinematics show no trace of Galactic rotation or association with the Galactic bar. Near longitude zero the clouds can have values of VLSR = +-200 km/s. No clouds have been detected with |VLSR| > 350 km/s. The clouds are concentrated toward the Galactic plane, but some are still found to |b|=10 degrees, or z > 1 kpc at the Galactic Center, where the current surveys end. These clouds are important tracers of conditions in the nuclear wind of the Milky Way.

THE EFFECT OF A DYNAMIC INNER HELIOSHEATH THICKNESS ON COSMIC-RAY MODULATION

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

Manuel, R.; Ferreira, S. E. S.; Potgieter, M. S., E-mail: rexmanuel@live.com

2015-02-01

The time-dependent modulation of galactic cosmic rays in the heliosphere is studied over different polarity cycles by computing 2.5 GV proton intensities using a two-dimensional, time-dependent modulation model. By incorporating recent theoretical advances in the relevant transport parameters in the model, we showed in previous work that this approach gave realistic computed intensities over a solar cycle. New in this work is that a time dependence of the solar wind termination shock (TS) position is implemented in our model to study the effect of a dynamic inner heliosheath thickness (the region between the TS and heliopause) on the solar modulationmore » of galactic cosmic rays. The study reveals that changes in the inner heliosheath thickness, arising from a time-dependent shock position, does affect cosmic-ray intensities everywhere in the heliosphere over a solar cycle, with the smallest effect in the innermost heliosphere. A time-dependent TS position causes a phase difference between the solar activity periods and the corresponding intensity periods. The maximum intensities in response to a solar minimum activity period are found to be dependent on the time-dependent TS profile. It is found that changing the width of the inner heliosheath with time over a solar cycle can shift the time of when the maximum or minimum cosmic-ray intensities occur at various distances throughout the heliosphere, but more significantly in the outer heliosphere. The time-dependent extent of the inner heliosheath, as affected by solar activity conditions, is thus an additional time-dependent factor to be considered in the long-term modulation of cosmic rays.« less

The PAndAS Field of Streams: Stellar Structures in the Milky Way Halo toward Andromeda and Triangulum

NASA Astrophysics Data System (ADS)

Martin, Nicolas F.; Ibata, Rodrigo A.; Rich, R. Michael; Collins, Michelle L. M.; Fardal, Mark A.; Irwin, Michael J.; Lewis, Geraint F.; McConnachie, Alan W.; Babul, Arif; Bate, Nicholas F.; Chapman, Scott C.; Conn, Anthony R.; Crnojević, Denija; Ferguson, Annette M. N.; Mackey, A. Dougal; Navarro, Julio F.; Peñarrubia, Jorge; Tanvir, Nial T.; Valls-Gabaud, David

2014-05-01

We reveal the highly structured nature of the Milky Way (MW) stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars. We map no fewer than five stellar structures within a heliocentric range of ~5-30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In particular, we trace a new faint stellar stream located at a heliocentric distance of ~17 kpc. With a surface brightness of Σ V ~ 32-32.5 mag arcsec-2, it follows an orbit that is almost parallel to the Galactic plane north of M31 and has so far eluded surveys of the MW halo as these tend to steer away from regions dominated by the Galactic disk. Investigating our follow-up spectroscopic observations of PAndAS, we serendipitously uncover a radial velocity signature from stars that have colors and magnitudes compatible with the stream. From the velocity of eight likely member stars, we show that this stellar structure is dynamically cold, with an unresolved velocity dispersion that is lower than 7.1 km s-1 at the 90% confidence level. Along with the width of the stream (300-650 pc), its dynamics point to a dwarf-galaxy-accretion origin. The numerous stellar structures we can map in the MW stellar halo between 5 and 30 kpc and their varying morphology is a testament to the complex nature of the stellar halo at these intermediate distances.

A density cusp of quiescent X-ray binaries in the central parsec of the Galaxy

NASA Astrophysics Data System (ADS)

Hailey, Charles J.; Mori, Kaya; Bauer, Franz E.; Berkowitz, Michael E.; Hong, Jaesub; Hord, Benjamin J.

2018-04-01

The existence of a ‘density cusp’—a localized increase in number—of stellar-mass black holes near a supermassive black hole is a fundamental prediction of galactic stellar dynamics. The best place to detect such a cusp is in the Galactic Centre, where the nearest supermassive black hole, Sagittarius A*, resides. As many as 20,000 black holes are predicted to settle into the central parsec of the Galaxy as a result of dynamical friction; however, so far no density cusp of black holes has been detected. Low-mass X-ray binary systems that contain a stellar-mass black hole are natural tracers of isolated black holes. Here we report observations of a dozen quiescent X-ray binaries in a density cusp within one parsec of Sagittarius A*. The lower-energy emission spectra that we observed in these binaries is distinct from the higher-energy spectra associated with the population of accreting white dwarfs that dominates the central eight parsecs of the Galaxy. The properties of these X-ray binaries, in particular their spatial distribution and luminosity function, suggest the existence of hundreds of binary systems in the central parsec of the Galaxy and many more isolated black holes. We cannot rule out a contribution to the observed emission from a population (of up to about one-half the number of X-ray binaries) of rotationally powered, millisecond pulsars. The spatial distribution of the binary systems is a relic of their formation history, either in the stellar disk around Sagittarius A* (ref. 7) or through in-fall from globular clusters, and constrains the number density of sources in the modelling of gravitational waves from massive stellar remnants, such as neutron stars and black holes.

Star Count Density Profiles and Structural Parameters of 26 Galactic Globular Clusters

NASA Astrophysics Data System (ADS)

Miocchi, P.; Lanzoni, B.; Ferraro, F. R.; Dalessandro, E.; Vesperini, E.; Pasquato, M.; Beccari, G.; Pallanca, C.; Sanna, N.

2013-09-01

We used an appropriate combination of high-resolution Hubble Space Telescope observations and wide-field, ground-based data to derive the radial stellar density profiles of 26 Galactic globular clusters from resolved star counts (which can be all freely downloaded on-line). With respect to surface brightness (SB) profiles (which can be biased by the presence of sparse, bright stars), star counts are considered to be the most robust and reliable tool to derive cluster structural parameters. For each system, a detailed comparison with both King and Wilson models has been performed and the most relevant best-fit parameters have been obtained. This collection of data represents the largest homogeneous catalog collected so far of star count profiles and structural parameters derived therefrom. The analysis of the data of our catalog has shown that (1) the presence of the central cusps previously detected in the SB profiles of NGC 1851, M13, and M62 is not confirmed; (2) the majority of clusters in our sample are fit equally well by the King and the Wilson models; (3) we confirm the known relationship between cluster size (as measured by the effective radius) and galactocentric distance; (4) the ratio between the core and the effective radii shows a bimodal distribution, with a peak at ~0.3 for about 80% of the clusters and a secondary peak at ~0.6 for the remaining 20%. Interestingly, the main peak turns out to be in agreement with that expected from simulations of cluster dynamical evolution and the ratio between these two radii correlates well with an empirical dynamical-age indicator recently defined from the observed shape of blue straggler star radial distribution, thus suggesting that no exotic mechanisms of energy generation are needed in the cores of the analyzed clusters.

The PAndAS field of streams: Stellar structures in the milky way halo toward Andromeda and Triangulum

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

Martin, Nicolas F.; Ibata, Rodrigo A.; Rich, R. Michael

We reveal the highly structured nature of the Milky Way (MW) stellar halo within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS) photometric survey from blue main sequence (MS) and MS turn-off stars. We map no fewer than five stellar structures within a heliocentric range of ∼5-30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. In particular, we trace a new faint stellar stream located at a heliocentric distance of ∼17more » kpc. With a surface brightness of Σ {sub V} ∼ 32-32.5 mag arcsec{sup –2}, it follows an orbit that is almost parallel to the Galactic plane north of M31 and has so far eluded surveys of the MW halo as these tend to steer away from regions dominated by the Galactic disk. Investigating our follow-up spectroscopic observations of PAndAS, we serendipitously uncover a radial velocity signature from stars that have colors and magnitudes compatible with the stream. From the velocity of eight likely member stars, we show that this stellar structure is dynamically cold, with an unresolved velocity dispersion that is lower than 7.1 km s{sup –1} at the 90% confidence level. Along with the width of the stream (300-650 pc), its dynamics point to a dwarf-galaxy-accretion origin. The numerous stellar structures we can map in the MW stellar halo between 5 and 30 kpc and their varying morphology is a testament to the complex nature of the stellar halo at these intermediate distances.« less

Intermediate mass black holes in AGN discs - I. Production and growth

NASA Astrophysics Data System (ADS)

McKernan, B.; Ford, K. E. S.; Lyra, W.; Perets, H. B.

2012-09-01

Here we propose a mechanism for efficiently growing intermediate mass black holes (IMBH) in discs around supermassive black holes. Stellar mass objects can efficiently agglomerate when facilitated by the gas disc. Stars, compact objects and binaries can migrate, accrete and merge within discs around supermassive black holes. While dynamical heating by cusp stars excites the velocity dispersion of nuclear cluster objects (NCOs) in the disc, gas in the disc damps NCO orbits. If gas damping dominates, NCOs remain in the disc with circularized orbits and large collision cross-sections. IMBH seeds can grow extremely rapidly by collisions with disc NCOs at low relative velocities, allowing for super-Eddington growth rates. Once an IMBH seed has cleared out its feeding zone of disc NCOs, growth of IMBH seeds can become dominated by gas accretion from the active galactic nucleus (AGN) disc. However, the IMBH can migrate in the disc and expand its feeding zone, permitting a super-Eddington accretion rate to continue. Growth of IMBH seeds via NCO collisions is enhanced by a pile-up of migrators. We highlight the remarkable parallel between the growth of IMBH in AGN discs with models of giant planet growth in protoplanetary discs. If an IMBH becomes massive enough it can open a gap in the AGN disc. IMBH migration in AGN discs may stall, allowing them to survive the end of the AGN phase and remain in galactic nuclei. Our proposed mechanisms should be more efficient at growing IMBH in AGN discs than the standard model of IMBH growth in stellar clusters. Dynamical heating of disc NCOs by cusp stars is transferred to the gas in an AGN disc helping to maintain the outer disc against gravitational instability. Model predictions, observational constraints and implications are discussed in a companion paper (Paper II).

The Physics of AGN Feedback During Galaxy Formation

NASA Astrophysics Data System (ADS)

Quataert, Eliot

A key lesson in our modern understanding of how galaxies form is that the release of energy by newly formed stars and accreting black holes -- in the form of both radiation and powerful outflows -- has a dramatic effect on the process of star formation and black hole growth itself. As a result, developing more realistic treatments of these stellar and black hole feedback processes is one of the primary challenges facing predictive models of galaxy formation. This proposal centers on understanding the dynamics of gas in galactic nuclei, with an emphasis on how black holes at the centers of galaxies grow and the resulting effects of black hole feedback on the scale of individual galaxies. Some of the calculations we propose will also have direct application to feedback by star formation. Our proposed work consists of two interrelated sets of projects. In the first, we will study in detail the mechanisms by which radiation and outflows from an accreting black hole interact with surrounding gas: this is the key science question at the heart of understanding black hole feedback. It is also important, however, to place this understanding of the key feedback processes in the broader context of gas dynamics in galaxies. With this in mind, we will carry out numerical simulations of gas in galactic nuclei and study, for the first time, the competition between gas inflow, star formation, and stellar and black hole feedback at the radii that the accretion rate onto a central black hole is determined and that galaxy-scale outflows of gas are likely initiated. Our work bears directly on, and will be applied to, observations by current NASA missions such as HST, Chandra, GALEX, Xmm-Newton, Herschel, and NuSTAR, and future missions such as JWST.

Self-shadowing effects of slim accretion disks in active galactic nuclei: the diverse appearance of the broad-line region

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

Wang, Jian-Min; Qiu, Jie; Du, Pu

2014-12-10

Supermassive black holes in active galactic nuclei (AGNs) undergo a wide range of accretion rates, which lead to diversity of appearance. We consider the effects of anisotropic radiation from accretion disks on the broad-line region (BLR) from the Shakura-Sunyaev regime to slim disks with super-Eddington accretion rates. The geometrically thick funnel of the inner region of slim disks produces strong self-shadowing effects that lead to very strong anisotropy of the radiation field. We demonstrate that the degree of anisotropy of the radiation fields grows with increasing accretion rate. As a result of this anisotropy, BLR clouds receive different spectral energymore » distributions depending on their location relative to the disk, resulting in the diverse observational appearance of the BLR. We show that the self-shadowing of the inner parts of the disk naturally produces two dynamically distinct regions of the BLR, depending on accretion rate. These two regions manifest themselves as kinematically distinct components of the broad Hβ line profile with different line widths and fluxes, which jointly account for the Lorentzian profile generally observed in narrow-line Seyfert 1 galaxies. In the time domain, these two components are expected to reverberate with different time lags with respect to the varying ionizing continuum, depending on the accretion rate and the viewing angle of the observer. The diverse appearance of the BLR due to the anisotropic ionizing energy source can be tested by reverberation mapping of Hβ and other broad emission lines (e.g., Fe II), providing a new tool to diagnose the structure and dynamics of the BLR. Other observational consequences of our model are also explored.« less

A density cusp of quiescent X-ray binaries in the central parsec of the Galaxy.

PubMed

Hailey, Charles J; Mori, Kaya; Bauer, Franz E; Berkowitz, Michael E; Hong, Jaesub; Hord, Benjamin J

2018-04-04

The existence of a 'density cusp'-a localized increase in number-of stellar-mass black holes near a supermassive black hole is a fundamental prediction of galactic stellar dynamics. The best place to detect such a cusp is in the Galactic Centre, where the nearest supermassive black hole, Sagittarius A*, resides. As many as 20,000 black holes are predicted to settle into the central parsec of the Galaxy as a result of dynamical friction; however, so far no density cusp of black holes has been detected. Low-mass X-ray binary systems that contain a stellar-mass black hole are natural tracers of isolated black holes. Here we report observations of a dozen quiescent X-ray binaries in a density cusp within one parsec of Sagittarius A*. The lower-energy emission spectra that we observed in these binaries is distinct from the higher-energy spectra associated with the population of accreting white dwarfs that dominates the central eight parsecs of the Galaxy. The properties of these X-ray binaries, in particular their spatial distribution and luminosity function, suggest the existence of hundreds of binary systems in the central parsec of the Galaxy and many more isolated black holes. We cannot rule out a contribution to the observed emission from a population (of up to about one-half the number of X-ray binaries) of rotationally powered, millisecond pulsars. The spatial distribution of the binary systems is a relic of their formation history, either in the stellar disk around Sagittarius A* (ref. 7) or through in-fall from globular clusters, and constrains the number density of sources in the modelling of gravitational waves from massive stellar remnants, such as neutron stars and black holes.

Electromagnetic dissociation effects in galactic heavy-ion fragmentation

NASA Technical Reports Server (NTRS)

Norbury, J. W.; Townsend, L. W.

1986-01-01

Methods for calculating cross sections for the breakup of galactic heavy ions by the Coulomb fields of the interacting nuclei are presented. By using the Weizsacker-Williams method of virtual quanta, estimates of electromagnetic dissociation cross sections for a variety of reactions applicable to galactic cosmic ray shielding studies are presented and compared with other predictions and with available experimental data.

On galactic origin of cosmic rays with energy up to 10(19) eV

NASA Technical Reports Server (NTRS)

Efimov, N. N.; Mikhailov, A. A.

1985-01-01

The experimental data on ultrahigh energy cosmic ray anisotropy are considered. In supposed models of galactic magnetic field the main characteristics of expected anisotropy are estimated and are compared with the experimental data. It is shown that particles with energy up to 10 to the 19th power eV are of galactic origin.

Evaluating Galactic Cosmic Ray Environment Models Using RaD-X Flight Data

NASA Technical Reports Server (NTRS)

Norman, R. B.; Mertens, C. J.; Slaba, T. C.

2016-01-01

Galactic cosmic rays enter Earth's atmosphere after interacting with the geomagnetic field. The primary galactic cosmic rays spectrum is fundamentally changed as it interacts with Earth's atmosphere through nuclear and atomic interactions. At points deeper in the atmosphere, such as at airline altitudes, the radiation environment is a combination of the primary galactic cosmic rays and the secondary particles produced through nuclear interactions. The RaD-X balloon experiment measured the atmospheric radiation environment above 20 km during 2 days in September 2015. These experimental measurements were used to validate and quantify uncertainty in physics-based models used to calculate exposure levels for commercial aviation. In this paper, the Badhwar-O'Neill 2014, the International Organization for Standardization 15390, and the German Aerospace Company galactic cosmic ray environment models are used as input into the same radiation transport code to predict and compare dosimetric quantities to RaD-X measurements. In general, the various model results match the measured tissue equivalent dose well, with results generated by the German Aerospace Center galactic cosmic ray environment model providing the best comparison. For dose equivalent and dose measured in silicon, however, the models were compared less favorably to the measurements.

Interstellar Scattering Towards the Galactic Center as Probed by OH/IR Stars

NASA Technical Reports Server (NTRS)

Vanlangevelde, Huib Jan; Frail, Dale A.; Cordes, James M.; Diamond, Philip J.

1992-01-01

Angular broadening measurements are reported of 20 OH/IR stars near the galactic center. This class of sources is known to have bright, intrinsically compact (less than or equal to 20 mas) maser components within their circumstellar shells. VLBA antennas and the VLA were used to perform a MKII spectral line VLBI experiment. The rapid drop in correlated flux with increasing baseline, especially for sources closest to the galactic center, is attributed to interstellar scattering. Angular diameters were measured for 13 of our sources. Lower limits were obtained for the remaining seven. With the data, together with additional data taken from the literature, the distribution was determined of interstellar scattering toward the galactic center. A region was found of pronounced scattering nearly centered on SgrA*. Two interpretations are considered for the enhanced scattering. One hypothesis is that the scattering is due to a clump of enhanced turbulence, such as those that lie along lines of sight to other known objects, that has no physical relationship to the galactic center. The other model considers the location of the enhanced scattering to arise in the galactic center itself. The physical implications of the models yield information on the nature of interstellar scattering.

Probing the Galactic Structure of the Milky Way with H II Regions

NASA Astrophysics Data System (ADS)

Red, Wesley Alexander; Wenger, Trey V.; Balser, Dana; Anderson, Loren; Bania, Thomas

2018-01-01

Mapping the structure of the Milky Way is challenging since we reside within the Galactic disk and distances are difficult to determine. Elemental abundances provide important constraints on theories of the formation and evolution of the Milky Way. HII regions are the brightest objects in the Galaxy at radio wavelengths and are detected across the entire Galactic disk. We use the Jansky Very Large Array (VLA) to observe the radio recombination line (RRL) and continuum emission of 120 Galactic HII regions located across the Galactic disk. In thermal equilibrium, metal abundances are expected to set the nebular electron temperature with high abundances producing low temperatures. We derive the metallicity of HII regions using an empirical relation between an HII region's radio recombination line-to-continuum ratio and nebular metallicity. Here we focus on a subset of 20 HII regions from our sample that have been well studied with the Green Bank Telescope (GBT) to test our data reduction pipeline and analysis methods. Our goal is to expand this study to the Southern skies with the Australia Telescope Compact Array and create a metallicity map of the entire Galactic disk.

A possible origin of gamma rays from the Fermi Bubbles

NASA Astrophysics Data System (ADS)

Thoudam, Satyendra

2014-11-01

One of the most exciting discoveries of recent years is a pair of gigantic gamma-ray emission regions, the so-called Fermi bubbles, above and below the Galactic center. The bubbles, discovered by the Fermi space telescope, extend up to ∼50° in Galactic latitude and are ∼40° wide in Galactic longitude. The gamma-ray emission is also found to correlate with radio, microwave and X-rays emission. The origin of the bubbles and the associated non-thermal emissions are still not clearly understood. Possible explanations for the non-thermal emission include cosmic-ray injection from the Galactic center by high speed Galactic winds/jets, acceleration by multiple shocks or plasma turbulence present inside the bubbles, and acceleration by strong shock waves associated with the expansion of the bubbles. In this paper, I will discuss the possibility that the gamma-ray emission is produced by the injection of Galactic cosmic-rays mainly protons during their diffusive propagation through the Galaxy. The protons interact with the bubble plasma producing π°-decay gamma rays, while at the same time, radio and microwave synchrotron emissions are produced by the secondary electrons/positrons resulting from the π± decays.

A WISE Survey of New Star Clusters in the Central Plane Region of the Milky Way

NASA Astrophysics Data System (ADS)

Ryu, Jinhyuk; Lee, Myung Gyoon

2018-04-01

We present the discovery of new star clusters in the central plane region (| l| < 30^\\circ and | b| < 6^\\circ ) of the Milky Way. In order to overcome the extinction problem and the spatial limit of previous surveys, we use the Wide-field Infrared Survey Explorer (WISE) data to find clusters. We also use other infrared survey data in the archive for additional analysis. We find 923 new clusters, of which 202 clusters are embedded clusters. These clusters are concentrated toward the Galactic plane and show a symmetric distribution with respect to the Galactic latitude. The embedded clusters show a stronger concentration to the Galactic plane than the nonembedded clusters. The new clusters are found more in the first Galactic quadrant, while previously known clusters are found more in the fourth Galactic quadrant. The spatial distribution of the combined sample of known clusters and new clusters is approximately symmetric with respect to the Galactic longitude. We estimate reddenings, distances, and relative ages of the 15 class A clusters using theoretical isochrones. Ten of them are relatively old (age >800 Myr) and five are young (age ≈4 Myr).

Neutrino diagnostics of ultrahigh energy cosmic ray protons

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

Ahlers, Markus; Sarkar, Subir; Anchordoqui, Luis A.

2009-04-15

The energy at which cosmic rays from extra-galactic sources begin to dominate over those from galactic sources is an important open question in astroparticle physics. A natural candidate is the energy at the 'ankle' in the approximately power-law energy spectrum which is indicative of a crossover from a falling galactic component to a flatter extra-galactic component. The transition can occur without such flattening but this requires some degree of conspiracy of the spectral shapes and normalizations of the two components. Nevertheless, it has been argued that extra-galactic sources of cosmic ray protons that undergo interactions on the CMB can reproducemore » the energy spectrum below the ankle if the crossover energy is as low as the 'second knee' in the spectrum. This low crossover model is constrained by direct measurements by the Pierre Auger Observatory, which indicate a heavier composition at these energies. We demonstrate that upper limits on the cosmic diffuse neutrino flux provide a complementary constraint on the proton fraction in ultra-high energy extra-galactic cosmic rays and forthcoming data from IceCube will provide a definitive test of this model.« less

Producing an Infrared Multiwavelength Galactic Plane Atlas Using Montage, Pegasus, and Amazon Web Services

NASA Astrophysics Data System (ADS)

Rynge, M.; Juve, G.; Kinney, J.; Good, J.; Berriman, B.; Merrihew, A.; Deelman, E.

2014-05-01

In this paper, we describe how to leverage cloud resources to generate large-scale mosaics of the galactic plane in multiple wavelengths. Our goal is to generate a 16-wavelength infrared Atlas of the Galactic Plane at a common spatial sampling of 1 arcsec, processed so that they appear to have been measured with a single instrument. This will be achieved by using the Montage image mosaic engine process observations from the 2MASS, GLIMPSE, MIPSGAL, MSX and WISE datasets, over a wavelength range of 1 μm to 24 μm, and by using the Pegasus Workflow Management System for managing the workload. When complete, the Atlas will be made available to the community as a data product. We are generating images that cover ±180° in Galactic longitude and ±20° in Galactic latitude, to the extent permitted by the spatial coverage of each dataset. Each image will be 5°x5° in size (including an overlap of 1° with neighboring tiles), resulting in an atlas of 1,001 images. The final size will be about 50 TBs. This paper will focus on the computational challenges, solutions, and lessons learned in producing the Atlas. To manage the computation we are using the Pegasus Workflow Management System, a mature, highly fault-tolerant system now in release 4.2.2 that has found wide applicability across many science disciplines. A scientific workflow describes the dependencies between the tasks and in most cases the workflow is described as a directed acyclic graph, where the nodes are tasks and the edges denote the task dependencies. A defining property for a scientific workflow is that it manages data flow between tasks. Applied to the galactic plane project, each 5 by 5 mosaic is a Pegasus workflow. Pegasus is used to fetch the source images, execute the image mosaicking steps of Montage, and store the final outputs in a storage system. As these workflows are very I/O intensive, care has to be taken when choosing what infrastructure to execute the workflow on. In our setup, we choose to use dynamically provisioned compute clusters running on the Amazon Elastic Compute Cloud (EC2). All our instances are using the same base image, which is configured to come up as a master node by default. The master node is a central instance from where the workflow can be managed. Additional worker instances are provisioned and configured to accept work assignments from the master node. The system allows for adding/removing workers in an ad hoc fashion, and could be run in large configurations. To-date we have performed 245,000 CPU hours of computing and generated 7,029 images and totaling 30 TB. With the current set up our runtime would be 340,000 CPU hours for the whole project. Using spot m2.4xlarge instances, the cost would be approximately $5,950. Using faster AWS instances, such as cc2.8xlarge could potentially decrease the total CPU hours and further reduce the compute costs. The paper will explore these tradeoffs.

Orbital Decay in Binaries with Evolved Stars

NASA Astrophysics Data System (ADS)

Sun, Meng; Arras, Phil; Weinberg, Nevin N.; Troup, Nicholas; Majewski, Steven R.

2018-01-01

Two mechanisms are often invoked to explain tidal friction in binary systems. The ``dynamical tide” is the resonant excitation of internal gravity waves by the tide, and their subsequent damping by nonlinear fluid processes or thermal diffusion. The ``equilibrium tide” refers to non-resonant excitation of fluid motion in the star’s convection zone, with damping by interaction with the turbulent eddies. There have been numerous studies of these processes in main sequence stars, but less so on the subgiant and red giant branches. Motivated by the newly discovered close binary systems in the Apache Point Observatory Galactic Evolution Experiment (APOGEE-1), we have performed calculations of both the dynamical and equilibrium tide processes for stars over a range of mass as the star’s cease core hydrogen burning and evolve to shell burning. Even for stars which had a radiative core on the main sequence, the dynamical tide may have very large amplitude in the newly radiative core in post-main sequence, giving rise to wave breaking. The resulting large dynamical tide dissipation rate is compared to the equilibrium tide, and the range of secondary masses and orbital periods over which rapid orbital decay may occur will be discussed, as well as applications to close APOGEE binaries.

Understanding EROS2 observations toward the spiral arms within a classical Galactic model framework

NASA Astrophysics Data System (ADS)

Moniez, M.; Sajadian, S.; Karami, M.; Rahvar, S.; Ansari, R.

2017-08-01

Aims: EROS (Expérience de Recherche d'Objets Sombres) has searched for microlensing toward four directions in the Galactic plane away from the Galactic center. The interpretation of the catalog optical depth is complicated by the spread of the source distance distribution. We compare the EROS microlensing observations with Galactic models (including the Besançon model), tuned to fit the EROS source catalogs, and take into account all observational data such as the microlensing optical depth, the Einstein crossing durations, and the color and magnitude distributions of the catalogued stars. Methods: We simulated EROS-like source catalogs using the HIgh-Precision PARallax COllecting Satellite (Hipparcos) database, the Galactic mass distribution, and an interstellar extinction table. Taking into account the EROS star detection efficiency, we were able to produce simulated color-magnitude diagrams that fit the observed diagrams. This allows us to estimate average microlensing optical depths and event durations that are directly comparable with the measured values. Results: Both the Besançon model and our Galactic model allow us to fully understand the EROS color-magnitude data. The average optical depths and mean event durations calculated from these models are in reasonable agreement with the observations. Varying the Galactic structure parameters through simulation, we were also able to deduce contraints on the kinematics of the disk, the disk stellar mass function (at a few kpc distance from the Sun), and the maximum contribution of a thick disk of compact objects in the Galactic plane (Mthick< 5 - 7 × 1010M⊙ at 95%, depending on the model). We also show that the microlensing data toward one of our monitored directions are significantly sensitive to the Galactic bar parameters, although much larger statistics are needed to provide competitive constraints. Conclusions: Our simulation gives a better understanding of the lens and source spatial distributions in the microlensing events. The goodness of a global fit taking into account all the observables (from the color-magnitude diagrams and microlensing observations) shows the validity of the Galactic models. Our tests with the parameters excursions show the unique sensitivity of the microlensing data to the kinematical parameters and stellar initial mass function. http://www.lal.in2p3.fr/recherche/eros

Chandra Deep X-ray Observation of a Typical Galactic Plane Region and Near-Infrared Identification

NASA Technical Reports Server (NTRS)

Ebisawa, K.; Tsujimoto, M.; Paizis, A.; Hamaguichi, K.; Bamba, A.; Cutri, R.; Kaneda, H.; Maeda, Y.; Sato, G.; Senda, A.

2004-01-01

Using the Chandra Advanced CCD Imaging Spectrometer Imaging array (ACIS-I), we have carried out a deep hard X-ray observation of the Galactic plane region at (l,b) approx. (28.5 deg,0.0 deg), where no discrete X-ray source has been reported previously. We have detected 274 new point X-ray sources (4 sigma confidence) as well as strong Galactic diffuse emission within two partidly overlapping ACIS-I fields (approx. 250 sq arcmin in total). The point source sensitivity was approx. 3 x 10(exp -15)ergs/s/sq cm in the hard X-ray band (2-10 keV and approx. 2 x 10(exp -16) ergs/s/sq cm in the soft band (0.5-2 keV). Sum of all the detected point source fluxes account for only approx. 10 % of the total X-ray fluxes in the field of view. In order to explain the total X-ray fluxes by a superposition of fainter point sources, an extremely rapid increase of the source population is required below our sensitivity limit, which is hardly reconciled with any source distribution in the Galactic plane. Therefore, we conclude that X-ray emission from the Galactic plane has truly diffuse origin. Only 26 point sources were detected both in the soft and hard bands, indicating that there are two distinct classes of the X-ray sources distinguished by the spectral hardness ratio. Surface number density of the hard sources is only slightly higher than observed at the high Galactic latitude regions, strongly suggesting that majority of the hard X-ray sources are active galaxies seen through the Galactic plane. Following the Chandra observation, we have performed a near-infrared (NIR) survey with SOFI at ESO/NTT to identify these new X-ray sources. Since the Galactic plane is opaque in NIR, we did not see the background extragalactic sources in NIR. In fact, only 22 % of the hard sources had NIR counterparts which are most likely to be Galactic origin. Composite X-ray energy spectrum of those hard X-ray sources having NIR counterparts exhibits a narrow approx. 6.7 keV iron emission line, which is a signature of Galactic quiescent cataclysmic variables (CVs).

Gamma-ray Astrophysics: a New Look at the Universe

NASA Technical Reports Server (NTRS)

Trombka, J. I.; Fichtel, C. E.; Grindlay, J.; Hofstadter, R.

1978-01-01

Gamma-ray astronomy which includes the spectral region from above approximately 100 keV to greater than or equal to 1000 GeV permits investigation of the most energetic photons originating in our galaxy and beyond and provides the most direct means of studying the largest transfers of energy occurring in astrophysical processes. Of all the electromagnetic spectrum, high-energy gamma-ray astronomy measures most directly the presence and dynamic effects of the energetic charged cosmic ray particles, element synthesis, and particle acceleration. Further, gamma rays suffer negligible absorption or scatterings as they travel in straight paths; hence, they may survive billions of years and still reveal their source. The high energy processes in stellar objects (including our Sun), the dynamics of the cosmic-ray gas, the formation of clouds and nebulae, galactic evolution and even certain aspects of cosmology and the origin of the universe may be explored by gamma-ray observations.

Local stability of galactic discs in modified dynamics

NASA Astrophysics Data System (ADS)

Shenavar, Hossein; Ghafourian, Neda

2018-04-01

The local stability of stellar and fluid discs, under a new modified dynamical model, is surveyed by using WKB approximation. The exact form of the modified Toomre criterion is derived for both types of systems and it is shown that the new model is, in all situations, more locally stable than Newtonian model. In addition, it has been proved that the central surface density of the galaxies plays an important role in the local stability in the sense that low surface brightness (LSB) galaxies are more stable than high surface brightness (HSBs). Furthermore, the growth rate in the new model is found to be lower than the Newtonian one. We found that, according to this model, the local instability is related to the ratio of surface density of the disc to a critical surface density Σcrit. We provide observational evidence to support this result based on star formation rate in HSBs and LSBs.

ON THE STAR FORMATION LAW FOR SPIRAL AND IRREGULAR GALAXIES

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

Elmegreen, Bruce G., E-mail: bge@us.ibm.com

2015-12-01

A dynamical model for star formation on a galactic scale is proposed in which the interstellar medium is constantly condensing to star-forming clouds on the dynamical time of the average midplane density, and the clouds are constantly being disrupted on the dynamical timescale appropriate for their higher density. In this model, the areal star formation rate scales with the 1.5 power of the total gas column density throughout the main regions of spiral galaxies, and with a steeper power, 2, in the far outer regions and in dwarf irregular galaxies because of the flaring disks. At the same time, theremore » is a molecular star formation law that is linear in the main and outer parts of disks and in dIrrs because the duration of individual structures in the molecular phase is also the dynamical timescale, canceling the additional 0.5 power of surface density. The total gas consumption time scales directly with the midplane dynamical time, quenching star formation in the inner regions if there is no accretion, and sustaining star formation for ∼100 Gyr or more in the outer regions with no qualitative change in gas stability or molecular cloud properties. The ULIRG track follows from high densities in galaxy collisions.« less

New science from the phase space of old stellar systems

NASA Astrophysics Data System (ADS)

Varri, Anna Lisa; Breen, Philip G.; Heggie, Douglas C.; Tiongco, Maria; Vesperini, Enrico

2017-06-01

Our traditional interpretative picture of the internal dynamics of globular clusters has been recently revolutionized by a series of discoveries about their chemical, structural, and kinematic properties. The empirical evidence that their velocity space is much more complex than usually expected encourages us to use them as refreshingly novel phase space laboratories for some long-forgotten aspects of collisional gravitational dynamics. Such a realization, coupled with the discovery that the stars in clusters were not all born at once in a single population, makes them new, challenging chemodynamical puzzles.Thanks to the proper motions of thousands of stars that will be available from the Gaia mission, we are about to enter a new ''golden age'' for the study of the dynamics of this class of stellar systems, as the full phase space of several Galactic globular clusters will be soon unlocked for the first time. In this context, I will present the highlights of a more realistic dynamical paradigm for these intriguing stellar systems, with emphasis on the role of angular momentum, velocity anisotropy and external tidal field. Such a fundamental understanding of the emerging phase space complexity of globulars will allow us to address many open questions about their rich dynamical evolution, their elusive stellar populations and putative black holes, and their role within the history of our Galaxy.

Galactic bulge population II Cepheids in the VVV survey: period-luminosity relations and a distance to the Galactic centre

NASA Astrophysics Data System (ADS)

Bhardwaj, A.; Rejkuba, M.; Minniti, D.; Surot, F.; Valenti, E.; Zoccali, M.; Gonzalez, O. A.; Romaniello, M.; Kanbur, S. M.; Singh, H. P.

2017-09-01

Context. Multiple stellar populations of different ages and metallicities reside in the Galactic bulge that trace its structure and provide clues to its formation and evolution. Aims: We present the near-infrared observations of population II Cepheids in the Galactic bulge from VISTA Variables in the Vía Láctea (VVV) survey. The JHKs photometry together with optical data from Optical Gravitational Lensing Experiment (OGLE) survey provide an independent estimate of the distance to the Galactic centre. The old, metal-poor and low-mass population II Cepheids are also investigated as useful tracers for the structure of the Galactic bulge. Methods: We identify 340 population II Cepheids in the VVV survey Galactic bulge catalogue based on their match with the OGLE-III Catalogue. The single-epoch JH and multi-epoch Ks observations complement the accurate periods and optical (VI) mean-magnitudes from OGLE. The sample consisting of BL Herculis and W Virginis subtypes is used to derive period-luminosity relations after correcting mean-magnitudes for the extinction. Our Ks-band period-luminosity relation, Ks = -2.189(0.056) [log (P)-1] + 11.187(0.032), is consistent with published work for BL Herculis and W Virginis variables in the Large Magellanic Cloud. Results: We present a combined OGLE-III and VVV catalogue with periods, classification, mean magnitudes, and extinction for 264 Galactic bulge population II Cepheids that have good-quality Ks-band light curves. The absolute magnitudes for population II Cepheids and RR Lyraes calibrated using Gaia and Hubble Space Telescope parallaxes, together with calibrated magnitudes for Large Magellanic Cloud population II Cepheids, are used to obtain a distance to the Galactic centre, R0 = 8.34 ± 0.03(stat.) ± 0.41(syst.), which changes by with different extinction laws. While noting the limitation of small number statistics, we find that the present sample of population II Cepheids in the Galactic bulge shows a nearly spheroidal spatial distribution, similar to metal-poor RR Lyrae variables. We do not find evidence of the inclined bar as traced by the metal-rich red-clump stars. Conclusions: Population II Cepheid and RR Lyrae variables follow similar period-luminosity relations and trace the same metal-poor old population in the Galactic bulge. The number density for population II Cepheids is more limited as compared to abundant RR Lyraes but they are bright and exhibit a wide range in period that provides a robust period-luminosity relation for an accurate estimate of the distance to the Galactic centre. The full Table 1 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/605/A100

Galactic cosmic ray composition

NASA Technical Reports Server (NTRS)

Meyer, J. P.

1986-01-01

An assessment is given of the galactic cosmic ray source (GCRS) elemental composition and its correlation with first ionization potential. The isotopic composition of heavy nuclei; spallation cross sections; energy spectra of primary nuclei; electrons; positrons; local galactic reference abundances; comparison of solar energetic particles and solar coronal compositions; the hydrogen; lead; nitrogen; helium; and germanium deficiency problems; and the excess of elements are among the topics covered.

New detections of embedded clusters in the Galactic halo

NASA Astrophysics Data System (ADS)

Camargo, D.; Bica, E.; Bonatto, C.

2016-09-01

Context. Until recently it was thought that high Galactic latitude clouds were a non-star-forming ensemble. However, in a previous study we reported the discovery of two embedded clusters (ECs) far away from the Galactic plane (~ 5 kpc). In our recent star cluster catalogue we provided additional high and intermediate latitude cluster candidates. Aims: This work aims to clarify whether our previous detection of star clusters far away from the disc represents just an episodic event or whether star cluster formation is currently a systematic phenomenon in the Galactic halo. We analyse the nature of four clusters found in our recent catalogue and report the discovery of three new ECs each with an unusually high latitude and distance from the Galactic disc midplane. Methods: The analysis is based on 2MASS and WISE colour-magnitude diagrams (CMDs), and stellar radial density profiles (RDPs). The CMDs are built by applying a field-star decontamination procedure, which uncovers the cluster's intrinsic CMD morphology. Results: All of these clusters are younger than 5 Myr. The high-latitude ECs C 932, C 934, and C 939 appear to be related to a cloud complex about 5 kpc below the Galactic disc, under the Local arm. The other clusters are above the disc, C 1074 and C 1100 with a vertical distance of ~3 kpc, C 1099 with ~ 2 kpc, and C 1101 with ~1.8 kpc. Conclusions: According to the derived parameters ECs located below and above the disc occur, which gives evidence of widespread star cluster formation throughout the Galactic halo. This study therefore represents a paradigm shift, by demonstrating that a sterile halo must now be understood as a host for ongoing star formation. The origin and fate of these ECs remain open. There are two possibilities for their origin, Galactic fountains or infall. The discovery of ECs far from the disc suggests that the Galactic halo is more actively forming stars than previously thought. Furthermore, since most ECs do not survive the infant mortality, stars may be raining from the halo into the disc, and/or the halo may be harbouring generations of stars formed in clusters like those detected in our survey.

A Complete Census of the ~7000 Milky Way HII Regions

NASA Astrophysics Data System (ADS)

Armentrout, William Paul; Anderson, Loren Dean; Wenger, Trey; Bania, Thomas; Balser, Dana; Dame, Thomas; Dickey, John M.; Dawson, Joanne; Jordan, Christopher H.; McClure-Griffiths, Naomi M.; Andersen, Morten

2018-01-01

HII regions are the archetypical tracers of high-mass star formation. Because of their high luminosities, they can be seen across the entire Galactic disk from mid-infrared to radio wavelengths. A uniformly sensitive survey of Galactic HII regions would allow us to constrain the properties of Galactic structure and star formation. We have cataloged over 8000 HII regions and candidates in the WISE Catalog of Galactic HII Regions (astro.phys.wvu.edu/wise), but only 2000 of these are confirmed HII regions to date.To bring us closer to a complete census of high-mass star formation regions in the Milky Way, we have several ongoing observational campaigns. These efforts include (1) Green Bank Telescope radio recombination line (RRL) observations as part of the HII Region Discovery Survey (HRDS); (2) Australia Telescope Compact Array observations of southern HII region candidates in the Southern HII Region Discovery Survey (SHRDS); (3) Green Bank and Gemini North Telescope observations of star formation regions thought to reside at the edge of the star forming disk in the Outer Scutum-Centaurus Arm (OSC); and (4) Very Large Array continuum observations of the faintest HII region candidates in the second and third Galactic quadrants.Together, these observations will detect the RRL emission from all Galactic HII regions with peak cm-wavelength flux densities > 60mJy, establish the outer edge of Galactic high-mass star formation, and determine the number of HII regions in the Galaxy. The HRDS and SHRDS surveys have more than doubled the known population of Galactic HII regions. We use the OSC observations to determine the properties of high-mass star formation in the extreme outer Galaxy and our VLA observations to determine how many of our faint candidates are indeed HII regions. We combine the completeness limits we obtain through these HII region surveys with an HII region population synthesis model to estimate the total number of Galactic HII regions. From this, we predict nearly 7000 HII regions in the Milky Way created by a central star of type B2 or earlier.

Physics of Gamma Ray Burst Sources

NASA Technical Reports Server (NTRS)

Meszaros, Peter

2004-01-01

During this grant period, the physics of gamma-ray bursts was investigated. A number of new results have emerged. The importance of pair formation in high compactness burst spectra may help explain x-ray flashes; a universal jet shape is a likely explanation for the distribution of jet break times; gravitational waves may be copiously produced both in short bursts from compact mergers and in long bursts arising from collapsars; x-ray iron lines are likely to be due to interaction with the stellar atmosphere of the progenitor; prompt optical flashes from reverse shocks will give diagnostics on the Lorentz factor and the environment; GeV and TeV emission from bursts may be expected in the external shock; etc. The group working with the PI included postdocs Dr. Bing Zhang (now assistant professor at University of Nevada); Dr. Shiho Kobayashi; graduate student Lijun Gou; collaborators Drs. Tim Kallman and Martin Rees. Meszaros shared with Rees and Dr. Bohan Paczynsky the AAS Rossi Prize in 2000 for their work on the theory of gamma ray bursts. The refereed publications and conference proceedings resulting from this research are summarized below. The PI gave a number of invited talks at major conferences, also listed.

GRBs: The Most Distant Signposts in our Universe

NASA Technical Reports Server (NTRS)

Kouveliotou, Chryssa

2007-01-01

Gamma-Ray Bursts (GRBs) are the most powerful photon sources in the Universe, rivaled only by supernovae in the magnitude of their energy release. In 1997 GRB were found to originate in host galaxies at cosmological distances, revealing the total energy of their explosions to be an astounding approx.10(exp 52) - 10(exp 53)ergs. GRB durations span over five orders of magnitude, ranging from milliseconds to thousands of seconds. The underlying sources of the energy release remain, however, unknown. Leading candidates are mergers, either of two neutron stars or of a black hole and a neutron star, and core collapses of very massive stars, called "collapsars". To date the furthest GRB galaxy has been found at a cosmological redshift of 6.29, very close to the most distant quasar (at z=6.4). Since the Swift satellite continues to observe these phenomena at a rate of approx.120 per year, and with the upcoming launch of GLAST with two burst instruments on board, we will be able to use GRBs as beacons to probe very high redshifts. Thus bursts found at 6

Evolution of the polarization of the optical afterglow of the gamma-ray burst GRB030329.

PubMed

Greiner, Jochen; Klose, Sylvio; Reinsch, Klaus; Schmid, Hans Martin; Sari, Re'em; Hartmann, Dieter H; Kouveliotou, Chryssa; Rau, Arne; Palazzi, Eliana; Straubmeier, Christian; Stecklum, Bringfried; Zharikov, Sergej; Tovmassian, Gaghik; Bärnbantner, Otto; Ries, Christoph; Jehin, Emmanuel; Henden, Arne; Kaas, Anlaug A; Grav, Tommy; Hjorth, Jens; Pedersen, Holger; Wijers, Ralph A M J; Kaufer, Andreas; Park, Hye-Sook; Williams, Grant; Reimer, Olaf

2003-11-13

The association of a supernova with GRB030329 strongly supports the 'collapsar' model of gamma-ray bursts, where a relativistic jet forms after the progenitor star collapses. Such jets cannot be spatially resolved because gamma-ray bursts lie at cosmological distances; their existence is instead inferred from 'breaks' in the light curves of the afterglows, and from the theoretical desire to reduce the estimated total energy of the burst by proposing that most of it comes out in narrow beams. Temporal evolution of the polarization of the afterglows may provide independent evidence for the jet structure of the relativistic outflow. Small-level polarization ( approximately 1-3 per cent) has been reported for a few bursts, but its temporal evolution has yet to be established. Here we report polarimetric observations of the afterglow of GRB030329. We establish the polarization light curve, detect sustained polarization at the per cent level, and find significant variability. The data imply that the afterglow magnetic field has a small coherence length and is mostly random, probably generated by turbulence, in contrast with the picture arising from the high polarization detected in the prompt gamma-rays from GRB021206 (ref. 18).

Dynamical analysis of bounded and unbounded orbits in a generalized Hénon-Heiles system

NASA Astrophysics Data System (ADS)

Dubeibe, F. L.; Riaño-Doncel, A.; Zotos, Euaggelos E.

2018-04-01

The Hénon-Heiles potential was first proposed as a simplified version of the gravitational potential experimented by a star in the presence of a galactic center. Currently, this system is considered a paradigm in dynamical systems because despite its simplicity exhibits a very complex dynamical behavior. In the present paper, we perform a series expansion up to the fifth-order of a potential with axial and reflection symmetries, which after some transformations, leads to a generalized Hénon-Heiles potential. Such new system is analyzed qualitatively in both regimes of bounded and unbounded motion via the Poincaré sections method and plotting the exit basins. On the other hand, the quantitative analysis is performed through the Lyapunov exponents and the basin entropy, respectively. We find that in both regimes the chaoticity of the system decreases as long as the test particle energy gets far from the critical energy. Additionally, we may conclude that despite the inclusion of higher order terms in the series expansion, the new system shows wider zones of regularity (islands) than the ones present in the Hénon-Heiles system.

THE DYNAMICAL RELATIONSHIP BETWEEN THE BAR AND SPIRAL PATTERNS OF NGC 1365

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

Speights, Jason C.; Rooke, Paul C., E-mail: jcspeights@frostburg.edu

2016-07-20

Theories that attempt to explain the dynamical relationship between bar and spiral patterns in galactic disks make different predictions about the radial profile of the pattern speed. These are tested for the H-alpha bar and spiral patterns of NGC 1365. The radial profile of the pattern speed is measured by fitting mathematical models that are based on the Tremaine–Weinberg method. The results show convincing evidence for the bar rotating at a faster rate than the spiral pattern, inconsistent with a global wave mode or a manifold. There is evidence for mode coupling of the bar and spiral patterns at themore » overlap of corotation and inner Lindblad resonances (ILRs), but the evidence is unreliable and inconsistent. The results are the most consistent with the bar and spiral patterns being dynamically distinct features. The pattern speed of the bar begins near an ILR and ends near the corotation resonance (CR). The radial profile of the pattern speed beyond the bar most closely resembles what is expected for coupled spiral modes and tidal interactions.« less

The effect of host cluster gravitational tidal forces on the internal dynamics of spiral galaxies

NASA Astrophysics Data System (ADS)

Mayer, Alexander

2013-04-01

New empirical observation by Bidin, Carraro, Mendez & Smith finds ``a lack of dark matter in the Solar neighborhood" (2012 ApJ 751, 30). This, and the discovery of a vast polar structure of Milky Way satellites by Pawlowski, Pflamm-Altenburg & Kroupa (2012 MNRAS 423, 1109), conflict with the prevailing interpretation of the measured Galactic rotation curve. Simulating the dynamical effects of host cluster tidal forces on galaxy disks reveals radial migration in a spiral structure and an orbital velocity that accelerates with increasing galactocentric radial coordinate. A virtual ``toy model,'' which is based on an Earth-orbiting system of particles and is physically realizable in principle, is available at GravitySim.net. Given the perturbing gravitational effect of the host cluster on a spiral galaxy disk and that a similar effect does not exist for the Solar System, the two systems represent distinct classes of gravitational dynamical systems. The observed `flat' and accelerating rotation curves of spiral galaxies can be attributed to gravitational interaction with the host cluster; no `dark matter halo' is required to explain the observable.

Resolving the structure of the Galactic foreground using Herschel measurements and the Kriging technique

NASA Astrophysics Data System (ADS)

Pinter, S.; Bagoly, Z.; Balázs, L. G.; Horvath, I.; Racz, I. I.; Zahorecz, S.; Tóth, L. V.

2018-05-01

Investigating the distant extragalactic Universe requires a subtraction of the Galactic foreground. One of the major difficulties deriving the fine structure of the galactic foreground is the embedded foreground and background point sources appearing in the given fields. It is especially so in the infrared. We report our study subtracting point sources from Herschel images with Kriging, an interpolation method where the interpolated values are modelled by a Gaussian process governed by prior covariances. Using the Kriging method on Herschel multi-wavelength observations the structure of the Galactic foreground can be studied with much higher resolution than previously, leading to a better foreground subtraction at the end.

The galactic distribution of carbon monoxide: An out-of-plane survey. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Cohen, R. S.

1978-01-01

Galactic CO line emission at 115 GHz has been surveyed. This survey confirms the finding that CO is concentrated in a ring. It provides a determination of the thickness of this molecular ring as a function of galactic radius and shows that CO is displaced from the conventional galactic plane. These results were arrived at by least-squares fitting the survey data to a circularly symmetric model of the Galaxy. A comparison of the CO and HI distributions shows that there are marked differences in the distributions of these species, both radially and out of the plane. A detailed discussion of the antenna characteristics, including the radiation pattern and pointing characteristics is presented.

Pitch angle of galactic spiral arms

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

Michikoshi, Shugo; Kokubo, Eiichiro, E-mail: michiko@mail.doshisha.ac.jp, E-mail: kokubo@th.nao.ac.jp

2014-06-01

One of the key parameters that characterizes spiral arms in disk galaxies is a pitch angle that measures the inclination of a spiral arm to the direction of galactic rotation. The pitch angle differs from galaxy to galaxy, which suggests that the rotation law of galactic disks determines it. In order to investigate the relation between the pitch angle of spiral arms and the shear rate of galactic differential rotation, we perform local N-body simulations of pure stellar disks. We find that the pitch angle increases with the epicycle frequency and decreases with the shear rate and obtain the fittingmore » formula. This dependence is explained by the swing amplification mechanism.« less

Propagation of Galactic cosmic rays: the influence of anisotropic diffusion

NASA Astrophysics Data System (ADS)

AL-Zetoun, A.; Achterberg, A.

2018-06-01

We consider the anisotropic diffusion of cosmic rays in the large-scale Galactic magnetic field, where diffusion along the field and diffusion across the field proceeds at different rates. To calculate this diffusion, we use stochastic differential equations to describe the cosmic ray propagation, solving these numerically. The Galactic magnetic field is described using the Jansson-Farrar model for the Galactic magnetic field. In this paper, we study the influence of perpendicular diffusion on the residence time of cosmic rays in the Galaxy. This provides an estimate for the influence of anisotropic diffusion on the residence time and the amount of matter (grammage) that a typical cosmic ray traverses during its residence in the Galaxy.

Galactic Cosmic-ray Transport in the Global Heliosphere: A Four-Dimensional Stochastic Model

NASA Astrophysics Data System (ADS)

Florinski, V.

2009-04-01

We study galactic cosmic-ray transport in the outer heliosphere and heliosheath using a newly developed transport model based on stochastic integration of the phase-space trajectories of Parker's equation. The model employs backward integration of the diffusion-convection transport equation using Ito calculus and is four-dimensional in space+momentum. We apply the model to the problem of galactic proton transport in the heliosphere during a negative solar minimum. Model results are compared with the Voyager measurements of galactic proton radial gradients and spectra in the heliosheath. We show that the heliosheath is not as efficient in diverting cosmic rays during solar minima as predicted by earlier two-dimensional models.

The distances of the Galactic Novae

NASA Astrophysics Data System (ADS)

Ozdonmez, Aykut; Guver, Tolga; Cabrera-Lavers, Antonio; Ak, Tansel

2016-07-01

Using location of the RC stars on the CMDs obtained from the UKIDSS, VISTA and 2MASS photometry, we have derived the reddening-distance relations towards each Galactic nova for which at least one independent reddening measurement exists. We were able to determine the distances of 72 Galactic novae and set lower limits on the distances of 45 systems. The reddening curves of the systems are presented. These curves can be also used to estimate reddening or the distance of any source, whose location is close to the position of the nova in our sample. The distance measurement method in our study can be easily applicable to any source, especially for ones that concentrated along the Galactic plane.

Search for Gamma-Ray Emission from Galactic Novae using Fermi-LAT Pass 8

NASA Astrophysics Data System (ADS)

Buson, Sara; Franckowiak, Anna; Cheung, Teddy; Jean, Pierre; Fermi-LAT Collaboration

2016-01-01

Recently Galactic novae have been identified as a new class of GeV gamma-ray emitters, with 6 detected so far with the Fermi Large Area Telescope (Fermi-LAT) data. Based on optical observations we have compiled a catalog of ~70 Galactic novae, which peak (in optical) during the operations of the Fermi mission. Based on the properties of known gamma-ray novae we developed a search procedure that we apply to all novae in the catalog to detect these slow transient sources or set flux upper limits using the Fermi-LAT Pass 8 data set. This is the first time a large sample of Galactic novae has been uniformly studied.

Parameter estimation accuracies of Galactic binaries with eLISA

NASA Astrophysics Data System (ADS)

Błaut, Arkadiusz

2018-09-01

We study parameter estimation accuracy of nearly monochromatic sources of gravitational waves with the future eLISA-like detectors. eLISA will be capable of observing millions of such signals generated by orbiting pairs of compact binaries consisting of white dwarf, neutron star or black hole and to resolve and estimate parameters of several thousands of them providing crucial information regarding their orbital dynamics, formation rates and evolutionary paths. Using the Fisher matrix analysis we compare accuracies of the estimated parameters for different mission designs defined by the GOAT advisory team established to asses the scientific capabilities and the technological issues of the eLISA-like missions.

Biological Bases of Space Radiation Risk

NASA Technical Reports Server (NTRS)

1997-01-01

In this session, Session JP4, the discussion focuses on the following topics: Hematopoiesis Dynamics in Irradiated Mammals, Mathematical Modeling; Estimating Health Risks in Space from Galactic Cosmic Rays; Failure of Heavy Ions to Affect Physiological Integrity of the Corneal Endothelial Monolayer; Application of an Unbiased Two-Gel CDNA Library Screening Method to Expression Monitoring of Genes in Irradiated Versus Control Cells; Detection of Radiation-Induced DNA Strand Breaks in Mammalian Cells By Enzymatic Post-Labeling; Evaluation of Bleomycin-Induced Chromosome Aberrations Under Microgravity Conditions in Human Lymphocytes, Using "Fish" Techniques; Technical Description of the Space Exposure Biology Assembly Seba on ISS; and Cytogenetic Research in Biological Dosimetry.

HST update - Science amid setbacks

NASA Astrophysics Data System (ADS)

Fienberg, Richard T.

1991-09-01

Recent data obtained from the Hubble Space Telescope (HST) are presented that indicate that the mission of the beleagered telescope has reached a turning point. Among these observations is a spectrogram revealing the complex dynamic structure of the Beta Pictoris's gas disk, the Lyman-alpha lines from clouds of cool hydrogen atoms in the Milky Way, the UV spectrum of Chi Lupi, the images of Eta Carinae and the Homunculus nebula ejected by the star during the 1843 outburst, and the structure of energetic jets from active galactic nuclei. The paper discusses corrective measures planned by the NASA and Hubble project astronomers to restore the observatory to near-perfect health.

Unstable spiral modes in disk-shaped galaxies

PubMed Central

Lau, Y. Y.; Lin, C. C.; Mark, James W.-K.

1976-01-01

The mechanisms for the maintenance and the excitation of trailing spiral modes of density waves in diskshaped galaxies, as proposed by Lin in 1969 and by Mark recently, are substantiated by an analysis of the gas-dynamical model of the galaxy. The self-excitation of the unstable mode in caused by waves propagating outwards from the corotation circle, which carry away angular momentum of a sign opposite to that contained in the wave system inside that circle. Specifically, a simple dispersion relationship is given as a definite integral, which allows the immediate determination of the pattern frequency and the amplification rate, once the basic galactic model is known. PMID:16592313

Beyond Pluto: The Search for the Edge of the Solar System

ScienceCinema

Funsten, Herb

2018-01-16

In July, we finally visited the last major body of our solar system, Pluto. But what lies beyond? The stellar wind from our Sun forms an enormous bubble in interstellar space. This “sphere of our Sun,” or heliosphere, extends far beyond Pluto and forms a protective cocoon that shields us from cosmic radiation. In this talk, we will travel to the edge of the solar system, peer into the structure and dynamics of the outer heliosphere as it interacts with the interstellar medium and anticipate the future of the solar system as it moves through our galactic neighborhood.

Physical conditions, dynamics, and mass distribution in the center of the Galaxy

NASA Technical Reports Server (NTRS)

Genzel, R.; Townes, C. H.

1987-01-01

Recent observations and theoretical models of the Galactic center (GC) are reviewed. An overview of phenomena seen in the GC is given, including the stellar cluster, radio continuum emission and interstellar clouds, the Sgr A complex, and X-ray and gamma emission. Also discussed are the energetics and physical conditions in the central 4 pc (star burst or central source?); the circumnuclear ring, ionized streamers, and relativistic and hot gas in the cavity; the mass distribution and the possibility of a massive black hole, and the central 0.1 pc (Sgr A and IRS 16). Diagrams, graphs, photographs, and tables of numerical data are provided.

A Catalog of Molecular Clouds in the Milky Way Galaxy

NASA Astrophysics Data System (ADS)

Wahl, Matthew; Koda, J.

2010-01-01

We have created a complete catalog of molecular clouds in the Milky Way Galaxy. This is an extension of our previous study (Koda et al. 2006) which used a preliminary data set from The Boston University Five College Radio Astronomy Observatory Galactic Ring Survey (BUFCRAO GRS). This work is of the complete data set from this GRS. The data covers the inner part of the northern Galactic disk between galactic longitudes 15 to 56 degrees, galactic latitudes -1.1 to 1.1 degrees, and the entire Galactic velocities. We used the standard cloud identification method. This method searches the data cube for a peak in temperature above a specified value, and then searches around that peak in all directions until the extents of the cloud are found. This method is iterated until all clouds are found. We prefer this method over other methods, because of its simplicity. The properties of our molecular clouds are very similar to those based on a more evolved method (Rathborne et al. 2009).

Molecular diagnostics of Galactic star-formation regions

NASA Astrophysics Data System (ADS)

Loenen, Edo; Baan, Willem; Spaans, Marco

2007-10-01

We propose a sensitive spectral survey of Galactic star-formation regions. Using the broadband correlator at two different frequencies, we expect to detect the (1-0) transition of CO, CN, HNC, HCN, HCO+, and HCO and various of their isotopes lines, as well as the (12-11) and (10-9) transitions of HC3N. The purpose of these observations is to create a consistent (public) database of molecular emission from galactic star-formation regions. The data will be interpreted using extensive physical and chemical modeling of the whole ensemble of lines, in order to get an accurate description of the molecular environment of these regions. In particular, this diagnostic approach will describe the optical depths, the densities, and the radiation fields in the medium and will allow the establishment of dominant temperature gradients. These observations are part of a program to study molecular emission on all scales, going from individual Galactic star-formation regions, through resolved nearby galaxies, to unresolved extra-galactic emission.

Impact of Distance Determinations on Galactic Structure. I. Young and Intermediate-Age Tracers

NASA Astrophysics Data System (ADS)

Matsunaga, Noriyuki; Bono, Giuseppe; Chen, Xiaodian; de Grijs, Richard; Inno, Laura; Nishiyama, Shogo

2018-06-01

Here we discuss impacts of distance determinations on the Galactic disk traced by relatively young objects. The Galactic disk, ˜40 kpc in diameter, is a cross-road of studies on the methods of measuring distances, interstellar extinction, evolution of galaxies, and other subjects of interest in astronomy. A proper treatment of interstellar extinction is, for example, crucial for estimating distances to stars in the disk outside the small range of the solar neighborhood. We'll review the current status of relevant studies and discuss some new approaches to the extinction law. When the extinction law is reasonably constrained, distance indicators found in today and future surveys are telling us stellar distribution and more throughout the Galactic disk. Among several useful distance indicators, the focus of this review is Cepheids and open clusters (especially contact binaries in clusters). These tracers are particularly useful for addressing the metallicity gradient of the Galactic disk, an important feature for which comparison between observations and theoretical models can reveal the evolution of the disk.

The Southern HII Region Discovery Survey: The Bright Catalog

NASA Astrophysics Data System (ADS)

Wenger, Trey V.; Dickey, John M.; Jordan, Christopher H.; Balser, Dana; Armentrout, William Paul; Anderson, Loren; Bania, Thomas; Dawson, Joanne; McClure-Griffiths, Naomi M.; Shea, Jeanine

2018-01-01

HII regions, the zones of ionized gas surrounding recently formed high-mass stars, are the archetypical tracers of Galactic structure. The census of Galactic HII regions in the Southern sky is vastly incomplete due to a lack of sensitive radio recombination line (RRL) surveys. The Southern HII Region Discovery Survey (SHRDS) is a 900-hour Australia Telescope Compact Array cm-wavelength RRL and continuum emission survey of hundreds of third and fourth quadrant Galactic HII region candidates. These candidates are identified in the Widefield Infrared Survey Explorer (WISE) Catalog of Galactic HII Regions based on coincident 10 micron (WISE) and 20 cm (Southern Galactic Plane Survey) emission. The SHRDS is an extension of HII Region Discovery Surveys in the Northern sky with the Green Bank Telescope and Arecibo Telescope which discovered ~800 new HII regions. In the first 500 hours of the SHRDS, we targeted the 249 brightest HII region candidates and 33 previously known HII regions. We discuss the data reduction, analysis, and preliminary results from this first stage of the survey.

Fine structure of Galactic foreground ISM towards high-redshift AGN - utilizing Herschel PACS and SPIRE data

NASA Astrophysics Data System (ADS)

Perger, K.; Pinter, S.; Frey, S.; Tóth, L. V.

2018-05-01

One of the most certain ways to determine star formation rate in galaxies is based on far infrared (FIR) measurements. To decide the origin of the observed FIR emission, subtracting the Galactic foreground is a crucial step. We utilized Herschel photometric data to determine the hydrogen column densities in three galactic latitude regions, at b = 27°, 50° and -80°. We applied a pixel-by-pixel fit to the spectral energy distribution (SED) for the images aquired from parallel PACS-SPIRE observations in all three sky areas. We determined the column densities with resolutions 45'' and 6', and compared the results with values estimated from the IRAS dust maps. Column densities at 27° and 50° galactic latitudes determined from the Herschel data are in a good agreement with the literature values. However, at the highest galactic latitude we found that the column densities from the Herschel data exceed those derived from the IRAS dust map.

The GALAH Survey and Galactic Archaeology in the Next Decade

NASA Astrophysics Data System (ADS)

Martell, S. L.

2016-10-01

The field of Galactic Archaeology aims to understand the origins and evolution of the stellar populations in the Milky Way, as a way to understand galaxy formation and evolution in general. The GALAH (Galactic Archaeology with HERMES) Survey is an ambitious Australian-led project to explore the Galactic history of star formation, chemical evolution, minor mergers and stellar migration. GALAH is using the HERMES spectrograph, a novel, highly multiplexed, four-channel high-resolution optical spectrograph, to collect high-quality R˜28,000 spectra for one million stars in the Milky Way. From these data we will determine stellar parameters, radial velocities and abundances for up to 29 elements per star, and carry out a thorough chemical tagging study of the nearby Galaxy. There are clear complementarities between GALAH and other ongoing and planned Galactic Archaeology surveys, and also with ancillary stellar data collected by major cosmological surveys. Combined, these data sets will provide a revolutionary view of the structure and history of the Milky Way.

Consistency between the luminosity function of resolved millisecond pulsars and the galactic center excess

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

Ploeg, Harrison; Gordon, Chris; Crocker, Roland

Fermi Large Area Telescope data reveal an excess of GeV gamma rays from the direction of the Galactic Center and bulge. Several explanations have been proposed for this excess including an unresolved population of millisecond pulsars (MSPs) and self-annihilating dark matter. It has been claimed that a key discriminant for or against the MSP explanation can be extracted from the properties of the luminosity function describing this source population. Specifically, is the luminosity function of the putative MSPs in the Galactic Center consistent with that characterizing the resolved MSPs in the Galactic disk? To investigate this we have used amore » Bayesian Markov Chain Monte Carlo to evaluate the posterior distribution of the parameters of the MSP luminosity function describing both resolved MSPs and the Galactic Center excess. At variance with some other claims, our analysis reveals that, within current uncertainties, both data sets can be well fit with the same luminosity function.« less

The Milky Way, the Galactic halo, and the Halos of Galaxies

NASA Astrophysics Data System (ADS)

Gerhard, Ortwin

2015-08-01

The Milky Way, "our" Galaxy, is currently the subject of intense study with many ground-based surveys, in anticipation of upcoming results from the GAIA mission. From this work we have been learning about the full three-dimensional structure of the Galactic box/peanut bulge, the distribution of stars in the bar and disk, and the many streams in the Galactic halo. The data tell us that most of the Galactic bulge formed from the disk, and that a large fraction of the Galactic halo has been accreted from outside. Similarly, in many external galaxy halos there is now evidence for tidal streams and accretion of satellites. To see these features requires exquisite data - mostly very deep photometry, but some halo substructures have also been found with kinematic data. These observations illustrate how galaxy halos are still growing, and sometimes can be used to "time" the accretion events. In comparison with cosmological simulations, the structure of galaxy halos gives us a vivid illustration of the hierarchical nature of our Universe.

Determination of Galactic Aberration from VLBI Measurements and Its Effect on VLBI Reference Frames and Earth Orientation Parameters.

NASA Astrophysics Data System (ADS)

MacMillan, D. S.

2014-12-01

Galactic aberration is due to the motion of the solar system barycenter around the galactic center. It results in a systematic pattern of apparent proper motion of radio sources observed by VLBI. This effect is not currently included in VLBI analysis. Estimates of the size of this effect indicate that it is important that this secular aberration drift be accounted for in order to maintain an accurate celestial reference frame and allow astrometry at the several microarcsecond level. Future geodetic observing systems are being designed to be capable of producing a future terrestrial reference frame with an accuracy of 1 mm and stability of 0.1 mm/year. We evaluate the effect galactic aberration on attaining these reference frame goals. This presentation will discuss 1) the estimation of galactic aberration from VLBI data and 2) the effect of aberration on the Terrestrial and Celestial Reference Frames and the Earth Orientation Parameters that connect these frames.

On Al-26 and other short-lived interstellar radioactivity

NASA Technical Reports Server (NTRS)

Clayton, Donald D.; Hartmann, Dieter H.; Leising, Mark D.

1993-01-01

Several authors have shown that massive stars exploding at a rate of about three per century can account for a large portion, if not all, of the observed interstellar Al-26. In a separate argument using models of Galactic chemical evolution, Clayton (1984) showed that the Al-26/Al-27 production ratio was not large enough to maintain enough Al-26 in the Galactic disk gas of about 10 exp 10 solar masses having solar composition. We present a resolution of those conflicting arguments. A past history of Galactic infall growing the Galactic disk so dilutes the stable Al-27 concentration that the two approaches can be brought into near agreement. If massive stars dominate the production of Al-26, we suggest that the apparent shortfall of their Al-26/Al-27 yield ratio is to be interpreted as evidence for significant growth of the Galactic disk. We also discuss the implications of these arguments for other extinct radioactivities in meteorites, using I-129 and Sm-146 as examples.

Metallic Winds in Dwarf Galaxies

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

Robles-Valdez, F.; Rodríguez-González, A.; Hernández-Martínez, L.

2017-02-01

We present results from models of galactic winds driven by energy injected from nuclear (at the galactic center) and non-nuclear starbursts. The total energy of the starburst is provided by very massive young stellar clusters, which can push the galactic interstellar medium and produce an important outflow. Such outflow can be a well or partially mixed wind, or a highly metallic wind. We have performed adiabatic 3D N -Body/Smooth Particle Hydrodynamics simulations of galactic winds using the gadget-2 code. The numerical models cover a wide range of parameters, varying the galaxy concentration index, gas fraction of the galactic disk, andmore » radial distance of the starburst. We show that an off-center starburst in dwarf galaxies is the most effective mechanism to produce a significant loss of metals (material from the starburst itself). At the same time, a non-nuclear starburst produces a high efficiency of metal loss, in spite of having a moderate to low mass loss rate.« less

The black hole at the Galactic Center: observations and models in a nutshell

NASA Astrophysics Data System (ADS)

Zakharov, Alexander

2017-12-01

The Galactic Center (Sgr A*) is a peculiar place in our Galaxy (Milky Way). Our Solar system is located at a distance around 8 kpc from the Galactic Center (GC). There were a number of different including exotic ones such as boson stars, fermion balls, neutrino balls, a cluster of neutron stars. Some of these models are significantly constrained with consequent observations and now supermassive black hole with mass around 4 × 106 M ⊙ is the preferable model for GC. Moreover, one can test alternative theories of gravity with observations of bright stars near the Galactic Center and and observations of bright structures near the black hole at the Galactic Center to reconstruct shadow structure around the black hole with current and future observational VLBI facilities such as the Event Horizon Telescope. In particular, we got a graviton mass constraint which is comparable and consistent with constraints obtained recently by the LIGO-Virgo collaboration.

Primary gamma rays. [resulting from cosmic ray interaction with interstellar matter

NASA Technical Reports Server (NTRS)

Fichtel, C. E.

1974-01-01

Within this galaxy, cosmic rays reveal their presence in interstellar space and probably in source regions by their interactions with interstellar matter which lead to gamma rays with a very characteristic energy spectrum. From the study of the intensity of the high energy gamma radiation as a function of galactic longitude, it is already clear that cosmic rays are almost certainly not uniformly distributed in the galaxy and are not concentrated in the center of the galaxy. The galactic cosmic rays appear to be tied to galactic structural features, presumably by the galactic magnetic fields which are in turn held by the matter in the arm segments and the clouds. On the extragalactic scale, it is now possible to say that cosmic rays are not universal at the density seen near the earth. The diffuse celestial gamma ray spectrum that is observed presents the interesting possibility of cosmological studies and possible evidence for a residual universal cosmic ray density, which is much lower than the present galactic cosmic ray density.

The DECam Plane Survey: Optical photometry of two billion objects in the southern Galactic plane

NASA Astrophysics Data System (ADS)

Schlafly, Edward; Green, Gregory M.; Lang, Dustin; Daylan, Tansu; Finkbeiner, Douglas; Lee, Albert; Meisner, Aaron; Schlegel, David; Valdes, Francisco

2018-01-01

The DECam Plane Survey is a five-band optical and near-infrared survey of the southern Galactic plane with the Dark Energy Camera at Cerro Tololo. The survey is designed to reach past the main-sequence turn-off at the distance of the Galactic center through a reddening E(B-V) of 1.5 mag. Typical single-exposure depths are 23.7, 22.8, 22.3, 21.9, and 21.0 mag in the grizY bands, with seeing around 1 arcsecond. The footprint covers the Galactic plane with |b| < 4°, 5° > l > -120°. The survey pipeline simultaneously solves for the positions and fluxes of tens of thousands of sources in each image, delivering positions and fluxes of roughly two billion stars with better than 10 mmag precision. Most of these objects are highly reddened and deep in the Galactic disk, probing the structure and properties of the Milky Way and its interstellar medium. The full survey is publicly available.

The Large Scale Structure of the Galactic Magnetic Field and High Energy Cosmic Ray Anisotropy

NASA Astrophysics Data System (ADS)

Alvarez-Muñiz, Jaime; Stanev, Todor

2006-10-01

Measurements of the magnetic field in our Galaxy are complex and usually difficult to interpret. A spiral regular field in the disk is favored by observations, however the number of field reversals is still under debate. Measurements of the parity of the field across the Galactic plane are also very difficult due to the presence of the disk field itself. In this work we demonstrate that cosmic ray protons in the energy range 1018 to 1019eV, if accelerated near the center of the Galaxy, are sensitive to the large scale structure of the Galactic Magnetic Field (GMF). In particular if the field is of even parity, and the spiral field is bi-symmetric (BSS), ultra high energy protons will predominantly come from the Southern Galactic hemisphere, and predominantly from the Northern Galactic hemisphere if the field is of even parity and axi-symmetric (ASS). There is no sensitivity to the BSS or ASS configurations if the field is of odd parity.

Fermi Large Area Telescope Measurements of the Diffuse Gamma-Ray Emission at Intermediate Galactic Latitudes

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

Abdo, A.A.; /Naval Research Lab, Wash., D.C.; Ackermann, M.

The diffuse galactic {gamma}-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess {gamma}-ray emission {ge}1 GeV relative to diffuse galactic {gamma}-ray emission models consistent with directly measured CR spectra (the so-called 'EGRET GeV excess'). The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse {gamma}-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements for energies 100 MeV to 10 GeV and galactic latitudes 10{sup o}more » {le} |b| {le} 20{sup o}. The LAT spectrum for this region of the sky is well reproduced by a diffuse galactic {gamma}-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.« less

Fermi Large Area Telescope Measurements of the Diffuse Gamma-Ray Emission at Intermediate Galactic Latitudes

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2009-12-16

We report that the diffuse galactic γ-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess γ-ray emission ≳1 GeV relative to diffuse galactic γ-ray emission models consistent with directly measured CR spectra (the so-called “EGRET GeV excess”). The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse γ -ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements for energies 100 MeV to 10 GeV andmore » galactic latitudes 10° ≤ | b | ≤ 20°. Finally, the LAT spectrum for this region of the sky is well reproduced by a diffuse galactic γ-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.« less

Fermi large area telescope measurements of the diffuse gamma-ray emission at intermediate galactic latitudes.

PubMed

Abdo, A A; Ackermann, M; Ajello, M; Anderson, B; Atwood, W B; Axelsson, M; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Baughman, B M; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cecchi, C; Charles, E; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Dereli, H; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; Di Bernardo, G; Dormody, M; do Couto e Silva, E; Drell, P S; Dubois, R; Dumora, D; Edmonds, Y; Farnier, C; Favuzzi, C; Fegan, S J; Focke, W B; Frailis, M; Fukazawa, Y; Funk, S; Fusco, P; Gaggero, D; Gargano, F; Gehrels, N; Germani, S; Giebels, B; Giglietto, N; Giordano, F; Glanzman, T; Godfrey, G; Grenier, I A; Grondin, M-H; Grove, J E; Guillemot, L; Guiriec, S; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Hughes, R E; Jóhannesson, G; Johnson, A S; Johnson, R P; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knödlseder, J; Kocian, M L; Kuehn, F; Kuss, M; Lande, J; Latronico, L; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Mazziotta, M N; McConville, W; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Nuss, E; Ohsugi, T; Okumura, A; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Panetta, J H; Parent, D; Pelassa, V; Pepe, M; Pesce-Rollins, M; Piron, F; Porter, T A; Rainò, S; Rando, R; Razzano, M; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Rodriguez, A Y; Roth, M; Ryde, F; Sadrozinski, H F-W; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Sellerholm, A; Sgrò, C; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Stecker, F W; Striani, E; Strickman, M S; Strong, A W; Suson, D J; Tajima, H; Takahashi, H; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Uchiyama, Y; Usher, T L; Vasileiou, V; Vilchez, N; Vitale, V; Waite, A P; Wang, P; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M

2009-12-18

The diffuse galactic gamma-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess gamma-ray emission greater, > or approximately equal to 1 GeV relative to diffuse galactic gamma-ray emission models consistent with directly measured CR spectra (the so-called "EGRET GeV excess"). The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse gamma-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements for energies 100 MeV to 10 GeV and galactic latitudes 10 degrees < or = |b| < or = 20 degrees. The LAT spectrum for this region of the sky is well reproduced by a diffuse galactic gamma-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.

Polarization of the diffuse galactic light.

NASA Technical Reports Server (NTRS)

Sparrow, J. G.; Ney, E. P.

1972-01-01

Polarization measurements made from the satellite OSO-5 show that the polarized intensity in the direction of the Scutum arm of the Galaxy is different in intensity and direction of the polarization from that observed due to the zodiacal light. The observations are consistent with polarized diffuse galactic light superposed on the zodiacal light. The results are interpreted in terms of a model in which the galactic starlight is scattered by interstellar dust.

AGILE detection of prolonged gamma-ray emission from the Galactic Nova ASASSN-18fv

NASA Astrophysics Data System (ADS)

Piano, G.; Lucarelli, F.; Pittori, C.; Verrecchia, F.; Tavani, M.; Bulgarelli, A.; Parmiggiani, N.; Cardillo, M.; Ursi, A.; Minervini, G.; Donnarumma, I.; Vercellone, S.; Fioretti, V.; Pilia, M.; Gianotti, F.; Trifoglio, M.; Giuliani, A.; Mereghetti, S.; Caraveo, P.; Perotti, F.; Chen, A.; Argan, A.; Costa, E.; Del Monte, E.; Evangelista, Y.; Feroci, M.; Lazzarotto, F.; Lapshov, I.; Pacciani, L.; Soffitta, P.; Sabatini, S.; Vittorini, V.; Pucella, G.; Rapisarda, M.; Di Cocco, G.; Fuschino, F.; Galli, M.; Labanti, C.; Marisaldi, M.; Pellizzoni, A.; Trois, A.; Barbiellini, G.; Vallazza, E.; Longo, F.; Morselli, A.; Picozza, P.; Prest, M.; Lipari, P.; Zanello, D.; Cattaneo, P. W.; Rappoldi, A.; Ferrari, A.; Colafrancesco, S.; Paoletti, F.; Antonelli, A.; Giommi, P.; Salotti, L.; Valentini, G.; D'Amico, F.

2018-04-01

AGILE detected intense gamma-ray emission above 100 MeV from a source at Galactic coordinates (l, b) = (287.08, -1.08) +/- 0.6 deg (68% stat. c.l.) +/- 0.1 deg (syst.) (R.A., Dec. = 159.94, -59.84 deg, J2000), positionally consistent with the Galactic Nova ASASSN-18fv, previously reported in a gamma-ray flaring state by Fermi-LAT (ATel #11546).

A Search for Extraterrestrial Intelligence (SETI) toward the Galactic Anticenter with the Murchison Widefield Array

NASA Astrophysics Data System (ADS)

Tingay, S. J.; Tremblay, C. D.; Croft, S.

2018-03-01

Following the results of the first systematic modern low-frequency search for extraterrestrial intelligence using the Murchison Widefield Array (MWA), which was directed toward a Galactic Center field, we report a second survey toward a Galactic Anticenter field. Using the MWA in the frequency range 99–122 MHz over a three-hour period, a 625 deg2 field centered on Orion KL (in the general direction of the Galactic Anticenter) was observed with a frequency resolution of 10 kHz. Within this field, 22 exoplanets are known. At the positions of these exoplanets, we searched for narrowband signals consistent with radio transmissions from intelligent civilizations. No such signals were found with a 5σ detection threshold. Our sample is significantly different to the 45 exoplanets previously studied with the MWA toward the Galactic Center, since the Galactic Center sample is dominated by exoplanets detected using microlensing, and hence at much larger distances than the exoplanets toward the Anticenter, found via radial velocity and transit detection methods. Our average effective sensitivity to extraterrestrial transmitter power is therefore much improved for the Anticenter sample. Added to this, our data processing techniques have improved, reducing our observational errors, leading to our best detection limit being reduced by approximately a factor of four compared to our previously published results.

Introducing CGOLS: The Cholla Galactic Outflow Simulation Suite

NASA Astrophysics Data System (ADS)

Schneider, Evan E.; Robertson, Brant E.

2018-06-01

We present the Cholla Galactic OutfLow Simulations (CGOLS) suite, a set of extremely high resolution global simulations of isolated disk galaxies designed to clarify the nature of multiphase structure in galactic winds. Using the GPU-based code Cholla, we achieve unprecedented resolution in these simulations, modeling galaxies over a 20 kpc region at a constant resolution of 5 pc. The simulations include a feedback model designed to test the effects of different mass- and energy-loading factors on galactic outflows over kiloparsec scales. In addition to describing the simulation methodology in detail, we also present the results from an adiabatic simulation that tests the frequently adopted analytic galactic wind model of Chevalier & Clegg. Our results indicate that the Chevalier & Clegg model is a good fit to nuclear starburst winds in the nonradiative region of parameter space. Finally, we investigate the role of resolution and convergence in large-scale simulations of multiphase galactic winds. While our largest-scale simulations show convergence of observable features like soft X-ray emission, our tests demonstrate that simulations of this kind with resolutions greater than 10 pc are not yet converged, confirming the need for extreme resolution in order to study the structure of winds and their effects on the circumgalactic medium.

Secular Stellar Dynamics near a Massive Black Hole

NASA Astrophysics Data System (ADS)

Madigan, Ann-Marie; Hopman, Clovis; Levin, Yuri

2011-09-01

The angular momentum evolution of stars close to massive black holes (MBHs) is driven by secular torques. In contrast to two-body relaxation, where interactions between stars are incoherent, the resulting resonant relaxation (RR) process is characterized by coherence times of hundreds of orbital periods. In this paper, we show that all the statistical properties of RR can be reproduced in an autoregressive moving average (ARMA) model. We use the ARMA model, calibrated with extensive N-body simulations, to analyze the long-term evolution of stellar systems around MBHs with Monte Carlo simulations. We show that for a single-mass system in steady state, a depression is carved out near an MBH as a result of tidal disruptions. Using Galactic center parameters, the extent of the depression is about 0.1 pc, of similar order to but less than the size of the observed "hole" in the distribution of bright late-type stars. We also find that the velocity vectors of stars around an MBH are locally not isotropic. In a second application, we evolve the highly eccentric orbits that result from the tidal disruption of binary stars, which are considered to be plausible precursors of the "S-stars" in the Galactic center. We find that RR predicts more highly eccentric (e > 0.9) S-star orbits than have been observed to date.

X-Ray Ejecta Kinematics of the Galactic Core-Collapse Supernova Remnant G292.0+1.8

NASA Astrophysics Data System (ADS)

Bhalerao, Jayant; Park, Sangwook; Dewey, Daniel; Hughes, John P.; Mori, Koji; Lee, Jae-Joon

2015-02-01

We report on the results from the analysis of our 114 ks Chandra High Energy Transmision Grating Spectrometer observation of the Galactic core-collapse supernova remnant G292.0+1.8. To probe the three-dimensional structure of the clumpy X-ray emitting ejecta material in this remnant, we measured Doppler shifts in emission lines from metal-rich ejecta knots projected at different radial distances from the expansion center. We estimate radial velocities of ejecta knots in the range of -2300 lsim vr lsim 1400 km s-1. The distribution of ejecta knots in velocity versus projected-radius space suggests an expanding ejecta shell with a projected angular thickness of ~90'' (corresponding to ~3 pc at d = 6 kpc). Based on this geometrical distribution of the ejecta knots, we estimate the location of the reverse shock approximately at the distance of ~4 pc from the center of the supernova remnant, putting it in close proximity to the outer boundary of the radio pulsar wind nebula. Based on our observed remnant dynamics and the standard explosion energy of 1051 erg, we estimate the total ejecta mass to be lsim8 M ⊙, and we propose an upper limit of lsim35 M ⊙ on the progenitor's mass.

The fate of close encounters between binary stars and binary supermassive black holes

NASA Astrophysics Data System (ADS)

Wang, Yi-Han; Leigh, Nathan; Yuan, Ye-Fei; Perna, Rosalba

2018-04-01

The evolution of main-sequence binaries that reside in the Galactic Centre can be heavily influenced by the central supermassive black hole (SMBH). Due to these perturbative effects, the stellar binaries in dense environments are likely to experience mergers, collisions, or ejections through secular and/or non-secular interactions. More direct interactions with the central SMBH are thought to produce hypervelocity stars (HVSs) and tidal disruption events (TDEs). In this paper, we use N-body simulations to study the dynamics of stellar binaries orbiting a central SMBH primary with an outer SMBH secondary orbiting this inner triple. The effects of the secondary SMBH on the event rates of HVSs, TDEs, and stellar mergers are investigated, as a function of the SMBH-SMBH binary mass ratio. Our numerical experiments reveal that, relative to the isolated SMBH case, the TDE and HVS rates are enhanced for, respectively, the smallest and largest mass ratio SMBH-SMBH binaries. This suggests that the observed event rates of TDEs and HVSs have the potential to serve as a diagnostic of the mass ratio of a central SMBH-SMBH binary. The presence of a secondary SMBH also allows for the creation of hypervelocity binaries. Observations of these systems could thus constrain the presence of a secondary SMBH in the Galactic Centre.

Geometrically Thick Obscuration by Radiation-driven Outflow from Magnetized Tori of Active Galactic Nuclei

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

Chan, Chi-Ho; Krolik, Julian H.

2017-07-01

Near-Eddington radiation from active galactic nuclei (AGNs) has significant dynamical influence on the surrounding dusty gas, plausibly furnishing AGNs with geometrically thick obscuration. We investigate this paradigm with radiative magnetohydrodynamics simulations. The simulations solve the magnetohydrodynamics equations simultaneously with the infrared (IR) and ultraviolet (UV) radiative transfer (RT) equations; no approximate closure is used for RT. We find that our torus, when given a suitable sub-Keplerian angular momentum profile, spontaneously evolves toward a state in which its opening angle, density distribution, and flow pattern change only slowly. This “steady” state lasts for as long as there is gas resupply towardmore » the inner edge. The torus is best described as a midplane inflow and a high-latitude outflow. The outflow is launched from the torus inner edge by UV radiation and expands in solid angle as it ascends; IR radiation continues to drive the wide-angle outflow outside the central hole. The dusty outflow obscures the central source in soft X-rays, the IR, and the UV over three-quarters of solid angle, and each decade in column density covers roughly equal solid angle around the central source; these obscuration properties are similar to what observations imply.« less

Active Galactic Nucleus Obscuration from Winds: From Dusty Infrared-Driven to Warm and X-Ray Photoionized

NASA Technical Reports Server (NTRS)

Dorodnitsyn, Anton V.; Kallman, Timothy R.

2012-01-01

We present calculations of active galactic nucleus winds at approx.parsec scales along with the associated obscuration. We take into account the pressure of infrared radiation on dust grains and the interaction of X-rays from a central black hole with hot and cold plasma. Infrared radiation (IR) is incorporated in radiation-hydrodynamic simulations adopting the flux-limited diffusion approximation. We find that in the range of X-ray luminosities L = 0.05-0.6 L(sub Edd), the Compton-thick part of the flow (aka torus) has an opening angle of approximately 72deg - 75deg regardless of the luminosity. At L > or approx. 0.1, the outflowing dusty wind provides the obscuration with IR pressure playing a major role. The global flow consists of two phases: the cold flow at inclinations (theta) > or approx.70deg and a hot, ionized wind of lower density at lower inclinations. The dynamical pressure of the hot wind is important in shaping the denser IR-supported flow. At luminosities < or = 0.1 L(sub Edd) episodes of outflow are followed by extended periods when the wind switches to slow accretion. Key words: acceleration of particles . galaxies: active . hydrodynamics . methods: numerical Online-only material: color figures

The 4MOST instrument concept overview

NASA Astrophysics Data System (ADS)

Haynes, Roger; Barden, Samuel; de Jong, Roelof; Schnurr, Olivier; Bellido, Olga; Walcher, Jakob; Haynes, Dionne; Winkler, Roland; Bauer, Svend-Marian; Dionies, Frank; Saviauk, Allar; Chiappini, Cristina; Schwope, Axel; Brynnel, Joar; Steinmetz, Matthias; McMahon, Richard; Feltzing, Sofia; Francois, Patrick; Trager, Scott; Parry, Ian; Irwin, Mike; Walton, Nicholas; King, David; Sun, David; Gonzalez-Solares, Eduaro; Tosh, Ian; Dalton, Gavin; Middleton, Kevin; Bonifacio, Piercarlo; Jagourel, Pascal; Mignot, Shan; Cohen, Mathieu; Amans, Jean-Philippe; Royer, Frederic; Sartoretti, Paola; Pragt, Johan; Gerlofsma, Gerrit; Roelfsema, Ronald; Navarro, Ramon; Thimm, Guido; Seifert, Walter; Christlieb, Norbert; Mandel, Holger; Trifonov, Trifon; Xu, Wenli; Lang-Bardl, Florian; Muschielok, Bernard; Schlichter, Jörg; Hess, Hans-Joachim; Grupp, Frank; Boehringer, Hans; Boller, Thomas; Dwelly, Tom; Bender, Ralf; Rosati, Piero; Iwert, Olaf; Finger, Gert; Lizon L'Allemand, Jean-Louis; Saunders, Will; Sheinis, Andrew; Frost, Gabriella; Farrell, Tony; Waller, Lewis; Depagne, Eric; Laurent, Florence; Caillier, Patrick; Kosmalski, Johan; Richard, Johan; Bacon, Roland; Ansorge, Wolfgang

2014-07-01

The 4MOST[1] instrument is a concept for a wide-field, fibre-fed high multiplex spectroscopic instrument facility on the ESO VISTA telescope designed to perform a massive (initially >25x106 spectra in 5 years) combined all-sky public survey. The main science drivers are: Gaia follow up of chemo-dynamical structure of the Milky Way, stellar radial velocities, parameters and abundances, chemical tagging; eROSITA follow up of cosmology with x-ray clusters of galaxies, X-ray AGN/galaxy evolution to z~5, Galactic X-ray sources and resolving the Galactic edge; Euclid/LSST/SKA and other survey follow up of Dark Energy, Galaxy evolution and transients. The surveys will be undertaken simultaneously requiring: highly advanced targeting and scheduling software, also comprehensive data reduction and analysis tools to produce high-level data products. The instrument will allow simultaneous observations of ~1600 targets at R~5,000 from 390-900nm and ~800 targets at R<18,000 in three channels between ~395-675nm (channel bandwidth: 45nm blue, 57nm green and 69nm red) over a hexagonal field of view of ~ 4.1 degrees. The initial 5-year 4MOST survey is currently expect to start in 2020. We provide and overview of the 4MOST systems: optomechanical, control, data management and operations concepts; and initial performance estimates.

Black Hole Mergers in Galactic Nuclei Induced by the Eccentric Kozai–Lidov Effect

NASA Astrophysics Data System (ADS)

Hoang, Bao-Minh; Naoz, Smadar; Kocsis, Bence; Rasio, Frederic A.; Dosopoulou, Fani

2018-04-01

Nuclear star clusters around a central massive black hole (MBH) are expected to be abundant in stellar black hole (BH) remnants and BH–BH binaries. These binaries form a hierarchical triple system with the central MBH, and gravitational perturbations from the MBH can cause high-eccentricity excitation in the BH–BH binary orbit. During this process, the eccentricity may approach unity, and the pericenter distance may become sufficiently small so that gravitational-wave emission drives the BH–BH binary to merge. In this work, we construct a simple proof-of-concept model for this process, and specifically, we study the eccentric Kozai–Lidov mechanism in unequal-mass, soft BH–BH binaries. Our model is based on a set of Monte Carlo simulations for BH–BH binaries in galactic nuclei, taking into account quadrupole- and octupole-level secular perturbations, general relativistic precession, and gravitational-wave emission. For a typical steady-state number of BH–BH binaries, our model predicts a total merger rate of ∼1–3 {Gpc} ‑3 {yr} ‑1, depending on the assumed density profile in the nucleus. Thus, our mechanism could potentially compete with other dynamical formation processes for merging BH–BH binaries, such as the interactions of stellar BHs in globular clusters or in nuclear star clusters without an MBH.

Milky Way scattering properties and intrinsic sizes of active galactic nuclei cores probed by very long baseline interferometry surveys of compact extragalactic radio sources

NASA Astrophysics Data System (ADS)

Pushkarev, A. B.; Kovalev, Y. Y.

2015-10-01

We have measured the angular sizes of radio cores of active galactic nuclei (AGNs) and analysed their sky distributions and frequency dependences to study synchrotron opacity in AGN jets and the strength of angular broadening in the interstellar medium. We have used archival very long baseline interferometry (VLBI) data of more than 3000 compact extragalactic radio sources observed at frequencies, ν, from 2 to 43 GHz to measure the observed angular size of VLBI cores. We have found a significant increase in the angular sizes of the extragalactic sources seen through the Galactic plane (|b| ≲ 10°) at 2, 5 and 8 GHz, about one-third of which show significant scattering. These sources are mainly detected in directions to the Galactic bar, the Cygnus region and a region with galactic longitudes 220° ≲ l ≲ 260° (the Fitzgerald window). The strength of interstellar scattering of the AGNs is found to correlate with the Galactic Hα intensity, free-electron density and Galactic rotation measure. The dependence of scattering strengths on source redshift is insignificant, suggesting that the dominant scattering screens are located in our Galaxy. The observed angular size of Sgr A* is found to be the largest among thousands of AGNs observed over the sky; we discuss possible reasons for this strange result. Excluding extragalactic radio sources with significant scattering, we find that the angular size of opaque cores in AGNs scales typically as ν-1, confirming predictions of a conical synchrotron jet model with equipartition.

Conversion of gas into stars in the Galactic center

NASA Astrophysics Data System (ADS)

Longmore, S. N.

2014-05-01

The star formation rate in the central 500 pc of the Milky Way is lower by a factor of > 10 than expected for the substantial amount of dense gas it contains, which challenges current star formation theories. I discuss which physical mechanisms could be causing this observation and put forward a self-consistent cycle of star formation in the Galactic center, in which the plausible star formation inhibitors are combined. Their ubiquity suggests that the perception of a lowered central SFR should be a common phenomenon in other galaxies with direct implications for galactic star formation and also potentially supermassive black hole growth. I then describe a scenario to explain the presence of super star clusters in the Galactic center environment, in which their formation is triggered by gas streams passing close to the minimum of the global Galactic gravitational potential at the location of the central supermassive black hole, Sgr A*. If this triggering mechanism can be verified, we can use the known time interval since closest approach to Sgr A* to study the physics of stellar mass assembly in an extreme environment as a function of absolute time. I outline the first results from detailed numerical simulations testing this scenario. Finally, I describe a study showing that in terms of the baryonic composition, kinematics, and densities, the gas in the Galactic center is indistinguishable from high-redshift clouds and galaxies. As such, the Galactic center clouds may be used as a template to understand the evolution (and possibly the life cycle) of high-redshift clouds and galaxies.

The Galactic Club or Galactic Cliques? Exploring the limits of interstellar hegemony and the Zoo Hypothesis

NASA Astrophysics Data System (ADS)

Forgan, Duncan H.

2017-10-01

The Zoo solution to Fermi's Paradox proposes that extraterrestrial intelligences (ETIs) have agreed to not contact the Earth. The strength of this solution depends on the ability for ETIs to come to agreement, and establish/police treaties as part of a so-called `Galactic Club'. These activities are principally limited by the causal connectivity of a civilization to its neighbours at its inception, i.e. whether it comes to prominence being aware of other ETIs and any treaties or agreements in place. If even one civilization is not causally connected to the other members of a treaty, then they are free to operate beyond it and contact the Earth if wished, which makes the Zoo solution `soft'. We should therefore consider how likely this scenario is, as this will give us a sense of the Zoo solution's softness, or general validity. We implement a simple toy model of ETIs arising in a Galactic Habitable Zone, and calculate the properties of the groups of culturally connected civilizations established therein. We show that for most choices of civilization parameters, the number of culturally connected groups is >1, meaning that the Galaxy is composed of multiple Galactic Cliques rather than a single Galactic Club. We find in our models for a single Galactic Club to establish interstellar hegemony, the number of civilizations must be relatively large, the mean civilization lifetime must be several millions of years, and the inter-arrival time between civilizations must be a few million years or less.

THE BOLOCAM GALACTIC PLANE SURVEY. VIII. A MID-INFRARED KINEMATIC DISTANCE DISCRIMINATION METHOD

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

Ellsworth-Bowers, Timothy P.; Glenn, Jason; Battersby, Cara

2013-06-10

We present a new distance estimation method for dust-continuum-identified molecular cloud clumps. Recent (sub-)millimeter Galactic plane surveys have cataloged tens of thousands of these objects, plausible precursors to stellar clusters, but detailed study of their physical properties requires robust distance determinations. We derive Bayesian distance probability density functions (DPDFs) for 770 objects from the Bolocam Galactic Plane Survey in the Galactic longitude range 7. Degree-Sign 5 {<=} l {<=} 65 Degree-Sign . The DPDF formalism is based on kinematic distances, and uses any number of external data sets to place prior distance probabilities to resolve the kinematic distance ambiguity (KDA)more » for objects in the inner Galaxy. We present here priors related to the mid-infrared absorption of dust in dense molecular regions and the distribution of molecular gas in the Galactic disk. By assuming a numerical model of Galactic mid-infrared emission and simple radiative transfer, we match the morphology of (sub-)millimeter thermal dust emission with mid-infrared absorption to compute a prior DPDF for distance discrimination. Selecting objects first from (sub-)millimeter source catalogs avoids a bias towards the darkest infrared dark clouds (IRDCs) and extends the range of heliocentric distance probed by mid-infrared extinction and includes lower-contrast sources. We derive well-constrained KDA resolutions for 618 molecular cloud clumps, with approximately 15% placed at or beyond the tangent distance. Objects with mid-infrared contrast sufficient to be cataloged as IRDCs are generally placed at the near kinematic distance. Distance comparisons with Galactic Ring Survey KDA resolutions yield a 92% agreement. A face-on view of the Milky Way using resolved distances reveals sections of the Sagittarius and Scutum-Centaurus Arms. This KDA-resolution method for large catalogs of sources through the combination of (sub-)millimeter and mid-infrared observations of molecular cloud clumps is generally applicable to other dust-continuum Galactic plane surveys.« less

GOT C+: A Herschel Space Observatory Key Program to Study the Diffuse ISM

NASA Astrophysics Data System (ADS)

Langer, William; Goldsmith, P. F.; Li, D.; Velusamy, T.; Yorke, H. W.

2009-01-01

Galactic Observations of the Terahertz C+ Line (GOT C+) is a Herschel Space Observatory (HSO) Key Program to study the diffuse interstellar medium by sampling the C+ fine structure line emission at 1.9 THz (158 microns) in the Galactic disk. Star formation activity is regulated by pressures in the interstellar medium, which in turn depend on heating and cooling rates, modulated by the gravitational potential, and shock and turbulent pressures. To understand these processes we need information about properties of the diffuse atomic and diffuse molecular gas clouds. The 158-micron CII line is an important tracer of diffuse regions, and C+ is a major ISM coolant, the Galaxy's strongest emission line virtually unobscured by dust, with a total luminosity about a 1000 times that of CO J=1-0. The GOT C+ program will obtain high spectral resolution CII spectra using the Heterodyne Instrument for the Far Infrared (HIFI) receiver. It will employ deep integrations, wide velocity coverage (350 km/s) with 0.22 km/s resolution, and systematic sparse sampling of the Galactic disk together with observations of selected targets, of over 900 lines of sight. It will be a resource to determine the properties of the atomic gas, in the (a) overall Galactic disk, (b) central 300pc of the Galactic center, (c) Galactic warp, (d) high latitude HI clouds, and (e) Photon Dominated Regions (PDRs). These spectra will provide the astronomical community with a rich statistical database of diffuse cloud properties, especially those of the atomic gas, sampled throughout the Galaxy for understanding the role of barometric pressure and turbulence in cloud evolution in the Galactic ISM and, by extension, other galaxies. The GOT C+ project will provide a template for future even larger-scale Galactic C+ surveys. This research was conducted at the Jet Propulsion Laboratory and is supported by a NASA grant.

Near-parabolic comets observed in 2006-2010 - II. Their past and future motion under the influence of the Galaxy field and known nearby stars

NASA Astrophysics Data System (ADS)

Dybczyński, Piotr A.; Królikowska, Małgorzata

2015-03-01

In the first part of this research we extensively investigated and carefully determined osculating, original (when entering Solar system) and future (when leaving it), orbits of 22 near-parabolic comets with small perihelion distance (qosc < 3.1 au), discovered in years 2006-2010. Here, we continue this research with a detailed study of their past and future motion during previous and next orbital periods under the perturbing action of our Galactic environment. At all stages of our dynamical study, we precisely propagate in time the observational uncertainties of cometary orbits. For the first time in our calculations, we fully take into account individual perturbations from all known stars or stellar systems that closely (less than 3.5 pc) approach the Sun during the cometary motion in the investigated time interval of several million years. This is done by means of a direct numerical integration of the N-body system comprising of a comet, the Sun and 90 potential stellar perturbers. We show a full review of various examples of individual stellar action on cometary motion. We conclude that perturbations from all known stars or stellar systems do not change the overall picture of the past orbit evolution of long-period comets. Their future motion might be seriously perturbed during the predicted close approach of Gliese 710 star but we do not observe significant energy changes. The importance of stellar perturbations is tested on the whole sample of 108 comets investigated by us so far and our previous results, obtained with only Galactic perturbations included, are fully confirmed. We present how our results can be used to discriminate between dynamically new and old near-parabolic comets and discuss the relevance of the so-called Jupiter-Saturn barrier phenomenon. Finally, we show how the Oort spike in the 1/a-distribution of near-parabolic comets is built from both dynamically new and old comets. We also point out that C/2007 W1 seems to be the first serious candidate for interstellar provenance.

Dynamics of Gas Near the Galactic Centre

NASA Astrophysics Data System (ADS)

Jenkins, A.; Binney, J.

1994-10-01

We simulate the flow of gas in the Binney et al. model of the bar at the centre of the Milky Way. We argue that the flow of a clumpy interstellar medium is most realistically simulated by a sticky-particle scheme, and investigate two such schemes. In both schemes orbits close to the cusped orbit rapidly become depopulated. This depopulation places a lower limit on the pattern speed since it implies that in the (1, v) plane the cusped orbit lies significantly inside the peak of the Hi terminal-velocity envelope at 1 20. We find that the size of the central molecular disc and the magnitudes of the observed forbidden velocities constrain the eccentricity of the Galactic bar to values similar to that arbitrarily assumed by Binney et al. We study the accretion by the nuclear disc of matter shed by dying bulge stars. We estimate that mass loss by the bulge can replenish the Hi in the nuclear disc within two bar rotation periods, in good agreement with the predictions of the simulations. When accretion of gas from the bulge is included, fine-scale irregular structure persists in the nuclear disc. This structure gives rise to features in longitude-velocity plots which depend significantly on viewing angle, and consequently give rise to asymmetries in longitude. These asymmetries are, however, much less pronounced than those in the observational plots. We conclude that the addition of hydrodynamics to the Binney et al. model does not resolve some important discrepancies between theory and observation. The model's basic idea does, however, have high a priori probability and has enjoyed some significant successes, while a number of potentially important physical processes - most notably the self-gravity of interstellar gas - are neglected in the present simulations. In view of the deficiencies of our simulations and interesting parallels we do observe between simulated and observational longitude-velocity plots, we believe it would be premature to reject the Binney et al. model prior to exploring high-quality three-dimensional simulations that include self-gravitating stars and gas. Key words: accretion, accretion discs - ISM: kinematics and dynamics - ISM: structure -Galaxy: centre - Galaxy: kinematics and dynamics - radio lines: ISM.

VizieR Online Data Catalog: Planck Catalogue of Galactic cold clumps (PGCC) (Planck+, 2016)

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoit, A.; Benoit-Levy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Catalano, A.; Chamballu, A.; Chiang, H. C.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; De Rosa, A.; de Zotti, G.; Delabrouille, J.; Desert, F.-X.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Dore, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Ensslin, T. A.; Eriksen, H. K.; Falgarone, E.; Fergusson, J.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Heraud, Y.; Gjerlow, E.; Gonzalez-Nuevo, J.; Gorsk, I. K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Helou, G.; Henrot-Versille, S.; Hernandez-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kisner, T. S.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vornle, M.; Lopez-Caniego, M.; Lubin, P. M.; Macias-Perez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Marshall, D. J.; Martin, P. G.; Martinez-Gonzalez, E.; Masi, S.; Matarrese, S.; Mazzotta, P.; McGehee, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschenes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Norgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Pelkonen, V.-M.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Pratt, G. W.; Prezeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubino-Martin, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Stolyarov, V.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Valiviita, J.; van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Yvon, D.; Zacchei, A.; Zonca, A.

2017-01-01

The Planck Catalogue of Galactic Cold Clumps (PGCC) is a list of 13188 Galactic sources and 54 sources located in the Small and Large Magellanic Clouds. The sources have been identified in Planck data as sources colder than their environment. It has been built using the 48 months Planck data at 857, 545, and 353GHz combined with the 3THz IRAS data. (1 data file).

Giant Comets, Evolution and Civilization

DTIC Science & Technology

1998-01-01

Depending on the assumed scale height of dark matter in the Galactic disc, the periodic modulations may easily attain amplitudes of 3:1 or more...an in-plane density pz - 0.18 M® p- 3 for the ambient Galactic disc [18], im- 4 plying the presence of dark matter in the disc with an extreme...poles and equator, broadly in accordance with the Galactic tide [19] complemented by individ- ual (stellar and dark matter ) perturbers. In addition

VLBI Monitoring of the Bright Gamma-Ray Blazar PKS 0537-441

DTIC Science & Technology

2010-06-01

active state by Fermi. It is one of the brightest ,),-ray blazars detected in the southern sky so far. The TANAMI (Tracking Active Galactic Nuclei...Active Galactic Nuclei with Austral Milliarcsecond Interferometry (TAN AMI) program (Ojha et a1. (2010» has been monitoring south- ern sky blazars such...Telescope. Studying Active Galactic Nuclei (AGN) at different wavelengths is crucial in order to understand AGN-jets and differentiate between

The Galactic interstellar medium: foregrounds and star formation

NASA Astrophysics Data System (ADS)

Miville-Deschênes, Marc-Antoine

2018-05-01

This review presents briefly two aspects of Galactic interstellar medium science that seem relevant for studying EoR. First, we give some statistical properties of the Galactic foreground emission in the diffuse regions of the sky. The properties of the emission observed in projection on the plane of the sky are then related to how matter is organised along the line of sight. The diffuse atomic gas is multi-phase, with dense filamentary structures occupying only about 1% of the volume but contributing to about 50% of the emission. The second part of the review presents aspect of structure formation in the Galactic interstellar medium that could be relevant for the subgrid physics used to model the formation of the first stars.

The emergence of the galactic stellar mass function from a non-universal IMF in clusters

NASA Astrophysics Data System (ADS)

Dib, Sami; Basu, Shantanu

2018-06-01

We investigate the dependence of a single-generation galactic mass function (SGMF) on variations in the initial stellar mass functions (IMF) of stellar clusters. We show that cluster-to-cluster variations of the IMF lead to a multi-component SGMF where each component in a given mass range can be described by a distinct power-law function. We also show that a dispersion of ≈0.3 M⊙ in the characteristic mass of the IMF, as observed for young Galactic clusters, leads to a low-mass slope of the SGMF that matches the observed Galactic stellar mass function even when the IMFs in the low-mass end of individual clusters are much steeper.

Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, volume 73

NASA Technical Reports Server (NTRS)

Haas, Michael R. (Editor); Davidson, Jacqueline A. (Editor); Erickson, Edwin F. (Editor)

1995-01-01

This symposium was organized to review the science related to NASA's Airborne Astronomy Program on the occasion of the twentieth anniversary of the Kuiper Airborne Observatory (KAO). The theme selected, 'The Galactic Ecosystem: From Gas to Stars to Dust,' was considered to capture the underlying commonality of much of the research discussed. The 8 sessions were as follows: The Interstellar Medium; The Life Cycle of the ISM in Other Galaxies; Star and Planetary System Formation; Our Planetary System: The Solar System; The Enrichment of the Interstellar Medium; The Galactic Center: A Unique Region of the Galactic Ecosystem; Instrumentation for Airborne Astronomy; KAO History and Education; and Missions and the Future of Infrared Astronomy.

Rapid Monte Carlo Simulation of Gravitational Wave Galaxies

NASA Astrophysics Data System (ADS)

Breivik, Katelyn; Larson, Shane L.

2015-01-01

With the detection of gravitational waves on the horizon, astrophysical catalogs produced by gravitational wave observatories can be used to characterize the populations of sources and validate different galactic population models. Efforts to simulate gravitational wave catalogs and source populations generally focus on population synthesis models that require extensive time and computational power to produce a single simulated galaxy. Monte Carlo simulations of gravitational wave source populations can also be used to generate observation catalogs from the gravitational wave source population. Monte Carlo simulations have the advantes of flexibility and speed, enabling rapid galactic realizations as a function of galactic binary parameters with less time and compuational resources required. We present a Monte Carlo method for rapid galactic simulations of gravitational wave binary populations.

Detection of sulfur in the galactic center

NASA Technical Reports Server (NTRS)

Herter, T.; Briotta, D. A., Jr.; Gull, G. E.; Shure, M. A.; Houck, J. R.

1983-01-01

A strong detection at the S III forbidden 18.71 micron line is reported for the galactic center region, Sgr A West. A line flux of 1.7 + or - 0.2 x 10 to the -17th W/sq cm is found for a 20 inch beam size measurement centered on IRS 1. A preliminary analysis indicates that the S III abundance relative to hydrogen is consistent with the cosmic abundance of sulfur, 0.000016, if a filling factor of unity within the known clumps is assumed. However, the sulfur abundance in the galactic center may be as much as a factor of 3 overabundant if a filling factor of 0.03 is adopted, a value found to hold for some galactic H II regions.