Cosmic Star–Forming Gas as seen from the Milky Way

NASA Astrophysics Data System (ADS)

Kauffmann, Jens

2018-01-01

We still struggle to understand the star formation properties of galaxies throughout the cosmos. Is star formation driven by the structure of galaxies? Or is it plainly controlled by the mass of dense gas that can be found in a galaxy?This poster presents results from several recent projects that deliver important insights on the global star formation activity of galaxies, based on detailed studies of star-forming regions in the Milky Way. First, the proberties of dense clouds in the Galactic Center are discussed, using data from interferometers likw ALMA. Second, the kinematics of Milky Way molecular clouds are discussed based on a variety of data sets. Third, the LEGO survey (Line Emission in Galaxy Observations) is discussed. This latter study challenges concepts of how dense gas in galaxies can be traced. In combination these studies deliver a fresh look at the various factors controlling how galaxies form stars.

Near-Field Cosmology with Low-Mass Galaxies: Constraining the Escape of Radiation from the UV-slopes of Local Galaxies

NASA Astrophysics Data System (ADS)

Venkatesan, Aparna; Rosenberg, Jessica L.; Salzer, John Joseph; Gronke, Max; Cannon, John M.; Miller, Christopher J.; Dijkstra, Mark

2018-06-01

Low-mass galaxies are thought to play a large role in reionizing the Universe at redshifts, z > 6. However, due to limited UV data on low-mass galaxies, the models used to estimate the escape of radiation are poorly constrained. Using theoretical models of radiation transport in dusty galaxies with clumpy gas media, we translate measurements of the UV slopes of a sample of low-mass low-z KISSR galaxies to their escape fraction values in Ly-alpha radiation, fesc (LyA), and in the Ly-continuum, fesc (LyC). These low-mass starforming systems have potentially steep UV slopes, and could provide a much-needed relation between easily measured spectral properties such as UV slope or LyA line properties, and the escape of LyA/LyC radiation. Such a relation could advance studies of primordial star clusters and the underlying physical conditions characterizing early galaxies, one of the target observation goals of the soon to-be-launched James Webb Space Telescope. This work was supported by the University of San Francisco Faculty Development Fund, and NSF grant AST-1637339. We thank the Aspen Center for Physics, where some of this work was conducted, and which is supported by National Science Foundation grant PHY-1607611.

Hα3: an Hα imaging survey of HI selected galaxies from ALFALFA. IV. Structure of galaxies in the Local and Coma superclusters

NASA Astrophysics Data System (ADS)

Fossati, M.; Gavazzi, G.; Savorgnan, G.; Fumagalli, M.; Boselli, A.; Gutiérrez, L.; Hernández Toledo, H.; Giovanelli, R.; Haynes, M. P.

2013-05-01

Context. We present the analysis of the galaxy structural parameters from Hα3, an Hα narrow-band imaging follow-up survey of ~800 galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Local supercluster, including the Virgo cluster, and in the Coma supercluster. Aims: Taking advantage of Hα3, which provides the complete census of the recent star-forming, HI-rich galaxies in the local universe, we aim to investigate the structural parameters of the young (<10 Myr) and the old (>1 Gyr) stellar populations. By comparing the sizes of these stellar components, we investigated the spatial scale on which galaxies are growing at the present cosmological epoch and the role of the environment in quenching the star-formation activity. Methods: We computed the concentration, asymmetry, and clumpiness (CAS) structural parameters for recently born and old stars. To quantify the sizes we computed half-light radii and a new parameter dubbed EW/r based on the half-light radius of the Hα equivalent width map. To highlight the environmental perturbation, we adopt an updated calibration of the HI-deficiency parameter (DefHI) that we use to divide the sample in unperturbed galaxies (DefHI ≤ 0.3) and perturbed galaxies (DefHI > 0.3). Results: The concentration index computed in the r band depends on the stellar mass and on the Hubble type these variables are related because most massive galaxies are bulge dominated therefore highly concentrated. Going toward later spirals and irregulars the concentration index and the mass decrease along with the bulge-to-disk ratio. Blue compact dwarfs (BCDs) are an exception because they have similar mass, but they are more concentrated than dwarf irregulars. The asymmetry and the clumpiness increase along the spiral sequence up to Sc-Sd, but they decrease going in the dwarf regime, where the light distribution is smooth and more symmetric. When measured on Hα images, the CAS parameters show no obvious correlations with Hubble type. Irrespective of whether we used the ratio between effective radii or the EW/r parameter, we found that the concentration index is the main parameter that describes the current growth of isolated galaxies but, for a fixed concentration, the stellar mass plays a second-order role. At the present epoch, massive galaxies are growing inside-out, conversely, the dwarfs are growing on the scale of their already assembled mass. Observations taken at the observatory of San Pedro Martir (Baja California, Mexico), belonging to the Mexican Observatorio Astronómico Nacional.Tables A.1 and A.2 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/553/A91

The Inner Structure of OH Megamaser Galaxies: The Genesis of the Unified Scheme of Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Axon, David

OH megamaser galaxies (OHMG) represent a key post-merger phase in the evolution of the Ultra-Luminous Infrared Galaxies (ULIRGs) population, in which an edge-on circum-nuclear gas disk (proto-torus) has already formed. Detailed interferometric mapping of maser sources implies that they originate in dense edge-on rotating molecular gas within a few tens of parsecs of the AGN. In addition, the OH lines are often broad (Doppler widths ~ 1000 km/s), implying large dynamical masses in the central few parsecs. In many systems the OH lines also show high velocity asymmetric tails suggesting large-scale outflows that could be clearing away enshrouding dense molecular material. Taken together this evidence points to a picture in which an OHMG hosts a nascent QSO surrounded by a flattened distribution of dense molecular gas that is in the process of being cleared away along the rotation axis of the maser disk. A great advantage of studying OHMG systems over the general ULIRG population is that the circum-nuclear disks are effectively "fixed" at an edge on orientation, thereby breaking the degeneracy between the number of clumps and inclination in state of the art clumpy torus models. We have been awarded HST time in cycle 17 to conduct a comprehensive study of structure of the circum-nuclear gas, and its relationship to the radio structure and that of the maser disk, of large sample (80) of OHMG. This work is supported by ground-based spectropolarimetry, integral field spectroscopy and new radio continuum observations, Our overall objective is to probe the final stages of evolution immediately before the full- emergence of an enshrouded AGN as the circum-nuclear dust is dispersed by starburst and AGN-induced outflows. The specific scientific goals of this ADP proposal are to retrieve and analyze the Spitzer thermal-IR 5-70 micron imaging and IRS spectra of the subset of 72 of our targets for which Spitzer observations are available in the archive. We aim to establish the relationship between host and circum-nuclear ionized gas and dust structures in different OHMG spectroscopic types (AGN, Starburst, Composite) and model the AGN and starburst contributions to the mid-IR SED. Combining these with our other data we will address a number of important questions: is the mid-IR SED consistent with an edge-on circum-nuclear dust structure, as expected from the maser observations? What is the relative orientation of the Maser molecular structure and the ionized gas? Is there a connection between AGN heating of the circum-nuclear dust and wind or radiation driven outflows from the nucleus? How does the bolometric luminosity of the AGN relate to the OH line luminosity, FWHM and line shape? In turn these will relate the ionizing luminosity to the covering factor of the torus and the enclosed dynamical mass. When complete, this study should provide new insights on the relationships between the fundamental physical parameters of the AGN, including black hole mass, accretion and mass outflow rates, and the large scale properties of the host galaxy.

Discovery of a large-scale clumpy structure around the Lynx supercluster at z~ 1.27

NASA Astrophysics Data System (ADS)

Nakata, Fumiaki; Kodama, Tadayuki; Shimasaku, Kazuhiro; Doi, Mamoru; Furusawa, Hisanori; Hamabe, Masaru; Kimura, Masahiko; Komiyama, Yutaka; Miyazaki, Satoshi; Okamura, Sadanori; Ouchi, Masami; Sekiguchi, Maki; Ueda, Yoshihiro; Yagi, Masafumi; Yasuda, Naoki

2005-03-01

We report the discovery of a probable large-scale structure composed of many galaxy clumps around the known twin clusters at z= 1.26 and 1.27 in the Lynx region. Our analysis is based on deep, panoramic, and multicolour imaging, 26.4 × 24.1 arcmin2 in VRi'z' bands with the Suprime-Cam on the 8.2-m Subaru telescope. This unique, deep and wide-field imaging data set allows us for the first time to map out the galaxy distribution in the highest-redshift supercluster known. We apply a photometric redshift technique to extract plausible cluster members at z~ 1.27 down to i'= 26.15 (5σ) corresponding to ~M*+ 2.5 at this redshift. From the two-dimensional distribution of these photometrically selected galaxies, we newly identify seven candidates of galaxy groups or clusters where the surface density of red galaxies is significantly high (>5σ), in addition to the two known clusters. These candidates show clear red colour-magnitude sequences consistent with a passive evolution model, which suggests the existence of additional high-density regions around the Lynx superclusters.

VLA+WSRT HI Imaging of Two "Almost Dark" Galaxies

NASA Astrophysics Data System (ADS)

Ball, Catie; Singer, Quinton; Cannon, John M.; Leisman, Luke; Haynes, Martha P.; Adams, Elizabeth A.; Bernal Neira, David; Giovanelli, Riccardo; Hallenbeck, Gregory L.; Janesh, William; Janowiecki, Steven; Jozsa, Gyula; Rhode, Katherine L.; Salzer, John Joseph

2017-01-01

We present sensitive HI imaging of the "Almost Dark" galaxies AGC229385 and AGC229101. Selected from the ALFALFA survey, "Almost Dark" galaxies have significant HI reservoirs but lack an obvious stellar counterpart in survey-depth ground-based optical imaging. Deeper ground- and space-based imaging reveals very low surface brightness optical counterparts in both systems. The resulting M_HI/L_B ratios are among the highest ever measured for individual galaxies. Here we combine VLA and WSRT imaging of these two systems, allowing us to preserve surface brightness sensitivity while working at high angular resolution. The resulting maps of HI mass surface density, velocity field, and velocity dispersion are compared to deep optical and ultraviolet imaging. In both systems the highest column density HI gas is clumpy and resolved into multiple components. In the case of AGC229385, the kinematics are inconsistent with a simple rotating disk and may be the result of either an infall episode or an interaction between two HI-rich disks.Support for this work was provided by NSF grant 1211683 to JMC at Macalester College.

Dense Cores in Galaxies Out to z = 2.5 in SDSS, UltraVISTA, and the Five 3D-HST/CANDELS Fields

NASA Astrophysics Data System (ADS)

van Dokkum, Pieter G.; Bezanson, Rachel; van der Wel, Arjen; Nelson, Erica June; Momcheva, Ivelina; Skelton, Rosalind E.; Whitaker, Katherine E.; Brammer, Gabriel; Conroy, Charlie; Förster Schreiber, Natascha M.; Fumagalli, Mattia; Kriek, Mariska; Labbé, Ivo; Leja, Joel; Marchesini, Danilo; Muzzin, Adam; Oesch, Pascal; Wuyts, Stijn

2014-08-01

The dense interiors of massive galaxies are among the most intriguing environments in the universe. In this paper,we ask when these dense cores were formed and determine how galaxies gradually assembled around them. We select galaxies that have a stellar mass >3 × 1010 M ⊙ inside r = 1 kpc out to z = 2.5, using the 3D-HST survey and data at low redshift. Remarkably, the number density of galaxies with dense cores appears to have decreased from z = 2.5 to the present. This decrease is probably mostly due to stellar mass loss and the resulting adiabatic expansion, with some contribution from merging. We infer that dense cores were mostly formed at z > 2.5, consistent with their largely quiescent stellar populations. While the cores appear to form early, the galaxies in which they reside show strong evolution: their total masses increase by a factor of 2-3 from z = 2.5 to z = 0 and their effective radii increase by a factor of 5-6. As a result, the contribution of dense cores to the total mass of the galaxies in which they reside decreases from ~50% at z = 2.5 to ~15% at z = 0. Because of their early formation, the contribution of dense cores to the total stellar mass budget of the universe is a strong function of redshift. The stars in cores with M 1 kpc > 3 × 1010 M ⊙ make up ~0.1% of the stellar mass density of the universe today but 10%-20% at z ~ 2, depending on their initial mass function. The formation of these cores required the conversion of ~1011 M ⊙ of gas into stars within ~1 kpc, while preventing significant star formation at larger radii.

The Secular Evolution Of Disc Galaxies And The Origin Of Exponential And Double Exponential Surface Density Profiles

NASA Astrophysics Data System (ADS)

Elmegreen, Bruce G.

2016-10-01

Exponential radial profiles are ubiquitous in spiral and dwarf Irregular galaxies, but the origin of this structural form is not understood. This talk will review the observations of exponential and double exponential disks, considering both the light and the mass profiles, and the contributions from stars and gas. Several theories for this structure will also be reviewed, including primordial collapse, bar and spiral torques, clump torques, galaxy interactions, disk viscosity and other internal processes of angular momentum exchange, and stellar scattering off of clumpy structure. The only process currently known that can account for this structure in the most theoretically difficult case is stellar scattering off disks clumps. Stellar orbit models suggest that such scattering can produce exponentials even in isolated dwarf irregulars that have no bars or spirals, little shear or viscosity, and profiles that go out too far for the classical Mestel case of primordial collapse with specific angular momentum conservation.

Hidden Lair at the Heart of Galaxy NGC 1068

NASA Image and Video Library

2015-12-17

Galaxy NGC 1068 can be seen in close-up in this view from NASA's Hubble Space Telescope. NuSTAR's high-energy X-rays eyes were able to obtain the best view yet into the hidden lair of the galaxy's central, supermassive black hole. This active black hole -- shown as an illustration in the zoomed-in inset -- is one of the most obscured known, meaning that it is surrounded by extremely thick clouds of gas and dust. The NuSTAR data revealed that the torus of gas and dust surrounding the black hole, also referred to as a doughnut, is more clumpy than previously thought. doughnuts around active, supermassive black holes were originally proposed in the mid-1980s to be smooth entities. More recently, researchers have been finding that doughnuts are not so smooth but have lumps. NuSTAR's latest finding shows that this is true for even the thickest of doughnuts. http://photojournal.jpl.nasa.gov/catalog/PIA20058

Ionization processes in a local analogue of distant clumpy galaxies: VLT MUSE IFU spectroscopy and FORS deep images of the TDG NGC 5291N

NASA Astrophysics Data System (ADS)

Fensch, J.; Duc, P.-A.; Weilbacher, P. M.; Boquien, M.; Zackrisson, E.

2016-01-01

Context. We present Integral Field Unit (IFU) observations with MUSE and deep imaging with FORS of a dwarf galaxy recently formed within the giant collisional HI ring surrounding NGC 5291. This Tidal Dwarf Galaxy (TDG) -like object has the characteristics of typical z = 1-2 gas-rich spiral galaxies: a high gas fraction, a rather turbulent clumpy interstellar medium, the absence of an old stellar population, and a moderate metallicity and star formation efficiency. Aims: The MUSE spectra allow us to determine the physical conditions within the various complex substructures revealed by the deep optical images and to scrutinize the ionization processes at play in this specific medium at unprecedented spatial resolution. Methods: Starburst age, extinction, and metallicity maps of the TDG and the surrounding regions were determined using the strong emission lines Hβ, [OIII], [OI], [NII], Hα, and [SII] combined with empirical diagnostics. Different ionization mechanisms were distinguished using BPT-like diagrams and shock plus photoionization models. Results: In general, the physical conditions within the star-forming regions are homogeneous, in particular with a uniform half-solar oxygen abundance. On small scales, the derived extinction map shows narrow dust lanes. Regions with atypically strong [OI] emission line immediately surround the TDG. The [OI]/ Hα ratio cannot be easily accounted for by the photoionization by young stars or shock models. At greater distances from the main star-foming clumps, a faint diffuse blue continuum emission is observed, both with the deep FORS images and the MUSE data. It does not have a clear counterpart in the UV regime probed by GALEX. A stacked spectrum towards this region does not exhibit any emission line, excluding faint levels of star formation, or stellar absorption lines that might have revealed the presence of old stars. Several hypotheses are discussed for the origin of these intriguing features. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile: ESO MUSE programme 60.A-9320(A) and FORS programme 382.B-0213(A).

Compact configurations within small evolving groups of galaxies

NASA Astrophysics Data System (ADS)

Mamon, G. A.

Small virialized groups of galaxies are evolved with a gravitational N-body code, where the galaxies and a diffuse background are treated as single particles, but with mass and luminosity profiles attached, which enbles the estimation of parameters such as internal energies, half-mass radii, and the softened potential energies of interaction. The numerical treatment includes mergers, collisional stripping, tidal limitation by the mean-field of the background (evaluated using a combination of instantaneous and impulsive formulations), galaxy heating from collisons, and background heating from dynamical friction. The groups start out either as dense as appear the groups in Hickson's (1982) catalog, or as loose as appear those in Turner and Gott's (1976a) catalog, and they are simulated many times (usually 20) with different initial positions and velocities. Dense groups of galaxies with massive dark haloes coalesce into a single galaxy and lose their compact group appearance in approximately 3 group half-mass crossing times, while dense groups of galaxies without massive haloes survive the merger instability for 15 half-mass crossing times (in a more massive background to keep the same total group mass).

Imaging the Hot Stellar Content of Early Type Galaxies

NASA Astrophysics Data System (ADS)

Bertola, Francesco

1991-07-01

WE PROPOSE TO IMAGE WITH THE FOC IN THE F/96 CONFIGURATION FIVE EARLY TYPE GALAXIES IN FOUR PASSBANDS CENTERED AT 1500 A, 2200 A, 2800 A AND 3400 A. WHEN COUPLED WITH PHOTOMETRY OBTAINED FROM THE GROUND OUR OBSERVATIONS WILL ALLOW US TO DERIVE COMPLETE SED OF THESE GALAXIES AS A FUNCTION OF THE DISTANCE FROM THE CENTER. THIS IS A KEY STEP TOWARDS THE UNDERSTANDING OF STELLAR POPULATIONS - IN PARTICULAR THE ONE RESPONSIBLE FOR THE UV EMISSION - IN EARLY TYPE GALAXIES AND WILL PROVIDE IMPORTANT INSIGHT IN THEIR FORMATION AND EVOLUTION. WE PLAN TO OBSERVE NGC 1399, NGC 2681, NGC 4552, NGC 5018 AND NGC 4627 WHICH SAMPLE A WIDE RANGE OF INTRINSIC PROPERTIES AS INDICATED BY PREVIOUS IUE OBSERVATIONS. FOR NGC 4627 THERE IS EVIDENCE OF ONGOING STAR FORMATION AND THE HST WILL BE ABLE TO SHOW THE CHARACTERISTIC CLUMPINESS. NGC 2681 HAD A STARBUST OF AGE GREATER THAN 1 GYR. NGC 4552 IS ONE OF THE MOST METAL RICH GALAXY KNOWN. NGC 1399 HAS THE SAME METALLICITY AND LUMINOSITY OF THE PREVIOUS GALAXY BUT IS A MUCH STRONGER X-RAY EMITTER. NGC 5018 IS A VERY GOOD CANDIDATE FOR ONGOING STAR FORMATION. WE BELIEVE IN THIS WAY WE CAN OBTAIN SED FOR THE TWO-DIMENSIONAL IMAGES OF EARLY TYPE GALAXIES FROM BROAD BAND IMAGING ALONE. THE CALIBRATION OF OUR FILTER SYSTEM WILL ALLOW US TO APPLY IT TO THE BIDIMENSIONAL ANALYSIS OF THE GENERAL SAMPLE OF EARLY TYPE GALAXIES.

A MULTIWAVELENGTH STUDY OF TADPOLE GALAXIES IN THE HUBBLE ULTRA DEEP FIELD

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

Straughn, Amber N.; Eufrasio, Rafael T.; Gardner, Jonathan P.

2015-12-01

Multiwavelength data are essential in order to provide a complete picture of galaxy evolution and to inform studies of galaxies’ morphological properties across cosmic time. Here we present the results of a multiwavelength investigation of the morphologies of “tadpole” galaxies at intermediate redshift (0.314 < z < 3.175) in the Hubble Ultra Deep Field. These galaxies were previously selected from deep Hubble Space Telescope (HST) F775W data based on their distinct asymmetric knot-plus-tail morphologies. Here we use deep Wide Field Camera 3 near-infrared imaging in addition to the HST optical data in order to study the rest-frame UV/optical morphologies ofmore » these galaxies across the redshift range 0.3 < z < 3.2. This study reveals that the majority of these galaxies do retain their general asymmetric morphology in the rest-frame optical over this redshift range, if not the distinct “tadpole” shape. The average stellar mass of tadpole galaxies is lower than that of field galaxies, with the effect being slightly greater at higher redshift within the errors. Estimated from spectral energy distribution fits, the average age of tadpole galaxies is younger than that of field galaxies in the lower-redshift bin, and the average metallicity is lower (whereas the specific star formation rate for tadpoles is roughly the same as field galaxies across the redshift range probed here). These average effects combined support the conclusion that this subset of galaxies is in an active phase of assembly, either late-stage merging or cold gas accretion causing localized clumpy star formation.« less

CLUMPY: A code for γ-ray signals from dark matter structures

NASA Astrophysics Data System (ADS)

Charbonnier, Aldée; Combet, Céline; Maurin, David

2012-03-01

We present the first public code for semi-analytical calculation of the γ-ray flux astrophysical J-factor from dark matter annihilation/decay in the Galaxy, including dark matter substructures. The core of the code is the calculation of the line of sight integral of the dark matter density squared (for annihilations) or density (for decaying dark matter). The code can be used in three modes: i) to draw skymaps from the Galactic smooth component and/or the substructure contributions, ii) to calculate the flux from a specific halo (that is not the Galactic halo, e.g. dwarf spheroidal galaxies) or iii) to perform simple statistical operations from a list of allowed DM profiles for a given object. Extragalactic contributions and other tracers of DM annihilation (e.g. positrons, anti-protons) will be included in a second release.

Resolving the Circumgalactic Medium in the NEPHTHYS Simulations

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

Characterising the Circum-Galactic Medium of Damped Lyman-α Absorbing Galaxies

NASA Astrophysics Data System (ADS)

Augustin, Ramona; Péroux, Céline; Møller, Palle; Kulkarni, Varsha; Rahmani, Hadi; Milliard, Bruno; Pieri, Matthew; York, Donald G.; Vladilo, Giovanni; Aller, Monique; Zwaan, Martin

2018-05-01

Gas flows in and out of galaxies through their circumgalactic medium (CGM) are poorly constrained and direct observations of this faint, diffuse medium remain challenging. We use a sample of five z ˜ 1-2 galaxy counterparts to Damped Lyman-α Absorbers (DLAs) to combine data on cold gas, metals and stellar content of the same galaxies. We present new HST/WFC3 imaging of these fields in 3-5 broadband filters and characterise the stellar properties of the host galaxies. By fitting the spectral energy distribution, we measure their stellar masses to be in the range of log(M*/M⊙) ˜ 9.1-10.7. Combining these with IFU observations, we find a large spread of baryon fractions inside the host galaxies, between 7 and 100 percent. Similarly, we find gas fractions between 3 and 56 percent. Given their star formation rates, these objects lie on the expected main sequence of galaxies. Emission line metallicities indicate they are consistent with the mass-metallicity relation for DLAs. We also report an apparent anti-correlation between the stellar masses and N(H I), which could be due to a dust bias effect or lower column density systems tracing more massive galaxies. We present new ALMA observations of one of the targets leading to a molecular gas mass of log(Mmol/M⊙) < 9.89. We also investigate the morphology of the DLA counterparts and find that most of the galaxies show a clumpy structure and suggest ongoing tidal interaction. Thanks to our high spatial resolution HST data, we gain new insights in the structural complexity of the CGM.

Radio Jets Clearing the Way Through a Galaxy: Watching Feedback in Action in the Seyfert Galaxy IC 5063

NASA Astrophysics Data System (ADS)

Morganti, R.; Oosterloo, T. A.; Oonk, J. B. R.; Frieswijk, W.; Tadhunter, C. N.

2015-12-01

High-resolution (0.5 arcsec) CO(2-1) observations performed with the Atacama Large Millimetre/submillimetre Array have been used to trace the kinematics of the molecular gas in the Seyfert 2 galaxy{IC 5063}. Although one of the most radio-loud Seyfert galaxy, IC 5063 is a relatively weak radio source (P1.4GHz=3 ×1023 W Hz-1). The data reveal that the kinematics of the gas is very complex. A fast outflow of molecular gas extends along the entire radio jet (˜ 1 kpc), with the highest outflow velocities about 0.5 kpc from the nucleus, at the location of the brighter hot-spot in the W lobe. All the observed characteristics can be described by a scenario of a radio plasma jet expanding into a clumpy medium, interacting directly with the clouds and inflating a cocoon that drives a lateral outflow into the interstellar medium. This suggests that most of the observed cold molecular outflow is due to fast cooling of the gas after the passage of a shock and that it is the end product of the cooling process.

Simulating galaxies in the reionization era with FIRE-2: morphologies and sizes

NASA Astrophysics Data System (ADS)

Ma, Xiangcheng; Hopkins, Philip F.; Boylan-Kolchin, Michael; Faucher-Giguère, Claude-André; Quataert, Eliot; Feldmann, Robert; Garrison-Kimmel, Shea; Hayward, Christopher C.; Kereš, Dušan; Wetzel, Andrew

2018-06-01

We study the morphologies and sizes of galaxies at z ≥ 5 using high-resolution cosmological zoom-in simulations from the Feedback In Realistic Environments project. The galaxies show a variety of morphologies, from compact to clumpy to irregular. The simulated galaxies have more extended morphologies and larger sizes when measured using rest-frame optical B-band light than rest-frame UV light; sizes measured from stellar mass surface density are even larger. The UV morphologies are usually dominated by several small, bright young stellar clumps that are not always associated with significant stellar mass. The B-band light traces stellar mass better than the UV, but it can also be biased by the bright clumps. At all redshifts, galaxy size correlates with stellar mass/luminosity with large scatter. The half-light radii range from 0.01 to 0.2 arcsec (0.05-1 kpc physical) at fixed magnitude. At z ≥ 5, the size of galaxies at fixed stellar mass/luminosity evolves as (1 + z)-m, with m ˜ 1-2. For galaxies less massive than M* ˜ 108 M⊙, the ratio of the half-mass radius to the halo virial radius is ˜ 10 per cent and does not evolve significantly at z = 5-10; this ratio is typically 1-5 per cent for more massive galaxies. A galaxy's `observed' size decreases dramatically at shallower surface brightness limits. This effect may account for the extremely small sizes of z ≥ 5 galaxies measured in the Hubble Frontier Fields. We provide predictions for the cumulative light distribution as a function of surface brightness for typical galaxies at z = 6.

Molecular Line Emission as a Tool for Galaxy Observations (LEGO). I. HCN as a tracer of moderate gas densities in molecular clouds and galaxies

NASA Astrophysics Data System (ADS)

Kauffmann, Jens; Goldsmith, Paul F.; Melnick, Gary; Tolls, Volker; Guzman, Andres; Menten, Karl M.

2017-09-01

Trends observed in galaxies, such as the Gao & Solomon relation, suggest a linear relationship between the star formation rate and the mass of dense gas available for star formation. Validation of such trends requires the establishment of reliable methods to trace the dense gas in galaxies. One frequent assumption is that the HCN (J = 1-0) transition is unambiguously associated with gas at H2 densities ≫ 104 cm-3. If so, the mass of gas at densities ≫ 104 cm-3 could be inferred from the luminosity of this emission line, LHCN (1-0). Here we use observations of the Orion A molecular cloud to show that the HCN (J = 1-0) line traces much lower densities 103 cm-3 in cold sections of this molecular cloud, corresponding to visual extinctions AV ≈ 6 mag. We also find that cold and dense gas in a cloud like Orion produces too little HCN emission to explain LHCN (1-0) in star forming galaxies, suggesting that galaxies might contain a hitherto unknown source of HCN emission. In our sample of molecules observed at frequencies near 100 GHz (also including 12CO, 13CO, C18O, CN, and CCH), N2H+ is the only species clearly associated with relatively dense gas.

A COMPARATIVE STUDY OF KNOTS OF STAR FORMATION IN INTERACTING VERSUS SPIRAL GALAXIES

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

Smith, Beverly J.; Olmsted, Susan; Jones, Keith

2016-03-15

Interacting galaxies are known to have higher global rates of star formation on average than normal galaxies, relative to their stellar masses. Using UV and IR photometry combined with new and published Hα images, we have compared the star formation rates (SFRs) of ∼700 star forming complexes in 46 nearby interacting galaxy pairs with those of regions in 39 normal spiral galaxies. The interacting galaxies have proportionally more regions with high SFRs than the spirals. The most extreme regions in the interacting systems lie at the intersections of spiral/tidal structures, where gas is expected to pile up and trigger starmore » formation. Published Hubble Space Telescope images show unusually large and luminous star clusters in the highest luminosity regions. The SFRs of the clumps correlate with measures of the dust attenuation, consistent with the idea that regions with more interstellar gas have more star formation. For the clumps with the highest SFRs, the apparent dust attenuation is consistent with the Calzetti starburst dust attenuation law. This suggests that the high luminosity regions are dominated by a central group of young stars surrounded by a shell of clumpy interstellar gas. In contrast, the lower luminosity clumps are bright in the UV relative to Hα, suggesting either a high differential attenuation between the ionized gas and the stars, or a post-starburst population bright in the UV but faded in Hα. The fraction of the global light of the galaxies in the clumps is higher on average for the interacting galaxies than for the spirals. Thus either star formation in interacting galaxies is “clumpier” on average, or the star forming regions in interacting galaxies are more luminous, dustier, or younger on average.« less

WHERE DO WET, DRY, AND MIXED GALAXY MERGERS OCCUR? A STUDY OF THE ENVIRONMENTS OF CLOSE GALAXY PAIRS IN THE DEEP2 GALAXY REDSHIFT SURVEY

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

Lin, Lihwai; Cooper, Michael C.; Willmer, Christopher N. A.

2010-08-01

We study the environments of wet, dry, and mixed galaxy mergers at 0.75 < z < 1.2 using close pairs in the DEEP2 Galaxy Redshift Survey. We find that the typical environment of dry and mixed merger candidates is denser than that of wet mergers, mostly due to the color-density relation. While the galaxy companion rate (N{sub c}) is observed to increase with overdensity, using N-body simulations, we find that the fraction of pairs that will eventually merge decreases with the local density, predominantly because interlopers are more common in dense environments. After taking into account the merger probability ofmore » pairs as a function of local density, we find only marginal environment dependence of the galaxy merger rate for wet mergers. On the other hand, the dry and mixed merger rates increase rapidly with local density due to the increased population of red galaxies in dense environments, implying that the dry and mixed mergers are most effective in overdense regions. We also find that the environment distribution of K+A galaxies is similar to that of wet mergers alone and of wet+mixed mergers, suggesting a possible connection between K+A galaxies and wet and/or wet+mixed mergers. Based on our results, we therefore expect that the properties, including structures and masses, of red-sequence galaxies should be different between those in underdense regions and those in overdense regions since the dry mergers are significantly more important in dense environments. We conclude that, as early as z {approx} 1, high-density regions are the preferred environment in which dry mergers occur, and that present-day red-sequence galaxies in overdense environments have, on average, undergone 1.2 {+-} 0.3 dry mergers since this time, accounting for (38 {+-} 10)% of their mass accretion in the last 8 billion years. The main uncertainty in this finding is the conversion from the pair fraction to the galaxy merger rate, which is possibly as large as a factor of 2. Our findings suggest that dry mergers are crucial in the mass assembly of massive red galaxies in dense environments, such as brightest cluster galaxies in galaxy groups and clusters.« less

HCN Survey of Normal Spiral, Infrared-luminous, and Ultraluminous Galaxies

NASA Astrophysics Data System (ADS)

Gao, Yu; Solomon, Philip M.

2004-05-01

We report systematic HCN J=1-0 (and CO) observations of a sample of 53 infrared (IR) and/or CO-bright and/or luminous galaxies, including seven ultraluminous infrared galaxies, nearly 20 luminous infrared galaxies, and more than a dozen of the nearest normal spiral galaxies. This is the largest and most sensitive HCN survey of galaxies to date. All galaxies observed so far follow the tight correlation between the IR luminosity LIR and the HCN luminosity LHCN initially proposed by Solomon, Downes, & Radford, which is detailed in a companion paper. We also address here the issue of HCN excitation. There is no particularly strong correlation between LHCN and the 12 μm luminosity; in fact, of all the four IRAS bands, the 12 μm luminosity has the weakest correlation with the HCN luminosity. There is also no evidence of stronger HCN emission or a higher ratio of HCN and CO luminosities LHCN/LCO for galaxies with excess 12 μm emission. This result implies that mid-IR radiative pumping, or populating, of the J=1 level of HCN by a mid-IR vibrational transition is not important compared with the collisional excitation by dense molecular hydrogen. Furthermore, large velocity gradient calculations justify the use of HCN J=1-0 emission as a tracer of high-density molecular gas (>~3×104/τcm-3) and give an estimate of the mass of dense molecular gas from HCN observations. Therefore, LHCN may be used as a measure of the total mass of dense molecular gas, and the luminosity ratio LHCN/LCO may indicate the fraction of molecular gas that is dense.

THE JAMES CLERK MAXWELL TELESCOPE NEARBY GALAXIES LEGACY SURVEY. II. WARM MOLECULAR GAS AND STAR FORMATION IN THREE FIELD SPIRAL GALAXIES

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

Warren, B. E.; Wilson, C. D.; Sinukoff, E.

2010-05-01

We present the results of large-area {sup 12}CO J = 3-2 emission mapping of three nearby field galaxies, NGC 628, NGC 3521, and NGC 3627, completed at the James Clerk Maxwell Telescope as part of the Nearby Galaxies Legacy Survey. These galaxies all have moderate to strong {sup 12}CO J = 3-2 detections over large areas of the fields observed by the survey, showing resolved structure and dynamics in their warm/dense molecular gas disks. All three galaxies were part of the Spitzer Infrared Nearby Galaxies Survey sample, and as such have excellent published multiwavelength ancillary data. These data sets allowmore » us to examine the star formation properties, gas content, and dynamics of these galaxies on sub-kiloparsec scales. We find that the global gas depletion time for dense/warm molecular gas in these galaxies is consistent with other results for nearby spiral galaxies, indicating this may be independent of galaxy properties such as structures, gas compositions, and environments. Similar to the results from The H I Nearby Galaxy Survey, we do not see a correlation of the star formation efficiency with the gas surface density consistent with the Schmidt-Kennicutt law. Finally, we find that the star formation efficiency of the dense molecular gas traced by {sup 12}CO J = 3-2 is potentially flat or slightly declining as a function of molecular gas density, the {sup 12}CO J = 3-2/J = 1-0 ratio (in contrast to the correlation found in a previous study into the starburst galaxy M83), and the fraction of total gas in molecular form.« less

Massive Galaxies Are Larger in Dense Environments: Environmental Dependence of Mass-Size Relation of Early-type Galaxies

NASA Astrophysics Data System (ADS)

Yoon, Yongmin; Im, Myungshin; Kim, Jae-Woo

2017-01-01

Under the Λ cold dark matter (ΛCDM) cosmological models, massive galaxies are expected to be larger in denser environments through frequent hierarchical mergers with other galaxies. Yet, observational studies of low-redshift early-type galaxies have shown no such trend, standing as a puzzle to solve during the past decade. We analyzed 73,116 early-type galaxies at 0.1 ≤ z < 0.15, adopting a robust nonparametric size measurement technique and extending the analysis to many massive galaxies. We find for the first time that local early-type galaxies heavier than 1011.2 M⊙ show a clear environmental dependence in mass-size relation, in such a way that galaxies are as much as 20%-40% larger in the densest environments than in underdense environments. Splitting the sample into the brightest cluster galaxies (BCGs) and non-BCGs does not affect the result. This result agrees with the ΛCDM cosmological simulations and suggests that mergers played a significant role in the growth of massive galaxies in dense environments as expected in theory.

HUBBLE PROBES THE VIOLENT BIRTH OF STARS IN GALAXY NGC 253 [Left

NASA Technical Reports Server (NTRS)

2002-01-01

An image of the spiral galaxy NGC 253, taken with a ground-based telescope. The galaxy is located about 8 million light-years away in the constellation Sculptor. Credit: Jay Gallagher (University of Wisconsin-Madison), Alan Watson (Lowell Observatory, Flagstaff, AZ), and NASA [Right] This NASA Hubble Space Telescope image of the core of the nearest starburst spiral galaxy, NGC 253, reveals violent star formation within a region 1,000 light-years across. A starburst galaxy has an exceptionally high rate of star birth, first identified by its excess of infrared radiation from warm dust. Hubble's high resolution allows astronomers to quantify complex structures in the starburst core of the galaxy for the first time, including luminous star clusters, dust lanes which trace regions of dense gas and filaments of glowing gas. Hubble identifies several regions of intense star formation, which include a bright, super-compact star cluster. These observations confirm that stars are often born in dense clusters within starbursts, and that dense gas coexists with and obscures the starburst core. This image was taken with Hubble's Wide Field Planetary Camera 2 (in PC mode). Credit: Carnegie Institution of Washington

SHARDS: constraints on the dust attenuation law of star-forming galaxies at z ˜ 2

NASA Astrophysics Data System (ADS)

Tress, Mónica; Mármol-Queraltó, Esther; Ferreras, Ignacio; Pérez-González, Pablo G.; Barro, Guillermo; Pampliega, Belén Alcalde; Cava, Antonio; Domínguez-Sánchez, Helena; Eliche-Moral, Carmen; Espino-Briones, Néstor; Esquej, Pilar; Hernán-Caballero, Antonio; Rodighiero, Giulia; Rodriguez-Muñoz, Lucía

2018-04-01

We make use of the Survey of High-z Absorption Red and Dead Sources, an ultradeep (<26.5AB) galaxy survey that provides optical photospectra at resolution R ˜ 50, via medium-band filters (FWHM ˜ 150 Å). This data set is combined with ancillary optical and NIR fluxes to constrain the dust attenuation law in the rest-frame NUV region of star-forming galaxies within the redshift window 1.5 < z < 3. We focus on the NUV bump strength (B) and the total-to-selective extinction ratio (RV), targeting a sample of 1753 galaxies. By comparing the data with a set of population synthesis models coupled to a parametric dust attenuation law, we constrain RV and B, as well as the colour excess, E(B - V). We find a correlation between RV and B, which can be interpreted either as a result of the grain size distribution, or a variation of the dust geometry among galaxies. According to the former, small dust grains are associated with a stronger NUV bump. The latter would lead to a range of clumpiness in the distribution of dust within the interstellar medium of star-forming galaxies. The observed wide range of NUV bump strengths can lead to a systematic in the interpretation of the UV slope β typically used to characterize the dust content. In this study, we quantify these variations, concluding that the effects are Δβ ˜ 0.4.

Clumpy Disks as a Testbed for Feedback-regulated Galaxy Formation

NASA Astrophysics Data System (ADS)

Mayer, Lucio; Tamburello, Valentina; Lupi, Alessandro; Keller, Ben; Wadsley, James; Madau, Piero

2016-10-01

We study the dependence of fragmentation in massive gas-rich galaxy disks at z > 1 on stellar feedback schemes and hydrodynamical solvers, employing the GASOLINE2 SPH code and the lagrangian mesh-less code GIZMO in finite mass mode. Non-cosmological galaxy disk runs with the standard delayed-cooling blastwave feedback are compared with runs adopting a new superbubble feedback, which produces winds by modeling the detailed physics of supernova-driven bubbles and leads to efficient self-regulation of star formation. We find that, with blastwave feedback, massive star-forming clumps form in comparable number and with very similar masses in GASOLINE2 and GIZMO. Typical clump masses are in the range 107-108 M ⊙, lower than in most previous works, while giant clumps with masses above 109 M ⊙ are exceedingly rare. By contrast, superbubble feedback does not produce massive star-forming bound clumps as galaxies never undergo a phase of violent disk instability. In this scheme, only sporadic, unbound star-forming overdensities lasting a few tens of Myr can arise, triggered by non-linear perturbations from massive satellite companions. We conclude that there is severe tension between explaining massive star-forming clumps observed at z > 1 primarily as the result of disk fragmentation driven by gravitational instability and the prevailing view of feedback-regulated galaxy formation. The link between disk stability and star formation efficiency should thus be regarded as a key testing ground for galaxy formation theory.

How does ionizing radiation escape from galaxies?

NASA Astrophysics Data System (ADS)

Orlitova, Ivana

2016-10-01

Search for sources that reionized the Universe from z 15 to z 6 is one of the main drivers of present-day astronomy. Low-mass star-forming galaxies are the most favoured sources of ionizing photons, but the searches of escaping Lyman continuum (LyC) have not been extremely successful. Our team has recently detected prominent LyC escape from five Green Pea galaxies at redshift 0.3, using the HST/COS spectrograph, which represents a significant breakthrough. We propose here to study the LyC escape of the strongest among these leakers, J1152, with spatial resolution. From the comparison of the ionizing and non-ionizing radiation maps, and surface brightness profiles, we will infer the major mode in which LyC is escaping: from the strongest starburst, from the galaxy edge, through a hole along our line-of-sight, through clumpy medium, or directly from all the production sites due to highly ionized medium in the entire galaxy. In parallel, we will test the predictive power of two highly debated indirect indicators of LyC leakage: the [OIII]5007/[OII]3727 ratio, and Lyman-alpha. We predict that their spatial distribution should closely follow that of the ionizing continuum if column densities of the neutral gas are low. This combined study, which relies on the HST unique capabilities, will bring crucial information on the structure of the leaking galaxies, provide constraints for hydrodynamic simulations, and will lead to efficient future searches for LyC leakers across a large range of redshifts.

Understanding Emission From The Ism In The Milky Way And Other Galaxies Using [Nii] And Other Tracers

NASA Astrophysics Data System (ADS)

Goldsmith, Paul

We propose to combine recently-obtained data on the far-infrared fine structure lines of ionized nitrogen ([NII]) with studies of radio continuum and other far-infrared lines, to address a number of key questions about the structure of the interstellar medium, star formation, and to bootstrap our detailed understanding of processes in the Milky Way to more distant galaxies. The [CII] 158 μm line is the most powerful single far-infrared line emitted by galaxies, but since carbon can be ionized by photons having wavelengths longer than required to ionized hydrogen, [CII] emission can originate in atomic, molecular, and ionized regions. Due to its ionization potential being higher than that of hydrogen, nitrogen is a more selective tracer than carbon, and can serve as a critical ingredient to determine how much of the [CII] emission is produced in HII regions powered by massive young stars. We propose to take advantage of a newly-completed Herschel survey of the Galactic plane in both of the [NII] lines at 205 μm and 122 μm wavelength, complementing the GOT C+ survey of [CII]. The relative intensity of the two [NII] lines is a direct indicator of the electron density, and thus allows determination of the N+ column density. With the two data sets we can then determine what fraction of the [CII] emission is produced in HII regions, and what may be from the more diffuse components, thus enabling reconciliation of the Herschel and COBE measurements of this critical tracer. We also propose to use Planck and WMAP all-sky maps of the radio free-free emission to determine the emission measure. Comparison with the electron density and ionized nitrogen column density enables a novel probe of clumpiness in this component of the interstellar medium in addition to giving an improved method of determining the overall Galactic electron density distribution. A second aspect of our investigation of clumpiness will be to utilize the fact that each [NII] observation with the PACS instrument on Herschel consists of 25 spectra on a 5x5 grid. Using these, we will compare derived column densities and electron densities over these small regions to assess the degree of clumpiness. A third input to our analysis of inhomogeneities will be to compare the Planck & WMAP images of selected regions with much higher resolution ground-based data from survey such as CORNISH and GALFACTS. We also will use the improved understanding of [CII] and [NII] emission to develop a template for use in interpreting emission of these (and possibly other) tracers from other galaxies. We will be able to calculate the relative luminosities of these two tracers as a function of Galactocentric distance in the Milky Way, which will be available for comparison with existing and future data on other galaxies. This very active field suffers from an inability to distinguish the multiple sources of [CII] emission, and the understanding of how this spectral line works as a tracer of star formation is of very great interest to a large community of extragalactic astronomers. Together these studies will significantly improve our understanding of [CII] emission and its role as a coolant of the ISM, and the role of HII regions produced by massive young stars as sources of far-infrared line emission. In addition to a better appreciation of the life cycle of the interstellar medium, this work will also set the stage for better understanding of far-infrared emission from other galaxies though development of an improved Milky Way template. All of the data have been taken and are available including our own Herschel [NII] data, which have been reduced. As indicated in the proposal, we have made a limited demonstration of the required techniques, so that we are confident that this proposal will yield the desired new information and astrophysical results.

The Host Galaxies of X-Ray Selected Active Galactic Nuclei to z - 2.5: Structure, Star-Formation and Their Relationships from CANDELS and Herschel/Pacs

NASA Technical Reports Server (NTRS)

Rosario, D.J.; McIntosh, D. H.; van der Wel, A.; Kartaltepe, J.; Lang, P.; Santini, P.; Wuyts, S.; Lutz, D.; Rafelski, M.; Villforth, C.;

Galaxy population properties of the massive X-ray luminous galaxy cluster XDCP J0044.0-2033 at z = 1.58. Red-sequence formation, massive galaxy assembly, and central star formation activity

NASA Astrophysics Data System (ADS)

Fassbender, R.; Nastasi, A.; Santos, J. S.; Lidman, C.; Verdugo, M.; Koyama, Y.; Rosati, P.; Pierini, D.; Padilla, N.; Romeo, A. D.; Menci, N.; Bongiorno, A.; Castellano, M.; Cerulo, P.; Fontana, A.; Galametz, A.; Grazian, A.; Lamastra, A.; Pentericci, L.; Sommariva, V.; Strazzullo, V.; Šuhada, R.; Tozzi, P.

2014-08-01

Context. Recent observational progress has enabled the detection of galaxy clusters and groups out to very high redshifts and for the first time allows detailed studies of galaxy population properties in these densest environments in what was formerly known as the "redshift desert" at z> 1.5. Aims: We aim to investigate various galaxy population properties of the massive X-ray luminous galaxy cluster XDCP J0044.0-2033 at z = 1.58, which constitutes the most extreme currently known matter-density peak at this redshift. Methods: We analyzed deep VLT/HAWK-I near-infrared data with an image quality of 0.5'' and limiting Vega magnitudes (50% completeness) of 24.2 in J- and 22.8 in the Ks band, complemented by similarly deep Subaru imaging in i and V, Spitzer observations at 4.5 μm, and new spectroscopic observations with VLT/FORS 2. Results: We detect a cluster-associated excess population of about 90 galaxies, most of them located within the inner 30'' (250 kpc) of the X-ray centroid, which follows a centrally peaked, compact NFW galaxy surface-density profile with a concentration of c200 ≃ 10. Based on the Spitzer 4.5 μm imaging data, we measure a total enclosed stellar mass of M∗500 ≃ (6.3 ± 1.6) × 1012 M⊙ and a resulting stellar mass fraction of f∗,500 = M∗,500/M500 = (3.3 ± 1.4)%, consistent with local values. The total J- and Ks-band galaxy luminosity functions of the core region yield characteristic magnitudes J* and Ks* consistent with expectations from simple zf = 3 burst models. However, a detailed look at the morphologies and color distributions of the spectroscopically confirmed members reveals that the most massive galaxies are undergoing a very active mass-assembly epoch through merging processes. Consequently, the bright end of the cluster red sequence is not in place, while a red-locus population is present at intermediate magnitudes [Ks*, Ks* + 1.6], which is then sharply truncated at magnitudes fainter than Ks* + 1.6. The dominant cluster-core population comprises post-quenched galaxies transitioning toward the red sequence at intermediate magnitudes, while additionally a significant blue-cloud population of faint star-forming galaxies is present even in the densest central regions. Based on a color-color selection performed to separate different cluster galaxy types, we find that the blue star-forming population is concentrated in clumpy structures and dominates in particular at and beyond the R500 radius. On the other hand, the fraction of post-starburst galaxies steadily increases toward the center, while the red-locus population and red-sequence transition galaxies seem to reach their peak fractions already at intermediate cluster-centric radii of about r ~ 200 kpc. Conclusions: Our observations support the scenario in which the dominant effect of the dense z ≃ 1.6 cluster environment is an accelerated mass-assembly timescale (~1 Gyr or shorter) through merging activity that is responsible for driving core galaxies across the mass-quenching threshold of log (M∗/M⊙) ≃ 10.4. Beyond this mass limit, star formation is suppressed on timescales of ~1 Gyr, while the direct environmental quenching process seems to be subdominant and is acting on significantly longer timescales (~2-3 Gyr). Based on observations under programme ID 084.A-0844, 087.A-0351, and 089.A-0419 collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile.J- and Ks-band FITS files are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568/A5

Warm Molecular Gas Traced with CO J = 7 --> 6 in the Galaxy's Central 2 Parsecs: Dynamical Heating of the Circumnuclear Disks

NASA Technical Reports Server (NTRS)

Bradford, C. M.; Stacey, G. J.; Nikola, T.; Bolatto, A. D.; Jackson, J. M.; Savage, M. L.; Davidson, J. A.

2005-01-01

We present an 11" resolution map of the central 2 pc of the Galaxy in the CO J = 7 --> 6 rotational transition. The CO emission shows rotation about Sgr A* but also evidence for noncircular turbulent motion and a clumpy morphology. We combine our data set with available CO measurements to model the physical conditions in the disk. We find that the molecular gas in the region is both warm and dense, with T approx. 200-300 K and n(sub H2) approx. (5-7) x 10(exp 4) cm(exp -3). The mass of warm molecular gas we measure in the central 2 pc is at least 2000 M(solar), about 20 times the UV-excited atomic gas mass, ruling out a UV heating scenario for the molecular material. We compare the available spectral tracers with theoretical models and conclude that molecular gas is heated with magnetohydrodynamic shocks with v approx. 10-20 km s(exp -1) and B approx. 0.3- 0.5 mG. Using the conditions derived with the CO analysis, we include the other important coolants, neutral oxygen and molecular hydrogen, to estimate the total cooling budget of the molecular material. We derive a mass-to-luminosity ratio of approx. 2-3 M(solar)(L(solar)exp -1), which is consistent with the total power dissipated via turbulent decay in 0.1 pc cells with v(sub rms) approx. 15 kilometers per second. These size and velocity scales are comparable to the observed clumping scale and the velocity dispersion. At this rate, the material near Sgr A* is dissipating its orbital energy on an orbital timescale and cannot last for more than a few orbits. Our conclusions support a scenario in which the features near Sgr A* such as the circumnuclear disk and northern arm are generated by infalling clouds with low specific angular momentum.

Celestial Cities and the Roads That Connect Them

NASA Image and Video Library

2008-01-25

Observations from NASA Spitzer Space Telescope show that filamentary galaxies form stars at twice the rate of their densely clustered counterparts. This is a representation of galaxies in and surrounding a galaxy cluster called Abell 1763.

Spitzer Spies Spectacular Sombrero

NASA Image and Video Library

2005-05-04

NASA's Spitzer Space Telescope set its infrared eyes on one of the most famous objects in the sky, Messier 104, also called the Sombrero galaxy. In this striking infrared picture, Spitzer sees an exciting new view of a galaxy that in visible light has been likened to a "sombrero," but here looks more like a "bulls-eye." Recent observations using Spitzer's infrared array camera uncovered the bright, smooth ring of dust circling the galaxy, seen in red. In visible light, because this galaxy is seen nearly edge-on, only the near rim of dust can be clearly seen in silhouette. Spitzer's full view shows the disk is warped, which is often the result of a gravitational encounter with another galaxy, and clumpy areas spotted in the far edges of the ring indicate young star-forming regions. Spitzer's infrared view of the starlight from this galaxy, seen in blue, can pierce through obscuring murky dust that dominates in visible light. As a result, the full extent of the bulge of stars and an otherwise hidden disk of stars within the dust ring are easily seen. The Sombrero galaxy is located some 28 million light years away. Viewed from Earth, it is just six degrees south of its equatorial plane. Spitzer detected infrared emission not only from the ring, but from the center of the galaxy too, where there is a huge black hole, believed to be a billion times more massive than our Sun. This picture is composed of four images taken at 3.6 (blue), 4.5 (green), 5.8 (orange), and 8.0 (red) microns. The contribution from starlight (measured at 3.6 microns) has been subtracted from the 5.8 and 8-micron images to enhance the visibility of the dust features. http://photojournal.jpl.nasa.gov/catalog/PIA07899

Dense cloud cores revealed by CO in the low metallicity dwarf galaxy WLM.

PubMed

Rubio, Monica; Elmegreen, Bruce G; Hunter, Deidre A; Brinks, Elias; Cortés, Juan R; Cigan, Phil

2015-09-10

Understanding stellar birth requires observations of the clouds in which they form. These clouds are dense and self-gravitating, and in all existing observations they are molecular, with H2 the dominant species and carbon monoxide (CO) the best available tracer. When the abundances of carbon and oxygen are low compared with that of hydrogen, and the opacity from dust is also low, as in primeval galaxies and local dwarf irregular galaxies, CO forms slowly and is easily destroyed, so it is difficult for it to accumulate inside dense clouds. Here we report interferometric observations of CO clouds in the local group dwarf irregular galaxy Wolf-Lundmark-Melotte (WLM), which has a metallicity that is 13 per cent of the solar value and 50 per cent lower than the previous CO detection threshold. The clouds are tiny compared to the surrounding atomic and H2 envelopes, but they have typical densities and column densities for CO clouds in the Milky Way. The normal CO density explains why star clusters forming in dwarf irregulars have similar densities to star clusters in giant spiral galaxies. The low cloud masses suggest that these clusters will also be low mass, unless some galaxy-scale compression occurs, such as an impact from a cosmic cloud or other galaxy. If the massive metal-poor globular clusters in the halo of the Milky Way formed in dwarf galaxies, as is commonly believed, then they were probably triggered by such an impact.

History of Hubble Space Telescope (HST)

NASA Image and Video Library

2003-06-09

The razor sharp eye of the Hubble Space Telescope (HST) easily resolves the Sombrero galaxy, Messier 104 (M104). 50,000 light-years across, the galaxy is located 28 million light-years from Earth at the southern edge of the rich Virgo cluster of galaxies. Equivalent to 800 billion suns, Sombrero is one of the most massive objects in that group. The hallmark of Sombrero is a brilliant white, bulbous core encircled by the thick dust lanes comprising the spiral structure of the galaxy. As seen from Earth, the galaxy is tilted nearly edge-on. We view it from just six degrees north of its equatorial plane. This rich system of globular clusters is estimated to be nearly 2,000 in number which is 10 times as many as in our Milky Way galaxy. Similar to the clusters in the Milky Way, the ages range from 10-13 billion years old. Embedded in the bright core of M104 is a smaller disk, which is tilted relative to the large disk. The HST paired with the Spitzer infrared telescope, offers this striking composite capturing the magnificence of the Sombrero galaxy. In the Hubble view, the galaxy resembles a broad-rimmed Mexican hat, whereas in the Spitzer striking infrared view, the galaxy looks more like a bulls eye. The full view provided by Spitzer shows the disk is warped, which is often the result of a gravitational encounter with another galaxy, and clumpy areas spotted in the far edges of the ring indicate young star forming regions. Spitzer detected infrared emission not only from the ring, but from the center of the galaxy as well, where there is a huge black hole believed to be a billion times more massive than our Sun. The Marshall Space Flight Center (MSFC) had responsibility for design, development, and construction of the HST.

Galaxy And Mass Assembly: resolving the role of environment in galaxy evolution

NASA Astrophysics Data System (ADS)

Brough, S.; Croom, S.; Sharp, R.; Hopkins, A. M.; Taylor, E. N.; Baldry, I. K.; Gunawardhana, M. L. P.; Liske, J.; Norberg, P.; Robotham, A. S. G.; Bauer, A. E.; Bland-Hawthorn, J.; Colless, M.; Foster, C.; Kelvin, L. S.; Lara-Lopez, M. A.; López-Sánchez, Á. R.; Loveday, J.; Owers, M.; Pimbblet, K. A.; Prescott, M.

2013-11-01

We present observations of 18 galaxies from the Galaxy And Mass Assembly (GAMA) survey made with the SPIRAL optical integral field unit (IFU) on the Anglo-Australian Telescope. The galaxies are selected to have a narrow range in stellar mass (6 × 109 < M* < 2 × 1010 M⊙) in order to focus on the effects of environment. Local galaxy environments are measured quantitatively using fifth nearest neighbour surface densities. We find that the total star formation rates (SFR) measured from the IFU data are consistent with total SFRs measured from aperture correcting either GAMA or Sloan Digital Sky Survey single-fibre observations. The mean differences are SFRGAMA/SFRIFU = 1.26 ± 0.23, σ = 0.90 and for the Sloan Digital Sky Survey we similarly find SFRBrinchmann/SFRIFU = 1.34 ± 0.17, σ = 0.67. Examining the relationships with environment, we find that off-centre and clumpy Hα emission is not significantly dependent on environment, being present in 2/7 (29^{+20}_{-11} per cent) galaxies in high-density environments (>0.77 Mpc-2), and 5/11 (45^{+15}_{-13} per cent) galaxies in low-density environments (<0.77 Mpc-2). We find a weak but not significant relationship of the total SFRs of star-forming galaxies with environment. Due to the size of our sample and the scatter observed we do not draw a definitive conclusion about a possible SFR dependence on environment. Examining the spatial distribution of the Hα emission, we find no evidence for a change in shape or amplitude of the radial profile of star-forming galaxies with environment. If these observations are borne out in larger samples, this would infer that any environment-driven star formation suppression must either act very rapidly (the `infall-and-quench' model) or that galaxies must evolve in a density-dependent manner (an `in situ evolution' model).

New Ultra-Compact Dwarf Galaxies in Clusters

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-02-01

How do ultra-compact dwarf galaxies (UCDs) galaxies that are especially small and dense form and evolve? Scientists have recently examined distant galaxy clusters, searching for more UCDs to help us answer this question.Origins of DwarfsIn recent years we have discovered a growing sample of small, very dense galaxies. Galaxies that are tens to hundreds of light-years across, with masses between a million and a billion solar masses, fall into category of ultra-compact dwarfs (UCDs).An example of an unresolved compact object from the authors survey that is likely an ultra-compact dwarf galaxy. [Adapted from Zhang Bell 2017]How do these dense and compact galaxies form? Two possibilities are commonly suggested:An initially larger galaxy was tidally stripped during interactions with other galaxies in a cluster, leaving behind only its small, dense core as a UCD.UCDs formed as compact galaxies at very early cosmic times. The ones living in a massive dark matter halo may have been able to remain compact over time, evolving into the objectswe see today.To better understand which of these formation scenarios applies to which galaxies, we need a larger sample size! Our census of UCDs is fairly limited and because theyare small and dim, most of the ones weve discovered are in the nearby universe. To build a good sample, we need to find UCDs at higher redshifts as well.A New SampleIn a recent study, two scientists from University of Michigan have demonstrated how we might find more UCDs. Yuanyuan Zhang (also affiliated with Fermilab) and Eric Bell used the Cluster Lensing and Supernova Survey with Hubble (CLASH) to search 17 galaxy clusters at intermediate redshifts of 0.2 z 0.6, looking for unresolved objects that might be UCDs.The mass and size distributions of the UCD candidates reported in this study, in the context of previously known nuclear star clusters, globular clusters (GCs), UCDs, compact elliptical galaxies (cEs), and dwarf galaxies. [Zhang Bell 2017]Zhang and Bell discovered a sample of compact objects grouped around the central galaxies of the clusters that are consistent with ultra-compact galaxies. The inferred sizes (many around 600 light-years in radius) and masses (roughly one billion solar masses) of these objects suggest that this sample may contain some of the densest UCDs discovered to date.The properties of this new set of UCD candidates arent enough to distinguish between formation scenarios yet, but the authors argue that if we find more such galaxies, we will be able to use the statistics of their spatial and color distributions to determine how they were formed.Zhang and Bell estimate that the 17 CLASH clusters studied in this work each contain an average of 2.7 of these objects in the central million light-years of the cluster. The authors work here suggests that searching wide-field survey data for similar discoveries is a plausible way to increase our sample of UCDs. This will allow us to statistically characterize these dense, compact galaxies and better understand their origins.CitationYuanyuan Zhang and Eric F. Bell 2017 ApJL 835 L2. doi:10.3847/2041-8213/835/1/L2

VizieR Online Data Catalog: Metallicity of MPA-JHU SDSS-DR7 dwarf galaxies (Douglass+, 2017)

NASA Astrophysics Data System (ADS)

Douglass, K. A.; Vogeley, M. S.

2017-07-01

We study how the cosmic environment affects galaxy evolution in the universe by comparing the metallicities of dwarf galaxies in voids with dwarf galaxies in more dense regions. Ratios of the fluxes of emission lines, particularly those of the forbidden [OIII] and [SII] transitions, provide estimates of a region's electron temperature and number density. From these two quantities and the emission line fluxes [OII]λ3727, [OIII]λ4363, and [OIII]λλ4959,5007, we estimate the abundance of oxygen with the direct Te method. We estimate the metallicity of 42 blue, star-forming void dwarf galaxies and 89 blue, star-forming dwarf galaxies in more dense regions using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, as reprocessed in the MPA-JHU value-added catalog. We find very little difference between the two sets of galaxies, indicating little influence from the large-scale environment on their chemical evolution. Of particular interest are a number of extremely metal-poor dwarf galaxies that are less prevalent in voids than in the denser regions. (1 data file).

Gas Content and Kinematics in Clumpy, Turbulent Star-forming Disks

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

White, Heidi A.; Abraham, Roberto G.; Fisher, David B.

2017-09-01

We present molecular gas-mass estimates for a sample of 13 local galaxies whose kinematic and star-forming properties closely resemble those observed in z ≈ 1.5 main-sequence galaxies. Plateau de Bure observations of the CO[1-0] emission line and Herschel Space Observatory observations of the dust emission both suggest molecular gas-mass fractions of ∼20%. Moreover, dust emission modeling finds T {sub dust} < 30 K, suggesting a cold dust distribution compared to their high infrared luminosity. The gas-mass estimates argue that z ∼ 0.1 DYNAMO galaxies not only share similar kinematic properties with high- z disks, but they are also similarly richmore » in molecular material. Pairing the gas-mass fractions with existing kinematics reveals a linear relationship between f {sub gas} and σ / v {sub c}, consistent with predictions from stability theory of a self-gravitating disk. It thus follows that high gas-velocity dispersions are a natural consequence of large gas fractions. We also find that the systems with the lowest t {sub dep} (∼0.5 Gyr) have the highest ratios of σ / v{sub c} and more pronounced clumps, even at the same high molecular gas fraction.« less

CLUMPY DISKS AS A TESTBED FOR FEEDBACK-REGULATED GALAXY FORMATION

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

Mayer, Lucio; Tamburello, Valentina; Lupi, Alessandro

2016-10-10

We study the dependence of fragmentation in massive gas-rich galaxy disks at z >1 on stellar feedback schemes and hydrodynamical solvers, employing the GASOLINE2 SPH code and the lagrangian mesh-less code GIZMO in finite mass mode. Non-cosmological galaxy disk runs with the standard delayed-cooling blastwave feedback are compared with runs adopting a new superbubble feedback, which produces winds by modeling the detailed physics of supernova-driven bubbles and leads to efficient self-regulation of star formation. We find that, with blastwave feedback, massive star-forming clumps form in comparable number and with very similar masses in GASOLINE2 and GIZMO. Typical clump masses aremore » in the range 10{sup 7}–10{sup 8} M {sub ⊙}, lower than in most previous works, while giant clumps with masses above 10{sup 9} M {sub ⊙} are exceedingly rare. By contrast, superbubble feedback does not produce massive star-forming bound clumps as galaxies never undergo a phase of violent disk instability. In this scheme, only sporadic, unbound star-forming overdensities lasting a few tens of Myr can arise, triggered by non-linear perturbations from massive satellite companions. We conclude that there is severe tension between explaining massive star-forming clumps observed at z >1 primarily as the result of disk fragmentation driven by gravitational instability and the prevailing view of feedback-regulated galaxy formation. The link between disk stability and star formation efficiency should thus be regarded as a key testing ground for galaxy formation theory.« less

Spatially Resolved Hα Maps and Sizes of 57 Strongly Star-forming Galaxies at z ~ 1 from 3D-HST: Evidence for Rapid Inside-out Assembly of Disk Galaxies

NASA Astrophysics Data System (ADS)

Nelson, Erica June; van Dokkum, Pieter G.; Brammer, Gabriel; Förster Schreiber, Natascha; Franx, Marijn; Fumagalli, Mattia; Patel, Shannon; Rix, Hans-Walter; Skelton, Rosalind E.; Bezanson, Rachel; Da Cunha, Elisabete; Kriek, Mariska; Labbe, Ivo; Lundgren, Britt; Quadri, Ryan; Schmidt, Kasper B.

2012-03-01

We investigate the buildup of galaxies at z ~ 1 using maps of Hα and stellar continuum emission for a sample of 57 galaxies with rest-frame Hα equivalent widths >100 Å in the 3D-HST grism survey. We find that the Hα emission broadly follows the rest-frame R-band light but that it is typically somewhat more extended and clumpy. We quantify the spatial distribution with the half-light radius. The median Hα effective radius re (Hα) is 4.2 ± 0.1 kpc but the sizes span a large range, from compact objects with re (Hα) ~ 1.0 kpc to extended disks with re (Hα) ~ 15 kpc. Comparing Hα sizes to continuum sizes, we find =1.3 ± 0.1 for the full sample. That is, star formation, as traced by Hα, typically occurs out to larger radii than the rest-frame R-band stellar continuum; galaxies are growing their radii and building up from the inside out. This effect appears to be somewhat more pronounced for the largest galaxies. Using the measured Hα sizes, we derive star formation rate surface densities, ΣSFR. We find that ΣSFR ranges from ~0.05 M ⊙ yr-1 kpc-2 for the largest galaxies to ~5 M ⊙ yr-1 kpc-2 for the smallest galaxies, implying a large range in physical conditions in rapidly star-forming z ~ 1 galaxies. Finally, we infer that all galaxies in the sample have very high gas mass fractions and stellar mass doubling times <500 Myr. Although other explanations are also possible, a straightforward interpretation is that we are simultaneously witnessing the rapid formation of compact bulges and large disks at z ~ 1.

Mapping out the origins of compact stellar systems

NASA Astrophysics Data System (ADS)

Romanowsky, Aaron J.; Brodie, Jean P.; SAGES Collaboration

2017-03-01

We present a suite of extragalactic explorations of the origins and nature of globular clusters (GCs) and ultra-compact dwarfs (UCDs), and the connections between them. An example of GC metallicity bimodality is shown to reflect underlying, distinct metal-poor and metal-rich stellar halo populations. Metallicity-matching methods are used to trace the birth sites and epochs of GCs in giant E/S0s, pointing to clumpy disk galaxies at z ~ 3 for the metal-rich GCs, and to a combination of accreted and in-situ formation modes at z ~ 5-6 for the metal-poor GCs. An increasingly diverse zoo of compact stellar systems is being discovered, including objects that bridge the gaps between UCDs and faint fuzzies, and between UCDs and compact ellipticals. Many of these have properties pointing to origins as the stripped nuclei of larger galaxies, and a smoking-gun example is presented of an ω Cen-like star cluster embedded in a tidal stream.

Probing star formation relations of mergers and normal galaxies across the CO ladder

NASA Astrophysics Data System (ADS)

Greve, Thomas R.

We examine integrated luminosity relations between the IR continuum and the CO rotational ladder observed for local (ultra) luminous infra-red galaxies ((U)LIRGs, L IR >= 1011 M⊙) and normal star forming galaxies in the context of radiation pressure regulated star formation proposed by Andrews & Thompson (2011). This can account for the normalization and linear slopes of the luminosity relations (log L IR = α log L'CO + β) of both low- and high-J CO lines observed for normal galaxies. Super-linear slopes occur for galaxy samples with significantly different dense gas fractions. Local (U)LIRGs are observed to have sub-linear high-J (J up > 6) slopes or, equivalently, increasing L COhigh-J /L IR with L IR. In the extreme ISM conditions of local (U)LIRGs, the high-J CO lines no longer trace individual hot spots of star formation (which gave rise to the linear slopes for normal galaxies) but a more widespread warm and dense gas phase mechanically heated by powerful supernovae-driven turbulence and shocks.

Galaxy evolution. Evidence for mature bulges and an inside-out quenching phase 3 billion years after the Big Bang.

PubMed

Tacchella, S; Carollo, C M; Renzini, A; Förster Schreiber, N M; Lang, P; Wuyts, S; Cresci, G; Dekel, A; Genzel, R; Lilly, S J; Mancini, C; Newman, S; Onodera, M; Shapley, A; Tacconi, L; Woo, J; Zamorani, G

2015-04-17

Most present-day galaxies with stellar masses ≥10(11) solar masses show no ongoing star formation and are dense spheroids. Ten billion years ago, similarly massive galaxies were typically forming stars at rates of hundreds solar masses per year. It is debated how star formation ceased, on which time scales, and how this "quenching" relates to the emergence of dense spheroids. We measured stellar mass and star-formation rate surface density distributions in star-forming galaxies at redshift 2.2 with ~1-kiloparsec resolution. We find that, in the most massive galaxies, star formation is quenched from the inside out, on time scales less than 1 billion years in the inner regions, up to a few billion years in the outer disks. These galaxies sustain high star-formation activity at large radii, while hosting fully grown and already quenched bulges in their cores. Copyright © 2015, American Association for the Advancement of Science.

Stellar feedback in galaxies and the origin of galaxy-scale winds

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.; Quataert, Eliot; Murray, Norman

2012-04-01

Feedback from massive stars is believed to play a critical role in driving galactic super-winds that enrich the intergalactic medium and shape the galaxy mass function, mass-metallicity relation and other global galaxy properties. In previous papers, we have introduced new numerical methods for implementing stellar feedback on sub-giant molecular cloud (sub-GMC) through galactic scales in numerical simulations of galaxies; the key physical processes include radiation pressure in the ultraviolet through infrared, supernovae (Type I and Type II), stellar winds ('fast' O star through 'slow' asymptotic giant branch winds), and H II photoionization. Here, we show that these feedback mechanisms drive galactic winds with outflow rates as high as ˜10-20 times the galaxy star formation rate. The mass-loading efficiency (wind mass-loss rate divided by the star formation rate) scales roughly as ? (where Vc is the galaxy circular velocity), consistent with simple momentum-conservation expectations. We use our suite of simulations to study the relative contribution of each feedback mechanism to the generation of galactic winds in a range of galaxy models, from Small Magellanic Cloud like dwarfs and Milky Way (MW) analogues to z˜ 2 clumpy discs. In massive, gas-rich systems (local starbursts and high-z galaxies), radiation pressure dominates the wind generation. By contrast, for MW-like spirals and dwarf galaxies the gas densities are much lower and sources of shock-heated gas such as supernovae and stellar winds dominate the production of large-scale outflows. In all of our models, however, the winds have a complex multiphase structure that depends on the interaction between multiple feedback mechanisms operating on different spatial scales and time-scales: any single feedback mechanism fails to reproduce the winds observed. We use our simulations to provide fitting functions to the wind mass loading and velocities as a function of galaxy properties, for use in cosmological simulations and semi-analytic models. These differ from typically adopted formulae with an explicit dependence on the gas surface density that can be very important in both low-density dwarf galaxies and high-density gas-rich galaxies.

High resolution radio and optical observations of the central starburst in the low-metallicity dwarf galaxy II Zw 40

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

Kepley, Amanda A.; Reines, Amy E.; Johnson, Kelsey E.

2014-02-01

The extent to which star formation varies in galaxies with low masses, low metallicities, and high star formation rate surface densities is not well constrained. To gain insight into star formation under these physical conditions, this paper estimates the ionizing photon fluxes, masses, and ages for young massive clusters in the central region of II Zw 40—the prototypical low-metallicity dwarf starburst galaxy—from radio continuum and optical observations. Discrete, cluster-sized sources only account for half the total radio continuum emission; the remainder is diffuse. The young (≲ 5 Myr) central burst has a star formation rate surface density that significantly exceedsmore » that of the Milky Way. Three of the 13 sources have ionizing photon fluxes (and thus masses) greater than R136 in 30 Doradus. Although isolating the effects of galaxy mass and metallicity is difficult, the H II region luminosity function and the internal extinction in the center of II Zw 40 appear to be primarily driven by a merger-related starburst. The relatively flat H II region luminosity function may be the result of an increase in interstellar medium pressure during the merger and the internal extinction is similar to that generated by the clumpy and porous dust in other starburst galaxies.« less

SUZAKU OBSERVATIONS OF THE X-RAY BRIGHTEST FOSSIL GROUP ESO 3060170

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

Su, Yuanyuan; White, Raymond E. III; Miller, Eric D., E-mail: ysu@crimson.ua.edu

2013-10-01

'Fossil' galaxy groups, each dominated by a relatively isolated giant elliptical galaxy, have many properties intermediate between groups and clusters of galaxies. We used the Suzaku X-ray observatory to observe the X-ray brightest fossil group, ESO 3060170, out to R{sub 200}, in order to better elucidate the relation between fossil groups, normal groups, and clusters. We determined the intragroup gas temperature, density, and metal abundance distributions and derived the entropy, pressure, and mass profiles for this group. The entropy and pressure profiles in the outer regions are flatter than in simulated clusters, similar to what is seen in observations ofmore » massive clusters. This may indicate that the gas is clumpy and/or the gas has been redistributed. Assuming hydrostatic equilibrium, the total mass is estimated to be ∼1.7 × 10{sup 14} M{sub ☉} within a radius R{sub 200} of ∼1.15 Mpc, with an enclosed baryon mass fraction of 0.13. The integrated iron mass-to-light ratio of this fossil group is larger than in most groups and comparable to those of clusters, indicating that this fossil group has retained the bulk of its metals. A galaxy luminosity density map on a scale of 25 Mpc shows that this fossil group resides in a relatively isolated environment, unlike the filamentary structures in which typical groups and clusters are embedded.« less

What Determines Star Formation Rates?

NASA Astrophysics Data System (ADS)

Evans, Neal John

2017-06-01

The relations between star formation and gas have received renewed attention. We combine studies on scales ranging from local (within 0.5 kpc) to distant galaxies to assess what factors contribute to star formation. These include studies of star forming regions in the Milky Way, the LMC, nearby galaxies with spatially resolved star formation, and integrated galaxy studies. We test whether total molecular gas or dense gas provides the best predictor of star formation rate. The star formation ``efficiency," defined as star formation rate divided by mass, spreads over a large range when the mass refers to molecular gas; the standard deviation of the log of the efficiency decreases by a factor of three when the mass of relatively dense molecular gas is used rather than the mass of all the molecular gas. We suggest ways to further develop the concept of "dense gas" to incorporate other factors, such as turbulence.

The XMM Cluster Outskirts Project (X-COP): Thermodynamic properties of the intracluster medium out to R200 in Abell 2319

NASA Astrophysics Data System (ADS)

Ghirardini, V.; Ettori, S.; Eckert, D.; Molendi, S.; Gastaldello, F.; Pointecouteau, E.; Hurier, G.; Bourdin, H.

2018-06-01

Aims: We present the joint analysis of the X-ray and Sunyaev-Zel'dovich (SZ) signals in Abell 2319, the galaxy cluster with the highest signal-to-noise ratio in SZ Planck maps and that has been surveyed within our XMM-Newton Cluster Outskirts Project (X-COP), a very large program which aims to grasp the physical condition in 12 local (z < 0.1) and massive (M200 > 3 × 1014 M⊙) galaxy clusters out to R200 and beyond. Methods: We recover the profiles of the thermodynamic properties by the geometrical deprojection of the X-ray surface brightness, of the SZ Comptonization parameter, and accurate and robust spectroscopic measurements of the gas temperature out to 3.2 Mpc (1.6 R200), 4 Mpc (2 R200), and 1.6 Mpc (0.8 R200), respectively. We resolve the clumpiness of the gas density to be below 20% over the entire observed volume. We also demonstrate that most of this clumpiness originates from the ongoing merger and can be associated with large-scale inhomogeneities (the "residual" clumpiness). We estimate the total mass through the hydrostatic equilibrium equation. This analysis is done both in azimuthally averaged radial bins and in eight independent angular sectors, enabling us to study in detail the azimuthal variance of the recovered properties. Results: Given the exquisite quality of the X-ray and SZ datasets, their radial extension, and their complementarity, we constrain at R200 the total hydrostatic mass, modelled with a Navarro-Frenk-White profile at very high precision (M200 = 10.7 ± 0.5stat. ± 0.9syst. × 1014 M⊙). We identify the ongoing merger and how it is affecting differently the gas properties in the resolved azimuthal sectors. We have several indications that the merger has injected a high level of non-thermal pressure in this system: the clumping free density profile is above the average profile obtained by stacking Rosat/PSPC observations; the gas mass fraction recovered using our hydrostatic mass profile exceeds the expected cosmic gas fraction beyond R500; the pressure profile is flatter than the fit obtained by the Planck Collaboration; the entropy profile is flatter than the mean profile predicted from non-radiative simulations; the analysis in azimuthal sectors has revealed that these deviations occur in a preferred region of the cluster. All these tensions are resolved by requiring a relative support of about 40% from non-thermal to the total pressure at R200.

DETERMINING THE LARGE-SCALE ENVIRONMENTAL DEPENDENCE OF GAS-PHASE METALLICITY IN DWARF GALAXIES

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

Douglass, Kelly A.; Vogeley, Michael S., E-mail: kelly.a.douglass@drexel.edu

2017-01-10

We study how the cosmic environment affects galaxy evolution in the universe by comparing the metallicities of dwarf galaxies in voids with dwarf galaxies in more dense regions. Ratios of the fluxes of emission lines, particularly those of the forbidden [O iii] and [S ii] transitions, provide estimates of a region’s electron temperature and number density. From these two quantities and the emission line fluxes [O ii] λ 3727, [O iii] λ 4363, and [O iii] λλ 4959, 5007, we estimate the abundance of oxygen with the direct T{sub e}  method. We estimate the metallicity of 42 blue, star-forming voidmore » dwarf galaxies and 89 blue, star-forming dwarf galaxies in more dense regions using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, as reprocessed in the MPA-JHU value-added catalog. We find very little difference between the two sets of galaxies, indicating little influence from the large-scale environment on their chemical evolution. Of particular interest are a number of extremely metal-poor dwarf galaxies that are less prevalent in voids than in the denser regions.« less

Fast Molecular Cloud Destruction Requires Fast Cloud Formation

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

Mac Low, Mordecai-Mark; Burkert, Andreas; Ibáñez-Mejía, Juan C., E-mail: mordecai@amnh.org, E-mail: burkert@usm.lmu.de, E-mail: ibanez@ph1.uni-koeln.de

A large fraction of the gas in the Galaxy is cold, dense, and molecular. If all this gas collapsed under the influence of gravity and formed stars in a local free-fall time, the star formation rate in the Galaxy would exceed that observed by more than an order of magnitude. Other star-forming galaxies behave similarly. Yet, observations and simulations both suggest that the molecular gas is indeed gravitationally collapsing, albeit hierarchically. Prompt stellar feedback offers a potential solution to the low observed star formation rate if it quickly disrupts star-forming clouds during gravitational collapse. However, this requires that molecular cloudsmore » must be short-lived objects, raising the question of how so much gas can be observed in the molecular phase. This can occur only if molecular clouds form as quickly as they are destroyed, maintaining a global equilibrium fraction of dense gas. We therefore examine cloud formation timescales. We first demonstrate that supernova and superbubble sweeping cannot produce dense gas at the rate required to match the cloud destruction rate. On the other hand, Toomre gravitational instability can reach the required production rate. We thus argue that, although dense, star-forming gas may last only around a single global free-fall time; the dense gas in star-forming galaxies can globally exist in a state of dynamic equilibrium between formation by gravitational instability and disruption by stellar feedback. At redshift z ≳ 2, the Toomre instability timescale decreases, resulting in a prediction of higher molecular gas fractions at early times, in agreement with the observations.« less

SHORT-LIVED STAR-FORMING GIANT CLUMPS IN COSMOLOGICAL SIMULATIONS OF z Almost-Equal-To 2 DISKS

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

Genel, Shy; Genzel, Reinhard; Foerster Schreiber, Natascha M.

Many observed massive star-forming z Almost-Equal-To 2 galaxies are large disks that exhibit irregular morphologies, with Almost-Equal-To 1 kpc, Almost-Equal-To 10{sup 8}-10{sup 10}M{sub o-dot} clumps. We present the largest sample to date of high-resolution cosmological smoothed particle hydrodynamics simulations that zoom-in on the formation of individual M{sub *} Almost-Equal-To 10{sup 10.5}M{sub o-dot} galaxies in Almost-Equal-To 10{sup 12}M{sub o-dot} halos at z Almost-Equal-To 2. Our code includes strong stellar feedback parameterized as momentum-driven galactic winds. This model reproduces many characteristic features of this observed class of galaxies, such as their clumpy morphologies, smooth and monotonic velocity gradients, high gas fractions (f{submore » g} Almost-Equal-To 50%), and high specific star formation rates ({approx}>1 Gyr{sup -1}). In accord with recent models, giant clumps (M{sub clump} Almost-Equal-To (5 Multiplication-Sign 10{sup 8}-10{sup 9})M{sub o-dot}) form in situ via gravitational instabilities. However, the galactic winds are critical for their subsequent evolution. The giant clumps we obtain are short-lived and are disrupted by wind-driven mass loss. They do not virialize or migrate to the galaxy centers as suggested in recent work neglecting strong winds. By phenomenologically implementing the winds that are observed from high-redshift galaxies and in particular from individual clumps, our simulations reproduce well new observational constraints on clump kinematics and clump ages. In particular, the observation that older clumps appear closer to their galaxy centers is reproduced in our simulations, as a result of inside-out formation of the disks rather than inward clump migration.« less

Star Formation at z = 2.481 in the Lensed Galaxy SDSS J1110 = 6459. I. Lens Modeling and Source Reconstruction

NASA Astrophysics Data System (ADS)

Johnson, Traci L.; Sharon, Keren; Gladders, Michael D.; Rigby, Jane R.; Bayliss, Matthew B.; Wuyts, Eva; Whitaker, Katherine E.; Florian, Michael; Murray, Katherine T.

2017-07-01

Using the combined resolving power of the Hubble Space Telescope and gravitational lensing, we resolve star-forming structures in a z˜ 2.5 galaxy on scales much smaller than the usual kiloparsec diffraction limit of HST. SGAS J111020.0+645950.8 is a clumpy, star-forming galaxy lensed by the galaxy cluster SDSS J1110+6459 at z=0.659, with a total magnification ˜ 30× across the entire arc. We use a hybrid parametric/non-parametric strong lensing mass model to compute the deflection and magnification of this giant arc, reconstruct the light distribution of the lensed galaxy in the source plane, and resolve the star formation into two dozen clumps. We develop a forward-modeling technique to model each clump in the source plane. We ray-trace the model to the image plane, convolve with the instrumental point-spread function (PSF), and compare with the GALFIT model of the clumps in the image plane, which decomposes clump structure from more extended emission. This technique has the advantage, over ray-tracing, of accounting for the asymmetric lensing shear of the galaxy in the image plane and the instrument PSF. At this resolution, we can begin to study star formation on a clump-by-clump basis, toward the goal of understanding feedback mechanisms and the buildup of exponential disks at high redshift. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program # 13003.

Star formation in simulated galaxies: understanding the transition to quiescence at 3 × 1010 M⊙

NASA Astrophysics Data System (ADS)

Taylor, Philip; Federrath, Christoph; Kobayashi, Chiaki

2017-08-01

Star formation in galaxies relies on the availability of cold, dense gas, which, in turn, relies on factors internal and external to the galaxies. In order to provide a simple model for how star formation is regulated by various physical processes in galaxies, we analyse data at redshift z = 0 from a hydrodynamical cosmological simulation that includes prescriptions for star formation and stellar evolution, active galactic nuclei, and their associated feedback processes. This model can determine the star formation rate (SFR) as a function of galaxy stellar mass, gas mass, black hole mass, and environment. We find that gas mass is the most important quantity controlling star formation in low-mass galaxies, and star-forming galaxies in dense environments have higher SFR than their counterparts in the field. In high-mass galaxies, we find that black holes more massive than ˜ 107.5 M⊙ can be triggered to quench star formation in their host; this mass scale is emergent in our simulations. Furthermore, this black hole mass corresponds to a galaxy bulge mass ˜ 2 × 1010 M⊙, consistent with the mass at which galaxies start to become dominated by early types ( ˜ 3 × 1010 M⊙, as previously shown in observations by Kauffmann et al.). Finally, we demonstrate that our model can reproduce well the SFR measured from observations of galaxies in the Galaxy And Mass Assembly and Arecibo Legacy Fast ALFA surveys.

Modelling the spectral energy distribution of galaxies. V. The dust and PAH emission SEDs of disk galaxies

NASA Astrophysics Data System (ADS)

Popescu, C. C.; Tuffs, R. J.; Dopita, M. A.; Fischera, J.; Kylafis, N. D.; Madore, B. F.

2011-03-01

We present a self-consistent model of the spectral energy distributions (SEDs) of spiral galaxies from the ultraviolet (UV) to the mid-infrared (MIR)/far-infrared (FIR)/submillimeter (submm) based on a full radiative transfer calculation of the propagation of starlight in galaxy disks. This model predicts not only the total integrated energy absorbed in the UV/optical and re-emitted in the infrared/submm, but also the colours of the dust emission based on an explicit calculation of the strength and colour of the UV/optical radiation fields heating the dust, and incorporating a full calculation of the stochastic heating of small dust grains and PAH molecules. The geometry of the translucent components of the model is empirically constrained using the results from the radiation transfer analysis of Xilouris et al. on spirals in the middle range of the Hubble sequence, while the geometry of the optically thick components is constrained from physical considerations with a posteriori checks of the model predictions with observational data. Following the observational constraints, the model has both a distribution of diffuse dust associated with the old and young disk stellar populations as well as a clumpy component arising from dust in the parent molecular clouds in star forming regions. In accordance with the fragmented nature of dense molecular gas in typical star-forming regions, UV light from massive stars is allowed to either freely stream away into the diffuse medium in some fraction of directions or be geometrically blocked and locally absorbed in clumps. These geometrical constraints enable the dust emission to be predicted in terms of a minimum set of free parameters: the central face-on dust opacity in the B-band τ^f_B, a clumpiness factor F for the star-forming regions, the star-formation rate SFR, the normalised luminosity of the old stellar population old and the bulge-to-disk ratio B/D. We show that these parameters are almost orthogonal in their predicted effect on the colours of the dust/PAH emission. In most practical applications B/D will actually not be a free parameter but (together with the angular size θgal and inclination i of the disk) act as a constraint derived from morphological decomposition of higher resolution optical images. This also extends the range of applicability of the model along the Hubble sequence. We further show that the dependence of the dust emission SED on the colour of the stellar photon field depends primarily on the ratio between the luminosities of the young and old stellar populations (as specified by the parameters SFR and old) rather than on the detailed colour of the emissions from either of these populations. The model is thereby independent of a priori assumptions of the detailed mathematical form of the dependence of SFR on time, allowing UV/optical SEDs to be dereddened without recourse to population synthesis models. Utilising these findings, we show how the predictive power of radiative transfer calculations can be combined with measurements of θgal, i and B/D from optical images to self-consistently fit UV/optical-MIR/FIR/submm SEDs observed in large statistical surveys in a fast and flexible way, deriving physical parameters on an object-by-object basis. We also identify a non-parametric test of the fidelity of the model in practical applications through comparison of the model predictions for FIR colour and surface brightness with the corresponding observed quantities. This should be effective in identifying objects such as AGNs or star-forming galaxies with markedly different geometries to those of the calibrators of Xilouris et al. The results of the calculations are made available in the form of a large library of simulated dust emission SEDs spanning the whole parameter space of our model, together with the corresponding library of dust attenuation calculated using the same model. We dedicate this paper to the memory of Angelos Misiriotis, sorely missed as a friend, collaborator and exceptional scientist.Appendices are only available in electronic form at http://www.aanda.orgThe data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/527/A109

Dense gas and star formation in individual Giant Molecular Clouds in M31

NASA Astrophysics Data System (ADS)

Viaene, S.; Forbrich, J.; Fritz, J.

2018-04-01

Studies both of entire galaxies and of local Galactic star formation indicate a dependency of a molecular cloud's star formation rate (SFR) on its dense gas mass. In external galaxies, such measurements are derived from HCN(1-0) observations, usually encompassing many Giant Molecular Clouds (GMCs) at once. The Andromeda galaxy (M31) is a unique laboratory to study the relation of the SFR and HCN emission down to GMC scales at solar-like metallicities. In this work, we correlate our composite SFR determinations with archival HCN, HCO+, and CO observations, resulting in a sample of nine reasonably representative GMCs. We find that, at the scale of individual clouds, it is important to take into account both obscured and unobscured star formation to determine the SFR. When correlated against the dense-gas mass from HCN, we find that the SFR is low, in spite of these refinements. We nevertheless retrieve an SFR-dense-gas mass correlation, confirming that these SFR tracers are still meaningful on GMC scales. The correlation improves markedly when we consider the HCN/CO ratio instead of HCN by itself. This nominally indicates a dependency of the SFR on the dense-gas fraction, in contradiction to local studies. However, we hypothesize that this partly reflects the limited dynamic range in dense-gas mass, and partly that the ratio of single-pointing HCN and CO measurements may be less prone to systematics like sidelobes. In this case, the HCN/CO ratio would importantly be a better empirical measure of the dense-gas content itself.

Astronomers Discover Most Distant Galaxy Showing Key Evidence For Furious Star Formation

NASA Astrophysics Data System (ADS)

2003-12-01

Astronomers have discovered a key signpost of rapid star formation in a galaxy 11 billion light-years from Earth, seen as it was when the Universe was only 20 percent of its current age. Using the National Science Foundation's Very Large Array (VLA) radio telescope, the scientists found a huge quantity of dense interstellar gas -- the environment required for active star formation -- at the greatest distance yet detected. A furious spawning of the equivalent of 1,000 Suns per year in a distant galaxy dubbed the Cloverleaf may be typical of galaxies in the early Universe, the scientists say. Cloverleaf galaxy VLA image (green) of radio emission from HCN gas, superimposed on Hubble Space Telescope image of the Cloverleaf galaxy. The four images of the Cloverleaf are the result of gravitational lensing. CREDIT: NRAO/AUI/NSF, STScI (Click on Image for Larger Version) "This is a rate of star formation more than 300 times greater than that in our own Milky Way and similar spiral galaxies, and our discovery may provide important information about the formation and evolution of galaxies throughout the Universe," said Philip Solomon, of Stony Brook University in New York. While the raw material for star formation has been found in galaxies at even greater distances, the Cloverleaf is by far the most distant galaxy showing this essential signature of star formation. That essential signature comes in the form of a specific frequency of radio waves emitted by molecules of the gas hydrogen cyanide (HCN). "If you see HCN, you are seeing gas with the high density required to form stars," said Paul Vanden Bout of the National Radio Astronomy Observatory (NRAO). Solomon and Vanden Bout worked with Chris Carilli of NRAO and Michel Guelin of the Institute for Millimeter Astronomy in France. They reported their results in the December 11 issue of the scientific journal Nature. In galaxies like the Milky Way, dense gas traced by HCN but composed mainly of hydrogen molecules is always associated with regions of active star formation. What is different about the Cloverleaf is the huge quantity of dense gas along with very powerful infrared radiation from the star formation. Ten billion times the mass of the Sun is contained in dense, star-forming gas clouds. "At the rate this galaxy is seen to be forming stars, that dense gas will be used up in only about 10 million years," Solomon said. In addition to giving astronomers a fascinating glimpse of a huge burst of star formation in the early Universe, the new information about the Cloverleaf helps answer a longstanding question about bright galaxies of that era. Many distant galaxies have supermassive black holes at their cores, and those black holes power "central engines" that produce bright emission. Astronomers have wondered specifically about those distant galaxies that emit large amounts of infrared light, galaxies like the Cloverleaf which has a black hole and central engine. "Is this bright infrared light caused by the black-hole-powered core of the galaxy or by a huge burst of star formation? That has been the question. Now we know that, in at least one case, much of the infrared light is produced by intense star formation," Carilli said. The rapid star formation, called a starburst, and the black hole are both generating the bright infrared light in the Cloverleaf. The starburst is a major event in the formation and evolution of this galaxy. "This detection of HCN gives us a unique new window through which we can study star formation in the early Universe," Carilli said. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Clumpy Galaxies in CANDELS. II. Physical Properties of UV-bright Clumps at 0.5 ≤ z < 3

NASA Astrophysics Data System (ADS)

Guo, Yicheng; Rafelski, Marc; Bell, Eric F.; Conselice, Christopher J.; Dekel, Avishai; Faber, S. M.; Giavalisco, Mauro; Koekemoer, Anton M.; Koo, David C.; Lu, Yu; Mandelker, Nir; Primack, Joel R.; Ceverino, Daniel; de Mello, Duilia F.; Ferguson, Henry C.; Hathi, Nimish; Kocevski, Dale; Lucas, Ray A.; Pérez-González, Pablo G.; Ravindranath, Swara; Soto, Emmaris; Straughn, Amber; Wang, Weichen

2018-02-01

Studying giant star-forming clumps in distant galaxies is important to understand galaxy formation and evolution. At present, however, observers and theorists have not reached a consensus on whether the observed “clumps” in distant galaxies are the same phenomenon that is seen in simulations. In this paper, as a step to establish a benchmark of direct comparisons between observations and theories, we publish a sample of clumps constructed to represent the commonly observed “clumps” in the literature. This sample contains 3193 clumps detected from 1270 galaxies at 0.5≤slant z< 3.0. The clumps are detected from rest-frame UV images, as described in our previous paper. Their physical properties (e.g., rest-frame color, stellar mass ({M}* ), star formation rate (SFR), age, and dust extinction) are measured by fitting the spectral energy distribution (SED) to synthetic stellar population models. We carefully test the procedures of measuring clump properties, especially the method of subtracting background fluxes from the diffuse component of galaxies. With our fiducial background subtraction, we find a radial clump U ‑ V color variation, where clumps close to galactic centers are redder than those in outskirts. The slope of the color gradient (clump color as a function of their galactocentric distance scaled by the semimajor axis of galaxies) changes with redshift and {M}* of the host galaxies: at a fixed {M}* , the slope becomes steeper toward low redshift, and at a fixed redshift, it becomes slightly steeper with {M}* . Based on our SED fitting, this observed color gradient can be explained by a combination of a negative age gradient, a negative E(B ‑ V) gradient, and a positive specific SFR gradient of the clumps. We also find that the color gradients of clumps are steeper than those of intra-clump regions. Correspondingly, the radial gradients of the derived physical properties of clumps are different from those of the diffuse component or intra-clump regions.

SUSTAINING STAR FORMATION RATES IN SPIRAL GALAXIES: SUPERNOVA-DRIVEN TURBULENT ACCRETION DISK MODELS APPLIED TO THINGS GALAXIES

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

Vollmer, Bernd; Leroy, Adam K., E-mail: bvollmer@astro.u-strasbg.fr

2011-01-15

Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps contains free parameters, which can be constrained by observations of molecular gas, atomic gas, and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproducedmore » by the model. In the framework of this model, the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in the star formation regime is realized by replacing the free-fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log M(M{sub sun}) {approx}< 10) can balance gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion. In the absence of this external accretion, star formation slowly exhausts the gas within the optical disk within the star formation timescale.« less

Sustaining Star Formation Rates in Spiral Galaxies Supernova-driven Turbulent Accretion Disk Models Applied to THINGS Galaxies

NASA Astrophysics Data System (ADS)

Vollmer, Bernd; Leroy, Adam K.

2011-01-01

Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps contains free parameters, which can be constrained by observations of molecular gas, atomic gas, and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproduced by the model. In the framework of this model, the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in the star formation regime is realized by replacing the free-fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log M(M ⊙) <~ 10) can balance gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion. In the absence of this external accretion, star formation slowly exhausts the gas within the optical disk within the star formation timescale.

Science of active galactic nuclei with the GTC and CanariCam

NASA Astrophysics Data System (ADS)

Levenson, Nancy A.; Packham, Christopher C.; Alonso-Herrero, Almudena; Aretxaga, Itziar; Colina, Luis; Díaz-Santos, Tanio; Elitzur, Moshe; Mason, Rachel E.; Perlman, Eric S.; Radomski, James T.; Roche, Patrick F.; Rodríguez Espinosa, José Miguel; Young, Stuart; Telesco, Charles M.

2008-07-01

CanariCam is the facility mid-infrared (MIR) instrument for the Gran Telescopio Canarias (GTC), a 10.4m telescope at the Observatorio del Roque de los Muchachos on La Palma. One of the science drivers for CanariCam is the study of active galactic nuclei (AGN). We will exploit the instrument's high sensitivity in imaging, spectroscopy, and polarimetry modes to answer fundamental questions of AGN and their host galaxies. Dust in the nucleus of an active galaxy reprocesses the intrinsic radiation of the central engine to emerge in the MIR. Current work demonstrates that the hot dust immediately associated with the AGN, which blocks direct views of the AGN from some lines of sight, is confined to small (parsec) scales. Thus, high spatial resolution is essential to probe the "torus" of unified AGN models separate from the host galaxy. CanariCam provides a 0.08" pixel scale for Nyquist sampling the diffraction-limited point spread function at 8μm, and narrow (0.2") spectroscopy slits (with R=120-1300). New observations with the GTC/CanariCam will provide key constraints on the physical conditions in the clumpy torus, and we will sensitively determine AGN obscuration as a function of nuclear activity. We will therefore address the fueling process and its relationship to the torus, the interaction with the host galaxy, and dust chemistry. These data will be essential preparation for the next generation of telescopes that will observe the distant universe directly to explore galaxy and black hole formation and evolution, and the GTC/CanariCam system uniquely provides multiple modes to probe AGN.

Star formation across cosmic time and its influence on galactic dynamics

NASA Astrophysics Data System (ADS)

Freundlich, Jonathan

2015-12-01

Observations show that ten billion years ago, galaxies formed their stars at rates up to twenty times higher than now. As stars are formed from cold molecular gas, a high star formation rate means a significant gas supply, and galaxies near the peak epoch of star formation are indeed much more gas-rich than nearby galaxies. Is the decline of the star formation rate mostly driven by the diminishing cold gas reservoir, or are the star formation processes also qualitatively different earlier in the history of the Universe? Ten billion years ago, young galaxies were clumpy and prone to violent gravitational instabilities, which may have contributed to their high star formation rate. Stars indeed form within giant, gravitationally-bound molecular clouds. But the earliest phases of star formation are still poorly understood. Some scenarii suggest the importance of interstellar filamentary structures as a first step towards core and star formation. How would their filamentary geometry affect pre-stellar cores? Feedback mechanisms related to stellar evolution also play an important role in regulating star formation, for example through powerful stellar winds and supernovae explosions which expel some of the gas and can even disturb the dark matter distribution in which each galaxy is assumed to be embedded. This PhD work focuses on three perspectives: (i) star formation near the peak epoch of star formation as seen from observations at sub-galactic scales; (ii) the formation of pre-stellar cores within the filamentary structures of the interstellar medium; and (iii) the effect of feedback processes resulting from star formation and evolution on the dark matter distribution.

Evolution of galaxy structure using visual morphologies in CANDELS and Hydro-ART simulations

NASA Astrophysics Data System (ADS)

Mozena, Mark W.

2013-08-01

The general properties, morphologies, and classes of galaxies in the local Universe are well studied. Most local galaxies are morphologically members of the Hubble sequence and can be crudely separated into elliptical red quiescent galaxies or disky blue star-forming galaxies. This Hubble sequence of relaxed structures has been shown to dominate galaxy populations out to a redshift of z~1. The description of galaxies at earlier times is not well known nor is it understood how and at what epoch the Hubble sequence formed. Of particular interest is the structure of galaxies at z~2. This epoch was an active time for galaxy growth and was the peak epoch for star formation rate, active galactic nuclei activity, and mergers between galaxies. With the installation of the near-infrared Wide Field Camera 3 (WFC3) on the Hubble Space Telescope in 2009, large area photometric surveys of galaxies were able to be performed for the first time at moderate redshifts (z~2) in wavebands that effectively trace the older stellar populations and stellar mass of the galaxies rather than the clumpy star-forming regions. Using WFC3 HST images, an in-depth morphology classification system was developed to probe the galaxy populations at higher redshifts (focusing on z~2). These visual classifications were used with other galaxy parameters (stellar mass, color, star formation rate, radius, Sersic profiles, etc) to identify and quantify the moderate redshift galaxy populations and study how these populations changed with time to form the relaxed Hubble sequence Universe we observe today. Additionally, these same tools that were used to probe galaxy populations at z~2 in the observed Universe were also used on simulated galaxy images produced from state-of-the-art cosmological simulations. These Hydro-ART simulations build artificial galaxies that are compared to observations so as to shed light on the relevant mechanisms in galaxy evolution. By classifying and comparing the populations present in the simulations with our observations, we are able to probe the model's ability to create realistic galaxy populations. The first chapter of this thesis focuses on visually classifying and studying galaxy populations at z~2 and how they change with redshift for a given mass. The second chapter focuses on applying our techniques to Hydro-ART simulations at z~2 and comparing these mock 'observed' simulations with our real WFC3 HST observations. Both of these chapters closely resemble manuscripts in the process of being submitted for independent publication.

Radiation hydrodynamical instabilities in cosmological and galactic ionization fronts

NASA Astrophysics Data System (ADS)

Whalen, Daniel J.; Norman, Michael L.

2011-11-01

Ionization fronts, the sharp radiation fronts behind which H/He ionizing photons from massive stars and galaxies propagate through space, were ubiquitous in the universe from its earliest times. The cosmic dark ages ended with the formation of the first primeval stars and galaxies a few hundred Myr after the Big Bang. Numerical simulations suggest that stars in this era were very massive, 25-500 solar masses, with H(II) regions of up to 30,000 light-years in diameter. We present three-dimensional radiation hydrodynamical calculations that reveal that the I-fronts of the first stars and galaxies were prone to violent instabilities, enhancing the escape of UV photons into the early intergalactic medium (IGM) and forming clumpy media in which supernovae later exploded. The enrichment of such clumps with metals by the first supernovae may have led to the prompt formation of a second generation of low-mass stars, profoundly transforming the nature of the first protogalaxies. Cosmological radiation hydrodynamics is unique because ionizing photons coupled strongly to both gas flows and primordial chemistry at early epochs, introducing a hierarchy of disparate characteristic timescales whose relative magnitudes can vary greatly throughout a given calculation. We describe the adaptive multistep integration scheme we have developed for the self-consistent transport of both cosmological and galactic ionization fronts.

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

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

Glimpsing the imprint of local environment on the galaxy stellar mass function

NASA Astrophysics Data System (ADS)

Tomczak, Adam R.; Lemaux, Brian C.; Lubin, Lori M.; Gal, Roy R.; Wu, Po-Feng; Holden, Bradford; Kocevski, Dale D.; Mei, Simona; Pelliccia, Debora; Rumbaugh, Nicholas; Shen, Lu

2017-12-01

We investigate the impact of local environment on the galaxy stellar mass function (SMF) spanning a wide range of galaxy densities from the field up to dense cores of massive galaxy clusters. Data are drawn from a sample of eight fields from the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey. Deep photometry allow us to select mass-complete samples of galaxies down to 109 M⊙. Taking advantage of >4000 secure spectroscopic redshifts from ORELSE and precise photometric redshifts, we construct three-dimensional density maps between 0.55 < z < 1.3 using a Voronoi tessellation approach. We find that the shape of the SMF depends strongly on local environment exhibited by a smooth, continual increase in the relative numbers of high- to low-mass galaxies towards denser environments. A straightforward implication is that local environment proportionally increases the efficiency of (a) destroying lower mass galaxies and/or (b) growth of higher mass galaxies. We also find a presence of this environmental dependence in the SMFs of star-forming and quiescent galaxies, although not quite as strongly for the quiescent subsample. To characterize the connection between the SMF of field galaxies and that of denser environments, we devise a simple semi-empirical model. The model begins with a sample of ≈106 galaxies at zstart = 5 with stellar masses distributed according to the field. Simulated galaxies then evolve down to zfinal = 0.8 following empirical prescriptions for star-formation, quenching and galaxy-galaxy merging. We run the simulation multiple times, testing a variety of scenarios with differing overall amounts of merging. Our model suggests that a large number of mergers are required to reproduce the SMF in dense environments. Additionally, a large majority of these mergers would have to occur in intermediate density environments (e.g. galaxy groups).

Observations of the andromeda galaxy at 11-centimeter wavelength.

PubMed

Cooley, R C; Roberts, M S; Swenson, G W

1967-05-26

Observations of the Andromeda galaxy (M31) at 2695 megahertz reveal more detail than do earlier measurements at lower frequency. The region is highly confused but there is apparently a more dense clustering of sources within the optical outline of the galaxy than without. One source (OA33) near M31 has an interesting. flat spectrum.

Witnessing Gas Mixing in the Metal Distribution of the Hickson Compact Group HCG 31

NASA Astrophysics Data System (ADS)

Torres-Flores, S.; Mendes de Oliveira, C.; Amram, P.; Alfaro-Cuello, M.; Carrasco, E. R.; de Mello, D. F.

2015-01-01

We present for the first time direct evidence that in a merger of disk galaxies, the pre-existing central metallicities will mix as a result of gas being transported in the merger interface region along the line that joins the two coalescing nuclei. This is shown using detailed two-dimensional kinematics as well as metallicity measurements for the nearby ongoing merger in the center of the compact group HCG 31. We focus on the emission line gas, which is extensive in the system. The two coalescing cores display similar oxygen abundances. While in between the two nuclei, the metallicity changes smoothly from one nucleus to the other indicating a mix of metals in this region, which is confirmed by the high-resolution Hα kinematics (R = 45,900). This nearby system is especially important because it involves the merging of two fairly low-mass and clumpy galaxies (LMC-like galaxies), making it an important system for comparison with high-redshift galaxies. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina) - Observing run: GS-2012B-Q-60.

A2111: A z= 0.23 Butcher-Oemler Cluster with a Non-Isothermal Atmosphere and Normal Metallicity

NASA Technical Reports Server (NTRS)

Wang, Q. Daniel; Henriksen, Mark

1998-01-01

We report results from an x-ray spectral study of the z=0.23 Abell 2111 galaxy cluster using the Advanced Satellite for Astrophysics and Cosmology and the ROSAT Position Sensitive Proportional Counter. By correcting for the energy-dependent point-spread function of the instruments, we have examined the temperature structure of the cluster. The cluster's core within 3 is found to have a temperature of 5.4 +/- 0.5 keV, significantly higher than 2.8 +/-0.7 keV in the surrounding region of r = 3-6. This radially decreasing temperature structure can be parameterized by a polytropic index of gamma less than 1.4. Furthermore, the intracluster medium appears clumpy on scales less than 1. Early studies have revealed that the x-ray centroid of the cluster shifts with spatial scale and the overall optical and x-ray morphology is strongly elongated. These results together suggest that A2111 in undergoing a merger, which is likely responsible for the high fraction of blue galaxies observed in the cluster. We have further measured the abundance of the medium as 0.25 +/- 0.14 solar. This value is similar to those of nearby clusters which do not show a large blue galaxy function, suggesting that star formation in disk galaxies and subsequent loss to the intracluster medium do not drastically alter the average abundance of a cluster since z=0.23.

Mid-Infrared Silicate Dust Features in Seyfert 1 Spectra

NASA Astrophysics Data System (ADS)

Thompson, Grant D.; Levenson, N. A.; Sirocky, M. M.; Uddin, S.

2007-12-01

Silicate dust emission dominates the mid-infrared spectra of galaxies, and the dust produces two spectral features, at 10 and 18 μm. These features' strengths (in emission or absorption) and peak wavelengths reveal the geometry of the dust distribution, and they are sensitive to the dust composition. We examine mid-infrared spectra of 32 Seyfert 1 active galactic nuclei (AGN), observed with the Infrared Spectrograph aboard the Spitzer Space Telescope. In the spectra, we typically find the shorter-wavelength feature in emission, at an average peak wavelength of 10.0 μm, although it is known historically as the "9.7 μm" feature. In addition, peak wavelength increases with feature strength. The 10 and 18 μm feature strengths together are sensitive to the dust geometry surrounding the central heating engine. Numerical calculations of radiative transfer distinguish between clumpy and smooth distributions, and we find that the surroundings of these AGN (the obscuring "tori" of unified AGN schemes) are clumpy. Polycyclic aromatic hydrocarbon (PAH) features are associated with star formation, and we find strong PAH emission (luminosity ≥ 1042 erg/s) in only four sources, three of which show independent evidence for starbursts. We will explore the effects of luminosity on dust geometry and chemistry in a comparison sample of quasars. We acknowledge work supported by the NSF under grant number 0237291.

Intensity of primary cosmic-ray electrons of energy exceeding 8 GeV

NASA Technical Reports Server (NTRS)

Freier, P.; Gilman, C.; Waddington, C. J.

1977-01-01

Results are reported for measurement of the intensity and energy spectrum of primary cosmic-ray electrons with a spark-chamber-counter-emulsion detector flown at a mean altitude of 3 g/sq cm residual atmosphere. A least-squares fit to the flight data yields an electron spectrum from 8 to 80 GeV of approximately 93E to the -2.91 power electrons/sq m/sec per sr/GeV. The results are compared with those of previous experiments as well as with the spectrum obtained for galactic nonthermal radiation. It is concluded that a 'clumpy' magnetic field proportional to the square root of matter density is consistent with measurements of high-energy electrons and synchrotron radiation toward the center of the Galaxy, that a gradual steepening of the electron spectrum relative to the proton spectrum is consistent with an electron lifetime of 1 million years, and that the density of cosmic-ray nucleons and electrons should be essentially uniform throughout the Galaxy if the nucleons have the same lifetime as the electrons and if they traversed 4 to 5 g/sq cm in that lifetime.

The dark matter of galaxy voids

NASA Astrophysics Data System (ADS)

Sutter, P. M.; Lavaux, Guilhem; Wandelt, Benjamin D.; Weinberg, David H.; Warren, Michael S.

2014-03-01

How do observed voids relate to the underlying dark matter distribution? To examine the spatial distribution of dark matter contained within voids identified in galaxy surveys, we apply Halo Occupation Distribution models representing sparsely and densely sampled galaxy surveys to a high-resolution N-body simulation. We compare these galaxy voids to voids found in the halo distribution, low-resolution dark matter and high-resolution dark matter. We find that voids at all scales in densely sampled surveys - and medium- to large-scale voids in sparse surveys - trace the same underdensities as dark matter, but they are larger in radius by ˜20 per cent, they have somewhat shallower density profiles and they have centres offset by ˜ 0.4Rv rms. However, in void-to-void comparison we find that shape estimators are less robust to sampling, and the largest voids in sparsely sampled surveys suffer fragmentation at their edges. We find that voids in galaxy surveys always correspond to underdensities in the dark matter, though the centres may be offset. When this offset is taken into account, we recover almost identical radial density profiles between galaxies and dark matter. All mock catalogues used in this work are available at http://www.cosmicvoids.net.

Cold dark matter. 2: Spatial and velocity statistics

NASA Technical Reports Server (NTRS)

Gelb, James M.; Bertschinger, Edmund

1994-01-01

We examine high-resolution gravitational N-body simulations of the omega = 1 cold dark matter (CDM) model in order to determine whether there is any normalization of the initial density fluctuation spectrum that yields acceptable results for galaxy clustering and velocities. Dense dark matter halos in the evolved mass distribution are identified with luminous galaxies; the most massive halos are also considered as sites for galaxy groups, with a range of possibilities explored for the group mass-to-light ratios. We verify the earlier conclusions of White et al. (1987) for the low-amplitude (high-bias) CDM model-the galaxy correlation function is marginally acceptable but that there are too many galaxies. We also show that the peak biasing method does not accurately reproduce the results obtained using dense halos identified in the simulations themselves. The Cosmic Background Explorer (COBE) anisotropy implies a higher normalization, resulting in problems with excessive pairwise galaxy velocity dispersion unless a strong velocity bias is present. Although we confirm the strong velocity bias of halos reported by Couchman & Carlberg (1992), we show that the galaxy motions are still too large on small scales. We find no amplitude for which the CDM model can reconcile simultaneously and galaxy correlation function, the low pairwise velocity dispersion, and the richness distribution of groups and clusters. With the normalization implied by COBE, the CDM spectrum has too much power on small scales if omega = 1.

The VIMOS Public Extragalactic Redshift Survey (VIPERS). The distinct build-up of dense and normal massive passive galaxies

NASA Astrophysics Data System (ADS)

Gargiulo, A.; Bolzonella, M.; Scodeggio, M.; Krywult, J.; De Lucia, G.; Guzzo, L.; Garilli, B.; Granett, B. R.; de la Torre, S.; Abbas, U.; Adami, C.; Arnouts, S.; Bottini, D.; Cappi, A.; Cucciati, O.; Davidzon, I.; Franzetti, P.; Fritz, A.; Haines, C.; Hawken, A. J.; Iovino, A.; Le Brun, V.; Le Fèvre, O.; Maccagni, D.; Małek, K.; Marulli, F.; Moutard, T.; Polletta, M.; Pollo, A.; Tasca, L. A. M.; Tojeiro, R.; Vergani, D.; Zanichelli, A.; Zamorani, G.; Bel, J.; Branchini, E.; Coupon, J.; Ilbert, O.; Moscardini, L.; Peacock, J. A.

2017-10-01

We have used the final data from the VIPERS redshift survey to extract an unparalleled sample of more than 2000 massive ℳ≥1011 M⊙ passive galaxies (MPGs) at redshift 0.5≤z≤1.0, based on their NUVrK colours. This has enabled us to investigate how the population of these objects was built up over cosmic time. We find that the evolution of the number density depends on the galaxy mean surface stellar mass density, Σ. In particular, dense (Σ≥2000 M⊙ pc-2) MPGs show a constant comoving number density over this redshift range, whilst this increases by a factor of approximately four for the least dense objects, defined as having Σ < 1000 M⊙ pc-2. We estimated stellar ages for the MPG population both fitting the spectral energy distribution (SED) and through the D4000n index, obtaining results in good agreement. Our findings are consistent with passive ageing of the stellar content of dense MPGs. We show that at any redshift the less dense MPGs are younger than dense ones and that their stellar populations evolve at a slower rate than predicted by passive evolution. This points to a scenario in which the overall population of MPGs was built up over the cosmic time by continuous addition of less dense galaxies: on top of an initial population of dense objects that passively evolves, new, larger, and younger MPGs continuously join the population at later epochs. Finally, we demonstrate that the observed increase in the number density of MPGs is totally accounted for by the observed decrease in the number density of correspondingly massive star forming galaxies (I.e. all the non-passive ℳ≥1011 M⊙ objects). Such systems observed at z ≃ 1 in VIPERS, therefore, represent the most plausible progenitors of the subsequent emerging class of larger MPGs. Based on observations collected at the European Southern Observatory, Cerro Paranal, Chile, using the Very Large Telescope under programs 182.A-0886 and partly 070.A-9007. Also based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. The VIPERS web site is http://www.vipers.inaf.it/

CO line emission from galaxies in the Epoch of Reionization

NASA Astrophysics Data System (ADS)

Vallini, L.; Pallottini, A.; Ferrara, A.; Gallerani, S.; Sobacchi, E.; Behrens, C.

2018-01-01

We study the CO line luminosity (LCO), the shape of the CO spectral line energy distribution (SLED), and the value of the CO-to-H2 conversion factor in galaxies in the Epoch of Reionization (EoR). For this aim, we construct a model that simultaneously takes into account the radiative transfer and the clumpy structure of giant molecular clouds (GMCs) where the CO lines are excited. We then use it to post-process state-of-the-art zoomed, high resolution (30 pc), cosmological simulation of a main-sequence (M* ≈ 1010 M⊙, SFR ≈ 100 M⊙ yr- 1) galaxy, 'Althæa', at z ≈ 6. We find that the CO emission traces the inner molecular disc (r ≈ 0.5 kpc) of Althæa with the peak of the CO surface brightness co-located with that of the [C II] 158 μm emission. Its LCO(1-0) = 104.85 L⊙ is comparable to that observed in local galaxies with similar stellar mass. The high (Σgas ≈ 220 M⊙ pc- 2) gas surface density in Althæa, its large Mach number (M ≈ 30) and the warm kinetic temperature (Tk ≈ 45 K) of GMCs yield a CO SLED peaked at the CO(7-6) transition, i.e. at relatively high-J and a CO-to-H2 conversion factor α _CO≈ 1.5 M_{⊙} (K km s^{-1} pc^2)^{-1} lower than that of the Milky Way. The Atacama Large Millimeter/submillimeter Array observing time required to detect (resolve) at 5σ the CO(7-6) line from galaxies similar to Althæa is ≈13 h (≈38 h).

A Wealth of Dust Grains in Quasar Winds

NASA Technical Reports Server (NTRS)

2007-01-01

[figure removed for brevity, see original site] Click on image for larger poster version

This plot of data captured by NASA's Spitzer Space Telescope reveals dust entrained in the winds rushing away from a quasar, or growing black hole. The quasar, called PG2112+059, is located deep inside a galaxy 8 billion light-years away. Astronomers believe the dust might have been forged in the winds, which would help explain where dust in the very early universe came from.

The data were captured by Spitzer's infrared spectrograph, an instrument that splits apart light from the quasar into a spectrum that reveals telltale signs of different minerals. Each type of mineral, or dust grain, has a unique signature, as can be seen in the graph, or spectrum, above.

The strongest features are from the mineral amorphous olivine, or glass (purple); the mineral forsterite found in sand (blue); and the mineral corundum found in rubies (light blue). The detection of forsterite and corundum is highly unusual in galaxies without quasars. Therefore, their presence is a key clue that these grains might have been created in the quasar winds and not by dying stars as they are in our Milky Way galaxy. Forsterite is destroyed quickly in normal galaxies by radiation, so it must be continually produced to be detected by Spitzer.

Corundum is hard, and provides a seed that softer, more common minerals usually cover up. As a result, corundum is usually not seen in spectra of galaxies. Since Spitzer did detect the mineral, it is probably forming in a clumpy environment, which is expected in quasar winds. All together, the signatures of the unusual minerals in this spectrum point towards dust grains forming in the winds blowing away from quasars.

Toward Measuring Galactic Dense Molecular Gas Properties and 3D Distribution with Hi-GAL

NASA Astrophysics Data System (ADS)

Zetterlund, Erika; Glenn, Jason; Maloney, Phil

2016-01-01

The Herschel Space Observatory's submillimeter dust continuum survey Hi-GAL provides a powerful new dataset for characterizing the structure of the dense interstellar medium of the Milky Way. Hi-GAL observed a 2° wide strip covering the entire 360° of the Galactic plane in broad bands centered at 70, 160, 250, 350, and 500 μm, with angular resolution ranging from 10 to 40 arcseconds. We are adapting a molecular cloud clump-finding algorithm and a distance probability density function distance-determination method developed for the Bolocam Galactic Plane Survey (BGPS) to the Hi-GAL data. Using these methods we expect to generate a database of 105 cloud clumps, derive distance information for roughly half the clumps, and derive precise distances for approximately 20% of them. With five-color photometry and distances, we will measure the cloud clump properties, such as luminosities, physical sizes, and masses, and construct a three-dimensional map of the Milky Way's dense molecular gas distribution.The cloud clump properties and the dense gas distribution will provide critical ground truths for comparison to theoretical models of molecular cloud structure formation and galaxy evolution models that seek to emulate spiral galaxies. For example, such models cannot resolve star formation and use prescriptive recipes, such as converting a fixed fraction of interstellar gas to stars at a specified interstellar medium density threshold. The models should be compared to observed dense molecular gas properties and galactic distributions.As a pilot survey to refine the clump-finding and distance measurement algorithms developed for BGPS, we have identified molecular cloud clumps in six 2° × 2° patches of the Galactic plane, including one in the inner Galaxy along the line of sight through the Molecular Ring and the termination of the Galactic bar and one toward the outer Galaxy. Distances have been derived for the inner Galaxy clumps and compared to Bolocam Galactic Plane Survey results. We present the pilot survey clump catalog, distances, clump properties, and a comparison to BGPS.

Submillimeter Galaxies as Progenitors of Compact Quiescent Galaxies

NASA Technical Reports Server (NTRS)

Toft, S.; Smolcic, V.; Magnelli, B.; Karim, A.; Zirm, A.; Michalowski, M.; Capak, P.; Sheth, K.; Schawinski, K.; Krogager, J.-K.;

Submillimeter Galaxies as Progenitors of Compact Quiescent Galaxies

NASA Astrophysics Data System (ADS)

Toft, S.; Smolčić, V.; Magnelli, B.; Karim, A.; Zirm, A.; Michalowski, M.; Capak, P.; Sheth, K.; Schawinski, K.; Krogager, J.-K.; Wuyts, S.; Sanders, D.; Man, A. W. S.; Lutz, D.; Staguhn, J.; Berta, S.; Mccracken, H.; Krpan, J.; Riechers, D.

2014-02-01

Three billion years after the big bang (at redshift z = 2), half of the most massive galaxies were already old, quiescent systems with little to no residual star formation and extremely compact with stellar mass densities at least an order of magnitude larger than in low-redshift ellipticals, their descendants. Little is known about how they formed, but their evolved, dense stellar populations suggest formation within intense, compact starbursts 1-2 Gyr earlier (at 3 < z < 6). Simulations show that gas-rich major mergers can give rise to such starbursts, which produce dense remnants. Submillimeter-selected galaxies (SMGs) are prime examples of intense, gas-rich starbursts. With a new, representative spectroscopic sample of compact, quiescent galaxies at z = 2 and a statistically well-understood sample of SMGs, we show that z = 3-6 SMGs are consistent with being the progenitors of z = 2 quiescent galaxies, matching their formation redshifts and their distributions of sizes, stellar masses, and internal velocities. Assuming an evolutionary connection, their space densities also match if the mean duty cycle of SMG starbursts is 42^{+40}_{-29} Myr (consistent with independent estimates), which indicates that the bulk of stars in these massive galaxies were formed in a major, early surge of star formation. These results suggest a coherent picture of the formation history of the most massive galaxies in the universe, from their initial burst of violent star formation through their appearance as high stellar-density galaxy cores and to their ultimate fate as giant ellipticals.

The global star formation law of galaxies revisited in the radio continuum

NASA Astrophysics Data System (ADS)

Liu, LiJie; Gao, Yu

2012-02-01

We study the global star formation law, the relation between the gas and star formation rate (SFR) in a sample of 130 local galaxies with infrared (IR) luminosities spanning over three orders of magnitude (109-1012 L⊙), which includes 91 normal spiral galaxies and 39 (ultra)luminous IR galaxies [(U)LIRGs]. We derive their total (atomic and molecular) gas and dense molecular gas masses using newly available HI, CO and HCN data from the literature. The SFR of galaxies is determined from total IR (8-1000 μm) and 1.4 GHz radio continuum (RC) luminosities. The galaxy disk sizes are defined by the de-convolved elliptical Gaussian FWHM of the RC maps. We derive the galaxy disk-averaged SFRs and various gas surface densities, and investigate their relationships. We find that the galaxy disk-averaged surface density of dense molecular gas mass has the tightest correlation with that of SFR (scatter ˜0.26 dex), and is linear in log-log space (power-law slope of N=1.03±0.02) across the full galaxy sample. The correlation between the total gas and SFR surface densities for the full sample has a somewhat larger scatter (˜0.48 dex), and is best fit by a power-law with slope 1.45±0.02. However, the slope changes from ˜1 when only normal spirals are considered, to ˜1.5 when more and more (U)LIRGs are included in the fitting. When different CO-to-H2 conversion factors are used to infer molecular gas masses for normal galaxies and (U)LIRGs, the bi-modal relations claimed recently in CO observations of high-redshift galaxies appear to also exist in local populations of star-forming galaxies.

The VIMOS Ultra-Deep Survey: A major merger origin for the high fraction of galaxies at 2 < z < 6 with two bright clumps

NASA Astrophysics Data System (ADS)

Ribeiro, B.; Le Fèvre, O.; Cassata, P.; Garilli, B.; Lemaux, B. C.; Maccagni, D.; Schaerer, D.; Tasca, L. A. M.; Zamorani, G.; Zucca, E.; Amorín, R.; Bardelli, S.; Hathi, N. P.; Koekemoer, A.; Pforr, J.

2017-11-01

The properties of stellar clumps in star-forming galaxies and their evolution over the redshift range 2 ≲ z ≲ 6 are presented and discussed in the context of the build-up of massive galaxies at early cosmic times. We focused on galaxies with spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS) and stellar masses log 10(M⋆/M⊙) > -0.204 × (z-4.5) + 9.35. We analyzed HST-ACS images to identify clumps within a 20 kpc radius using a method taking into account differential surface brightness dimming and luminosity evolution with redshift. We find that the population of galaxies with more than one clump is dominated by galaxies with two clumps, representing 21-25% of the population, while the fraction of galaxies with three, or four and more, clumps is 8-11% and 7-9%, respectively. The fraction of clumpy galaxies is in the range 35-55% over 2 < z < 6, increasing at higher redshifts, indicating that the fraction of irregular galaxies remains high up to the highest redshifts. The large and bright clumps (M⋆ 109 up to 1010 M⊙) are found to reside predominantly in galaxies with two clumps. Smaller and lower luminosity clumps (M⋆ < 109 M⊙) are found in galaxies with three clumps or more. We interpret these results as evidence for two different modes of clump formation working in parallel. The small low luminosity clumps are likely the result of disk fragmentation, with violent disk instabilities (VDI) forming several long-lived clumps in-situ as suggested from simulations. A fraction of these clumps is also likely coming from minor mergers as confirmed from spectroscopy in several cases. The clumps in the dominating population of galaxies with two clumps are significantly more massive and have properties akin to those in galaxy pairs undergoing massive merging observed at similar redshifts; they appear as more massive than the most massive clumps observed in numerical simulations of disks with VDI. We infer from these properties that the bright and large clumps are most likely the result of major mergers bringing-in ex situ matter onto a galaxy, and we derive a high major merger fraction of 20%. The diversity of clump properties therefore suggests that the assembly of star-forming galaxies at z 2-6 proceeds from several different dissipative processes including an important contribution from major and minor mergers. Based on data obtained with the European Southern Observatory Very Large Telescope, Paranal, Chile, under Large Program 185.A-0791.

CANDELS+3D-HST: Compact SFGs at z ∼ 2-3, the progenitors of the first quiescent galaxies

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

Barro, G.; Faber, S. M.; Koo, D. C.

We analyze the star-forming and structural properties of 45 massive (log(M/M{sub ☉}) >10) compact star-forming galaxies (SFGs) at 2 < z < 3 to explore whether they are progenitors of compact quiescent galaxies at z ∼ 2. The optical/NIR and far-IR Spitzer/Herschel colors indicate that most compact SFGs are heavily obscured. Nearly half (47%) host an X-ray-bright active galactic nucleus (AGN). In contrast, only about 10% of other massive galaxies at that time host AGNs. Compact SFGs have centrally concentrated light profiles and spheroidal morphologies similar to quiescent galaxies and are thus strikingly different from other SFGs, which typically aremore » disk-like and sometimes clumpy or irregular. Most compact SFGs lie either within the star formation rate (SFR)-mass main sequence (65%) or below it (30%), on the expected evolutionary path toward quiescent galaxies. These results show conclusively that galaxies become more compact before they lose their gas and dust, quenching star formation. Using extensive HST photometry from CANDELS and grism spectroscopy from the 3D-HST survey, we model their stellar populations with either exponentially declining (τ) star formation histories (SFHs) or physically motivated SFHs drawn from semianalytic models (SAMs). SAMs predict longer formation timescales and older ages ∼2 Gyr, which are nearly twice as old as the estimates of the τ models. Both models yield good spectral energy distribution fits, indicating that the systematic uncertainty in the age due to degeneracies in the SFH is of that order of magnitude. However, SAM SFHs better match the observed slope and zero point of the SFR-mass main sequence. Contrary to expectations, some low-mass compact SFGs (log(M/M{sub ☉}) =10-10.6) have younger ages but lower specific SFRs than that of more massive galaxies, suggesting that the low-mass galaxies reach the red sequence faster. If the progenitors of compact SFGs are extended SFGs, state-of-the-art SAMs show that mergers and disk instabilities (DIs) are both able to shrink galaxies, but DIs are more frequent (60% versus 40%) and form more concentrated galaxies. We confirm this result via high-resolution hydrodynamic simulations.« less

The origin of the mid-infrared nuclear polarization of active galactic nuclei

NASA Astrophysics Data System (ADS)

Lopez-Rodriguez, E.; Alonso-Herrero, A.; Diaz-Santos, T.; Gonzalez-Martin, O.; Ichikawa, K.; Levenson, N. A.; Martinez-Paredes, M.; Nikutta, R.; Packham, C.; Perlman, E.; Almeida, C. Ramos; Rodriguez-Espinosa, J. M.; Telesco, C. M.

2018-05-01

We combine new (NGC 1275, NGC 4151, and NGC 5506) and previously published (Cygnus A, Mrk 231, and NGC 1068) sub-arcsecond resolution mid-infrared (MIR; 8-13 μm) imaging- and spectro-polarimetric observations of six Seyfert galaxies using CanariCam on the 10.4-m Gran Telescopio CANARIAS. These observations reveal a diverse set of physical processes responsible for the nuclear polarization, and permit characterization of the origin of the MIR nuclear polarimetric signature of active galactic nuclei (AGN). For all radio quiet objects, we found that the nuclear polarization is low (<1 per cent), and the degree of polarization is often a few per cent over extended regions of the host galaxy where we have sensitivity to detect such extended emission (i.e., NGC 1068 and NGC 4151). We suggest that the higher degree of polarization previously found in lower resolution data arises only on the larger-than-nuclear scales. Only the radio-loud Cygnus A exhibits significant nuclear polarization (˜11 per cent), attributable to synchrotron emission from the pc-scale jet close to the core. We present polarization models that suggest that the MIR nuclear polarization for highly obscured objects arises from a self-absorbed MIR polarized clumpy torus and/or dichroism from the host galaxy, while for unabsorbed cores, MIR polarization arises from dust scattering in the torus and/or surrounding nuclear dust.

Does the X-ray outflow quasar PDS 456 have a UV outflow at 0.3c?

NASA Astrophysics Data System (ADS)

Hamann, Fred; Chartas, George; Reeves, James; Nardini, Emanuele

2018-05-01

The quasar PDS 456 (at redshift ˜0.184) has a prototype ultra-fast outflow (UFO) measured in X-rays. This outflow is highly ionized with relativistic speeds, large total column densities log NH(cm-2) > 23, and large kinetic energies that could be important for feedback to the host galaxy. A UV spectrum of PDS 456 obtained with the Hubble Space Telescope in 2000 contains one well-measured broad absorption line (BAL) at ˜1346 Å (observed) that might be Ly α at v ≈ 0.06c or N V λ1240 at v ≈ 0.08c. However, we use photoionization models and comparisons to other outflow quasars to show that these BAL identifications are problematic because other lines that should accompany them are not detected. We argue that the UV BAL is probably C IV at v ≈ 0.30c. This would be the fastest UV outflow ever reported, but its speed is similar to the X-ray outflow and its appearance overall is similar to relativistic UV BALs observed in other quasars. The C IV BAL identification is also supported indirectly by the tentative detection of another broad C IV line at v ≈ 0.19c. The high speeds suggest that the UV outflow originates with the X-ray UFO crudely 20-30 rg from the central black hole. We speculate that the C IV BAL might form in dense clumps embedded in the X-ray UFO, requiring density enhancements of only ≳0.4 dex compared to clumpy structures already inferred for the soft X-ray absorber in PDS 456. The C IV BAL might therefore be the first detection of low-ionization clumps proposed previously to boost the opacities in UFOs for radiative driving.

Multi-phase gas, clumping and non-thermal pressure in cluster outskirts via X-ray, SZ and lensing data

NASA Astrophysics Data System (ADS)

Morandi, Andrea

2017-09-01

We propose to study multitemperature structure, clumpy gas distribution and non-thermal pressure in the outskirts of a sample of galaxy clusters by means of Chandra X-ray, Sunyaev Zeldovich and lensing data. We propose to recover the X-ray spectroscopic temperatures close to the virial radius and compare them to the average (gas mass-weighted) temperature probed through SZ. Our preliminary analysis reveals compelling evidence of a substantial amounts of cold gas (T 0.8 keV) at subvirial temperature which coexists with the hot (>4 keV) thermal component of the intracluster medium (ICM). The proposed investigation has important implications for understanding the astrophysics of the ICM in the outer volumes and the CDM scenario, and it has crucial ramifications for the cosmology.

Young stellar populations in early-type galaxies in the Sloan Digital Sky Survey

NASA Astrophysics Data System (ADS)

Nolan, Louisa A.; Raychaudhury, Somak; Kabán, Ata

2007-02-01

We use a purely data-driven rectified factor analysis to identify early-type galaxies with recent star formation in Data Release 4 of the Sloan Digital Sky Survey Spectroscopic Catalogue. We compare the spectra and environment of these galaxies with those of `normal' early-type galaxies, and a sample of independently selected E+A galaxies. We calculate the projected local galaxy surface density from the nearest five and 10 neighbours (Σ5 and Σ10) for each galaxy in our sample, and find that the dependence on projected local density, of the properties of E+A galaxies, is not significantly different from that of early-type galaxies with young stellar populations, dropping off rapidly towards denser environments, and flattening off at densities <~0.1-0.3 Mpc-2. The dearth of E+A galaxies in dense environments confirms that E+A galaxies are most likely the products of galaxy-galaxy merging or interactions, rather than star-forming galaxies whose star formation has been quenched by processes unique to dense environments, such as ram-pressure stripping or galaxy harassment. We see a tentative peak in the number of E+A galaxies at Σ10 ~ 0.1-0.3 Mpc-2, which may represent the local galaxy density at which the rate of galaxy-galaxy merging or interaction rate peaks. Analysis of the spectra of our early-type galaxies with young stellar populations suggests that they have a stellar component dominated by F stars, ~1-4 Gyr old, together with a mature, metal-rich population characteristic of `typical' early-type galaxies. The young stars represent >~10 per cent of the stellar mass in these galaxies. This, together with the similarity of the environments in which this `E+F' population and the E+A galaxy sample are found, suggests that E+F galaxies used to be E+A galaxies, but have evolved by a further ~ one to a few Gyr. Our rectified factor analysis is sensitive enough to identify this hidden population, which allows us to study the global and intrinsic properties of early-type galaxies created in major mergers or interactions, and compare them with those early-types which have had the bulk of their stars in place since a much earlier epoch.

Dancing to CHANGA: a self-consistent prediction for close SMBH pair formation time-scales following galaxy mergers

NASA Astrophysics Data System (ADS)

Tremmel, M.; Governato, F.; Volonteri, M.; Quinn, T. R.; Pontzen, A.

2018-04-01

We present the first self-consistent prediction for the distribution of formation time-scales for close supermassive black hole (SMBH) pairs following galaxy mergers. Using ROMULUS25, the first large-scale cosmological simulation to accurately track the orbital evolution of SMBHs within their host galaxies down to sub-kpc scales, we predict an average formation rate density of close SMBH pairs of 0.013 cMpc-3 Gyr-1. We find that it is relatively rare for galaxy mergers to result in the formation of close SMBH pairs with sub-kpc separation and those that do form are often the result of Gyr of orbital evolution following the galaxy merger. The likelihood and time-scale to form a close SMBH pair depends strongly on the mass ratio of the merging galaxies, as well as the presence of dense stellar cores. Low stellar mass ratio mergers with galaxies that lack a dense stellar core are more likely to become tidally disrupted and deposit their SMBH at large radii without any stellar core to aid in their orbital decay, resulting in a population of long-lived `wandering' SMBHs. Conversely, SMBHs in galaxies that remain embedded within a stellar core form close pairs in much shorter time-scales on average. This time-scale is a crucial, though often ignored or very simplified, ingredient to models predicting SMBH mergers rates and the connection between SMBH and star formation activity.

Reconstructing The Star Formation Histories Of Galaxies Through Sed Fitting Using The Dense Basis Method

NASA Astrophysics Data System (ADS)

Iyer, Kartheik; Gawiser, Eric

2017-06-01

The Dense Basis SED fitting method reveals previously inaccessible information about the number and duration of star formation episodes and the timing of stellar mass assembly as well as uncertainties in these quantities, in addition to accurately recovering traditional SED parameters including M*, SFR and dust attenuation. This is done using basis Star Formation Histories (SFHs) chosen by comparing the goodness-of-fit of mock galaxy SEDs to the goodness-of-reconstruction of their SFHs, trained and validated using three independent datasets of mock galaxies at z=1 from SAMs, Hydrodynamic simulations and stochastic realizations. Of the six parametrizations of SFHs considered, we reject the traditional parametrizations of constant and exponential SFHs and suggest four novel improvements, quantifying the bias and scatter of each parametrization. We then apply the method to a sample of 1100 CANDELS GOODS-S galaxies at 110^9 M_sun, in contrast to current simulations. About 40% of the CANDEL galaxies have SFHs whose maximum occurs at or near the epoch of observation. These results are presented in Iyer and Gawiser (2017, ApJ 838 127), available at https://arxiv.org/abs/1702.04371

Simulating The Dynamical Evolution Of Galaxies In Group And Cluster Environments

NASA Astrophysics Data System (ADS)

Vijayaraghavan, Rukmani

2015-07-01

Galaxy clusters are harsh environments for their constituent galaxies. A variety of physical processes effective in these dense environments transform gas-rich, spiral, star-forming galaxies to elliptical or spheroidal galaxies with very little gas and therefore minimal star formation. The consequences of these processes are well understood observationally. Galaxies in progressively denser environments have systematically declining star formation rates and gas content. However, a theoretical understanding of of where, when, and how these processes act, and the interplay between the various galaxy transformation mechanisms in clusters remains elusive. In this dissertation, I use numerical simulations of cluster mergers as well as galaxies evolving in quiescent environments to develop a theoretical framework to understand some of the physics of galaxy transformation in cluster environments. Galaxies can be transformed in smaller groups before they are accreted by their eventual massive cluster environments, an effect termed `pre-processing'. Galaxy cluster mergers themselves can accelerate many galaxy transformation mechanisms, including tidal and ram pressure stripping of galaxies and galaxy-galaxy collisions and mergers that result in reassemblies of galaxies' stars and gas. Observationally, cluster mergers have distinct velocity and phase-space signatures depending on the observer's line of sight with respect to the merger direction. Using dark matter only as well as hydrodynamic simulations of cluster mergers with random ensembles of particles tagged with galaxy models, I quantify the effects of cluster mergers on galaxy evolution before, during, and after the mergers. Based on my theoretical predictions of the dynamical signatures of these mergers in combination with galaxy transformation signatures, one can observationally identify remnants of mergers and quantify the effect of the environment on galaxies in dense group and cluster environments. The presence of long-lived, hot X-ray emitting coronae observed in a large fraction of group and cluster galaxies is not well-understood. These coronae are not fully stripped by ram pressure and tidal forces that are efficient in these environments. Theoretically, this is a fascinating and challenging problem that involves understanding and simulating the multitude of physical processes in these dense environments that can remove or replenish galaxies' hot coronae. To solve this problem, I have developed and implemented a robust simulation technique where I simulate the evolution of a realistic cluster environment with a population of galaxies and their gas. With this technique, it is possible to isolate and quantify the importance of the various cluster physical processes for coronal survival. To date, I have performed hydrodynamic simulations of galaxies being ram pressure stripped in quiescent group and cluster environments. Using these simulations, I have characterized the physics of ram pressure stripping and investigated the survival of these coronae in the presence of tidal and ram pressure stripping. I have also generated synthetic X-ray observations of these simulated systems to compare with observed coronae. I have also performed magnetohydrodynamic simulations of galaxies evolving in a magnetized intracluster medium plasma to isolate the effect of magnetic fields on coronal evolution, as well the effect of orbiting galaxies in amplifying magnetic fields. This work is an important step towards understanding the effect of cluster environments on galactic gas, and consequently, their long term evolution and impact on star formation rates.

Sub-mm galaxies as progenitors of compact quiescent galaxies

NASA Astrophysics Data System (ADS)

Toft, Sune

2015-08-01

Three billion years after the big bang (at redshift z=2), half of the most massive galaxies were already old, quiescent systems with little to no residual star formation and extremely compact with stellar mass densities at least an order of magnitude larger than in low redshift ellipticals, their descendants. Little is known about how they formed, but their evolved, dense stellar populations suggest formation within intense, compact starbursts 1-2 Gyr earlier (at 3 < z < 6). Simulations show that gas-rich major mergers can give rise to such starbursts which produce dense remnants. Sub-millimetre selected galaxies (SMGs) are prime examples of intense, gas-rich, starbursts. With a new, mass-complete spectroscopic sample of compact quiescent galaxies at z=2 and a statistically well-understood sample of SMGs, we show that z = 3 -6 SMGs are consistent with being the progenitors of z = 2 quiescent galaxies, matching their formation redshifts and their distributions of sizes, stellar masses and internal velocities. Assuming an evolutionary connection, their space densities also match if the mean duty cycle of SMG starbursts is 42 (+40/-29) Myr (consistent with independent estimates), indicating that the bulk of stars in these massive galaxies were formed in a major, early surge of star-formation. These results suggests a coherent picture of the formation history of the most massive galaxies in the universe, from their initial burst of violent star-formation through their appearance as high stellardensity galaxy cores and to their ultimate fate as giant ellipticals.If time permits i will show novel, spatially resolved spectroscopic observations of the inner regions (r2, allowing for strong new constraints on their formation and evolutionary path

The Inhomogeneous Centers of Cooling Flows in Galaxy Clusters

NASA Astrophysics Data System (ADS)

Sharma, Mangala

2004-04-01

The intracluster medium (ICM) in the centers of galaxy clusters is cool, dense and may be imhomogeneous. We present Chandra X-ray Observatory imaging spectroscopic data on two galaxy clusters, Abell 1991 and MS 0839.8+2938, that have cooling flows in their central few hundred kpc. Their cD galaxies show current star formation, and host compact radio sources. The hot ICM at both their centers has nonhomogeneities on kiloparsec scales. These finer structures are likely to be signatures of the formation of clusters through infall of smaller, cooler subclusters.

Featured Image: A Molecular Cloud Outside Our Galaxy

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-06-01

What do molecular clouds look like outside of our own galaxy? See for yourself in the images above and below of N55, a molecular cloud located in the Large Magellanic Cloud (LMC). In a recent study led by Naslim Neelamkodan (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan), a team of scientists explore N55 to determine how its cloud properties differ from clouds within the Milky Way. The image above reveals the distribution of infrared-emitting gas and dust observed in three bands by the Spitzer Space Telescope. Overplotted in cyan are observations from the Atacama Submillimeter Telescope Experiment tracing the clumpy, warm molecular gas. Below, new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the sub-parsec-scale molecular clumps in greater detail, showing the correlation of massive clumps with Spitzer-identified young stellar objects (crosses). The study presented here indicates that this cloud in the LMC is the site of massive star formation, with properties similar to equivalent clouds in the Milky Way. To learn more about the authors findings, check out the article linked below.CitationNaslim N. et al 2018 ApJ 853 175. doi:10.3847/1538-4357/aaa5b0

Measuring the power spectrum of dark matter substructure using strong gravitational lensing

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

Hezaveh, Yashar; Dalal, Neal; Holder, Gilbert

2016-11-01

In recent years, it has become possible to detect individual dark matter subhalos near images of strongly lensed extended background galaxies. Typically, only the most massive subhalos in the strong lensing region may be detected this way. In this work, we show that strong lenses may also be used to constrain the much more numerous population of lower mass subhalos that are too small to be detected individually. In particular, we show that the power spectrum of projected density fluctuations in galaxy halos can be measured using strong gravitational lensing. We develop the mathematical framework of power spectrum estimation, andmore » test our method on mock observations. We use our results to determine the types of observations required to measure the substructure power spectrum with high significance. We predict that deep observations (∼10 hours on a single target) with current facilities can measure this power spectrum at the 3σ level, with no apparent degeneracy with unknown clumpiness in the background source structure or fluctuations from detector noise. Upcoming ALMA measurements of strong lenses are capable of placing strong constraints on the abundance of dark matter subhalos and the underlying particle nature of dark matter.« less

Ultrafast Outflows: Galaxy-scale Active Galactic Nucleus Feedback

NASA Astrophysics Data System (ADS)

Wagner, A. Y.; Umemura, M.; Bicknell, G. V.

2013-01-01

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

ULTRAFAST OUTFLOWS: GALAXY-SCALE ACTIVE GALACTIC NUCLEUS FEEDBACK

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

Wagner, A. Y.; Umemura, M.; Bicknell, G. V., E-mail: ayw@ccs.tsukuba.ac.jp

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves inmore » the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.« less

Kelvin-Helmholtz evolution in subsonic cold streams feeding galaxies

NASA Astrophysics Data System (ADS)

Angulo, Adrianna; Coffing, S.; Kuranz, C.; Drake, R. P.; Klein, S.; Trantham, M.; Malamud, G.

2017-10-01

The most prolific star formers in cosmological history lie in a regime where dense filament structures carried substantial mass into the galaxy to sustain star formation without producing a shock. However, hydrodynamic instabilities present on the filament surface limit the ability of such structures to deliver dense matter deeply enough to sustain star formation. Simulations lack the finite resolution necessary to allow fair treatment of the instabilities present at the stream boundary. Using the Omega EP laser, we simulate this mode of galaxy formation with a cold, dense, filament structure within a hotter, subsonic flow and observe the interface evolution. Machined surface perturbations stimulate the development of the Kelvin-Helmholtz (KH) instability due to the resultant shear between the two media. A spherical crystal imaging system produces high-resolution radiographs of the KH structures along the filament surface. The results from the first experiments of this kind, using a rod with single-mode, long-wavelength modulations, will be discussed. This work is funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956, and the National Laser User Facility Program, Grant Number DE-NA0002719, and through.

Short-Wavelength Infrared Views of Messier 81

NASA Technical Reports Server (NTRS)

2003-01-01

The magnificent spiral arms of the nearby galaxy Messier 81 are highlighted in this NASA Spitzer Space Telescope image. Located in the northern constellation of Ursa Major (which also includes the Big Dipper), this galaxy is easily visible through binoculars or a small telescope. M81 is located at a distance of 12 million light-years from Earth.

Because of its proximity, M81 provides astronomers with an enticing opportunity to study the anatomy of a spiral galaxy in detail. The unprecedented spatial resolution and sensitivity of Spitzer at infrared wavelengths show a clear separation between the several key constituents of the galaxy: the old stars, the interstellar dust heated by star formation activity, and the embedded sites of massive star formation. The infrared images also permit quantitative measurements of the galaxy's overall dust content, as well as the rate at which new stars are being formed.

The infrared image was obtained by Spitzer's infrared array camera. It is a four-color composite of invisible light, showing emissions from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (yellow) and 8.0 microns (red). Winding outward from the bluish-white central bulge of the galaxy, where old stars predominate and there is little dust, the grand spiral arms are dominated by infrared emission from dust. Dust in the galaxy is bathed by ultraviolet and visible light from the surrounding stars. Upon absorbing an ultraviolet or visible-light photon, a dust grain is heated and re-emits the energy at longer infrared wavelengths. The dust particles, composed of silicates (which are chemically similar to beach sand) and polycyclic aromatic hydrocarbons, trace the gas distribution in the galaxy. The well-mixed gas (which is best detected at radio wavelengths) and dust provide a reservoir of raw materials for future star formation.

The infrared-bright clumpy knots within the spiral arms denote where massive stars are being born in giant H II (ionized hydrogen) regions. The 8-micron emission traces the regions of active star formation in the galaxy. Studying the locations of these regions with respect to the overall mass distribution and other constituents of the galaxy (e.g., gas) will help identify the conditions and processes needed for star formation. With the Spitzer observations, this information comes to us without complications from absorption by cold dust in the galaxy, which makes interpretation of visible-light features uncertain.

The white stars scattered throughout the field of view are foreground stars within our own Milky Way galaxy.

Too Fast, Too Furious: A Galaxy's Fatal Plunge

NASA Astrophysics Data System (ADS)

2004-01-01

Trailing 200,000-light-year-long streamers of seething gas, a galaxy that was once like our Milky Way is being shredded as it plunges at 4.5 million miles per hour through the heart of a distant cluster of galaxies. In this unusually violent collision with ambient cluster gas, the galaxy is stripped down to its skeletal spiral arms as it is eviscerated of fresh hydrogen for making new stars. The galaxy's untimely demise is offering new clues to solving the mystery of what happens to spiral galaxies in a violent universe. Views of the early universe show that spiral galaxies were once much more abundant in rich clusters of galaxies. But they seem to have been vanishing over cosmic time. Where have these "missing bodies" gone? Astronomers are using a wide range of telescopes and analysis techniques to conduct a "CSI" or Crime Scene Investigator-style look at what is happening to this galaxy inside its cluster's rough neighborhood. "It's a clear case of galaxy assault and battery," says William Keel of the University of Alabama. "This is the first time we have a full suite of results from such disparate techniques showing the crime being committed, and the modus operandi." Keel and colleagues are laying out the "forensic evidence" of the galaxy's late life, in a series of presentations today in Atlanta, Ga., at the 203rd meeting of the American Astronomical Society. Astronomers have assembled the evidence by combining a variety of diagnostic observations from telescopes analyzing the galaxy's appearance in X-ray, optical, and radio light. Parallel observations at different wavelengths trace how stars, gas, and dust are being tossed around and torn from the fragile galaxy, called C153. Though such "distressed" galaxies have been seen before, this one's demise is unusually swift and violent. The galaxy belongs to a cluster of galaxies that slammed into another cluster about 100 million years ago. This galaxy took the brunt of the beating as it fell along a trajectory straight through the dense core of the colliding cluster. "This helps explain the weird X-ray and radio emissions we see," says Keel. "The galaxy is a laboratory for studying how gas can be stripped away when it flies through the hot cluster gas, shutting down star birth and transforming the galaxy." The first suggestion of galactic mayhem in this cluster came in 1994 when the Very Large Array radio telescope near Socorro, N.M., detected an unusual number of radio galaxies in the cluster, called Abell 2125. Radio sources trace both star formation and the feeding of central black holes in galaxy clusters. The radio observations also showed that C153 stood out from the other galaxies as an exceptionally powerful radio source. Keel's team began an extensive program of further observations to uncover details about the galaxies. "This was designed to see what the connection could possibly be between events on the 10-million-light-year scale of the cluster merger and what happens deep inside individual galaxies," says Keel. X-ray observations from the ROSAT satellite (an acronym for the Roentgen Satellite) demonstrated that the cluster contains vast amounts of 36-million-degree Fahrenheit (20-million-degree Kelvin) gas that envelops the galaxies. The gas is concentrated into two main lumps rather than smoothly distributed across the cluster, as is more commonly the case. This bolstered the suspicion that two galaxy clusters are actually colliding. In the mid-to-late 1990s astronomers turned the Mayall 4-meter telescope and the WIYN 3.5-meter telescope at the Kitt Peak National Observatory on the cluster to analyze the starlight via spectroscopy. They found many star-forming systems and even active galactic black holes fueled by the collision. The disintegrating galaxy C153 stood out dramatically when the KPNO telescopes were used to photomap the cluster in color. Astronomers then trained NASA's Hubble Space Telescope (HST) onto C153 and resolved a bizarre shape. They found that the galaxy looks unusually clumpy with many young star clusters and chaotic dust features. Besides the disrupted features in the galaxy's disk, HST also showed that the light in the tail is mostly attributed to recent star formation, providing a direct link to the stripping of the galaxy as it passed through the cluster core. Gas compressed along the galaxy's leading edge, like snow before a plow, ignited a firestorm of new star birth. Evidence of recent star formation also comes from the optical spectrum obtained at the 10-meter Gemini North telescope in Hawaii. The spectrum allows the researchers to estimate the time since the most recent burst of star formation. This conclusion was further bolstered when the Mosaic camera on Kitt Peak's Mayall telescope found a very long tail of extended gas coming off the galaxy. The tail was apparently generated in part by a hurricane of stellar winds boiling off the new star-birth regions and being blown backwards as the galaxy streaks through the surrounding hot gas of the cluster. Spectroscopic observations with the Gemini telescope allowed astronomers to age-date the starburst. They find that 90 percent of C153's blue light is from a population of stars that are 100 million years old. This age corresponds to the time the galaxy should have gone careening through the densest gas in the cluster core. The Gemini spectroscopic observations show the stars are in a regular pattern of orbital motion around the center, as usual for disk galaxies. However, there are multiple widespread clouds of gas moving independently of the stars. "This is an important clue that something beyond gravitational forces must be at work, since stars and gas respond the same way to purely gravitational forces," says Keel. "In other words, the galaxy's gas doesn't know what the stars are doing." NASA's Chandra X-ray Observatory discovered that the cooler clouds detected with optical telescopes and an associated radio feature are embedded in a much larger multimillion-degree trail of gas. Chandra's data indicate that this hot gas was probably enriched in heavy elements by the starburst and driven out of the galaxy by its supersonic motion through the much larger cloud of gas that pervades the cluster. Collectively, these observations offer evidence that the ram pressure of external gas in the cluster is stripping away the galaxy's own gas. This process has long been hypothesized to account for the forced evolution of cluster galaxies. Its aftermath has been seen in several ways. Some nearby examples, Seyfert's Sextet and Stefan's Quintet, are tight clusters that show the aftermath of high-velocity collisions. The galaxy C153 is destined to lose the last vestiges of its spiral arms and become a bland S0-type galaxy having a central bulge and disk, but no spiral-arm structure. These types of galaxies are common in the dense galaxy clusters seen today. Astronomers plan to make new observations with Gemini again in 2004 to study the dynamics of the gas and stars in the tail. The science team members are William Keel (University of Alabama), Frazer Owen (National Radio Astronomy Observatory), Michael Ledlow (Gemini Observatory), and Daniel Wang (University of Massachusetts). 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. Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

Evidence for a dwarf galaxy remnant around M82 from deep Hubble Space Telescope imaging

NASA Astrophysics Data System (ADS)

Suwannajak, Chutipong; Sarajedini, Ata

2018-01-01

We present HST/ACS photometry of an over-dense region of stars in the southern halo of the edge-on galaxy M82. The structure is located at a projected distance of 5 kpc from the disk of the galaxy, and its color-magnitude diagram reveals a population of predominantly young stars, which are largely absent from the surrounding halo. Their ages are similar to those of the young stars formed in the tidal debris between M81, M82, and NGC3077 as a result of their interactions. We derive the mean metallicity of the surrounding stars, which are considered to be the halo population of M82, to be similar to that of the red giant branch (RGB) population of the halo of M81. However, the mean metallicity of the RGB in the over-dense structure is significantly more metal-rich than the halo. We theorize that this over-density existed as a dwarf galaxy prior to its interaction with M82 with the young stars forming later from the gas remaining in its main body.

THE MERGER HISTORY, ACTIVE GALACTIC NUCLEUS, AND DWARF GALAXIES OF HICKSON COMPACT GROUP 59

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

Konstantopoulos, I. S.; Charlton, J. C.; Brandt, W. N.

2012-01-20

Compact group galaxies often appear unaffected by their unusually dense environment. Closer examination can, however, reveal the subtle, cumulative effects of multiple galaxy interactions. Hickson Compact Group (HCG) 59 is an excellent example of this situation. We present a photometric study of this group in the optical (Hubble Space Telescope), infrared (Spitzer), and X-ray (Chandra) regimes aimed at characterizing the star formation and nuclear activity in its constituent galaxies and intra-group medium. We associate five dwarf galaxies with the group and update the velocity dispersion, leading to an increase in the dynamical mass of the group of up to amore » factor of 10 (to 2.8 Multiplication-Sign 10{sup 13} M{sub Sun }), and a subsequent revision of its evolutionary stage. Star formation is proceeding at a level consistent with the morphological types of the four main galaxies, of which two are star-forming and the other are two quiescent. Unlike in some other compact groups, star-forming complexes across HCG 59 closely follow mass-radius scaling relations typical of nearby galaxies. In contrast, the ancient globular cluster populations in galaxies HCG 59A and B show intriguing irregularities, and two extragalactic H II regions are found just west of B. We age-date a faint stellar stream in the intra-group medium at {approx}1 Gyr to examine recent interactions. We detect a likely low-luminosity active galactic nucleus in HCG 59A by its {approx}10{sup 40} erg s{sup -1} X-ray emission; the active nucleus rather than star formation can account for the UV+IR spectral energy distribution. We discuss the implications of our findings in the context of galaxy evolution in dense environments.« less

The Merger History, AGN and Dwarf Galaxies of Hickson Compact Group 59

NASA Technical Reports Server (NTRS)

Konstantopoulos, I. S.; Gallagher, S. C.; Fedotov, K.; Durrell, P. R.; Tzanavaris, P.; Hill, A. R.; Zabludoff, A. I.; Maier, M. L.; Elmegreen, D. M.; Charlton, J. C.;

Survey of Water and Ammonia in Nearby Galaxies (SWAN): Resolved Ammonia Thermometry and Water and Methanol Masers in IC 342, NGC 6946, and NGC 2146

NASA Astrophysics Data System (ADS)

Gorski, Mark; Ott, Jürgen; Rand, Richard; Meier, David S.; Momjian, Emmanuel; Schinnerer, Eva

2018-04-01

The Survey of Water and Ammonia in Nearby galaxies (SWAN) studies atomic and molecular species across the nuclei of four star-forming galaxies: NGC 253, IC 342, NGC 6946, and NGC 2146. As part of this survey, we present Karl G. Jansky Very Large Array molecular line observations of three galaxies: IC 342, NGC 6946, and NGC 2146. NGC 253 is covered in a previous paper. These galaxies were chosen to span an order of magnitude in star formation rates and to select a variety of galaxy types. We target the metastable transitions of ammonia NH3(1, 1) to (5, 5), the 22 GHz water (H2O) (616–523) transition, and the 36.1 GHz methanol (CH3OH) (4‑1–30) transition. We use the NH3 metastable lines to perform thermometry of the dense molecular gas. We show evidence for uniform heating across the central kiloparsec of IC 342 with two temperature components for the molecular gas, similar to NGC 253, of 27 and 308 K, and that the dense molecular gas in NGC 2146 has a temperature <86 K. We identify two new water masers in IC 342, and one new water maser in each of NGC 6946 and NGC 2146. The two galaxies NGC 253 and NGC 2146, with the most vigorous star formation, host H2O kilomasers. Lastly, we detect the first 36 GHz CH3OH masers in IC 342 and NGC 6946. For the four external galaxies the total CH3OH luminosity in each galaxy suggests a correlation with galactic star formation rate, whereas the morphology of the emission is similar to that of HNCO, a weak shock tracer.

MALATANG: MApping the dense moLecular gAs in the sTrongest stAr-formiNg Galaxies

NASA Astrophysics Data System (ADS)

Gao, Yu; Zhang, Zhiyu; Greve, Thomas; MALATANG Team

2017-01-01

The MALATANG Large Program is a 390 hr campaign, using the heterodyne array HARP on the JCMT to map theHCN and HCO+ J = 4 - 3 line emission in 23 of the nearest IR-brightest galaxies beyond the Local Group. Theobservations will reach a sensitivity of 0.3 K km/s (~ 4.5 x 10^6 Msun) at linear resolutions of 0.2-2.8kpc. It is thefirst survey to systematically map the distribution of dense molecular gas out to large galactocentric distances in a statisticallysignificant sample of nearby galaxies. MALATANG will bridge the gap, in terms of physical scale and luminosity,between extragalactic (i.e., galaxy-integrated) and Galactic (i.e., single molecular clouds) observations. A primarygoal of the survey is to delineate for the first time the distributed dense gas star-formation relations, as traced by theHCN and HCO+ J = 4-3, on scales of ~1kpc across our targets. Exploring the behaviour of these star-formationrelations in low surface density regions found in the disks as well as in the nuclear regions where surface densitiesare high, will shed new light on whether such environments are host to fundamentally different star-formation modes.The MALATANG data products of resolved HCN and HCO+ J = 4-3 maps of 23 IR-bright local galaxies, will beof great value to the extragalactic community and, in and of themselves, carry significant legacy value. At the moment,about 50% (~195hrs) of the 390hrs of time allocated to MALATANG has been observed. We here show somevery preliminary results as well after introducing our project.

Dust extinction of the stellar continua in starburst galaxies: The ultraviolet and optical extinction law

NASA Technical Reports Server (NTRS)

Calzetti, Daniela; Kinney, Anne L.; Storchi-Bergmann, Thaisa

1994-01-01

We analyze the International Ultraviolet Explorer (IUE) UV and the optical spectra of 39 starburst and blue compact galaxies in order to study the average properties of dust extinction in extended regions of galaxies. The optical spectra have been obtained using an aperture which matches that of IUE, so comparable regions within each galaxy are sampled. The data from the 39 galaxies are compared with five models for the geometrical distribution of dust, adopting as extinction laws both the Milky Way and the Large Magellanic Cloud laws. The commonly used uniform dust screen is included among the models. We find that none of the five models is in satisfactory agreement with the data. In order to understand the discrepancy between the data and the models, we have derived an extinction law directly from the data in the UV and optical wavelength range. The resulting curve is characterized by an overall slope which is more gray than the Milky Way extinction law's slope, and by the absence of the 2175 A dust feature. Remarkably, the difference in optical depth between the Balmer emission lines H(sub alpha) and H(sub beta) is about a factor of 2 larger than the difference in the optical depth between the continuum underlying the two Balmer lines. We interpret this discrepancy as a consequence of the fact that the hot ionizing stars are associated with dustier regions than the cold stellar population is. The absence of the 2175 A dust feature can be due either to the effects of the scattering and clumpiness of the dust or to a chemical composition different from that of the Milky Way dust grains. Disentangling the two interpretations is not easy because of the complexity of the spatial distribution of the emitting regions. The extinction law of the UV and optical spectral continua of extended regions can be applied to the spectra of medium- and high-redshift galaxies, where extended regions of a galaxy are, by necessity, sampled.

IRAS galaxies and the large-scale structure in the CfA slice

NASA Technical Reports Server (NTRS)

Babul, Arif; Postman, Marc

1990-01-01

The spatial distributions of the IRAS and the optical galaxies in the first CfA slice are compared. The IRAS galaxies are generally less clustered than optical ones, but their distribution is essentially identical to that of late-type optical galaxies. The discrepancy between the clustering properties of the IRAS and optical samples in the CfA slice region is found to be entirely due to the paucity of IRAS galaxies in the core of the Coma cluster. The spatial distributions of the IRAS and the optical galaxies, both late and early types, outside the dense core of the Coma cluster are entirely consistent with each other. This conflicts with the prediction of the linear biasing scenario.

Dense Gas, Dynamical Equilibrium Pressure, and Star Formation in Nearby Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Gallagher, Molly J.; Leroy, Adam K.; Bigiel, Frank; Cormier, Diane; Jiménez-Donaire, María J.; Ostriker, Eve; Usero, Antonio; Bolatto, Alberto D.; García-Burillo, Santiago; Hughes, Annie; Kepley, Amanda A.; Krumholz, Mark; Meidt, Sharon E.; Meier, David S.; Murphy, Eric J.; Pety, Jérôme; Rosolowsky, Erik; Schinnerer, Eva; Schruba, Andreas; Walter, Fabian

2018-05-01

We use new ALMA observations to investigate the connection between dense gas fraction, star formation rate (SFR), and local environment across the inner region of four local galaxies showing a wide range of molecular gas depletion times. We map HCN (1–0), HCO+ (1–0), CS (2–1), 13CO (1–0), and C18O (1–0) across the inner few kiloparsecs of each target. We combine these data with short-spacing information from the IRAM large program EMPIRE, archival CO maps, tracers of stellar structure and recent star formation, and recent HCN surveys by Bigiel et al. and Usero et al. We test the degree to which changes in the dense gas fraction drive changes in the SFR. {I}HCN}/{I}CO} (tracing the dense gas fraction) correlates strongly with I CO (tracing molecular gas surface density), stellar surface density, and dynamical equilibrium pressure, P DE. Therefore, {I}HCN}/{I}CO} becomes very low and HCN becomes very faint at large galactocentric radii, where ratios as low as {I}HCN}/{I}CO}∼ 0.01 become common. The apparent ability of dense gas to form stars, {{{Σ }}}SFR}/{{{Σ }}}dense} (where Σdense is traced by the HCN intensity and the star formation rate is traced by a combination of Hα and 24 μm emission), also depends on environment. {{{Σ }}}SFR}/{{{Σ }}}dense} decreases in regions of high gas surface density, high stellar surface density, and high P DE. Statistically, these correlations between environment and both {{{Σ }}}SFR}/{{{Σ }}}dense} and {I}HCN}/{I}CO} are stronger than that between apparent dense gas fraction ({I}HCN}/{I}CO}) and the apparent molecular gas star formation efficiency {{{Σ }}}SFR}/{{{Σ }}}mol}. We show that these results are not specific to HCN.

The SAMI Galaxy Survey: spatially resolving the environmental quenching of star formation in GAMA galaxies

NASA Astrophysics Data System (ADS)

Schaefer, A. L.; Croom, S. M.; Allen, J. T.; Brough, S.; Medling, A. M.; Ho, I.-T.; Scott, N.; Richards, S. N.; Pracy, M. B.; Gunawardhana, M. L. P.; Norberg, P.; Alpaslan, M.; Bauer, A. E.; Bekki, K.; Bland-Hawthorn, J.; Bloom, J. V.; Bryant, J. J.; Couch, W. J.; Driver, S. P.; Fogarty, L. M. R.; Foster, C.; Goldstein, G.; Green, A. W.; Hopkins, A. M.; Konstantopoulos, I. S.; Lawrence, J. S.; López-Sánchez, A. R.; Lorente, N. P. F.; Owers, M. S.; Sharp, R.; Sweet, S. M.; Taylor, E. N.; van de Sande, J.; Walcher, C. J.; Wong, O. I.

2017-01-01

We use data from the Sydney-AAO Multi-Object Integral Field Spectrograph Galaxy Survey and the Galaxy And Mass Assembly (GAMA) survey to investigate the spatially resolved signatures of the environmental quenching of star formation in galaxies. Using dust-corrected measurements of the distribution of Hα emission, we measure the radial profiles of star formation in a sample of 201 star-forming galaxies covering three orders of magnitude in stellar mass (M*; 108.1-1010.95 M⊙) and in fifth nearest neighbour local environment density (Σ5; 10-1.3-102.1 Mpc-2). We show that star formation rate gradients in galaxies are steeper in dense (log10(Σ5/Mpc2) > 0.5) environments by 0.58 ± 0.29 dex re^{-1} in galaxies with stellar masses in the range 10^{10} < M_{*}/M_{⊙} < 10^{11} and that this steepening is accompanied by a reduction in the integrated star formation rate. However, for any given stellar mass or environment density, the star formation morphology of galaxies shows large scatter. We also measure the degree to which the star formation is centrally concentrated using the unitless scale-radius ratio (r50,Hα/r50,cont), which compares the extent of ongoing star formation to previous star formation. With this metric, we find that the fraction of galaxies with centrally concentrated star formation increases with environment density, from ˜5 ± 4 per cent in low-density environments (log10(Σ5/Mpc2) < 0.0) to 30 ± 15 per cent in the highest density environments (log10(Σ5/Mpc2) > 1.0). These lines of evidence strongly suggest that with increasing local environment density, the star formation in galaxies is suppressed, and that this starts in their outskirts such that quenching occurs in an outside-in fashion in dense environments and is not instantaneous.

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.

The Planck Dusty Gravitationally Enhanced subMillimeter Sources (GEMS)

NASA Astrophysics Data System (ADS)

Frye, Brenda

2015-10-01

The brightest, strongly lensed high-redshift galaxies are veritable gems to study intense star formation in the early Universe. How do the high and irregular clumpy stellar and gas mass surface densities, strong radiation fields, and high turbulence regulate the rapid growth of these galaxies? We will use HST/WFC3 to investigate the stellar component of 6 of the brightest high-redshift sub-millimeter galaxies on the sky, which were recently discovered with the Planck all-sky survey. All are giant arcs or partial Einstein rings with angular sizes up to 17 in shallow CFHT K-band or Spitzer/IRAC imaging. FIR luminosities are 10^13-14 L_sun, with dust SEDs strongly dominated by intense star formation near the maximum possible rates (maximal starbursts). All have spectroscopic redshifts z=2.2-3.6 and magnification factors >/=20. We already have multiwavelength data sets to characterize their gas and dust column densities and kinematics, and propose here to acquire deep, high-resolution rest-frame optical imaging to study the stellar populations and morphologies. With WFC3 imaging in F110W & F160W we will: (1) constrain the stellar morphologies, ages, and mass-to-light ratios (2) Identify clumps and measure their properties to test several clump formation scenarios(3) Enhance our on-going lens modeling through the most accurate positions, morphologies and colorsOnly the brightest of the arc clumps are visible from the ground in the NIR. To register the flux along the full extent of the arcs, and importantly to probe individual star forming regions of the size of 30 Dor at z 2-3 in the brightest high-z sub-mm galaxies requires HST.

CHANDRA X-RAY AND HUBBLE SPACE TELESCOPE IMAGING OF OPTICALLY SELECTED KILOPARSEC-SCALE BINARY ACTIVE GALACTIC NUCLEI. II. HOST GALAXY MORPHOLOGY AND AGN ACTIVITY

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

Shangguan, Jinyi; Ho, Luis C.; Liu, Xin

Binary active galactic nuclei (AGNs) provide clues to how gas-rich mergers trigger and fuel AGNs and how supermassive black hole (SMBH) pairs evolve in a gas-rich environment. While significant effort has been invested in their identification, the detailed properties of binary AGNs and their host galaxies are still poorly constrained. In a companion paper, we examined the nature of ionizing sources in the double nuclei of four kiloparsec-scale binary AGNs with redshifts between 0.1 and 0.2. Here, we present their host galaxy morphology based on F336W ( U -band) and F105W ( Y -band) images taken by the Wide Fieldmore » Camera 3 on board the Hubble Space Telescope . Our targets have double-peaked narrow emission lines and were confirmed to host binary AGNs with follow-up observations. We find that kiloparsec-scale binary AGNs occur in galaxy mergers with diverse morphological types. There are three major mergers with intermediate morphologies and a minor merger with a dominant disk component. We estimate the masses of the SMBHs from their host bulge stellar masses and obtain Eddington ratios for each AGN. Compared with a representative control sample drawn at the same redshift and stellar mass, the AGN luminosities and Eddington ratios of our binary AGNs are similar to those of single AGNs. The U − Y color maps indicate that clumpy star-forming regions could significantly affect the X-ray detection of binary AGNs, e.g., the hardness ratio. Considering the weak X-ray emission in AGNs triggered in merger systems, we suggest that samples of X-ray-selected AGNs may be biased against gas-rich mergers.« less

Distributions of Gas and Galaxies from Galaxy Clusters to Larger Scales

NASA Astrophysics Data System (ADS)

Patej, Anna

2017-01-01

We address the distributions of gas and galaxies on three scales: the outskirts of galaxy clusters, the clustering of galaxies on large scales, and the extremes of the galaxy distribution. In the outskirts of galaxy clusters, long-standing analytical models of structure formation and recent simulations predict the existence of density jumps in the gas and dark matter profiles. We use these features to derive models for the gas density profile, obtaining a simple fiducial model that is in agreement with both observations of cluster interiors and simulations of the outskirts. We next consider the galaxy density profiles of clusters; under the assumption that the galaxies in cluster outskirts follow similar collisionless dynamics as the dark matter, their distribution should show a steep jump as well. We examine the profiles of a low-redshift sample of clusters and groups, finding evidence for the jump in some of these clusters. Moving to larger scales where massive galaxies of different types are expected to trace the same large-scale structure, we present a test of this prediction by measuring the clustering of red and blue galaxies at z 0.6, finding low stochasticity between the two populations. These results address a key source of systematic uncertainty - understanding how target populations of galaxies trace large-scale structure - in galaxy redshift surveys. Such surveys use baryon acoustic oscillations (BAO) as a cosmological probe, but are limited by the expense of obtaining sufficiently dense spectroscopy. With the intention of leveraging upcoming deep imaging data, we develop a new method of detecting the BAO in sparse spectroscopic samples via cross-correlation with a dense photometric catalog. This method will permit the extension of BAO measurements to higher redshifts than possible with the existing spectroscopy alone. Lastly, we connect galaxies near and far: the Local Group dwarfs and the high redshift galaxies observed by Hubble and Spitzer. We examine how the local dwarfs may have appeared in the past and compare their properties to the detection limits of the upcoming James Webb Space Telescope (JWST), finding that JWST should be able to detect galaxies similar to the progenitors of a few of the brightest of the local galaxies, revealing a hitherto unobserved population of galaxies at high redshifts.

The Grism Lens-Amplified Survey from Space (GLASS): Dissecting reionization, z~2 galaxies, and dense environments

NASA Astrophysics Data System (ADS)

Treu, Tommaso; GLASS Team

2016-01-01

The Grism Lens-Amplified Survey from Space (GLASS) is a large HST cycle-21 program targeting 10 massive galaxy clusters with extensive HST imaging from CLASH and the Frontier Field Initiative. The program consists of 140 primary and 140 parallel orbits of near-infrared WCF3 and optical ACS grism observations, which result in spatially resolved spectroscopy of thousands of galaxies. GLASS has three primary science drivers although a wide variety of other science investigations are possible with the public GLASS data (e.g. SN 'Refsdal'). The key science goals of GLASS are to: 1) shed light on the epoch of reionization, by measuring the lyman alpha optical depth at z>6 2) Study gas accretion, star formation, and outflows by spatially mapping resolved star formation and determine metallicity gradients from emission lines of galaxies at 1.3

The History and Evolution of Young and Distant Radio Sources

NASA Astrophysics Data System (ADS)

Collier, Jordan

We study two classes of object to gain a better understanding of the evolution of Active Galactic Nuclei (AGN): Infrared-Faint Radio Sources (IFRSs) and Gigahertz Peaked Spectrum (GPS) / Compact Steep Spectrum (CSS) sources. IFRSs are a recently discovered rare class of object, which were found to be strong in the radio but undetectable in extremely sensitive infrared observations from the Spitzer Space Telescope, even in stacked images with sigma < 1muJy. IFRSs were found to exhibit a relatively high sky density, and were thought to represent AGN at z > 3. Therefore, IFRSs may significantly increase the number of known high-redshift galaxies. However, their non-detections in the optical and infrared prevented confirmation of their nature. Previous studies of IFRSs focused on very sensitive observations of a few small regions of the sky, and the largest sample consisted of 55 IFRSs. However, we follow the strategy of combining radio data with IR and optical data for a large region of the sky. Using these data, we discover a population of >1300 brighter IFRSs which are, for the first time, reliably detected in the infrared and optical. We present the first spectroscopic redshifts of IFRSs and show that the brightest IFRSs are at z > 2. Furthermore, we rule out that IFRSs are Star Forming Galaxies, hotspots, lobes or misidentifications. We find the first X-ray counterparts of IFRSs, and increase the number of known polarised IFRSs five-fold. We present an analysis of their radio spectra and show that IFRSs consist of GPS, CSS and ultra-steep-spectrum sources. We follow up >50 of these using VLBI observations, and confirm the AGN status of IFRSs. GPS and CSS sources are compact radio sources with a convex radio spectrum. They are widely thought to represent young and evolving radio galaxies that have recently launched their jets. However, good evidence exists in individual cases that GPS and CSS sources are one of the following: 1) frustrated by interactions with dense gas and dust in their environment; 2) prematurely dying radio sources; 3) recurrent radio galaxies. Their convex spectrum is generally thought to be caused by Synchrotron Self Absorption (SSA), an internal process in which the same population of electrons is responsible for the synchrotron emission and self-absorption. However, recent studies have shown that the convex spectrum may be caused by Free-Free Absorption (FFA), an external process in which an inhomogeneous screen absorbs the synchrotron emission. The majority of GPS and CSS samples consist of Jy-level and therefore, high-luminosity sources. VLBI images show that GPS and CSS sources typically have double-lobed, edge-brightened morphologies on mas scales, appearing as scaled down versions of Fanaroff-Riley Class II (FR II) galaxies. Recently, two low-luminosity GPS sources were found to have jet-brightened morphologies, which appeared as scaled down versions of Fanaroff-Riley Class I (FR I) galaxies. From this, it was proposed that there exists a morphology-luminosity break analogous to the FR I/II break and that low-luminosity GPS and CSS sources are the compact counterparts of FR I galaxies. However, this hypothesis remains unconfirmed, since very few samples of low-luminosity GPS and CSS sources exist. We conclude that, despite being historically favoured, single inhomogeneous SSA is not the dominant form of absorption amongst a large fraction of GPS and CSS sources. We find that FFA provides a good model for the majority of the spectra with observable turnovers, suggesting an inhomogeneous and clumpy ambient medium. Furthermore, we conclude that the majority of our GPS and CSS sources are young and evolving and may undergo recurrent activity over small time scales. We conclude that a very small fraction of GPS and CSS sources consists of frustrated, dying or restarted radio galaxies. (Abstract shortened by ProQuest.).

Multi-scale simulations of black hole accretion in barred galaxies. Self-gravitating disk models

NASA Astrophysics Data System (ADS)

Jung, M.; Illenseer, T. F.; Duschl, W. J.

2018-06-01

Due to the non-axisymmetric potential of the central bar, in addition to their characteristic arms and bar, barred spiral galaxies form a variety of structures within the thin gas disk, such as nuclear rings, inner spirals, and dust lanes. These structures in the inner kiloparsec are extremely important in order to explain and understand the rate of black hole feeding. The aim of this work is to investigate the influence of stellar bars in spiral galaxies on the thin self-gravitating gas disk. We focus on the accretion of gas onto the central supermassive black hole and its time-dependent evolution. We conducted multi-scale simulations simultaneously resolving the galactic disk and the accretion disk around the central black hole. In all the simulations we varied the initial gas disk mass. As an additional parameter we chose either the gas temperature for isothermal simulations or the cooling timescale for non-isothermal simulations. Accretion was either driven by a gravitationally unstable or clumpy accretion disk or by energy dissipation in strong shocks. Most of the simulations show a strong dependence of the accretion rate at the outer boundary of the central accretion disk (r < 300 pc) on the gas flow at kiloparsec scales. The final black hole masses reach up to 109 M⊙ after 1.6 Gyr. Our models show the expected influence of the Eddington limit and a decline in growth rate at the corresponding sub-Eddington limit.

NEUTRAL HYDROGEN OPTICAL DEPTH NEAR STAR-FORMING GALAXIES AT z Almost-Equal-To 2.4 IN THE KECK BARYONIC STRUCTURE SURVEY

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

Rakic, Olivera; Schaye, Joop; Steidel, Charles C.

We study the interface between galaxies and the intergalactic medium by measuring the absorption by neutral hydrogen in the vicinity of star-forming galaxies at z Almost-Equal-To 2.4. Our sample consists of 679 rest-frame UV-selected galaxies with spectroscopic redshifts that have impact parameters <2 (proper) Mpc to the line of sight of one of the 15 bright, background QSOs and that fall within the redshift range of its Ly{alpha} forest. We present the first two-dimensional maps of the absorption around galaxies, plotting the median Ly{alpha} pixel optical depth as a function of transverse and line-of-sight separation from galaxies. The Ly{alpha} opticalmore » depths are measured using an automatic algorithm that takes advantage of all available Lyman series lines. The median optical depth, and hence the median density of atomic hydrogen, drops by more than an order of magnitude around 100 kpc, which is similar to the virial radius of the halos thought to host the galaxies. The median remains enhanced, at the >3{sigma} level, out to at least 2.8 Mpc (i.e., >9 comoving Mpc), but the scatter at a given distance is large compared with the median excess optical depth, suggesting that the gas is clumpy. Within 100 (200) kpc, and over {+-}165 km s{sup -1}, the covering fraction of gas with Ly{alpha} optical depth greater than unity is 100{sup +0}{sub -32}% (66% {+-} 16%). Absorbers with {tau}{sub Ly{alpha}} > 0.1 are typically closer to galaxies than random. The mean galaxy overdensity around absorbers increases with the optical depth and also as the length scale over which the galaxy overdensity is evaluated is decreased. Absorbers with {tau}{sub Ly{alpha}} {approx} 1 reside in regions where the galaxy number density is close to the cosmic mean on scales {>=}0.25 Mpc. We clearly detect two types of redshift space anisotropies. On scales <200 km s{sup -1}, or <1 Mpc, the absorption is stronger along the line of sight than in the transverse direction. This 'finger of God' effect may be due to redshift errors, but is probably dominated by gas motions within or very close to the halos. On the other hand, on scales of 1.4-2.0 Mpc the absorption is compressed along the line of sight (with >3{sigma} significance), an effect that we attribute to large-scale infall (i.e., the Kaiser effect).« less

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.

Dependence of the clustering properties of galaxies on stellar velocity dispersion in the Main galaxy sample of SDSS DR10

NASA Astrophysics Data System (ADS)

Deng, Xin-Fa; Song, Jun; Chen, Yi-Qing; Jiang, Peng; Ding, Ying-Ping

2014-08-01

Using two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we investigate the dependence of the clustering properties of galaxies on stellar velocity dispersion by cluster analysis. It is found that in the luminous volume-limited Main galaxy sample, except at r=1.2, richer and larger systems can be more easily formed in the large stellar velocity dispersion subsample, while in the faint volume-limited Main galaxy sample, at r≥0.9, an opposite trend is observed. According to statistical analyses of the multiplicity functions, we conclude in two volume-limited Main galaxy samples: small stellar velocity dispersion galaxies preferentially form isolated galaxies, close pairs and small group, while large stellar velocity dispersion galaxies preferentially inhabit the dense groups and clusters. However, we note the difference between two volume-limited Main galaxy samples: in the faint volume-limited Main galaxy sample, at r≥0.9, the small stellar velocity dispersion subsample has a higher proportion of galaxies in superclusters ( n≥200) than the large stellar velocity dispersion subsample.

Galaxy evolution in extreme environments: Molecular gas content star formation and AGN in isolated void galaxies

NASA Astrophysics Data System (ADS)

Das, Mousumi; Iono, Daisuke; Saito, Toshiki; Subramanian, Smitha

Since the early redshift surveys of the large scale structure of our universe, it has become clear that galaxies cluster along walls, sheet and filaments leaving large, empty regions called voids between them. Although voids represent the most under dense parts of our universe, they do contain a sparse but significant population of isolated galaxies that are generally low luminosity, late type disk galaxies. Recent studies show that most void galaxies have ongoing star formation and are in an early stage of evolution. We present radio, optical studies of the molecular gas content and star formation in a sample of void galaxies. Using SDSS data, we find that AGN are rare in these systems and are found only in the Bootes void; their black hole masses and radio properties are similar to bright spirals galaxies. Our studies suggest that close galaxy interactions and gas accretion are the main drivers of galaxy evolution in these systems despite their location in the underdense environment of the voids.

NuSTAR View of the Black Hole Wind in the Galaxy Merger IRAS F11119+3257

NASA Astrophysics Data System (ADS)

Tombesi, F.; Veilleux, S.; Meléndez, M.; Lohfink, A.; Reeves, J. N.; Piconcelli, E.; Fiore, F.; Feruglio, C.

2017-12-01

Galactic winds driven by active galactic nuclei (AGNs) have been invoked to play a fundamental role in the co-evolution between supermassive black holes and their host galaxies. Finding observational evidence of such feedback mechanisms is of crucial importance and it requires a multi-wavelength approach in order to compare winds at different scales and phases. In Tombesi et al., we reported the detection of a powerful ultra-fast outflow (UFO) in the Suzaku X-ray spectrum of the ultra-luminous infrared galaxy IRAS F11119+3257. The comparison with a galaxy-scale OH molecular outflow observed with Herschel in the same source supported the energy-conserving scenario for AGN feedback. The main objective of this work is to perform an independent check of the Suzaku results using the higher sensitivity and wider X-ray continuum coverage of NuSTAR. We clearly detect a highly ionized Fe K UFO in the 100 ks NuSTAR spectrum with parameters N H = (3.2 ± 1.5) × 1024 cm-2, log ξ = {4.0}-0.3+1.2 erg s-1 cm, and {v}{out}={0.253}-0.118+0.061c. The launching radius is likely at a distance of r ≥ 16r s from the black hole. The mass outflow rate is in the range of {\\dot{M}}{out} ≃ 0.5-2 M ⊙ yr-1. The UFO momentum rate and power are {\\dot{P}}{out} ≃ 0.5-2 L AGN/c and {\\dot{E}}{out} ≃ 7%-27% L AGN, respectively. The UFO parameters are consistent between the 2013 Suzaku and the 2015 NuSTAR observations. Only the column density is found to be variable, possibly suggesting a clumpy wind. The comparison with the energetics of molecular outflows estimated in infrared and millimeter wavelengths support a connection between the nuclear and galaxy-scale winds in luminous AGNs.

HERschel Observations of Edge-on Spirals (HEROES). I. Far-infrared morphology and dust mass determination

NASA Astrophysics Data System (ADS)

Verstappen, J.; Fritz, J.; Baes, M.; Smith, M. W. L.; Allaert, F.; Bianchi, S.; Blommaert, J. A. D. L.; De Geyter, G.; De Looze, I.; Gentile, G.; Gordon, K. D.; Holwerda, B. W.; Viaene, S.; Xilouris, E. M.

2013-08-01

Context. Edge-on spiral galaxies with prominent dust lanes provide us with an excellent opportunity to study the distribution and properties of the dust within them. The HEROES project was set up to observe a sample of seven large edge-on galaxies across various wavelengths for this investigation. Aims: Within this first paper, we present the Herschel observations and perform a qualitative and quantitative analysis on them, and we derive some global properties of the far infrared and submillimetre emission. Methods: We determine horizontal and vertical profiles from the Herschel observations of the galaxies in the sample and describe the morphology. Modified black-body fits to the global fluxes, measured using aperture photometry, result in dust temperatures and dust masses. The latter values are compared to those that are derived from radiative transfer models taken from the literature. Results: On the whole, our Herschel flux measurements agree well with archival values. We find that the exponential horizontal dust distribution model often used in the literature generally provides a good description of the observed horizontal profiles. Three out of the seven galaxies show signatures of extended vertical emission at 100 and 160 μm at the 5σ level, but in two of these it is probably due to deviations from an exactly edge-on orientation. Only for NGC 4013, a galaxy in which vertically extended dust has already been detected in optical images, we can detect vertically extended dust, and the derived scaleheight agrees with the value estimated through radiative transfer modelling. Our analysis hints at a correlation between the dust scaleheight and its degree of clumpiness, which we infer from the difference between the dust masses as calculated from modelling of optical data and from fitting the spectral energy distribution of Herschel datapoints. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Emergence of the mass discrepancy-acceleration relation from dark matter-baryon interactions

NASA Astrophysics Data System (ADS)

Famaey, Benoit; Khoury, Justin; Penco, Riccardo

2018-03-01

The observed tightness of the mass discrepancy-acceleration relation (MDAR) poses a fine-tuning challenge to current models of galaxy formation. We propose that this relation could arise from collisional interactions between baryons and dark matter (DM) particles, without the need for modification of gravity or ad hoc feedback processes. We assume that these interactions satisfy the following three conditions: (i) the relaxation time of DM particles is comparable to the dynamical time in disk galaxies; (ii) DM exchanges energy with baryons due to elastic collisions; (iii) the product between the baryon-DM cross section and the typical energy exchanged in a collision is inversely proportional to the DM number density. As a proof of principle, we present an example of a particle physics model that gives a DM-baryon cross section with the desired density and velocity dependence. For consistency with direct detection constraints, our DM particles must be either very light (m ll mb) or very heavy (mgg mb), corresponding respectively to heating and cooling of DM by baryons. In both cases, our mechanism applies and an equilibrium configuration can in principle be reached. In this exploratory paper, we focus on the heavy DM/cooling case because it is technically simpler, since the average energy exchanged turns out to be approximately constant throughout galaxies. Under these assumptions, we find that rotationally-supported disk galaxies could naturally settle to equilibrium configurations satisfying a MDAR at all radii without invoking finely tuned feedback processes. We also discuss issues related to the small scale clumpiness of baryons, as well as predictions for pressure-supported systems. We argue in particular that galaxy clusters do not follow the MDAR despite being DM-dominated because they have not reached their equilibrium configuration. Finally, we revisit existing phenomenological, astrophysical and cosmological constraints on baryon-DM interactions in light of the unusual density dependence of the cross section of DM particles.

The first CO+ image: I. Probing the HI/H2 layer around the ultracompact HII region Mon R2

PubMed Central

Treviño-Morales, S. P.; Fuente, A.; Sánchez-Monge, Á.; Pilleri, P.; Goicoechea, J. R.; Ossenkopf-Okada, V.; Roueff, E.; Rizzo, J. R.; Gerin, M.; Berné, O.; Cernicharo, J.; Gónzalez-García, M.; Kramer, C.; García-Burillo, S.; Pety, J.

2016-01-01

The CO+ reactive ion is thought to be a tracer of the boundary between a HII region and the hot molecular gas. In this study, we present the spatial distribution of the CO+ rotational emission toward the Mon R2 star-forming region. The CO+ emission presents a clumpy ring-like morphology, arising from a narrow dense layer around the HII region. We compare the CO+ distribution with other species present in photon-dominated regions (PDR), such as [CII] 158 µm, H2 S(3) rotational line at 9.3 µm, polycyclic aromatic hydrocarbons (PAHs) and HCO+. We find that the CO+ emission is spatially coincident with the PAHs and [CII] emission. This confirms that the CO+ emission arises from a narrow dense layer of the HI/H2 interface. We have determined the CO+ fractional abundance, relative to C+ toward three positions. The abundances range from 0.1 to 1.9 ×10−10 and are in good agreement with previous chemical model, which predicts that the production of CO+ in PDRs only occurs in dense regions with high UV fields. The CO+ linewidth is larger than those found in molecular gas tracers, and their central velocity are blue-shifted with respect to the molecular gas velocity. We interpret this as a hint that the CO+ is probing photo-evaporating clump surfaces. PMID:27721515

Galactic Teamwork Makes Distant Bubbles

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-03-01

During the period of reionization that followed the dark ages of our universe, hydrogen was transformed from a neutral state, which is opaque to radiation, to an ionized one, which is transparent to radiation. But what generated the initial ionizing radiation? The recent discovery of multiple distant galaxies offers evidence for how this process occurred.Two Distant GalaxiesWe believe reionization occurred somewhere between a redshift of z = 6 and 7, because Ly-emitting galaxies drop out at roughly this redshift. Beyond this distance, were generally unable to see the light from these galaxies, because the universe is no longer transparent to their emission. This is not always the case, however: if a bubble of ionized gas exists around a distant galaxy, the radiation can escape, allowing us to see the galaxy.This is true of two recently-discovered Ly-emitting galaxies, confirmed to be at a redshift of z~7 and located near one another in a region known as the Bremer Deep Field. The fact that were able to see the radiation from these galaxies means that they are in an ionized HII region presumably one of the earlier regions to have become reionized in the universe.But on their own, neither of these galaxies is capable of generating an ionized bubble large enough for their light to escape. So what ionized the region around them, and what does this mean for our understanding of how reionization occurred in the universe?A Little Help From FriendsLocation in different filters of the objects in the Hubble Bremer Deep Field catalog. The z~7 selection region is outlined by the grey box. BDF-521 and BDF-3299 were the two originally discovered galaxies; the remaining red markers indicate the additional six galaxies discovered in the same region. [Castellano et al. 2016]A team of scientists led by Marco Castellano (Rome Observatory, INAF) investigated the possibility that there are other, faint galaxies near these two that have helped to ionize the region. Performing a survey using deep field Hubble observations, Castellano and collaborators found an additional 6 galaxies in the same region as the first two, also at a redshift of z~7!The authors believe these galaxies provide a simple explanation of the ionized bubble: each of these faint, normal galaxies produced a small ionized bubble. The overlap of these many small bubbles provided the larger ionized region from which the light of the two originally discovered galaxies was able to escape.How normal is this clustering of galaxies found by Castellano and collaborators? The team demonstrates via cosmological modeling that the number density of galaxies in this region is a factor of 34 greater than would be expected at this distance in a random pointing of the same size.These results greatly support the theoretical prediction that the first ionization fronts in the universe were formed in regions with significant galaxy overdensities. The discovery of this deep-field collection of galaxies strongly suggests that reionization was driven by faint, normal star-forming galaxies in a clumpy process.CitationM. Castellano et al 2016 ApJ 818 L3. doi:10.3847/2041-8205/818/1/L3

MOLECULAR GAS AND STAR-FORMATION PROPERTIES IN THE CENTRAL AND BAR REGIONS OF NGC 6946

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

Pan, Hsi-An; Sorai, Kazuo; Kuno, Nario

In this work, we investigate the molecular gas and star-formation properties in the barred spiral galaxy NGC 6946 using multiple molecular lines and star-formation tracers. A high-resolution image (100 pc) of {sup 13}CO (1–0) is created for the inner 2 kpc disk by the single-dish Nobeyama Radio Observatory 45 m telescope and interferometer Combined Array for Research in Millimeter-wave Astronomy, including the central region (nuclear ring and bar) and the offset ridges of the primary bar. Single-dish HCN (1–0) observations were also made to constrain the amount of dense gas. The physical properties of molecular gas are inferred from (1)more » the large velocity gradient calculations using our observations and archival {sup 12}CO (1–0), {sup 12}CO(2–1) data, (2) the dense gas fraction suggested by the luminosity ratio of HCN to {sup 12}CO (1–0), and (3) the infrared color. The results show that the molecular gas in the central region is warmer and denser than that of the offset ridges. The dense gas fraction of the central region is similar to that of luminous infrared galaxies/ultraluminous infrared galaxies, whereas the offset ridges are close to the global average of normal galaxies. The coolest and least-dense region is found in a spiral-like structure, which was misunderstood to be part of the southern primary bar in previous low-resolution observations. The star-formation efficiency (SFE) changes by about five times in the inner disk. The variation of SFE agrees with the prediction in terms of star formation regulated by the galactic bar. We find a consistency between the star-forming region and the temperature inferred by the infrared color, suggesting that the distribution of subkiloparsec-scale temperature is driven by star formation.« less

Extreme emission-line galaxies out to z ~ 1 in zCOSMOS. I. Sample and characterization of global properties

NASA Astrophysics Data System (ADS)

Amorín, R.; Pérez-Montero, E.; Contini, T.; Vílchez, J. M.; Bolzonella, M.; Tasca, L. A. M.; Lamareille, F.; Zamorani, G.; Maier, C.; Carollo, C. M.; Kneib, J.-P.; Le Fèvre, O.; Lilly, S.; Mainieri, V.; Renzini, A.; Scodeggio, M.; Bardelli, S.; Bongiorno, A.; Caputi, K.; Cucciati, O.; de la Torre, S.; de Ravel, L.; Franzetti, P.; Garilli, B.; Iovino, A.; Kampczyk, P.; Knobel, C.; Kovač, K.; Le Borgne, J.-F.; Le Brun, V.; Mignoli, M.; Pellò, R.; Peng, Y.; Presotto, V.; Ricciardelli, E.; Silverman, J. D.; Tanaka, M.; Tresse, L.; Vergani, D.; Zucca, E.

2015-06-01

Context. The study of large and representative samples of low-metallicity star-forming galaxies at different cosmic epochs is of great interest to the detailed understanding of the assembly history and evolution of low-mass galaxies. Aims: We present a thorough characterization of a large sample of 183 extreme emission-line galaxies (EELGs) at redshift 0.11 ≤ z ≤ 0.93 selected from the 20k zCOSMOS bright survey because of their unusually large emission line equivalent widths. Methods: We use multiwavelength COSMOS photometry, HST-ACS I-band imaging, and optical zCOSMOS spectroscopy to derive the main global properties of star-forming EELGs, such as sizes, stellar masses, star formation rates (SFR), and reliable oxygen abundances using both "direct" and "strong-line" methods. Results: The EELGs are extremely compact (r50 ~ 1.3 kpc), low-mass (M∗ ~ 107-1010 M⊙) galaxies forming stars at unusually high specific star formation rates (sSFR ≡ SFR/M⋆ up to 10-7 yr-1) compared to main sequence star-forming galaxies of the same stellar mass and redshift. At rest-frame UV wavelengths, the EELGs are luminous and show high surface brightness and include strong Lyα emitters, as revealed by GALEX spectroscopy. We show that zCOSMOS EELGs are high-ionization, low-metallicity systems, with median 12+log (O/H) = 8.16 ± 0.21 (0.2 Z⊙) including a handful of extremely metal-deficient (<0.1 Z⊙) EELGs. While ~80% of the EELGs show non-axisymmetric morphologies, including clumpy and cometary or tadpole galaxies, we find that ~29% of them show additional low-surface-brightness features, which strongly suggests recent or ongoing interactions. As star-forming dwarfs in the local Universe, EELGs are most often found in relative isolation. While only very few EELGs belong to compact groups, almost one third of them are found in spectroscopically confirmed loose pairs or triplets. Conclusions: The zCOSMOS EELGs are galaxies caught in a transient and probably early period of their evolution, where they are efficiently building up a significant fraction of their present-day stellar mass in an ongoing, galaxy-wide starburst. Therefore, the EELGs constitute an ideal benchmark for comparison studies between low- and high-redshift low-mass star-forming galaxies. Full Tables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/578/A105

Interstellar Matter

NASA Astrophysics Data System (ADS)

Savage, B.; Murdin, P.

2000-11-01

The enormous volume of space between the stars in the Milky Way Galaxy is filled with interstellar matter (ISM). The ISM plays a central role in the processes of STAR FORMATION and GALAXY EVOLUTION. Stars form from the ISM in dense molecular clouds. The radiant and mechanical energy produced by stars heats, ionizes, and produces structures in the ISM. Gradual or catastrophic mass loss from stars ...

Dense Molecular Gas Tracers in the Outflow of the Starburst Galaxy NGC 253

NASA Astrophysics Data System (ADS)

Walter, Fabian; Bolatto, Alberto D.; Leroy, Adam K.; Veilleux, Sylvain; Warren, Steven R.; Hodge, Jacqueline; Levy, Rebecca C.; Meier, David S.; Ostriker, Eve C.; Ott, Jürgen; Rosolowsky, Erik; Scoville, Nick; Weiss, Axel; Zschaechner, Laura; Zwaan, Martin

2017-02-01

We present a detailed study of a molecular outflow feature in the nearby starburst galaxy NGC 253 using ALMA. We find that this feature is clearly associated with the edge of NGC 253's prominent ionized outflow, has a projected length of ˜300 pc, with a width of ˜50 pc, and a velocity dispersion of ˜40 km s-1, which is consistent with an ejection from the disk about 1 Myr ago. The kinematics of the molecular gas in this feature can be interpreted (albeit not uniquely) as accelerating at a rate of 1 km s-1 pc-1. In this scenario, the gas is approaching an escape velocity at the last measured point. Strikingly, bright tracers of dense molecular gas (HCN, CN, HCO+, CS) are also detected in the molecular outflow: we measure an HCN(1-0)/CO(1-0) line ratio of ˜ 1/10 in the outflow, similar to that in the central starburst region of NGC 253 and other starburst galaxies. By contrast, the HCN/CO line ratio in the NGC 253 disk is significantly lower (˜ 1/30), similar to other nearby galaxy disks. This strongly suggests that the streamer gas originates from the starburst, and that its physical state does not change significantly over timescales of ˜1 Myr during its entrainment in the outflow. Simple calculations indicate that radiation pressure is not the main mechanism for driving the outflow. The presence of such dense material in molecular outflows needs to be accounted for in simulations of galactic outflows.

Evolution in the Dust Lane Fraction of Edge-on L* V Spiral Galaxies Since z = 0.8

NASA Astrophysics Data System (ADS)

Holwerda, B. W.; Dalcanton, J. J.; Radburn-Smith, D.; de Jong, R. S.; Guhathakurta, P.; Koekemoer, A.; Allen, R. J.; Böker, T.

2012-07-01

The presence of a well-defined and narrow dust lane in an edge-on spiral galaxy is the observational signature of a thin and dense molecular disk, in which gravitational collapse has overcome turbulence. Using a sample of galaxies out to z ~ 1 extracted from the COSMOS survey, we identify the fraction of massive (L* V ) disks that display a dust lane. Our goal is to explore the evolution in the stability of the molecular interstellar medium (ISM) disks in spiral galaxies over a cosmic timescale. We check the reliability of our morphological classifications against changes in rest-frame wavelength, resolution, and cosmic dimming with (artificially redshifted) images of local galaxies from the Sloan Digital Sky Survey. We find that the fraction of L* V disks with dust lanes in COSMOS is consistent with the local fraction (≈80%) out to z ~ 0.7. At z = 0.8, the dust lane fraction is only slightly lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively supports the notion that a high specific star formation rate can efficiently destroy or inhibit a dense molecular disk. A small subsample of higher redshift COSMOS galaxies display low internal reddening (E[B - V]), as well as a low incidence of dust lanes. These may be disks in which the growth of the dusty ISM disk lags behind that of the stellar disk. We note that at z = 0.8, the most massive galaxies display a lower dust lane fraction than lower mass galaxies. A small contribution of recent mergers or starbursts to this most massive population may be responsible. The fact that the fraction of galaxies with dust lanes in COSMOS is consistent with little or no evolution implies that models to explain the spectral energy distribution or the host galaxy dust extinction of supernovae based on local galaxies are still applicable to higher redshift spirals. It also suggests that dust lanes are long-lived phenomena or can be reformed over very short timescales.

EVOLUTION IN THE DUST LANE FRACTION OF EDGE-ON L*{sub V} SPIRAL GALAXIES SINCE z = 0.8

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

Holwerda, B. W.; Boeker, T.; Dalcanton, J. J.

2012-07-01

The presence of a well-defined and narrow dust lane in an edge-on spiral galaxy is the observational signature of a thin and dense molecular disk, in which gravitational collapse has overcome turbulence. Using a sample of galaxies out to z {approx} 1 extracted from the COSMOS survey, we identify the fraction of massive (L*{sub V}) disks that display a dust lane. Our goal is to explore the evolution in the stability of the molecular interstellar medium (ISM) disks in spiral galaxies over a cosmic timescale. We check the reliability of our morphological classifications against changes in rest-frame wavelength, resolution, andmore » cosmic dimming with (artificially redshifted) images of local galaxies from the Sloan Digital Sky Survey. We find that the fraction of L*{sub V} disks with dust lanes in COSMOS is consistent with the local fraction ( Almost-Equal-To 80%) out to z {approx} 0.7. At z = 0.8, the dust lane fraction is only slightly lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively supports the notion that a high specific star formation rate can efficiently destroy or inhibit a dense molecular disk. A small subsample of higher redshift COSMOS galaxies display low internal reddening (E[B - V]), as well as a low incidence of dust lanes. These may be disks in which the growth of the dusty ISM disk lags behind that of the stellar disk. We note that at z = 0.8, the most massive galaxies display a lower dust lane fraction than lower mass galaxies. A small contribution of recent mergers or starbursts to this most massive population may be responsible. The fact that the fraction of galaxies with dust lanes in COSMOS is consistent with little or no evolution implies that models to explain the spectral energy distribution or the host galaxy dust extinction of supernovae based on local galaxies are still applicable to higher redshift spirals. It also suggests that dust lanes are long-lived phenomena or can be reformed over very short timescales.« less

Multiband observations of Cygnus A: A study of pressure balance in the core of a powerful radio galaxy

NASA Technical Reports Server (NTRS)

Carilli, Chris; Conner, Sam; Dreher, John; Perley, Rick

1990-01-01

Cygnus A is a powerful double radio source associated with a giant elliptical galaxy at the center of a poor cluster of galaxies. The radio source also sits within the core radius of a dense, cooling flow, x ray emitting cluster gas. Optical spectroscopy and narrow band imaging have revealed copious amounts of narrow line emission from the inner 20 kpc of the associated galaxy. Researchers assume H sub o = 75 km sec (-1) Mpc(-1). Discussed here are the pressures in the three components of the Interstellar Medium (ISM) (i.e., the radio, x ray, and line emitting fluids) within a radius of about 15 kpc of the active nucleus of the Cygnus A galaxy.

NGC 346: Looking in the Cradle of a Massive Star Cluster

NASA Astrophysics Data System (ADS)

Gouliermis, Dimitrios A.; Hony, Sacha

2017-03-01

How does a star cluster of more than few 10,000 solar masses form? We present the case of the cluster NGC 346 in the Small Magellanic Cloud, still embedded in its natal star-forming region N66, and we propose a scenario for its formation, based on observations of the rich stellar populations in the region. Young massive clusters host a high fraction of early-type stars, indicating an extremely high star formation efficiency. The Milky Way galaxy hosts several young massive clusters that fill the gap between young low-mass open clusters and old massive globular clusters. Only a handful, though, are young enough to study their formation. Moreover, the investigation of their gaseous natal environments suffers from contamination by the Galactic disk. Young massive clusters are very abundant in distant starburst and interacting galaxies, but the distance of their hosting galaxies do not also allow a detailed analysis of their formation. The Magellanic Clouds, on the other hand, host young massive clusters in a wide range of ages with the youngest being still embedded in their giant HII regions. Hubble Space Telescope imaging of such star-forming complexes provide a stellar sampling with a high dynamic range in stellar masses, allowing the detailed study of star formation at scales typical for molecular clouds. Our cluster analysis on the distribution of newly-born stars in N66 shows that star formation in the region proceeds in a clumpy hierarchical fashion, leading to the formation of both a dominant young massive cluster, hosting about half of the observed pre-main-sequence population, and a self-similar dispersed distribution of the remaining stars. We investigate the correlation between stellar surface density (and star formation rate derived from star-counts) and molecular gas surface density (derived from dust column density) in order to unravel the physical conditions that gave birth to NGC 346. A power law fit to the data yields a steep correlation between these two parameters with a considerable scatter. The fraction of stellar over the total (gas plus young stars) mass is found to be systematically higher within the central 15 pc (where the young massive cluster is located) than outside, which suggests variations in the star formation efficiency within the same star-forming complex. This trend possibly reflects a change of star formation efficiency in N66 between clustered and non-clustered star formation. Our findings suggest that the formation of NGC 346 is the combined result of star formation regulated by turbulence and of early dynamical evolution induced by the gravitational potential of the dense interstellar medium.

Exploring the Merger/Starburst/AGN Connection in Nearby Infrared- Luminous Galaxies

NASA Astrophysics Data System (ADS)

Chynoweth, Katie; Knop, Robert; Gibbons, Rachel

2007-02-01

We propose to explore the connection between galaxy interactions, starburst activity, and (in a few cases) AGN activity by obtaining spatially resolved optical spectroscopy of a sample of 11 infrared- luminous galaxies. The targets are chosen from the IRAS Bright Galaxy Sample (BGS), all of which show evidence for an ongoing starburst. Additionally, many of these galaxies are advanced mergers, or show clear signs of strong interactions. The kinematics of these galaxies are complicated, and many of them have significant off-nuclear star formation activity. We plan to use the DensePak Fiber Array on the WIYN 3.5m telescope to obtain spectra across the entire face of each galaxy system. These data in combination with similar data obtained for southern galaxies will contribute to understanding of interacting galaxies, galaxy evolution, and star formation. We will use line ratios, velocities, and profile as a means of tracing the dynamics of the gas, the age, strength, and progress of starburst activity throughout the system, and (for those few galaxies that show it) dynamical processes (e.g. outflows) arising from a central AGN.

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE). II. Constraining the quenching time in the stripped galaxy NGC 4330

NASA Astrophysics Data System (ADS)

Fossati, M.; Mendel, J. T.; Boselli, A.; Cuillandre, J. C.; Vollmer, B.; Boissier, S.; Consolandi, G.; Ferrarese, L.; Gwyn, S.; Amram, P.; Boquien, M.; Buat, V.; Burgarella, D.; Cortese, L.; Côté, P.; Côté, S.; Durrell, P.; Fumagalli, M.; Gavazzi, G.; Gomez-Lopez, J.; Hensler, G.; Koribalski, B.; Longobardi, A.; Peng, E. W.; Roediger, J.; Sun, M.; Toloba, E.

2018-06-01

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band Hα + [NII] imaging survey carried out with MegaCam at the Canada-France-Hawaii Telescope. During pilot observations taken in the spring of 2016 we observed NGC 4330, an intermediate mass (M* ≃ 109.8 M⊙) edge-on star forming spiral currently falling into the core of the Virgo cluster. While previous Hα observations showed a clumpy complex of ionised gas knots outside the galaxy disc, new deep observations revealed a low surface brightness 10 kpc tail exhibiting a peculiar filamentary structure. The filaments are remarkably parallel to one another and clearly indicate the direction of motion of the galaxy in the Virgo potential. Motivated by the detection of these features which indicate ongoing gas stripping, we collected literature photometry in 15 bands from the far-UV to the far-IR and deep optical long-slit spectroscopy using the FORS2 instrument at the ESO Very Large Telescope. Using a newly developed Monte Carlo code that jointly fits spectroscopy and photometry, we reconstructed the star formation histories in apertures along the major axis of the galaxy. Our results have been validated against the output of CIGALE, a fitting code which has been previously used for similar studies. We found a clear outside-in gradient with radius of the time when the quenching event started: the outermost radii were stripped 500 Myr ago, while the stripping reached the inner 5 kpc from the centre in the last 100 Myr. Regions at even smaller radii are currently still forming stars fueled by the presence of HI and H2 gas. When compared to statistical studies of the quenching timescales in the local Universe we find that ram pressure stripping of the cold gas is an effective mechanism to reduce the transformation times for galaxies falling into massive clusters. Future systematic studies of all the active galaxies observed by VESTIGE in the Virgo cluster will extend these results to a robust statistical framework.

Legacy ExtraGalactic UV Survey (LEGUS): The HST View of Star Formation in Nearby Galaxies

NASA Astrophysics Data System (ADS)

Calzetti, Daniela; Lee, J. C.; Adamo, A.; Aloisi, A.; Andrews, J. E.; Brown, T. M.; Chandar, R.; Christian, C. A.; Cignoni, M.; Clayton, G. C.; Da Silva, R. L.; de Mink, S. E.; Dobbs, C.; Elmegreen, B.; Elmegreen, D. M.; Evans, A. S.; Fumagalli, M.; Gallagher, J. S.; Gouliermis, D.; Grebel, E.; Herrero-Davo`, A.; Hilbert, B.; Hunter, D. A.; Johnson, K. E.; Kennicutt, R.; Kim, H.; Krumholz, M. R.; Lennon, D. J.; Martin, C. D.; Nair, P.; Nota, A.; Pellerin, A.; Prieto, J.; Regan, M. W.; Sabbi, E.; Schaerer, D.; Schiminovich, D.; Smith, L. J.; Thilker, D. A.; Tosi, M.; Van Dyk, S. D.; Walterbos, R. A.; Whitmore, B. C.; Wofford, A.

2014-01-01

The Treasury program LEGUS (HST/GO-13364) is the first HST UV Atlas of nearby galaxies, and is aimed at the thorough investigation of star formation and its relation with galaxy environment, from the scales of individual stars to those of ~kpc clustered structures. The 154-orbits program is obtaining NUV,U,B,V,I images of 50 star-forming galaxies in the distance range 4-12 Mpc, covering the full range of morphology, star formation rate (SFR), mass, metallicity, internal structure, and interaction state found in the local Universe. The imaging survey will yield accurate recent (<50 Myr) star formation histories (SFHs) from resolved massive stars, and the extinction-corrected ages and masses of star clusters and associations. These extensive inventories of massive stars, clustered systems, and SFHs will be used to: (1) quantify how the clustering of star formation evolves both in space and in time; (2) discriminate among models of star cluster evolution; (3) investigate the effects of SFH on the UV SFR calibrations; (4) explore the impact of environment on star formation and cluster evolution across the full range of galactic and ISM properties. LEGUS observations will inform theories of star formation and galaxy evolution, and improve the understanding of the physical underpinning of the gas-star formation relation and the nature of the clumpy star formation at high redshift. LEGUS will generate the most homogeneous high-resolution, wide-field UV dataset to date, building and expanding on the GALEX legacy. Data products that will be delivered to the community include: catalogs of massive stars and star clusters, catalogs of star cluster properties (ages, masses, extinction), and a one-stop shop for all the ancillary data available for this well-studied galaxy sample. LEGUS will provide the reference survey and the foundation for future observations with JWST and with ALMA. This abstract accompanies another one from the same project, and presents the status of the project, its structure, and the data products that will be delivered to the community; the other abstract presents the science goals of LEGUS and how these will be addressed by the HST observations.

The unusual ISM in Blue and Dusty Gas Rich Galaxies (BADGRS).

NASA Astrophysics Data System (ADS)

Dunne, L.; Zhang, Z.; De Vis, P.; Clark, C. J. R.; Oteo, I.; Maddox, S. J.; Cigan, P.; de Zotti, G.; Gomez, H. L.; Ivison, R. J.; Rowlands, K.; Smith, M. W. L.; van der Werf, P.; Vlahakis, C.; Millard, J. S.

2018-06-01

The Herschel-ATLAS unbiased survey of cold dust in the local Universe is dominated by a surprising population of very blue (FUV - K < 3.5), dust-rich galaxies with high gas fractions ({f_{HI}=M_{HI}/({ M_{\\ast }}+M_{HI})}>0.5). Dubbed `Blue and Dusty Gas Rich Sources' (BADGRS) they have cold diffuse dust temperatures, and the highest dust-to-stellar mass ratios of any galaxies in the local Universe. Here, we explore the molecular ISM in a representative sample of BADGRS, using very deep {CO(J_{up}=1,2,3)} observations across the central and outer disk regions. We find very low CO brightnesses (Tp = 5 - 30 mK), despite the bright far-infrared emission and metallicities in the range 0.5 < Z/Z⊙ < 1.0. The CO line ratios indicate a range of conditions with R_{21}={T_b^{21}/T_b^{10}=0.6-2.1} and R_{31}={T_b^{32}/T_b^{10}=0.2-1.2}. Using a metallicity dependent conversion from CO luminosity to molecular gas mass we find M_{H2}/{M_d}˜ 7-27 and Σ _{H2} = 0.5-6 M_{⊙} {pc^{-2}}, around an order of magnitude lower than expected. The BADGRS have lower molecular gas depletion timescales (τd ˜ 0.5 Gyr) than other local spirals, lying offset from the Kennicutt-Schmidt relation by a similar factor to Blue Compact Dwarf galaxies. The cold diffuse dust temperature in BADGRS (13-16 K) requires an interstellar radiation field 10-20 times lower than that inferred from their observed surface brightness. We speculate that the dust in these sources has either a very clumpy geometry or a very different opacity in order to explain the cold temperatures and lack of CO emission. BADGRS also have low UV attenuation for their UV colour suggestive of an SMC-type dust attenuation curve, different star formation histories or different dust/star geometry. They lie in a similar part of the IRX-β space as z ˜ 5 galaxies and may be useful as local analogues for high gas fraction galaxies in the early Universe.

Was the Milky Way Bulge Formed from the Buckling Disk Instability, Hierarchical Collapse, Accretion of Clumps, or All of the Above?

NASA Astrophysics Data System (ADS)

Nataf, David M.

2017-09-01

The assembly of the Milky Way bulge is an old topic in astronomy, one now in a period of renewed and rapid development. That is due to tremendous advances in observations of bulge stars, motivating observations of both local and high-redshift galaxies, and increasingly sophisticated simulations. The dominant scenario for bulge formation is that of the Milky Way as a nearly pure disk galaxy, with the inner disk having formed a bar and buckled. This can potentially explain virtually all bulge stars with [Fe/H] ≳ -1.0, which comprise 95% of the stellar population. The evidence is the incredible success in N-body models of this type in making non-trivial, non-generic predictions, such as the rotation curve and velocity dispersion measured from radial velocities, and the spatial morphologies of the peanut/X-shape and the long bar. The classical bulge scenario, whereby the bulge formed from early dissipative collapse and mergers, remains viable for stars with [Fe/H] ≲ -1.0 and potentially a minority of the other stars. A classical bulge is expected from Λ-CDM cosmological simulations, can accentuate the properties of an existing bar in a hybrid system, and is most consistent with the bulge abundance trends such as [Mg/Fe], which are elevated relative to both the thin and thick disks. Finally, the clumpy-galaxy scenario is considered, as it is the correct description of most Milky Way precursors given observations of high-redshift galaxies. Simulations predict that these star-forming clumps will sometimes migrate to the centres of galaxies where they may form a bulge, and galaxies often include a bulge clump as well. They will possibly form a bar with properties consistent with those of the Milky Way, such as the exponential profile and metallicity gradient. Given the relative successes of these scenarios, the Milky Way bulge is plausibly of composite origin, with a classical bulge and/or inner halo numerically dominant for stars with [Fe/H] ≲ -1.0, a buckling thick disk for stars with - 1.0 ≲ [Fe/H

Properties and evolution of dense structures in the interstellar medium

NASA Astrophysics Data System (ADS)

Parikka, Anna

2015-09-01

In this thesis I present a study of two kinds of dense ISM structures: compact cold sources detected by Planck and dense condensations in a photodissociation region (PDR), namely the Orion Bar detected by ground-based and Herschel telescopes. Both kinds of structures are closely related to star formation. The cold sources are investigated as potentially gravitationally bound, prestellar, objects. The Orion Bar is a highly FUV-illuminated (G0=10^4) prototypical PDR, with several known protoplanetary disks, illuminated by the young Trapezium stars. First I introduce a paper published in A&A: The Physical state of selected cold clumps. In this paper we compared the Herschel dust continuum observations from the open time key program Galactic Cold Cores to ground based molecular line observations from the 20-m radio telescope of the Onsala Space Observatory in Sweden. The clumps were selected based on their brightness and low dust color temperatures (T=10-15 K). We calculated the virial and Bonnor-Ebert masses and compared them to the masses calculated from the observations. The results indicate that most of the observed cold clumps are not necessarily prestellar.Then I move on to the warm and dense condensations of the ISM. In my study of the Orion Bar, I use observations from PACS instrument on board Herschel from the open time program Unveiling the origin and excitation mechanisms of the warm CO, OH and CH+. I present maps of 110"x110" of the methylidyne cation (CH+ J=3-2), OH doublets at 84 μm, and high-J CO (J=19-18). This is the first time that these PDR tracers are presented in such a high spatial resolution and high signal-to-noise ratio. The CH+ and OH have critical densities (10^10 cm-3) and upper level energy temperatures (250 K). In addition the endothermicity of the CH+ + H2 reaction (4300 K) that forms CH+ is comparable to the activation barrier of the O + H2 reaction (4800 K) forming OH. Given these similarities it is interesting to compare their emission. The spatial distribution of CH+ and OH shows the same clumpy structure of the Bar that has been seen in other observations. The morphology of CH+ and H2 confirms that CH+ formation and excitation is strongly dependent on the vibrationally excited H2, while OH is not. The peak in the OH 84 μm emission corresponds to a bright young object, identified as the externally illuminated protoplanetary disk 244-440.Finally, I study the high-J CO in the Orion Bar. I also introduce low- and mid-J CO observations of the area. The high-J CO morphology shows a clumpy structure in the Bar and we establish a link between the dense core of the clumps, traced in CS J=2-1 by Lee et al. (2013) and in H13CN by Lis and Schilke (2003). We also show that the high-J CO is mainly excited by the UV heating.

Mid-infrared interferometry of AGNs: A statistical view into the dusty nuclear environment of the Seyfert Galaxies.

NASA Astrophysics Data System (ADS)

Lopez-Gonzaga, N.

2015-09-01

The high resolution achieved by the instrument MIDI at the VLTI allowed to obtain more detail information about the geometry and structure of the nuclear mid-infrared emission of AGNs, but due to the lack of real images, the interpretation of the results is not an easy task. To profit more from the high resolution data, we developed a statistical tool that allows interpret these data using clumpy torus models. A statistical approach is needed to overcome effects such as, the randomness in the position of the clouds and the uncertainty of the true position angle on the sky. Our results, obtained by studying the mid-infrared emission at the highest resolution currently available, suggest that the dusty environment of Type I objects is formed by a lower number of clouds than Type II objects.

Do Circumnuclear Dense Gas Disks Drive Mass Accretion onto Supermassive Black Holes?

NASA Astrophysics Data System (ADS)

Izumi, Takuma; Kawakatu, Nozomu; Kohno, Kotaro

2016-08-01

We present a positive correlation between the mass of dense molecular gas ({M}{{dense}}) of ˜100 pc scale circumnuclear disks (CNDs) and the black hole mass accretion rate ({\\dot{M}}{{BH}}) in a total of 10 Seyfert galaxies, based on data compiled from the literature and an archive (median aperture θ med = 220 pc). A typical {M}{{dense}} of CNDs is 107-8 {M}⊙ , estimated from the luminosity of the dense gas tracer, the HCN(1-0) emission line. Because dense molecular gas is the site of star formation, this correlation is virtually equivalent to the one between the nuclear star-formation rate and {\\dot{M}}{{BH}} revealed previously. Moreover, the {M}{{dense}}{--}{\\dot{M}}{{BH}} correlation was tighter for CND-scale gas than for the gas on kiloparsec or larger scales. This indicates that CNDs likely play an important role in fueling black holes, whereas greater than kiloparesec scale gas does not. To demonstrate a possible approach for studying the CND-scale accretion process with the Atacama Large Millimeter/submillimeter Array, we used a mass accretion model where angular momentum loss due to supernova explosions is vital. Based on the model prediction, we suggest that only the partial fraction of the mass accreted from the CND ({\\dot{M}}{{acc}}) is consumed as {\\dot{M}}{{BH}}. However, {\\dot{M}}{{acc}} agrees well with the total nuclear mass flow rate (I.e., {\\dot{M}}{{BH}} + outflow rate). Although these results are still tentative with large uncertainties, they support the view that star formation in CNDs can drive mass accretion onto supermassive black holes in Seyfert galaxies.

Large turbulent reservoirs of cold molecular gas around high-redshift starburst galaxies.

PubMed

Falgarone, E; Zwaan, M A; Godard, B; Bergin, E; Ivison, R J; Andreani, P M; Bournaud, F; Bussmann, R S; Elbaz, D; Omont, A; Oteo, I; Walter, F

2017-08-24

Starburst galaxies at the peak of cosmic star formation are among the most extreme star-forming engines in the Universe, producing stars over about 100 million years (ref. 2). The star-formation rates of these galaxies, which exceed 100 solar masses per year, require large reservoirs of cold molecular gas to be delivered to their cores, despite strong feedback from stars or active galactic nuclei. Consequently, starburst galaxies are ideal for studying the interplay between this feedback and the growth of a galaxy. The methylidyne cation, CH + , is a most useful molecule for such studies because it cannot form in cold gas without suprathermal energy input, so its presence indicates dissipation of mechanical energy or strong ultraviolet irradiation. Here we report the detection of CH + (J = 1-0) emission and absorption lines in the spectra of six lensed starburst galaxies at redshifts near 2.5. This line has such a high critical density for excitation that it is emitted only in very dense gas, and is absorbed in low-density gas. We find that the CH + emission lines, which are broader than 1,000 kilometres per second, originate in dense shock waves powered by hot galactic winds. The CH + absorption lines reveal highly turbulent reservoirs of cool (about 100 kelvin), low-density gas, extending far (more than 10 kiloparsecs) outside the starburst galaxies (which have radii of less than 1 kiloparsec). We show that the galactic winds sustain turbulence in the 10-kiloparsec-scale environments of the galaxies, processing these environments into multiphase, gravitationally bound reservoirs. However, the mass outflow rates are found to be insufficient to balance the star-formation rates. Another mass input is therefore required for these reservoirs, which could be provided by ongoing mergers or cold-stream accretion. Our results suggest that galactic feedback, coupled jointly to turbulence and gravity, extends the starburst phase of a galaxy instead of quenching it.

Black hole feedback in a multiphase interstellar medium

NASA Astrophysics Data System (ADS)

Bourne, Martin A.; Nayakshin, Sergei; Hobbs, Alexander

2014-07-01

Ultrafast outflows (UFOs) from supermassive black holes (SMBHs) are thought to regulate the growth of SMBHs and host galaxies, resulting in a number of observational correlations. We present high-resolution numerical simulations of the impact of a thermalized UFO on the ambient gas in the inner part of the host galaxy. Our results depend strongly on whether the gas is homogeneous or clumpy. In the former case all of the ambient gas is driven outward rapidly as expected based on commonly used energy budget arguments, while in the latter the flows of mass and energy de-couple. Carrying most of the energy, the shocked UFO escapes from the bulge via paths of least resistance, taking with it only the low-density phase of the host. Most of the mass is however in the high-density phase, and is affected by the UFO much less strongly, and may even continue to flow inwards. We suggest that the UFO energy leakage through the pores in the multiphase interstellar medium (ISM) may explain why observed SMBHs are so massive despite their overwhelmingly large energy production rates. The multiphase ISM effects reported here are probably under-resolved in cosmological simulations but may be included in prescriptions for active galactic nuclei feedback in future simulations and in semi-analytical models.

SUBSTRUCTURE WITHIN THE SSA22 PROTOCLUSTER AT z ≈ 3.09

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

Topping, Michael W.; Shapley, Alice E.; Steidel, Charles C., E-mail: mtopping@astro.ucla.edu

We present the results of a densely sampled spectroscopic survey of the SSA22 protocluster at z ≈ 3.09. Our sample with Keck/LRIS spectroscopy includes 106 Ly α emitters (LAEs) and 40 Lyman break galaxies (LBGs) at z = 3.05–3.12. These galaxies are contained within the 9′ × 9′ region in which the protocluster was discovered, which also hosts the maximum galaxy overdensity in the SSA22 region. The redshift histogram of our spectroscopic sample reveals two distinct peaks, at z = 3.069 (blue; 43 galaxies) and z = 3.095 (red; 103 galaxies). Furthermore, objects in the blue and red peaks aremore » segregated on the sky, with galaxies in the blue peak concentrating toward the western half of the field. These results suggest that the blue and red redshift peaks represent two distinct structures in physical space. Although the double-peaked redshift histogram is traced in the same manner by LBGs and LAEs, and brighter and fainter galaxies, we find that 9 out of 10 X-ray AGNs in SSA22, and all 7 spectroscopically confirmed giant Ly α “blobs,” reside in the red peak. We combine our data set with sparsely sampled spectroscopy from the literature over a significantly wider area, finding preliminary evidence that the double-peaked structure in redshift space extends beyond the region of our dense spectroscopic sampling. In order to fully characterize the three-dimensional structure, dynamics, and evolution of large-scale structure in the SSA22 overdensity, we require the measurement of large samples of LAE and LBG redshifts over a significantly wider area, as well as detailed comparisons with cosmological simulations of massive cluster formation.« less

Impact of magnetic fields on ram pressure stripping in disk galaxies

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

Ruszkowski, M.; Brüggen, M.; Lee, D.

Ram pressure stripping can remove significant amounts of gas from galaxies in clusters and massive groups and thus has a large impact on the evolution of cluster galaxies. Recent observations have shown that key properties of ram-pressure-stripped tails of galaxies, such as their width and structure, are in conflict with predictions by simulations. To increase the realism of existing simulations, we simulated for the first time a disk galaxy exposed to a uniformly magnetized wind including radiative cooling and self-gravity of the gas. We find that magnetic fields have a strong effect on the morphology of the gas in themore » tail of the galaxy. While in the purely hydrodynamical case the tail is very clumpy, the magnetohydrodynamical case shows very filamentary structures in the tail. The filaments can be strongly supported by magnetic pressure and, wherever this is the case, the magnetic fields vectors tend to be aligned with the filaments. The ram pressure stripping process may lead to the formation of magnetized density tails that appear as bifurcated in the plane of the sky and resemble the double tails observed in ESO 137-001 and ESO 137-002. Such tails can be formed under a variety of situations, both for the disks oriented face-on with respect to the intracluster medium (ICM) wind and for the tilted ones. While this bifurcation is the consequence of the generic tendency for the magnetic fields to produce very filamentary tail morphology, the tail properties are further shaped by the combination of the magnetic field orientation and the sliding of the field past the disk surface exposed to the wind. Despite the fact that the effect of the magnetic field on the morphology of the tail is strong, magnetic draping does not strongly change the rate of gas stripping. For a face-on galaxy, the field tends to reduce the amount of gas stripping compared to the pure hydrodynamical case, and is associated with the formation of a stable magnetic draping layer on the side of the galaxy exposed to the incoming ICM wind. For significantly tilted disks, the situation may be reversed and the stripping rate may be enhanced by the 'scraping' of the disk surface by the magnetic fields sliding past the ISM/ICM interface. Instabilities, such as gravitational instabilities, undo the protective effect of this layer and allow the gas to leak out of the galaxy.« less

The galaxy cluster outskirts probed by Chandra

NASA Astrophysics Data System (ADS)

Morandi, Andrea; Sun, Ming; Forman, William; Jones, Christine

2015-08-01

Exploring the virialization region of galaxy clusters has recently raised the attention of the scientific community, offering a direct view of structure formation. In this talk, I will present recent results on the physical properties of the intracluster medium in the outer volumes of a sample of 320 clusters (0.056 3 keV) in the Chandra archive, with a total integration time of ~20 Ms. We stacked the emission measure profiles of the clusters to detect a signal out to R_{100}. We then measured the average emission measure, gas density and gas fraction, which scale according to the self-similar model of cluster formation. We observe a steepening of the density profiles beyond R_{500} with slope beta ~ 0.68 at R_{500} and beta ~ 1 at R_{200} and beyond. By tracking the direction of the cosmic filaments where the clusters are embedded, we report that galaxy clusters deviate from spherical symmetry. We also did not find evolution of the gas density with redshift, confirming the self-similar evolution of the gas density. The value of the baryon fraction reaches the cosmic value at R_{200}: however, systematics due to non-thermal pressure support and clumpiness might enhance the measured gas fraction, leading to an actual deficit of the baryon budget with respect to the primordial value). This novel method, the stacking the X-ray signal of cluster outskirts, has the capacity to provide a generational leap forward in our understanding of cluster physics and formation, and the use of clusters as cosmological probes.

`Zwicky's Nonet': a compact merging ensemble of nine galaxies and 4C 35.06, a peculiar radio galaxy with dancing radio jets

NASA Astrophysics Data System (ADS)

Biju, K. G.; Bagchi, Joydeep; Ishwara-Chandra, C. H.; Pandey-Pommier, M.; Jacob, Joe; Patil, M. K.; Kumar, P. Sunil; Pandge, Mahadev; Dabhade, Pratik; Gaikwad, Madhuri; Dhurde, Samir; Abraham, Sheelu; Vivek, M.; Mahabal, Ashish A.; Djorgovski, S. G.

2017-10-01

We report the results of our radio, optical and infrared studies of a peculiar radio source 4C 35.06, an extended radio-loud active galactic nucleus (AGN) at the centre of galaxy cluster Abell 407 (z = 0.047). The central region of this cluster hosts a remarkably tight ensemble of nine galaxies, the spectra of which resemble those of passive red ellipticals, embedded within a diffuse stellar halo of ˜1 arcmin size. This system (named 'Zwicky's Nonet') provides unique and compelling evidence for a multiple-nucleus cD galaxy precursor. Multifrequency radio observations of 4C 35.06 with the Giant Meterwave Radio Telescope (GMRT) at 610, 235 and 150 MHz reveal a system of 400-kpc scale helically twisted and kinked radio jets and outer diffuse lobes. The outer extremities of jets contain extremely steep-spectrum (spectral index -1.7 to -2.5) relic/fossil radio plasma with a spectral age of a few ×(107-108) yr. Such ultra-steep spectrum relic radio lobes without definitive hotspots are rare and they provide an opportunity to understand the life cycle of relativistic jets and physics of black hole mergers in dense environments. We interpret our observations of this radio source in the context of growth of its central black hole, triggering of its AGN activity and jet precession, all possibly caused by galaxy mergers in this dense galactic system. A slow conical precession of the jet axis due to gravitational perturbation between interacting black holes is invoked to explain the unusual jet morphology.

Synthetic Absorption Lines for a Clumpy Medium: A Spectral Signature for Cloud Acceleration in AGN?

NASA Technical Reports Server (NTRS)

Waters, Tim; Proga, Daniel; Dannen, Randall; Kallman, Timothy R.

2017-01-01

There is increasing evidence that the highly ionized multiphase components of AGN disc winds may be due to thermal instability. The ions responsible for forming the observed X-ray absorption lines may only exist in relatively cool clumps that can be identified with the so-called warm absorbers. Here we calculate synthetic absorption lines for such warm absorbers from first principles by combining 2D hydrodynamic solutions of a two-phase medium with a dense grid of photoionization models to determine the detailed ionization structure of the gas. Our calculations reveal that cloud disruption, which leads to a highly complicated velocity field (i.e. a clumpy flow), will only mildly affect line shapes and strengths when the warm gas becomes highly mixed but not depleted. Prior to complete disruption, clouds that are optically thin to the driving UV resonance lines will cause absorption at an increasingly blueshifted line-of-sight velocity as they are accelerated. This behavior will imprint an identifiable signature on the line profile if warm absorbers are enshrouded in an even broader absorption line produced by a high column of intercloud gas. Interestingly, we show that it is possible to develop a spectral diagnostic for cloud acceleration by differencing the absorption components of a doublet line, a result that can be qualitatively understood using a simple partial covering model. Our calculations also permit us to comment on the spectral differences between cloud disruption and ionization changes driven by flux variability. Notably, cloud disruption offers another possibility for explaining absorption line variability.

First Results from the Dense Extragalactic GBT+ARGUS Survey (DEGAS): A Direct, Quantitative Test of the Role of Gas Density in Star Formation

NASA Astrophysics Data System (ADS)

Kepley, Amanda; Bigiel, Frank; Bolatto, Alberto; Church, Sarah; Cleary, Kieran; Frayer, David; Gallagher, Molly; Gundersen, Joshua; Harris, Andrew; Hughes, Annie; Jimenez-Donaire, Maria Jesus; Kessler, Sarah; Lee, Cheoljong; Leroy, Adam; Li, Jialu; Donovan Meyer, Jennifer; Rosolowsky, Erik; Sandstrom, Karin; Schinnener, Eva; Schruba, Andreas; Sieth, Matt; Usero, Antonio

2018-01-01

Gas density plays a central role in all modern theories of star formation. A key test of these theories involves quantifying the resolved gas density distribution and its relationship to star formation within a wide range of galactic environments. Until recently, this experiment has been difficult to perform owing to the faint nature of key molecular gas tracers like HCN and HCO+, but the superior sensitivity of modern millimeter instruments like ALMA and the IRAM 30m make these types of experiments feasible. In particular, the sensitivity and resolution provided by large aperture of the GBT combined with fast mapping speeds made possible by its new 16-pixel, 3mm focal plane array (Argus) make the GBT an almost-ideal instrument for this type of study. The Dense Extragalactic GBT+Argus Survey (DEGAS) will leverage these capabilities to perform the largest, resolved survey of molecular gas tracers in nearby galaxies, ultimately mapping a suite of four molecular gas tracers in the inner 2’ by 2’ of 36 nearby galaxies. When complete in 2020, DEGAS will be the largest resolved survey of dense molecular gas tracers in nearby galaxies. This talk will present early results from the first observations for this Green Bank Telescope large survey and highlight some exciting future possibilities for this survey.

Neutral Hydrogen Optical Depth near Star-forming Galaxies at z ≈ 2.4 in the Keck Baryonic Structure Survey

NASA Astrophysics Data System (ADS)

Rakic, Olivera; Schaye, Joop; Steidel, Charles C.; Rudie, Gwen C.

2012-06-01

We study the interface between galaxies and the intergalactic medium by measuring the absorption by neutral hydrogen in the vicinity of star-forming galaxies at z ≈ 2.4. Our sample consists of 679 rest-frame UV-selected galaxies with spectroscopic redshifts that have impact parameters <2 (proper) Mpc to the line of sight of one of the 15 bright, background QSOs and that fall within the redshift range of its Lyα forest. We present the first two-dimensional maps of the absorption around galaxies, plotting the median Lyα pixel optical depth as a function of transverse and line-of-sight separation from galaxies. The Lyα optical depths are measured using an automatic algorithm that takes advantage of all available Lyman series lines. The median optical depth, and hence the median density of atomic hydrogen, drops by more than an order of magnitude around 100 kpc, which is similar to the virial radius of the halos thought to host the galaxies. The median remains enhanced, at the >3σ level, out to at least 2.8 Mpc (i.e., >9 comoving Mpc), but the scatter at a given distance is large compared with the median excess optical depth, suggesting that the gas is clumpy. Within 100 (200) kpc, and over ±165 km s-1, the covering fraction of gas with Lyα optical depth greater than unity is 100+0 - 32% (66% ± 16%). Absorbers with τLyα > 0.1 are typically closer to galaxies than random. The mean galaxy overdensity around absorbers increases with the optical depth and also as the length scale over which the galaxy overdensity is evaluated is decreased. Absorbers with τLyα ~ 1 reside in regions where the galaxy number density is close to the cosmic mean on scales >=0.25 Mpc. We clearly detect two types of redshift space anisotropies. On scales <200 km s-1, or <1 Mpc, the absorption is stronger along the line of sight than in the transverse direction. This "finger of God" effect may be due to redshift errors, but is probably dominated by gas motions within or very close to the halos. On the other hand, on scales of 1.4-2.0 Mpc the absorption is compressed along the line of sight (with >3σ significance), an effect that we attribute to large-scale infall (i.e., the Kaiser effect). Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

Testing the universality of the star-formation efficiency in dense molecular gas

NASA Astrophysics Data System (ADS)

Shimajiri, Y.; André, Ph.; Braine, J.; Könyves, V.; Schneider, N.; Bontemps, S.; Ladjelate, B.; Roy, A.; Gao, Y.; Chen, H.

2017-08-01

Context. Recent studies with, for example, Spitzer and Herschel have suggested that star formation in dense molecular gas may be governed by essentially the same "law" in Galactic clouds and external galaxies. This conclusion remains controversial, however, in large part because different tracers have been used to probe the mass of dense molecular gas in Galactic and extragalactic studies. Aims: We aimed to calibrate the HCN and HCO+ lines commonly used as dense gas tracers in extragalactic studies and to test the possible universality of the star-formation efficiency in dense gas (≳104 cm-3), SFEdense. Methods: We conducted wide-field mapping of the Aquila, Ophiuchus, and Orion B clouds at 0.04 pc resolution in the J = 1 - 0 transition of HCN, HCO+, and their isotopomers. For each cloud, we derived a reference estimate of the dense gas mass MHerschelAV > 8, as well as the strength of the local far-ultraviolet (FUV) radiation field, using Herschel Gould Belt survey data products, and estimated the star-formation rate from direct counting of the number of Spitzer young stellar objects. Results: The H13CO+(1-0) and H13CN(1-0) lines were observed to be good tracers of the dense star-forming filaments detected with Herschel. Comparing the luminosities LHCN and LHCO+ measured in the HCN and HCO+ lines with the reference masses MHerschelAV > 8, the empirical conversion factors αHerschel - HCN (=MHerschelAV > 8/LHCN) and αHerschel - HCO+ (=MHerschelAV > 8/LHCO+) were found to be significantly anti-correlated with the local FUV strength. In agreement with a recent independent study of Orion B by Pety et al., the HCN and HCO+ lines were found to trace gas down to AV ≳ 2. As a result, published extragalactic HCN studies must be tracing all of the moderate density gas down to nH2 ≲ 103 cm-3. Estimating the contribution of this moderate density gas from the typical column density probability distribution functions in nearby clouds, we obtained the following G0-dependent HCN conversion factor for external galaxies: αHerschel - HCNfit' = 64 × G0-0.34. Re-estimating the dense gas masses in external galaxies with αHerschel - HCNfit'(G0), we found that SFEdense is remarkably constant, with a scatter of less than 1.5 orders of magnitude around 4.5 × 10-8 yr-1, over eight orders of magnitude in dense gas mass. Conclusions: Our results confirm that SFEdense of galaxies is quasi-universal on a wide range of scales from 1-10 pc to > 10 kpc. Based on the tight link between star formation and filamentary structure found in Herschel studies of nearby clouds, we argue that SFEdense is primarily set by the "microphysics" of core and star formation along filaments. Partly based on observations carried out with the IRAM 30 m Telescope under project numbers 150-14 and 032-15. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

DENSE GAS FRACTION AND STAR FORMATION EFFICIENCY VARIATIONS IN THE ANTENNAE GALAXIES

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

Bigiel, F.; Leroy, A. K.; Blitz, L.

2015-12-20

We use the Combined Array for Research in Millimeter-wave Astronomy (CARMA) millimeter interferometer to map the Antennae Galaxies (NGC 4038/39), tracing the bulk of the molecular gas via the {sup 12}CO(1–0) line and denser molecular gas via the high density transitions HCN(1–0), HCO{sup +}(1–0), CS(2–1), and HNC(1–0). We detect bright emission from all tracers in both the two nuclei and three locales in the overlap region between the two nuclei. These three overlap region peaks correspond to previously identified “supergiant molecular clouds.” We combine the CARMA data with Herschel infrared (IR) data to compare observational indicators of the star formationmore » efficiency (star formation rate/H{sub 2} ∝ IR/CO), dense gas fraction (HCN/CO), and dense gas star formation efficiency (IR/HCN). Regions within the Antennae show ratios consistent with those seen for entire galaxies, but these ratios vary by up to a factor of six within the galaxy. The five detected regions vary strongly in both their integrated intensities and these ratios. The northern nucleus is the brightest region in millimeter-wave line emission, while the overlap region is the brightest part of the system in the IR. We combine the CARMA and Herschel data with ALMA CO data to report line ratio patterns for each bright point. CO shows a declining spectral line energy distribution, consistent with previous studies. HCO{sup +} (1–0) emission is stronger than HCN (1–0) emission, perhaps indicating either more gas at moderate densities or higher optical depth than is commonly seen in more advanced mergers.« less

Environments of z~0.2 Star Forming Galaxies: Building on the Citizen Science Discovery of the Green Peas

NASA Astrophysics Data System (ADS)

Cardamone, Carolin; Cappelluti, Nico; Powell, Meredith; Urry, Meg; Galaxy Zoo Science Team

2018-01-01

‘Green Pea’ galaxies, discovered in the Galaxy Zoo citizen science project, are rare low-mass (M < 1 x 1010 M⊙) galaxies, experiencing an episode of compact, relatively low-metalicity (z ≈ 1/5 z⊙), intense starformation (3-60 M⊙/yr). While their spectra have been investigated in a wide-array of follow-up studies, a detailed study of their environments is missing. Two-point correlation functions have been used to show the environmental dependence of an array of galaxy properties (eg., mass, luminosity, color, star formation, and morphology). In this study, we present a cross-correlation analysis between the Green Peas and the Luminous Red Galaxies throughout the SDSS footprint, and we find that the population of Green Peas at 0.11

Reproducing the local and global morphological segregation between S and S0 galaxies in rich clusters by simple ram-pressure stripping

NASA Astrophysics Data System (ADS)

Solanes, Jose M.; Salvador-Sole, Eduardo

1992-08-01

We calculate the morphological segregation in rich galaxy clusters expected to arise from the possible evolution of S galaxies into S0 galaxies via the gas removal of their disks by ram-pressure stripping. The calculation is run on Monte Carlo simulations by following individual S galaxies in the potential well of a spherical anisotropic cluster making use of Gunn and Gott's (1972) stripping condition. The results are compared with both Dressler's (1980) local type/density relation and a global population-richness correlation inferred from real data in the present work. We find that, contrary to a rather extended opinion, this evolution scheme reproduces very well the observed morphological segregation between S and S0 galaxies in rich clusters provided that the initial populations are close to those i dense loose groups.

How Does Dense Molecular Gas Contribute to Star Formation in the Starburst Galaxy NGC 2146?

NASA Astrophysics Data System (ADS)

Wofford, Alia

2017-01-01

The starburst galaxy NGC 2146 is believed to have been formed approximately 800 Myr ago, when two galaxies collided with each other possibly leading to a burst of star formation. NGC 2146 is known as a starburst galaxy for the high frequency of star formation going on in its molecular clouds. These clouds serve as nurseries for star formation to occur. Hydrogen Cyanide (HCN) and Carbon monoxide (CO) are molecules found in molecular gas clouds. HCN molecules are tracers for high density star forming gas. Whereas, CO molecules are tracers for low density star forming gas. In this project, we are observing these two molecules and their proximity to where the stars are forming in the galaxy to determine if the star formation is occurring in the same area as the high and low density molecular gas areas in starburst galaxy NGC 2146.

Quenching of the Star Formation Activity of Galaxies in Dense Environments

NASA Astrophysics Data System (ADS)

Boselli, A.

2017-12-01

The nearby Universe is an ideal laboratory to study the effects of the environments on galaxy evolution. We have analysed the multifrequency properties of galaxies in the nearby clusters Virgo, Coma, and A1367. We have shown that the HI gas content and the activity of star formation of the late-type galaxies start to gradually decrease inwards ˜ one virial radius. We have also shown that late-type galaxies in these clusters have truncated HI, H_2, dust, and star forming discs once the HI gas content is removed by the harsh environment. Some of these galaxies also exibit spectacular tails of atomic neutral, ionised, or hot gas without any counterpart in the stellar component. All this evidence favors ram pressure stripping as the dominant mechanism responsible for the gas removal from the disc, and for the following quenching of the star formation activity.

HUBBLE SPACE TELESCOPE AND HI IMAGING OF STRONG RAM PRESSURE STRIPPING IN THE COMA SPIRAL NGC 4921: DENSE CLOUD DECOUPLING AND EVIDENCE FOR MAGNETIC BINDING IN THE ISM

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

Kenney, Jeffrey D. P.; Abramson, Anne; Bravo-Alfaro, Hector, E-mail: jeff.kenney@yale.edu

Remarkable dust extinction features in the deep Hubble Space Telescope (HST) V and I images of the face-on Coma cluster spiral galaxy NGC 4921 show in unprecedented ways how ram pressure strips the ISM from the disk of a spiral galaxy. New VLA HI maps show a truncated and highly asymmetric HI disk with a compressed HI distribution in the NW, providing evidence for ram pressure acting from the NW. Where the HI distribution is truncated in the NW region, HST images show a well-defined, continuous front of dust that extends over 90° and 20 kpc. This dust front separatesmore » the dusty from dust-free regions of the galaxy, and we interpret it as galaxy ISM swept up near the leading side of the ICM–ISM interaction. We identify and characterize 100 pc–1 kpc scale substructure within this dust front caused by ram pressure, including head–tail filaments, C-shaped filaments, and long smooth dust fronts. The morphology of these features strongly suggests that dense gas clouds partially decouple from surrounding lower density gas during stripping, but decoupling is inhibited, possibly by magnetic fields that link and bind distant parts of the ISM.« less

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

Yoon, Yongmin; Im, Myungshin; Kim, Jae-Woo, E-mail: yymx2@astro.snu.ac.kr, E-mail: mim@astro.snu.ac.kr

Under the Λ cold dark matter (ΛCDM) cosmological models, massive galaxies are expected to be larger in denser environments through frequent hierarchical mergers with other galaxies. Yet, observational studies of low-redshift early-type galaxies have shown no such trend, standing as a puzzle to solve during the past decade. We analyzed 73,116 early-type galaxies at 0.1 ≤  z  < 0.15, adopting a robust nonparametric size measurement technique and extending the analysis to many massive galaxies. We find for the first time that local early-type galaxies heavier than 10{sup 11.2} M {sub ⊙} show a clear environmental dependence in mass–size relation, in such amore » way that galaxies are as much as 20%–40% larger in the densest environments than in underdense environments. Splitting the sample into the brightest cluster galaxies (BCGs) and non-BCGs does not affect the result. This result agrees with the ΛCDM cosmological simulations and suggests that mergers played a significant role in the growth of massive galaxies in dense environments as expected in theory.« less

And the Title for Densest Galaxy Goes To…

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-07-01

Two surprisingly small heavy-weights have been discovered around galaxies in the nearby Virgo cluster by a team led by undergrads Michael Sandoval and Richard Vo and their advisor Aaron Romanowsky of San Jose State University. Setting a new record, these two objects now hold the title of the densest galaxy and the densest free-floating stellar system ever observed. Classification Difficulties What is the difference between large star clusters and small galaxies? Once thought to be distinct categories, the decade-old discovery of a new class of object, ultracompact dwarfs (UCDs), blurred the line between them somewhat: UCDs sit awkwardly between the two categories in size, mass and luminosity. So what are UCDs? It's hard to say — in part because their full range of possible parameters has yet to be carefully explored. Sandoval and his team set out to address this problem by combing through archival data from the Sloan Digital Sky Survey, searching for objects that display properties between those of star clusters and galaxies. Their search yielded two especially interesting objects: one around the galaxy M59, and the other around M85 (see figure 2). Follow-up observations with Subaru Telescope and the Southern Astrophysical Research telescope provided additional imaging and spectroscopic information. Plot of stellar surface mass density vs. mass of known stellar systems. The data include the two new objects (M85-HCC1 and M59-UCD3) as well as globular clusters, UCDs, and compact elliptical galaxies. Credit: Sandoval et al. 2015 Record-Breakers What makes these two discoveries so unusual? Both are remarkably dense compared to similar objects! The first, M59-UCD3, was categorized as an ultracompact dwarf galaxy — but it's significantly more dense than any other galaxy discovered. The night sky in M59-UCD3 would appear to contain roughly a million stars, compared to the few thousand we see overhead here in the Solar neighborhood. M85-HCC1 is another ten times denser than even that! It's such an unusual stellar system that it defies classification in the usual categories, which is why Sandoval and collaborators created a new name for this type of object: hypercompact cluster. In spite of the differences between these two stellar systems, the team argues that there is evidence that they were formed the same way. They believe that both objects are galactic centers that have been tidally stripped of all of the outlying stars and gas, leaving only the dense cores behind. They argue that this could be caused by mergers of M59 and M85 with intermediate mass galaxies. If true, searching for more of these unique objects could provide us with clues to how galaxies were assembled. Citation: Michael Sandoval et al. 2015 ApJ 808 L32 doi:10.1088/2041-8205/808/1/L32 Bonus: Check out this cool visualization from the authors of how tidal stripping of a small galaxy might happen. This is one theory of how UCDs are formed. Click here to view the video on YouTube.

Identifying Ranges of Stellar Ages and Metallicities for Blue Supergiants in the Starburst Galaxy IC 10

NASA Astrophysics Data System (ADS)

Bordwell, Baylee; Ho, N.; Geha, M. C.; West, M.

2014-01-01

Dwarf galaxies transition from active star formation to relative quiescence after entering a dense environment such as a galaxy cluster. However, the mechanism behind this change is not fully understood. The problem is complicated by its heavy dependence on the initial conditions of the galaxy in question. To investigate the conditions of a galaxy prior to transition, we chose one of the best and nearest examples of a dwarf with active star formation, the Local Group member IC 10. We have obtained DEIMOS spectra of blue supergiants in this galaxy and determined the range of metallicities and ages for these stars using the equivalent width of the calcium triplet feature and isochrone fitting to photometry. By looking at the distribution of these metallicities in space and time we are able to gain insight into IC 10's recent evolutionary history and to get a clearer picture of the physical state of a dwarf galaxy prior to transition.

Confronting models of star formation quenching in galaxy clusters with archival Spitzer data

NASA Astrophysics Data System (ADS)

Rudnick, Gregory

Large scale structures in the universe form hierarchically: small structures merge to form larger ones. Over the same epoch where these structures experience significant growth, the fraction of star forming galaxies within them decreases, and at a faster rate than for field galaxies. It is now widely accepted that there must be physical processes at work in these dense environments to actively quench star formation. However, despite no shortage of candidate mechanisms, sophisticated cosmological simulations still cannot reproduce the star formation rate distributions within dense environments, such as galaxy clusters. Insufficient observational constraints are a primary obstacle to further progress. In particular, the interpretation of observations of nearby clusters relies on untested assumptions about the properties of galaxies before they entered the dense cluster environment at higher redshifts. Clearly, direct constraints on these properties are required. Our group has assembled two data sets designed to address these concerns. The first focuses on an intermediate wide-field cluster sample and the second focuses on a well-matched low-redshift cluster sample. We will use these samples, along with sophisticated models of hierarchical galaxy formation, to meet the following objectives: 1. Directly measure the SFR distribution of the progenitors of present-day cluster galaxies. We will use ground-based spectroscopy to identify cluster members within four virial radii of eight intermediate-redshift clusters. We will couple this with archival Spitzer/MIPS data to measure the SFRs of galaxies out to the cluster outskirts. 2. Measure the SFR distribution of the present-day cluster galaxies using Spitzer and WISE. Robust N-body simulations tell us statistically which galaxies at intermediate redshifts will have entered the cluster virial radius by the current epoch. By combining our wide-field coverage at high redshift with our local cluster sample, we will determine the evolution in cluster galaxy SFRs over 6 billion years making minimal assumptions about the infalling galaxy population. 3. Provide a rigorous test of the quenching processes embedded in the theoretical models. We will create observed realizations of the theoretical models by subjecting them to our observational selection. This will enable a fair comparison between the models and the data, which will provide a valuable test of current theoretical implementations of quenching processes. We will also modify the quenching prescriptions in the models to determine the parameters required to reproduce the observations. The proposed research is novel for several reasons. 1) We have wide-field Spitzer/MIPS data that allows us to robustly measure SFRs in our distant cluster galaxies. WISE data on local clusters will provide us with analogous measurements in the nearby Universe. 2) Our significant investment in ancillary spectroscopy allows us to identify infalling galaxies that will eventually join the central regions of the cluster z=0. 3) Our intermediate redshift cluster sample was chosen to have characteristics expected for the progenitors of a large fraction of the known clusters at z=0. 4) We will take advantage of our own cosmological simulations of structure growth to interpret our data. 5) We have optical photometry over the full infall region, allowing us to control for stellar masses and to distinguish passive from dusty star-forming galaxies. We will learn which, if any, of the quenching prescriptions currently employed in semi-analytic models correctly reproduces the observed characteristics of the galaxies that will become cluster galaxies at z=0. We will pinpoint the cluster-centric radii over which quenching takes place between. We will determine the timescale (as a function of stellar mass) over which it must take place. This program will cement the legacy of Spitzer and WISE as tools for studying galaxy formation in clusters.

Nanolensed Fast Radio Bursts

NASA Astrophysics Data System (ADS)

Eichler, David

2017-12-01

It is suggested that fast radio bursts can probe gravitational lensing by clumpy dark matter objects that range in mass from 10-3 M ⊙-102 M ⊙. They may provide a more sensitive probe than observations of lensings of objects in the Magellanic Clouds, and could find or rule out clumpy dark matter with an extended mass spectrum.

Mapping the spatial distribution of star formation in cluster galaxies at z ~0.5 with the Grism Lens-Amplified Survey from Space (GLASS)

NASA Astrophysics Data System (ADS)

Vulcani, Benedetta

2015-08-01

What physical processes regulate star formation in dense environments? Understanding why galaxy evolution is environment dependent is one of the key questions of current astrophysics. I will present the first characterization of the spatial distribution of star formation in cluster galaxies at z~0.5, in order to quantify the role of different physical processes that are believed to be responsible for shutting down star formation. The analysis makes use of data from the Grism Lens-Amplified Survey from Space (GLASS), a large HST cycle-21 program targeting 10 massive galaxy clusters with extensive HST imaging from CLASH and the Frontier Field Initiative. The program consists of 140 primary and 140 parallel orbits of near-infrared WCF3 and optical ACS slitless grism observations, which result in 3D spectroscopy of hundreds of galaxies. The grism data are used to produce spatially resolved maps of the star formation density, while the stellar mass density and optical surface brightness are obtained from multiband imaging. I will describe quantitative measures of the spatial location and extend of the star formation rate, showing that about half of the cluster members with significant Halpha detection have diffused star formation, larger than the optical counterpart. This suggests that star formation occurs out to larger radii than the rest frame continuum. For some systems, nuclear star forming regions are found. I will also present a comparison between the Halpha distribution observed in cluster and field galaxies. The characterization of the spatial distribution of Halpha provides a new window, yet poorly exploited, on the mechanisms that regulate star formation and morphological transformation in dense environments.

Chandra X-Ray and Hubble Space Telescope Imaging of Optically Selected Kiloparsec-scale Binary Active Galactic Nuclei. II. Host Galaxy Morphology and AGN Activity

NASA Astrophysics Data System (ADS)

Shangguan, Jinyi; Liu, Xin; Ho, Luis C.; Shen, Yue; Peng, Chien Y.; Greene, Jenny E.; Strauss, Michael A.

2016-05-01

Binary active galactic nuclei (AGNs) provide clues to how gas-rich mergers trigger and fuel AGNs and how supermassive black hole (SMBH) pairs evolve in a gas-rich environment. While significant effort has been invested in their identification, the detailed properties of binary AGNs and their host galaxies are still poorly constrained. In a companion paper, we examined the nature of ionizing sources in the double nuclei of four kiloparsec-scale binary AGNs with redshifts between 0.1 and 0.2. Here, we present their host galaxy morphology based on F336W (U-band) and F105W (Y-band) images taken by the Wide Field Camera 3 on board the Hubble Space Telescope. Our targets have double-peaked narrow emission lines and were confirmed to host binary AGNs with follow-up observations. We find that kiloparsec-scale binary AGNs occur in galaxy mergers with diverse morphological types. There are three major mergers with intermediate morphologies and a minor merger with a dominant disk component. We estimate the masses of the SMBHs from their host bulge stellar masses and obtain Eddington ratios for each AGN. Compared with a representative control sample drawn at the same redshift and stellar mass, the AGN luminosities and Eddington ratios of our binary AGNs are similar to those of single AGNs. The U - Y color maps indicate that clumpy star-forming regions could significantly affect the X-ray detection of binary AGNs, e.g., the hardness ratio. Considering the weak X-ray emission in AGNs triggered in merger systems, we suggest that samples of X-ray-selected AGNs may be biased against gas-rich mergers. Based, in part, on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program number GO 12363.

A high definition view of the COSMOS Wall at z ~ 0.73

NASA Astrophysics Data System (ADS)

Iovino, A.; Petropoulou, V.; Scodeggio, M.; Bolzonella, M.; Zamorani, G.; Bardelli, S.; Cucciati, O.; Pozzetti, L.; Tasca, L.; Vergani, D.; Zucca, E.; Finoguenov, A.; Ilbert, O.; Tanaka, M.; Salvato, M.; Kovač, K.; Cassata, P.

2016-08-01

Aims: We present a study of a large filamentary structure at z ~ 0.73 in the field of the COSMOS survey, the so-called COSMOS Wall. This structure encompasses a comprehensive range of environments from a dense cluster and a number of galaxy groups to filaments, less dense regions, and adjacent voids. It thus provides a valuable laboratory for the accurate mapping of environmental effects on galaxy evolution at a look-back time of ~6.5 Gyr, when the Universe was roughly half its present age. Methods: We performed deep spectroscopic observations with VIMOS at VLT of a K-band selected sample of galaxies in this complex structure, building a sample of galaxies complete in galaxy stellar mass down to a lower limit of log(ℳ∗/ℳ⊙) ~ 9.8, which is significantly deeper than previously available data. Thanks to its location within the COSMOS survey, each galaxy benefits from a wealth of ancillary information: HST-ACS data with I-band exposures down to IAB ~ 28 complemented by extensive multiwavelength ground- and space-based observations spanning the entire electromagnetic spectrum. Results: In this paper we detail the survey strategy and weighting scheme adopted to account for the biases introduced by the photometric preselection of our targets. We present our galaxy stellar mass and rest-frame magnitudes estimates together with a group catalog obtained with our new data and their member galaxies color/mass distribution. Conclusions: Owing to our new sample we can perform a detailed, high definition mapping of the complex COSMOS Wall structure. The sharp environmental information, coupled with high quality spectroscopic information and rich ancillary data available in the COSMOS field, enables a detailed study of galaxy properties as a function of local environment in a redshift slice where environmental effects are important, and in a stellar mass range where mass and environment driven effects are both at work. Based on observations collected at the European Southern Observatory, Cerro Paranal, Chile, using the Very Large Telescope under program ESO 085.A-0664.

Dark Murky Clouds in the Bright Milky Way

NASA Image and Video Library

2011-08-24

This infrared image from NASA Wide-field Infrared Survey Explorer shows exceptionally cold, dense cloud cores seen in silhouette against the bright diffuse infrared glow of the plane of the Milky Way galaxy.

Thick discs, and an outflow, of dense gas in the nuclei of nearby Seyfert galaxies

NASA Astrophysics Data System (ADS)

Lin, Ming-Yi; Davies, R. I.; Burtscher, L.; Contursi, A.; Genzel, R.; González-Alfonso, E.; Graciá-Carpio, J.; Janssen, A.; Lutz, D.; Orban de Xivry, G.; Rosario, D.; Schnorr-Müller, A.; Sternberg, A.; Sturm, E.; Tacconi, L.

2016-05-01

We discuss the dense molecular gas in central regions of nearby Seyfert galaxies, and report new arcsec resolution observations of HCN (1-0) and HCO+ (1-0) for three objects. In NGC 3079, the lines show complex profiles as a result of self-absorption and saturated continuum absorption. H13CN reveals the continuum absorption profile, with a peak close to the galaxy's systemic velocity that traces disc rotation, and a second feature with a blue wing extending to -350 km s-1 that most likely traces a nuclear outflow. The morphological and spectral properties of the emission lines allow us to constrain the dense gas dynamics. We combine our kinematic analysis for these three objects, as well as another with archival data, with a previous comparable analysis of four other objects, to create a sample of eight Seyferts. In seven of these, the emission line kinematics imply thick disc structures on radial scales of ˜100 pc, suggesting such structures are a common occurrence. We find a relation between the circum-nuclear LHCN and Mdyn that can be explained by a gas fraction of 10 per cent and a conversion factor αHCN ˜ 10 between gas mass and HCN luminosity. Finally, adopting a different perspective to probe the physical properties of the gas around active galactic nuclei, we report on an analysis of molecular line ratios which indicates that the clouds in this region are not self-gravitating.

Warm Absorbers in X-rays (WAX), a comprehensive high resolution grating spectral study of a sample of Seyfert galaxies

NASA Astrophysics Data System (ADS)

Laha, S.; Guainazzi, M.; Dewangan, G.; Chakravorty, S.; Kembhavi, A.

2014-07-01

We present results from a homogeneous analysis of the broadband 0.3-10 keV CCD resolution as well as of soft X-ray high-resolution grating spectra of a hard X-ray flux-limited sample of 26 Seyfert galaxies observed with XMM-Newton. We could put a strict lower limit on the detection fraction of 50%. We find a gap in the distribution of the ionisation parameter in the range 0.5

Structure and dynamics of star-forming galaxies across the history of the Universe using GRBs

NASA Astrophysics Data System (ADS)

Thöne, Christina; Fynbo, Johan; de Ugarte Postigo, Antonio

2015-08-01

Gamma-ray bursts are exploding massive stars and some of the most luminous explosions in the Universe. They can serve as powerful light houses that probe the structure and abundances of the dense ISM in their hosts at almost any redshift and not accessible by other types of observations, e.g. using quasars. Since 2009 our collaboration has collected UV to nIR medium-resolution spectra of over 70 GRB afterglows using the ESO/VLT X-shooter spectrograph. Our sample covers a redshift range from 0.06 to 6.3 allowing us to study the dynamics of the ISM in star-forming galaxies from the nearby Universe out to the epoch of reionization and for the first time in a statistically sound way. Absorption lines usually show a rich structure of different components due to galaxy dynamics, turbulences or in-/outflows and different ionization levels seem to arise from different regions in the host. Fine-structure lines some of which are uniquely observed in GRB hosts are excited in the dense regions close to the GRB site itself. For some host with z < 3 we can also simultaenously observe emission lines from the hot ISM, comparing the origin of hot and cold gas within the same galaxy. The large wavelength coverage of the sample gives us the unique opportunity to study the evolution of gas dynamics across most of the time galaxies have existed, how the gas structure changed over time and what is the importance and consistency of in- and ouflows. Here we will present the X-shooter GRB afterglow sample, our results on the study of absorption and emission line features and compare the observed structures with theoretical models of galaxies to get a unique insight on the distrubution and dynamics of the ISM in starforming galaxies at any redshift.

The HETDEX pilot survey. V. The physical origin of Lyα emitters probed by near-infrared spectroscopy

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

Song, Mimi; Finkelstein, Steven L.; Gebhardt, Karl

2014-08-10

We present the results from a Very Large Telescope/SINFONI and Keck/NIRSPEC near-infrared spectroscopic survey of 16 Lyα emitters (LAEs) at z = 2.1-2.5 in the COSMOS and GOODS-N fields discovered from the Hobby Eberly Telescope Dark Energy Experiment Pilot Survey. We detect rest-frame optical nebular lines (Hα and/or [O III] λ5007) for 10 of the LAEs and measure physical properties, including the star formation rate (SFR), gas-phase metallicity, gas mass fraction, and Lyα velocity offset. We find that LAEs may lie below the mass-metallicity relation for continuum-selected star-forming galaxies at the same redshift. The LAEs all show velocity shifts ofmore » Lyα relative to the systemic redshift ranging between +85 and +296 km s{sup –1} with a mean of +180 km s{sup –1}. This value is smaller than measured for continuum-selected star-forming galaxies at similar redshifts. The Lyα velocity offsets show a moderate correlation with the measured SFR (2.5σ), but no significant correlations are seen with the SFR surface density, specific SFR, stellar mass, or dynamical mass (≲1.5σ). Exploring the role of dust, kinematics of the interstellar medium (ISM), and geometry on the escape of Lyα photons, we find no signature of selective quenching of resonantly scattered Lyα photons. However, we also find no evidence that a clumpy ISM is enhancing the Lyα equivalent width. Our results suggest that the low metallicity in LAEs may be responsible for yielding an environment with a low neutral hydrogen column density and less dust, easing the escape of Lyα photons over that in continuum-selected star-forming galaxies.« less

Baryons Matter: Why Luminous Satellite Galaxies have Reduced Central Masses

NASA Astrophysics Data System (ADS)

Zolotov, Adi; Brooks, Alyson M.; Willman, Beth; Governato, Fabio; Pontzen, Andrew; Christensen, Charlotte; Dekel, Avishai; Quinn, Tom; Shen, Sijing; Wadsley, James

2012-12-01

Using high-resolution cosmological hydrodynamical simulations of Milky Way-massed disk galaxies, we demonstrate that supernovae feedback and tidal stripping lower the central masses of bright (-15 < MV < -8) satellite galaxies. These simulations resolve high-density regions, comparable to giant molecular clouds, where stars form. This resolution allows us to adopt a prescription for H2 formation and destruction that ties star formation to the presence of shielded, molecular gas. Before infall, supernova feedback from the clumpy, bursty star formation captured by this physically motivated model leads to reduced dark matter (DM) densities and shallower inner density profiles in the massive satellite progenitors (M vir >= 109 M ⊙, M * >= 107 M ⊙) compared with DM-only simulations. The progenitors of the lower mass satellites are unable to maintain bursty star formation histories, due to both heating at reionization and gas loss from initial star-forming events, preserving the steep inner density profile predicted by DM-only simulations. After infall, gas stripping from satellites reduces the total central masses of satellites simulated with DM+baryons relative to DM-only satellites. Additionally, enhanced tidal stripping after infall due to the baryonic disk acts to further reduce the central DM densities of the luminous satellites. Satellites that enter with cored DM halos are particularly vulnerable to the tidal effects of the disk, exacerbating the discrepancy in the central masses predicted by baryon+DM and DM-only simulations. We show that DM-only simulations, which neglect the highly non-adiabatic evolution of baryons described in this work, produce denser satellites with larger central velocities. We provide a simple correction to the central DM mass predicted for satellites by DM-only simulations. We conclude that DM-only simulations should be used with great caution when interpreting kinematic observations of the Milky Way's dwarf satellites.

Warm absorbers in X-rays (WAX), a comprehensive high-resolution grating spectral study of a sample of Seyfert galaxies - I. A global view and frequency of occurrence of warm absorbers.

NASA Astrophysics Data System (ADS)

Laha, Sibasish; Guainazzi, Matteo; Dewangan, Gulab C.; Chakravorty, Susmita; Kembhavi, Ajit K.

2014-07-01

We present results from a homogeneous analysis of the broad-band 0.3-10 keV CCD resolution as well as of the soft X-ray high-resolution grating spectra of a hard X-ray flux-limited sample of 26 Seyfert galaxies observed with XMM-Newton. Our goal is to characterize warm absorbers (WAs) along the line of sight to the active nucleus. We significantly detect WAs in 65 per cent of the sample sources. Our results are consistent with WAs being present in at least half of the Seyfert galaxies in the nearby Universe, in agreement with previous estimates. We find a gap in the distribution of the ionization parameter in the range 0.5 < log ξ < 1.5 which we interpret as a thermally unstable region for WA clouds. This may indicate that the WA flow is probably constituted by a clumpy distribution of discrete clouds rather than a continuous medium. The distribution of the WA column densities for the sources with broad Fe Kα lines are similar to those sources which do not have broadened emission lines. Therefore, the detected broad Fe Kα emission lines are bona fide and not artefacts of ionized absorption in the soft X-rays. The WA parameters show no correlation among themselves, with the exception of the ionization parameter versus column density. The shallow slope of the log ξ versus log vout linear regression (0.12 ± 0.03) is inconsistent with the scaling laws predicted by radiation or magnetohydrodynamic-driven winds. Our results also suggest that WA and ultra fast outflows do not represent extreme manifestation of the same astrophysical system.

The Carla Survey: Insights From The Densest Carla Structures At 1.4 < Z < 2.8.

NASA Astrophysics Data System (ADS)

Noirot, Gaël; Stern, Daniel; Wylezalek, Dominika; Cooke, Elizabeth A.; Mei, Simona; De Breuck, Carlos; Vernet, Joël; Brodwin, Mark; Eisenhardt, Peter; Galametz, Audrey; Gonzalez, Anthony H.; Hatch, Nina A.; Jarvis, Matt; Rettura, Alessandro; Seymour, Nick; Stanford, S. A.

2017-06-01

Radio-loud AGN (RLAGN) tend to reside in the most massive dark matter halos, and have a long history of being used to efficiently identify rich high-z structures (i.e., clusters and protoclusters). Our team contributed to this effort with a targeted 400hr Spitzer program surveying 420 RLAGN (radio-loud quasars and high-z radio galaxies) at z=1.3-3.2 across the full sky: Clusters Around RLAGN (CARLA; Wylezalek+2013,2014). The CARLA Survey identified 200 cluster candidates at z=1.3-3.2 as 2-8σ overdensities of red color-selected Spitzer/IRAC galaxies around the targeted powerful RLAGN. We present results from our follow-up 40-orbit HST program on the 20 densest CARLA cluster candidates at z=1.4-2.8 (Noirot+2016,2017). We spectroscopically confirm 16/20 distant structures associated with the RLAGN, up to z=2.8. For the first time at these redshifts, we statistically investigate the star-formation content of a large sample of galaxies in dense structures. We show that >10^(10) M⊙ cluster galaxies form significantly fewer stars than their field star-forming counterparts at all redshifts within 1.4 ≤ z ≤ 2. This survey represents a unique and large homogenous sample of spectroscopically confirmed clusters at high redshifts, ideal to investigate quenching mechanisms in dense environments.

On the Contribution of Large-Scale Structure to Strong Gravitational Lensing

NASA Astrophysics Data System (ADS)

Faure, C.; Kneib, J.-P.; Hilbert, S.; Massey, R.; Covone, G.; Finoguenov, A.; Leauthaud, A.; Taylor, J. E.; Pires, S.; Scoville, N.; Koekemoer, Anton M.

2009-04-01

We study the correlation between the locations of galaxy-galaxy strong-lensing candidates and tracers of large-scale structure from both weak lensing (WL) or X-ray emission. The Cosmological Evolution Survey (COSMOS) is a unique data set, combining deep, high resolution and contiguous imaging in which strong lenses have been discovered, plus unparalleled multiwavelength coverage. To help interpret the COSMOS data, we have also produced mock COSMOS strong- and WL observations, based on ray-tracing through the Millennium Simulation. In agreement with the simulations, we find that strongly lensed images with the largest angular separations are found in the densest regions of the COSMOS field. This is explained by a prevalence among the lens population in dense environments of elliptical galaxies with high total-to-stellar mass ratios, which can deflect light through larger angles. However, we also find that the overall fraction of elliptical galaxies with strong gravitational lensing is independent of the local mass density; this observation is not true of the simulations, which predict an increasing fraction of strong lenses in dense environments. The discrepancy may be a real effect, but could also be explained by various limitations of our analysis. For example, our visual search of strong lens systems could be incomplete and suffer from selection bias; the luminosity function of elliptical galaxies may differ between our real and simulated data; or the simplifying assumptions and approximations used in our lensing simulations may be inadequate. Work is therefore ongoing. Automated searches for strong lens systems will be particularly important in better constraining the selection function.

Iron Low-ionization Broad Absorption Line quasars - the missing link in galaxy evolution?

NASA Astrophysics Data System (ADS)

Lawther, Daniel Peter; Vestergaard, Marianne; Fan, Xiaohui

2015-08-01

A peculiar and rare type of quasar with strong low-ionization iron absorption lines - known as FeLoBAL quasars - may be the missing link between star forming (or starbursting) galaxies and quasars. They are hypothesized to be quasars breaking out of their dense birth blanket of gas and dust. In that case they are expected to have high rates of star formation in their galaxies. With the aim of addressing and settling this issue we have studied deep Hubble Space Telescope restframe UV and optical imaging of a subset of such quasars in order to characterize the host galaxy properties of these quasars. We present the results of this study along with simulations to characterize the uncertainties and robustness of our results.

Secular Evolution in Disk Galaxies

NASA Astrophysics Data System (ADS)

Kormendy, John

2013-10-01

Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo bulges because the latter retain a `memory' of their disky origin. That is, they have one or more characteristics of disks: (1) flatter shapes than those of classical bulges, (2) correspondingly large ratios of ordered to random velocities, (3) small velocity dispersions with respect to the Faber-Jackson correlation between velocity dispersion and bulge luminosity, (4) spiral structure or nuclear bars in the `bulge' part of the light profile, (5) nearly exponential brightness profiles and (6) starbursts. So the cleanest examples of pseudobulges are recognisable. However, pseudo and classical bulges can coexist in the same galaxy. I review two important implications of secular evolution: (1) The existence of pseudobulges highlights a problem with our theory of galaxy formation by hierarchical clustering. We cannot explain galaxies that are completely bulgeless. Galaxy mergers are expected to happen often enough so that every giant galaxy should have a classical bulge. But we observe that bulgeless giant galaxies are common in field environments. We now realise that many dense centres of galaxies that we used to think are bulges were not made by mergers; they were grown out of disks. So the challenge gets more difficult. This is the biggest problem faced by our theory of galaxy formation. (2) Pseudobulges are observed to contain supermassive black holes (BHs), but they do not show the well-known, tight correlations between BH mass and the mass and velocity dispersion of the host bulge. This leads to the suggestion that there are two fundamentally different BH feeding processes. Rapid global inward gas transport in galaxy mergers leads to giant BHs that correlate with host ellipticals and classical bulges, whereas local and more stochastic feeding of small BHs in largely bulgeless galaxies evidently involves too little energy feedback to result in BH-host coevolution. It is an important success of the secular evolution picture that morphological differences can be used to divide bulges into two types that correlate differently with their BHs. I review environmental secular evolution -- the transformation of gas-rich, star-forming spiral and irregular galaxies into gas-poor, `red and dead' S0 and spheroidal (`Sph') galaxies. I show that Sph galaxies such as NGC205 and Draco are not the low-luminosity end of the structural sequence (the `fundamental plane') of elliptical galaxies. Instead, Sph galaxies have structural parameters like those of low-luminosity S+Im galaxies. Spheroidals are continuous in their structural parameters~with~the disks of S0 galaxies. They are bulgeless S0s. S+Im -->S0+Sph transformation involves a variety of internal (supernova-driven baryon ejection) and environmental processes (e.g., ram-pressure gas stripping, harassment, and starvation). Finally, I summarise how hierarchical clustering and secular processes can be combined into a consistent and comprehensive picture of galaxy evolution.

An X-Ray Spectral Model for Clumpy Tori in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Liu, Yuan; Li, Xiaobo

2014-05-01

We construct an X-ray spectral model for the clumpy torus in an active galactic nucleus (AGN) using Geant4, which includes the physical processes of the photoelectric effect, Compton scattering, Rayleigh scattering, γ conversion, fluorescence line, and Auger process. Since the electrons in the torus are expected to be bounded instead of free, the deviation of the scattering cross section from the Klein-Nishina cross section has also been included, which changes the X-ray spectra by up to 25% below 10 keV. We have investigated the effect of the clumpiness parameters on the reflection spectra and the strength of the fluorescent line Fe Kα. The volume filling factor of the clouds in the clumpy torus only slightly influences the reflection spectra, however, the total column density and the number of clouds along the line of sight significantly change the shapes and amplitudes of the reflection spectra. The effect of column density is similar to the case of a smooth torus, while a small number of clouds along the line of sight will smooth out the anisotropy of the reflection spectra and the fluorescent line Fe Kα. The smoothing effect is mild in the low column density case (N H = 1023 cm-2), whereas it is much more evident in the high column density case (N H = 1025 cm-2). Our model provides a quantitative tool for the spectral analysis of the clumpy torus. We suggest that the joint fits of the broad band spectral energy distributions of AGNs (from X-ray to infrared) should better constrain the structure of the torus.

A Game of Hide and Seek: Expectations of Clumpy Resources Influence Hiding and Searching Patterns

PubMed Central

Wilke, Andreas; Minich, Steven; Panis, Megane; Langen, Tom A.; Skufca, Joseph D.; Todd, Peter M.

2015-01-01

Resources are often distributed in clumps or patches in space, unless an agent is trying to protect them from discovery and theft using a dispersed distribution. We uncover human expectations of such spatial resource patterns in collaborative and competitive settings via a sequential multi-person game in which participants hid resources for the next participant to seek. When collaborating, resources were mostly hidden in clumpy distributions, but when competing, resources were hidden in more dispersed (random or hyperdispersed) patterns to increase the searching difficulty for the other player. More dispersed resource distributions came at the cost of higher overall hiding (as well as searching) times, decreased payoffs, and an increased difficulty when the hider had to recall earlier hiding locations at the end of the experiment. Participants’ search strategies were also affected by their underlying expectations, using a win-stay lose-shift strategy appropriate for clumpy resources when searching for collaboratively-hidden items, but moving equally far after finding or not finding an item in competitive settings, as appropriate for dispersed resources. Thus participants showed expectations for clumpy versus dispersed spatial resources that matched the distributions commonly found in collaborative versus competitive foraging settings. PMID:26154661

Ionised gas structure of 100 kpc in an over-dense region of the galaxy group COSMOS-Gr30 at z 0.7

NASA Astrophysics Data System (ADS)

Epinat, B.; Contini, T.; Finley, H.; Boogaard, L. A.; Guérou, A.; Brinchmann, J.; Carton, D.; Michel-Dansac, L.; Bacon, R.; Cantalupo, S.; Carollo, M.; Hamer, S.; Kollatschny, W.; Krajnović, D.; Marino, R. A.; Richard, J.; Soucail, G.; Weilbacher, P. M.; Wisotzki, L.

2018-01-01

We report the discovery of a 104 kpc2 gaseous structure detected in [O II]λλ3727, 3729 in an over-dense region of the COSMOS-Gr30 galaxy group at z 0.725 with deep MUSE Guaranteed Time Observations. We estimate the total amount of diffuse ionised gas to be of the order of ( 5 ± 3) × 1010 M⊙ and explore its physical properties to understand its origin and the source(s) of the ionisation. The MUSE data allow the identification of a dozen group members that are embedded in this structure through emission and absorption lines. We extracted spectra from small apertures defined for both the diffuse ionised gas and the galaxies. We investigated the kinematics and ionisation properties of the various galaxies and extended gas regions through line diagnostics (R23, O32, and [O III]/Hβ) that are available within the MUSE wavelength range. We compared these diagnostics to photo-ionisation models and shock models. The structure is divided into two kinematically distinct sub-structures. The most extended sub-structure of ionised gas is likely rotating around a massive galaxy and displays filamentary patterns that link some galaxies. The second sub-structure links another massive galaxy that hosts an active galactic nucleus (AGN) to a low-mass galaxy, but it also extends orthogonally to the AGN host disc over 35 kpc. This extent is likely ionised by the AGN itself. The location of small diffuse regions in the R23 vs. O32 diagram is compatible with photo-ionisation. However, the location of three of these regions in this diagram (low O32, high R23) can also be explained by shocks, which is supported by their high velocity dispersions. One edge-on galaxy shares the same properties and may be a source of shocks. Regardless of the hypothesis, the extended gas seems to be non-primordial. We favour a scenario where the gas has been extracted from galaxies by tidal forces and AGN triggered by interactions between at least the two sub-structures. Based on observations made with ESO telescopes at the Paranal Observatory under programs 094.A-0247 and 095.A-0118.

Voids and constraints on nonlinear clustering of galaxies

NASA Technical Reports Server (NTRS)

Vogeley, Michael S.; Geller, Margaret J.; Park, Changbom; Huchra, John P.

1994-01-01

Void statistics of the galaxy distribution in the Center for Astrophysics Redshift Survey provide strong constraints on galaxy clustering in the nonlinear regime, i.e., on scales R equal to or less than 10/h Mpc. Computation of high-order moments of the galaxy distribution requires a sample that (1) densely traces the large-scale structure and (2) covers sufficient volume to obtain good statistics. The CfA redshift survey densely samples structure on scales equal to or less than 10/h Mpc and has sufficient depth and angular coverage to approach a fair sample on these scales. In the nonlinear regime, the void probability function (VPF) for CfA samples exhibits apparent agreement with hierarchical scaling (such scaling implies that the N-point correlation functions for N greater than 2 depend only on pairwise products of the two-point function xi(r)) However, simulations of cosmological models show that this scaling in redshift space does not necessarily imply such scaling in real space, even in the nonlinear regime; peculiar velocities cause distortions which can yield erroneous agreement with hierarchical scaling. The underdensity probability measures the frequency of 'voids' with density rho less than 0.2 -/rho. This statistic reveals a paucity of very bright galaxies (L greater than L asterisk) in the 'voids.' Underdensities are equal to or greater than 2 sigma more frequent in bright galaxy samples than in samples that include fainter galaxies. Comparison of void statistics of CfA samples with simulations of a range of cosmological models favors models with Gaussian primordial fluctuations and Cold Dark Matter (CDM)-like initial power spectra. Biased models tend to produce voids that are too empty. We also compare these data with three specific models of the Cold Dark Matter cosmogony: an unbiased, open universe CDM model (omega = 0.4, h = 0.5) provides a good match to the VPF of the CfA samples. Biasing of the galaxy distribution in the 'standard' CDM model (omega = 1, b = 1.5; see below for definitions) and nonzero cosmological constant CDM model (omega = 0.4, h = 0.6 lambda(sub 0) = 0.6, b = 1.3) produce voids that are too empty. All three simulations match the observed VPF and underdensity probability for samples of very bright (M less than M asterisk = -19.2) galaxies, but produce voids that are too empty when compared with samples that include fainter galaxies.

Galaxy and Mass Assembly (GAMA): galaxies at the faint end of the Hα luminosity function

NASA Astrophysics Data System (ADS)

Brough, S.; Hopkins, A. M.; Sharp, R. G.; Gunawardhana, M.; Wijesinghe, D.; Robotham, A. S. G.; Driver, S. P.; Baldry, I. K.; Bamford, S. P.; Liske, J.; Loveday, J.; Norberg, P.; Peacock, J. A.; Bland-Hawthorn, J.; Brown, M. J. I.; Cameron, E.; Croom, S. M.; Frenk, C. S.; Foster, C.; Hill, D. T.; Jones, D. H.; Kelvin, L. S.; Kuijken, K.; Nichol, R. C.; Parkinson, H. R.; Pimbblet, K.; Popescu, C. C.; Prescott, M.; Sutherland, W. J.; Taylor, E.; Thomas, D.; Tuffs, R. J.; van Kampen, E.

2011-05-01

We present an analysis of the properties of the lowest Hα-luminosity galaxies (LHα≤ 4 × 1032 W; SFR < 0.02 M⊙ yr-1, with SFR denoting the star formation rate) in the Galaxy And Mass Assembly survey. These galaxies make up the rise above a Schechter function in the number density of systems seen at the faint end of the Hα luminosity function. Above our flux limit, we find that these galaxies are principally composed of intrinsically low stellar mass systems (median stellar mass = 2.5 × 108 M⊙) with only 5/90 having stellar masses M > 1010 M⊙. The low-SFR systems are found to exist predominantly in the lowest-density environments (median density ˜0.02 galaxy Mpc-2) with none in environments more dense than ˜1.5 galaxy Mpc-2. Their current specific SFRs (SSFRs; -8.5 < log [SSFR (yr -1)] < -12) are consistent with their having had a variety of star formation histories. The low-density environments of these galaxies demonstrate that such low-mass, star-forming systems can only remain as low mass and form stars if they reside sufficiently far from other galaxies to avoid being accreted, dispersed through tidal effects or having their gas reservoirs rendered ineffective through external processes.

Chemical pre-processing of cluster galaxies over the past 10 billion years in the IllustrisTNG simulations

NASA Astrophysics Data System (ADS)

Gupta, Anshu; Yuan, Tiantian; Torrey, Paul; Vogelsberger, Mark; Martizzi, Davide; Tran, Kim-Vy H.; Kewley, Lisa J.; Marinacci, Federico; Nelson, Dylan; Pillepich, Annalisa; Hernquist, Lars; Genel, Shy; Springel, Volker

2018-06-01

We use the IllustrisTNG simulations to investigate the evolution of the mass-metallicity relation (MZR) for star-forming cluster galaxies as a function of the formation history of their cluster host. The simulations predict an enhancement in the gas-phase metallicities of star-forming cluster galaxies (109 < M* < 1010 M⊙ h-1) at z ≤ 1.0 in comparisons to field galaxies. This is qualitatively consistent with observations. We find that the metallicity enhancement of cluster galaxies appears prior to their infall into the central cluster potential, indicating for the first time a systematic `chemical pre-processing' signature for infalling cluster galaxies. Namely, galaxies that will fall into a cluster by z = 0 show a ˜0.05 dex enhancement in the MZR compared to field galaxies at z ≤ 0.5. Based on the inflow rate of gas into cluster galaxies and its metallicity, we identify that the accretion of pre-enriched gas is the key driver of the chemical evolution of such galaxies, particularly in the stellar mass range (109 < M* < 1010 M⊙ h-1). We see signatures of an environmental dependence of the ambient/inflowing gas metallicity that extends well outside the nominal virial radius of clusters. Our results motivate future observations looking for pre-enrichment signatures in dense environments.

Hunting for Supermassive Black Holes in Nearby Galaxies With the Hobby-Eberly Telescope

NASA Astrophysics Data System (ADS)

van den Bosch, Remco C. E.; Gebhardt, Karl; Gültekin, Kayhan; Yıldırım, Akin; Walsh, Jonelle L.

2015-05-01

We have conducted an optical long-slit spectroscopic survey of 1022 galaxies using the 10 m Hobby-Eberly Telescope (HET) at McDonald Observatory. The main goal of the HET Massive Galaxy Survey (HETMGS) is to find nearby galaxies that are suitable for black hole mass measurements. In order to measure accurately the black hole mass, one should kinematically resolve the region where the black hole dominates the gravitational potential. For most galaxies, this region is much less than an arcsecond. Thus, black hole masses are best measured in nearby galaxies with telescopes that obtain high spatial resolution. The HETMGS focuses on those galaxies predicted to have the largest sphere-of-influence, based on published stellar velocity dispersions or the galaxy fundamental plane. To ensure coverage over galaxy types, the survey targets those galaxies across a face-on projection of the fundamental plane. We present the sample selection and resulting data products from the long-slit observations, including central stellar kinematics and emission line ratios. The full data set, including spectra and resolved kinematics, is available online. Additionally, we show that the current crop of black hole masses are highly biased toward dense galaxies and that especially large disks and low dispersion galaxies are under-represented. This survey provides the necessary groundwork for future systematic black hole mass measurement campaigns.

HUNTING FOR SUPERMASSIVE BLACK HOLES IN NEARBY GALAXIES WITH THE HOBBY–EBERLY TELESCOPE

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

Bosch, Remco C. E. van den; Yıldırım, Akin; Gebhardt, Karl

2015-05-15

We have conducted an optical long-slit spectroscopic survey of 1022 galaxies using the 10 m Hobby–Eberly Telescope (HET) at McDonald Observatory. The main goal of the HET Massive Galaxy Survey (HETMGS) is to find nearby galaxies that are suitable for black hole mass measurements. In order to measure accurately the black hole mass, one should kinematically resolve the region where the black hole dominates the gravitational potential. For most galaxies, this region is much less than an arcsecond. Thus, black hole masses are best measured in nearby galaxies with telescopes that obtain high spatial resolution. The HETMGS focuses on thosemore » galaxies predicted to have the largest sphere-of-influence, based on published stellar velocity dispersions or the galaxy fundamental plane. To ensure coverage over galaxy types, the survey targets those galaxies across a face-on projection of the fundamental plane. We present the sample selection and resulting data products from the long-slit observations, including central stellar kinematics and emission line ratios. The full data set, including spectra and resolved kinematics, is available online. Additionally, we show that the current crop of black hole masses are highly biased toward dense galaxies and that especially large disks and low dispersion galaxies are under-represented. This survey provides the necessary groundwork for future systematic black hole mass measurement campaigns.« less

Transient iron fluorescence: new clues on the AGN disk/corona?

NASA Astrophysics Data System (ADS)

Nardini, E.

2017-10-01

Deep X-ray observations of the so-called `bare' active galaxies represent the most effective means of probing the physical conditions in the immediate surroundings of a radiatively efficient supermassive black hole, thus aiding our understanding of the emission processes in AGN. Indeed, the structure and properties of the putative X-ray corona, and the nature of coupling with the disk, are still largely unknown. The recent, surprising discovery of transient iron fluorescence on timescales of 10-15 hours during the 7.5 days of XMM-Newton monitoring of Ark 120, the nearest and X-ray brightest bare AGN, poses several challenges to the commonly adopted X-ray emission paradigm of a very compact corona. Such a rapid variability implies that the inner accretion flow is highly dynamic and inhomogeneous, involving the presence of orbiting hotspots, density gradients, or other forms of clumpiness and instability. Whatever the case, these results offer a compelling glimpse of what could be achieved in the future with Athena's capabilities.

ON THE FATE OF THE MATTER REINSERTED WITHIN YOUNG NUCLEAR STELLAR CLUSTERS

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

Hueyotl-Zahuantitla, Filiberto; Palous, Jan; Wuensch, Richard

2013-04-01

This paper presents a hydrodynamical model describing the evolution of the gas reinserted by stars within a rotating young nuclear star cluster (NSC). We explicitly consider the impact of the stellar component on the flow by means of a uniform insertion of mass and energy within the stellar cluster. The model includes the gravity force of the stellar component and a central supermassive black hole (SMBH), and accounts for the heating from the central source of radiation and the radiative cooling of the thermalized gas. By using a set of parameters typical for NSCs and SMBHs in Seyfert galaxies, ourmore » simulations show that a filamentary/clumpy structure is formed in the inner part of the cluster. This 'torus' is Compton-thick and covers a large fraction of the sky (as seen from the SMBH). In the outer parts of the cluster a powerful wind is produced that inhibits the infall of matter from larger scales and thus the NSC-SMBH interplay occurs in isolation.« less

The role of orbital dynamics and cloud-cloud collisions in the formation of giant molecular clouds in global spiral structures

NASA Technical Reports Server (NTRS)

Roberts, William W., Jr.; Stewart, Glen R.

1987-01-01

The role of orbit crowding and cloud-cloud collisions in the formation of GMCs and their organization in global spiral structure is investigated. Both N-body simulations of the cloud system and a detailed analysis of individual particle orbits are used to develop a conceptual understanding of how individual clouds participate in the collective density response. Detailed comparisons are made between a representative cloud-particle simulation in which the cloud particles collide inelastically with one another and give birth to and subsequently interact with young star associations and stripped down simulations in which the cloud particles are allowed to follow ballistic orbits in the absence of cloud-cloud collisions or any star formation processes. Orbit crowding is then related to the behavior of individual particle trajectories in the galactic potential field. The conceptual picture of how GMCs are formed in the clumpy ISMs of spiral galaxies is formulated, and the results are compared in detail with those published by other authors.

Resolving the Large Scale Spectral Variability of the Luminous Seyfert 1 Galaxy 1H 0419-577: Evidence for a New Emission Component and Absorption by Cold Dense Matter

NASA Technical Reports Server (NTRS)

Pounds, K. A.; Reeves, J. N.; Page, K. L.; OBrien, P. T.

2004-01-01

An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 in September 2002, when the source was in an extreme low-flux state, found a very hard X-ray spectrum at 1-10 keV with a strong soft excess below -1 keV. Comparison with an earlier XMM-Newton observation when 1H 0419-577 was X-ray bright indicated the dominant spectral variability was due to a steep power law or cool Comptonised thermal emission. Four further XMM-Newton observations, with 1H 0419-577 in intermediate flux states, now support that conclusion, while we also find the variable emission component in intermediate state difference spectra to be strongly modified by absorption in low ionisation matter. The variable soft excess then appears to be an artefact of absorption of the underlying continuum while the core soft emission can be attributed to re- combination in an extended region of more highly ionised gas. We note the wider implications of finding substantial cold dense matter overlying (or embedded in) the X-ray continuum source in a luminous Seyfert 1 galaxy.

Simulation and Preliminary Design of a Cold Stream Experiment on Omega EP

NASA Astrophysics Data System (ADS)

Coffing, Shane; Angulo, Adrianna; Trantham, Matt; Malamud, Guy; Kuranz, Carolyn; Drake, R. P.

2017-10-01

Galaxies form within dark matter halos, accreting gas that may clump and eventually form stars. Infalling matter gradually increases the density of the halo, and, if cooling is insufficient, rising pressure forms a shock that slows the infalling gas, reducing star formation. However, galaxies with sufficient cooling become prolific star formers. A recent theory suggests that so called ``stream fed galaxies'' are able to acquire steady streams of cold gas via galactic ``filaments'' that penetrate the halo. The cold, dense filament flowing into a hot, less dense environment is potentially Kelvin-Helmholtz unstable. This instability may hinder the ability of the stream to deliver gas deeply enough into the halo. To study this process, we have begun preliminary design of a well-scaled laser experiment on Omega EP. We present here early simulation results and the physics involved. This work is funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956, and the National Laser User Facility Program, Grant Number DE-NA0002719, and through the Laboratory for Laser Energetics, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-NA0001944.

A novel mechanism for creating double pulsars

NASA Technical Reports Server (NTRS)

Sigurdsson, Steinn; Hernquist, Lars

1992-01-01

Simulations of encounters between pairs of hard binaries, each containing a neutron star and a main-sequence star, reveal a new formation mechanism for double pulsars in dense cores of globular clusters. In many cases, the two normal stars are disrupted to form a common envelope around the pair of neutron stars, both of which will be spun up to become millisecond pulsars. We predict that a new class of pulsars, double millisecond pulsars, will be discovered in the cores of dense globular clusters. The genesis proceeds through a short-lived double-core common envelope phase, with the envelope ejected in a fast wind. It is possible that the progenitor may also undergo a double X-ray binary phase. Any circular, short-period double pulsar found in the galaxy would necessarily come from disrupted disk clusters, unlike Hulse-Taylor class pulsars or low-mass X-ray binaries which may be ejected from clusters or formed in the galaxy.

Hydrodynamic Studies of Turbulent AGN Tori

NASA Astrophysics Data System (ADS)

Schartmann, M.; Meisenheimer, K.; Klahr, H.; Camenzind, M.; Wolf, S.; Henning, Th.; Burkert, A.; Krause, M.

Recently, the MID-infrared Interferometric instrument (MIDI) at the VLTI has shown that dust tori in the two nearby Seyfert galaxies NGC 1068 and the Circinus galaxy are geometrically thick and can be well described by a thin, warm central disk, surrounded by a colder and fluffy torus component. By carrying out hydrodynamical simulations with the help of the TRAMP code (Klahr et al. 1999), we follow the evolution of a young nuclear star cluster in terms of discrete mass-loss and energy injection from stellar processes. This naturally leads to a filamentary large scale torus component, where cold gas is able to flow radially inwards. The filaments join into a dense and very turbulent disk structure. In a post-processing step, we calculate spectral energy distributions and images with the 3D radiative transfer code MC3D Wolf (2003) and compare them to observations. Turbulence in the dense disk component is investigated in a separate project.

Full-disc 13CO(1-0) mapping across nearby galaxies of the EMPIRE survey and the CO-to-H2 conversion factor

NASA Astrophysics Data System (ADS)

Cormier, D.; Bigiel, F.; Jiménez-Donaire, M. J.; Leroy, A. K.; Gallagher, M.; Usero, A.; Sandstrom, K.; Bolatto, A.; Hughes, A.; Kramer, C.; Krumholz, M. R.; Meier, D. S.; Murphy, E. J.; Pety, J.; Rosolowsky, E.; Schinnerer, E.; Schruba, A.; Sliwa, K.; Walter, F.

2018-04-01

Carbon monoxide (CO) provides crucial information about the molecular gas properties of galaxies. While 12CO has been targeted extensively, isotopologues such as 13CO have the advantage of being less optically thick and observations have recently become accessible across full galaxy discs. We present a comprehensive new data set of 13CO(1-0) observations with the IRAM 30-m telescope of the full discs of nine nearby spiral galaxies from the EMPIRE survey at a spatial resolution of ˜1.5 kpc. 13CO(1-0) is mapped out to 0.7 - 1 r25 and detected at high signal-to-noise ratio throughout our maps. We analyse the 12CO(1-0)-to-13CO(1-0) ratio (ℜ) as a function of galactocentric radius and other parameters such as the 12CO(2-1)-to-12CO(1-0) intensity ratio, the 70-to-160 μm flux density ratio, the star formation rate surface density, the star formation efficiency, and the CO-to-H2 conversion factor. We find that ℜ varies by a factor of 2 at most within and amongst galaxies, with a median value of 11 and larger variations in the galaxy centres than in the discs. We argue that optical depth effects, most likely due to changes in the mixture of diffuse/dense gas, are favoured explanations for the observed ℜ variations, while abundance changes may also be at play. We calculate a spatially resolved 13CO(1-0)-to-H2 conversion factor and find an average value of 1.0 × 1021 cm-2 (K km s-1)-1 over our sample with a standard deviation of a factor of 2. We find that 13CO(1-0) does not appear to be a good predictor of the bulk molecular gas mass in normal galaxy discs due to the presence of a large diffuse phase, but it may be a better tracer of the mass than 12CO(1-0) in the galaxy centres where the fraction of dense gas is larger.

Bias properties of extragalactic distance indicators. 3: Analysis of Tully-Fisher distances for the Mathewson-Ford-Buchhorn sample of 1355 galaxies

NASA Technical Reports Server (NTRS)

Federspiel, Martin; Sandage, Allan; Tammann, G. A.

1994-01-01

The observational selection bias properties of the large Mathewson-Ford-Buchhorn (MFB) sample of axies are demonstrated by showing that the apparent Hubble constant incorrectly increases outward when determined using Tully-Fisher (TF) photometric distances that are uncorreted for bias. It is further shown that the value of H(sub 0) so determined is also multivlaued at a given redshift when it is calculated by the TF method using galaxies with differenct line widths. The method of removing this unphysical contradiction is developed following the model of the bias set out in Paper II. The model developed further here shows that the appropriate TF magnitude of a galaxy that is drawn from a flux-limited catalog not only is a function of line width but, even in the most idealistic cases, requires a triple-entry correction depending on line width, apparent magnitude, and catalog limit. Using the distance-limited subset of the data, it is shown that the mean intrinsic dispersion of a bias-free TF relation is high. The dispersion depends on line width, decreasing from sigma(M) = 0.7 mag for galaxies with rotational velocities less than 100 km s(exp-1) to sigma(M) = 0.4 mag for galaxies with rotational velocities greater than 250 km s(exp-1). These dispersions are so large that the random errors of the bias-free TF distances are too gross to detect any peculiar motions of individual galaxies, but taken together the data show again the offset of 500 km s(exp-1) fond both by Dressler & Faber and by MFB for galaxies in the direction of the putative Great Attractor but described now in a different way. The maximum amplitude of the bulk streaming motion at the Local Group is approximately 500 km s(exp-1) but the perturbation dies out, approaching the Machian frame defined by the CMB at a distance of approximately 80 Mpc (v is approximately 4000 km s(exp -1)). This decay to zero perturbation at v is approximately 4000 km s(exp -1) argues against existing models with a single attraction at approximately 4500 km s(exp -1) (the Great Attactor model) pulling the local region. Rather, the cause of the perturbation appears to be the well-known clumpy mass distribution within 4000 km s(exp -1) in the busy directions of Hydra, Centaurus, Antila and Dorado, as postulated earlier (Tammann & Sandage 1985).

Long-Duration Gamma-Ray Burst Host Galaxies in Emission and Absorption

NASA Astrophysics Data System (ADS)

Perley, Daniel A.; Niino, Yuu; Tanvir, Nial R.; Vergani, Susanna D.; Fynbo, Johan P. U.

2016-12-01

The galaxy population hosting long-duration GRBs provides a means to constrain the progenitor and an opportunity to use these violent explosions to characterize the nature of the high-redshift universe. Studies of GRB host galaxies in emission reveal a population of star-forming galaxies with great diversity, spanning a wide range of masses, metallicities, and redshifts. However, as a population GRB hosts are significantly less massive and poorer in metals than the hosts of other core-collapse transients, suggesting that GRB production is only efficient at metallicities significantly below Solar. GRBs may also prefer compact galaxies, and dense and/or central regions of galaxies, more than other types of core-collapse explosion. Meanwhile, studies of hosts in absorption against the luminous GRB optical afterglow provide a unique means of unveiling properties of the ISM in even the faintest and most distant galaxies; these observations are helping to constrain the chemical evolution of galaxies and the properties of interstellar dust out to very high redshifts. New ground- and space-based instrumentation, and the accumulation of larger and more carefully-selected samples, are continually enhancing our view of the GRB host population.

A massive galaxy in its core formation phase three billion years after the Big Bang

NASA Astrophysics Data System (ADS)

Nelson, Erica; van Dokkum, Pieter; Franx, Marijn; Brammer, Gabriel; Momcheva, Ivelina; Schreiber, Natascha Förster; da Cunha, Elisabete; Tacconi, Linda; Bezanson, Rachel; Kirkpatrick, Allison; Leja, Joel; Rix, Hans-Walter; Skelton, Rosalind; van der Wel, Arjen; Whitaker, Katherine; Wuyts, Stijn

2014-09-01

Most massive galaxies are thought to have formed their dense stellar cores in early cosmic epochs. Previous studies have found galaxies with high gas velocity dispersions or small apparent sizes, but so far no objects have been identified with both the stellar structure and the gas dynamics of a forming core. Here we report a candidate core in the process of formation 11 billion years ago, at redshift z = 2.3. This galaxy, GOODS-N-774, has a stellar mass of 100 billion solar masses, a half-light radius of 1.0 kiloparsecs and a star formation rate of solar masses per year. The star-forming gas has a velocity dispersion of 317 +/- 30 kilometres per second. This is similar to the stellar velocity dispersions of the putative descendants of GOODS-N-774, which are compact quiescent galaxies at z ~ 2 (refs 8, 9, 10, 11) and giant elliptical galaxies in the nearby Universe. Galaxies such as GOODS-N-774 seem to be rare; however, from the star formation rate and size of this galaxy we infer that many star-forming cores may be heavily obscured, and could be missed in optical and near-infrared surveys.

A massive galaxy in its core formation phase three billion years after the Big Bang.

PubMed

Nelson, Erica; van Dokkum, Pieter; Franx, Marijn; Brammer, Gabriel; Momcheva, Ivelina; Schreiber, Natascha Förster; da Cunha, Elisabete; Tacconi, Linda; Bezanson, Rachel; Kirkpatrick, Allison; Leja, Joel; Rix, Hans-Walter; Skelton, Rosalind; van der Wel, Arjen; Whitaker, Katherine; Wuyts, Stijn

2014-09-18

Most massive galaxies are thought to have formed their dense stellar cores in early cosmic epochs. Previous studies have found galaxies with high gas velocity dispersions or small apparent sizes, but so far no objects have been identified with both the stellar structure and the gas dynamics of a forming core. Here we report a candidate core in the process of formation 11 billion years ago, at redshift z = 2.3. This galaxy, GOODS-N-774, has a stellar mass of 100 billion solar masses, a half-light radius of 1.0 kiloparsecs and a star formation rate of solar masses per year. The star-forming gas has a velocity dispersion of 317 ± 30 kilometres per second. This is similar to the stellar velocity dispersions of the putative descendants of GOODS-N-774, which are compact quiescent galaxies at z ≈ 2 (refs 8-11) and giant elliptical galaxies in the nearby Universe. Galaxies such as GOODS-N-774 seem to be rare; however, from the star formation rate and size of this galaxy we infer that many star-forming cores may be heavily obscured, and could be missed in optical and near-infrared surveys.

Toward Gas Chemistry in Low Metallicity Starburst Galaxies

NASA Astrophysics Data System (ADS)

Meier, David S.; Anderson, Crystal N.; Turner, Jean; Ott, Juergen; Beck, Sara C.

2017-01-01

Dense gas, which is intimately connected with star formation, is key to understanding star formation. Though challenging to study, dense gas in low metallicity starbursts is important given these system's often extreme star formation and their potential implications for high redshift analogs. High spatial resolution (~50 pc) ALMA observations of several key probes of gas chemistry, including HCN(1-0), HCO+(1-0), CS(2-1), CCH(1-0;3/2-1/2) and SiO(2-1), towards the nearby super star-cluster (SSC) forming, sub-solar metallicity galaxy NGC 5253 are discussed. Dense gas is observed to be extended well beyond the current compact starburst, reaching into the apparently infalling molecular streamer. The faintness of HCN, the standard dense gas tracer, is extreme both in an absolute sense relative to high metallicity starbursts of a similar intensity and in a relative sense, with the HCO+/HCN ratio being one of the most elevated observed. UV-irradiated molecular gas, traced by CCH, is also extended over the mapped region, not being strongly correlated with the SSC. Despite the accretion of molecular gas from the halo and the intense burst of star formation, chemical signatures of shocked gas, traced by SiO (and HNCO), are not obvious. By placing NGC 5253 in context with other local starbursts, like 30 Doradus in the Large Magellanic Clouds and the high metallicity proto-typical starburst NGC 253, it is suggested that a combination of gas excitation and abundance changes associated with the sub solar metallicity may explain these anomalous dense gas properties.

The combined effect of AGN and supernovae feedback in launching massive molecular outflows in high-redshift galaxies

NASA Astrophysics Data System (ADS)

Biernacki, Pawel; Teyssier, Romain

2018-04-01

We have recently improved our model of active galactic nucleus (AGN) by attaching the supermassive black hole (SMBH) to a massive nuclear star cluster (NSC). Here, we study the effects of this new model in massive, gas-rich galaxies with several simulations of different feedback recipes with the hydrodynamics code RAMSES. These simulations are compared to a reference simulation without any feedback, in which the cooling halo gas is quickly consumed in a burst of star formation. In the presence of strong supernovae (SN) feedback, we observe the formation of a galactic fountain that regulates star formation over a longer period, but without halting it. If only AGN feedback is considered, as soon as the SMBH reaches a critical mass, strong outflows of hot gas are launched and prevent the cooling halo gas from reaching the disc, thus efficiently halting star formation, leading to the so-called `quenching'. If both feedback mechanisms act in tandem, we observe a non-linear coupling, in the sense that the dense gas in the supernovae-powered galactic fountain is propelled by the hot outflow powered by the AGN at much larger radii than without AGN. We argue that these particular outflows are able to unbind dense gas from the galactic halo, thanks to the combined effect of SN and AGN feedback. We speculate that this mechanism occurs at the end of the fast growing phase of SMBH, and is at the origin of the dense molecular outflows observed in many massive high-redshift galaxies.

Observational Searches for Star-Forming Galaxies at z > 6

NASA Astrophysics Data System (ADS)

Finkelstein, Steven L.

2016-08-01

Although the universe at redshifts greater than six represents only the first one billion years (< 10%) of cosmic time, the dense nature of the early universe led to vigorous galaxy formation and evolution activity which we are only now starting to piece together. Technological improvements have, over only the past decade, allowed large samples of galaxies at such high redshifts to be collected, providing a glimpse into the epoch of formation of the first stars and galaxies. A wide variety of observational techniques have led to the discovery of thousands of galaxy candidates at z > 6, with spectroscopically confirmed galaxies out to nearly z = 9. Using these large samples, we have begun to gain a physical insight into the processes inherent in galaxy evolution at early times. In this review, I will discuss (i) the selection techniques for finding distant galaxies, including a summary of previous and ongoing ground and space-based searches, and spectroscopic follow-up efforts, (ii) insights into galaxy evolution gleaned from measures such as the rest-frame ultraviolet luminosity function, the stellar mass function, and galaxy star-formation rates, and (iii) the effect of galaxies on their surrounding environment, including the chemical enrichment of the universe, and the reionisation of the intergalactic medium. Finally, I conclude with prospects for future observational study of the distant universe, using a bevy of new state-of-the-art facilities coming online over the next decade and beyond.

The morphological transformation of red sequence galaxies in clusters since z ˜ 1

NASA Astrophysics Data System (ADS)

Cerulo, P.; Couch, W. J.; Lidman, C.; Demarco, R.; Huertas-Company, M.; Mei, S.; Sánchez-Janssen, R.; Barrientos, L. F.; Muñoz, R.

2017-11-01

The study of galaxy morphology is fundamental to understand the physical processes driving the structural evolution of galaxies. It has long been known that dense environments host high fractions of early-type galaxies and low fractions of late-type galaxies, indicating that the environment affects the structural evolution of galaxies. In this paper, we present an analysis of the morphological composition of red sequence galaxies in a sample of nine galaxy clusters at 0.8 < z < 1.5 drawn from the HAWK-I Cluster Survey (HCS), with the aim of investigating the evolutionary paths of galaxies with different morphologies. We classify galaxies according to their apparent bulge-to-total light ratio and compare with red sequence galaxies from the lower redshift WIde-field Nearby Galaxy-cluster Survey (WINGS) and ESO Distant Cluster Survey (EDisCS). We find that, while the HCS red sequence is dominated by elliptical galaxies at all luminosities and stellar masses, the WINGS red sequence is dominated by elliptical galaxies only at its bright end (MV < -21.0 mag), while S0s become the most frequent class at fainter luminosities. Disc-dominated galaxies comprise 10-14 per cent of the red sequence population in the low (WINGS) and high (HCS) redshift samples, although their fraction increases up to 40 per cent at 0.4 < z < 0.8 (EDisCS). We find a 20 per cent increase in the fraction of S0 galaxies from z ∼ 1.5 to 0.05 on the red sequence. These results suggest that elliptical and S0 galaxies follow different evolutionary histories and, in particular, that S0 galaxies result, at least at intermediate luminosities (-22.0 < MV < -20.0), from the morphological transformation of quiescent spiral galaxies.

VIVA (VLA Imaging of Virgo in Atomic gas): H I Stripping in Virgo Galaxies

NASA Astrophysics Data System (ADS)

Chung, A.; van Gorkom, J. H.; Crowl, H.; Kenney, J. D. P.; Vollmer, B.

2008-08-01

We present results of a new Very Large Array survey of 53 Virgo galaxies (48 spirals and 5 dwarf/irregular systems). The goal is to study how the H I gas properties are affected by the cluster environment. The survey covers galaxies in a wide range of densities from the center of the cluster to more than 3 Mpc from M 87. The gas is imaged down to a column-density sensitivity of a few times 1019cm-2. We find examples of gas stripping at all stages. Within ˜0.5 Mpc from M 87, most galaxies are severely H I stripped. The H I disks are truncated to well within the optical disks. While the H I looks asymmetric, the outer stellar disks look undisturbed. The fact that only the gas and not the stars has been stripped suggests that those galaxies have been affected by the hot and dense cluster gas. Interestingly we also find a few truncated disks at large projected distances from the center. Although some of these may have been stripped while crossing the cluster core, a detailed population-synthesis study of the outer disk of one of these shows that star formation was terminated recently. The time since stripping is too short for the galaxy to have traveled from the core to its current location. So at least one galaxy has lost its gas from the outer disk by another mechanism than ram-pressure stripping in the dense cluster core. At intermediate- to low-density regions (>0.6 Mpc) we find H I tails with various lengths. We find seven galaxies with long one-sided H I tails pointing away from M 87. The galaxies are at 0.6-1 Mpc from M 87. Since these galaxies are only mildly H I deficient and the tails point away from M 87, these galaxies are probably falling into the cluster for the first time on highly radial orbits. For all but two of the galaxies the estimated ram pressure at their location in the cluster would be sufficient to pull out the H I in the very outer disks. One galaxy also looks optically disturbed and a simulation suggests that a combination of ram pressure plus a tidal interaction has pulled out the tail. In the outskirts of the cluster we find several examples of tidally interacting galaxies. We possibly see evidence for some accretion of gas as well. Lastly, the merging of subclusters with Virgo can cause bulk motions of the ICM. We see one example of a galaxy far out that appears to be ram-pressure stripped by a dynamic ICM. In summary, our results show that galaxies are already affected in the low-density outer regions of the cluster through ram-pressure stripping and tidal interactions, or a combination of both.

The Impact of Assembly Bias on the Galaxy Content of Dark Matter Halos

NASA Astrophysics Data System (ADS)

Zehavi, Idit; Contreras, Sergio; Padilla, Nelson; Smith, Nicholas J.; Baugh, Carlton M.; Norberg, Peder

2018-01-01

We study the dependence of the galaxy content of dark matter halos on large-scale environment and halo formation time using semi-analytic galaxy models applied to the Millennium simulation. We analyze subsamples of halos at the extremes of these distributions and measure the occupation functions for the galaxies they host. We find distinct differences among these occupation functions. The main effect with environment is that central galaxies (and in one model, also the satellites) in denser regions start populating lower-mass halos. A similar, but significantly stronger, trend exists with halo age, where early-forming halos are more likely to host central galaxies at lower halo mass. We discuss the origin of these trends and the connection to the stellar mass–halo mass relation. We find that, at fixed halo mass, older halos and to some extent also halos in dense environments tend to host more massive galaxies. Additionally, we see a reverse trend for the occupation of satellite galaxies where early-forming halos have fewer satellites, likely due to having more time for them to merge with the central galaxy. We describe these occupancy variations in terms of the changes in the occupation function parameters, which can aid in constructing realistic mock galaxy samples. Finally, we study the corresponding galaxy auto- and cross-correlation functions of the different samples and elucidate the impact of assembly bias on galaxy clustering. Our results can inform theoretical modeling of galaxy assembly bias and attempts to detect it in the real universe.

The Relationship between the Dense Neutral and Diffuse Ionized Gas in the Thick Disks of Two Edge-on Spiral Galaxies

NASA Astrophysics Data System (ADS)

Rueff, Katherine M.; Howk, J. Christopher; Pitterle, Marissa; Hirschauer, Alec S.; Fox, Andrew J.; Savage, Blair D.

2013-03-01

We present high-resolution, optical images (BVI + Hα) of the multiphase interstellar medium (ISM) in the thick disks of the edge-on spiral galaxies NGC 4013 and NGC 4302. Our images from the Hubble Space Telescope (HST), Large Binocular Telescope, and WIYN 3.5 m telescope reveal an extensive population of filamentary dust absorption seen to z ~2-2.5 kpc. Many of these dusty thick disk structures have characteristics reminiscent of molecular clouds found in the Milky Way disk. Our Hα images show that the extraplanar diffuse ionized gas (DIG) in these galaxies is dominated by a smooth, diffuse component. The strongly filamentary morphologies of the dust absorption have no counterpart in the smoothly distributed Hα emission. We argue that the thick disk DIG and dust-bearing filaments trace physically distinct phases of the thick disk ISM, the latter tracing a dense, warm or cold neutral medium. The dense, dusty matter in the thick disks of spiral galaxies is largely tracing matter ejected from the thin disk via energetic feedback from massive stars. The high densities of the gas may be a result of converging gas flows. This dense material fuels some thick disk star formation, as evidenced by the presence of thick disk H II regions. Based on observations obtained with the NASA/ESA Hubble Space Telescope operated at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Also, based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the US, Italy, and Germany. LBT Corporation partners are the University of Arizona, on behalf of the Arizona University System; Instituto Nazionale do Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical Institute of Potsdam, and Heidelberg University; Ohio State University, and the Research Corporation, on behalf of the University of Notre Dame, the University of Minnesota, and the University of Virginia. Also, based on observations obtained by the WIYN Observatory which is a joint facility of the University of Wisconsin-Madison, Yale University, Indiana University, and the National Optical Astronomy Observatories.

A common origin for globular clusters and ultra-faint dwarfs in simulations of the first galaxies

DOE PAGES

Ricotti, Massimo; Parry, Owen H.; Gnedin, Nickolay Y.

2016-11-09

In this study, the first in a series on galaxy formation before reionization, we focus on understanding what determines the size and morphology of stellar objects in the first low-mass galaxies, using parsec-scale cosmological simulations performed with an adaptive mesh hydrodynamics code. Although the dense gas in which stars are formed tends to have a disk structure, stars are found in spheroids with little rotation. Halos with masses betweenmore » $${10}^{6}\\,{M}_{\\odot }$$ and $$5\\times {10}^{8}\\,{M}_{\\odot }$$ form stars stochastically, with stellar masses in the range $${10}^{4}\\,{M}_{\\odot }$$ to $$2\\times {10}^{6}\\,{M}_{\\odot }$$. We observe, nearly independent of stellar mass, a large range of half-light radii for the stars, from a few parsecs to a few hundred parsecs and surface brightnesses and mass-to-light ratios ranging from those typical of globular clusters to ultra-faint dwarfs. In our simulations, stars form in dense stellar clusters with high gas-to-star conversion efficiencies and rather uniform metallicities. A fraction of these clusters remain bound after the gas is removed by feedback, but others are destroyed, and their stars, which typically have velocity dispersions of 20–40 km s –1, expand until they become bound by the dark matter halo. We thus speculate that the stars in ultra-faint dwarf galaxies may show kinematic and chemical signatures consistent with their origin in a few distinct stellar clusters. On the other hand, some globular clusters may form at the center of primordial dwarf galaxies and may contain dark matter, perhaps detectable in the outer parts.« less

A common origin for globular clusters and ultra-faint dwarfs in simulations of the first galaxies

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

Ricotti, Massimo; Parry, Owen H.; Gnedin, Nickolay Y.

In this study, the first in a series on galaxy formation before reionization, we focus on understanding what determines the size and morphology of stellar objects in the first low-mass galaxies, using parsec-scale cosmological simulations performed with an adaptive mesh hydrodynamics code. Although the dense gas in which stars are formed tends to have a disk structure, stars are found in spheroids with little rotation. Halos with masses betweenmore » $${10}^{6}\\,{M}_{\\odot }$$ and $$5\\times {10}^{8}\\,{M}_{\\odot }$$ form stars stochastically, with stellar masses in the range $${10}^{4}\\,{M}_{\\odot }$$ to $$2\\times {10}^{6}\\,{M}_{\\odot }$$. We observe, nearly independent of stellar mass, a large range of half-light radii for the stars, from a few parsecs to a few hundred parsecs and surface brightnesses and mass-to-light ratios ranging from those typical of globular clusters to ultra-faint dwarfs. In our simulations, stars form in dense stellar clusters with high gas-to-star conversion efficiencies and rather uniform metallicities. A fraction of these clusters remain bound after the gas is removed by feedback, but others are destroyed, and their stars, which typically have velocity dispersions of 20–40 km s –1, expand until they become bound by the dark matter halo. We thus speculate that the stars in ultra-faint dwarf galaxies may show kinematic and chemical signatures consistent with their origin in a few distinct stellar clusters. On the other hand, some globular clusters may form at the center of primordial dwarf galaxies and may contain dark matter, perhaps detectable in the outer parts.« less

Minor Merger Origin for the Circumnuclear Starburst in NGC 7742

NASA Technical Reports Server (NTRS)

Mazzuca, Lisa M.; Sarzi, M.; Knapen, J. H.; Veilleux, S.; Swaters, R.

2006-01-01

We present an emission-line diagnostic analysis of integral-field spectroscopic observations that cover the central kiloparsec of NGC 7742. This Sa galaxy hosts a spectacular nuclear starburst ring and nuclear regions characterized by low-ionization emission. The gas in the ring rotates in the opposite sense to the stars in the galaxy, suggesting a recent merging or acquisition event. The combination of integral-field measurements for the H alpha+[N II] emission lines from DensePak and the H beta and [O 111] emission from SAURON allow the construction of diagnostic diagrams that highlight the transition from star formation in the nuclear ring to excitation by high-velocity shocks or by a central AGN towards the center. DensePak measurements for the [S II] line ratio reveal very low gas densities in the nuclear ring, N(sub e) less than 100 per cubic centimeters, characteristic of massive H II regions. Comparison with MAPPINGS III models for starbursts with low gas densities show that the ring is of roughly solar metallicity. This suggests that the gas in the nuclear ring originated in a stellar system capable of substantially enriching the gas metallicity through sustained star formation. We propose that NGC 7742 cannibalised a smaller galaxy rich in metal-poor gas, and that star formation episodes in the ring have since increased the metallicity to its present value. The techniques explored here can be widely used to study similar systems, including composite (AGN+starburst) galaxies.

Observational properties of compact groups of galaxies

NASA Technical Reports Server (NTRS)

Hickson, Paul

1990-01-01

Compact groups are small, relatively isolated, systems of galaxies with projected separations comparable to the diameters of the galaxies themselves. Two well-known examples are Stephan's Quintet (Stephan, 1877) and Seyfert's Sextet (Seyfert 1948a,b). In groups such as these, the apparent space density of galaxies approaches 10(exp 6) Mpc(sub -3), denser even than the cores of rich clusters. The apparent unlikeliness of the chance occurrence of such tight groupings lead Ambartsumyan (1958, 1975) to conclude that compact groups must be physically dense systems. This view is supported by clear signs of galaxy interactions that are seen in many groups. Spectroscopic observations reveal that typical relative velocities of galaxies in the groups are comparable to their internal stellar velocities. This should be conducive to strong gravitational interactions - more so than in rich clusters, where galaxy velocities are typically much higher. This suggests that compact groups could be excellent laboratories in which to study galaxy interactions and their effects. Compact groups often contain one or more galaxies whose redshift differs greatly from those of the other group members. If these galaxies are at the same distance as the other members, either entire galaxies are being ejected at high velocities from these groups, or some new physical phenomena must be occurring. If their redshifts are cosmological, we must explain why so many discordant galaxies are found in compact groups. In recent years much progress has been made in addressing these questions. Here, the author discusses the current observational data on compact groups and their implications.

Dependence of GAMA galaxy halo masses on the cosmic web environment from 100 deg2 of KiDS weak lensing data

NASA Astrophysics Data System (ADS)

Brouwer, Margot M.; Cacciato, Marcello; Dvornik, Andrej; Eardley, Lizzie; Heymans, Catherine; Hoekstra, Henk; Kuijken, Konrad; McNaught-Roberts, Tamsyn; Sifón, Cristóbal; Viola, Massimo; Alpaslan, Mehmet; Bilicki, Maciej; Bland-Hawthorn, Joss; Brough, Sarah; Choi, Ami; Driver, Simon P.; Erben, Thomas; Grado, Aniello; Hildebrandt, Hendrik; Holwerda, Benne W.; Hopkins, Andrew M.; de Jong, Jelte T. A.; Liske, Jochen; McFarland, John; Nakajima, Reiko; Napolitano, Nicola R.; Norberg, Peder; Peacock, John A.; Radovich, Mario; Robotham, Aaron S. G.; Schneider, Peter; Sikkema, Gert; van Uitert, Edo; Verdoes Kleijn, Gijs; Valentijn, Edwin A.

2016-11-01

Galaxies and their dark matter haloes are part of a complex network of mass structures, collectively called the cosmic web. Using the tidal tensor prescription these structures can be classified into four cosmic environments: voids, sheets, filaments and knots. As the cosmic web may influence the formation and evolution of dark matter haloes and the galaxies they host, we aim to study the effect of these cosmic environments on the average mass of galactic haloes. To this end we measure the galaxy-galaxy lensing profile of 91 195 galaxies, within 0.039 < z < 0.263, from the spectroscopic Galaxy And Mass Assembly survey, using {˜ }100 ° ^2 of overlapping data from the Kilo-Degree Survey. In each of the four cosmic environments we model the contributions from group centrals, satellites and neighbouring groups to the stacked galaxy-galaxy lensing profiles. After correcting the lens samples for differences in the stellar mass distribution, we find no dependence of the average halo mass of central galaxies on their cosmic environment. We do find a significant increase in the average contribution of neighbouring groups to the lensing profile in increasingly dense cosmic environments. We show, however, that the observed effect can be entirely attributed to the galaxy density at much smaller scales (within 4 h-1 Mpc), which is correlated with the density of the cosmic environments. Within our current uncertainties we find no direct dependence of galaxy halo mass on their cosmic environment.

Hubble Sees 'Island Universe' in the Coma Cluster

NASA Image and Video Library

2017-12-08

NASA image release August 10, 2010 A long-exposure Hubble Space Telescope image shows a majestic face-on spiral galaxy located deep within the Coma Cluster of galaxies, which lies 320 million light-years away in the northern constellation Coma Berenices. The galaxy, known as NGC 4911, contains rich lanes of dust and gas near its center. These are silhouetted against glowing newborn star clusters and iridescent pink clouds of hydrogen, the existence of which indicates ongoing star formation. Hubble has also captured the outer spiral arms of NGC 4911, along with thousands of other galaxies of varying sizes. The high resolution of Hubble's cameras, paired with considerably long exposures, made it possible to observe these faint details. NGC 4911 and other spirals near the center of the cluster are being transformed by the gravitational tug of their neighbors. In the case of NGC 4911, wispy arcs of the galaxy's outer spiral arms are being pulled and distorted by forces from a companion galaxy (NGC 4911A), to the upper right. The resultant stripped material will eventually be dispersed throughout the core of the Coma Cluster, where it will fuel the intergalactic populations of stars and star clusters. The Coma Cluster is home to almost 1,000 galaxies, making it one of the densest collections of galaxies in the nearby universe. It continues to transform galaxies at the present epoch, due to the interactions of close-proximity galaxy systems within the dense cluster. Vigorous star formation is triggered in such collisions. Galaxies in this cluster are so densely packed that they undergo frequent interactions and collisions. When galaxies of nearly equal masses merge, they form elliptical galaxies. Merging is more likely to occur in the center of the cluster where the density of galaxies is higher, giving rise to more elliptical galaxies. This natural-color Hubble image, which combines data obtained in 2006, 2007, and 2009 from the Wide Field Planetary Camera 2 and the Advanced Camera for Surveys, required 28 hours of exposure time. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc. in Washington, D.C. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA) Acknowledgment: K. Cook (Lawrence Livermore National Laboratory) To learn more about Hubble go to: www.nasa.gov/mission_pages/hubble/main/index.html NASA Goddard Space Flight Center is home to the nation's largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe. Follow us on Twitter Join us on Facebook

Characterising the Dense Molecular Gas in Exceptional Local Galaxies

NASA Astrophysics Data System (ADS)

Tunnard, Richard C. A.

2016-08-01

The interferometric facilities now coming online (the Atacama Large Millimetre Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA)) and those planned for the coming decade (the Next Generation Very Large Array (ngVLA) and the Square Kilometre Array (SKA)) in the radio to sub-millimetre regimes are opening a window to the molecular gas in high-redshift galaxies. However, our understanding of similar galaxies in the local universe is still far from complete and the data analysis techniques and tools needed to interpret the observations in consistent and comparable ways are yet to be developed. I first describe the Monte Carlo Markov Chain (MCMC) script developed to empower a public radiative transfer code. I characterise both the public code and MCMC script, including an exploration of the effect of observing molecular lines at high redshift where the Cosmic Microwave Background (CMB) can provide a significant background, as well as the effect this can have on well-known local correlations. I present two studies of ultraluminous infrared galaxies (ULIRGs) in the local universe making use of literature and collaborator data. In the first of these, NGC6240, I use the wealth of available data and the geometry of the source to develop a multi-phase, multi-species model, finding evidence for a complex medium of hot diffuse and cold dense gas in pressure equilibrium. Next, I study the prototypical ULIRG Arp 220; an extraordinary galaxy rendered especially interesting by the controversy over the power source of the western of the two merger nuclei and its immense luminosity and dust obscuration. Using traditional grid based methods I explore the molecular gas conditions within the nuclei and find evidence for chemical differentiation between the two nuclei, potentially related to the obscured power source. Finally, I investigate the potential evolution of proto-clusters over cosmic time with sub-millimetre observations of 14 radio galaxies, unexpectedly finding little to no evidence for cluster evolution.

THE PHYSICS OF THE FAR-INFRARED-RADIO CORRELATION. I. CALORIMETRY, CONSPIRACY, AND IMPLICATIONS

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

Lacki, Brian C.; Thompson, Todd A.; Quataert, Eliot, E-mail: lacki@astronomy.ohio-state.ed

2010-07-01

The far-infrared (FIR) and radio luminosities of star-forming galaxies are linearly correlated over a very wide range in star formation rate, from normal spirals like the Milky Way to the most intense starbursts. Using one-zone models of cosmic ray (CR) injection, cooling, and escape in star-forming galaxies, we attempt to reproduce the observed FIR-radio correlation (FRC) over its entire span. The normalization and linearity of the FRC, together with constraints on the CR population in the Milky Way, have strong implications for the CR and magnetic energy densities in star-forming galaxies. We show that for consistency with the FRC, {approx}2%more » of the kinetic energy from supernova explosions must go into high-energy primary CR electrons and that {approx}10%-20% must go into high-energy primary CR protons. Secondary electrons and positrons are likely comparable to or dominate primary electrons in dense starburst galaxies. We discuss the implications of our models for the magnetic field strengths of starbursts, the detectability of starbursts by Fermi, and CR feedback. Overall, our models indicate that both CR protons and electrons escape from low surface density galaxies, but lose most of their energy before escaping dense starbursts. The FRC is caused by a combination of the efficient cooling of CR electrons (calorimetry) in starbursts and a conspiracy of several factors. For lower surface density galaxies, the decreasing radio emission caused by CR escape is balanced by the decreasing FIR emission caused by the low effective UV dust opacity. In starbursts, bremsstrahlung, ionization, and inverse Compton cooling decrease the radio emission, but they are countered by secondary electrons/positrons and the dependence of synchrotron frequency on energy, both of which increase the radio emission. Our conclusions hold for a broad range of variations in our fiducial model, such as those including winds, different magnetic field strengths, and different diffusive escape times.« less

Unbiased clustering estimation in the presence of missing observations

NASA Astrophysics Data System (ADS)

Bianchi, Davide; Percival, Will J.

2017-11-01

In order to be efficient, spectroscopic galaxy redshift surveys do not obtain redshifts for all galaxies in the population targeted. The missing galaxies are often clustered, commonly leading to a lower proportion of successful observations in dense regions. One example is the close-pair issue for SDSS spectroscopic galaxy surveys, which have a deficit of pairs of observed galaxies with angular separation closer than the hardware limit on placing neighbouring fibres. Spatially clustered missing observations will exist in the next generations of surveys. Various schemes have previously been suggested to mitigate these effects, but none works for all situations. We argue that the solution is to link the missing galaxies to those observed with statistically equivalent clustering properties, and that the best way to do this is to rerun the targeting algorithm, varying the angular position of the observations. Provided that every pair has a non-zero probability of being observed in one realization of the algorithm, then a pair-upweighting scheme linking targets to successful observations, can correct these issues. We present such a scheme, and demonstrate its validity using realizations of an idealized simple survey strategy.

Mass Chart for Dead Stars and Black Holes

NASA Image and Video Library

2014-10-08

This chart illustrates relative masses of super-dense cosmic objects, ranging from white dwarfs to supermassive black holes encased in the cores of most galaxies. The first three dead stars left all form when stars more massive than our sun explode.

Alignment of galaxies relative to their local environment in SDSS-DR8

NASA Astrophysics Data System (ADS)

Hirv, A.; Pelt, J.; Saar, E.; Tago, E.; Tamm, A.; Tempel, E.; Einasto, M.

2017-03-01

Aims: We study the alignment of galaxies relative to their local environment in SDSS-DR8 and, using these data, we discuss evolution scenarios for different types of galaxies. Methods: We defined a vector field of the direction of anisotropy of the local environment of galaxies. We summed the unit direction vectors of all close neighbours of a given galaxy in a particular way to estimate this field. We found the alignment angles between the spin axes of disc galaxies, or the minor axes of elliptical galaxies, and the direction of anisotropy. The distributions of cosines of these angles are compared to the random distributions to analyse the alignment of galaxies. Results: Sab galaxies show perpendicular alignment relative to the direction of anisotropy in a sparse environment, for single galaxies and galaxies of low luminosity. Most of the parallel alignment of Scd galaxies comes from dense regions, from 2...3 member groups and from galaxies with low luminosity. The perpendicular alignment of S0 galaxies does not depend strongly on environmental density nor luminosity; it is detected for single and 2...3 member group galaxies, and for main galaxies of 4...10 member groups. The perpendicular alignment of elliptical galaxies is clearly detected for single galaxies and for members of ≤10 member groups; the alignment increases with environmental density and luminosity. Conclusions: We confirm the existence of fossil tidally induced alignment of Sab galaxies at low z. The alignment of Scd galaxies can be explained via the infall of matter to filaments. S0 galaxies may have encountered relatively massive mergers along the direction of anisotropy. Major mergers along this direction can explain the alignment of elliptical galaxies. Less massive, but repeated mergers are possibly responsible for the formation of elliptical galaxies in sparser areas and for less luminous elliptical galaxies.

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.

GASP. V. Ram-pressure stripping of a ring Hoag's-like galaxy in a massive cluster

NASA Astrophysics Data System (ADS)

Moretti, A.; Poggianti, B. M.; Gullieuszik, M.; Mapelli, M.; Jaffé, Y. L.; Fritz, J.; Biviano, A.; Fasano, G.; Bettoni, D.; Vulcani, B.; D'Onofrio, M.

2018-04-01

Through an ongoing MUSE program dedicated to study gas removal processes in galaxies (GAs Stripping Phenomena in galaxies with MUSE, GASP), we have obtained deep and wide integral field spectroscopy of the galaxy JO171. This galaxy resembles the Hoag's galaxy, one of the most spectacular examples of ring galaxies, characterized by a completely detached ring of young stars surrounding a central old spheroid. At odds with the isolated Hoag's galaxy, JO171 is part of a dense environment, the cluster Abell 3667, which is causing gas stripping along tentacles. Moreover, its ring counter-rotates with respect to the central spheroid. The joint analysis of the stellar populations and the gas/stellar kinematics shows that the origin of the ring was not due to an internal mechanism, but was related to a gas accretion event that happened in the distant past, prior to accretion on to Abell 3667, most probably within a filament. More recently, since infall in the cluster, the gas in the ring has been stripped by ram pressure, causing the quenching of star formation in the stripped half of the ring. This is the first observed case of ram-pressure stripping in action in a ring galaxy, and MUSE observations are able to reveal both of the events (accretion and stripping) that caused dramatic transformations in this galaxy.

Does the LFIR-LHCN Correlation Hold for Low LFIR Isolated Galaxies?

NASA Astrophysics Data System (ADS)

Flaquer, B. O.; Leon, S.; Espada, D.; Martín, S.; Lisenfeld, U.; Verley, S.; Sabater, J.; Verdes-Montenegro, L.

2010-10-01

Gao & Solomon (2004a,b) (GS) found a tight linear correlation between LFIR, a good tracer of the SF rate, and LHCN, probing the dense molecular gas for IR-Luminous galaxies. It is open whether this correlation is also followed by galaxies with less active SF. We observed in HCN(1-0) 15 Isolated Galaxies (IG) from the AMIGA sample (VerdesMontenegro et al. 2005) with the IRAM 30m, with the purpose to test whether the GS relation is independent of environment and luminosity. We found that IG have lower LHCN than expected (Fig.1a), with LHCN / LCO ˜ 0.05. However, this might be due to extended HCN missed by our observations in most cases only done at one central pointing. Four galaxies of our sample were mapped. In 2 of them there is substantial emission outside the central parts (Fig.1b+c), and their LHCN value derived from the mapping, follows much closer the relation from GS. Further mapping is needed.

The Ages of Passive Galaxies in a z = 1:62 Protocluster

NASA Astrophysics Data System (ADS)

Lee-Brown, Donald B.

Understanding how galaxies stop forming stars is a principle pursuit of extragalactic astrophysics. Here, I present a study of the relation between galaxy stellar age and mass in the z = 1:62 protocluster IRC 0218. After separating star forming and quiescent galaxies on the basis of their UVJ colors, we find that at stellar masses M⋆ ≥ 1010.8 M [solar mass] the quiescent fraction in IRC 0218 is fQ = 1.0+0.00-0.36, approximately 2 - 3x higher than the field value. At lower masses, fQ is consistent with the field. Using galaxy Dn(4000) values as measures of stellar age, we find no relation between age and mass. This may indicate that the mass dependence of fQ was imprinted early in IRC 0218's history. Alternatively, the lack of a relation may be due to mass redistribution through gasless merging. Ultimately, our results place constraints on the mechanism(s) responsible for quenching in dense environments at z ≥ 1.5.

The ATLASGAL survey: distribution of cold dust in the Galactic plane. Combination with Planck data

NASA Astrophysics Data System (ADS)

Csengeri, T.; Weiss, A.; Wyrowski, F.; Menten, K. M.; Urquhart, J. S.; Leurini, S.; Schuller, F.; Beuther, H.; Bontemps, S.; Bronfman, L.; Henning, Th.; Schneider, N.

2016-01-01

Context. Sensitive ground-based submillimeter surveys, such as ATLASGAL, provide a global view on the distribution of cold dense gas in the Galactic plane at up to two-times better angular-resolution compared to recent space-based surveys with Herschel. However, a drawback of ground-based continuum observations is that they intrinsically filter emission, at angular scales larger than a fraction of the field-of-view of the array, when subtracting the sky noise in the data processing. The lost information on the distribution of diffuse emission can be, however, recovered from space-based, all-sky surveys with Planck. Aims: Here we aim to demonstrate how this information can be used to complement ground-based bolometer data and present reprocessed maps of the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. Methods: We use the maps at 353 GHz from the Planck/HFI instrument, which performed a high sensitivity all-sky survey at a frequency close to that of the APEX/LABOCA array, which is centred on 345 GHz. Complementing the ground-based observations with information on larger angular scales, the resulting maps reveal the distribution of cold dust in the inner Galaxy with a larger spatial dynamic range. We visually describe the observed features and assess the global properties of dust distribution. Results: Adding information from large angular scales helps to better identify the global properties of the cold Galactic interstellar medium. To illustrate this, we provide mass estimates from the dust towards the W43 star-forming region and estimate a column density contrast of at least a factor of five between a low intensity halo and the star-forming ridge. We also show examples of elongated structures extending over angular scales of 0.5°, which we refer to as thin giant filaments. Corresponding to > 30 pc structures in projection at a distance of 3 kpc, these dust lanes are very extended and show large aspect ratios. We assess the fraction of dense gas by determining the contribution of the APEX/LABOCA maps to the combined maps, and estimate 2-5% for the dense gas fraction (corresponding to Av> 7 mag) on average in the Galactic plane. We also show probability distribution functions of the column density (N-PDF), which reveal the typically observed log-normal distribution for low column density and exhibit an excess at high column densities. As a reference for extragalactic studies, we show the line-of-sight integrated N-PDF of the inner Galaxy, and derive a contribution of this excess to the total column density of ~ 2.2%, corresponding to NH2 = 2.92 × 1022 cm-2. Taking the total flux density observed in the maps, we provide an independent estimate of the mass of molecular gas in the inner Galaxy of ~ 1 × 109 M⊙, which is consistent with previous estimates using CO emission. From the mass and dense gas fraction (fDG), we estimate a Galactic SFR of Ṁ = 1.3 M⊙ yr-1. Conclusions: Retrieving the extended emission helps to better identify massive giant filaments which are elongated and confined structures. We show that the log-normal distribution of low column density gas is ubiquitous in the inner Galaxy. While the distribution of diffuse gas is relatively homogenous in the inner Galaxy, the central molecular zone (CMZ) stands out with a higher dense gas fraction despite its low star formation efficiency.Altogether our findings explain well the observed low star formation efficiency of the Milky Way by the low fDG in the Galactic ISM. In contrast, the high fDG observed towards the CMZ, despite its low star formation activity, suggests that, in that particular region of our Galaxy, high density gas is not the bottleneck for star formation.

Bulgeless dwarf galaxies and dark matter cores from supernova-driven outflows.

PubMed

Governato, F; Brook, C; Mayer, L; Brooks, A; Rhee, G; Wadsley, J; Jonsson, P; Willman, B; Stinson, G; Quinn, T; Madau, P

2010-01-14

For almost two decades the properties of 'dwarf' galaxies have challenged the cold dark matter (CDM) model of galaxy formation. Most observed dwarf galaxies consist of a rotating stellar disk embedded in a massive dark-matter halo with a near-constant-density core. Models based on the dominance of CDM, however, invariably form galaxies with dense spheroidal stellar bulges and steep central dark-matter profiles, because low-angular-momentum baryons and dark matter sink to the centres of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present-day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different dark-matter particle candidate. Here we report hydrodynamical simulations (in a framework assuming the presence of CDM and a cosmological constant) in which the inhomogeneous interstellar medium is resolved. Strong outflows from supernovae remove low-angular-momentum gas, which inhibits the formation of bulges and decreases the dark-matter density to less than half of what it would otherwise be within the central kiloparsec. The analogues of dwarf galaxies-bulgeless and with shallow central dark-matter profiles-arise naturally in these simulations.

OH megamasers: dense gas & the infrared radiation field

NASA Astrophysics Data System (ADS)

Huang, Yong; Zhang, JiangShui; Liu, Wei; Xu, Jie

2018-06-01

To investigate possible factors related to OH megamaser formation (OH MM, L_{H2O}>10L_{⊙}), we compiled a large HCN sample from all well-sampled HCN measurements so far in local galaxies and identified with the OH MM, OH kilomasers (L_{H2O}<10L_{⊙}, OH kMs), OH absorbers and OH non-detections (non-OH MM). Through comparative analysis on their infrared emission, CO and HCN luminosities (good tracers for the low-density gas and the dense gas, respectively), we found that OH MM galaxies tend to have stronger HCN emission and no obvious difference on CO luminosity exists between OH MM and non-OH MM. This implies that OH MM formation should be related to the dense molecular gas, instead of the low-density molecular gas. It can be also supported by other facts: (1) OH MMs are confirmed to have higher mean molecular gas density and higher dense gas fraction (L_{HCN}/L_{CO}) than non-OH MMs. (2) After taking the distance effect into account, the apparent maser luminosity is still correlated with the HCN luminosity, while no significant correlation can be found at all between the maser luminosity and the CO luminosity. (3) The OH kMs tend to have lower values than those of OH MMs, including the dense gas luminosity and the dense gas fraction. (4) From analysis of known data of another dense gas tracer HCO^+, similar results can also be obtained. However, from our analysis, the infrared radiation field can not be ruled out for the OH MM trigger, which was proposed by previous works on one small sample (Darling in ApJ 669:L9, 2007). On the contrary, the infrared radiation field should play one more important role. The dense gas (good tracers of the star formation) and its surrounding dust are heated by the ultra-violet (UV) radiation generated by the star formation and the heating of the high-density gas raises the emission of the molecules. The infrared radiation field produced by the re-radiation of the heated dust in turn serves for the pumping of the OH MM.

A Stellar Mass Threshold for Quenching of Field Galaxies

NASA Astrophysics Data System (ADS)

Geha, M.; Blanton, M. R.; Yan, R.; Tinker, J. L.

2012-09-01

We demonstrate that dwarf galaxies (107 < M stellar < 109 M ⊙, -12 > Mr > -18) with no active star formation are extremely rare (<0.06%) in the field. Our sample is based on the NASA-Sloan Atlas which is a reanalysis of the Sloan Digital Sky Survey Data Release 8. We examine the relative number of quenched versus star-forming dwarf galaxies, defining quenched galaxies as having no Hα emission (EWHα < 2 Å) and a strong 4000 Å break. The fraction of quenched dwarf galaxies decreases rapidly with increasing distance from a massive host, leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of a massive host galaxy to be in the field. We demonstrate that there is a stellar mass threshold of M stellar < 1.0 × 109 M ⊙ below which quenched galaxies do not exist in the field. Below this threshold, we find that none of the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show evidence for recent star formation. Correcting for volume effects, this corresponds to a 1σ upper limit on the quenched fraction of 0.06%. In more dense environments, quenched galaxies account for 23% of the dwarf population over the same stellar mass range. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii. Thus, for galaxies with stellar mass less than 1.0 × 109 M ⊙, ending star formation requires the presence of a more massive neighbor, providing a stringent constraint on models of star formation feedback.

INTEGRAL-FIELD STELLAR AND IONIZED GAS KINEMATICS OF PECULIAR VIRGO CLUSTER SPIRAL GALAXIES

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

Cortés, Juan R.; Hardy, Eduardo; Kenney, Jeffrey D. P., E-mail: jcortes@alma.cl, E-mail: ehardy@nrao.cl, E-mail: jeff.kenney@yale.edu

2015-01-01

We present the stellar and ionized gas kinematics of 13 bright peculiar Virgo cluster galaxies observed with the DensePak Integral Field Unit at the WIYN 3.5 m telescope in order to look for kinematic evidence that these galaxies have experienced gravitational interactions or gas stripping. Two-dimensional maps of the stellar velocity V, stellar velocity dispersion σ, and the ionized gas velocity (Hβ and/or [O III]) are presented for the galaxies in the sample. The stellar rotation curves and velocity dispersion profiles are determined for 13 galaxies, and the ionized gas rotation curves are determined for 6 galaxies. Misalignments between themore » optical and kinematical major axes are found in several galaxies. While in some cases this is due to a bar, in other cases it seems to be associated with gravitational interaction or ongoing ram pressure stripping. Non-circular gas motions are found in nine galaxies, with various causes including bars, nuclear outflows, or gravitational disturbances. Several galaxies have signatures of kinematically distinct stellar components, which are likely signatures of accretion or mergers. For all of our galaxies, we compute the angular momentum parameter λ {sub R}. An evaluation of the galaxies in the λ {sub R} ellipticity plane shows that all but two of the galaxies have significant support from random stellar motions, and have likely experienced gravitational interactions. This includes some galaxies with very small bulges and truncated/compact Hα morphologies, indicating that such galaxies cannot be fully explained by simple ram pressure stripping, but must have had significant gravitational encounters. Most of the sample galaxies show evidence for ICM-ISM stripping as well as gravitational interactions, indicating that the evolution of a significant fraction of cluster galaxies is likely strongly impacted by both effects.« less

A Quantitative Analysis Of Pre-Processing In The Coma And Perseus-Pisces Superclusters Using Galex And Wise Survey Data

NASA Astrophysics Data System (ADS)

Yun, Min

Studies of massive galaxy clusters and groups at redshifts below 1 typically find environments with little-to-no star formation activity, in sharp contrast with the field. Over-dense regions are dominated by passively-evolving spheroidal (S0) and elliptical galaxies, whereas galaxies in the field tend to have spiral morphologies, younger stellar populations, and systematically higher star formation rates. Studies of the galaxy populations of clusters and massive galaxy groups have found that the increase in the fraction of spirals at higher redshifts corresponds to a decline in the fraction of S0 galaxies, which strongly suggests that field spirals are transformed into S0 galaxies at some point in their transition between field and cluster regions. This transformation necessarily involves an increase in the stellar content of the bulge relative to the disk, and then a removal of disk gas accompanied by either a rapid or gradual decline in star formation to eventually produce a red, spheroidal, passively-evolving S0 galaxy. Deep and wide area cosmological surveys such as the GOODS and COSMOS have shown that both environment and stellar mass play a distinct role in the overall galaxy evolution over a wide redshift range (to z~3). The density-morphology relation and the blue-fraction, first noted in the targeted studies of clusters and groups, also appears to be an extension of the evolutionary trends seen in the field sample. However, the trends seen in these large cosmological surveys should be taken with a caution since they are broad statistical trends of primarily massive galaxies with relatively poor sensitivity on star formation rate (SFR), associated with a relatively narrow range of sparsely sampled galaxy density. This can lead to potentially serious shortcomings when studying the role of environment because many of the physical mechanisms involved may preferentially impact the lower mass galaxies. The dominant physical mechanism(s) responsible for this transformation are still being debated, but the overwhelming evidence has shown that spirals are readily altered in groups or cluster outskirts prior to falling into a galaxy cluster (pre-processing). This implies that the best approach to catch galaxy transformation in the act is to examine galaxies in lower density environments. A complete accounting of star-formation activity for galaxies over a wide range masses and environments is needed to assess which of many possible mechanisms is the dominant cause of galaxy transformation in over-dense regions. The main goal of this proposed study is to examine the SF and quenching activities associated with galaxies using the high spatial resolution of the targeted studies of individual clusters, but covering much larger areas and density ranges (from voids to cluster cores) with the sample statistics approaching those of the cosmological surveys such as COSMOS, using exquisite stellar mass and SFR (both UV and IR) sensitivity. To achieve this, we propose a multi-wavelength study (with a specific emphasis on GALEX and WISE) of the two most prominent large scale structures in the local universe: the Coma and Perseus-Pisces Superclusters. The total sample area covers ~3000 sq. degree and contains about 7000 spectroscopically identified galaxies (from SDSS and archival spectra). In addition, we will evaluate the impacts of the high mass and SFR cut employed by deep cosmological surveys by paring down our sample in stellar mass and SFR (and resulting coarse galaxy density estimates) and examine whether any important insights are missed as a result.

Galaxy formation in the Planck cosmology - IV. Mass and environmental quenching, conformity and clustering

NASA Astrophysics Data System (ADS)

Henriques, Bruno M. B.; White, Simon D. M.; Thomas, Peter A.; Angulo, Raul E.; Guo, Qi; Lemson, Gerard; Wang, Wenting

2017-08-01

We study the quenching of star formation as a function of redshift, environment and stellar mass in the galaxy formation simulations of Henriques et al. (2015), which implement an updated version of the Munich semi-analytic model (L-GALAXIES) on the two Millennium Simulations after scaling to a Planck cosmology. In this model, massive galaxies are quenched by active galactic nucleus (AGN) feedback depending on both black hole and hot gas mass, and hence indirectly on stellar mass. In addition, satellite galaxies of any mass can be quenched by ram-pressure or tidal stripping of gas and through the suppression of gaseous infall. This combination of processes produces quenching efficiencies which depend on stellar mass, host halo mass, environment density, distance to group centre and group central galaxy properties in ways which agree qualitatively with observation. Some discrepancies remain in dense regions and close to group centres, where quenching still seems too efficient. In addition, although the mean stellar age of massive galaxies agrees with observation, the assumed AGN feedback model allows too much ongoing star formation at late times. The fact that both AGN feedback and environmental effects are stronger in higher density environments leads to a correlation between the quenching of central and satellite galaxies which roughly reproduces observed conformity trends inside haloes.

An X-ray and optical study of the cluster of galaxies Abell 754

NASA Technical Reports Server (NTRS)

Fabricant, D.; Beers, T. C.; Geller, M. J.; Gorenstein, P.; Huchra, J. P.

1986-01-01

X-ray and optical data for A754 are used to study the relative distribution of the luminous and dark matter in this dense, rich cluster of galaxies with X-ray luminosity comparable to that of the Coma Cluster. A quantitative statistical comparison is made of the galaxy positions with the total mass responsible for maintaining the X-ray emitting gas in hydrostatic equilibrium. A simple bimodal model which fits both the X-ray and optical data suggests that the galaxies are distributed consistently with the projected matter distribution within the region covered by the X-ray map (0.5-1 Mpc). The X-ray and optical estimates of the mass in the central region of the cluster are 2.9 x 10 to the 14th and 3.6 + or - 0.5 x 10 to the 14th solar masses, respectively.

CCD photometry of Andromeda IV - Dwarf irregular galaxy or M31 open cluster?

NASA Technical Reports Server (NTRS)

Jones, Joseph H.

1993-01-01

CCD photometry of Andromeda IV was obtained during discretionary time in August of 1989 at the Canada-France-Hawaii Telescope on Mauna Kea and the data were reduced at CFHT during the summer of 1991. And IV has been catalogued both as a dwarf galaxy and as an open star cluster in M31. The color-magnitude diagrams presented indicate that this object has a young population of stars with a narrow age range, consistent with the characteristics of an open star cluster or stellar association. A radial velocity measurement taken from the literature and analyzed with respect to the rotation curve of M31 indicates this object resides in the disk of the Andromeda Galaxy, strengthening the conclusion that it is indeed a very large open star cluster or a densely populated stellar association rather than a dwarf irregular galaxy.

Interaction of NGC 2276 with the NGC 2300 group - Fabry-Perot observations of the H-alpha velocity field

NASA Technical Reports Server (NTRS)

Gruendl, Robert A.; Vogel, Stuart N.; Davis, David S.; Mulchaey, John S.

1993-01-01

We report kinematic observations of H-alpha emission from the spiral galaxy NGC 2276 obtained with a Fabry-Perot Camera. The 'bow shock' appearance and enhanced star formation in NGC 2276 have been attributed by Mulchaey et al. (1993) to a ram-pressure interaction with the dense IGM detected in ROSAT observations of the NGC 2300 group of galaxies. Along the 'bow shock' limb of the galaxy, we observe strong H-alpha emission and significant kinematic perturbations located immediately interior to an abrupt decrease in the scale length of the optical disk. Although ram-pressure forces may be important in the evolution of the outer gaseous disk, the peculiar kinematics and the truncation in the stellar disk are difficult to explain in a ram-pressure model; a more likely cause is tidal interaction, probably with the elliptical galaxy NGC 2300.

PHIBSS: MOLECULAR GAS, EXTINCTION, STAR FORMATION, AND KINEMATICS IN THE z = 1.5 STAR-FORMING GALAXY EGS13011166

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

Genzel, R.; Tacconi, L. J.; Kurk, J.

We report matched resolution imaging spectroscopy of the CO 3-2 line (with the IRAM Plateau de Bure millimeter interferometer) and of the H{alpha} line (with LUCI at the Large Binocular Telescope) in the massive z = 1.53 main-sequence galaxy EGS 13011166, as part of the ''Plateau de Bure high-z, blue-sequence survey'' (PHIBSS: Tacconi et al.). We combine these data with Hubble Space Telescope V-I-J-H-band maps to derive spatially resolved distributions of stellar surface density, star formation rate, molecular gas surface density, optical extinction, and gas kinematics. The spatial distribution and kinematics of the ionized and molecular gas are remarkably similarmore » and are well modeled by a turbulent, globally Toomre unstable, rotating disk. The stellar surface density distribution is smoother than the clumpy rest-frame UV/optical light distribution and peaks in an obscured, star-forming massive bulge near the dynamical center. The molecular gas surface density and the effective optical screen extinction track each other and are well modeled by a ''mixed'' extinction model. The inferred slope of the spatially resolved molecular gas to star formation rate relation, N = dlog{Sigma}{sub starform}/dlog{Sigma}{sub molgas}, depends strongly on the adopted extinction model, and can vary from 0.8 to 1.7. For the preferred mixed dust-gas model, we find N = 1.14 {+-} 0.1.« less

A Local Laboratory for Studying Positive Feedback from Supermassive Black Holes

NASA Astrophysics Data System (ADS)

Croft, Steve

2016-10-01

AGN feedback is a critical regulator of galaxy growth. As well as curtailing star formation in diffuse, hot gas, it is increasingly understood to sometimes enhance star formation in the clumpy ISM through shock-induced collapse of clouds. Simulations have shown that such positive feedback may play a significant role in determining the stellar populations of galaxies. Minkowsi's Object (MO) provides an excellent local laboratory to probe this poorly-studied process in detail. The detection of a Type II supernova in MO (unexpected given the low mass of MO) suggests that jet-induced star formation may overproduce massive stars, and that models of the initial mass function in such systems may need to be revised. Recent results also suggest that star formation efficiency is enhanced in MO. Using WFC3, we will obtain morphologies, SEDs, H-a luminosities, equivalent widths, sizes, and population synthesis models of star forming regions across MO in order to address these questions, critical for understanding not just this single object, but the general process: 1. Does jet induced star formation change the luminosities and initial mass functions of star clusters? 2. What do the age gradients of the star clusters tell us about the process of conversion of gas (HI, CO) into stars as the radio jet progressed through the parent cloud? Does this match numerical simulations? 3. By using observations to refine simulations, what can we learn about intrinsic properties of these kinds of radio jets, such as propagation speed, age, pressure and jet energy flux?

CO excitation in four IR luminous galaxies

NASA Technical Reports Server (NTRS)

Radford, Simon J. E.; Solomon, P. M.; Downes, Dennis

1990-01-01

The correlation between the CO and far infrared luminosities of spiral galaxies is well established. The luminosity ration, L sub FIR/L sub CO in IR luminous active galaxies is, however, systematically five to ten times higher than in ordinary spirals and molecular clouds in our Galaxy. Furthermore, the masses of molecular hydrogen in luminous galaxies are large, M (H2) approx. equals 10(exp 10) solar magnitude, which indicates the observed luminosity ratios are due to an excess of infrared output, rather than a deficiency of molecular gas. These large amounts of molecular gas may fuel luminous galaxies through either star formation or nuclear activity. This interpretation rests on applying the M (H2)/L sub CO ratio calibrated in our Galaxy to galaxies with strikingly different luminosity ratios. But are the physical conditions of the molecular gas different in galaxies with different luminosity ratios. And, if so, does the proportionality between CO and H2 also vary among galaxies. To investigate these questions researchers observed CO (2 to 1) and (1 to 0) emission from four luminous galaxies with the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope. Researchers conclude that most of the CO emission from these Arp 193, Arp 220, and Mrk 231 arises in regions with moderate ambient densities similar to the clouds in the Milky Way molecular ring. The emission is neither from dense hot cloud cores nor from the cold low density gas characteristic of the envelopes of dark clouds.

Recognising Axionic Dark Matter by Compton and de-Broglie Scale Modulation of Pulsar Timing

NASA Astrophysics Data System (ADS)

De Martino, Ivan; Broadhurst, Tom; Tye, S.-H. Henry; Chiueh, Tzihong; Schive, Hsi-Yu; Lazkoz, Ruth

2017-11-01

Light Axionic Dark Matter, motivated by string theory, is increasingly favored for the "no-WIMP era". Galaxy formation is suppressed below a Jeans scale, of ≃ 10^8 M_⊙ by setting the axion mass to, m_B ˜ 10^{-22}eV, and the large dark cores of dwarf galaxies are explained as solitons on the de-Broglie scale. This is persuasive, but detection of the inherent scalar field oscillation at the Compton frequency, ω_B= (2.5 months)^{-1}(m_B/10^{-22}eV), would be definitive. By evolving the coupled Schrödinger-Poisson equation for a Bose-Einstein condensate, we predict the dark matter is fully modulated by de-Broglie interference, with a dense soliton core of size ≃ 150pc, at the Galactic center. The oscillating field pressure induces General Relativistic time dilation in proportion to the local dark matter density and pulsars within this dense core have detectably large timing residuals, of ≃ 400nsec/(m_B/10^{-22}eV). This is encouraging as many new pulsars should be discovered near the Galactic center with planned radio surveys. More generally, over the whole Galaxy, differences in dark matter density between pairs of pulsars imprints a pairwise Galactocentric signature that can be distinguished from an isotropic gravitational wave background.

The essential signature of a massive starburst in a distant quasar.

PubMed

Solomon, P; Vanden Bout, P; Carilli, C; Guelin, M

2003-12-11

Observations of carbon monoxide emission in high-redshift (zeta > 2) galaxies indicate the presence of large amounts of molecular gas. Many of these galaxies contain an active galactic nucleus powered by accretion of gas onto a supermassive black hole, and a key question is whether their extremely high infrared luminosities result from the active galactic nucleus, from bursts of massive star formation (associated with the molecular gas), or both. In the Milky Way, high-mass stars form in the dense cores of interstellar molecular clouds, where gas densities are n(H2) > 10(5) cm(-3) (refs 1, 2). Recent surveys show that virtually all galactic sites of high-mass star formation have similarly high densities. The bulk of the cloud material traced by CO observations, however, is at a much lower density. For galaxies in the local Universe, the HCN molecule is an effective tracer of high-density molecular gas. Here we report observations of HCN emission from the infrared-luminous 'Cloverleaf' quasar (at a redshift zeta = 2.5579). The HCN line luminosity indicates the presence of 10 billion solar masses of very dense gas, an essential feature of an immense starburst, which contributes, together with the active galactic nucleus it harbours, to its high infrared luminosity.

The impact of radiation feedback on the assembly of star clusters in a galactic context

NASA Astrophysics Data System (ADS)

Guillard, Nicolas; Emsellem, Eric; Renaud, Florent

2018-07-01

Massive star clusters are observed in galaxies spanning a broad range of luminosities and types, and are assumed to form in dense gas-rich environments. Using a parsec-resolution hydrodynamical simulation of an isolated gas-rich low-mass galaxy, we discuss here the non-linear effects of stellar feedback on the properties of star clusters with a focus on the progenitors of nuclear clusters. Our simulation shows two categories of star clusters: those for which feedback expels gas leftovers associated with their formation sites, and those, in a denser environment, around which feedback fails to totally clear the gas. We confirm that radiation feedback (photoionization and radiative pressure) plays a more important role than Type II supernovae in destroying dense gas structures, and in altering or quenching the subsequent cluster formation. Radiation feedback also disturbs the cluster mass growth, by increasing the internal energy of the gas component to the point at which radiation pressure overcomes the cluster gravity. We discuss how these effects may depend on the local properties of the interstellar medium, and also on the details of the subgrid recipes, which can affect the available cluster gas reservoirs, the evolution of potential nuclear cluster progenitors, and the overall galaxy morphology.

Galaxy And Mass Assembly (GAMA): galaxy environments and star formation rate variations

NASA Astrophysics Data System (ADS)

Wijesinghe, D. B.; Hopkins, A. M.; Brough, S.; Taylor, E. N.; Norberg, P.; Bauer, A.; Brown, M. J. I.; Cameron, E.; Conselice, C. J.; Croom, S.; Driver, S.; Grootes, M. W.; Jones, D. H.; Kelvin, L.; Loveday, J.; Pimbblet, K. A.; Popescu, C. C.; Prescott, M.; Sharp, R.; Baldry, I.; Sadler, E. M.; Liske, J.; Robotham, A. S. G.; Bamford, S.; Bland-Hawthorn, J.; Gunawardhana, M.; Meyer, M.; Parkinson, H.; Drinkwater, M. J.; Peacock, J.; Tuffs, R.

2012-07-01

We present a detailed investigation into the effects of galaxy environment on their star formation rates (SFRs) using galaxies observed in the Galaxy And Mass Assembly (GAMA) survey. We use three independent volume-limited samples of galaxies within z < 0.2 and Mr < -17.8. We investigate the known SFR-density relationship and explore in detail the dependence of SFR on stellar mass and density. We show that the SFR-density trend is only visible when we include the passive galaxy population along with the star-forming population. This SFR-density relation is absent when we consider only the star-forming population of galaxies, consistent with previous work. While there is a strong dependence of the EWHα on density we find, as in previous studies, that these trends are largely due to the passive galaxy population and this relationship is absent when considering a 'star-forming' sample of galaxies. We find that stellar mass has the strongest influence on SFR and EWHα with the environment having no significant effect on the star formation properties of the star-forming population. We also show that the SFR-density relationship is absent for both early- and late-type star-forming galaxies. We conclude that the stellar mass has the largest impact on the current SFR of a galaxy, and any environmental effect is not detectable. The observation that the trends with density are due to the changing morphology fraction with density implies that the time-scales must be very short for any quenching of the SFR in infalling galaxies. Alternatively, galaxies may in fact undergo predominantly in situ evolution where the infall and quenching of galaxies from the field into dense environments is not the dominant evolutionary mode.

Explaining compact groups as change alignments

NASA Technical Reports Server (NTRS)

Mamon, Gary A.

1990-01-01

The physical nature of the apparently densest groups of galaxies, known as compact groups is a topic of some recent controversy, despite the detailed observations of a well-defined catalog of 100 isolated compact groups compiled by Hickson (1982). Whereas many authors have espoused the view that compact groups are bound systems, typically as dense as they appear in projection on the sky (e.g., Williams & Rood 1987; Sulentic 1987; Hickson & Rood 1988), others see them as the result of chance configurations within larger systems, either in 1D (chance alignments: Mamon 1986; Walke & Mamon 1989), or in 3D (transient cores: Rose 1979). As outlined in the companion review to this contribution (Mamon, in these proceedings), the implication of Hickson's compact groups (HCGs) being dense bound systems is that they would then constitute the densest isolated systems of galaxies in the Universe and the privileged site for galaxy interactions. In a previous paper (Mamon 1986), the author reviewed the arguments given for the different theories of compact groups. Since then, a dozen papers have been published on the subject, including a thorough and perceptive review by White (1990), thus more than doubling the amount written on the subject. Here, the author first enumerates the arguments that he brought up in 1986 substantiating the chance alignment hypothesis, then he reviews the current status of the numerous recent arguments arguing against chance alignments and/or for the bound dense group hypothesis (both for the majority of HCGs but not all of them), and finally he reconsiders each one of these anti-chance alignment arguments and shows that, rather than being discredited, the chance alignment hypothesis remains a fully consistent explanation for the nature of compact groups.

The Role of Cosmic-Ray Pressure in Accelerating Galactic Outflows

NASA Astrophysics Data System (ADS)

Simpson, Christine M.; Pakmor, Rüdiger; Marinacci, Federico; Pfrommer, Christoph; Springel, Volker; Glover, Simon C. O.; Clark, Paul C.; Smith, Rowan J.

2016-08-01

We study the formation of galactic outflows from supernova (SN) explosions with the moving-mesh code AREPO in a stratified column of gas with a surface density similar to the Milky Way disk at the solar circle. We compare different simulation models for SN placement and energy feedback, including cosmic rays (CRs), and find that models that place SNe in dense gas and account for CR diffusion are able to drive outflows with similar mass loading as obtained from a random placement of SNe with no CRs. Despite this similarity, CR-driven outflows differ in several other key properties including their overall clumpiness and velocity. Moreover, the forces driving these outflows originate in different sources of pressure, with the CR diffusion model relying on non-thermal pressure gradients to create an outflow driven by internal pressure and the random-placement model depending on kinetic pressure gradients to propel a ballistic outflow. CRs therefore appear to be non-negligible physics in the formation of outflows from the interstellar medium.

THE ROLE OF COSMIC-RAY PRESSURE IN ACCELERATING GALACTIC OUTFLOWS

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

Simpson, Christine M.; Pakmor, Rüdiger; Pfrommer, Christoph

We study the formation of galactic outflows from supernova (SN) explosions with the moving-mesh code AREPO in a stratified column of gas with a surface density similar to the Milky Way disk at the solar circle. We compare different simulation models for SN placement and energy feedback, including cosmic rays (CRs), and find that models that place SNe in dense gas and account for CR diffusion are able to drive outflows with similar mass loading as obtained from a random placement of SNe with no CRs. Despite this similarity, CR-driven outflows differ in several other key properties including their overallmore » clumpiness and velocity. Moreover, the forces driving these outflows originate in different sources of pressure, with the CR diffusion model relying on non-thermal pressure gradients to create an outflow driven by internal pressure and the random-placement model depending on kinetic pressure gradients to propel a ballistic outflow. CRs therefore appear to be non-negligible physics in the formation of outflows from the interstellar medium.« less

The structure and nature of NGC 2017 IRS. 1: High-resolution radio continuum maps

NASA Technical Reports Server (NTRS)

Smith, Howard A.; Beck, Sara C.

1994-01-01

We have observed the star formation cluster NGC 2071 IRS 1, 2, and 3, with 0.14 sec spatial resolution at 2 cm. The strong source IRS 1 breaks up into a bright peak sitting on a narrow line emission extending over about 400 AU, with three much weaker peaks. This ridge, which has a p.a. = 100 deg, is not aligned with any of the other structures that have previously been seen around IRS 1: its orientation is about 55 deg from the CO outflow direction, and 35 deg from a hypothetical disk direction. The spectral and spatial results, combined with earlier radio and infrared observations, indicate that most likely the radio and infrared emission from the exciting source, IRS 1, is produced by a dense wind hidden by at least 100 visual magnitudes of extinction; the extended ridge of emission comes from an optically thin H II region with characteristic dimensions of approximately AU and which may result from a clumpy distribution of local gas and dust.

From Cosmic Dusk till Dawn with RELICS

NASA Astrophysics Data System (ADS)

Bradac, Marusa

When did galaxies start forming stars? What is the role of distant galaxies in galaxy formation models and the epoch of reionization? What are the conditions in typical lowmass, star-forming galaxies at z 4? Why is galaxy evolution dependent on environment? Recent observations indicate several critical puzzles in studies that address these questions. Chief among these, galaxies might have started forming stars earlier than previously thought (<400Myr after the Big Bang) and their star formation history differs from what is predicted from simulations. Furthermore, the details of the mechanisms that regulate star formation and morphological transformation in dense environments are still unknown. To solve these puzzles of galaxy evolution, we will use 41 galaxy clusters from the RELICS program (Reionization Lensing Cluster Survey) that are among the most powerful cosmic telescopes. Their magnification will allow us to study stellar properties of a large number of galaxies all the way to the reionization era. Accurate knowledge of stellar masses, ages, and star formation rates (SFRs) requires measuring both rest-frame UV and optical light, which only Spitzer can probe at z>0.5-11 for a sufficiently large sample of typical galaxies. This program will combine Spitzer imaging from two large programs, Director Discretionary Time (DDT) and the SRELICS program led by the PI.The main challenge in a study such as this is the capability to perform reliable photometry in crowded fields. Our team recently helped develop TPHOT, which is a much improved and much faster version of previously available codes. TPHOT is specifically designed to extract fluxes in crowded fields with very different PSFs. We will combine Spitzer photometry with ground based imaging and spectroscopy to obtain robust measurements of galaxy star formation rates, stellar masses, and stellar ages. This program will be a crucial legacy complement to previous Spitzer/IRAC deep blank field surveys and cluster studies, and will open up new parameter space by probing intrinsically fainter objects than most current surveys with a significantly improved sample variance over deep field surveys. It will allow us to study the properties (e.g. SFRs and stellar masses) of a large number of galaxies (200 at z=6-10), thus meeting our goal of reconstructing the cosmic SFR density with sufficient precision to better understand the role of galaxies in the reionization process. We will measure the presence (or absence) of established stellar populations with Spitzer for the largest sample to date. Furthermore this proposal will allow us to study the SFRs of the intrinsically faint (and magnified) intermediate redshift (z 4) galaxies, as well as the stellar mass function of z=0.3-0.7 galaxy members of our cluster sample, thereby expanding our understanding of star formation from reionization to the epoch of galaxy formation and dense environments. Many of the science goals of this proposal are main science drivers for JWST. Due to magnification our effective depth and resolution match those of the JWST blank fields and affords us a sneak preview of JWST sources with Spitzer now. This program will thus provide a valuable test-bed for simulations, observation planning and source selection just in time for JWST Cycle 1.

Ultra-deep Large Binocular Camera U-band Imaging of the GOODS-North Field: Depth Versus Resolution

NASA Astrophysics Data System (ADS)

Ashcraft, Teresa A.; Windhorst, Rogier A.; Jansen, Rolf A.; Cohen, Seth H.; Grazian, Andrea; Paris, Diego; Fontana, Adriano; Giallongo, Emanuele; Speziali, Roberto; Testa, Vincenzo; Boutsia, Konstantina; O’Connell, Robert W.; Rutkowski, Michael J.; Ryan, Russell E.; Scarlata, Claudia; Weiner, Benjamin

2018-06-01

We present a study of the trade-off between depth and resolution using a large number of U-band imaging observations in the GOODS-North field from the Large Binocular Camera (LBC) on the Large Binocular Telescope (LBT). Having acquired over 30 hr of data (315 images with 5–6 minutes exposures), we generated multiple image mosaics, starting with the best atmospheric seeing images (FWHM ≲ 0.″8), which constitute ∼10% of the total data set. For subsequent mosaics, we added in data with larger seeing values until the final, deepest mosaic included all images with FWHM ≲ 1.″8 (∼94% of the total data set). From the mosaics, we made object catalogs to compare the optimal-resolution, yet shallower image to the lower-resolution but deeper image. We show that the number counts for both images are ∼90% complete to U AB ≲ 26 mag. Fainter than U AB ∼ 27 mag, the object counts from the optimal-resolution image start to drop-off dramatically (90% between U AB = 27 and 28 mag), while the deepest image with better surface-brightness sensitivity ({μ }U{AB} ≲ 32 mag arcsec‑2) show a more gradual drop (10% between U AB ≃ 27 and 28 mag). For the brightest galaxies within the GOODS-N field, structure and clumpy features within the galaxies are more prominent in the optimal-resolution image compared to the deeper mosaics. We conclude that for studies of brighter galaxies and features within them, the optimal-resolution image should be used. However, to fully explore and understand the faintest objects, the deeper imaging with lower resolution are also required. Finally, we find—for 220 brighter galaxies with U AB ≲ 23 mag—only marginal differences in total flux between the optimal-resolution and lower-resolution light-profiles to {μ }U{AB} ≲ 32 mag arcsec‑2. In only 10% of the cases are the total-flux differences larger than 0.5 mag. This helps constrain how much flux can be missed from galaxy outskirts, which is important for studies of the Extragalactic Background Light. Based on data acquired using the Large Binocular Telescope (LBT).

A galactic mega-merger

NASA Image and Video Library

2016-01-11

The subject of this NASA/ESA Hubble Space Telescope image is known as NGC 3597. It is the product of a collision between two good-sized galaxies, and is slowly evolving to become a giant elliptical galaxy. This type of galaxy has grown more and more common as the Universe has evolved, with initially small galaxies merging and progressively building up into larger galactic structures over time. NGC 3597 is located approximately 150 million light-years away in the constellation of Crater (The Cup). Astronomers study NGC 3597 to learn more about how elliptical galaxies form — many ellipticals began their lives far earlier in the history of the Universe. Older ellipticals are nicknamed “red and dead” by astronomers because these bloated galaxies are not anymore producing new, bluer, stars in ages, and are thus packed full of old and redder stellar populations. Before infirmity sets in, some freshly formed elliptical galaxies experience a final flush of youth, as is the case with NGC 3597. Galaxies smashing together pool their available gas and dust, triggering new rounds of star birth. Some of this material ends up in dense pockets initially called proto-globular clusters, dozens of which festoon NGC 3597. These pockets will go on to collapse and form fully-fledged globular clusters, large spheres that orbit the centres of galaxies like satellites, packed tightly full of millions of stars.

Physically detached 'compact groups'

NASA Technical Reports Server (NTRS)

Hernquist, Lars; Katz, Neal; Weinberg, David H.

1995-01-01

A small fraction of galaxies appear to reside in dense compact groups, whose inferred crossing times are much shorter than a Hubble time. These short crossing times have led to considerable disagreement among researchers attempting to deduce the dynamical state of these systems. In this paper, we suggest that many of the observed groups are not physically bound but are chance projections of galaxies well separated along the line of sight. Unlike earlier similar proposals, ours does not require that the galaxies in the compact group be members of a more diffuse, but physically bound entity. The probability of physically separated galaxies projecting into an apparent compact group is nonnegligible if most galaxies are distributed in thin filaments. We illustrate this general point with a specific example: a simulation of a cold dark matter universe, in which hydrodynamic effects are included to identify galaxies. The simulated galaxy distribution is filamentary and end-on views of these filaments produce apparent galaxy associations that have sizes and velocity dispersions similar to those of observed compact groups. The frequency of such projections is sufficient, in principle, to explain the observed space density of groups in the Hickson catalog. We discuss the implications of our proposal for the formation and evolution of groups and elliptical galaxies. The proposal can be tested by using redshift-independent distance estimators to measure the line-of-sight spatial extent of nearby compact groups.

A Universe of ultradiffuse galaxies: theoretical predictions from ΛCDM simulations

NASA Astrophysics Data System (ADS)

Rong, Yu; Guo, Qi; Gao, Liang; Liao, Shihong; Xie, Lizhi; Puzia, Thomas H.; Sun, Shuangpeng; Pan, Jun

2017-10-01

A particular population of galaxies have drawn much interest recently, which are as faint as typical dwarf galaxies but have the sizes as large as L* galaxies, the so called ultradiffuse galaxies (UDGs). The lack of tidal features of UDGs in dense environments suggests that their host haloes are perhaps as massive as that of the Milky Way. On the other hand, galaxy formation efficiency should be much higher in the haloes of such masses. Here, we use the model galaxy catalogue generated by populating two large simulations: the Millennium-II cosmological simulation and Phoenix simulations of nine big clusters with the semi-analytic galaxy formation model. This model reproduces remarkably well the observed properties of UDGs in the nearby clusters, including the abundance, profile, colour and morphology, etc. We search for UDG candidates using the public data and find two UDG candidates in our Local Group and 23 in our Local Volume, in excellent agreement with the model predictions. We demonstrate that UDGs are genuine dwarf galaxies, formed in the haloes of ˜1010 M⊙. It is the combination of the late formation time and high spins of the host haloes that results in the spatially extended feature of this particular population. The lack of tidal disruption features of UDGs in clusters can also be explained by their late infall-time.

GREEN GALAXIES IN THE COSMOS FIELD

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

Pan, Zhizheng; Kong, Xu; Fan, Lulu, E-mail: panzz@mail.ustc.edu.cn, E-mail: xkong@ustc.edu.cn

2013-10-10

We present research on the morphologies, spectra, and environments of ≈2350 'green valley' galaxies at 0.2 < z < 1.0 in the COSMOS field. The bimodality of dust-corrected NUV–r {sup +} color is used to define 'green valley'; it removes dusty star-forming galaxies from galaxies that are truly transitioning between the blue cloud and the red sequence. Morphological parameters of green galaxies are intermediate between those of blue and red galaxy populations, both on the Gini-asymmetry and the Gini-M{sub 20} planes. Approximately 60%-70% of green disk galaxies have intermediate or big bulges, and only 5%-10% are pure disk systems, basedmore » on morphological classification using the Zurich Estimator of Structural Types. The obtained average spectra of green galaxies are intermediate between blue and red ones in terms of [O II], Hα, and Hβ emission lines. Stellar population synthesis on the average spectra shows that green galaxies are on average older than blue galaxies but younger than red galaxies. Green galaxies and blue galaxies have similar projected galaxy density (Σ{sub 10}) distributions at z > 0.7. At z < 0.7, the fractions of M{sub *} < 10{sup 10.0} M{sub ☉} green galaxies located in a dense environment are found to be significantly larger than those of blue galaxies. The morphological and spectral properties of green galaxies are consistent with the transitioning population between the blue cloud and the red sequence. The possible mechanisms for quenching star formation activities in green galaxies are discussed. The importance of active galactic nucleus feedback cannot be well constrained in our study. Finally, our findings suggest that environmental conditions, most likely starvation and harassment, significantly affect the transformation of M{sub *} < 10{sup 10.0} M{sub ☉} blue galaxies into red galaxies, especially at z < 0.5.« less

Multi-Wavelength Views of Messier 81

NASA Technical Reports Server (NTRS)

2003-01-01

[figure removed for brevity, see original site] Click on individual images below for larger view

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[figure removed for brevity, see original site]

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The magnificent spiral arms of the nearby galaxy Messier 81 are highlighted in this image from NASA's Spitzer Space Telescope. Located in the northern constellation of Ursa Major (which also includes the Big Dipper), this galaxy is easily visible through binoculars or a small telescope. M81 is located at a distance of 12 million light-years.

The main image is a composite mosaic obtained with the multiband imaging photometer for Spitzer and the infrared array camera. Thermal infrared emission at 24 microns detected by the photometer (red, bottom left inset) is combined with camera data at 8.0 microns (green, bottom center inset) and 3.6 microns (blue, bottom right inset).

A visible-light image of Messier 81, obtained at Kitt Peak National Observatory, a ground-based telescope, is shown in the upper right inset. Both the visible-light picture and the 3.6-micron near-infrared image trace the distribution of stars, although the Spitzer image is virtually unaffected by obscuring dust. Both images reveal a very smooth stellar mass distribution, with the spiral arms relatively subdued.

As one moves to longer wavelengths, the spiral arms become the dominant feature of the galaxy. The 8-micron emission is dominated by infrared light radiated by hot dust that has been heated by nearby luminous stars. Dust in the galaxy is bathed by ultraviolet and visible light from nearby stars. Upon absorbing an ultraviolet or visible-light photon, a dust grain is heated and re-emits the energy at longer infrared wavelengths. The dust particles are composed of silicates (chemically similar to beach sand), carbonaceous grains and polycyclic aromatic hydrocarbons and trace the gas distribution in the galaxy. The well-mixed gas (which is best detected at radio wavelengths) and dust provide a reservoir of raw materials for future star formation.

The 24-micron multiband imaging photometer image shows emission from warm dust heated by the most luminous young stars. The infrared-bright clumpy knots within the spiral arms show where massive stars are being born in giant H II (ionized hydrogen) regions. Studying the locations of these star forming regions with respect to the overall mass distribution and other constituents of the galaxy (e.g., gas) will help identify the conditions and processes needed for star formation.

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

NASA Astrophysics Data System (ADS)

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

2012-10-01

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

Testing AGN unification via inference from large catalogs

NASA Astrophysics Data System (ADS)

Nikutta, Robert; Ivezic, Zeljko; Elitzur, Moshe; Nenkova, Maia

2018-01-01

Source orientation and clumpiness of the central dust are the main factors in AGN classification. Type-1 QSOs are easy to observe and large samples are available (e.g. in SDSS), but obscured type-2 AGN are dimmer and redder as our line of sight is more obscured, making it difficult to obtain a complete sample. WISE has found up to a million QSOs. With only 4 bands and a relatively small aperture the analysis of individual sources is challenging, but the large sample allows inference of bulk properties at a very significant level.CLUMPY (www.clumpy.org) is arguably the most popular database of AGN torus SEDs. We model the ensemble properties of the entire WISE AGN content using regularized linear regression, with orientation-dependent CLUMPY color-color-magnitude (CCM) tracks as basis functions. We can reproduce the observed number counts per CCM bin with percent-level accuracy, and simultaneously infer the probability distributions of all torus parameters, redshifts, additional SED components, and identify type-1/2 AGN populations through their IR properties alone. We increase the statistical power of our AGN unification tests even further, by adding other datasets as axes in the regression problem. To this end, we make use of the NOAO Data Lab (datalab.noao.edu), which hosts several high-level large datasets and provides very powerful tools for handling large data, e.g. cross-matched catalogs, fast remote queries, etc.

Evolutionary models of rotating dense stellar systems: challenges in software and hardware

NASA Astrophysics Data System (ADS)

Fiestas, Jose

2016-02-01

We present evolutionary models of rotating self-gravitating systems (e.g. globular clusters, galaxy cores). These models are characterized by the presence of initial axisymmetry due to rotation. Central black hole seeds are alternatively included in our models, and black hole growth due to consumption of stellar matter is simulated until the central potential dominates the kinematics in the core. Goal is to study the long-term evolution (~ Gyr) of relaxed dense stellar systems, which deviate from spherical symmetry, their morphology and final kinematics. With this purpose, we developed a 2D Fokker-Planck analytical code, which results we confirm by detailed N-Body techniques, applying a high performance code, developed for GPU machines. We compare our models to available observations of galactic rotating globular clusters, and conclude that initial rotation modifies significantly the shape and lifetime of these systems, and can not be neglected in studying the evolution of globular clusters, and the galaxy itself.

The kinematics of dense clusters of galaxies. II - The distribution of velocity dispersions

NASA Technical Reports Server (NTRS)

Zabludoff, Ann I.; Geller, Margaret J.; Huchra, John P.; Ramella, Massimo

1993-01-01

From the survey of 31 Abell R above 1 cluster fields within z of 0.02-0.05, we extract 25 dense clusters with velocity dispersions omicron above 300 km/s and with number densities exceeding the mean for the Great Wall of galaxies by one deviation. From the CfA Redshift Survey (in preparation), we obtain an approximately volume-limited catalog of 31 groups with velocity dispersions above 100 km/s and with the same number density limit. We combine these well-defined samples to obtain the distribution of cluster velocity dispersions. The group sample enables us to correct for incompleteness in the Abell catalog at low velocity dispersions. The clusters from the Abell cluster fields populate the high dispersion tail. For systems with velocity dispersions above 700 km/s, approximately the median for R = 1 clusters, the group and cluster abundances are consistent. The combined distribution is consistent with cluster X-ray temperature functions.

Climbing to the top of the galactic mass ladder: evidence for frequent prolate-like rotation among the most massive galaxies

NASA Astrophysics Data System (ADS)

Krajnović, Davor; Emsellem, Eric; den Brok, Mark; Marino, Raffaella Anna; Schmidt, Kasper Borello; Steinmetz, Matthias; Weilbacher, Peter M.

2018-07-01

We present the stellar velocity maps of 25 massive early-type galaxies located in dense environments observed with MUSE. Galaxies are selected to be brighter than MK = -25.7 mag, reside in the core of the Shapley Super Cluster or be the brightest galaxy in clusters richer than the Virgo Cluster. We thus targeted galaxies more massive than 1012 M⊙ and larger than 10 kpc (half-light radius). The velocity maps show a large variety of kinematic features: oblate-like regular rotation, kinematically distinct cores, and various types of non-regular rotation. The kinematic misalignment angles show that massive galaxies can be divided into two categories: those with small or negligible misalignment and those with misalignment consistent with being 90°. Galaxies in this latter group, comprising just under half of our galaxies, have prolate-like rotation (rotation around the major axis). Among the brightest cluster galaxies the incidence of prolate-like rotation is 50 per cent, while for a magnitude limited sub-sample of objects within the Shapley Super Cluster (mostly satellites), 35 per cent of galaxies show prolate-like rotation. Placing our galaxies on the mass-size diagram, we show that they all fall on a branch extending almost an order of magnitude in mass and a factor of 5 in size from the massive end of galaxies, previously recognized as associated with major dissipation-less mergers. The presence of galaxies with complex kinematics and, particularly, prolate-like rotators suggests, according to current numerical simulations, that the most massive galaxies grow predominantly through dissipation-less equal-mass mergers.

Climbing to the top of the galactic mass ladder: evidence for frequent prolate-like rotation among the most massive galaxies

NASA Astrophysics Data System (ADS)

Krajnović, Davor; Emsellem, Eric; den Brok, Mark; Marino, Raffaella Anna; Schmidt, Kasper Borello; Steinmetz, Matthias; Weilbacher, Peter M.

2018-04-01

We present the stellar velocity maps of 25 massive early-type galaxies located in dense environments observed with MUSE. Galaxies are selected to be brighter than MK = -25.7 magnitude, reside in the core of the Shapley Super Cluster or be the brightest galaxy in clusters richer than the Virgo Cluster. We thus targeted galaxies more massive than 1012 M⊙ and larger than 10 kpc (half-light radius). The velocity maps show a large variety of kinematic features: oblate-like regular rotation, kinematically distinct cores and various types of non-regular rotation. The kinematic misalignment angles show that massive galaxies can be divided into two categories: those with small or negligible misalignment, and those with misalignment consistent with being 90°. Galaxies in this latter group, comprising just under half of our galaxies, have prolate-like rotation (rotation around the major axis). Among the brightest cluster galaxies the incidence of prolate-like rotation is 50 per cent, while for a magnitude limited sub-sample of objects within the Shapley Super Cluster (mostly satellites), 35 per cent of galaxies show prolate-like rotation. Placing our galaxies on the mass - size diagram, we show that they all fall on a branch extending almost an order of magnitude in mass and a factor of 5 in size from the massive end of galaxies, previously recognised as associated with major dissipation-less mergers. The presence of galaxies with complex kinematics and, particularly, prolate-like rotators suggests, according to current numerical simulations, that the most massive galaxies grow predominantly through dissipation-less equal-mass mergers.

The Topsy-Turvy Galaxy

NASA Astrophysics Data System (ADS)

2006-11-01

The captivating appearance of this image of the starburst galaxy NGC 1313, taken with the FORS instrument at ESO's Very Large Telescope, belies its inner turmoil. The dense clustering of bright stars and gas in its arms, a sign of an ongoing boom of star births, shows a mere glimpse of the rough times it has seen. Probing ever deeper into the heart of the galaxy, astronomers have revealed many enigmas that continue to defy our understanding. ESO PR Photo 43a/06 ESO PR Photo 43a/06 The Topsy-Turvy Galaxy NGC 1313 This FORS image of the central parts of NGC 1313 shows a stunning natural beauty. The galaxy bears some resemblance to some of the Milky Way's closest neighbours, the Magellanic Clouds. NGC 1313 has a barred spiral shape, with the arms emanating outwards in a loose twist from the ends of the bar. The galaxy lies just 15 million light-years away from the Milky Way - a mere skip on cosmological scales. The spiral arms are a hotbed of star-forming activity, with numerous young clusters of hot stars being born continuously at a staggering rate out of the dense clouds of gas and dust. Their light blasts through the surrounding gas, creating an intricately beautiful pattern of light and dark nebulosity. But NGC 1313 is not just a pretty picture. A mere scratch beneath the elegant surface reveals evidence of some of the most puzzling problems facing astronomers in the science of stars and galaxies. Starburst galaxies are fascinating objects to study in their own right; in neighbouring galaxies, around one quarter of all massive stars are born in these powerful engines, at rates up to a thousand times higher than in our own Milky Way Galaxy. In the majority of starbursts the upsurge in star's births is triggered when two galaxies merge, or come too close to each other. The mutual attraction between the galaxies causes immense turmoil in the gas and dust, causing the sudden 'burst' in star formation. ESO PR Photo 43b/06 ESO PR Photo 43b/06 Larger View of NGC 1313 NGC 1313's appearance suggests it has seen troubled times: its spiral arms look lop-sided and gas globules are spread out widely around them. This is more easily seen in ESO 43b/06, showing a larger area of the sky around the galaxy. Moreover, observations with ESO's 3.6-m telescope at La Silla have revealed that its 'real' centre, around which it rotates, does not coincide with the central bar. Its rotation is therefore also off kilter. Strangely enough NGC 1313 seems to be an isolated galaxy. It is not part of a group and has no neighbour, and it is not clear whether it may have swallowed a small companion in its past. So what caused its asymmetry and stellar baby boom? An explanation based on the presence of the central bar also does not hold for NGC 1313: the majority of its star formation is actually taking place not in its bar but in dense gassy regions scattered around the arms. By what mechanism the gas is compressed for stars to form at this staggering rate, astronomers simply aren't sure. Probing further into NGC 1313's insides reveals yet more mysteries. In the midst of the cosmic violence of the starburst regions lie two objects that emit large amounts of highly energetic X-rays - so-called ultra-luminous X-ray sources (ULX). Astronomers suspect that they might be black holes with masses of perhaps a few hundred times the mass of our Sun each, that formed as part of a binary star system. How such objects are created out of ordinary stars cannot be conclusively explained by current models. NGC 1313 is an altogether very intriguing target for astronomy. This image, obtained with ESO's Very Large Telescope, demonstrates once again how the imager FORS is ideally suited to capturing the beauty and stunning complexity of galaxies by observing them in different wavelength filters, combined here to form a stunning colour image. A high resolution image (with zoom-in possibilities) and its caption is available on this page.

JELLYFISH: EVIDENCE OF EXTREME RAM-PRESSURE STRIPPING IN MASSIVE GALAXY CLUSTERS

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

Ebeling, H.; Stephenson, L. N.; Edge, A. C.

Ram-pressure stripping by the gaseous intracluster medium has been proposed as the dominant physical mechanism driving the rapid evolution of galaxies in dense environments. Detailed studies of this process have, however, largely been limited to relatively modest examples affecting only the outermost gas layers of galaxies in nearby and/or low-mass galaxy clusters. We here present results from our search for extreme cases of gas-galaxy interactions in much more massive, X-ray selected clusters at z > 0.3. Using Hubble Space Telescope snapshots in the F606W and F814W passbands, we have discovered dramatic evidence of ram-pressure stripping in which copious amounts ofmore » gas are first shock compressed and then removed from galaxies falling into the cluster. Vigorous starbursts triggered by this process across the galaxy-gas interface and in the debris trail cause these galaxies to temporarily become some of the brightest cluster members in the F606W passband, capable of outshining even the Brightest Cluster Galaxy. Based on the spatial distribution and orientation of systems viewed nearly edge-on in our survey, we speculate that infall at large impact parameter gives rise to particularly long-lasting stripping events. Our sample of six spectacular examples identified in clusters from the Massive Cluster Survey, all featuring M {sub F606W} < –21 mag, doubles the number of such systems presently known at z > 0.2 and facilitates detailed quantitative studies of the most violent galaxy evolution in clusters.« less

The Ultraviolet and Infrared Star Formation Rates of Compact Group Galaxies: An Expanded Sample

NASA Technical Reports Server (NTRS)

Lenkic, Laura; Tzanavaris, Panayiotis; Gallagher, Sarah C.; Desjardins, Tyler D.; Walker, Lisa May; Johnson, Kelsey E.; Fedotov, Konstantin; Charlton, Jane; Cardiff, Ann H.; Durell, Pat R.

2016-01-01

Compact groups of galaxies provide insight into the role of low-mass, dense environments in galaxy evolution because the low velocity dispersions and close proximity of galaxy members result in frequent interactions that take place over extended time-scales. We expand the census of star formation in compact group galaxies by Tzanavaris et al. (2010) and collaborators with Swift UVOT, Spitzer IRAC and MIPS 24 m photometry of a sample of 183 galaxies in 46 compact groups. After correcting luminosities for the contribution from old stellar populations, we estimate the dust-unobscured star formation rate (SFRUV) using the UVOT uvw2 photometry. Similarly, we use the MIPS 24 m photometry to estimate the component of the SFR that is obscured by dust (SFRIR). We find that galaxies which are MIR-active (MIR-red), also have bluer UV colours, higher specific SFRs, and tend to lie in Hi-rich groups, while galaxies that are MIR-inactive (MIR-blue) have redder UV colours, lower specific SFRs, and tend to lie in Hi-poor groups. We find the SFRs to be continuously distributed with a peak at about 1 M yr1, indicating this might be the most common value in compact groups. In contrast, the specific SFR distribution is bimodal, and there is a clear distinction between star-forming and quiescent galaxies. Overall, our results suggest that the specific SFR is the best tracer of gas depletion and galaxy evolution in compact groups.

Ultra-compact high velocity clouds in the ALFALFA HI survey: Candidate Local Group galaxies?

NASA Astrophysics Data System (ADS)

Adams, Elizabeth Ann Kovenz

The increased sensitivity and spatial resolution of the ALFALFA HI survey has resulted in the detection of ultra-compact high velocity clouds (UCHVCs). These objects are good candidates to represent low mass gas-rich galaxies in the Local Group and Local Volume with stellar populations that are too faint to be detected in extant optical surveys. This idea is referred to as the "minihalo hypothesis". We identify the UCHVCs within the ALFALFA dataset via the use of a 3D matched filtering signal identification algorithm. UCHVCs are selected based on a compact size (< 30'), separation from Galactic HI (|upsilon LSR| > 120 km s-1) and isolation. Within the 40% complete ALFALFA survey (alpha.40), 59 UCHVCs are identified; 19 are in a most-isolated subset and are the best galaxy candidates. Due to the presence of large HVC complexes in the fall sky, most notably the Magellanic Stream, the association of UCHVCs with existing structure cannot be ruled out. In the spring sky, the spatial and kinematic distribution of the UCHVCs is consistent with simulations of dark matter halos within the Local Group. In addition, the HI properties of the UCHVCs (if placed at 1 Mpc) are consistent with both theoretical and observational predictions for low mass gas-rich galaxies. Importantly, the HI properties of the UCHVCs are consistent with those of two recently discovered low mass gas-rich galaxies in the Local Group and Local Volume, Leo T and Leo P. Detailed follow-up observations are key for addressing the minihalo hypothesis. High resolution HI observations can constrain the environment of a UCHVC and offer evidence for a hosting dark matter halo through evidence of rotation support and comparison to theoretical models. Observations of one UCHVC at high resolution (15'') reveal the presence of a clumpy HI distribution, similar to both low mass galaxies and circumgalactic compact HVCs. An extended envelope containing ˜50% of the HI flux is resolved out by the array configuration; observations at lower spatial resolution can recover this envelope and constrain the overall morphology and environment. The most direct way to address the minihalo hypothesis is by detection of a stellar counterpart, immediately identifying a UCHVC as a galaxy and allowing a distance to be measured. We have selected a sample of best galaxy candidates from the UCHVCs based on isolation, compactness, surface brightness, and kinematics. We are undertaking targeted optical observations of these systems in two filters to conduct a focused search for a coherent stellar population. Observations are in-hand for 29 systems, and an analysis of a single system is presented as a test case. These data were obtained via "shared-risk" observing, and analysis for all systems is awaiting further pipeline development. If (some of) the UCHVCs represent nearby low mass galaxies, they will help us understand the evolution of the lowest mass galaxies and address the small scale crisis in cosmology. Understanding the nature of the UCHVCs is a complicated and ongoing project. Both optical and HI synthesis imaging data will continue to be acquired and analyzed in order to address the minihalo hypothesis. Future HI surveys of nearby galaxy groups will be able to robustly address the minihalo hypothesis by being sensitive to UCHVCs in other galaxy groups.

Multiwavelength Characterization of an ACT-selected, Lensed Dusty Star-forming Galaxy at z = 2.64

NASA Astrophysics Data System (ADS)

Roberts-Borsani, G. W.; Jiménez-Donaire, M. J.; Daprà, M.; Alatalo, K.; Aretxaga, I.; Álvarez-Márquez, J.; Baker, A. J.; Fujimoto, S.; Gallardo, P. A.; Gralla, M.; Hilton, M.; Hughes, J. P.; Jiménez, C.; Laporte, N.; Marriage, T. A.; Nati, F.; Rivera, J.; Sievers, A.; Weiß, A.; Wilson, G. W.; Wollack, E. J.; Yun, M. S.

2017-08-01

We present C I(2-1) and multi-transition 12CO observations of a dusty star-forming galaxy, ACT J2029+0120, which we spectroscopically confirm to lie at z = 2.64. We detect CO(3-2), CO(5-4), CO(7-6), CO(8-7), and C I(2-1) at high significance, tentatively detect HCO+(4-3), and place strong upper limits on the integrated strength of dense gas tracers (HCN(4-3) and CS(7-6)). Multi-transition CO observations and dense gas tracers can provide valuable constraints on the molecular gas content and excitation conditions in high-redshift galaxies. We therefore use this unique data set to construct a CO spectral line energy distribution (SLED) of the source, which is most consistent with that of a ULIRG/Seyfert or QSO host object in the taxonomy of the Herschel Comprehensive ULIRG Emission Survey. We employ RADEX models to fit the peak of the CO SLED, inferring a temperature of T ˜ 117 K and {n}{{{H}}2}˜ {10}5 cm-3, most consistent with a ULIRG/QSO object and the presence of high-density tracers. We also find that the velocity width of the C I line is potentially larger than seen in all CO transitions for this object, and that the {L}{{C} {{I}}(2-1)}\\prime /{L}{CO(3-2)}\\prime ratio is also larger than seen in other lensed and unlensed submillimeter galaxies and QSO hosts; if confirmed, this anomaly could be an effect of differential lensing of a shocked molecular outflow.

Multiwavelength Characterization of an ACT-Selected, Lensed Dusty Star-Forming Galaxy at zeta 2.64

NASA Technical Reports Server (NTRS)

Roberts-Borsani, G. W.; Jimenez-Donaire, M. J.; Dapra, M.; Alatalo, K.; Aretxaga, I.; Alvarez-Marquez, J.; Baker, A. J.; Fujimoto, S.; Gallardo, P. A.; Gralla, M.;

Amazing Andromeda Galaxy

NASA Technical Reports Server (NTRS)

2006-01-01

The many 'personalities' of our great galactic neighbor, the Andromeda galaxy, are exposed in this new composite image from NASA's Galaxy Evolution Explorer and the Spitzer Space Telescope.

The wide, ultraviolet eyes of Galaxy Evolution Explorer reveal Andromeda's 'fiery' nature -- hotter regions brimming with young and old stars. In contrast, Spitzer's super-sensitive infrared eyes show Andromeda's relatively 'cool' side, which includes embryonic stars hidden in their dusty cocoons.

Galaxy Evolution Explorer detected young, hot, high-mass stars, which are represented in blue, while populations of relatively older stars are shown as green dots. The bright yellow spot at the galaxy's center depicts a particularly dense population of old stars.

Swaths of red in the galaxy's disk indicate areas where Spitzer found cool, dusty regions where stars are forming. These stars are still shrouded by the cosmic clouds of dust and gas that collapsed to form them.

Together, Galaxy Evolution Explorer and Spitzer complete the picture of Andromeda's swirling spiral arms. Hints of pinkish purple depict regions where the galaxy's populations of hot, high-mass stars and cooler, dust-enshrouded stars co-exist.

Located 2.5 million light-years away, the Andromeda is our largest nearby galactic neighbor. The galaxy's entire disk spans about 260,000 light-years, which means that a light beam would take 260,000 years to travel from one end of the galaxy to the other. By comparison, our Milky Way galaxy's disk is about 100,000 light-years across.

This image is a false color composite comprised of data from Galaxy Evolution Explorer's far-ultraviolet detector (blue), near-ultraviolet detector (green), and Spitzer's multiband imaging photometer at 24 microns (red).

Hubble Sees Spiral Bridge of Young Stars Between Two Ancient Galaxies

NASA Image and Video Library

2014-07-11

NASA's Hubble Space Telescope has photographed the dense galaxy cluster SDSS J1531+3414 in the northern constellation Corona Borealis. Made up primarily of giant elliptical galaxies with a few spirals and irregular galaxies thrown in for good measure, the cluster's powerful gravity warps the image of background galaxies into blue streaks and arcs. At the center of the bull's-eye of blue, gravitationally lensed filaments lies a pair of elliptical galaxies that are also exhibiting some interesting features. A 100,000-light-year-long structure that looks like a string of pearls twisted into a corkscrew shape winds around the cores of the two massive galaxies. The "pearls" are superclusters of blazing, blue-white, newly born stars. These super star clusters are evenly spaced along the chain at separations of 3,000 light-years from one another. Read more: 1.usa.gov/1ztQvL9 Credit: NASA/ESA NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

A Massive Galaxy in Its Core Formation Phase Three Billion Years After the Big Bang

NASA Technical Reports Server (NTRS)

Nelson, Erica; van Dokkum, Pieter; Franx, Marijn; Brammer, Gabriel; Momcheva, Ivelina; Schreiber, Natascha M. Forster; da Cunha, Elisabete; Tacconi, Linda; Bezanson, Rachel; Kirkpatrick, Allison;

Why Are Galaxies So Smooth?

NASA Image and Video Library

2009-04-30

This image from NASA's Spitzer Space Telescope shows the spiral galaxy NGC 2841, located about 46 million light-years from Earth in the constellation Ursa Major. The galaxy is helping astronomers solve one of the oldest puzzles in astronomy: Why do galaxies look so smooth, with stars sprinkled evenly throughout? An international team of astronomers has discovered that rivers of young stars flow from their hot, dense stellar nurseries, dispersing out to form large, smooth distributions. This image is a composite of three different wavelengths from Spitzer's infrared array camera. The shortest wavelengths are displayed inblue, and mostly show the older stars in NGC 2841, as well as foreground stars in our own Milky Way galaxy. The cooler areas are highlighted in red, and show the dusty, gaseous regions of the galaxy. Blue shows infrared light of 3.6 microns, green represents 4.5-micron light and red, 8.0-micron light. The contribution from starlight measured at 3.6 microns has been subtracted from the 8.0-micron data to enhance the visibility of the dust features.The shortest wavelengths are displayed inblue, and mostly show the older stars in NGC 2841, as well as foreground stars in our own Milky Way galaxy. http://photojournal.jpl.nasa.gov/catalog/PIA12001

Peas in a Pod: Environment and Ionization in Green Pea Galaxies

NASA Astrophysics Data System (ADS)

Kurtz, Heather; Jaskot, Anne; Drew, Patrick; Pare, Dylan; Griffin, Jon; Petersen, Michael

2016-01-01

The Green Peas are extreme, highly ionized, starburst galaxies with strong [OIII] 5007 emission. Using the Sloan Digital Sky Survey, we present statistics on the environment of Green Peas and investigate its effects on their ionized gas properties. Although most dwarf starburst galaxies are in low-density environments, we identify a sample of Green Peas in dense environments. Emission line observations with the WIYN 0.9-meter telescope at Kitt Peak reveal that one cluster Green Pea is more highly ionized in the direction of the cluster center. Ram pressure stripping likely generates this ionization gradient. We explore the role of the environment in enhancing star formation rates and ionization, and we compare the nebular properties of Green Peas in high-density environments to those in low-density environments.

Galactic Center Fly-in

NASA Astrophysics Data System (ADS)

Hanson, A.; Fu, C.-W.; Li, Y.; Frisch, P. C.

2006-06-01

Beginning with the familiar constellations of the night sky, we present a multispectral zoom into the core of the Milky Way Galaxy. After traveling over seven orders of magnitude in spatial scale, we discover the violent phenomena occurring within one light year of the Black Hole at the Galactic Core. This animated zoom includes data with wavelengths from radio to X-ray, and is based entirely on data or models that have been aligned at all spatial scales in order to provide a single continuous visual trip into the Center of the Milky Way Galaxy. The visualization challenge has been to align and choreograph data acquired over a wide range of wavelength and spatial scales, and obtain a new scientific as well as educational perspective of the dense core of our Galaxy.

The rate and latency of star formation in dense, massive clumps in the Milky Way

NASA Astrophysics Data System (ADS)

Heyer, M.; Gutermuth, R.; Urquhart, J. S.; Csengeri, T.; Wienen, M.; Leurini, S.; Menten, K.; Wyrowski, F.

2016-04-01

Context. Newborn stars form within the localized, high density regions of molecular clouds. The sequence and rate at which stars form in dense clumps and the dependence on local and global environments are key factors in developing descriptions of stellar production in galaxies. Aims: We seek to observationally constrain the rate and latency of star formation in dense massive clumps that are distributed throughout the Galaxy and to compare these results to proposed prescriptions for stellar production. Methods: A sample of 24 μm-based Class I protostars are linked to dust clumps that are embedded within molecular clouds selected from the APEX Telescope Large Area Survey of the Galaxy. We determine the fraction of star-forming clumps, f∗, that imposes a constraint on the latency of star formation in units of a clump's lifetime. Protostellar masses are estimated from models of circumstellar environments of young stellar objects from which star formation rates are derived. Physical properties of the clumps are calculated from 870 μm dust continuum emission and NH3 line emission. Results: Linear correlations are identified between the star formation rate surface density, ΣSFR, and the quantities ΣH2/τff and ΣH2/τcross, suggesting that star formation is regulated at the local scales of molecular clouds. The measured fraction of star forming clumps is 23%. Accounting for star formation within clumps that are excluded from our sample due to 24 μm saturation, this fraction can be as high as 31%, which is similar to previous results. Dense, massive clumps form primarily low mass (<1-2 M⊙) stars with emergent 24 μm fluxes below our sensitivity limit or are incapable of forming any stars for the initial 70% of their lifetimes. The low fraction of star forming clumps in the Galactic center relative to those located in the disk of the Milky Way is verified. Full Tables 2-4 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/588/A29

The Milky Way as a Star Formation Engine

NASA Astrophysics Data System (ADS)

Molinari, S.; Bally, J.; Glover, S.; Moore, T.; Noriega-Crespo, A.; Plume, R.; Testi, L.; Vázquez-Semadeni, E.; Zavagno, A.; Bernard, J.-P.; Martin, P.

The cycling of material from the interstellar medium (ISM) into stars and the return of stellar ejecta into the ISM is the engine that drives the galactic ecology in normal spirals. This ecology is a cornerstone in the formation and evolution of galaxies through cosmic time. There remain major observational and theoretical challenges in determining the processes responsible for converting the low-density, diffuse components of the ISM into dense molecular clouds, forming dense filaments and clumps, fragmenting them into stars, expanding OB associations and bound clusters, and characterizing the feedback that limits the rate and efficiency of star formation. This formidable task can be attacked effectively for the first time thanks to the synergistic combination of new global-scale surveys of the Milky Way from infrared (IR) to radio wavelengths, offering the possibility of bridging the gap between local and extragalactic star-formation studies. The Herschel Space Observatory Galactic Plane Survey (Hi-GAL) survey, with its five-band 70-500-μm full Galactic Plane mapping at 6"-36" resolution, is the keystone of a set of continuum surveys that include the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE)(360)+MIPSGAL@Spitzer, Wide-field Infrared Survey Explorer (WISE), Midcourse Space Experiment (MSX), APEX Telescope Large Area Survey of the Galaxy (ATLASGAL)@Atacama Pathfinder EXperiment (APEX), Bolocam Galactic Plane Survey (BGPS)@Caltech Submillimeter Observatory (CSO), and CORNISH@Very Large Array (VLA). This suite enables us to measure the Galactic distribution and physical properties of dust on all scales and in all components of the ISM from diffuse clouds to filamentary complexes and hundreds of thousands of dense clumps. A complementary suite of spectroscopic surveys in various atomic and molecular tracers is providing the chemical fingerprinting of dense clumps and filaments, as well as essential kinematic information to derive distances and thus transform panoramic data into a three-dimensional representation. The latest results emerging from these Galaxy-scale surveys are reviewed. New insights into cloud formation and evolution, filaments and their relationship to channeling gas onto gravitationally-bound clumps, the properties of these clumps, density thresholds for gravitational collapse, and star and cluster formation rates are discussed.

The Arecibo Galaxy Environment Survey - VII. A dense filament with extremely long H I streams

NASA Astrophysics Data System (ADS)

Taylor, R.; Minchin, R. F.; Herbst, H.; Davies, J. I.; Rodriguez, R.; Vazquez, C.

2014-09-01

We present completed observations of the NGC 7448 galaxy group and background volume as part of the blind neutral hydrogen Arecibo Galaxy Environment Survey. Our observations cover a region spanning 5°× 4°, over a redshift range of approximately -2000

Canibalismo Extremo y Lente Gravitacional Intensa en el Cúmulo de Galaxias Abell 3827

NASA Astrophysics Data System (ADS)

Díaz, R. J.; West, M.; Bergmann, M.; Carrasco, E. R.; Gomez, P.; Lee, H.; Miller, B.; Turner, J.

Abell 3827 is one of the most massive known clusters and at its center we observe an extreme example of galactic canibalism: a super giant elliptical galaxy in its formation process, devoring five massive galaxies at the same time. Using high spatial resolution Gemini+GMOS imagery and multi-object spectroscopy, we derived the redshift (z=0.099) and the radial velocity dispersion of the 55 brightest galaxies in the cluster central region (1134 +- 125 km/s). The estimated virial mass is ~ 1E14 M(sun) inside a radius of 300 kpc of the cluster center. We have also found features corresponding to a strong gravitational lense, four anular features arranged in an Einstein Ring from a galaxy (z=0.2) at double redshift than the cluster, and a fifth arclet feature corresponding to the lensed light of a farther galaxy (z=0.4). The possible Einstein Ring is of small angular size and the gravitational lense morphology would confirm that the cluster is indeed very massive and dense. FULL TEXT IN SPANISH.

The Million-Body Problem: Particle Simulations in Astrophysics

ScienceCinema

Rasio, Fred

2018-05-21

Computer simulations using particles play a key role in astrophysics. They are widely used to study problems across the entire range of astrophysical scales, from the dynamics of stars, gaseous nebulae, and galaxies, to the formation of the largest-scale structures in the universe. The 'particles' can be anything from elementary particles to macroscopic fluid elements, entire stars, or even entire galaxies. Using particle simulations as a common thread, this talk will present an overview of computational astrophysics research currently done in our theory group at Northwestern. Topics will include stellar collisions and the gravothermal catastrophe in dense star clusters.

Mid-infrared interferometry of Seyfert galaxies: Challenging the Standard Model

NASA Astrophysics Data System (ADS)

López-Gonzaga, N.; Jaffe, W.

2016-06-01

Aims: We aim to find torus models that explain the observed high-resolution mid-infrared (MIR) measurements of active galactic nuclei (AGN). Our goal is to determine the general properties of the circumnuclear dusty environments. Methods: We used the MIR interferometric data of a sample of AGNs provided by the instrument MIDI/VLTI and followed a statistical approach to compare the observed distribution of the interferometric measurements with the distributions computed from clumpy torus models. We mainly tested whether the diversity of Seyfert galaxies can be described using the Standard Model idea, where differences are solely due to a line-of-sight (LOS) effect. In addition to the LOS effects, we performed different realizations of the same model to include possible variations that are caused by the stochastic nature of the dusty models. Results: We find that our entire sample of AGNs, which contains both Seyfert types, cannot be explained merely by an inclination effect and by including random variations of the clouds. Instead, we find that each subset of Seyfert type can be explained by different models, where the filling factor at the inner radius seems to be the largest difference. For the type 1 objects we find that about two thirds of our objects could also be described using a dusty torus similar to the type 2 objects. For the remaining third, it was not possible to find a good description using models with high filling factors, while we found good fits with models with low filling factors. Conclusions: Within our model assumptions, we did not find one single set of model parameters that could simultaneously explain the MIR data of all 21 AGN with LOS effects and random variations alone. We conclude that at least two distinct cloud configurations are required to model the differences in Seyfert galaxies, with volume-filling factors differing by a factor of about 5-10. A continuous transition between the two types cannot be excluded.

Panchromatic observations of dwarf starburst galaxies: Infant super star clusters and a low-luminosity AGN

NASA Astrophysics Data System (ADS)

Reines, Amy Ellen

2011-01-01

Globular star clusters and supermassive black holes are fundamental components of today's massive galaxies, with origins dating back to the very early universe. Both globular clusters and the seeds of supermassive black holes are believed to have formed in the progenitors of modern massive galaxies, although the details are poorly understood. Direct observations of these low-mass, distant, and hence faint systems are unobtainable with current capabilities. However, gas-rich dwarf starburst galaxies in the local universe, analogous in many ways to protogalaxies at high-redshift, can provide critical insight into the early stages of galaxy evolution including the formation of globular clusters and massive black holes. This thesis presents a panchromatic study of nearby dwarf starburst galaxies harboring nascent globular clusters still embedded in their birth material. Infant clusters are identified via their production of thermal radio emission at centimeter wavelengths, which comes from dense gas ionized by young massive stars. By combining radio observations with complementary data at ultraviolet, optical and infrared wavelengths, we obtain a comprehensive view of massive clusters emerging from their gaseous and dusty birth cocoons. This thesis also presents the first example of a nearby dwarf starburst galaxy hosting an actively accreting massive central black hole. The black hole in this dwarf galaxy is unusual in that it is not associated with a bulge, a nuclear star cluster, or any other well-defined nucleus, likely reflecting an early phase of black hole and galaxy evolution that has not been previously observed.

THE IMPACT OF STELLAR FEEDBACK ON THE STRUCTURE, SIZE, AND MORPHOLOGY OF GALAXIES IN MILKY-WAY-SIZED DARK MATTER HALOS

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

Agertz, Oscar; Kravtsov, Andrey V., E-mail: o.agertz@surrey.ac.uk

We use cosmological zoom-in simulations of galaxy formation in a Milky-Way-sized halo started from identical initial conditions to investigate the evolution of galaxy sizes, baryon fractions, morphologies, and angular momenta in runs with different parameters of the star formation–feedback cycle. Our fiducial model with a high local star formation efficiency, which results in efficient feedback, produces a realistic late-type galaxy that matches the evolution of basic properties of late-type galaxies: stellar mass, disk size, morphology dominated by a kinematically cold disk, stellar and gas surface density profiles, and specific angular momentum. We argue that feedback’s role in this success ismore » twofold: (1) removal of low angular momentum gas, and (2) maintaining a low disk-to-halo mass fraction, which suppresses disk instabilities that lead to angular momentum redistribution and a central concentration of baryons. However, our model with a low local star formation efficiency, but large energy input per supernova, chosen to produce a galaxy with a similar star formation history as our fiducial model, leads to a highly irregular galaxy with no kinematically cold component, overly extended stellar distribution, and low angular momentum. This indicates that only when feedback is allowed to become vigorous via locally efficient star formation in dense cold gas do resulting galaxy sizes, gas/stellar surface density profiles, and stellar disk angular momenta agree with observed z = 0 galaxies.« less

A STELLAR MASS THRESHOLD FOR QUENCHING OF FIELD GALAXIES

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

Geha, M.; Blanton, M. R.; Yan, R.

2012-09-20

We demonstrate that dwarf galaxies (10{sup 7} < M{sub stellar} < 10{sup 9} M{sub Sun }, -12 > M{sub r} > -18) with no active star formation are extremely rare (<0.06%) in the field. Our sample is based on the NASA-Sloan Atlas which is a reanalysis of the Sloan Digital Sky Survey Data Release 8. We examine the relative number of quenched versus star-forming dwarf galaxies, defining quenched galaxies as having no H{alpha} emission (EW{sub H{alpha}} < 2 A) and a strong 4000 A break. The fraction of quenched dwarf galaxies decreases rapidly with increasing distance from a massive host,more » leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of a massive host galaxy to be in the field. We demonstrate that there is a stellar mass threshold of M{sub stellar} < 1.0 Multiplication-Sign 10{sup 9} M{sub Sun} below which quenched galaxies do not exist in the field. Below this threshold, we find that none of the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show evidence for recent star formation. Correcting for volume effects, this corresponds to a 1{sigma} upper limit on the quenched fraction of 0.06%. In more dense environments, quenched galaxies account for 23% of the dwarf population over the same stellar mass range. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii. Thus, for galaxies with stellar mass less than 1.0 Multiplication-Sign 10{sup 9} M{sub Sun }, ending star formation requires the presence of a more massive neighbor, providing a stringent constraint on models of star formation feedback.« less

Strongly Magnetized Accretion Disks in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Begelman, Mitchell

Accretion disks likely provide the conduit for fueling active galactic nuclei (AGN), linking the black hole's immediate surroundings to the host galaxy's nuclear star cluster, and possibly beyond. Yet detailed AGN disk models fail to explain several of the most basic observational features of AGN: How do the outer regions of the disk avoid stalling as a result of wholesale gravitational fragmentation? What regulates the amount of star formation that is inferred to accompany accretion in some AGN? Why is the broad emission line region a ubiquitous feature of luminous AGN? What processes create and maintain the so-called "dusty torus"? Analytic work suggests that vertical pressure support of the disk primarily by a toroidal magnetic field, rather than by gas or radiation pressure, can readily resolve these problems. And recent numerical simulations have indicated that such a strong toroidal field is the inevitable consequence of the magnetorotational instability (MRI) when a disk accumulates a modest amount of net magnetic flux, thus providing a sound theoretical basis for strongly magnetized disks. We propose an analytic and computational study of such disks in the AGN context, focusing on: (1) The basic physical properties of strongly magnetized AGN disks. We will focus on the competition between field generation and buoyancy, improving on previous work by considering realistic equations of state, dissipative processes and radiative losses. We will use global simulations to test the limiting magnetic fields that can be produced by MRIdriven accretion disk dynamos and explore the driving mechanisms of disk winds and the resulting levels of mass, angular momentum and energy loss. (2) Gravitational fragmentation and star formation in strongly magnetized disks. We will determine how a strong field reduces and regulates gravitational fragmentation, by both lowering the disk density and creating a stratified structure in which star formation near the equator can co-exist with accretion at large heights. Using simulations, we will study fragmentation conditions, the clumpiness of stable AGN disks, and the mass function of collapsed clumps. (3) Physics of the broad emission line region and dusty torus . We will study the possible role of the strong toroidal field in promoting thermal instabilities to create dense lineemitting filaments, transporting them in height, and confining the line-emitting gas. Extrapolating to slightly larger distances, we will examine whether the field can elevate dusty gas to heights at which it can reprocess a substantial fraction of the AGN radiation. This study will establish a new theoretical framework for interpreting multi-wavelength observations of AGN, involving NASA s infrared, ultraviolet and X-ray observatories as well as ground-based detectors. It addresses fundamental questions about how supermassive black holes interact with their galactic environments, as well as broader issues of feedback and black hole-galaxy co-evolution.

APEX/SABOCA observations of small-scale structure of infrared-dark clouds . I. Early evolutionary stages of star-forming cores

NASA Astrophysics Data System (ADS)

Ragan, Sarah E.; Henning, Thomas; Beuther, Henrik

2013-11-01

Infrared-dark clouds (IRDCs) harbor the early phases of cluster and high-mass star formation and are comprised of cold (~20 K), dense (n > 104 cm-3) gas. The spectral energy distribution (SED) of IRDCs is dominated by the far-infrared and millimeter wavelength regime, and our initial Herschel study examined IRDCs at the peak of the SED with high angular resolution. Here we present a follow-up study using the SABOCA instrument on APEX which delivers 7.8″ angular resolution at 350 μm, matching the resolution we achieved with Herschel/PACS, and allowing us to characterize substructure on ~0.1 pc scales. Our sample of 11 nearby IRDCs are a mix of filamentary and clumpy morphologies, and the filamentary clouds show significant hierarchical structure, while the clumpy IRDCs exhibit little hierarchical structure. All IRDCs, regardless of morphology, have about 14% of their total mass in small scale core-like structures which roughly follow a trend of constant volume density over all size scales. Out of the 89 protostellar cores we identified in this sample with Herschel, we recover 40 of the brightest and re-fit their SEDs and find their properties agree fairly well with our previous estimates (⟨ T ⟩ ~ 19 K). We detect a new population of "cold cores" which have no 70 μm counterpart, but are 100 and 160 μm-bright, with colder temperatures (⟨ T ⟩ ~ 16 K). This latter population, along with SABOCA-only detections, are predominantly low-mass objects, but their evolutionary diagnostics are consistent with the earliest starless or prestellar phase of cores in IRDCs. Based on observations carried out with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between Max Planck Institut für Radioastronomie (MPIfR), Onsala Space Observatory (OSO), and the European Southern Observatory (ESO).Appendices are available in electronic form at http://www.aanda.org

Clumpy filaments of the Chamaeleon I cloud: C18O mapping with the SEST

NASA Astrophysics Data System (ADS)

Haikala, L. K.; Harju, J.; Mattila, K.; Toriseva, M.

2005-02-01

The Chamaeleon I dark cloud (Cha I) has been mapped in C18O with an angular resolution of 1 arcmin using the SEST telescope. The large scale structures previously observed with lower spatial resolution in the cloud turn into a network of clumpy filaments. The automatic Clumpfind routine developed by \\cite{williams1994} is used to identify individual clumps in a consistent way. Altogether 71 clumps were found and the total mass of these clumps is 230 M⊙. The dense ``cores'' detected with the NANTEN telescope (\\cite{mizuno1999}) and the very cold cores detected in the ISOPHOT serendipity survey (\\cite{toth2000}) form parts of these filaments but decompose into numerous ``clumps''. The filaments are preferentially oriented at right angles to the large-scale magnetic field in the region. We discuss the cloud structure, the physical characteristics of the clumps and the distribution of young stars. The observed clump mass spectrum is compared with the predictions of the turbulent fragmentation model of \\cite{padoan2002}. Agreement is found if fragmentation has been driven by very large-scale hypersonic turbulence, and if by now it has had time to dissipate into modestly supersonic turbulence in the interclump gas. According to numerical simulations, large-scale turbulence should have resulted in filamentary structures as seen in Cha I. The well-oriented magnetic field does not, however, support this picture, but suggests magnetically steered large-scale collapse. The origin of filaments and clumps in Cha I is thus controversial. A possible solution is that the characterization of the driving turbulence fails and that in fact different processes have been effective on small and large scales in this cloud. Based on observations collected at the European Southern Observatory, La Silla, Chile. FITS files are only available in electronic form at http://www.edpsciences.org

The Ages of Passive Galaxies in a z = 1.62 Protocluster

NASA Astrophysics Data System (ADS)

Lee-Brown, Donald B.; Rudnick, Gregory H.; Momcheva, Ivelina G.; Papovich, Casey; Lotz, Jennifer M.; Tran, Kim-Vy H.; Henke, Brittany; Willmer, Christopher N. A.; Brammer, Gabriel B.; Brodwin, Mark; Dunlop, James; Farrah, Duncan

2017-07-01

We present a study of the relation between galaxy stellar age and mass for 14 members of the z = 1.62 protocluster IRC 0218, using multiband imaging and HST G102 and G141 grism spectroscopy. Using UVJ colors to separate galaxies into star-forming and quiescent populations, we find that, at stellar masses {M}* ≥slant {10}10.85 {M}⊙ , the quiescent fraction in the protocluster is {f}Q={1.0}-0.37+0.00, consistent with a ˜ 2× enhancement relative to the field value, {f}Q={0.45}-0.03+0.03. At masses {10}10.2 {M}⊙ ≤slant {M}* ≤slant {10}10.85 {M}⊙ , f Q in the cluster is {f}Q={0.40}-0.18+0.20, consistent with the field value of {f}Q={0.28}-0.02+0.02. Using galaxy {D}n(4000) values derived from the G102 spectroscopy, we find no relation between galaxy stellar age and mass. These results may reflect the impact of merger-driven mass redistribution—which is plausible, as this cluster is known to host many dry mergers. Alternately, they may imply that the trend in f Q in IRC 0218 was imprinted over a short timescale in the protocluster’s assembly history. Comparing our results with those of other high-redshift studies and studies of clusters at z˜ 1, we determine that our observed relation between f Q and stellar mass only mildly evolves between z˜ 1.6 and z˜ 1, and only at stellar masses {M}* ≤slant {10}10.85 {M}⊙ . Both the z˜ 1 and z˜ 1.6 results are in agreement that the red sequence in dense environments was already populated at high redshift, z≳ 3, placing constraints on the mechanism(s) responsible for quenching in dense environments at z≥slant 1.5.

Mapping the spatial distribution of star formation in cluster galaxies at z ~0.5 with the Grism Lens-Amplified Survey from Space (GLASS)

NASA Astrophysics Data System (ADS)

Vulcani, B.; Treu, T.; Schmidt, K. B.; Poggianti, B. M.; Dressler, A.; Fontana, A.; Bradač, M.; Brammer, G. B.; Hoag, A.; Huang, K.; Malkan, M.; Pentericci, L.; Trenti, M.; von der Linden, A.; Abramson, L.; He, J.; Morris, G.

2016-06-01

What physical processes regulate star formation in dense environments? Understanding why galaxy evolution is environment dependent is one of the key questions of current astrophysics. I will present the first characterization of the spatial distribution of star formation in cluster galaxies at z~0.5, and compare to a field control sample, in order to quantify the role of different physical processes that are believed to be responsible for shutting down star formation (Vulcani et al. 2015, Vulcani et al. in prep). The analysis makes use of data from the Grism Lens-Amplified Survey from Space (GLASS), a large HST cycle-21 program targeting 10 massive galaxy clusters with extensive HST imaging from CLASH and the Frontier Field Initiative. The program consists of 140 primary and 140 parallel orbits of near-infrared WCF3 and optical ACS slitless grism observations, which result in 3D spectroscopy of hundreds of galaxies. The grism data are used to produce spatially resolved maps of the star formation density, while the stellar mass density and optical surface brightness are obtained from multiband imaging. I will describe quantitative measures of the spatial location and extent of the star formation rate. I will show that both in clusters and in the field, Hα is more extended than the rest-frame UV continuum in 60% of the cases, consistent with diffuse star formation and inside out growth. The Hα emission appears more extended in cluster galaxies than in the field, pointing perhaps to ionized gas being stripped and/or star formation being enhanced at large radii. The peak of the Hα emission and that of the continuum are offset by less than 1 kpc. I will also correlate the properties of the Hα maps to the cluster global properties, such as the hot gas density, and the surface mass density. The characterization of the spatial distribution of Halpha provides a new window, yet poorly exploited, on the mechanisms that regulate star formation and morphological transformation in dense environments.

Recognizing Axionic Dark Matter by Compton and de Broglie Scale Modulation of Pulsar Timing.

PubMed

De Martino, Ivan; Broadhurst, Tom; Tye, S-H Henry; Chiueh, Tzihong; Schive, Hsi-Yu; Lazkoz, Ruth

2017-12-01

Light axionic dark matter, motivated by string theory, is increasingly favored for the "no weakly interacting massive particle era". Galaxy formation is suppressed below a Jeans scale of ≃10^{8}  M_{⊙} by setting the axion mass to m_{B}∼10^{-22}  eV, and the large dark cores of dwarf galaxies are explained as solitons on the de Broglie scale. This is persuasive, but detection of the inherent scalar field oscillation at the Compton frequency ω_{B}=(2.5  months)^{-1}(m_{B}/10^{-22}  eV) would be definitive. By evolving the coupled Schrödinger-Poisson equation for a Bose-Einstein condensate, we predict the dark matter is fully modulated by de Broglie interference, with a dense soliton core of size ≃150  pc, at the Galactic center. The oscillating field pressure induces general relativistic time dilation in proportion to the local dark matter density and pulsars within this dense core have detectably large timing residuals of ≃400  nsec/(m_{B}/10^{-22}  eV). This is encouraging as many new pulsars should be discovered near the Galactic center with planned radio surveys. More generally, over the whole Galaxy, differences in dark matter density between pairs of pulsars imprints a pairwise Galactocentric signature that can be distinguished from an isotropic gravitational wave background.

The Cold Side of Galaxy Formation: Dense Gas Through Cosmic Time

NASA Astrophysics Data System (ADS)

Riechers, Dominik A.; ngVLA Galaxy Assembly through Cosmic Time Science Working Group, ngVLA Galaxy Ecosystems Science Working Group

2018-01-01

The processes that lead to the formation and evolution of galaxies throughout the history of the Universe involve the complex interplay between hierarchical merging of dark matter halos, accretion of primordial and recycled gas, transport of gas within galaxy disks, accretion onto central super-massive black holes, and the formation of molecular clouds which subsequently collapse and fragment. The resulting star formation and black hole accretion provide large sources of energy and momentum that light up galaxies and lead to feedback. The ngVLA will be key to further understand how gas is accreted onto galaxies, and the processes that regulate the growth of galaxies through cosmic history. It will reveal how and on which timescales star formation and black hole accretion impact the gas in galaxies, and how the physical properties and chemical state of the gas change as gas cycles between different phases for different galaxy populations over a broad range in redshifts. The ngVLA will have the capability to carry out unbiased, large cosmic volume surveys at virtually any redshift down to an order of magnitude lower gas masses than currently possible in the critical low-level CO lines, thus exposing the evolution of gaseous reservoirs from the earliest epochs to the peak of the cosmic history of star formation. It will also image routinely and systematically the sub-kiloparsec scale distribution and kinematic structure of molecular gas in both normal main-sequence galaxies and large starbursts. The ngVLA thus is poised to revolutionize our understanding of galaxy evolution through cosmic time.

Spatially resolved analysis of superluminous supernovae PTF 11hrq and PTF 12dam host galaxies

NASA Astrophysics Data System (ADS)

Cikota, Aleksandar; De Cia, Annalisa; Schulze, Steve; Vreeswijk, Paul M.; Leloudas, Giorgos; Gal-Yam, Avishay; Perley, Daniel A.; Cikota, Stefan; Kim, Sam; Patat, Ferdinando; Lunnan, Ragnhild; Quimby, Robert; Yaron, Ofer; Yan, Lin; Mazzali, Paolo A.

2017-08-01

Superluminous supernovae (SLSNe) are the most luminous supernovae in the Universe. They are found in extreme star-forming galaxies and are probably connected with the death of massive stars. One hallmark of very massive progenitors would be a tendency to explode in very dense, UV-bright and blue regions. In this paper, we investigate the resolved host galaxy properties of two nearby hydrogen-poor SLSNe, PTF 11hrq and PTF 12dam. For both galaxies Hubble Space Telescope multifilter images were obtained. Additionally, we perform integral field spectroscopy of the host galaxy of PTF 11hrq using the Very Large Telescope Multi Unit Spectroscopic Explorer (VLT/MUSE), and investigate the line strength, metallicity and kinematics. Neither PTF 11hrq nor PTF 12dam occurred in the bluest part of their host galaxies, although both galaxies have overall blue UV-to-optical colours. The MUSE data reveal a bright starbursting region in the host of PTF 11hrq, although far from the SN location. The SN exploded close to a region with disturbed kinematics, bluer colour, stronger [O III] and lower metallicity. The host galaxy is likely interacting with a companion. PTF 12dam occurred in one of the brightest pixels, in a starbursting galaxy with a complex morphology and a tidal tail, where interaction is also very likely. We speculate that SLSN explosions may originate from stars generated during star formation episodes triggered by interaction. High-resolution imaging and integral field spectroscopy are fundamental for a better understanding of SLSNe explosion sites and how star formation varies across their host galaxies.

Increased Prevalence of Bent Lobes for Double-lobed Radio Galaxies in Dense Environments

NASA Astrophysics Data System (ADS)

Silverstein, Ezekiel M.; Anderson, Michael E.; Bregman, Joel N.

2018-01-01

Double-lobed radio galaxies (DLRGs) often have radio lobes that subtend an angle of less than 180°, and these bent DLRGs have been shown to associate preferentially with galaxy clusters and groups. In this study, we utilize a catalog of DLRGs in SDSS quasars with radio lobes visible in VLA FIRST 20 cm radio data. We cross-match this catalog against three catalogs of galaxies over the redshift range 0< z< 0.70, obtaining 81 tentative matches. We visually examine each match and apply a number of selection criteria, eventually obtaining a sample of 44 securely detected DLRGs, which are paired to a nearby massive galaxy, galaxy group, or galaxy cluster. Most of the DLRGs identified in this manner are not central galaxies in the systems to which they are matched. Using this sample, we quantify the projected density of these matches as a function of projected separation from the central galaxy, finding a very steep decrease in matches as the impact parameter increases (for {{Σ }}\\propto {b}-m we find m={2.5}-0.3+0.4) out to b∼ 2 Mpc. In addition, we show that the fraction of DLRGs with bent lobes also decreases with radius, so that if we exclude DLRGs associated with the central galaxy in the system, the bent fraction is 78% within 1 Mpc and 56% within 2 Mpc, compared to just 29% in the field; these differences are significant at 3.6σ and 2.8σ , respectively. This behavior is consistent with ram pressure being the mechanism that causes the lobes to bend.

The diversity of evolutionary pathways of compact elliptical galaxies in cosmological simulations

NASA Astrophysics Data System (ADS)

Wellons, Sarah

2017-01-01

Observations of the high-redshift universe have revealed a population of galaxies which are already very massive (~1e11 solar masses at z=2) and have typical sizes of < 2 kpc, much smaller than their counterparts in the local universe. How such dense, massive galaxies form, and why they appear to be less common at low redshift, have been questions of interest for both theorists and observers. I will discuss these questions in the context of the Illustris simulation, a hydrodynamical cosmological simulation in which tens of thousands of galaxies form, evolve, and interact with each other, situated within a cosmological context. I select a group of massive compact galaxies at z=2 in the simulation and trace them back and forth in time to discover both how they formed at high redshift, and what they evolve into at the present day. I find a variety of both progenitors (compact galaxies form in the simulation either via central starbursts generally brought on by mergers, or by racing out to the tip of the SF main sequence and forming very early) and descendants (many formerly-compact galaxies lurk at the core of a more massive galaxy today, others were consumed in mergers, and some evolve passively and undisturbed). I will also discuss the implications of these results for observational methods of connecting galaxy populations across redshifts - in particular, the assumption of a constant cumulative comoving number density - and suggest an improvement to this method which takes the complexity and variety of galaxies' evolutionary paths into account.

Galaxy evolution. Quasar quartet embedded in giant nebula reveals rare massive structure in distant universe.

PubMed

Hennawi, Joseph F; Prochaska, J Xavier; Cantalupo, Sebastiano; Arrigoni-Battaia, Fabrizio

2015-05-15

All galaxies once passed through a hyperluminous quasar phase powered by accretion onto a supermassive black hole. But because these episodes are brief, quasars are rare objects typically separated by cosmological distances. In a survey for Lyman-α emission at redshift z ≈ 2, we discovered a physical association of four quasars embedded in a giant nebula. Located within a substantial overdensity of galaxies, this system is probably the progenitor of a massive galaxy cluster. The chance probability of finding a quadruple quasar is estimated to be ∼10(-7), implying a physical connection between Lyman-α nebulae and the locations of rare protoclusters. Our findings imply that the most massive structures in the distant universe have a tremendous supply (≃10(11) solar masses) of cool dense (volume density ≃ 1 cm(-3)) gas, which is in conflict with current cosmological simulations. Copyright © 2015, American Association for the Advancement of Science.

Real & Simulated IFU Observations of Low-Mass Early-Type Galaxies: Environmental Influence Probed for Cluster Galaxies

NASA Astrophysics Data System (ADS)

Sybilska, Agnieszka; Łokas, Ewa Luiza; Fouquet, Sylvain

2017-03-01

We combine high-quality IFU data with a new set of numerical simulations to study low-mass early type galaxies (dEs) in dense environments. Our earlier study of dEs in the Virgo cluster has produced the first large-scale maps of kinematic and stellar population properties of dEs in those environments (Ryś et al. 2013, 2014, 2015). A quantitative discrimination between various (trans)formation processes proposed for these objects is, however, a complex issue, requiring a priori assumptions about the progenitors of galaxies we observe and study today. To bridge this gap between observations and theoretical predictions, we use the expertise gained in the IFU data analysis to look ``through the eye of SAURON'' at our new suite of high-resolution N-body simulations of dEs in the Virgo cluster. Mimicking the observers perspective as closely as possible, we can also indicate the existing instrumental and viewer limitations regarding what we are/are not able to detect as observers.

Properties of the molecular gas in the fast outflow in the Seyfert galaxy IC 5063

NASA Astrophysics Data System (ADS)

Oosterloo, Tom; Raymond Oonk, J. B.; Morganti, Raffaella; Combes, Françoise; Dasyra, Kalliopi; Salomé, Philippe; Vlahakis, Nektarios; Tadhunter, Clive

2017-12-01

We present a detailed study of the properties of the molecular gas in the fast outflow driven by the active galactic nucleus (AGN) in the nearby radio-loud Seyfert galaxy IC 5063. By using ALMA observations of a number of tracers of the molecular gas (12CO(1-0), 12CO(2-1), 12CO(3-2), 13CO(2-1) and HCO+(4-3)), we map the differences in excitation, density and temperature of the gas as function of position and kinematics. The results show that in the immediate vicinity of the radio jet, a fast outflow, with velocities up to 800 km s-1, is occurring of which the gas has high excitation with excitation temperatures in the range 30-55 K, demonstrating the direct impact of the jet on the ISM. The relative brightness of the 12CO lines, as well as that of 13CO(2-1) vs. 12CO(2-1), show that the outflow is optically thin. We estimate the mass of the molecular outflow to be at least 1.2 × 106 M⊙ and likely to be a factor between two and three larger than this value. This is similar to that of the outflow of atomic gas, but much larger than that of the ionised outflow, showing that the outflow in IC 5063 is dominated by cold gas. The total mass outflow rate we estimated to be 12 M⊙ yr-1. The mass of the outflow is much smaller than the total gas mass of the ISM of IC 5063. Therefore, although the influence of the AGN and its radio jet is very significant in the inner regions of IC 5063, globally speaking the impact will be very modest. We used RADEX non-LTE modelling to explore the physical conditions of the molecular gas in the outflow. Models with the outflowing gas being quite clumpy give the most consistent results and our preferred solutions have kinetic temperatures in the range 20-100 K and densities between 105 and 106 cm-3. The resulting pressures are 106-107.5 K cm-3, about two orders of magnitude higher than in the outer quiescent disk. The highest densities and temperatures are found in the regions with the fastest outflow. The results strongly suggest that the outflow in IC 5063 is driven by the radio plasma jet expanding into a clumpy gaseous medium and creating a cocoon of (shocked) gas which is pushed away from the jet axis resulting in a lateral outflow, very similar to what is predicted by numerical simulations.

The Two-faced Whirlpool Galaxy

NASA Image and Video Library

2017-12-08

NASA image release January 13, 2011 These images by NASA's Hubble Space Telescope show off two dramatically different face-on views of the spiral galaxy M51, dubbed the Whirlpool Galaxy. The image here, taken in visible light, highlights the attributes of a typical spiral galaxy, including graceful, curving arms, pink star-forming regions, and brilliant blue strands of star clusters. In the image above, most of the starlight has been removed, revealing the Whirlpool's skeletal dust structure, as seen in near-infrared light. This new image is the sharpest view of the dense dust in M51. The narrow lanes of dust revealed by Hubble reflect the galaxy's moniker, the Whirlpool Galaxy, as if they were swirling toward the galaxy's core. To map the galaxy's dust structure, researchers collected the galaxy's starlight by combining images taken in visible and near-infrared light. The visible-light image captured only some of the light; the rest was obscured by dust. The near-infrared view, however, revealed more starlight because near-infrared light penetrates dust. The researchers then subtracted the total amount of starlight from both images to see the galaxy's dust structure. The red color in the near-infrared image traces the dust, which is punctuated by hundreds of tiny clumps of stars, each about 65 light-years wide. These stars have never been seen before. The star clusters cannot be seen in visible light because dense dust enshrouds them. The image reveals details as small as 35 light-years across. Astronomers expected to see large dust clouds, ranging from about 100 light-years to more than 300 light-years wide. Instead, most of the dust is tied up in smooth and diffuse dust lanes. An encounter with another galaxy may have prevented giant clouds from forming. Probing a galaxy's dust structure serves as an important diagnostic tool for astronomers, providing invaluable information on how the gas and dust collapse to form stars. Although Hubble is providing incisive views of the internal structure of galaxies such as M51, the planned James Webb Space Telescope (JWST) is expected to produce even crisper images. Researchers constructed the image by combining visible-light exposures from Jan. 18 to 22, 2005, with the Advanced Camera for Surveys (ACS), and near-infrared light pictures taken in December 2005 with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Join us on Facebook Credit: NASA, ESA, M. Regan and B. Whitmore (STScI), and R. Chandar (University of Toledo)

The Two-faced Whirlpool Galaxy

NASA Image and Video Library

2011-01-13

NASA image release January 13, 2011 These images by NASA's Hubble Space Telescope show off two dramatically different face-on views of the spiral galaxy M51, dubbed the Whirlpool Galaxy. The image above, taken in visible light, highlights the attributes of a typical spiral galaxy, including graceful, curving arms, pink star-forming regions, and brilliant blue strands of star clusters. In the image here, most of the starlight has been removed, revealing the Whirlpool's skeletal dust structure, as seen in near-infrared light. This new image is the sharpest view of the dense dust in M51. The narrow lanes of dust revealed by Hubble reflect the galaxy's moniker, the Whirlpool Galaxy, as if they were swirling toward the galaxy's core. To map the galaxy's dust structure, researchers collected the galaxy's starlight by combining images taken in visible and near-infrared light. The visible-light image captured only some of the light; the rest was obscured by dust. The near-infrared view, however, revealed more starlight because near-infrared light penetrates dust. The researchers then subtracted the total amount of starlight from both images to see the galaxy's dust structure. The red color in the near-infrared image traces the dust, which is punctuated by hundreds of tiny clumps of stars, each about 65 light-years wide. These stars have never been seen before. The star clusters cannot be seen in visible light because dense dust enshrouds them. The image reveals details as small as 35 light-years across. Astronomers expected to see large dust clouds, ranging from about 100 light-years to more than 300 light-years wide. Instead, most of the dust is tied up in smooth and diffuse dust lanes. An encounter with another galaxy may have prevented giant clouds from forming. Probing a galaxy's dust structure serves as an important diagnostic tool for astronomers, providing invaluable information on how the gas and dust collapse to form stars. Although Hubble is providing incisive views of the internal structure of galaxies such as M51, the planned James Webb Space Telescope (JWST) is expected to produce even crisper images. Researchers constructed the image by combining visible-light exposures from Jan. 18 to 22, 2005, with the Advanced Camera for Surveys (ACS), and near-infrared light pictures taken in December 2005 with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). Credit: NASA, ESA, S. Beckwith (STScI), and the Hubble Heritage Team (STScI/AURA) The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Join us on Facebook

ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179

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

Zhao Yinghe; Lu, Nanyao; Xu, C. Kevin

We present our high-resolution (0.″15 × 0.″13, ∼34 pc) observations of the CO (6−5) line emission, which probes the warm and dense molecular gas, and the 434 μ m dust continuum emission in the nuclear region of the starburst galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The CO (6−5) emission is spatially distributed in filamentary structures with many dense cores and shows a velocity field that is characteristic of a circumnuclear rotating gas disk, with 90% of the rotation speed arising within a radius of ≲150 pc. At the scale of our spatial resolution, the COmore » (6−5) and dust emission peaks do not always coincide, with their surface brightness ratio varying by a factor of ∼10. This result suggests that their excitation mechanisms are likely different, as further evidenced by the southwest to northeast spatial gradient of both CO-to-dust continuum ratio and Pa- α equivalent width. Within the nuclear region (radius ∼ 300 pc) and with a resolution of ∼34 pc, the CO line flux (dust flux density) detected in our ALMA observations is 180 ± 18 Jy km s{sup −1} (71 ± 7 mJy), which accounts for 22% (2.4%) of the total value measured by Herschel .« less

Radio Interferometry with the SMA: Uncovering Hidden Star Formation in Our Extreme Galactic Center

NASA Astrophysics Data System (ADS)

Gutierrez, Elizabeth; Battersby, Cara; MacGregor, Meredith Ann

2018-01-01

Radio interferometry provides the best tool to identify embedded star-forming cores in cold, dense, molecular clouds of gas and dust. Observations at long, submillimeter wavelengths can be used to investigate the physical properties in the youngest stages of star formation. Interferometers provide the resolution necessary to resolve small scale structures like dense cores where star formation is expected to occur. CMZoom is the first large area survey of the Central Molecular Zone (CMZ) at high resolution in the submillimeter, allowing us to identify early sites of star formation. The survey uses both the subcompact and compact configurations of the Submillimeter Array (SMA) interferometric radio telescope. The CMZ, or the inner 500 pc of the Milky Way Galaxy, is a high extinction region comprised of hot, dense, and turbulent molecular gas. This region is forming about an order of magnitude fewer stars than predicted based on simple star formation prescriptions. Here, we present new high resolution images of G0.068-0.075, a region from the CMZoom survey, obtained using CASA. We highlight the importance of interferometric observations of different baseline lengths by comparing the spatial information obtained through different configurations. We will use these new images, in conjunction with the rest of the CMZoom survey, to reveal the mechanisms driving star formation at the center of the galaxy.

Instability of supersonic cold streams feeding galaxies - I. Linear Kelvin-Helmholtz instability with body modes

NASA Astrophysics Data System (ADS)

Mandelker, Nir; Padnos, Dan; Dekel, Avishai; Birnboim, Yuval; Burkert, Andreas; Krumholz, Mark R.; Steinberg, Elad

2016-12-01

Massive galaxies at high redshift are predicted to be fed from the cosmic web by narrow, dense streams of cold gas that penetrate through the hot medium encompassed by a stable shock near the virial radius of the dark-matter halo. Our long-term goal is to explore the heating and dissipation rate of the streams and their fragmentation and possible breakup, in order to understand how galaxies are fed, and how this affects their star formation rate and morphology. We present here the first step, where we analyse the linear Kelvin-Helmholtz instability (KHI) of a cold, dense slab or cylinder in 3D flowing supersonically through a hot, dilute medium. The current analysis is limited to the adiabatic case with no gravity. By analytically solving the linear dispersion relation, we find a transition from a dominance of the familiar rapidly growing surface modes in the subsonic regime to more slowly growing body modes in the supersonic regime. The system is parametrized by three parameters: the density contrast between stream and medium, the Mach number of stream velocity with respect to the medium and the stream width with respect to the halo virial radius. A realistic choice for these parameters places the streams near the mode transition, with the KHI exponential-growth time in the range 0.01-10 virial crossing times for a perturbation wavelength comparable to the stream width. We confirm our analytic predictions with idealized hydrodynamical simulations. Our linear estimates thus indicate that KHI may be effective in the evolution of streams before they reach the galaxy. More definite conclusions await the extension of the analysis to the non-linear regime and the inclusion of cooling, thermal conduction, the halo potential well, self-gravity and magnetic fields.

Accretion of clumpy cold gas onto massive black hole binaries: the challenging formation of extended circumbinary structures

NASA Astrophysics Data System (ADS)

Maureira-Fredes, Cristián; Goicovic, Felipe G.; Amaro-Seoane, Pau; Sesana, Alberto

2018-05-01

Massive black hole binaries (MBHBs) represent an unavoidable outcome of hierarchical galaxy formation, but their dynamical evolution at sub-parsec scales is poorly understood. In gas rich environments, an extended, steady circumbinary gaseous disc could play an important role in the MBHB evolution, facilitating its coalescence. However, how gas on galactic scales is transported to the nuclear region to form and maintain such a stable structure is unclear. In the aftermath of a galaxy merger, cold turbulent gas condenses into clumps and filaments that can be randomly scattered towards the nucleus. This provides a natural way of feeding the binary with intermittent pockets of gas. The aim of this work is to investigate the gaseous structures arising from this interaction. We employ a suite of smoothed-particle-hydrodynamic simulations to study the influence of the infall rate and angular momentum distribution of the incoming clouds on the formation and evolution of structures around the MBHB. We find that the continuous supply of discrete clouds is a double-edge sword, resulting in intermittent formation and disruption of circumbinary structures. Anisotropic cloud distributions featuring an excess of co-rotating events generate more prominent co-rotating circumbinary discs. Similar structures are seen when mostly counter-rotating clouds are fed to the binary, even though they are more compact and less stable. In general, our simulations do not show the formation of extended smooth and stable circumbinary discs, typically assumed in analytical and numerical investigations of the the long term evolution of MBHBs.

Pressure of the hot gas in simulations of galaxy clusters

NASA Astrophysics Data System (ADS)

Planelles, S.; Fabjan, D.; Borgani, S.; Murante, G.; Rasia, E.; Biffi, V.; Truong, N.; Ragone-Figueroa, C.; Granato, G. L.; Dolag, K.; Pierpaoli, E.; Beck, A. M.; Steinborn, Lisa K.; Gaspari, M.

2017-06-01

We analyse the radial pressure profiles, the intracluster medium (ICM) clumping factor and the Sunyaev-Zel'dovich (SZ) scaling relations of a sample of simulated galaxy clusters and groups identified in a set of hydrodynamical simulations based on an updated version of the treepm-SPH GADGET-3 code. Three different sets of simulations are performed: the first assumes non-radiative physics, the others include, among other processes, active galactic nucleus (AGN) and/or stellar feedback. Our results are analysed as a function of redshift, ICM physics, cluster mass and cluster cool-coreness or dynamical state. In general, the mean pressure profiles obtained for our sample of groups and clusters show a good agreement with X-ray and SZ observations. Simulated cool-core (CC) and non-cool-core (NCC) clusters also show a good match with real data. We obtain in all cases a small (if any) redshift evolution of the pressure profiles of massive clusters, at least back to z = 1. We find that the clumpiness of gas density and pressure increases with the distance from the cluster centre and with the dynamical activity. The inclusion of AGN feedback in our simulations generates values for the gas clumping (√{C}_{ρ }˜ 1.2 at R200) in good agreement with recent observational estimates. The simulated YSZ-M scaling relations are in good accordance with several observed samples, especially for massive clusters. As for the scatter of these relations, we obtain a clear dependence on the cluster dynamical state, whereas this distinction is not so evident when looking at the subsamples of CC and NCC clusters.

Chandra High Resolution Spectroscopy of the Circumnuclear Matter in the Broad Line Radio Galaxy, 3C 445

NASA Technical Reports Server (NTRS)

Reeves, J. N.; Gofford, J.; Braito, V.; Sambruna, R.

2010-01-01

We present evidence for X-ray line emitting and absorbing gas in the nucleus of the Broad-Line Radio Galaxy (BLRG), 3C445. A 200 ks Chandra LETG observation of 3C 445 reveals the presence of several highly ionized emission lines in the soft X-ray spectrum, primarily from the He and H-like ions of O, Ne, Mg and Si. Radiative recombination emission is detected from O VII and O VIII, indicating that the emitting gas is photoionized. The He-like emission appears to be resolved into forbidden and intercombination line components, which implies a high density of greater than 10(sup 10) cm(sup -3), while the lines are velocity broadened with a mean width of 2600 km s(sup -1). The density and widths of the ionized lines indicate an origin of the gas on sub-parsec scales in the Broad Line Region (BLR). The X-ray continuum of 3C 445 is heavily obscured by a photoionized absorber of column density N(sub H) = 2 x 10(sup 23) cm(sup -2) and ionization parameter log xi = 1.4 erg cm s(sup -1). However the view of the X-ray line emission is unobscured, which requires the absorber to be located at radii well within any parsec scale molecular torus. Instead we suggest that the X-ray absorber in 3C 445 may be associated with an outflowing, but clumpy accretion disk wind, with an observed outflow velocity of approximately 10000 km s(sup -1).

VARIABLE REDDENING AND BROAD ABSORPTION LINES IN THE NARROW-LINE SEYFERT 1 GALAXY WPVS 007: AN ORIGIN IN THE TORUS

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

Leighly, Karen M.; Cooper, Erin; Grupe, Dirk

2015-08-10

We report the discovery of an occultation event in the low-luminosity narrow-line Seyfert 1 galaxy WPVS 007 in 2015 February and March. In concert with longer timescale variability, these observations place strong constraints on the nature and location of the absorbing material. Swift monitoring has revealed a secular decrease since ∼2010 accompanied by flattening of the optical and UV photometry that suggests variable reddening. Analysis of four Hubble Space Telescope COS observations since 2010, including a Director’s Discretionary time observation during the occultation, shows that the broad-absorption-line velocity offset and the C iv emission-line width both decrease as the reddeningmore » increases. The occultation dynamical timescale, the BAL variability dynamical timescale, and the density of the BAL gas show that both the reddening material and the broad-absorption-line gas are consistent with an origin in the torus. These observations can be explained by a scenario in which the torus is clumpy with variable scale height, and the BAL gas is blown from the torus material like spray from the crest of a wave. As the obscuring material passes into our line of sight, we alternately see high-velocity broad absorption lines and a clear view to the central engine, or low-velocity broad absorption lines and strong reddening. WPVS 007 has a small black hole mass, and correspondingly short timescales, and so we may be observing behavior that is common in BALQSOs, but is not typically observable.« less

The Eagle Nebula: a spectral template for star forming regions

NASA Astrophysics Data System (ADS)

Flagey, Nicolas; Boulanger, Francois; Carey, Sean; Compiegne, Mathieu; Dwek, Eli; Habart, Emilie; Indebetouw, Remy; Montmerle, Thierry; Noriega-Crespo, Alberto

2008-03-01

IRAC and MIPS have revealed spectacular images of massive star forming regions in the Galaxy. These vivid illustrations of the interaction between the stars, through their winds and radiation, and their environment, made of gas and dust, still needs to be explained. The large scale picture of layered shells of gas components, is affected by the small scale interaction of stars with the clumpy medium that surrounds them. To understand spatial variations of physical conditions and dust properties on small scales, spectroscopic imaging observations are required on a nearby object. The iconic Eagle Nebula (M16) is one of the nearest and most observed star forming region of our Galaxy and as such, is a well suited template to obtain this missing data set. We thus propose a complete spectral map of the Eagle Nebula (M16) with the IRS/Long Low module (15-38 microns) and MIPS/SED mode (55-95 microns). Analysis of the dust emission, spectral features and continuum, and of the H2 and fine-structure gas lines within our models will provide us with constraints on the physical conditions (gas ionization state, pressure, radiation field) and dust properties (temperature, size distribution) at each position within the nebula. Only such a spatially and spectrally complete map will allow us to characterize small scale structure and dust evolution within the global context and understand the impact of small scale structure on the evolution of dusty star forming regions. This project takes advantage of the unique ability of IRS at obtaining sensitive spectral maps covering large areas.

Identifying Protoclusters in the High Redshift Universe and Mapping Their Evolution

NASA Astrophysics Data System (ADS)

Franck, Jay Robert

2018-01-01

To investigate the growth and evolution of the earliest structures in the Universe, we identify more than 200 galaxy overdensities in the Candidate Cluster and Protocluster Catalog (CCPC). This compilation is produced by mining open astronomy data sets for over-densities of high redshift galaxies that are spectroscopically confirmed. At these redshifts, the Universe is only a few billion years old. This data mining approach yields a nearly 10 fold increase in the number of known protoclusters in the literature. The CCPC also includes the highest redshift, spectroscopically confirmed protocluster at z=6.56. For nearly 1500 galaxies contained in the CCPC between redshifts of 2.02, the brightest galaxies are older and more massive than anticipated by the model.

The CGM of Massive Galaxies: Where Cold Gas Goes to Die?

NASA Astrophysics Data System (ADS)

Howk, Jay

2017-08-01

We propose to survey the cold HI content and metallicity of the circumgalactic medium (CGM) around 50 (45 new, 5 archival) z 0.5 Luminous Red Galaxies (LRGs) to directly test a fundamental prediction of galaxy assembly models: that cold, metal-poor accretion does not survive to the inner halos of very massive galaxies. Accretion and feedback through the CGM play key roles in our models of the star formation dichotomy in galaxies. Low mass galaxies are thought to accrete gas in cold streams, while high mass galaxies host hot, dense halos that heat incoming gas and prevent its cooling, thereby quenching star formation. HST/COS has provided evidence for cold, metal-poor streams in the halos of star-forming galaxies (consistent with cold accretion). Observations have also demonstrated the presence of cool gas in the halos of passive galaxies, a potential challenge to the cold/hot accretion model. Our proposed observations will target the most massive galaxies and address the origin of the cool CGM gas by measuring the metallicity. This experiment is enabled by our novel approach to deriving metallicities, allowing the use of much fainter QSOs. It cannot be done with archival data, as these rare systems are not often probed along random sight lines. The H I column density (and metallicity) measurements require access to the UV. The large size of our survey is crucial to robustly assess whether the CGM in these galaxies is unique from that of star-forming systems, a comparison that provides the most stringent test of cold-mode accretion/quenching models to date. Conversely, widespread detections of metal-poor gas in these halos will seriously challenge the prevailing theory.

Discovery of Low-ionization Envelopes in the Planetary Nebula NGC 5189: Spatially-resolved Diagnostics from HST Observations

NASA Astrophysics Data System (ADS)

Danehkar, Ashkbiz; Karovska, Margarita; Maksym, Walter Peter; Montez, Rodolfo

2018-01-01

The planetary nebula NGC 5189 shows one of the most spectacular morphological structures among planetary nebulae with [WR]-type central stars. Using high-angular resolution HST/WFC3 imaging, we discovered inner, low-ionization structures within a region of 0.3 parsec × 0.2 parsec around the central binary system. We used Hα, [O III], and [S II] emission line images to construct line-ratio diagnostic maps, which allowed us to spatially resolve two distinct low-ionization envelopes within the inner, ionized gaseous environment, extending over a distance of 0.15 pc from the central binary. Both the low-ionization envelopes appear to be expanding along a NE to SW symmetric axis. The SW envelope appears smaller than its NE counterpart. Our diagnostic maps show that highly-ionized gas surrounds these low-ionization envelopes, which also include filamentary and clumpy structures. These envelopes could be a result of a powerful outburst from the central interacting binary, when one of the companions (now a [WR] star) was in its AGB evolutionary stage, with a strong mass-loss generating dense circumstellar shells. Dense material ejected from the progenitor AGB star is likely heated up as it propagates along a symmetric axis into the previously expelled low-density material. Our new diagnostic methodology is a powerful tool for high-angular resolution mapping of low-ionization structures in other planetary nebulae with complex structures possibly caused by past outbursts from their progenitors.

Properties and spatial distribution of galaxy superclusters

NASA Astrophysics Data System (ADS)

Liivamägi, Lauri Juhan

2017-01-01

Astronomy is a science that can offer plenty of unforgettable imagery, and the large-scale distribution of galaxies is no exception. Among the first features the viewer's eye is likely to be drawn to, are large concentrations of galaxies - galaxy superclusters, contrasting to the seemingly empty regions beside them. Superclusters can extend from tens to over hundred megaparsecs, they contain from hundreds to thousands of galaxies, and many galaxy groups and clusters. Unlike galaxy clusters, superclusters are clearly unrelaxed systems, not gravitationally bound as crossing times exceed the age of the universe, and show little to no radial symmetry. Superclusters, as part of the large-scale structure, are sensitive to the initial power spectrum and the following evolution. They are massive enough to leave an imprint on the cosmic microwave background radiation. Superclusters can also provide an unique environment for their constituent galaxies and galaxy clusters. In this study we used two different observational and one simulated galaxy samples to create several catalogues of structures that, we think, correspond to what are generally considered galaxy superclusters. Superclusters were delineated as continuous over-dense regions in galaxy luminosity density fields. When calculating density fields several corrections were applied to remove small-scale redshift distortions and distance-dependent selection effects. Resulting catalogues of objects display robust statistical properties, showing that flux-limited galaxy samples can be used to create nearly volume-limited catalogues of superstructures. Generally, large superclusters can be regarded as massive, often branching filamentary structures, that are mainly characterised by their length. Smaller superclusters, on the other hand, can display a variety of shapes. Spatial distribution of superclusters shows large-scale variations, with high-density concentrations often found in semi-regularly spaced groups. Future studies are needed to quantify the relations between superclusters and finer details of the galaxy distribution. Supercluster catalogues from this thesis have already been used in numerous other studies.

High-resolution molecular line observations of active galaxies

NASA Astrophysics Data System (ADS)

García-Burillo, S.; Combes, F.; Usero, A.; Graciá-Carpio, J.

2008-10-01

The study of the content, distribution and kinematics of interstellar gas is a key to understand the origin and maintenance of both starburst and nuclear (AGN) activity in galaxies. The processes involved in AGN fueling encompass a wide range of scales, both spatial and temporal, which have to be studied. Probing the gas flow from the outer disk down to the central engine of an AGN host, requires the use of specific tracers of the interstellar medium adapted to follow the change of phase of the gas as a function of radius. Current mm-interferometers can provide a sharp view of the distribution and kinematics of molecular gas in the circumnuclear disks of galaxies through extensive CO line mapping. As such, CO maps are an essential tool to study AGN feeding mechanisms in the local universe. This is the scientific driver of the NUclei of GAlaxies (NUGA) survey, whose latest results are here reviewed. On the other hand, the use of specific molecular tracers of the dense gas phase can probe the feedback influence of activity on the chemistry and energy balance/redistribution in the interstellar medium of nearby galaxies. Millimeter interferometers are able to unveil the strong chemical differentiation present in the molecular gas disks of nearby starbursts and AGNs. Nearby active galaxies can be used as local templates to address the study of more distant galaxies where both star formation and AGN activity are deeply embedded.

A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly Luminous Galaxy Cluster

NASA Technical Reports Server (NTRS)

McDonald, M.; Bayliss, M.; Benson, B. A.; Foley, R. J.; Ruel, J.; Sullivan, P.; Veilleux, S.; Aird, K. A.; Ashby, M. L. N.; Bautz, M.;

a Snapshot Survey of X-Ray Selected Central Cluster Galaxies

NASA Astrophysics Data System (ADS)

Edge, Alastair

1999-07-01

Central cluster galaxies are the most massive stellar systems known and have been used as standard candles for many decades. Only recently have central cluster galaxies been recognised to exhibit a wide variety of small scale {<100 pc} features that can only be reliably detected with HST resolution. The most intriguing of these are dust lanes which have been detected in many central cluster galaxies. Dust is not expected to survive long in the hostile cluster environment unless shielded by the ISM of a disk galaxy or very dense clouds of cold gas. WFPC2 snapshot images of a representative subset of the central cluster galaxies from an X-ray selected cluster sample would provide important constraints on the formation and evolution of dust in cluster cores that cannot be obtained from ground-based observations. In addition, these images will allow the AGN component, the frequency of multiple nuclei, and the amount of massive-star formation in central cluster galaxies to be ass es sed. The proposed HST observatio ns would also provide high-resolution images of previously unresolved gravitational arcs in the most massive clusters in our sample resulting in constraints on the shape of the gravitational potential of these systems. This project will complement our extensive multi-frequency work on this sample that includes optical spectroscopy and photometry, VLA and X-ray images for the majority of the 210 targets.

Star birth with a chance of Winds?

NASA Image and Video Library

2017-12-08

The lesser-known constellation of Canes Venatici (The Hunting Dogs), is home to a variety of deep-sky objects — including this beautiful galaxy, known as NGC 4861. Astronomers are still debating on how to classify it. While its physical properties — such as mass, size and rotational velocity — indicate it to be a spiral galaxy, its appearance looks more like a comet with its dense, luminous “head” and dimmer “tail” trailing off. Features more fitting with a dwarf irregular galaxy. Although small and messy, galaxies like NGC 4861 provide astronomers with interesting opportunities for study. Small galaxies have lower gravitational potentials, which simply means that it takes less energy to move stuff about inside them than it does in other galaxies. As a result, moving in, around, and through such a tiny galaxy is quite easy to do, making them far more likely to be filled with streams and outflows of speedy charged particles known as galactic winds, which can flood such galaxies with little effort. These galactic winds can be powered by the ongoing process of star formation, which involves huge amounts of energy. New stars are springing into life within the bright, colorful ‘head’ of NGC 4861 and ejecting streams of high-speed particles as they do so, which flood outwards to join the wider galactic wind. While NGC 4861 would be a perfect candidate to study such winds, recent studies did not find any galactic winds in it. Image credit: ESA/Hubble & NASA

Understanding Supermassive Black Hole Growth Mechanisms in the SSA22 Protocluster

NASA Astrophysics Data System (ADS)

Bonine, Brett; Lehmer, Bret

2018-01-01

The SSA22 protocluster is a collection of galaxies at redshift z = 3.09, corresponding to a look back time of 11.6 billion years. Observations of the protocluster allow for the investigation of galaxy properties of such protocluster environments in the early universe, potentially giving insight into the formation and evolution of galaxy clusters visible in the local universe (e.g., the Coma Cluster). Compared to other field galaxies at a similar redshift, a larger fraction of galaxies in SSA22 have been found to possess active galactic nuclei (AGN). This enhanced AGN activity suggests a relationship between the environment within the cluster and the growth of supermassive black holes (SMBHs). I will clarify the role that the protocluster environment at z = 3.09 plays in enhancing the growth of SMBHs in the cluster. To accomplish this, we are analyzing recently obtained WFC3 F160W data from the Hubble Space Telescope (HST) in SSA22, and equivalent archival CANDELS data in the Hubble Deep Field-North, to compare the merger rates and stellar mass distributions of galaxies in the SSA22 protocluster and in the field. Our goal is to assess the relative role that mergers play in enhancing the SMBH growth observed in over-dense regions in the z = 3 Universe.

Clues from Bent Jets

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-04-01

Powerful jets emitted from the centers of distant galaxies make for spectacular signposts in the radio sky. Can observations of these jets reveal information about the environments that surround them?Signposts in the SkyVLA FIRST images of seven bent double-lobed radio galaxies from the authors sample. [Adapted from Silverstein et al. 2018]An active supermassive black hole lurking in a galactic center can put on quite a show! These beasts fling out accreting material, often forming intense jets that punch their way out of their host galaxies. As the jets propagate, they expand into large lobes of radio emission that we can spot from Earth observable signs of the connection between distant supermassive black holes and the galaxies in which they live.These distinctive double-lobed radio galaxies (DLRGs) dont all look the same. In particular, though the jets are emitted from the black holes two poles, the lobes of DLRGs dont always extend perfectly in opposite directions; often, the jets become bent on larger scales, appearing to us to subtend angles of less than 180 degrees.Can we use our observations of DLRG shapes and distributions to learn about their surroundings? A new study led by Ezekiel Silverstein (University of Michigan) has addressed this question by exploring DLRGs living in dense galaxy-cluster environments.Projected density of DLRGcentral galaxy matches (black) compared to a control sample of random positionscentral galaxy matches (red) for different distances from acluster center. DLRGs have a higher likelihood of being located close to a cluster center. [Silverstein et al. 2018]Living Near the HubTo build a sample of DLRGs in dense environments, Silverstein and collaborators started from a large catalog of DLRGs in Sloan Digital Sky Survey quasars with radio lobes visible in Very Large Array data. They then cross-matched these against three galaxy catalogs to produce a sample of 44 DLRGs that are each paired to a nearby massive galaxy, galaxy group, or galaxy cluster.To determine if these DLRGs locations are unusual, the authors next constructed a control sample of random galaxies using the same selection biases as their DLRG sample.Silverstein and collaborators found that the density of DLRGs as a function of distance from a cluster center drops off more rapidly than the density of galaxies in a typical cluster. Observed DLRGs are therefore more likely than random galaxies to be found near galaxy groups and clusters. The authors speculate that this may be a selection effect: DLRGs further from cluster centers may be less bright, preventing their detection.Bent Under PressureThe angle subtended by the DLRG radio lobes, plotted against the distance of the DLRG to the cluster center. Central galaxies (red circle) experience different physics and are therefore excluded from the sample. In the remaining sample, bent DLRGs appear to favor cluster centers, compared to unbent DLRGs. [Silverstein et al. 2018]In addition, Silverstein and collaborators found that location appears to affect the shape of a DLRG. Bent DLRGs (those with a measured angle between their lobes of 170 or smaller) are more likely to be found near a cluster center than unbent DLRGs (those with angles of 170180). The fraction of bent DLRGs is 78% within 3 million light-years of the cluster center, and 56% within double that distance compared to a typical fraction of just 29% in the field.These results support the idea that ram pressure the pressure experienced by a galaxy as it moves through the higher density environment closer to the center of a cluster is what bends the DLRGs.Whats next to learn? This study relies on a fairly small sample, so Silverstein and collaborators hope that future deep optical surveys will increase the completeness of cluster catalogs, enabling further testing of these outcomes and the exploration of other physics of galaxy-cluster environments.CitationEzekiel M Silverstein et al 2018 AJ 155 14. doi:10.3847/1538-3881/aa9d2e

Turbulent AGN tori .

NASA Astrophysics Data System (ADS)

Schartmann, M.; Meisenheimer, K.; Klahr, H.; Camenzind, M.; Wolf, S.; Henning, Th.

Recently, the MID-infrared Interferometric instrument (MIDI) at the VLTI has shown that dust tori in the two nearby Seyfert galaxies NGC 1068 and the Circinus galaxy are geometrically thick and can be well described by a thin, warm central disk, surrounded by a colder and fluffy torus component. By carrying out hydrodynamical simulations with the help of the TRAMP code \\citep{schartmann_Klahr_99}, we follow the evolution of a young nuclear star cluster in terms of discrete mass-loss and energy injection from stellar processes. This naturally leads to a filamentary large scale torus component, where cold gas is able to flow radially inwards. The filaments open out into a dense and very turbulent disk structure. In a post-processing step, we calculate observable quantities like spectral energy distributions or images with the help of the 3D radiative transfer code MC3D \\citep{schartmann_Wolf_03}. Good agreement is found in comparisons with data due to the existence of almost dust-free lines of sight through the large scale component and the large column densities caused by the dense disk.

Chemistry and Evolution of Interstellar Clouds

NASA Technical Reports Server (NTRS)

Wooden, D. H.; Charnley, S. B.; Ehrenfreund, P.

2003-01-01

In this chapter we describe how elements have been and are still being formed in the galaxy and how they are transformed into the reservoir of materials present at the time of formation of our protosolar nebula. We discuss the global cycle of matter, beginning at its formation site in stars, where it is ejected through winds and explosions into the diffuse interstellar medium. In the next stage of the global cycle occurs in cold, dense molecular clouds, where the complexity of molecules and ices increases relative to the diffuse ISM.. When a protostar forms in a dense core within a molecular cloud, it heats the surrounding infalling matter warms and releases molecules from the solid phase into the gas phase in a warm, dense core, sponsoring a rich gas-phase chemistry. Some material from the cold and warm regions within molecular clouds probably survives as interstellar matter in the protostellar disk. For the diffuse ISM, for cold, dense clouds, and for dense-warm cores, the physio-chemical processes that occur within the gas and solid phases are discussed in detail.

Galaxy evolution in the densest environments: HST imaging

NASA Astrophysics Data System (ADS)

Jorgensen, Inger

2013-10-01

We propose to process in a consistent fashion all available HST/ACS and WFC3 imaging of seven rich clusters of galaxies at z=1.2-1.6. The clusters are part of our larger project aimed at constraining models for galaxy evolution in dense environments from observations of stellar populations in rich z=1.2-2 galaxy clusters. The main objective is to establish the star formation {SF} history and structural evolution over this epoch during which large changes in SF rates and galaxy structure are expected to take place in cluster galaxies.The observational data required to meet our main objective are deep HST imaging and high S/N spectroscopy of individual cluster members. The HST imaging already exists for the seven rich clusters at z=1.2-1.6 included in this archive proposal. However, the data have not been consistently processed to derive colors, magnitudes, sizes and morphological parameters for all potential cluster members bright enough to be suitable for spectroscopic observations with 8-m class telescopes. We propose to carry out this processing and make all derived parameters publicly available. We will use the parameters derived from the HST imaging to {1} study the structural evolution of the galaxies, {2} select clusters and galaxies for spectroscopic observations, and {3} use the photometry and spectroscopy together for a unified analysis aimed at the SF history and structural changes. The analysis will also utilize data from the Gemini/HST Cluster Galaxy Project, which covers rich clusters at z=0.2-1.0 and for which we have similar HST imaging and high S/N spectroscopy available.

The Dense Molecular Gas and Nuclear Activity in the ULIRG IRAS 13120-5453

NASA Astrophysics Data System (ADS)

Privon, G. C.; Aalto, S.; Falstad, N.; Muller, S.; González-Alfonso, E.; Sliwa, K.; Treister, E.; Costagliola, F.; Armus, L.; Evans, A. S.; Garcia-Burillo, S.; Izumi, T.; Sakamoto, K.; van der Werf, P.; Chu, J. K.

2017-02-01

We present new Atacama Large Millimeter/submillimeter Array Band 7 (˜340 GHz) observations of the dense gas tracers HCN, HCO+, and CS in the local, single-nucleus, ultraluminous infrared galaxy IRAS 13120-5453. We find centrally enhanced HCN (4-3) emission, relative to HCO+ (4-3), but do not find evidence for radiative pumping of HCN. Considering the size of the starburst (0.5 kpc) and the estimated supernovae rate of ˜1.2 yr-1, the high HCN/HCO+ ratio can be explained by an enhanced HCN abundance as a result of mechanical heating by the supernovae, though the active galactic nucleus and winds may also contribute additional mechanical heating. The starburst size implies a high ΣIR of 4.7 × 1012 L ⊙ kpc-2, slightly below predictions of radiation-pressure limited starbursts. The HCN line profile has low-level wings, which we tentatively interpret as evidence for outflowing dense molecular gas. However, the dense molecular outflow seen in the HCN line wings is unlikely to escape the Galaxy and is destined to return to the nucleus and fuel future star formation. We also present modeling of Herschel observations of the H2O lines and find a nuclear dust temperature of ˜40 K. IRAS 13120-5453 has a lower dust temperature and ΣIR than is inferred for the systems termed “compact obscured nuclei (CONs)” (such as Arp 220 and Mrk 231). If IRAS 13120-5453 has undergone a CON phase, we are likely witnessing it at a time when the feedback has already inflated the nuclear ISM and diluted star formation in the starburst/active galactic nucleus core.

Hot Dust in Ultraluminous Infrared Galaxies

NASA Astrophysics Data System (ADS)

Shchekinov, Yu. A.; Vasiliev, E. O.

2017-12-01

Ultraluminous infrared galaxies with total luminosities an order of magnitude greater than that of our galaxy over wavelengths of λλ = 10-800 μm are characterized by a high mass concentration of dust. Because of this, the optical thickness of the interstellar gas is extremely high, especially in the central regions of the galaxies, ranging from 1 at millimeter wavelengths to 104 in the visible. The average temperature of the dust in them is about Td=30 K, but the variations from one galaxy to another are large, with Td=20-70 K. The main source of dust in these galaxies seems to be type II supernova bursts and the main heating source is stars. In addition, given that shock waves from supernovae are an effective mechanism for destruction of interstellar dust in our galaxy and the high optical thickness of the gas with respect to the heating radiation from the stars, this conclusion merits detailed analysis. This paper provides estimates of the dust mass balance and details of its heating in these galaxies based on the example of the ultraluminous galaxy closest to us, Arp 220. It is shown that when supernovae are dominant in the production and destruction of dust in the interstellar gas, the resultant dust mass fraction is close to the observed value for Arp 220. It is also found that the observed stellar population of this galaxy can support a high ( Td ≃ 67 K ) temperature if the dust in its central region is concentrated in small, dense (n 105 cm-3) clouds with radii of 0.003 ≲ pc. Mechanisms capable of maintaining an interstellar gas structure in this state are discussed.

Warm-hot gas in X-ray bright galaxy clusters and the H I-deficient circumgalactic medium in dense environments

NASA Astrophysics Data System (ADS)

Burchett, Joseph N.; Tripp, Todd M.; Wang, Q. Daniel; Willmer, Christopher N. A.; Bowen, David V.; Jenkins, Edward B.

2018-04-01

We analyse the intracluster medium (ICM) and circumgalactic medium (CGM) in seven X-ray-detected galaxy clusters using spectra of background quasi-stellar objects (QSOs) (HST-COS/STIS), optical spectroscopy of the cluster galaxies (MMT/Hectospec and SDSS), and X-ray imaging/spectroscopy (XMM-Newton and Chandra). First, we report a very low covering fraction of H I absorption in the CGM of these cluster galaxies, f_c = 25^{+25}_{-15} {per cent}, to stringent detection limits (N(H I) <1013 cm-2). As field galaxies have an H I covering fraction of ˜ 100 per cent at similar radii, the dearth of CGM H I in our data indicates that the cluster environment has effectively stripped or overionized the gaseous haloes of these cluster galaxies. Secondly, we assess the contribution of warm-hot (105-106 K) gas to the ICM as traced by O VI and broad Ly α (BLA) absorption. Despite the high signal-to-noise ratio of our data, we do not detect O VI in any cluster, and we only detect BLA features in the QSO spectrum probing one cluster. We estimate that the total column density of warm-hot gas along this line of sight totals to ˜ 3 per cent of that contained in the hot T > 107 K X-ray emitting phase. Residing at high relative velocities, these features may trace pre-shocked material outside the cluster. Comparing gaseous galaxy haloes from the low-density `field' to galaxy groups and high-density clusters, we find that the CGM is progressively depleted of H I with increasing environmental density, and the CGM is most severely transformed in galaxy clusters. This CGM transformation may play a key role in environmental galaxy quenching.

Jellyfish: Evidence of Extreme Ram-pressure Stripping in Massive Galaxy Clusters

NASA Astrophysics Data System (ADS)

Ebeling, H.; Stephenson, L. N.; Edge, A. C.

2014-02-01

Ram-pressure stripping by the gaseous intracluster medium has been proposed as the dominant physical mechanism driving the rapid evolution of galaxies in dense environments. Detailed studies of this process have, however, largely been limited to relatively modest examples affecting only the outermost gas layers of galaxies in nearby and/or low-mass galaxy clusters. We here present results from our search for extreme cases of gas-galaxy interactions in much more massive, X-ray selected clusters at z > 0.3. Using Hubble Space Telescope snapshots in the F606W and F814W passbands, we have discovered dramatic evidence of ram-pressure stripping in which copious amounts of gas are first shock compressed and then removed from galaxies falling into the cluster. Vigorous starbursts triggered by this process across the galaxy-gas interface and in the debris trail cause these galaxies to temporarily become some of the brightest cluster members in the F606W passband, capable of outshining even the Brightest Cluster Galaxy. Based on the spatial distribution and orientation of systems viewed nearly edge-on in our survey, we speculate that infall at large impact parameter gives rise to particularly long-lasting stripping events. Our sample of six spectacular examples identified in clusters from the Massive Cluster Survey, all featuring M F606W < -21 mag, doubles the number of such systems presently known at z > 0.2 and facilitates detailed quantitative studies of the most violent galaxy evolution in clusters. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-10491, -10875, -12166, and -12884.

The Distinct Build-Up Of Dense And Normal Massive Passive Galaxies In Vipers

NASA Astrophysics Data System (ADS)

Gargiulo, Adriana; Vipers Team

2017-06-01

At fixed stellar mass, the population of passive galaxies has increased its mean effective radius < Re > by a factor 5 in the last 10 Gyr, decreasing its mean stellar mass density (S = Mstar/(2πRe 2 ) by a factor >> 10. Whether this increase in < Re > is mainly due to the size-growth of individual galaxies through dry mergers, or to the fact that newly quenched galaxies have a larger size, is still matter of debate. A promising approach to shed light on this issue is to investigate the evolution of the number density of passive galaxies as a function of their mass density. In this context, massive (Mstar >10^11 Msun) passive galaxies are the most intriguing systems to study, since, in a hierarchical scenario, they are expected to accrete their stellar mass mainly by mergers. The wide area (˜ 16 sq. deg) and high sampling rate (˜ 40%) of the spectroscopic survey VIPERS allowed us to collect a sample of ˜ 2000 passive massive galaxies over the redshift range 0.5 < z < 1.0 and to study, with unprecedented statistics, the evolution of their number density as function of their mean stellar mass density in this redshift range. Taking advantage of both spectroscopic (D4000) and photometric (SED fitting) data available, we studied the age of the stellar population of passive galaxies as function both of redshift and mass density. This information, combined with the evolution of the number density allowed us to put constraints on the mass accretion scenarios of passive galaxies. In this talk I will present our results and conclusions and how they depend on the environment in which the galaxies reside.

Large-scale environments of narrow-line Seyfert 1 galaxies

NASA Astrophysics Data System (ADS)

Järvelä, E.; Lähteenmäki, A.; Lietzen, H.; Poudel, A.; Heinämäki, P.; Einasto, M.

2017-09-01

Studying large-scale environments of narrow-line Seyfert 1 (NLS1) galaxies gives a new perspective on their properties, particularly their radio loudness. The large-scale environment is believed to have an impact on the evolution and intrinsic properties of galaxies, however, NLS1 sources have not been studied in this context before. We have a large and diverse sample of 1341 NLS1 galaxies and three separate environment data sets constructed using Sloan Digital Sky Survey. We use various statistical methods to investigate how the properties of NLS1 galaxies are connected to the large-scale environment, and compare the large-scale environments of NLS1 galaxies with other active galactic nuclei (AGN) classes, for example, other jetted AGN and broad-line Seyfert 1 (BLS1) galaxies, to study how they are related. NLS1 galaxies reside in less dense environments than any of the comparison samples, thus confirming their young age. The average large-scale environment density and environmental distribution of NLS1 sources is clearly different compared to BLS1 galaxies, thus it is improbable that they could be the parent population of NLS1 galaxies and unified by orientation. Within the NLS1 class there is a trend of increasing radio loudness with increasing large-scale environment density, indicating that the large-scale environment affects their intrinsic properties. Our results suggest that the NLS1 class of sources is not homogeneous, and furthermore, that a considerable fraction of them are misclassified. We further support a published proposal to replace the traditional classification to radio-loud, and radio-quiet or radio-silent sources with a division into jetted and non-jetted sources.

Hypercat - Hypercube of AGN tori

NASA Astrophysics Data System (ADS)

Nikutta, Robert; Lopez-Rodriguez, Enrique; Ichikawa, Kohei; Levenson, Nancy A.; Packham, Christopher C.

2018-06-01

AGN unification and observations hold that a dusty torus obscures the central accretion engine along some lines of sight. SEDs of dust tori have been modeled for a long time, but resolved emission morphologies have not been studied in much detail, because resolved observations are only possible recently (VLTI,ALMA) and in the near future (TMT,ELT,GMT). Some observations challenge a simple torus model, because in several objects most of MIR emission appears to emanate from polar regions high above the equatorial plane, i.e. not where the dust supposedly resides.We introduce our software framework and hypercube of AGN tori (Hypercat) made with CLUMPY (www.clumpy.org), a large set of images (6 model parameters + wavelength) to facilitate studies of emission and dust morphologies. We make use of Hypercat to study the morphological properties of the emission and dust distributions as function of model parameters. We find that a simple clumpy torus can indeed produce 10-micron emission patterns extended in polar directions, with extension ratios compatible with those found in observations. We are able to constrain the range of parameters that produce such morphologies.

A case study for hydromagnetic outflow in active galactic nuclei: NGC 5548

NASA Astrophysics Data System (ADS)

Bottorff, Mark Clinton

1999-01-01

A hydromagnetic (MHD) wind from a clumpy molecular accretion disk surrounding a supermassive black hole is invoked to explain observed emission and absorption features of gas at UV and X-ray energies in Seyfert 1 galaxies. It is the first attempt to explain a wide range of phenomena observed on the periphery of Active Galactic Nuclei (AGN) with a single dynamical model and within the framework of the AGN unification scheme. In the first part of this thesis, the results of long- term observations of the broadline region (BLR) in the Seyfert 1 galaxy NGC 5548 are analyzed and a critical comparison with the predictions of a hydromagnetically- driven outflow model is provided. The model reproduces the basic features of C IV line variability in this AGN, i.e., time evolution of the profile shape and strength of the C IV emission line without varying the model parameters . The best fit model provides the effective size, the dominant geometry, the emissivity distribution and the 3D velocity field of the C IV BLR and constrains the mass of the central black hole to ~3×107 Msolar . The inner part of the wind in NGC 5548 appears to be responsible for the anisotropically emitted C IV line, while its outer part remains dusty and molecular, thus having similar spectral characteristics to a molecular torus. In addition, the model predicts a differential response across the C IV line profile, producing a red-side-first response in the relative velocity interval of 3,000 km s-1 to 6,000 km s -1 followed by the blue mid-wing and finally by the line core. In the second part of this dissertation, we have analyzed the UV and X-ray absorption in NGC 5548 within the framework of warm absorbing gas. We focus on two important issues: (1)compatibility of kinematics and dynamics of the MHD wind with the observed properties of warm absorbers; and (2)the relationship between the UV and X-ray absorbing gases. An in-depth comparison between the MHD wind model and the well-studied Seyfert 1 galaxy NGC 5548 is made, which at high spectral resolution exhibits a number of discrete UV absorption components. Our results show that for NGC 5548: (1)the total column densities of O VII, O VIII and H, inferred from X-ray observations are reproduced by constraining the UV ion column densities of C IV and N V in each component to lie within a factor of 2 of their observed values; (2)the warm absorbing gas exists in the outer part of the wind and is not a continuation of the flow in the broad emission-line region; and (3)the warm absorber extends both in radial and polar directions and is ionization stratified. Analysis shows that the discrete absorption components along the line-of-sight are intrinsically clumpy. The applicability of the MHD wind to warm absorbers is further tested by constructing a quasi-continuous flow model and extending it to arbitrary aspect angles. We find that the ratio of O VII to O VIII optical depths can serve as a new diagnostic of AGN aspect angle. (Abstract shortened by UMI.)

HectoMAPping the Universe. Karl Schwarzschild Award Lecture 2014

NASA Astrophysics Data System (ADS)

Geller, Margaret J.; Hwang, Ho Seong

2015-06-01

During the last three decades progress in mapping the Universe from an age of 400 000 years to the present has been stunning. Instrument/telescope combinations have naturally determined the sampling of various redshift ranges. Here we outline the impact of the Hectospec on the MMT on exploration of the Universe in the redshift range 0.2 ⪉ z ⪉ 0.8. We focus on dense redshift surveys, SHELS and HectoMAP. SHELS is a complete magnitude limited survey covering 8 square degrees. The HectoMAP survey combines a red-selected dense redshift survey and a weak lensing map covering 50 square degrees. Combining the dense redshift survey with a Subaru HyperSuprimeCam (HSC) weak lensing map will provide a powerful probe of the way galaxies trace the distribution of dark matter on a wide range of physical scales.

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

The Origin and Evolution of the Galaxy Star Formation Rate-Stellar Mass Correlation

NASA Astrophysics Data System (ADS)

Gawiser, Eric; Iyer, Kartheik

2018-01-01

The existence of a tight correlation between galaxies’ star formation rates and stellar masses is far more surprising than usually noted. However, a simple analytical calculation illustrates that the evolution of the normalization of this correlation is driven primarily by the inverse age of the universe, and that the underlying correlation is one between galaxies’ instantaneous star formation rates and their average star formation rates since the Big Bang.Our new Dense Basis method of SED fitting (Iyer & Gawiser 2017, ApJ 838, 127) allows star formation histories (SFHs) to be reconstructed, along with uncertainties, for >10,000 galaxies in the CANDELS and 3D-HST catalogs at 0.5

A Deep Look at the Fornax Cluster

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-04-01

Traditionally, dense cluster centers are cannibalistic environments, with larger galaxies stripping stars from smaller interlopers in minor mergers and dynamical harassment. A recent survey of the Fornax cluster, one example of such an environment, reveals how this cluster may have been built.Clues in HalosContext for the southern constellation Fornax (the furnace). The Fornax cluster is marked with a red circle. [ESO, IAU and Sky Telescope]Deep surveys of dense cluster environments are necessary because the imprint of mass assembly is hidden in galactic halos, the faint outer regions of galaxies. Deep observations can reveal answers to questions about how the galaxies in these extreme environments formed and evolved for instance, did the majority of the galaxies stars form in situ, or were they accreted from interactions with other galaxies?The Fornax Deep Survey (FDS) is just such a campaign. FDS uses the European Southern Observatorys VLT Survey Telescope to obtain deep photometry of the entire 26 square degrees of the Fornax cluster, a spectacular galaxy cluster located 65 million light-years away.Central ObservationsThe FDS team plans to release the full results from the survey soon. For now, in an initial study led by Enrichetta Iodice (INAFs Astronomical Observatory of Capodimonte, Italy), the team presents their first findings from the two square degrees around NGC 1399, a supergiant elliptical galaxy in the cluster center.The two main results from this study are:The discovery of a faint stellar bridge between NGC 1399 and a nearby galaxy, NGC 1387.The characterization of NGC 1399s light profile, which shows that the galaxy consists of two main components separated by a strong break. The bright central galaxy is likely composed of stars that formed in situ, whereas the exponential outer component is a stellar halo composed of stars likely captured from accretion events.What do these points tell us about the history of the center of the Fornax cluster? These observations are indications that the Fornax cluster was built up by mergers and accretion events.A Violent PastThe light profile the authors found is consistent with those of simulated galaxies whose halos were formed through the multiple accretion of progenitors. This suggests that the stellar halo of NGC 1399 has been through a major merging event.This enlarged view of NGC 1399 and 1387 in the g band (top) and gi band (bottom) gives a better view of the faint stellar stream connecting the two galaxies. North is up and east is left. [Iodice et al. 2016]The faint stellar bridge is likely a sign of an ongoing interaction between NGC 1399 and NGC 1387, in which NGC 1387s outer envelope on its east side is being stripped away. But besides this indication, there is little evidence for recent merger activity, which would usually produce a significant number of luminous stellar streams and tidal tails.The authors argue that this means that any major mergers in the Fornax cluster center probably happened in an early formation epoch. The cluster is now in a more dynamically evolved stage, in which most of the gravitational interactions between galaxies have already taken place.Follow-up kinematics studies will be crucial to further interpreting these photometric observations from the center of the Fornax cluster. In the meantime, keep an eye out for future results from FDS!CitationE. Iodice et al 2016 ApJ 820 42. doi:10.3847/0004-637X/820/1/42

Ultrafaint Dwarf Galaxies—the Lowest-mass Relics from Before Reionization

NASA Astrophysics Data System (ADS)

Bland-Hawthorn, Joss; Sutherland, Ralph; Webster, David

2015-07-01

New observations suggest that ultrafaint dwarf galaxies (UFDs)—the least luminous systems bound by dark matter halos (≲ {10}5 {L}⊙ )—may have formed before reionization. The extrapolated virial masses today are uncertain, with estimates ranging from 108 {M}⊙ to as high as 109 {M}⊙ depending on the assumed form of the underlying potential. We show that the progenitor halo masses of UFDs can, in principle, be as low as {M}{vir} ≈ 107 {M}⊙ . Under the right conditions, such a halo can survive the energy input of a supernova (SN) and its radiative progenitor. A clumpy (fractal) medium is much less susceptible to both internal and external injections of energy. It is less prone to SN sweeping (particularly if it is off-centered) because the coupling efficiency of the explosive energy is much lower than for a diffuse interstellar medium. With the aid of the 3D hydro/ionization code Fyris, we show that sufficient baryons are retained to form stars following a single SN event in dark matter halos down to {M}{vir} ≈ 107 {M}⊙ in the presence of radiative cooling. In these models, the gas survives the SN explosion, is enriched with the specific abundance yields of the discrete events, and reaches surface densities where low-mass stars can form. Our highest-resolution simulations reveal why cooling is so effective in retaining gas compared to any other factor. In the early stages, the super-hot metal-enriched SN ejecta exhibit strong cooling, leading to much of the explosive energy being lost. Consistent with earlier work, the baryons do not survive in smooth or adiabatic models in the event of an SN. The smallest galaxies may not contribute a large fraction of matter to the formation of galaxies, but they carry signatures of the earliest epochs of star formation, as we show. These signatures may allow us to distinguish a small primordial galaxy from one that was stripped down to its present size through tidal interaction. We discuss these results in the context of local UFDs and damped Lyα systems (z ˜ 2) at very low metallicity ([Fe/H] ˜ -3). We show that both classes of objects are consistent with primordial low-mass systems that have experienced only a few enrichment events.

Cosmic Star Formation - Seen from the Milky Way with AtLAST Short Contributed Talk

NASA Astrophysics Data System (ADS)

Kauffmann, Jens

2018-01-01

Herschel and Spitzer provided first truly unbiased overviews of star formation environments in the Milky Way. Today, high–powered instruments like ALMA additionally resolve the immediate birth environments of individual stars in a few selected regions throughout the Galaxy. This progress in the Milky Way is important, because the same facilities also allow us to explore how galaxies evolved over time. Was star formation more efficient in the dense molecular clouds found in starburst galaxies? Why do galaxies often follow star formation relations like those from Kennicutt & Schmidt and Gao & Solomon? A cloud-scale understanding of the star formation processes, that can only be developed in the Milky Way, is necessary to make progress. Unfortunately, ALMA can resolve the detailed substructure only in SELECTED galactic molecular clouds, given mapping with ALMA is very slow. Here I show how surveys of dust continuum and line emission provided by a large and fast single–dish telescope can overcome these critical limitations, e.g. by breaking degeneracies in current theoretical models. My discussion draws on a white papers previously developed for similar telescopes.

ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179

NASA Astrophysics Data System (ADS)

Zhao, Yinghe; Lu, Nanyao; Díaz-Santos, Tanio; Xu, C. Kevin; Gao, Yu; Charmandaris, Vassilis; van der Werf, Paul; Zhang, Zhi-Yu; Cao, Chen

2017-08-01

We present our high-resolution (0.″15 × 0.″13, ˜34 pc) observations of the CO (6-5) line emission, which probes the warm and dense molecular gas, and the 434 μm dust continuum emission in the nuclear region of the starburst galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The CO (6-5) emission is spatially distributed in filamentary structures with many dense cores and shows a velocity field that is characteristic of a circumnuclear rotating gas disk, with 90% of the rotation speed arising within a radius of ≲150 pc. At the scale of our spatial resolution, the CO (6-5) and dust emission peaks do not always coincide, with their surface brightness ratio varying by a factor of ˜10. This result suggests that their excitation mechanisms are likely different, as further evidenced by the southwest to northeast spatial gradient of both CO-to-dust continuum ratio and Pa-α equivalent width. Within the nuclear region (radius ˜ 300 pc) and with a resolution of ˜34 pc, the CO line flux (dust flux density) detected in our ALMA observations is 180 ± 18 Jy km s-1 (71 ± 7 mJy), which accounts for 22% (2.4%) of the total value measured by Herschel. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Dense Gas-Star Systems: Evolution of Supermassive Stars

NASA Astrophysics Data System (ADS)

Amaro-Seoane, P.; Spurzem, R.

In the 60s and 70s super-massive central objects (from now onwards SMOs) were thought to be the main source of active galactic nuclei (AGNs) characteristics (luminosities of L ≅1012 Lodot). The release of gravitational binding energy by the accretion of material on to an SMO in the range of 107 - 109 Modot has been suggested to be the primary powerhouse (Lynden-Bell 1969). That rather exotic idea in early time has become common sense nowadays. Not only our own galaxy harbours a few million-solar mass black hole (Genzel 2001) but also many of other non-active galaxies show kinematic and gas-dynamic evidence of these objects (Magorrian et al. 1998) The concept of central super-massive stars (SMSs henceforth) (cal M ≥ 5 × 104 Modot, where cal M is the mass of the SMS) embedded in dense stellar systems was suggested as a possible explanation for high- energy emissions phenomena occurring in AGNs and quasars (Vilkoviski 1976, Hara 1978), such as X-ray emissions (Bahcall and Ostriker, 1975). SMSs and super-massive black holes (SMBHs) are two possibilities to explain the nature of SMOs, and SMSs may be an intermediate step towards the formation of SMBHs (Rees 1984). In this paper we give the equations that describe the dynamics of such a dense star-gas system which are the basis for the code that will be used in a prochain future to simulate this scenario. We also briefly draw the mathematical fundamentals of the code.

Disentangling The Evolution Of S0 Galaxies Using Spectral Data Cubes

NASA Astrophysics Data System (ADS)

Johnston, Evelyn; Tabor, Martha; Merrifield, Michael; Aragón-Salamanca, Alfonso; Häussler, Boris; Bamford, Steven; Cappellari, Michele

2016-09-01

While it is fairly well accepted that S0 galaxies evolve from spiral disk systems, the mechanism by which they do so is not well determined. A number of processes, ranging from simply running out of gas to environmentally-driven gas removal, interactions and mergers, have been proposed, and the reality is probably that there are multiple routes between these two states.One key way to explore how the disk and bulge components in S0 galaxies reached their current states is provided by studies of their spectra: stellar population analysis provides information on the sequence in which these components formed, while the kinematic information in these data holds clues to the degree of violence in the transformation process.With the availability of large integral-field unit (IFU) spectral surveys of nearby galaxies, there is now the potential to extract this information in a systematic way, to address the questions of which evolutionary channels S0 have galaxies evolved down, and whether these channels depend on other properties of the galaxy such as its mass or environment. Accordingly, we have been developing new tools to extract optimally the information contained within such data, to isolate the spectral properties of these galaxies' disks and bulges.Results to date are already proving interesting, with bulges of S0s in clusters systematically younger than the disks that surround them, implying a last chaotic burst of star formation near their centres in a reasonably violent transition, while those in less dense environments seem to show older bulges, consistent with star formation in a spiral galaxy simply ceasing.

Galactic Dark Matter Halos and Globular Cluster Populations. III. Extension to Extreme Environments

NASA Astrophysics Data System (ADS)

Harris, William E.; Blakeslee, John P.; Harris, Gretchen L. H.

2017-02-01

The total mass {M}{GCS} in the globular cluster (GC) system of a galaxy is empirically a near-constant fraction of the total mass {M}h\\equiv {M}{bary}+{M}{dark} of the galaxy across a range of 105 in galaxy mass. This trend is radically unlike the strongly nonlinear behavior of total stellar mass M ⋆ versus M h . We discuss extensions of this trend to two more extreme situations: (a) entire clusters of galaxies and (b) the ultra-diffuse galaxies (UDGs) recently discovered in Coma and elsewhere. Our calibration of the ratio {η }M={M}{GCS}/{M}h from normal galaxies, accounting for new revisions in the adopted mass-to-light ratio for GCs, now gives {η }M=2.9× {10}-5 as the mean absolute mass fraction. We find that the same ratio appears valid for galaxy clusters and UDGs. Estimates of {η }M in the four clusters we examine tend to be slightly higher than for individual galaxies, but more data and better constraints on the mean GC mass in such systems are needed to determine if this difference is significant. We use the constancy of {η }M to estimate total masses for several individual cases; for example, the total mass of the Milky Way is calculated to be {M}h=1.1× {10}12 {M}⊙ . Physical explanations for the uniformity of {η }M are still descriptive, but point to a picture in which massive dense star clusters in their formation stages were relatively immune to the feedback that more strongly influenced lower-density regions where most stars form.

Galaxies at the Extremes: Ultradiffuse Galaxies in the Virgo Cluster

NASA Astrophysics Data System (ADS)

Mihos, Chris

2017-08-01

The ultradiffuse galaxies (UDGs) recently discovered in massive galaxy clusters presents both challenges and opportunities for our understanding of galaxy evolution in dense clusters. Such large, low density galaxies should be most vulnerable to gravitational destruction within the cluster environment. Thus their presence in cluster cores argues either that they must be stabilized by massive dark halos or else be short-lived objects undergoing rapid transformation, perhaps leading to the formation of ultracompact dwarf galaxies (UCDs) if their destruction leaves only a compact nucleus behind. We propose deep imaging of four Virgo Cluster UDGs to probe their local environment within Virgo via accurate tip of the red giant branch (TRGB) distances. With a distance precision of 1 Mpc, we will accurately place the objects in the Virgo core, cluster outskirts, or intervening field. When coupled with our extant kinematic data, we can determine whether they are infalling objects or instead have already passed through the cluster core. We will also compare their compact nuclei to Virgo UCDs, and study their globular cluster (GC) populations in detail. Probing three magnitudes beyond the turnover in the GC luminosity function, we will construct larger and cleaner GC samples than possible with ground-based imaging, using the total mass and radial extent of the globular cluster systems to estimate the dark halo mass and tidal radius for each UDG. The new information provided by HST about the local environment and intrinsic properties of these Virgo UDGs will be used in conjunction with simulation data to study cluster-driven evolution and transformation of low density galaxies.

Galaxy evolution in protoclusters

NASA Astrophysics Data System (ADS)

Muldrew, Stuart I.; Hatch, Nina A.; Cooke, Elizabeth A.

2018-01-01

We investigate galaxy evolution in protoclusters using a semi-analytic model applied to the Millennium Simulation, scaled to a Planck cosmology. We show that the model reproduces the observed behaviour of the star formation history (SFH) both in protoclusters and the field. The rate of star formation peaks ∼0.7 Gyr earlier in protoclusters than in the field and declines more rapidly afterwards. This results in protocluster galaxies forming significantly earlier: 80 per cent of their stellar mass is already formed by z = 1.4, but only 45 per cent of the field stellar mass has formed by this time. The model predicts that field and protocluster galaxies have similar average specific star-formation rates (sSFR) at z > 3, and we find evidence of an enhancement of star formation in the dense protoclusters at early times. At z < 3, protoclusters have lower sSFRs, resulting in the disparity between the SFHs. We show that the stellar mass functions of protoclusters are top-heavy compared with the field due to the early formation of massive galaxies, and the disruption and merging of low-mass satellite galaxies in the main haloes. The fundamental cause of the different SFHs and mass functions is that dark matter haloes are biased tracers of the dark matter density field: the high density of haloes and the top-heavy halo mass function in protoclusters result in the early formation then rapid merging and quenching of galaxies. We compare our results with observations from the literature and highlight which observables provide the most informative tests of galaxy formation.

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

Walker, Lisa May; Johnson, Kelsey E.; Gallagher, Sarah C.

Compact groups of galaxies provide a unique environment to study the evolution of galaxies amid frequent gravitational encounters. These nearby groups have conditions similar to those in the earlier universe when galaxies were assembled and give us the opportunity to witness hierarchical formation in progress. To understand how the compact group environment affects galaxy evolution, we examine the gas and dust in these groups. We present new single-dish GBT neutral hydrogen (H i) observations of 30 compact groups and define a new way to quantify the group H i content as the H i-to-stellar mass ratio of the group asmore » a whole. We compare the H i content with mid-IR indicators of star formation and optical [g − r] color to search for correlations between group gas content and star formation activity of individual group members. Quiescent galaxies tend to live in H i-poor groups, and galaxies with active star formation are more commonly found in H i-rich groups. Intriguingly, we also find “rogue” galaxies whose star formation does not correlate with group H i content. In particular, we identify three galaxies (NGC 2968 in RSCG 34, KUG 1131+202A in RSCG 42, and NGC 4613 in RSCG 64) whose mid-IR activity is discrepant with the H i. We speculate that this mismatch between mid-IR activity and H i content is a consequence of strong interactions in this environment that can strip H i from galaxies and abruptly affect star formation. Ultimately, characterizing how and on what timescales the gas is processed in compact groups will help us understand the interstellar medium in complex, dense environments similar to the earlier universe.« less

Hubble Views a Galactic Mega-merger

NASA Image and Video Library

2016-01-15

The subject of this NASA/ESA Hubble Space Telescope image is known as NGC 3597. It is the product of a collision between two good-sized galaxies, and is slowly evolving to become a giant elliptical galaxy. This type of galaxy has grown more and more common as the universe has evolved, with initially small galaxies merging and progressively building up into larger galactic structures over time. NGC 3597 is located approximately 150 million light-years away in the constellation of Crater (The Cup). Astronomers study NGC 3597 to learn more about how elliptical galaxies form — many ellipticals began their lives far earlier in the history of the universe. Older ellipticals are nicknamed “red and dead” by astronomers because these bloated galaxies are not anymore producing new, bluer stars, and are thus packed full of old and redder stellar populations. Before infirmity sets in, some freshly formed elliptical galaxies experience a final flush of youth, as is the case with NGC 3597. Galaxies smashing together pool their available gas and dust, triggering new rounds of star birth. Some of this material ends up in dense pockets initially called proto-globular clusters, dozens of which festoon NGC 3597. These pockets will go on to collapse and form fully-fledged globular clusters, large spheres that orbit the centers of galaxies like satellites, packed tightly full of millions of stars. Image credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

ENHANCED WARM H{sub 2} EMISSION IN THE COMPACT GROUP MID-INFRARED ''GREEN VALLEY''

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

Cluver, M. E.; Ogle, P.; Guillard, P.

2013-03-10

We present results from a Spitzer mid-infrared spectroscopy study of a sample of 74 galaxies located in 23 Hickson Compact Groups (HCGs), chosen to be at a dynamically active stage of H I depletion. We find evidence for enhanced warm H{sub 2} emission (i.e., above that associated with UV excitation in star-forming regions) in 14 galaxies ({approx}20%), with 8 galaxies having extreme values of L(H{sub 2} S(0)-S(3))/L(7.7 {mu}m polycyclic aromatic hydrocarbon), in excess of 0.07. Such emission has been seen previously in the compact group HCG 92 (Stephan's Quintet), and was shown to be associated with the dissipation of mechanicalmore » energy associated with a large-scale shock caused when one group member collided, at high velocity, with tidal debris in the intragroup medium. Similarly, shock excitation or turbulent heating is likely responsible for the enhanced H{sub 2} emission in the compact group galaxies, since other sources of heating (UV or X-ray excitation from star formation or active galactic nuclei) are insufficient to account for the observed emission. The group galaxies fall predominantly in a region of mid-infrared color-color space identified by previous studies as being connected to rapid transformations in HCG galaxy evolution. Furthermore, the majority of H{sub 2}-enhanced galaxies lie in the optical ''green valley'' between the blue cloud and red sequence, and are primarily early-type disk systems. We suggest that H{sub 2}-enhanced systems may represent a specific phase in the evolution of galaxies in dense environments and provide new insight into mechanisms which transform galaxies onto the optical red sequence.« less

EFFECT OF ENVIRONMENT ON GALAXIES' MASS-SIZE DISTRIBUTION: UNVEILING THE TRANSITION FROM OUTSIDE-IN TO INSIDE-OUT EVOLUTION

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

Cappellari, Michele

2013-11-20

The distribution of galaxies on the mass-size plane as a function of redshift or environment is a powerful test for galaxy formation models. Here we use integral-field stellar kinematics to interpret the variation of the mass-size distribution in two galaxy samples spanning extreme environmental densities. The samples are both identically and nearly mass-selected (stellar mass M {sub *} ≳ 6 × 10{sup 9} M {sub ☉}) and volume-limited. The first consists of nearby field galaxies from the ATLAS{sup 3D} parent sample. The second consists of galaxies in the Coma Cluster (Abell 1656), one of the densest environments for which good, resolvedmore » spectroscopy can be obtained. The mass-size distribution in the dense environment differs from the field one in two ways: (1) spiral galaxies are replaced by bulge-dominated disk-like fast-rotator early-type galaxies (ETGs), which follow the same mass-size relation and have the same mass distribution as in the field sample; (2) the slow-rotator ETGs are segregated in mass from the fast rotators, with their size increasing proportionally to their mass. A transition between the two processes appears around the stellar mass M {sub crit} ≈ 2 × 10{sup 11} M {sub ☉}. We interpret this as evidence for bulge growth (outside-in evolution) and bulge-related environmental quenching dominating at low masses, with little influence from merging. In contrast, significant dry mergers (inside-out evolution) and halo-related quenching drives the mass and size growth at the high-mass end. The existence of these two processes naturally explains the diverse size evolution of galaxies of different masses and the separability of mass and environmental quenching.« less

THE HALO MASS FUNCTION CONDITIONED ON DENSITY FROM THE MILLENNIUM SIMULATION: INSIGHTS INTO MISSING BARYONS AND GALAXY MASS FUNCTIONS

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

Faltenbacher, A.; Finoguenov, A.; Drory, N.

2010-03-20

The baryon content of high-density regions in the universe is relevant to two critical unanswered questions: the workings of nurture effects on galaxies and the whereabouts of the missing baryons. In this paper, we analyze the distribution of dark matter and semianalytical galaxies in the Millennium Simulation to investigate these problems. Applying the same density field reconstruction schemes as used for the overall matter distribution to the matter locked in halos, we study the mass contribution of halos to the total mass budget at various background field densities, i.e., the conditional halo mass function. In this context, we present amore » simple fitting formula for the cumulative mass function accurate to {approx}<5% for halo masses between 10{sup 10} and 10{sup 15} h {sup -1} M{sub sun}. We find that in dense environments the halo mass function becomes top heavy and present corresponding fitting formulae for different redshifts. We demonstrate that the major fraction of matter in high-density fields is associated with galaxy groups. Since current X-ray surveys are able to nearly recover the universal baryon fraction within groups, our results indicate that the major part of the so-far undetected warm-hot intergalactic medium resides in low-density regions. Similarly, we show that the differences in galaxy mass functions with environment seen in observed and simulated data stem predominantly from differences in the mass distribution of halos. In particular, the hump in the galaxy mass function is associated with the central group galaxies, and the bimodality observed in the galaxy mass function is therefore interpreted as that of central galaxies versus satellites.« less

Central Stellar Mass Deficits in the Bulges of Local Lenticular Galaxies, and the Connection with Compact z ~ 1.5 Galaxies

NASA Astrophysics Data System (ADS)

Dullo, Bililign T.; Graham, Alister W.

2013-05-01

We have used the full radial extent of images from the Hubble Space Telescope's Advanced Camera for Surveys and Wide Field Planetary Camera 2 to extract surface brightness profiles from a sample of six, local lenticular galaxy candidates. We have modeled these profiles using a core-Sérsic bulge plus an exponential disk model. Our fast rotating lenticular disk galaxies with bulge magnitudes MV <~ -21.30 mag have central stellar deficits, suggesting that these bulges may have formed from "dry" merger events involving supermassive black holes (BHs) while their surrounding disk was subsequently built up, perhaps via cold gas accretion scenarios. The central stellar mass deficits M def are roughly 0.5-2 M BH (BH mass), rather than ~10-20 M BH as claimed from some past studies, which is in accord with core-Sérsic model mass deficit measurements in elliptical galaxies. Furthermore, these bulges have Sérsic indices n ~3, half-light radii Re < 2 kpc and masses >1011 M ⊙, and therefore appear to be descendants of the compact galaxies reported at z ~ 1.5-2. Past studies which have searched for these local counterparts by using single-component galaxy models to provide the z ~ 0 size comparisons have overlooked these dense, compact, and massive bulges in today's early-type disk galaxies. This evolutionary scenario not only accounts for what are today generally old bulges—which must be present in z ~ 1.5 images—residing in what are generally young disks, but it eliminates the uncomfortable suggestion of a factor of three to five growth in size for the compact, z ~ 1.5 galaxies that are known to possess infant disks.

The Number Density of Quiescent Compact Galaxies at Intermediate Redshift

NASA Astrophysics Data System (ADS)

Damjanov, Ivana; Hwang, Ho Seong; Geller, Margaret J.; Chilingarian, Igor

2014-09-01

Massive compact systems at 0.2 < z < 0.6 are the missing link between the predominantly compact population of massive quiescent galaxies at high redshift and their analogs and relics in the local volume. The evolution in number density of these extreme objects over cosmic time is the crucial constraining factor for the models of massive galaxy assembly. We select a large sample of ~200 intermediate-redshift massive compacts from the Baryon Oscillation Spectroscopic Survey (BOSS) spectroscopy by identifying point-like Sloan Digital Sky Survey photometric sources with spectroscopic signatures of evolved redshifted galaxies. A subset of our targets have publicly available high-resolution ground-based images that we use to augment the dynamical and stellar population properties of these systems by their structural parameters. We confirm that all BOSS compact candidates are as compact as their high-redshift massive counterparts and less than half the size of similarly massive systems at z ~ 0. We use the completeness-corrected numbers of BOSS compacts to compute lower limits on their number densities in narrow redshift bins spanning the range of our sample. The abundance of extremely dense quiescent galaxies at 0.2 < z < 0.6 is in excellent agreement with the number densities of these systems at high redshift. Our lower limits support the models of massive galaxy assembly through a series of minor mergers over the redshift range 0 < z < 2.

Early Formed Astrophysical Objects and Cosmological Antimatter

NASA Astrophysics Data System (ADS)

Dolgov, Alexander D.

Astronomical observations of recent years show that the universe at high redshifts (about ten) is densely populated by early formed objects: bright galaxies, quasars, gamma-bursters, and it contains a lot of metals and dust. Such a rich variety of early formed objects have not been expected in the standard model of formation of astrophysical objects. There is serious tension between the standard theory and the observations. We describe the model which relaxes this tension and nicely fits the data. The model naturally leads to the creation of cosmologically significant antimatter which may be abundant even in the Galaxy. Phenomenological consequences of our scenario and the possibility of distant registration of antimatter are discussed.

Early formed astrophysical objects and cosmological antimatter

NASA Astrophysics Data System (ADS)

Dolgov, Alexander D.

2016-10-01

Astronomical observations of recent years show that the universe at high redshifts (about ten) is densely populated by early formed objects: bright galaxies, quasars, gamma-bursters, and it contains a lot of metals and dust. Such a rich variety of early formed objects have not been expected in the standard model of formation of astrophysical objects. There is serious tension between the standard theory and the observations. We describe the model which relaxes this tension and nicely fits the data. The model naturally leads to the creation of cosmologically significant antimatter which may be abundant even in the Galaxy. Phenomenological consequences of our scenario and the possibility of distant registration of antimatter are discussed.

The nature, origin and evolution of embedded star clusters

NASA Technical Reports Server (NTRS)

Lada, Charles J.; Lada, Elizabeth A.

1991-01-01

The recent development of imaging infrared array cameras has enabled the first systematic studies of embedded protoclusters in the galaxy. Initial investigations suggest that rich embedded clusters are quite numerous and that a significant fraction of all stars formed in the galaxy may begin their lives in such stellar systems. These clusters contain extremely young stellar objects and are important laboratories for star formation research. However, observational and theoretical considerations suggest that most embedded clusters do not survive emergence from molecular clouds as bound clusters. Understanding the origin, nature, and evolution of embedded clusters requires understanding the intimate physical relation between embedded clusters and the dense molecular cloud cores from which they form.

Witnessing Atmospheric Motions in Cool Evolved Stars with VLTI/Amber

NASA Astrophysics Data System (ADS)

Ohnaka, Keiichi

2018-04-01

Studies of the mass loss from stars in late evolutionary stages are of utmost importance for improving our understanding of not only stellar evolution but also the chemical enrichment of galaxies. Despite such importance, the mass loss from cool evolved stars is one of the long-standing problems in stellar astrophysics. Milliarcsecond resolution achieved by optical/infrared long-baseline interferometry provides a unique opportunity to spatially resolve this innermost key region. We have recently succeeded not only in imaging the surface of the red supergiant Antares in the 2.3 micron CO lines in unprecedented detail but also in witnessing, for the first time, the complex gas dynamics over the surface and atmosphere of the star. Our 2-D velocity field map of Antares reveals vigorous upwelling and downdrafting motions of large gas clumps in the atmosphere extending out to 1.7 stellar radii. This suggests that the mass loss in red supergiants may be launched in a turbulent, clumpy manner. We will also present preliminary results of the velocity-resolved imaging of an AGB star. Our work opens an entirely new window to observe stars just like in observations of the Sun.

Hubble Space Telescope imaging of Eta Carinae

NASA Technical Reports Server (NTRS)

Hester, J. J.; Westphal, James A.; Light, Robert M.; Currie, Douglas G.; Groth, Edward J.

1991-01-01

New high spatial resolution observations of the material around Eta Carinae, obtained with the Hubble Space Telescope Wide Field/Planetary Camera, are presented. The star Eta Carinae is one of the most massive and luminous stars in the Galaxy, and has been episodically expelling significant quantities of gas over the last few centuries. The morphology of the bright central nebulosity (the homunculus) indicates that it is a thin shell with very well defined edges, and is clumpy on 0.2 arcsec (about 10 to the 16th cm) scales. An extension to the northeast of the star (NN/NS using Walborn's 1976 nomenclature) appears to be a stellar jet and its associated bow shock. The bow shock is notable for an intriguing series of parallel linear features across its face. The S ridge and the W arc appear to be part of a 'cap' of emission located to the SW and behind the star. Together, the NE jet and the SW cap suggest that the symmetry axis for the system runs NE-SW rather than SE-NW, as previously supposed. Overall, the data indicate that the material around the star may represent an oblate shell with polar blowouts, rather than a bipolar flow.

The H I chronicles of LITTLE THINGS blue compact dwarf galaxies

NASA Astrophysics Data System (ADS)

Ashley, Trisha Lynn

Star formation occurs when the gas (mostly atomic hydrogen; H I) in a galaxy becomes disturbed, forming regions of high density gas, which then collapses to form stars. In dwarf galaxies it is still uncertain which processes contribute to star formation and how much they contribute to star formation. Blue compact dwarf (BCD) galaxies are low mass, low shear, gas rich galaxies that have high star formation rates when compared to other dwarf galaxies. What triggers the dense burst of star formation in BCDs but not other dwarfs is not well understood. It is often suggested that BCDs may have their starburst triggered by gravitational interactions with other galaxies, dwarf-dwarf galaxy mergers, or consumption of intergalactic gas. However, there are BCDs that appear isolated with respect to other galaxies, making an external disturbance unlikely. Here, I study six apparently isolated BCDs from the LITTLE THINGS sample in an attempt to understand what has triggered their burst of star formation. LITTLE THINGS is an H I survey of 41 dwarf galaxies. Each galaxy has high angular and velocity resolution H I data from the Very Large Array (VLA) telescope and ancillary stellar data. I use these data to study the detailed morphology and kinematics of each galaxy, looking for signatures of starburst triggers. In addition to the VLA data, I have collected Green Bank Telescope data for the six BCDs. These high sensitivity, low resolution data are used to search the surrounding area of each galaxy for extended emission and possible nearby companion galaxies. The VLA data show evidence that each BCD has likely experienced some form of external disturbance despite their apparent isolation. These external disturbances potentially seen in the sample include: ongoing/advanced dwarf-dwarf mergers, an interaction with an unknown external object, and external gas consumption. The GBT data result in no nearby, separate H I companions at the sensitivity of the data. These data therefore suggest that even though these BCDs appear isolated, they have not been evolving in isolation. It is possible that these external disturbances may have triggered the starbursts that defines them as BCDs.

Growing up in a megalopolis: environmental effects on galaxy evolution in a supercluster at z ˜ 0.65 in UKIDSS UDS

NASA Astrophysics Data System (ADS)

Galametz, Audrey; Pentericci, Laura; Castellano, Marco; Mendel, Trevor; Hartley, Will G.; Fossati, Matteo; Finoguenov, Alexis; Almaini, Omar; Beifiori, Alessandra; Fontana, Adriano; Grazian, Andrea; Scodeggio, Marco; Kocevski, Dale D.

2018-04-01

We present a large-scale galaxy structure Cl J021734-0513 at z ˜ 0.65 discovered in the UKIDSS UDS field, made of ˜20 galaxy groups and clusters, spreading over 10 Mpc. We report on a VLT/VIMOS spectroscopic follow-up program that, combined with past spectroscopy, allowed us to confirm four galaxy clusters (M200 ˜ 1014 M⊙) and a dozen associated groups and star-forming galaxy overdensities. Two additional filamentary structures at z ˜ 0.62 and 0.69 and foreground and background clusters at 0.6 < z < 0.7 were also confirmed along the line of sight. The structure subcomponents are at different formation stages. The clusters have a core dominated by passive galaxies and an established red sequence. The remaining structures are a mix of star-forming galaxy overdensities and forming groups. The presence of quiescent galaxies in the core of the latter shows that `pre-processing' has already happened before the groups fall into their more massive neighbours. Our spectroscopy allows us to derive spectral index measurements e.g. emission/absorption line equivalent widths, strength of the 4000 Å break, valuable to investigate the star formation history of structure members. Based on these line measurements, we select a population of `post-starburst' galaxies. These galaxies are preferentially found within the virial radius of clusters, supporting a scenario in which their recent quenching could be prompted by gas stripping by the dense intracluster medium. We derive stellar age estimates using Markov Chain Monte Carlo-based spectral fitting for quiescent galaxies and find a correlation between ages and colours/stellar masses which favours a top-down formation scenario of the red sequence. A catalogue of ˜650 redshifts in UDS is released alongside the paper (via MNRAS online data).

On the fast quenching of young low-mass galaxies up to z ˜ 0.6. New spotlight on the lead role of environment

NASA Astrophysics Data System (ADS)

Moutard, Thibaud; Sawicki, Marcin; Arnouts, Stéphane; Golob, Anneya; Malavasi, Nicola; Adami, Christophe; Coupon, Jean; Ilbert, Olivier

2018-06-01

We investigate the connection between environment and the different quenching channels that galaxies are prone to follow in the rest-frame NUVrK colour diagram, as identified by Moutard et al. (2016b). Namely, the fast quenching channel followed by young low-mass galaxies and the slow quenching channel followed by old high-mass ones. We make use of the >22 deg2 covered the VIPERS Multi-Lambda Survey (VIPERS-MLS) to select a galaxy sample complete down to stellar masses of M* > 109.4M⊙ up to z ˜ 0.65 (M* > 108.8M⊙ up to z ˜ 0.5) and including 33,500 (43,000) quiescent galaxies properly selected at 0.2 < z < 0.65, while being characterized by reliable photometric redshifts (σδz/(1 + z) ≤ 0.04) that we use to measure galaxy local densities. We find that (1) the quiescence of low-mass [M* ≤ 109.7M⊙] galaxies requires a strong increase of the local density, which confirms the lead role played by environment in their fast quenching and, therefore, confirms that the low-mass upturn observed in the stellar mass function of quiescent galaxies is due to environmental quenching. We also observe that (2) the reservoir of low-mass star-forming galaxies located in very dense regions (prone to environmental quenching) has grown between z ˜ 0.6 and z ˜ 0.4 whilst the share of low-mass quiescent galaxies (expected to being environmentally quenched) may have simultaneously increased, which would plead for a rising importance of environmental quenching with cosmic time, compared to mass quenching. We finally discuss the composite picture of such environmental quenching of low-mass galaxies and, in particular, how this picture may be consistent with a delayed-then-rapid quenching scenario.

Neutral ISM, Ly α , and Lyman-continuum in the Nearby Starburst Haro 11

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

Rivera-Thorsen, T. Emil; Östlin, Göran; Hayes, Matthew

2017-03-01

Star-forming galaxies are believed to be a major source of Lyman continuum (LyC) radiation responsible for reionizing the early universe. Direct observations of escaping ionizing radiation have however been sparse and with low escape fractions. In the local universe, only 10 emitters have been observed, with typical escape fractions of a few percent. The mechanisms regulating this escape need to be strongly evolving with redshift in order to account for the epoch of reionization. Gas content and star formation feedback are among the main suspects, known to both regulate neutral gas coverage and evolve with cosmic time. In this paper,more » we reanalyze Hubble Space Telescope ( HST )-Cosmic Origins Spectrograph (COS) spectrocopy of the first detected local LyC leaker, Haro 11. We examine the connection between LyC leakage and Ly α line shape, and feedback-influenced neutral interstellar medium (ISM) properties like kinematics and gas distribution. We discuss the two extremes of an optically thin, density bounded ISM and a riddled, optically thick, ionization bounded ISM, and how Haro 11 fits into theoretical predictions. We find that the most likely ISM model is a clumpy neutral medium embedded in a highly ionized medium with a combined covering fraction of unity and a residual neutral gas column density in the ionized medium high enough to be optically thick to Ly α , but low enough to be at least partly transparent to LyC and undetected in Si ii. This suggests that star formation feedback and galaxy-scale interaction events play a major role in opening passageways for ionizing radiation through the neutral medium.« less

Prospects for Chemically Tagging Stars in the Galaxy

NASA Astrophysics Data System (ADS)

Ting, Yuan-Sen; Conroy, Charlie; Goodman, Alyssa

2015-07-01

It is now well-established that the elemental abundance patterns of stars hold key clues not only to their formation, but also to the assembly histories of galaxies. One of the most exciting possibilities is the use of stellar abundance patterns as “chemical tags” to identify stars that were born in the same molecular cloud. In this paper, we assess the prospects of chemical tagging as a function of several key underlying parameters. We show that in the fiducial case of 104 distinct cells in chemical space and {10}5-{10}6 stars in the survey, one can expect to detect ∼ {10}2-{10}3 groups that are ≥slant 5σ overdensities in the chemical space. However, we find that even very large overdensities in chemical space do not guarantee that the overdensity is due to a single set of stars from a common birth cloud. In fact, for our fiducial model parameters, the typical 5σ overdensity is comprised of stars from a wide range of clusters with the most dominant cluster contributing only 25% of the stars. The most important factors limiting the identification of disrupted clusters via chemical tagging are the number of chemical cells in the chemical space and the survey sampling rate of the underlying stellar population. Both of these factors can be improved through strategic observational plans. While recovering individual clusters through chemical tagging may prove challenging, we show, in agreement with previous work, that different CMFs imprint different degrees of clumpiness in chemical space. These differences provide the opportunity to statistically reconstruct the slope and high-mass cutoff of CMF and its evolution through cosmic time.

Shutting down or powering up a (U)LIRG? Merger components in distinctly different evolutionary states in IRAS 19115-2124 (the Bird)

NASA Astrophysics Data System (ADS)

Väisänen, Petri; Reunanen, Juha; Kotilainen, Jari; Mattila, Seppo; Johansson, Peter H.; Ramphul, Rajin; Romero-Cañizales, Cristina; Kuncarayakti, Hanindyo

2017-10-01

We present new SINFONI near-infrared (NIR) integral field unit (IFU) spectroscopy and Southern African Large Telescope (SALT) optical long-slit spectroscopy characterizing the history of a nearby merging luminous infrared galaxy, dubbed the Bird (IRAS19115-2124). The NIR line-ratio maps of the IFU data cubes and stellar population fitting of the SALT spectra now allow dating of the star formation (SF) over the triple system uncovered from our previous adaptive optics data. The distinct components separate clearly in line-ratio diagnostic diagrams, both thermal and non-thermal excitation is present. An off-nuclear starburst dominates the current SF of the Bird with 60-70 per cent of the total, with a 4-7 Myr age. The most massive nucleus, in contrast, is quenched with a starburst age of >40 Myr and shows hints of budding active galactic nucleus (AGN) activity. The secondary massive nucleus is at an intermediate stage. The two major components have signs of an older stellar population, consistent with a starburst triggered 1 Gyr ago in a first encounter. The simplest explanation of the history is that of a triple merger, where the strongly star-forming component has joined later. We detect multiple gas flows. The Bird offers an opportunity to witness multiple stages of galaxy evolution in the same system; triggering as well as very recent quenching of SF, and, perhaps, an early appearance of AGN activity. It also serves as a cautionary note on interpretations of observations with lower spatial resolution and/or without infrared data. At high redshift the system would look like a clumpy starburst with crucial pieces of its puzzle hidden in danger of misinterpretations.

Environmental Catastrophes in the Earth's History Due to Solar Systems Encounters with Giant Molecular Clouds

NASA Technical Reports Server (NTRS)

Pavlov, Alexander A.

2011-01-01

In its motion through the Milky Way galaxy, the solar system encounters an average density (>=330 H atoms/cubic cm) giant molecular cloud (GMC) approximately every 108 years, a dense (approx 2 x 103 H atoms/cubic cm) GMC every approx 109 years and will inevitably encounter them in the future. However, there have been no studies linking such events with severe (snowball) glaciations in Earth history. Here we show that dramatic climate change can be caused by interstellar dust accumulating in Earth's atmosphere during the solar system's immersion into a dense (approx ,2 x 103 H atoms/cubic cm) GMC. The stratospheric dust layer from such interstellar particles could provide enough radiative forcing to trigger the runaway ice-albedo feedback that results in global snowball glaciations. We also demonstrate that more frequent collisions with less dense GMCs could cause moderate ice ages.

Globular Cluster Systems in Interacting Galaxies

NASA Astrophysics Data System (ADS)

Zepf, S.; Murdin, P.

2000-11-01

GLOBULAR CLUSTERS are dynamically bound and dense collections of large numbers of coeval stars. Typical globular clusters have roughly one million stars within a radius of a few parsecs. They are also usually close to spherical, hence the name globular. By virtue of their rich, isolated population of stars they provide an important laboratory for studies of STELLAR EVOLUTION. Moreover, because of...

A model for collisionally induced disturbed structure in disk galaxies

NASA Technical Reports Server (NTRS)

Gerber, Richard A.; Lamb, Susan A.

1994-01-01

We derive analytic expressions, using the impulse and epicycle approximations, which describe the kinematic response of a disk galaxy following a collision with a second spherical galaxy which collides perpendicular to, but not through the center of, the disk. This model can reporduce the morphologies found in n-body experiments in which distant encounters produce two-armed spiral patterns and more central collisions produce rings in the disk galaxy, thereby confirming that simple kinematics can be used to describe the early evolution of these systems. Application of this procedure provides a convenient method with which to conduct parameter studies of these collisions. Comparison of the kinematic description with a fully self-gravitating, three-dimensional n-body/gasdynamics computer model shows that the disk galaxy's response is initially well represented by the kinematic model but that the self-gravity of the disk becomes important at longer times after the collision. The flows of gas and stars decouple from one another where stellar orbits cross, leaving regions of elevated gas density behind as the stars move freely past each other. If star formation rates are enhanced in these regions of high gas density, active star formation could be taking place where there is no corresponding dense feature in the old stellar population.

Spatially Resolved Imaging at 350 Micrometers of Cold Dust in Nearby Elliptical Galaxies

NASA Technical Reports Server (NTRS)

Leeuw, Lerothodi L.; Davidson, Jacqueline; Dowell, C. Darren; Matthews, Henry E.

2008-01-01

Continuum observations at 350 micrometers of seven nearby elliptical galaxies for which CO gas disks have recently been resolved with interferometry mapping are presented. These SHARC II mapping results provide the first clearly resolved far-infrared (FIR)-to-submillimeter continuum emission from cold dust (with temperatures 31 K is approximately greater than T approximately greater than 23 K) of any elliptical galaxy at a distance greater than 40 Mpc. The measured FIR excess shows that the most likely and dominant heating source of this dust is not dilute stellar radiation or cooling flows, but rather star formation that could have been triggered by an accretion or merger event and fueled by dust-rich material that has settled in a dense region cospatial with the central CO gas disks. The dust is detected even in two cluster ellipticals that are deficient in H (sub I), showing that, unlike H (sub I), cold dust and CO in ellipticals can survive in the presence of hot X-ray gas, even in galaxy clusters. No dust cooler than 20 K, either distributed outside the CO disks or cospatial with and heated by the entire dilute stellar optical galaxy (or very extended H (sub I)), is currently evident.

The formation of compact groups of galaxies. I: Optical properties

NASA Technical Reports Server (NTRS)

Diaferio, Antonaldo; Geller, Margaret J.; Ramella, Massimo

1994-01-01

The small crossing time of compact groups of galaxies (t(sub cr)H(sub 0) approximately less than 0.02) makes it hard to understand why they are observable at all. Our dissipationless N-body simulations show that within a single rich collapsing group compact groups of galaxies continually form. The mean lifetime of a particular compact configuration if approximately 1 Gyr. On this time scale, members may merge and/or other galaxies in the loose group may join the compact configuration. In other words, compact configurations are continually replaced by new systems. The frequency of this process explains the observability of compact groups. Our model produces compact configurations (compact groups (CG's) with optical properties remarkably similar to Hickson's (1982) compact groups (HCG's): (1) CG's have a frequency distribution of members similar to that of HCG's; (2) CG's are approximately equals 10 times as dense as loose groups; (3) CG's have dynamical properties remarkably similar to those of HCG's; (4) most of the galaxy members of CG's are not merger remnants. The crucial aspect of the model is the relationship between CG's and the surrounding rich loose group. Our model predicts the frequency of occurrence of CG's. A preliminary analysis of 18 rich loose groups is consistent with the model prediction. We suggest further observational tests of the model.

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

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

Brüggen, Marcus; Scannapieco, Evan

2016-05-01

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

The clumpy absorber in the high-mass X-ray binary Vela X-1

DOE PAGES

Grinberg, V.; Hell, N.; El Mellah, I.; ...

2017-12-15

Bright and eclipsing, the high-mass X-ray binary Vela X-1 offers a unique opportunity to study accretion onto a neutron star from clumpy winds of O/B stars and to disentangle the complex accretion geometry of these systems. In Chandra-HETGS spectroscopy at orbital phase ~0.25, when our line of sight towards the source does not pass through the large-scale accretion structure such as the accretion wake, we observe changes in overall spectral shape on timescales of a few kiloseconds. This spectral variability is, at least in part, caused by changes in overall absorption and we show that such strongly variable absorption cannotmore » be caused by unperturbed clumpy winds of O/B stars. We detect line features from high and low ionization species of silicon, magnesium, and neon whose strengths and presence depend on the overall level of absorption. Finally, these features imply a co-existence of cool and hot gas phases in the system, which we interpret as a highly variable, structured accretion flow close to the compact object such as has been recently seen in simulations of wind accretion in high-mass X-ray binaries.« less

The clumpy absorber in the high-mass X-ray binary Vela X-1

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

Grinberg, V.; Hell, N.; El Mellah, I.

Bright and eclipsing, the high-mass X-ray binary Vela X-1 offers a unique opportunity to study accretion onto a neutron star from clumpy winds of O/B stars and to disentangle the complex accretion geometry of these systems. In Chandra-HETGS spectroscopy at orbital phase ~0.25, when our line of sight towards the source does not pass through the large-scale accretion structure such as the accretion wake, we observe changes in overall spectral shape on timescales of a few kiloseconds. This spectral variability is, at least in part, caused by changes in overall absorption and we show that such strongly variable absorption cannotmore » be caused by unperturbed clumpy winds of O/B stars. We detect line features from high and low ionization species of silicon, magnesium, and neon whose strengths and presence depend on the overall level of absorption. Finally, these features imply a co-existence of cool and hot gas phases in the system, which we interpret as a highly variable, structured accretion flow close to the compact object such as has been recently seen in simulations of wind accretion in high-mass X-ray binaries.« less

Rapid formation of large dust grains in the luminous supernova 2010jl.

PubMed

Gall, Christa; Hjorth, Jens; Watson, Darach; Dwek, Eli; Maund, Justyn R; Fox, Ori; Leloudas, Giorgos; Malesani, Daniele; Day-Jones, Avril C

2014-07-17

The origin of dust in galaxies is still a mystery. The majority of the refractory elements are produced in supernova explosions, but it is unclear how and where dust grains condense and grow, and how they avoid destruction in the harsh environments of star-forming galaxies. The recent detection of 0.1 to 0.5 solar masses of dust in nearby supernova remnants suggests in situ dust formation, while other observations reveal very little dust in supernovae in the first few years after explosion. Observations of the spectral evolution of the bright SN 2010jl have been interpreted as pre-existing dust, dust formation or no dust at all. Here we report the rapid (40 to 240 days) formation of dust in its dense circumstellar medium. The wavelength-dependent extinction of this dust reveals the presence of very large (exceeding one micrometre) grains, which resist destruction. At later times (500 to 900 days), the near-infrared thermal emission shows an accelerated growth in dust mass, marking the transition of the dust source from the circumstellar medium to the ejecta. This provides the link between the early and late dust mass evolution in supernovae with dense circumstellar media.

An AZTEC/ASTE 1.1mm Survey Of The Young, Dense, Nearby Star-forming Region, Serpens South

NASA Astrophysics Data System (ADS)

Gutermuth, Robert A.; Bourke, T.; Matthews, B.; Dunham, M.; Allen, L.; Myers, P.; Jorgensen, J.; Wilson, G.; Yun, M.; Hughes, D.; Aretxaga, I.; Ryohei, K.; Kotaro, K.; Scott, K.; Austermann, J.

2010-01-01

The Serpens South embedded cluster, recently discovered by the Spitzer Gould Belt Legacy Survey, stands out among over 100 clusters and groups surveyed by Spitzer as the densest (>430 pc-2) and youngest (77% Class I protostars) clustered star forming region known within the nearest 400 pc. In order to better characterize the primordial structure of the cluster's natal cloud, we have made a 1.1mm dust continuum map of Serpens South from the AzTEC instrument on the 10m Atacama Submillimeter Telescope Experiment (ASTE). The projected morphology of the emission is best described by a central dense hub with numerous 0.5 pc-long filaments radiating away from the center. Large scale flux features that are typically removed via modern sky subtraction techniques are recovered using a novel iterative flux retrieval algorithm. Using standard assumptions (emissivity, dust-to-gas ratio, and T=10K), we compute the total mass of the Serpens South cloud core and filaments to be 480 Msun. We construct separate large and small scale structure maps via wavelet decomposition, and deploy a watershed structure isolation technique separately to each map in order to isolate all empirically observed substructure. This technique confirms our qualitative observation that the filaments north of the hub are notably less clumpy than those to the south, while the total mass is similar between the two regions. Both regions have relatively small numbers of young stellar objects, thus we speculate that we have caught this cloud in the act of fragmenting into pre-stellar cores.

Hubble Space Telescope and Spitzer Imaging of Red and Blue Galaxies at z ~ 2.5: A Correlation between Size and Star Formation Activity from Compact Quiescent Galaxies to Extended Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Toft, S.; van Dokkum, P.; Franx, M.; Labbe, I.; Förster Schreiber, N. M.; Wuyts, S.; Webb, T.; Rudnick, G.; Zirm, A.; Kriek, M.; van der Werf, P.; Blakeslee, J. P.; Illingworth, G.; Rix, H.-W.; Papovich, C.; Moorwood, A.

2007-12-01

We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies at 2

Why do Galaxies Stop Forming Stars? New Evidence for the Role of AGN-feedback in Driving Galaxy Bimodality

NASA Astrophysics Data System (ADS)

Bluck, Asa; Teimoorinia, Hossen; Ellison, Sara L.; Mendel, Trevor

2018-01-01

One of the most striking features of the population of local galaxies is that the distributions of several key galaxy properties are highly bimodal (e.g. color and star formation rate). In general, high mass galaxies in dense environments, with bulge-dominated morphologies and pressure supported kinematics are more frequently passive (non-star forming) than lower mass galaxies in low density environments, with disc-dominated morphologies and rotationally supported kinematics. Understanding which, if any, of these correlations is causally related to the ‘quenching’ of star formation in galaxies remains an active and hotly debated area of investigation in modern astrophysics.Theoretically, a wealth of physical processes have been evoked to account for central galaxy quenching, including halo mass quenching from virial shocks, feedback from active galactic nuclei (AGN; in either the quasar or radio mode), stabilizing torques from central mass concentrations, feedback from supernovae, or even magnetic fields interacting with the hot gas halo.I will present strong new statistical evidence which suggests that the quenched fraction of local central galaxies is primarily related to their central kinematics (Bluck et al. 2016; 2017 in prep.). I will show that this is broadly consistent with quenching from AGN feedback, through a detailed comparison with a semi-analytic model and a cosmological hydrodynamical simulation.Using a sample of over half a million local galaxies from the SDSS DR7, we go on to develop a number of sophisticated techniques, including machine learning with artificial neural networks, to rank the importance of galaxy properties to quenching (Teimoorinia, Bluck & Ellison 2016). We find that properties closely correlated with the central supermassive black hole are highly favoured statistically to predict whether a galaxy will be star forming or not. Perhaps surprisingly, stellar mass and halo mass have no impact on star formation activity in central galaxies selected at a fixed black hole mass; and environment is totally uncorrelated to quenching in centrals.I will conclude by assessing which physical mechanisms for quenching are viable in light of our new results.

Transition between order and chaos in a composite disk galaxy model with a massive nucleus and a dark matter halo

NASA Astrophysics Data System (ADS)

Caranicolas, Nicolaos D.; Zotos, Euaggelos E.

2013-02-01

We investigate the transition from regular to chaotic motion in a composite galaxy model with a disk-halo, a massive dense nucleus and a dark halo component. We obtain relationships connecting the critical value of the mass of the nucleus or the critical value of the angular momentum Lzc, with the mass Mh of the dark halo, where the transition from regular motion to chaos occurs. We also present 3D diagrams connecting the mass of nucleus the energy and the percentage of stars that can show chaotic motion. The fraction of the chaotic orbits observed in the (r,pr) phase plane, as a function of the mass of the dark halo is also computed. We use a semi-numerical method, that is a combination of theoretical and numerical procedure. The theoretical results obtained using the version 8.0 of the Mathematica package, while all the numerical calculations were made using a Bulirsch-Stöer FORTRAN routine in double precision. The results can be obtained in semi-numerical or numerical form and give good description for the connection of the physical quantities entering the model and the transition between regular and chaotic motion. We observe that the mass of the dark halo, the mass of the dense nucleus and the Lz component of the angular momentum, are important physical quantities, as they are linked to the regular or chaotic character of orbits in disk galaxies described by the model. Our numerical experiments suggest, that the amount of the dark matter plays an important role in disk galaxies represented by the model, as the mass of the halo affects, not only the regular or chaotic nature of motion but it is also connected with the existence of the different families of regular orbits. Comparison of the present results with earlier work is also presented.

Supermassive black hole formation by cold accretion shocks in the first galaxies

NASA Astrophysics Data System (ADS)

Inayoshi, Kohei; Omukai, Kazuyuki

2012-05-01

We propose a new scenario for supermassive star (SMS: >rsim 105 M⊙) formation in shocked regions of colliding cold accretion flows near the centres of the first galaxies. Recent numerical simulations indicate that assembly of a typical first galaxy with virial temperature Tvir≳104 K proceeds via cold and dense flows penetrating deep to the centre, where supersonic streams collide with each other to develop a hot (˜104 K) and dense (˜103 cm-3) shocked gas. The post-shock layer first cools by efficient Lyα emission and contracts isobarically until ≃8000 K. Whether the layer continues its isobaric contraction depends on the density at this moment: if the density is high enough to excite H2 rovibrational levels collisionally (>rsim 104 cm-3), enhanced H2 collisional dissociation suppresses the gas from cooling further. In this case, the layer fragments into massive (>rsim 105 M⊙) clouds, which collapse isothermally (˜8000 K) by Lyα cooling without subsequent fragmentation. As an outcome, SMSs are expected to form and eventually evolve into the seeds of supermassive black holes (SMBHs). By calculating the thermal evolution of the post-shock gas, we delimit the range of post-shock conditions for SMS formation, which can be expressed as T≳6000 K (nH/104 cm-3)-1 for ? and T>rsim 5000 -6000 K for nH≳104 cm-3, depending somewhat on the initial ionization degree. We found that metal enrichment does not affect the above condition for metallicity below ≃10-3 Z⊙ if metals are in the gas phase, while condensation of several per cent of metals into dust decreases this critical value of metallicity by an order of magnitude. Unlike the previously proposed scenario for SMS formation, which postulates extremely strong ultraviolet radiation to quench H2 cooling, our scenario here naturally explains SMBH seed formation in the assembly process of the first galaxies, even without such strong radiation.

Optical depth estimates and effective critical densities of dense gas tracers in the inner parts of nearby galaxy discs

NASA Astrophysics Data System (ADS)

Jiménez-Donaire, M. J.; Bigiel, F.; Leroy, A. K.; Cormier, D.; Gallagher, M.; Usero, A.; Bolatto, A.; Colombo, D.; García-Burillo, S.; Hughes, A.; Kramer, C.; Krumholz, M. R.; Meier, D. S.; Murphy, E.; Pety, J.; Rosolowsky, E.; Schinnerer, E.; Schruba, A.; Tomičić, N.; Zschaechner, L.

2017-04-01

High critical density molecular lines like HCN (1-0) or HCO+ (1-0) represent our best tool to study currently star-forming, dense molecular gas at extragalactic distances. The optical depth of these lines is a key ingredient to estimate the effective density required to excite emission. However, constraints on this quantity are even scarcer in the literature than measurements of the high-density tracers themselves. Here, we combine new observations of HCN, HCO+ and HNC (1-0) and their optically thin isotopologues H13CN, H13CO+ and HN13C (1-0) to measure isotopologue line ratios. We use IRAM 30-m observations from the large programme EMPIRE and new Atacama Large Millimetre/submillimetre Array observations, which together target six nearby star-forming galaxies. Using spectral stacking techniques, we calculate or place strong upper limits on the HCN/H13CN, HCO+/H13CO+ and HNC/HN13C line ratios in the inner parts of these galaxies. Under simple assumptions, we use these to estimate the optical depths of HCN (1-0) and HCO+ (1-0) to be τ ˜ 2-11 in the active, inner regions of our targets. The critical densities are consequently lowered to values between 5 and 20 × 105 cm-3, 1 and 3 × 105 cm-3 and 9 × 104 cm-3 for HCN, HCO+ and HNC, respectively. We study the impact of having different beam-filling factors, η, on these estimates and find that the effective critical densities decrease by a factor of η _{12}/η _{13} τ_{12}. A comparison to existing work in NGC 5194 and NGC 253 shows the HCN/H13CN and HCO+/H13CO+ ratios in agreement with our measurements within the uncertainties. The same is true for studies in other environments such as the Galactic Centre or nuclear regions of active galactic nucleus dominated nearby galaxies.

Stellar Populations and Radial Migrations in Virgo Disk Galaxies

NASA Astrophysics Data System (ADS)

Roediger, Joel C.; Courteau, Stéphane; Sánchez-Blázquez, Patricia; McDonald, Michael

2012-10-01

We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ("U-shapes") in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third (<=36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks (~11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail (>=50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely focused on field galaxies, fail to reproduce these results, thus calling for adequate hydrodynamical simulations of dense galaxy environments if we are to understand cluster disks. The current paper highlights numerous constraints for such simulations. In the Appendix, we confirm the claim by Erwin et al. that Type II breaks are absent in Virgo cluster S0s and discuss the detection of Type III breaks in such galaxies.

Accounting for the dispersion in the x ray properties of early-type galaxies

NASA Technical Reports Server (NTRS)

White, Raymond E., III; Sarazin, Craig L.

1990-01-01

The x ray luminosities of early-type galaxies are correlated with their optical (e.g., blue) luminosities (L sub X approx. L sub B exp 1.6), but the x ray luminosities exhibit considerable scatter for a given optical luminosity L sub B. This dispersion in x ray luminosity is much greater than the dispersion of other properties of early-type galaxies (for a given L sub B), such as luminosity scale-length, velocity dispersion, color, and metallicity. Here, researchers consider several possible sources for the dispersion in x ray luminosity. Some of the scatter in x ray luminosity may result from stellar population variations between galaxies with similar L sub B. Since the x ray emitting gas is from accumulated stellar mass loss, the L sub X dispersion may be due to variations in integrated stellar mass loss rates. Another possible cause of the L sub X dispersion may be variations in the amount of cool material in the galaxies; cool gas may act as an energy sink for the hot gas. Infrared emission may be used to trace such cool material, so researchers look for a correlation between the infrared emission and the x ray emission of early-type galaxies at fixed L sub B. Velocity dispersion variations between galaxies of similar L sub B may also contribute to the L sub X dispersion. The most likely a priori source of the dispersion in L sub X is probably the varying amount of ram-pressure stripping in a range of galaxy environments. The hot gaseous halos of early-type galaxies can be stripped in encounters with other galaxies or with ambient cluster gas if the intracluster gas is sufficiently dense. Researchers find that the most likely cause of dispersion in the x ray properties of early type galaxies is probably the ram-pressure stripping of gaseous halos from galaxies. For a sample of 81 early-type galaxies with x ray luminosities or upper limits derived from Einstein Observatory observations (CFT) researchers calculated the cumulative distribution of angular distances between the x ray sample members and bright galaxies from the Revised Shapley - Ames catalog. Collectively, galaxies with low x ray luminosities (for a given L sub B) tend to be in denser environments than galaxies with higher x ray luminosities.

On the Appearance of Thresholds in the Dynamical Model of Star Formation

NASA Astrophysics Data System (ADS)

Elmegreen, Bruce G.

2018-02-01

The Kennicutt–Schmidt (KS) relationship between the surface density of the star formation rate (SFR) and the gas surface density has three distinct power laws that may result from one model in which gas collapses at a fixed fraction of the dynamical rate. The power-law slope is 1 when the observed gas has a characteristic density for detection, 1.5 for total gas when the thickness is about constant as in the main disks of galaxies, and 2 for total gas when the thickness is regulated by self-gravity and the velocity dispersion is about constant, as in the outer parts of spirals, dwarf irregulars, and giant molecular clouds. The observed scaling of the star formation efficiency (SFR per unit CO) with the dense gas fraction (HCN/CO) is derived from the KS relationship when one tracer (HCN) is on the linear part and the other (CO) is on the 1.5 part. Observations of a threshold density or column density with a constant SFR per unit gas mass above the threshold are proposed to be selection effects, as are observations of star formation in only the dense parts of clouds. The model allows a derivation of all three KS relations using the probability distribution function of density with no thresholds for star formation. Failed galaxies and systems with sub-KS SFRs are predicted to have gas that is dominated by an equilibrium warm phase where the thermal Jeans length exceeds the Toomre length. A squared relation is predicted for molecular gas-dominated young galaxies.

Discovery of a Galaxy Cluster with a Violently Starbursting Core at z = 2.506

NASA Astrophysics Data System (ADS)

Wang, Tao; Elbaz, David; Daddi, Emanuele; Finoguenov, Alexis; Liu, Daizhong; Schreiber, Corentin; Martín, Sergio; Strazzullo, Veronica; Valentino, Francesco; van der Burg, Remco; Zanella, Anita; Ciesla, Laure; Gobat, Raphael; Le Brun, Amandine; Pannella, Maurilio; Sargent, Mark; Shu, Xinwen; Tan, Qinghua; Cappelluti, Nico; Li, Yanxia

2016-09-01

We report the discovery of a remarkable concentration of massive galaxies with extended X-ray emission at z spec = 2.506, which contains 11 massive (M * ≳ 1011 M ⊙) galaxies in the central 80 kpc region (11.6σ overdensity). We have spectroscopically confirmed 17 member galaxies with 11 from CO and the remaining ones from Hα. The X-ray luminosity, stellar mass content, and velocity dispersion all point to a collapsed, cluster-sized dark matter halo with mass M 200c = 1013.9±0.2 M ⊙, making it the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive galaxies classified as quiescent. The star formation rate (SFR) in the 80 kpc core reaches ˜3400 M ⊙ yr-1 with a gas depletion time of ˜200 Myr, suggesting that we caught this cluster in rapid build-up of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst fraction (˜25%, compared to 3%-5% in the field). The presence of both a collapsed, cluster-sized halo and a predominant population of massive SFGs suggests that this structure could represent an important transition phase between protoclusters and mature clusters. It provides evidence that the main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster, providing new insights into massive cluster formation at early epochs. The large integrated stellar mass at such high redshift challenges our understanding of massive cluster formation.

DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2.506

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

Wang, Tao; Elbaz, David; Daddi, Emanuele

2016-09-01

We report the discovery of a remarkable concentration of massive galaxies with extended X-ray emission at z {sub spec} = 2.506, which contains 11 massive (M {sub *} ≳ 10{sup 11} M {sub ⊙}) galaxies in the central 80 kpc region (11.6 σ overdensity). We have spectroscopically confirmed 17 member galaxies with 11 from CO and the remaining ones from H α . The X-ray luminosity, stellar mass content, and velocity dispersion all point to a collapsed, cluster-sized dark matter halo with mass M {sub 200} {sub c} = 10{sup 13.9±0.2} M {sub ⊙}, making it the most distant X-ray-detectedmore » cluster known to date. Unlike other clusters discovered so far, this structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive galaxies classified as quiescent. The star formation rate (SFR) in the 80 kpc core reaches ∼3400 M {sub ⊙} yr{sup −1} with a gas depletion time of ∼200 Myr, suggesting that we caught this cluster in rapid build-up of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst fraction (∼25%, compared to 3%–5% in the field). The presence of both a collapsed, cluster-sized halo and a predominant population of massive SFGs suggests that this structure could represent an important transition phase between protoclusters and mature clusters. It provides evidence that the main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster, providing new insights into massive cluster formation at early epochs. The large integrated stellar mass at such high redshift challenges our understanding of massive cluster formation.« less

Submillimeter Observations of CLASH 2882 and the Evolution of Dust in this Galaxy

NASA Technical Reports Server (NTRS)

Dwek, Eli; Staguhn, Johannes; Arendt, Richard G; Kovacs, Attila; Decarli, Roberto; Egami, Eiichi; Michalowski, Michal J.; Rawle, Timothy D.; Toft, Sune; Walter, Fabian

2015-01-01

Two millimeter observations of the MACS J1149.6+2223 cluster have detected a source that was consistent with the location of the lensed MACS 1149-JD galaxy at z = 9.6. A positive identification would have rendered this galaxy as the youngest dust forming galaxy in the universe. Follow up observation with the AzTEC 1.1 mm camera and the IRAM NOrthern Extended Millimeter Array (NOEMA) at 1.3 mm have not confirmed this association. In this paper we show that the NOEMA observations associate the 2 mm source with [PCB2012] 2882,12 source number 2882 in the Cluster Lensing And Supernova survey with Hubble (CLASH) catalog of MACS J1149.6 +2223. This source, hereafter referred to as CLASH 2882, is a gravitationally lensed spiral galaxy at z = 0.99. We combine the Goddard IRAM Superconducting 2-Millimeter Observer (GISMO) 2 mm and NOEMA 1.3 mm fluxes with other (rest frame) UV to far-IR observations to construct the full spectral energy distribution of this galaxy, and derive its star formation history, and stellar and interstellar dust content. The current star formation rate of the galaxy is 54/mu/Solar Mass/yr, and its dust mass is about 5 × 10(exp 7)/mu Solar Mass, where mu is the lensing magnification factor for this source, which has a mean value of 2.7. The inferred dust mass is higher than the maximum dust mass that can be produced by core collapse supernovae and evolved AGB stars. As with many other star forming galaxies, most of the dust mass in CLASH 2882 must have been accreted in the dense phases of the interstellar medium.

THE NUCLEAR ACTIVITIES OF NEARBY S0 GALAXIES

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

Xiao, Meng-Yuan; Gu, Qiu-Sheng; Chen, Yan-Mei

2016-11-01

We present a study of nuclear activities in nearby S0 galaxies. After cross-matching the Sloan Digital Sky Survey Data Release 7 with the Third Reference Catalog of Bright Galaxies (RC3) and visually checking the SDSS images, we derive a sample of 583 S0 galaxies with the central spectrophotometric information. In order to separate nebular emission lines from the underlying stellar contribution, we fit the stellar population model to the SDSS spectra of these S0 galaxies. According to the BPT diagram, we find that 8% of S0 galaxies show central star-forming activity, while the fractions of Seyfert, Composite, and low-ionization nuclearmore » emission-line regions (LINERs) are 2%, 8%, and 21.4%, respectively. We also find that star-forming S0s have the lowest stellar masses, over one magnitude lower than the others, and that the active S0s are mainly located in the sparse environment, while the normal S0s are located in the dense environment, which might suggest that the environment plays an important role in quenching star formation and/or AGN activity in S0 galaxies. By performing bulge-disk decomposition of 45 star-forming S0s in g - and r -bands with the 2D fitting software Galfit, as well as exploiting the catalog of 2D photometric decompositions of Meert et al., we find that the bulges of approximately one-third of star-forming S0 galaxies (16/45) are bluer than their disks, while for other types of S0s the bulge and disk components show similar color distributions. Besides, the Sérsic index of most star-forming S0s bulges is less than two, while for normal S0s, it is between two and six.« less

The Dust and [C II] Morphologies of Redshift ∼4.5 Sub-millimeter Galaxies at ∼200 pc Resolution: The Absence of Large Clumps in the Interstellar Medium at High-redshift

NASA Astrophysics Data System (ADS)

Gullberg, B.; Swinbank, A. M.; Smail, I.; Biggs, A. D.; Bertoldi, F.; De Breuck, C.; Chapman, S. C.; Chen, C.-C.; Cooke, E. A.; Coppin, K. E. K.; Cox, P.; Dannerbauer, H.; Dunlop, J. S.; Edge, A. C.; Farrah, D.; Geach, J. E.; Greve, T. R.; Hodge, J.; Ibar, E.; Ivison, R. J.; Karim, A.; Schinnerer, E.; Scott, D.; Simpson, J. M.; Stach, S. M.; Thomson, A. P.; van der Werf, P.; Walter, F.; Wardlow, J. L.; Weiss, A.

2018-05-01

We present deep, high-resolution (0.″03, 200 pc) ALMA Band 7 observations covering the dust continuum and [C II] λ157.7 μm emission in four z ∼ 4.4–4.8 sub-millimeter galaxies (SMGs) selected from the ALESS and AS2UDS surveys. The data show that the rest-frame 160 μm (observed 345 GHz) dust emission is consistent with smooth morphologies on kpc scales for three of the sources. One source, UDS 47.0, displays apparent substructure, but this is also consistent with a smooth morphology—as indicated by simulations showing that smooth exponential disks can appear clumpy when observed at the high angular resolution (0.″03) and depth of these observations ({σ }345{GHz}∼ 27{--}47 μJy beam‑1). The four SMGs are bright [C II] emitters. We extract [C II] spectra from the high-resolution data, and recover ∼20%–100% of the [C II] flux and ∼40%–80% of the dust continuum emission, compared to the previous lower-resolution observations. When tapered to 0.″2 resolution, our maps recover ∼80%–100% of the continuum emission, indicating that ∼60% of the emission is resolved out on ∼200 pc scales. We find that the [C II] emission in high-redshift galaxies is more spatially extended than the rest-frame 160 μm dust continuum by a factor of 1.6 ± 0.4. By considering the {L}[{{C}{{II}}]}/{L}FIR} ratio as a function of the star formation rate surface density ({{{Σ }}}SFR}), we revisit the [C II] deficit and suggest that the decline in the {L}[{{C}{{II}}]}/{L}FIR} ratio as a function of {{{Σ }}}SFR} is consistent with local processes. We also explore the physical drivers that may be responsible for these trends and can give rise to the properties found in the densest regions of SMGs.

The Central Molecular Zone of the Milky Way: Lessons about Star Formation from an extreme Environment

NASA Astrophysics Data System (ADS)

Kauffmann, Jens; Thushara Pillai, G. S.; Zhang, Qizhou; Lu, Xing; Immer, Katharina

2015-08-01

The Central Molecular Zone of the Milky Way (CMZ; innermost ~100pc) hosts a number of remarkably dense and massive clouds. These are subject to extreme environmental conditions, including very high cosmic ray fluxes and strong magnetic fields. Exploring star formation under such exceptional circumstances is essential for several of reasons. First, the CMZ permits to probe an extreme point in the star formation parameter space, which helps to test theoretical models. Second, CMZ clouds might help to understand the star formation under extreme conditions in more distant environments, such as in starbursts and the early universe.One particularly striking aspect is that — compared to the solar neighborhood — CMZ star formation in dense gas is suppressed by more than an order of magnitude (Longmore et al. 2012, Kauffmann et al. 2013). This questions current explanations for relations between the dense gas and the star formation rate (e.g., Gao & Solomon 2004, Lada et al. 2012). In other words, the unusually dense and massive CMZ molecular clouds form only very few stars, if any at all. Why is this so?Based on data from ALMA, CARMA, and SMA interferometers, we present results from the Galactic Center Molecular Cloud Survey (GCMS), the first study of a comprehensive sample of molecular clouds in the CMZ. This research yields a curious result: most of the major CMZ clouds are essentially devoid of significant substructure of the sort usually found in regions of high-mass star formation (Kauffmann et al. 2013). Preliminary analysis indicates that some clouds rather resemble homogeneous balls of gas. This suggests a highly dynamic picture of cloud evolution in the CMZ where clouds form, disperse, and re-assemble constantly. This concept is benchmarked against a new ALMA survey and first results from a legacy survey on the SMA.It is plausible that dense clouds in other galaxies have a similar internal structure. Instruments like ALMA and the JWST will soon permit to resolve such regions in nearby galaxies.

Extinction Mapping and Dust-to-Gas Ratios of Nearby Galaxies using LEGUS

NASA Astrophysics Data System (ADS)

Kahre, Lauren; Walterbos, Rene; Kim, Hwihyun; Thilker, David; Lee, Janice; LEGUS Team

2018-01-01

Dust is commonly used as a tracer for cold dense gas, either through IR and NIR emission maps or through extinction mapping, and dust abundance and gas metallicity are critical constraints for chemical and galaxy evolution models. Extinction mapping has been used to trace dust column densities in the Milky Way, the Magellanic Clouds, and M31. The maps for M31 use IR and NIR photometry of red giant branch stars, which is more difficult to obtain for more distant galaxies. Work by Kahre et al. (in prep) uses the extinctions derived for individual massive stars using the isochrone-matching method described by Kim et al. (2012) to generate extinction maps for these more distant galaxies.Isochrones of massive stars lie in the same location on a color-color diagram with little dependence on metallicity and luminosity class, so the extinction can be directly derived from the observed photometry. We generate extinction maps using photometry of massive stars from the Hubble Space Telescope for several of the nearly 50 galaxies observed by the Legacy Extragalactic Ultraviolet Survey (LEGUS). The derived extinction maps will allow us to correct ground-based and HST Halpha maps for extinction, and will be used to constrain changes in the dust-to-gas ratio across the galaxy sample and in different star formation, metallicity and morphological environments. Previous studies have found links between galaxy metallicity and the dust-to-gas mass ratio. We present a study of LEGUS galaxies spanning a range of distances, metallicities, and galaxy morphologies, expanding on our previous study of metal-poor dwarfs Holmberg I and II and giant spirals NGC 6503 and NGC 628. We see clear evidence for changes in the dust-to-gas mass ratio with changing metallicity. We also examine changes in the dust-to-gas mass ratio with galactocentric radius. Ultimately, we will provide constraints on the dust-to-gas mass ratio across a wide range of galaxy environments.

SDSS-IV MaNGA: Star Formation Cessation in Low-redshift Galaxies. I. Dependence on Stellar Mass and Structural Properties

NASA Astrophysics Data System (ADS)

Wang, Enci; Li, Cheng; Xiao, Ting; Lin, Lin; Bershady, Matthew; Law, David R.; Merrifield, Michael; Sanchez, Sebastian F.; Riffel, Rogemar A.; Riffel, Rogerio; Yan, Renbin

2018-04-01

We investigate radial gradients in the recent star formation history (SFH) of 1917 galaxies with 0.01 < z < 0.14 from the Mapping Nearby Galaxies at Apache Point Observatory project. For each galaxy, we obtain two-dimensional maps and radial profiles for three spectroscopically measured parameters that are sensitive to the recent SFH: D n (4000) (the 4000 Å break), EW(Hδ A ), and EW(Hα) (the equivalent width of the Hδ absorption and the Hα emission line). The majority of the spaxels are consistent with models of a continuously declining star formation rate, indicating that starbursts occur rarely in local galaxies with regular morphologies. We classify the galaxies into three classes: fully star-forming (SF), partly quenched (PQ), and totally quenched (TQ). The galaxies that are less massive than 1010 M ⊙ present at most weak radial gradients in the diagnostic parameters. In contrast, massive galaxies with a stellar mass above 1010 M ⊙ present significant gradients in the three diagnostic parameters if they are classified as SF or PQ but show weak gradients in D n (4000) and EW(Hδ A ) and no gradients in EW(Hα) if they are in the TQ class. This implies the existence of a critical stellar mass (∼1010 M ⊙) above which the star formation in a galaxy is shut down from the inside out. Galaxies tend to evolve synchronously from the inner to the outer regions before their mass reaches the critical value. We have further divided the sample at a fixed mass by both bulge-to-total luminosity ratio and morphological type, finding that our conclusions hold regardless of these factors; it appears that the presence of a central dense object is not a driving parameter but rather a by-product of the star formation cessation process.

New observational insight on shock interactions toward supernovae and supernova remnants

NASA Astrophysics Data System (ADS)

Kilpatrick, Charles Donald

2016-08-01

Supernovae (SNe) are energetic explosions that signal the end of a star's life. These events and the supernova remnants (SNRs) they leave behind play a central role in stellar feedback by adding energy and momentum and metals to the interstellar medium (ISM). Emission associated with these feedback processes, especially atomic and molecular line emission as well as thermal and nonthermal continuum emission is known to be enhanced in regions of high density, such as dense circumstellar matter (CSM) around SNe and molecular clouds (MCs). In this thesis, I begin with a brief overview of the physics of SN shocks in Chapter 1, focusing on a foundation for studying pan-chromatic signatures of interactions between SNe and dense environments. In Chapter 2, I examine an unusual SN with signatures of CSM interaction in the form of narrow lines of hydrogen (Type IIn) and thermal continuum emission. This SN appears to belong to a class of Type Ia SNe that shares spectroscopic features with Type IIn SNe. I discuss the difficulties of decomposing spectra in a regime where interaction occurs between SN ejecta and CSM, potentially confusing the underlying SN type. This is followed by a discussion of rebrightening that occurred at late-time in B and V band photometry of this SN, possibly associated with clumpy or dense CSM at large distances from the progenitor. In Chapter 3, I examine synchrotron emission from Cassiopeia A, observed in the Ks band over multiple epochs. The synchrotron emission is generally diffuse over the remnant, but there is one location in the southwest portion of the remnant where it appears to be enhanced and entrained as knots of emission in the SNR ejecta. I evaluate whether the Ks band knots are dominated by synchrotron emission by comparing them to other infrared and radio imaging that is known to be dominated by synchrotron emission. Concluding that they are likely synchrotron-emitting knots, I measure the magnetic field strength and electron density required for their evolution over the ˜10 yr baseline they were observed and find B 1.3 - 5.8 mG and ne ≈ 1,000 - 15,000 cm-3. The magnetic field strengths appear enhanced beyond values required by the adiabatic strong shock limit, arguing in favor of other forms of magnetic field amplification in the shock. In Chapter 4, I again discuss Cassiopeia A and interaction between the remnant and nearby MCs as seen at mid-infrared and millimeter wavelengths. I report detection of a SNR-MC interaction and analyze its signatures in broadened molecular lines. I extend this analysis in Chapter 5 to a large survey for SNR-MC interactions in the 12CO J = 2 - 1 line. Although broadened 12CO J = 2 - 1 line emission should be detectable toward virtually all SNR-MC interactions, I find relatively few examples; therefore, the number of interactions is low. This result favors mechanisms other than supernova feedback as the basic trigger for star formation. In addition, I find no significant association between TeV gamma-ray sources and MC interactions, contrary to predictions that SNR-MC interfaces are the primary venues for cosmic ray acceleration. I end this dissertation in Chapter 6 with a brief summary of my results and two extensions of this work: examining the late-time radio light curves of CSM-interacting SNe for signatures of radio synchrotron emission and dense or clumpy CSM at large distances from the progenitor and re-observing SNR-MC interactions in 12CO J = 3 - 2 in order to verify the presence of shock-heated molecular gas and perform a census on the densities and temperatures of post-shock molecular gas.

GASP. VII. Signs of Gas Inflow onto a Lopsided Galaxy

NASA Astrophysics Data System (ADS)

Vulcani, Benedetta; Poggianti, Bianca M.; Moretti, Alessia; Mapelli, Michela; Fasano, Giovanni; Fritz, Jacopo; Jaffé, Yara; Bettoni, Daniela; Gullieuszik, Marco; Bellhouse, Callum

2018-01-01

Theoretically, inflowing filaments of gas are one of the main causes of growth for a galaxy. Nonetheless, observationally, probing ongoing gas accretion is challenging. As part of the Gas Stripping Phenomena in galaxies with MUSE (GASP) program, we present the analysis of a spiral galaxy at z = 0.04648 whose characteristics indeed are consistent with a scenario in which gas accretion plays a major role. The most salient indirect parts of evidence that support this picture are as follows: (1) The galaxy is isolated, and its position rules out the mechanisms expected in dense environments. (2) It shows a pronounced lopsidedness extending toward the west. According to the spatially resolved star formation history, this component was formed < 6× {10}8 {years} ago. (3) It has many large and elongated H II regions that are an indication of a fragmentation due to disk instability. (4) The stellar and gas kinematics are quite symmetric around the same axis, but in the gas the locus of negative velocities shows a convexity toward the east, as if new gas has been infalling with different orientation and velocity. (5) The metallicity distribution is inhomogeneous and shows exceptionally steep gradients from the center toward the outskirts, especially in the southwest side. (6) The luminosity-weighted age is generally low (∼8 Gyr) and particularly low (<7 Gyr) along a trail crossing the galaxy from southwest toward the north. It might trace the path of the accreted gas. These findings point to an inflow of gas probably proceeding from the southwest side of the galaxy.

Characterizing bars in low surface brightness disc galaxies

NASA Astrophysics Data System (ADS)

Peters, Wesley; Kuzio de Naray, Rachel

2018-05-01

In this paper, we use B-band, I-band, and 3.6 μm azimuthal light profiles of four low surface brightness galaxies (LSBs; UGC 628, F568-1, F568-3, F563-V2) to characterize three bar parameters: length, strength, and corotation radius. We employ three techniques to measure the radius of the bars, including a new method using the azimuthal light profiles. We find comparable bar radii between the I-band and 3.6 μm for all four galaxies when using our azimuthal light profile method, and that our bar lengths are comparable to those in high surface brightness galaxies (HSBs). In addition, we find the bar strengths for our galaxies to be smaller than those for HSBs. Finally, we use Fourier transforms of the B-band, I-band, and 3.6 μm images to characterize the bars as either `fast' or `slow' by measuring the corotation radius via phase profiles. When using the B- and I-band phase crossings, we find three of our galaxies have faster than expected relative bar pattern speeds for galaxies expected to be embedded in centrally dense cold dark matter haloes. When using the B-band and 3.6 μm phase crossings, we find more ambiguous results, although the relative bar pattern speeds are still faster than expected. Since we find a very slow bar in F563-V2, we are confident that we are able to differentiate between fast and slow bars. Finally, we find no relation between bar strength and relative bar pattern speed when comparing our LSBs to HSBs.

Low-mass galaxy assembly in simulations: regulation of early star formation by radiation from massive stars

NASA Astrophysics Data System (ADS)

Trujillo-Gomez, Sebastian; Klypin, Anatoly; Colín, Pedro; Ceverino, Daniel; Arraki, Kenza S.; Primack, Joel

2015-01-01

Despite recent success in forming realistic present-day galaxies, simulations still form the bulk of their stars earlier than observations indicate. We investigate the process of stellar mass assembly in low-mass field galaxies, a dwarf and a typical spiral, focusing on the effects of radiation from young stellar clusters on the star formation (SF) histories. We implement a novel model of SF with a deterministic low efficiency per free-fall time, as observed in molecular clouds. Stellar feedback is based on observations of star-forming regions, and includes radiation pressure from massive stars, photoheating in H II regions, supernovae and stellar winds. We find that stellar radiation has a strong effect on the formation of low-mass galaxies, especially at z > 1, where it efficiently suppresses SF by dispersing cold and dense gas, preventing runaway growth of the stellar component. This behaviour is evident in a variety of observations but had so far eluded analytical and numerical models without radiation feedback. Compared to supernovae alone, radiation feedback reduces the SF rate by a factor of ˜100 at z ≲ 2, yielding rising SF histories which reproduce recent observations of Local Group dwarfs. Stellar radiation also produces bulgeless spiral galaxies and may be responsible for excess thickening of the stellar disc. The galaxies also feature rotation curves and baryon fractions in excellent agreement with current data. Lastly, the dwarf galaxy shows a very slow reduction of the central dark matter density caused by radiation feedback over the last ˜7 Gyr of cosmic evolution.

The Host Galaxies of Fast-Ejecta Core-Collapse Supernovae

NASA Technical Reports Server (NTRS)

Kelly, Patrick L.; Filippenko, Alexei V.; Modjaz, Maryam; Kocevski, Daniel

2014-01-01

Spectra of broad-lined Type Ic supernovae (SN Ic-BL), the only kind of SN observed at the locations of long-duration gamma-ray bursts (LGRBs), exhibit wide features indicative of high ejecta velocities ((is) approximately 0.1c). We study the host galaxies of a sample of 245 low-redshift (z (is) less than 0.2) core-collapse SN, including 17 SN Ic-BL, discovered by galaxy-untargeted searches, and 15 optically luminous and dust-obscured z (is) less than 1.2 LGRBs. We show that, in comparison with SDSS galaxies having similar stellar masses, the hosts of low-redshift SN Ic- BL and z (is) is less than 1.2 LGRBs have high stellar-mass and star-formation-rate densities. Core-collapse SN having typical ejecta velocities, in contrast, show no preference for such galaxies. Moreover, we find that the hosts of SN Ic-BL, unlike those of SN Ib/Ic and SN II, exhibit high gas velocity dispersions for their stellar masses. The patterns likely reflect variations among star-forming environments, and suggest that LGRBs can be used as probes of conditions in high-redshift galaxies. They may be caused by efficient formation of massive binary progenitors systems in densely star-forming regions, or, less probably, a higher fraction of stars created with the initial masses required for a SN Ic-BL or LGRB. Finally, we show that the preference of SN Ic-BL and LGRBs for galaxies with high stellar-mass and star-formation-rate densities cannot be attributed to a preference for low metal abundances but must reflect the influence of a separate environmental factor.

The dense gas mass fraction in the W51 cloud and its protoclusters

NASA Astrophysics Data System (ADS)

Ginsburg, Adam; Bally, John; Battersby, Cara; Youngblood, Allison; Darling, Jeremy; Rosolowsky, Erik; Arce, Héctor; Lebrón Santos, Mayra E.

2015-01-01

Context. The density structure of molecular clouds determines how they will evolve. Aims: We map the velocity-resolved density structure of the most vigorously star-forming molecular cloud in the Galactic disk, the W51 giant molecular cloud. Methods: We present new 2 cm and 6 cm maps of H2CO, radio recombination lines, and the radio continuum in the W51 star forming complex acquired with Arecibo and the Green Bank Telescope at ~ 50″ resolution. We use H2CO absorption to determine the relative line-of-sight positions of molecular and ionized gas. We measure gas densities using the H2CO densitometer, including continuous measurements of the dense gas mass fraction (DGMF) over the range 104cm-3 104cm-3, while it is low, f< 20%, in W51 B. We did not detect any H2CO emission throughout the W51 GMC; all gas dense enough to emit under normal conditions is in front of bright continuum sources and therefore is seen in absorption instead. Conclusions: (1) The dense gas fraction in the W51 A and B clouds shows that W51 A will continue to form stars vigorously, while star formation has mostly ended in W51 B. The lack of dense, star-forming gas around W51 C indicates that collect-and-collapse is not acting or is inefficient in W51. (2) Ongoing high-mass star formation is correlated with n ≳ 1 × 105cm-3 gas. Gas with n> 104cm-3 is weakly correlated with low and moderate mass star formation, but does not strongly correlate with high-mass star formation. (3) The nondetection of H2CO emission implies that the emission detected in other galaxies, e.g. Arp 220, comes from high-density gas that is not directly affiliated with already-formed massive stars. Either the non-star-forming ISM of these galaxies is very dense, implying the star formation density threshold is higher, or H ii regions have their emission suppressed. The data set has been made public at http://dx.doi.org/10.7910/DVN/26818Appendices are available in electronic form at http://www.aanda.org

Plausible Boosting of Millimeter-Galaxies in the COSMOS Field by Intervening Large-Scale Structure

NASA Astrophysics Data System (ADS)

Aretxaga, I.; Wilson, G. W.; Aguilar, E.; Alberts, S.; Scott, K. S.; Scoville, N.; Yun, M. S.; Austermann, J.; Downes, T. D.; Ezawa, H.; Hatsukade, B.; Hughes, D. H.; Kawabe, R.; Kohno, K.; Oshima, T.; Perera, T. A.; Tamura, Y.; Zeballos, M.

2011-10-01

The 0.72 sq. deg. contiguous 1.1mm survey in the central area of the COSMOS field, carried out to a 1σ≍1.26 mJy beam-1 depth with the AzTEC camera mounted on the 10m Atacama Submillimeter Telescope Experiment (ASTE), shows number counts with a significant excess of sources when compared to the number counts derived from the ˜0.5 sq. deg. area sampled at similar depths in the Scuba HAlf Degree Extragalactic Survey (SHADES, Austermann et al. 2010). They are, however, consistent with those derived from fields that were considered too small to characterize the overall blank-field population. We identify differences to be more significant in the S1.1mm ˜> 5 mJy regime, and demonstrate that these excesses in number counts are related to the areas where galaxies at redshifts ˜< 1.1 are more densely clustered. The positions of optical-IR galaxies in the redshift interval 0.6 ˜< z ˜< 0.75 are the ones that show the strongest correlation with the positions of the 1.1mm bright population (S1.mm ˜>5 mJy), a result which does not depend exclusively on the presence of rich clusters within the survey sampled area. The most likely explanation for the observed excess in number counts at 1.1mm is galaxy-galaxy and galaxy-group lensing at moderate amplification levels, that increases in amplitude as one samples larger and larger flux densities.

BULGES OF NEARBY GALAXIES WITH SPITZER: SCALING RELATIONS IN PSEUDOBULGES AND CLASSICAL BULGES

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

Fisher, David B.; Drory, Niv, E-mail: dbfisher@astro.as.utexas.ed

2010-06-20

We investigate scaling relations of bulges using bulge-disk decompositions at 3.6 {mu}m and present bulge classifications for 173 E-Sd galaxies within 20 Mpc. Pseudobulges and classical bulges are identified using Sersic index, Hubble Space Telescope morphology, and star formation activity (traced by 8 {mu}m emission). In the near-IR pseudobulges have n{sub b} < 2 and classical bulges have n{sub b} >2, as found in the optical. Sersic index and morphology are essentially equivalent properties for bulge classification purposes. We confirm, using a much more robust sample, that the Sersic index of pseudobulges is uncorrelated with other bulge structural properties, unlikemore » for classical bulges and elliptical galaxies. Also, the half-light radius of pseudobulges is not correlated with any other bulge property. We also find a new correlation between surface brightness and pseudobulge luminosity; pseudobulges become more luminous as they become more dense. Classical bulges follow the well-known scaling relations between surface brightness, luminosity, and half-light radius that are established by elliptical galaxies. We show that those pseudobulges (as indicated by Sersic index and nuclear morphology) that have low specific star formation rates are very similar to models of galaxies in which both a pseudobulge and classical bulge exist. Therefore, pseudobulge identification that relies only on structural indicators is incomplete. Our results, especially those on scaling relations, imply that pseudobulges are very different types of objects than elliptical galaxies.« less

How to quench a galaxy

NASA Astrophysics Data System (ADS)

Pontzen, Andrew; Tremmel, Michael; Roth, Nina; Peiris, Hiranya V.; Saintonge, Amélie; Volonteri, Marta; Quinn, Tom; Governato, Fabio

2017-02-01

We show how the interplay between active galactic nuclei (AGNs) and merger history determines whether a galaxy quenches star formation (SF) at high redshift. We first simulate, in a full cosmological context, a galaxy of total dynamical mass Mvir = 1012 M⊙ at z = 2. Then we systematically alter the accretion history of the galaxy by minimally changing the linear overdensity in the initial conditions. This `genetic modification' approach allows the generation of three sets of Λ CDM initial conditions leading to maximum merger ratios of 1:10, 1:5 and 2:3, respectively. The changes leave the final halo mass, large-scale structure and local environment unchanged, providing a controlled numerical experiment. Interaction between the AGN physics and mergers in the three cases leads, respectively, to a star-forming, temporarily quenched and permanently quenched galaxy. However, the differences do not primarily lie in the black hole accretion rates, but in the kinetic effects of the merger: the galaxy is resilient against AGN feedback unless its gaseous disc is first disrupted. Typical accretion rates are comparable in the three cases, falling below 0.1 M⊙ yr-1, equivalent to around 2 per cent of the Eddington rate or 10-3 times the pre-quenching star formation rate, in agreement with observations. This low level of black hole accretion can be sustained even when there is insufficient dense cold gas for SF. Conversely, supernova feedback is too distributed to generate outflows in high-mass systems, and cannot maintain quenching over periods longer than the halo gas cooling time.

Are starburst galaxies proton calorimeters?

NASA Astrophysics Data System (ADS)

Wang, Xilu; Fields, Brian D.

2018-03-01

Several starburst galaxies have been observed in the GeV and TeV bands. In these dense environments, gamma-ray emission should be dominated by cosmic ray (CR) interactions with the interstellar medium (pcrpism → π0 → γγ). Indeed, starbursts may act as proton `calorimeters' where a substantial fraction of CR energy input is emitted in gamma-rays. Here, we build a one-zone, `thick-target' model implementing calorimetry and placing a firm upper bound on gamma-ray emission from CR interactions. The model assumes that CRs are accelerated by supernovae (SNe), and all suffer nuclear interactions rather than escape. Our model has only two free parameters: the CR proton acceleration energy per SN ɛcr, and the proton injection spectral index s. We calculate the pionic gamma-ray emission from 10 MeV to 10 TeV, and derive thick-target parameters for six galaxies with Fermi, H.E.S.S., and/or VERITAS data. Our model provides good fits for the M82 and NGC 253, and yields ɛcr and s values suggesting that SN CR acceleration is similar in starbursts and in our Galaxy. We find that these starbursts are indeed nearly if not fully proton calorimeters. For NGC 4945 and NGC 1068, the models are consistent with calorimetry but are less well-constrained due to the lack of TeV data. However, the Circinus galaxy and the ultra-luminous infrared galaxy Arp 220 exceed our pionic upper-limit; possible explanations are discussed.

A Starburst in the Core of a Galaxy Cluster: the Dwarf Irregular NGC 1427A in Fornax

NASA Astrophysics Data System (ADS)

Mora, Marcelo D.; Chanamé, Julio; Puzia, Thomas H.

2015-09-01

Gas-rich galaxies in dense environments such as galaxy clusters and massive groups are affected by a number of possible types of interactions with the cluster environment, which make their evolution radically different than that of field galaxies. The dwarf irregular galaxy NGC 1427A, presently infalling toward the core of the Fornax galaxy cluster for the first time, offers a unique opportunity to study those processes at a level of detail not possible to achieve for galaxies at higher redshifts, when galaxy-scale interactions were more common. Using the spatial resolution of the Hubble Space Telescope/Advanced Camera for Surveys and auxiliary Very Large Telescope/FORS1 ground-based observations, we study the properties of the most recent episodes of star formation in this gas-rich galaxy, the only one of its type near the core of the Fornax cluster. We study the structural and photometric properties of young star cluster complexes in NGC 1427A, identifying 12 bright such complexes with exceptionally blue colors. The comparison of our broadband near-UV/optical photometry with simple stellar population models yields ages below ˜ 4× {10}6 years and stellar masses from a few 1000 up to ˜ 3× {10}4{M}⊙ , slightly dependent on the assumption of cluster metallicity and initial mass function. Their grouping is consistent with hierarchical and fractal star cluster formation. We use deep Hα imaging data to determine the current star formation rate in NGC 1427A and estimate the ratio, Γ, of star formation occurring in these star cluster complexes to that in the entire galaxy. We find Γ to be among the largest such values available in the literature, consistent with starburst galaxies. Thus a large fraction of the current star formation in NGC 1427A is occurring in star clusters, with the peculiar spatial arrangement of such complexes strongly hinting at the possibility that the starburst is being triggered by the passage of the galaxy through the cluster environment. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 70.B-0695.

NGC 3934: a shell galaxy in a compact galaxy environment

NASA Astrophysics Data System (ADS)

Bettoni, D.; Galletta, G.; Rampazzo, R.; Marino, A.; Mazzei, P.; Buson, L. M.

2011-10-01

Context. Mergers/accretions are considered the main drivers of the evolution of galaxies in groups. We investigate the NGC 3933 poor galaxy association that contains NGC 3934, which is classified as a polar-ring galaxy. Aims: The multi-band photometric analysis of NGC 3934 allows us to investigate the nature of this galaxy and to re-define the NGC 3933 group members with the aim to characterize the group's dynamical properties and its evolutionary phase. Methods: We imaged the group in the far (FUV, λeff = 1539 Å) and near (NUV, λeff = 2316 Å) ultraviolet (UV) bands of the Galaxy Evolution Explorer (GALEX). From the deep optical imaging we determined the fine structure of NGC 3934. We measured the recession velocity of PGC 213894 which shows that it belongs to the NGC 3933 group. We derived the spectral energy distribution (SED) from FUV to far-IR emission of the two brightest members of the group. We compared a grid of smooth particle hydrodynamical (SPH) chemo-photometric simulations with the SED and the integrated properties of NGC 3934 and NGC 3933 to devise their possible formation/evolutionary scenarios. Results: The NGC 3933 group has six bright members: a core composed of five galaxies, which have Hickson's compact group characteristics, and a more distant member, PGC 37112. The group velocity dispersion is relatively low (157 ± 44 km s-1). The projected mass, from the NUV photometry, is ~7 × 1012 M⊙ with a crossing time of 0.04 Hubble times, suggesting that at least in the center the group is virialized. We do not find evidence that NGC 3934 is a polar-ring galaxy, as suggested by the literature, but find that it is a disk galaxy with a prominent dust-lane structure and a wide type-II shell structure. Conclusions: NGC 3934 is a quite rare example of a shell galaxy in a likely dense galaxy region. The comparison between physically motivated SPH simulations with multi-band integrated photometry suggests that NGC 3934 is the product of a major merger.

Extended halos and intracluster light using Planetary Nebulae as tracers in nearby clusters

NASA Astrophysics Data System (ADS)

Arnaboldi, Magda

Since the first detection of intracluster planetary nebulae in 1996, imaging and spectroscopic surveys identified such stars to trace the radial extent and the kinematics of diffuse light in clusters. This topic of research is tightly linked with the studies of galaxy formation and evolution in dense environment, as the spatial distribution and kinematics of planetary nebulae in the outermost regions of galaxies and in the cluster cores is relevant for setting constraints on cosmological simulations. In this sense, extragalactic planetary nebulae play a very important role in the near-field cosmology, in order to measure the integrated mass as function of radius and the orbital distribution of stars in structures placed in the densest regions of the nearby universe.

Starburst galaxy Messier 94

NASA Image and Video Library

2015-10-19

This image shows the galaxy Messier 94, which lies in the small northern constellation of the Hunting Dogs, about 16 million light-years away. Within the bright ring around Messier 94 new stars are forming at a high rate and many young, bright stars are present within it – thanks to this, this feature is called a starburst ring. The cause of this peculiarly shaped star-forming region is likely a pressure wave going outwards from the galactic centre, compressing the gas and dust in the outer region. The compression of material means the gas starts to collapse into denser clouds. Inside these dense clouds, gravity pulls the gas and dust together until temperature and pressure are high enough for stars to be born.

SuperMassive Blackholes grow from stellar BHs of star formation history?

NASA Astrophysics Data System (ADS)

Rocca-Volmerange, Brigitte

The origin of the supermassive black hole masses M SMBH discovered at the highest redshifts is still actively debated. Moreover the statistically significant relation of M SMBH with bulge luminosities L V , extended on several magnitude orders, confirms a common physical process linking small (<= 1pc) to large (kpcs) size scales. The Spectral Energy Distributions (SEDs) of two z=3.8 radio galaxies 4C41.17 and TN J2007-1316, best-fitted by evolved early type galaxy and starburst scenarios also imply masses of stellar remnants. Computed with the evolutionary code Pegase.3, the cumulated stellar black hole mass M sBH reach up to several 109M⊙, similar to M SMBH at same z. We propose the SMBH growth is due to the migration of the stellar dense residues (sBH) towards the galaxy core by dynamical friction. Discussed in terms of time-scales, this process which is linking AGN and star formation, also fully justifies the famous relation M SMBH -L V .

Automata network models of galaxy evolution

NASA Technical Reports Server (NTRS)

Chappell, David; Scalo, John

1993-01-01

Two ideas appear frequently in theories of star formation and galaxy evolution: (1) star formation is nonlocally excitatory, stimulating star formation in neighboring regions by propagation of a dense fragmenting shell or the compression of preexisting clouds; and (2) star formation is nonlocally inhibitory, making H2 regions and explosions which can create low-density and/or high temperature regions and increase the macroscopic velocity dispersion of the cloudy gas. Since it is not possible, given the present state of hydrodynamic modeling, to estimate whether one of these effects greatly dominates the other, it is of interest to investigate the predicted spatial pattern of star formation and its temporal behavior in simple models which incorporate both effects in a controlled manner. The present work presents preliminary results of such a study which is based on lattice galaxy models with various types of nonlocal inhibitory and excitatory couplings of the local SFR to the gas density, temperature, and velocity field meant to model a number of theoretical suggestions.

Reconstructing Star Formation Histories to Reveal the Origin and Evolution of the SFR-M* Correlation

NASA Astrophysics Data System (ADS)

Gawiser, Eric

2016-10-01

Correlations have played an important role in advancing our knowledge of astrophysics, from the Schmidt-Kennicutt law to the black hole-bulge mass relation. A surprisingly tight correlation between galaxy star formation rates (SFR) and stellar masses (M*) was discovered in 2007, and models of galaxy formation and evolution can be constrained by studying the evolution of this SFR-M* correlation and its intrinsic scatter. At present, such investigations are weakened by the need to assume a simple parametric form for the star formation history, typically constant or exponentially declining.We propose to use our new dense basis method to reconstruct star-formation histories (SFHs) through SED fitting using multi-band photometry of >10,000 galaxies in the 3D-HST and CANDELS catalogs. Armed with these reconstructed SFHs, we will then:1. Better measure the SFR-M* correlation (aka star-forming sequence) in several redshift bins at 0.5

Vibrationally Excited HCN in the Luminous Infrared Galaxy NGC 4418

NASA Astrophysics Data System (ADS)

Sakamoto, Kazushi; Aalto, Susanne; Evans, Aaron S.; Wiedner, Martina C.; Wilner, David J.

2010-12-01

Infrared pumping and its effect on the excitation of HCN molecules can be important when using rotational lines of HCN to probe dense molecular gas in galaxy nuclei. We report the first extragalactic detection of (sub)millimeter rotational lines of vibrationally excited HCN, in the dust-enshrouded nucleus of the luminous infrared galaxy NGC 4418. We estimate the excitation temperature of Tvib ≈ 230 K between the vibrational ground and excited (v 2 = 1) states. This excitation is most likely due to infrared radiation. At this high vibrational temperature the path through the v 2 = 1 state must have a strong impact on the rotational excitation in the vibrational ground level, although it may not be dominant for all rotational levels. Our observations also revealed nearly confusion-limited lines of CO, HCN, HCO+, H13CN, HC15N, CS, N2H+, and HC3N at λ ~ 1 mm. Their relative intensities may also be affected by the infrared pumping.

The Dense Molecular Gas and Nuclear Activity in the ULIRG IRAS 13120–5453

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

Privon, G. C.; Treister, E.; Aalto, S.

2017-02-01

We present new Atacama Large Millimeter/submillimeter Array Band 7 (∼340 GHz) observations of the dense gas tracers HCN, HCO{sup +}, and CS in the local, single-nucleus, ultraluminous infrared galaxy IRAS 13120–5453. We find centrally enhanced HCN (4–3) emission, relative to HCO{sup +} (4–3), but do not find evidence for radiative pumping of HCN. Considering the size of the starburst (0.5 kpc) and the estimated supernovae rate of ∼1.2 yr{sup −1}, the high HCN/HCO{sup +} ratio can be explained by an enhanced HCN abundance as a result of mechanical heating by the supernovae, though the active galactic nucleus and winds maymore » also contribute additional mechanical heating. The starburst size implies a high Σ{sub IR} of 4.7 × 10{sup 12} L {sub ⊙} kpc{sup −2}, slightly below predictions of radiation-pressure limited starbursts. The HCN line profile has low-level wings, which we tentatively interpret as evidence for outflowing dense molecular gas. However, the dense molecular outflow seen in the HCN line wings is unlikely to escape the Galaxy and is destined to return to the nucleus and fuel future star formation. We also present modeling of Herschel observations of the H{sub 2}O lines and find a nuclear dust temperature of ∼40 K. IRAS 13120–5453 has a lower dust temperature and Σ{sub IR} than is inferred for the systems termed “compact obscured nuclei (CONs)” (such as Arp 220 and Mrk 231). If IRAS 13120–5453 has undergone a CON phase, we are likely witnessing it at a time when the feedback has already inflated the nuclear ISM and diluted star formation in the starburst/active galactic nucleus core.« less

Exploring the CO/CN line ratio in nearby galaxies with the ALMA archive

NASA Astrophysics Data System (ADS)

Wilson, Christine D.

2018-07-01

We describe an archival project using Cycle 0 data from the Atacama Large Millimeter/submillimeter Array to survey the CO/CN line ratio in 17 nearby galaxies. CN is an interesting molecule that traces dense gas exposed to ultraviolet radiation and its N = 1 - 0 lines can be observed simultaneously with the CO J = 1 - 0 line. We identify eight galaxies with distances <200 Mpc for which both lines are detected. Signal-to-noise ratio matched CO/CN ratios range from as low as 7 to as high as 65, while ratios using the total detected flux range from 20 to 140. Spatial variations greater than a factor of 3 are seen in several galaxies. These line ratio changes are likely due to changes in the [CN]/[H2] abundance ratio and/or the CN excitation. Additional measurements of the warm gas pressure and the CN excitation should help to distinguish between these two possibilities. Three of the four active galactic nuclei in our sample show CO/CN line ratios that are roughly a factor of 2-3 larger than those seen in starburst-dominated regions, which may be in conflict with models of molecular abundances in X-ray-dominated regions.

High Energy Neutrinos Produced in the Accretion Disks by Neutrons from Nuclei Disintegrated in the AGN Jets

NASA Astrophysics Data System (ADS)

Bednarek, W.

2016-12-01

We investigate the consequences of acceleration of nuclei in jets of active galaxies not far from the surface of an accretion disk. The nuclei can be accelerated in the re-connection regions in the jet and/or at the jet boundary, between the relativistic jet and its cocoon. It is shown that the relativistic nuclei can efficiently fragment onto specific nucleons in collisions with the disk radiation. Neutrons, directed toward the accretion disk, take a significant part of energy from the relativistic nuclei. These neutrons develop a cascade in the dense accretion disk. We calculate the neutrino spectra produced in such a hadronic cascade within the accretion disk. We propose that the neutrinos produced in such a scenario, from the whole population of super-massive black holes in active galaxies, can explain the extragalactic neutrino background recently measured by the IceCube neutrino detector, provided that a 5% fraction of galaxies have an active galactic nucleus and a few percent of neutrons reach the accretion disk. We predict that the neutrino signals in the present neutrino detectors, produced in terms of such a model, will not be detectable even from the nearby radio galaxies similar to M87.

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

Bednarek, W., E-mail: bednar@uni.lodz.pl

We investigate the consequences of acceleration of nuclei in jets of active galaxies not far from the surface of an accretion disk. The nuclei can be accelerated in the re-connection regions in the jet and/or at the jet boundary, between the relativistic jet and its cocoon. It is shown that the relativistic nuclei can efficiently fragment onto specific nucleons in collisions with the disk radiation. Neutrons, directed toward the accretion disk, take a significant part of energy from the relativistic nuclei. These neutrons develop a cascade in the dense accretion disk. We calculate the neutrino spectra produced in such amore » hadronic cascade within the accretion disk. We propose that the neutrinos produced in such a scenario, from the whole population of super-massive black holes in active galaxies, can explain the extragalactic neutrino background recently measured by the IceCube neutrino detector, provided that a 5% fraction of galaxies have an active galactic nucleus and a few percent of neutrons reach the accretion disk. We predict that the neutrino signals in the present neutrino detectors, produced in terms of such a model, will not be detectable even from the nearby radio galaxies similar to M87.« less

Highly efficient star formation in NGC 5253 possibly from stream-fed accretion.

PubMed

Turner, J L; Beck, S C; Benford, D J; Consiglio, S M; Ho, P T P; Kovács, A; Meier, D S; Zhao, J-H

2015-03-19

Gas clouds in present-day galaxies are inefficient at forming stars. Low star-formation efficiency is a critical parameter in galaxy evolution: it is why stars are still forming nearly 14 billion years after the Big Bang and why star clusters generally do not survive their births, instead dispersing to form galactic disks or bulges. Yet the existence of ancient massive bound star clusters (globular clusters) in the Milky Way suggests that efficiencies were higher when they formed ten billion years ago. A local dwarf galaxy, NGC 5253, has a young star cluster that provides an example of highly efficient star formation. Here we report the detection of the J = 3→2 rotational transition of CO at the location of the massive cluster. The gas cloud is hot, dense, quiescent and extremely dusty. Its gas-to-dust ratio is lower than the Galactic value, which we attribute to dust enrichment by the embedded star cluster. Its star-formation efficiency exceeds 50 per cent, tenfold that of clouds in the Milky Way. We suggest that high efficiency results from the force-feeding of star formation by a streamer of gas falling into the galaxy.

Evidence of Nuclear Disks from the Radial Distribution of CCSNe in Starburst Galaxies

NASA Astrophysics Data System (ADS)

Herrero-Illana, Rubén; Pérez-Torres, Miguel Ángel; Alberdi, Antxon

Galaxy-galaxy interactions are expected to be responsible for triggering massive star formation and possibly accretion onto a supermassive black hole, by providing large amounts of dense molecular gas down to the central kiloparsec region. Several scenarios to drive the gas further down to the central ˜ 100 pc, have been proposed, including the formation of a nuclear disk around the black hole, where massive stars would produce supernovae. Here, we probe the radial distribution of supernovae and supernova remnants in the nuclear regions of the starburst galaxies M82, Arp 299-A, and Arp 220, by using high-angular resolution (≲ 0.'1) radio observations. We derived scale-length values for the putative nuclear disks, which range from ˜ 20-30 pc for Arp 299-A and Arp 220, up to ˜ 140 pc for M82. The radial distribution of SNe for the nuclear disks in Arp 299-A and Arp 220 is also consistent with a power-law surface density profile of exponent γ = 1, as expected from detailed hydrodynamical simulations of nuclear disks. This study is detailed in Herrero-Illana, Perez-Torres, and Alberdi [11].

Compact radio sources in luminous infrared galaxies

NASA Astrophysics Data System (ADS)

Parra, Rodrigo

2007-08-01

Radio interferometry is an observational technique of high sensitivity and incomparably high spatial resolution. Moreover, because radio waves can freely propagate through interstellar dust and gas, it allows the study of regions of the universe completely obscured at other wavelengths. This thesis reports the observational and theoretical results of my research during the past four years which are mostly based on interferometric radio data. The COLA sample is an infrared selected sample of active star forming galaxies. We conducted 6 cm VLA and VLBI snapshot observations of the northern half of this sample. The radio emission seen at VLA scales is consistent with being powered by star formation activity because it follows the far infrared to radio correlation. We detect 22% of the sample sources in our VLBI snapshots. Based on luminosity arguments, we argue that these sub-parsec VLBI sources are powered by AGN activity. Furthermore, we find that VLBI detections are preferentially found in sources whose VLA scale structures have the highest peak brightnesses suggesting a strong correlation between compact starburst and AGN activity. This observational result is consistent with the theoretical picture of an Eddington-limited nuclear starburst acting as the last valve in the pipeline transporting the gas from kiloparsec scales onto the accretion disc of a buried AGN. Arp 220 is the archetypical ultra luminous infrared galaxy. For many years this source has been known to harbour a compact (~100 pc) cluster of unresolved 18 cm bright sources believed to be bright core collapse supernovae. Using multiwavelength VLBI observations, we obtained for the first time radio spectra for 18 of these sources. We find that over a half of them have spectra consistent with young supernovae. The rest can be better explained as older supernova remnants interacting with the high density starburst ISM. This finding allowed us to constrain the number of possible scenarios for the Arp 220 starburst. A subset of luminous infrared galaxies contain non-thermal spectral line emission from the OH radical. These OH megamasers often show diffuse extended (~100 pc) low gain emission surrounding compact ([Special characters omitted. 1 pc) high gain maser spots. These observational features have been explained in terms of unsaturated and saturated masers. Using numerical simulations we have shown how both the diffuse and compact components of the OH megamaser observed towards the luminous infrared galaxy IIIZw35 can be explained by a single phase of unsaturated maser clouds in which the compact bright masers are caused by the random line-of-sight overlap of several such clouds and the diffuse component by the beam spatial average of many low gain clouds too weak to be seen independently. The theoretical tools developed to analyse this particular case have been extended to the general problem of propagation of radiation in clumpy media.

Statistical Measures of Large-Scale Structure

NASA Astrophysics Data System (ADS)

Vogeley, Michael; Geller, Margaret; Huchra, John; Park, Changbom; Gott, J. Richard

1993-12-01

\\inv Mpc} To quantify clustering in the large-scale distribution of galaxies and to test theories for the formation of structure in the universe, we apply statistical measures to the CfA Redshift Survey. This survey is complete to m_{B(0)}=15.5 over two contiguous regions which cover one-quarter of the sky and include ~ 11,000 galaxies. The salient features of these data are voids with diameter 30-50\\hmpc and coherent dense structures with a scale ~ 100\\hmpc. Comparison with N-body simulations rules out the ``standard" CDM model (Omega =1, b=1.5, sigma_8 =1) at the 99% confidence level because this model has insufficient power on scales lambda >30\\hmpc. An unbiased open universe CDM model (Omega h =0.2) and a biased CDM model with non-zero cosmological constant (Omega h =0.24, lambda_0 =0.6) match the observed power spectrum. The amplitude of the power spectrum depends on the luminosity of galaxies in the sample; bright (L>L(*) ) galaxies are more strongly clustered than faint galaxies. The paucity of bright galaxies in low-density regions may explain this dependence. To measure the topology of large-scale structure, we compute the genus of isodensity surfaces of the smoothed density field. On scales in the ``non-linear" regime, <= 10\\hmpc, the high- and low-density regions are multiply-connected over a broad range of density threshold, as in a filamentary net. On smoothing scales >10\\hmpc, the topology is consistent with statistics of a Gaussian random field. Simulations of CDM models fail to produce the observed coherence of structure on non-linear scales (>95% confidence level). The underdensity probability (the frequency of regions with density contrast delta rho //lineρ=-0.8) depends strongly on the luminosity of galaxies; underdense regions are significantly more common (>2sigma ) in bright (L>L(*) ) galaxy samples than in samples which include fainter galaxies.

The Origin of Dust in the Early Universe: Probing the Star Formation History of Galaxies by Their Dust Content

NASA Technical Reports Server (NTRS)

Dwek, Eli; Cherchneff, Isabelle

2010-01-01

Two distinct scenarios for the origin of the approximately 4 x 10(exp 8) Solar Mass of dust observed in the high-redshift (z = 6.4) quasar J1148+5251 have been proposed. The first assumes that this galaxy is much younger than the age of the universe at that epoch so that only supernovae, could have produced this dust. The second scenario assumes a significantly older galactic age, so that the dust could have formed in lower-mass AGB stars. Presenting new integral solutions for the chemical evolution of metals and dust in galaxies, we offer a critical evaluation of these two scenarios. ^N;"(,, show that the AGB scenario is sensitive to the details of the galaxy's star formation history (SFH), which must consist of an early intense starburst followed by a period of low stellar activity. The presence or absence of massive amounts of dust in high-redshift galaxies can therefore be used to infer their SFH. However, a problem with the AGB scenario is that it produces a stellar mass that is significantly larger than the inferred dynamical mass of J1148+5251, an yet unresolved discrepancy. If this problem persists, then additional sites for the growth or formation of dust, such as molecular clouds or dense clouds around active galactic nuclei, must be considered.

Quantifying the coexistence of massive black holes and dense nuclear star clusters

NASA Astrophysics Data System (ADS)

Graham, Alister W.; Spitler, Lee R.

2009-08-01

In large spheroidal stellar systems, such as elliptical galaxies, one invariably finds a 106-109Msolar supermassive black hole at their centre. In contrast, within dwarf elliptical galaxies one predominantly observes a 105-107Msolar nuclear star cluster. To date, few galaxies have been found with both types of nuclei coexisting and even less have had the masses determined for both central components. Here, we identify one dozen galaxies housing nuclear star clusters and supermassive black holes whose masses have been measured. This doubles the known number of such hermaphrodite nuclei - which are expected to be fruitful sources of gravitational radiation. Over the host spheroid (stellar) mass range 108-1011Msolar, we find that a galaxy's nucleus-to-spheroid (baryon) mass ratio is not a constant value but decreases from a few per cent to ~0.3 per cent such that log[(MBH + MNC)/Msph] = -(0.39 +/- 0.07) log[Msph/1010Msolar] - (2.18 +/- 0.07). Once dry merging commences and the nuclear star clusters disappear, this ratio is expected to become a constant value. As a byproduct of our investigation, we have found that the projected flux from resolved nuclear star clusters is well approximated with Sérsic functions having a range of indices from ~0.5 to ~3, the latter index describing the Milky Way's nuclear star cluster.

Carbon monoxide in clouds at low metallicity in the dwarf irregular galaxy WLM.

PubMed

Elmegreen, Bruce G; Rubio, Monica; Hunter, Deidre A; Verdugo, Celia; Brinks, Elias; Schruba, Andreas

2013-03-28

Carbon monoxide (CO) is the primary tracer for interstellar clouds where stars form, but it has never been detected in galaxies in which the oxygen abundance relative to hydrogen is less than 20 per cent of that of the Sun, even though such 'low-metallicity' galaxies often form stars. This raises the question of whether stars can form in dense gas without molecules, cooling to the required near-zero temperatures by atomic transitions and dust radiation rather than by molecular line emission; and it highlights uncertainties about star formation in the early Universe, when the metallicity was generally low. Here we report the detection of CO in two regions of a local dwarf irregular galaxy, WLM, where the metallicity is 13 per cent of the solar value. We use new submillimetre observations and archival far-infrared observations to estimate the cloud masses, which are both slightly greater than 100,000 solar masses. The clouds have produced stars at a rate per molecule equal to 10 per cent of that in the local Orion nebula cloud. The CO fraction of the molecular gas is also low, about 3 per cent of the Milky Way value. These results suggest that in small galaxies both star-forming cores and CO molecules become increasingly rare in molecular hydrogen clouds as the metallicity decreases.

First X-ray Statistical Tests for Clumpy-Torus Models: Constraints from RXTEmonitoring of Seyfert AGN

NASA Astrophysics Data System (ADS)

Markowitz, Alex; Krumpe, Mirko; Nikutta, R.

2016-06-01

In two papers (Markowitz, Krumpe, & Nikutta 2014, and Nikutta et al., in prep.), we derive the first X-ray statistical constraints for clumpy-torus models in Seyfert AGN by quantifying multi-timescale variability in line of-sight X-ray absorbing gas as a function of optical classification.We systematically search for discrete absorption events in the vast archive of RXTE monitoring of 55 nearby type Is and Compton-thin type IIs. We are sensitive to discrete absorption events due to clouds of full-covering, neutral/mildly ionized gas transiting the line of sight. Our results apply to both dusty and non-dusty clumpy media, and probe model parameter space complementary to that for eclipses observed with XMM-Newton, Suzaku, and Chandra.We detect twelve eclipse events in eight Seyferts, roughly tripling the number previously published from this archive. Event durations span hours to years. Most of our detected clouds are Compton-thin, and most clouds' distances from the black hole are inferred to be commensurate with the outer portions of the BLR or the inner regions of infrared-emitting dusty tori.We present the density profiles of the highest-quality eclipse events; the column density profile for an eclipsing cloud in NGC 3783 is doubly spiked, possibly indicating a cloud that is being tidallysheared. We discuss implications for cloud distributions in the context of clumpy-torus models. We calculate eclipse probabilities for orientation-dependent Type I/II unification schemes.We present constraints on cloud sizes, stability, and radial distribution. We infer that clouds' small angular sizes as seen from the SMBH imply 107 clouds required across the BLR + torus. Cloud size is roughly proportional to distance from the black hole, hinting at the formation processes (e.g., disk fragmentation). All observed clouds are sub-critical with respect to tidal disruption; self-gravity alone cannot contain them. External forces, such as magnetic fields or ambient pressure, are needed to contain them; otherwise, clouds must be short-lived.

Properties of Dwarf Ellipticals in Low-Density Environments

NASA Astrophysics Data System (ADS)

Sur, Debnil; Guhathakurta, P.; Toloba, E.

2013-01-01

Dwarf elliptical galaxies have been studied only in dense cluster environments, where they are the most common type of object. While this suggests that their location affects their formation and evolution, the role of distance is not fully understood. Thus, to investigate the physical processes that shape these galaxies, we have conducted a study of dwarf elliptical galaxies (dEs) in low-density environments to compare their properties with those in clusters. Catalogs of such objects have not been created; thus, we have developed a novel objective method to find new dEs through comparing photometric properties with those of galaxies in the Virgo Cluster Catalog. This method utilizes optical colors, surface brightness and ellipticity, and it confirms smoothness through visual classification. In this last step, we found a very low contamination rate, which suggests the procedure’s utility in finding dEs. Through the NSA Sloan Atlas, we have analyzed the spectrophotometric properties of the dE candidates as a function of distance to the nearest massive galaxy, which we refer to as their host. We have found that these dEs are younger and more actively forming stars than dEs in denser regions. This is consistent with a transformation scenario in which low luminosity spiral galaxies are affected by the environment and transformed into quiescent galaxies. This low density regime contains objects in an intermediate state between the spiral galaxy and the classical dE in Virgo, where no star formation is ongoing. The correlation of the studied properties with the distance to the host galaxy provides new evidence that the dEs are created by a process called ram-pressure stripping: the interstellar medium of a host galaxy removes the gas of a smaller star-forming galaxy and provokes its quenching. We are currently analysing Keck/DEIMOS spectroscopy of some of the dE candidates from our catalog to explore in more detail their connection to cluster dEs. Possible similarities include their kinematic behaviour, stellar populations and chemical abundances. This research was supported by the Science Internship Program (SIP) at UCSC and the National Science Foundation.

How Supermassive Black Hole Feedback Might Work

NASA Astrophysics Data System (ADS)

Donahue, Megan

2017-01-01

How black holes regulate their own growth and the growth of their host galaxy is an unsolved problem in galaxy evolution. The problem is particularly acute in the centers of clusters of galaxies, where the largest and most massive galaxies in the universe are found. That is, coincidentally, also where the interaction between the black hole and the surrounding gas is the easiest to study because the gas is sufficiently hot and dense to emit X-rays. The massive central galaxies of clusters of galaxies (BCGs) exhibit striking patterns in their relationships between star formation, radio AGN activity, and the thermodynamic state of the hot, X-ray emitting intracluster gas (ICM) surrounding the galaxies. The AGN jets excavate giant, kpc-scale cavities in the hot gas, in principle, supplying enough heat to the ICM to replace energy lost to radiative cooling. Simulations suggest (by elimination) that AGN feedback must be required to explain the luminosity and colors of these galaxies, but cosmological simulations still struggle with modeling how AGN feedback works in detail. In clusters of galaxies with active AGN and star-forming BCGs, the AGN somehow regulates the gaseous atmosphere to be marginally critical, with a ratio of the cooling time to the free fall time of ~ 5-20. This behavior is also seen in elliptical galaxies, where the feedback is mostly coming from stars. I will discuss the observations that motivated this model. The precipitation model in BCGs is a class of models known as "preventative" feedback, regulated by jets in BCGs. Further, the complex behaviour seen in recent idealized simulations seem to follow emergent patterns predicted by this model, while reproducing the scatter and the time scales inferred from the observations. The link between the thermal instabilities and the depth of the gravitational potential may explain scaling laws such as the black hole mass-velocity dispersion relation, the galaxy mass-metallicity relation and the baryonic Tully-Fisher relation. I will discuss how future X-ray and UV telescopes could be used to test and inform this class of models.

The Galaxy Evolution Probe

NASA Astrophysics Data System (ADS)

Glenn, Jason; Galaxy Evolution Probe Team

2018-01-01

The Galaxy Evolution Probe (GEP) is a concept for a far-infrared observatory to survey large regions of sky for star-forming galaxies from z = 0 to beyond z = 3. Our knowledge of galaxy formation is incomplete and requires uniform surveys over a large range of redshifts and environments to accurately describe mass assembly, star formation, supermassive black hole growth, interactions between these processes, and what led to their decline from z ~ 2 to the present day. Infrared observations are sensitive to dusty, star-forming galaxies, which have bright polycyclic aromatic hydrocarbon (PAH) emission features and warm dust continuum in the rest-frame mid infrared and cooler thermal dust emission in the far infrared. Unlike previous far-infrared continuum surveys, the GEP will measure photometric redshifts commensurate with galaxy detections from PAH emission and Si absorption features, without the need for obtaining spectroscopic redshifts of faint counterparts at other wavelengths.The GEP design includes a 2 m diameter telescope actively cooled to 4 K and two instruments: (1) An imager covering 10 to 300 um with 25 spectral resolution R ~ 8 bands (with lower R at the longest wavelengths) to detect star-forming galaxies and measure their redshifts photometrically. (2) A 23 – 190 um, R ~ 250 dispersive spectrometer for redshift confirmation and identification of obscured AGN using atomic fine-structure lines. Lines including [Ne V], [O IV], [O III], [O I], and [C II] will probe gas physical conditions, radiation field hardness, and metallicity. Notionally, the GEP will have a two-year mission: galaxy surveys with photometric redshifts in the first year and a second year devoted to follow-up spectroscopy. A comprehensive picture of star formation in galaxies over the last 10 billion years will be assembled from cosmologically relevant volumes, spanning environments from field galaxies and groups, to protoclusters, to dense galaxy clusters.Commissioned by NASA, the GEP concept is being developed to demonstrate the ambitious science that could be enabled by a Probe-class mission (defined to be in the cost range $400M to $1B). GEP concept study partners are the University of Colorado Boulder, JPL, and Ball Aerospace.

Galaxy Evolution Explorer Spies Band of Stars

NASA Image and Video Library

2007-06-20

Globular star cluster NGC 362, in a false-color image from NASA's Galaxy Evolution Explorer. Image credit: NASA/JPL-Caltech/Univ. of Virginia The Galaxy Evolution Explorer's ultraviolet eyes have captured a globular star cluster, called NGC 362, in our own Milky Way galaxy. In this new image, the cluster appears next to stars from a more distant neighboring galaxy, known as the Small Magellanic Cloud. "This image is so interesting because it allows a study of the final stages of evolution of low-mass stars in NGC 362, as well as the history of star formation in the Small Magellanic Cloud," said Ricardo Schiavon of the University of Virginia, Charlottesville, Va. Globular clusters are densely packed bunches of old stars scattered in galaxies throughout the universe. NGC 362, located 30,000 light-years away, can be spotted as the dense collection of mostly yellow-tinted stars surrounding a large white-yellow spot toward the top-right of this image. The white spot is actually the core of the cluster, which is made up of stars so closely packed together that the Galaxy Evolution Explorer cannot see them individually. The light blue dots surrounding the cluster core are called extreme horizontal branch stars. These stars used to be very similar to our sun and are nearing the end of their lives. They are very hot, with temperatures reaching up to about four times that of the surface of our sun (25,000 Kelvin or 45,500 degrees Fahrenheit). A star like our sun spends most of its life fusing hydrogen atoms in its core into helium. When the star runs out of hydrogen in its core, its outer envelope will expand. The star then becomes a red giant, which burns hydrogen in a shell surrounding its inner core. Throughout its life as a red giant, the star loses a lot of mass, then begins to burn helium at its core. Some stars will have lost so much mass at the end of this process, up to 85 percent of their envelopes, that most of the envelope is gone. What is left is a very hot ultraviolet-bright core, or extreme horizontal branch star. Blue dots scattered throughout the image are hot, young stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way located approximately 200,000 light-years away. The stars in this galaxy are much brighter intrinsically than extreme horizontal branch stars, but they appear just as bright because they are farther away. The blue stars in the Small Magellanic Cloud are only about a few tens of millions of years old, much younger than the approximately 10-million-year-old stars in NGC 362. Because NGC 362 sits on the northern edge of the Small Magellanic Cloud galaxy, the blue stars are denser toward the south, or bottom, of the image. Some of the yellow spots in this image are stars in the Milky Way galaxy that are along this line of sight. Astronomers believe that some of the other spots, particularly those closer to NGC 362, might actually be a relatively ultraviolet-dim family of stars called "blue stragglers." These stars are formed from collisions or close encounters between two closely orbiting stars in a globular cluster. "This observation could only be done with the Galaxy Evolution Explorer because it is the only ultraviolet imager available to the astronomical community with such a large field of view," said Schiavon. This image is a false-color composite, where light detected by the Galaxy Evolution Explorer's far-ultraviolet detector is colored blue, and light from the telescope's near-ultraviolet detector is red. Written by Linda Vu, Spitzer Science Center Media contact: Whitney Clavin/JPL (818) 354-4673

COS-Weak: probing the CGM using analogues of weak Mg II absorbers at z < 0.3

NASA Astrophysics Data System (ADS)

Muzahid, S.; Fonseca, G.; Roberts, A.; Rosenwasser, B.; Richter, P.; Narayanan, A.; Churchill, C.; Charlton, J.

2018-06-01

We present a sample of 34 weak metal line absorbers at z < 0.3 selected by the simultaneous >3σ detections of the Si IIλ1260 and C IIλ1334 absorption lines, with Wr(Si II)<0.2 Å and Wr(C II)<0.3 Å, in archival HST/COS spectra. Our sample increases the number of known low-z `weak absorbers' by a factor of >5. The column densities of H I and low-ionization metal lines obtained from Voigt profile fitting are used to build simple photoionization models. The inferred densities and line-of-sight thicknesses of the absorbers are in the ranges of -3.3 < log nH/cm-3 < -2.4 and ˜1 pc-50 kpc (median ≈500 pc), respectively. Most importantly, 85 per cent (50 per cent) of these absorbers show a metallicity of [Si/H] > -1.0 (0.0). The fraction of systems showing near-/supersolar metallicity in our sample is significantly higher than in the H I-selected sample of Wotta et al., and the galaxy-selected sample of Prochaska et al., of absorbers probing the circum-galactic medium at similar redshift. A search for galaxies has revealed a significant galaxy-overdensity around these weak absorbers compared to random positions with a median impact parameter of 166 kpc from the nearest galaxy. Moreover, we find the presence of multiple galaxies in ≈80 per cent of the cases, suggesting group environments. The observed dN/dz of 0.8 ± 0.2 indicates that such metal-enriched, compact, dense structures are ubiquitous in the haloes of low-z group galaxies. We suggest that these are transient structures that are related to galactic outflows and/or stripping of metal-rich gas from galaxies.

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

Dullo, Bililign T.; Graham, Alister W., E-mail: Bdullo@astro.swin.edu.au

We have used the full radial extent of images from the Hubble Space Telescope's Advanced Camera for Surveys and Wide Field Planetary Camera 2 to extract surface brightness profiles from a sample of six, local lenticular galaxy candidates. We have modeled these profiles using a core-Sersic bulge plus an exponential disk model. Our fast rotating lenticular disk galaxies with bulge magnitudes M{sub V} {approx}< -21.30 mag have central stellar deficits, suggesting that these bulges may have formed from ''dry'' merger events involving supermassive black holes (BHs) while their surrounding disk was subsequently built up, perhaps via cold gas accretion scenarios.more » The central stellar mass deficits M{sub def} are roughly 0.5-2 M{sub BH} (BH mass), rather than {approx}10-20 M{sub BH} as claimed from some past studies, which is in accord with core-Sersic model mass deficit measurements in elliptical galaxies. Furthermore, these bulges have Sersic indices n {approx}3, half-light radii R{sub e} < 2 kpc and masses >10{sup 11} M{sub Sun }, and therefore appear to be descendants of the compact galaxies reported at z {approx} 1.5-2. Past studies which have searched for these local counterparts by using single-component galaxy models to provide the z {approx} 0 size comparisons have overlooked these dense, compact, and massive bulges in today's early-type disk galaxies. This evolutionary scenario not only accounts for what are today generally old bulges-which must be present in z {approx} 1.5 images-residing in what are generally young disks, but it eliminates the uncomfortable suggestion of a factor of three to five growth in size for the compact, z {approx} 1.5 galaxies that are known to possess infant disks.« less

Is the Size Evolution of Massive Galaxies Accelerated in Cluster Environments?

NASA Astrophysics Data System (ADS)

Wilson, Gillian

2013-10-01

At z 1.6 the main progenitors of present-day massive clusters are undergoing rapid collapse, and have the highest rates of galaxy merging and assembly. Recent observational studies have hinted at accelerated galaxy evolution in dense environments at this epoch, including increased merger rates and rapid growth in galaxy size relative to the field. We propose WFC3 G102 spectroscopy and F125W {Broad J} imaging of a sample of four massive spectroscopically-confirmed clusters at z = 1.6. Our primary scientific goal is to leverage the CANDELS Wide Legacy dataset to carry out a head-to-head comparison of the sizes of cluster members relative to the field {as a function of stellar mass and Sersic index}, and quantify the role of environment in the observed rapid evolution in galaxy sizes since z = 2. These clusters are four of the highest significance overdensities in the 50 square degree SWIRE fields, and will evolve over time to have present-day masses similar to Coma. They were detected using IRAC [3.6]-[4.5] color, which identifies galaxy overdensities regardless of optically red or blue color. A heroic ground-based spectroscopic campaign has resulted in 44 spectroscopically-confirmed members. However this sample is heavily biased toward star-forming {SF} galaxies, and WFC3 spectroscopy is essential to definitively determine cluster membership for 200 members, without bias with respect to quiescent or SF type. The F125W {rest-frame V-band} imaging is necessary to measure the sizes and morphologies of cluster members. 17-passband broadband imaging spanning UV, optical, near-IR, Spitzer IR and Herschel far-IR is already in hand.

Cooling Flow Spectra in Ginga Galaxy Clusters

NASA Technical Reports Server (NTRS)

White, Raymond E., III

1997-01-01

The primary focus of this research project has been a joint analysis of Ginga LAC and Einstein SSS X-ray spectra of the hot gas in galaxy clusters with cooling flows is reported. We studied four clusters (A496, A1795, A2142 & A2199) and found their central temperatures to be cooler than in the exterior, which is expected from their having cooling flows. More interestingly, we found central metal abundance enhancements in two of the clusters, A496 and A2142. We have been assessing whether the abundance gradients (or lack thereof) in intracluster gas is correlated with galaxy morphological gradients in the host clusters. In rich, dense galaxy clusters, elliptical and SO galaxies are generally found in the cluster cores, while spiral galaxies are found in the outskirts. If the metals observed in clusters came from proto-ellipticals and proto-S0s blowing winds, then the metal distribution in intracluster gas may still reflect the distribution of their former host galaxies. In a research project which was inspired by the success of the Ginga LAC/Einstein SSS work, we analyzed X-ray spectra from the HEAO-A2 MED and the Einstein SSS to look for temperature gradients in cluster gas. The HEAO-A2 MED was also a non-imaging detector with a large field of view compared to the SSS, so we used the differing fields of view of the two instruments to extract spatial information. We found some evidence of cool gas in the outskirts of clusters, which may indicate that the nominally isothermal mass density distributions in these clusters are steepening in the outer parts of these clusters.

The Nature and Origin of UCDs in the Coma Cluster

NASA Astrophysics Data System (ADS)

Chiboucas, Kristin; Tully, R. Brent; Madrid, Juan; Phillipps, Steven; Carter, David; Peng, Eric

2018-01-01

UCDs are super massive star clusters found largely in dense regions but have also been found around individual galaxies and in smaller groups. Their origin is still under debate but currently favored scenarios include formation as giant star clusters, either as the brightest globular clusters or through mergers of super star clusters, themselves formed during major galaxy mergers, or as remnant nuclei from tidal stripping of nucleated dwarf ellipticals. Establishing the nature of these enigmatic objects has important implications for our understanding of star formation, star cluster formation, the missing satellite problem, and galaxy evolution. We are attempting to disentangle these competing formation scenarios with a large survey of UCDs in the Coma cluster. Using ACS two-passband imaging from the HST/ACS Coma Cluster Treasury Survey, we are using colors and sizes to identify the UCD cluster members. With a large size limited sample of the UCD population within the core region of the Coma cluster, we are investigating the population size, properties, and spatial distribution, and comparing that with the Coma globular cluster and nuclear star cluster populations to discriminate between the threshing and globular cluster scenarios. In previous work, we had found a possible correlation of UCD colors with host galaxy and a possible excess of UCDs around a non-central giant galaxy with an unusually large globular cluster population, both suggestive of a globular cluster origin. With a larger sample size and additional imaging fields that encompass the regions around these giant galaxies, we have found that the color correlation with host persists and the giant galaxy with unusually large globular cluster population does appear to host a large UCD population as well. We present the current status of the survey.

Our Galactic Neighbor Hosts Complex Organic Molecules

NASA Astrophysics Data System (ADS)

Hensley, Kerry

2018-03-01

For the first time, data from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the presence of methyl formate and dimethyl ether in a star-forming region outside our galaxy. This discovery has important implications for the formation and survival of complex organic compounds importantfor the formation of life in low-metallicity galaxies bothyoung and old.No Simple Picture of Complex Molecule FormationALMA, pictured here with the Magellanic Clouds above, has observed organic molecules in our Milky Way Galaxy and beyond. [ESO/C. Malin]Complex organic molecules (those with at least six atoms, one or more of which must be carbon) are the precursors to the building blocks of life. Knowing how and where complex organic molecules can form is a key part of understanding how life came to be on Earth and how it might arise elsewhere in the universe. From exoplanet atmospheres to interstellar space, complex organic molecules are ubiquitous in the Milky Way.In our galaxy, complex organic molecules are often found in the intense environments of hot cores clumps of dense molecular gas surrounding the sites of star formation. However, its not yet fully understood how the complex organic molecules found in hot cores come to be. One possibility is that the compounds condense onto cold dust grains long before the young stars begin heating their natal shrouds. Alternatively, they might assemble themselves from the hot, dense gas surrounding the blazing protostars.Composite infrared and optical image of the N 113 star-forming region in the LMC. The ALMA coverage is indicated by the gray line. Click to enlarge. [Sewio et al. 2018]Detecting Complexity, a Galaxy AwayUsing ALMA, a team of researchers led by Marta Sewio (NASA Goddard Space Flight Center) recently detected two complex organic molecules methyl formate and dimethyl ether for the first time in our neighboring galaxy, the Large Magellanic Cloud (LMC). Previous searches for organic molecules in the LMC detected small amounts of methanol, the parentmolecule of the two newly-discovered compounds. By revealing the spectral signatures of dimethyl ether and methyl formate, Sewio and collaboratorsfurther prove thatorganic chemistry is hard at work in hot cores in the LMC.This discovery is momentous because dwarf galaxies like theLMC tend to have a lower abundance of the heavy elements that make up complex organic molecules most importantly, oxygen, carbon, and nitrogen. Beyond lacking the raw materials necessary to create complex molecules, the gas of low-metallicity galaxies does a poorer job preventing the penetration of high-energy photons. The impinging photons warm dust grains, resulting in a lower probability of forming and maintaining complex organic molecules. Despite this, organic molecules appear to beable todevelop and persist which has exciting implications for organic chemistry in low-metallicity environments.ALMA observation of emission by methyl formate in a hot core in the LMC.[Adapted from Sewio et al. 2018]A Lens into the PastIn the early universe, before the budding galaxies have had time to upcycle their abundant hydrogen into heavier elements, organic chemistry is thought to proceed slowly or not at all. The discovery of complex organic molecules in a nearby low-metallicity galaxy upends this theory and propels us toward a better understanding of the organic chemistry in the early universe.CitationMarta Sewio et al 2018ApJL853L19. doi:10.3847/2041-8213/aaa079

Feedback by AGN Jets and Wide-angle Winds on a Galactic Scale

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

Dugan, Zachary; Silk, Joseph; Gaibler, Volker

To investigate the differences in mechanical feedback from radio-loud and radio-quiet active galactic nuclei on the host galaxy, we perform 3D AMR hydrodynamic simulations of wide-angle, radio-quiet winds with different inclinations on a single, massive, gas-rich disk galaxy at a redshift of 2–3. We compare our results to hydrodynamic simulations of the same galaxy but with a jet. The jet has an inclination of 0° (perpendicular to the galactic plane), and the winds have inclinations of 0°, 45°, and 90°. We analyze the impact on the host’s gas, star formation, and circumgalactic medium. We find that jet feedback is energy-drivenmore » and wind feedback is momentum-driven. In all the simulations, the jet or wind creates a cavity mostly devoid of dense gas in the nuclear region where star formation is then quenched, but we find strong positive feedback in all the simulations at radii greater than 3 kpc. All four simulations have similar SFRs and stellar velocities with large radial and vertical components. However, the wind at an inclination of 90° creates the highest density regions through ram pressure and generates the highest rates of star formation due to its ongoing strong interaction with the dense gas of the galactic plane. With increased wind inclination, we find greater asymmetry in gas distribution and resulting star formation. Our model generates an expanding ring of triggered star formation with typical velocities of the order of 1/3 of the circular velocity, superimposed on the older stellar population. This should result in a potentially detectable blue asymmetry in stellar absorption features at kiloparsec scales.« less

Recent Advances in Organic Cosmochemistry

NASA Technical Reports Server (NTRS)

Sandford, Scott A.; Witteborn, Fred C. (Technical Monitor)

1994-01-01

The Astrochemistry Laboratory at NASA's Ames Research Center pursues a variety of activities, most of which center around the use of spectroscopy (ultraviolet to far-infrared) for the interpretation of astronomical and meteoritic data. One of our key activities is the study of the chemical and physical properties of cometary, interstellar, and planetary ice analogs and matrix-isolated molecules of astrophysical interest. As a result of these studies it is now known that a significant fraction of the carbon in the interstellar medium (ISM) is in reasonably complex forms, some of which are clearly of interest for exobiology. Examples of compounds known or suspected to be present in space include polycyclic aromatic hydrocarbons (PAHs), microdiamonds, an aliphatic-rich component found in the diffuse interstellar medium, and a variety of molecular species produced by the irradiation of mixed molecular ices in dense clouds. A number of the species produced by irradiation contain nitrogen and appear to offer an additional means of producing some of the amino acids found in meteorites. I will review these complex carbonaceous materials and discuss how they are connected with each other and the organic materials that ultimately ended up as part of our own Solar System. Specific points that will probably be covered include: (1) the composition of the ices in interstellar dense molecular clouds; (2) the more complex organic compounds produced when these ices are irradiated and/or warmed; (3) the detection of microdiamonds in space; (4) the discovery that aliphatic materials may constitute as much as 15% of all the carbon in the diffuse ISM, appears to be present everywhere in the galaxy, and yet seems to be present everywhere in the galaxy, and yet seems to be significantly concentrated towards the center of the galaxy.

Feedback by AGN Jets and Wide-angle Winds on a Galactic Scale

NASA Astrophysics Data System (ADS)

Dugan, Zachary; Gaibler, Volker; Silk, Joseph

2017-07-01

To investigate the differences in mechanical feedback from radio-loud and radio-quiet active galactic nuclei on the host galaxy, we perform 3D AMR hydrodynamic simulations of wide-angle, radio-quiet winds with different inclinations on a single, massive, gas-rich disk galaxy at a redshift of 2-3. We compare our results to hydrodynamic simulations of the same galaxy but with a jet. The jet has an inclination of 0° (perpendicular to the galactic plane), and the winds have inclinations of 0°, 45°, and 90°. We analyze the impact on the host’s gas, star formation, and circumgalactic medium. We find that jet feedback is energy-driven and wind feedback is momentum-driven. In all the simulations, the jet or wind creates a cavity mostly devoid of dense gas in the nuclear region where star formation is then quenched, but we find strong positive feedback in all the simulations at radii greater than 3 kpc. All four simulations have similar SFRs and stellar velocities with large radial and vertical components. However, the wind at an inclination of 90° creates the highest density regions through ram pressure and generates the highest rates of star formation due to its ongoing strong interaction with the dense gas of the galactic plane. With increased wind inclination, we find greater asymmetry in gas distribution and resulting star formation. Our model generates an expanding ring of triggered star formation with typical velocities of the order of 1/3 of the circular velocity, superimposed on the older stellar population. This should result in a potentially detectable blue asymmetry in stellar absorption features at kiloparsec scales.

Dense magnetized plasma associated with a fast radio burst.

PubMed

Masui, Kiyoshi; Lin, Hsiu-Hsien; Sievers, Jonathan; Anderson, Christopher J; Chang, Tzu-Ching; Chen, Xuelei; Ganguly, Apratim; Jarvis, Miranda; Kuo, Cheng-Yu; Li, Yi-Chao; Liao, Yu-Wei; McLaughlin, Maura; Pen, Ue-Li; Peterson, Jeffrey B; Roman, Alexander; Timbie, Peter T; Voytek, Tabitha; Yadav, Jaswant K

2015-12-24

Fast radio bursts are bright, unresolved, non-repeating, broadband, millisecond flashes, found primarily at high Galactic latitudes, with dispersion measures much larger than expected for a Galactic source. The inferred all-sky burst rate is comparable to the core-collapse supernova rate out to redshift 0.5. If the observed dispersion measures are assumed to be dominated by the intergalactic medium, the sources are at cosmological distances with redshifts of 0.2 to 1 (refs 10 and 11). These parameters are consistent with a wide range of source models. One fast burst revealed circular polarization of the radio emission, but no linear polarization was detected, and hence no Faraday rotation measure could be determined. Here we report the examination of archival data revealing Faraday rotation in the fast radio burst FRB 110523. Its radio flux and dispersion measure are consistent with values from previously reported bursts and, accounting for a Galactic contribution to the dispersion and using a model of intergalactic electron density, we place the source at a maximum redshift of 0.5. The burst has a much higher rotation measure than expected for this line of sight through the Milky Way and the intergalactic medium, indicating magnetization in the vicinity of the source itself or within a host galaxy. The pulse was scattered by two distinct plasma screens during propagation, which requires either a dense nebula associated with the source or a location within the central region of its host galaxy. The detection in this instance of magnetization and scattering that are both local to the source favours models involving young stellar populations such as magnetars over models involving the mergers of older neutron stars, which are more likely to be located in low-density regions of the host galaxy.

Characterizing the population of active galactic nuclei in dwarf galaxies

NASA Astrophysics Data System (ADS)

Baldassare, Vivienne F.; Reines, Amy E.; Gallo, Elena; Greene, Jenny E.

2017-01-01

Clues to super-massive black hole (BH) formation and growth reside in the population and properties of BHs in local dwarf galaxies. The masses of BHs in these systems are our best observational constraint on the masses of the first BH "seeds" at high redshift. Moreover, present-day dwarf galaxies are unlikely to have undergone major mergers, making them a relatively pristine testbed for studying triggers of BH accretion. However, in order to find BHs in dwarf galaxies outside the Local Group, it is necessary to search for signatures of accretion, i.e., active galactic nuclei (AGN). Until recently, only a handful of dwarf galaxies were known to contain AGN. However, large surveys such as the SDSS have led to the production of samples of over a hundred dwarf galaxies with AGN signatures (see e.g., Reines et al. 2013). My dissertation work has involved in-depth, multi-wavelength follow-up of nearby (z<0.055) dwarf galaxies with optical spectroscopic AGN signatures in SDSS.I analyzed high resolution spectra of dwarf galaxies with narrow-line AGN, which led to the discovery of a 50,000 MSun BH in the nucleus of RGG 118 - the smallest BH yet reported in a galaxy nucleus (Baldassare et al. 2015). I also used multi-epoch optical spectroscopy to study the nature of broad H-alpha emission in dwarf galaxies. A characteristic signature of dense gas orbiting around a BH, broad emission can also be produced by transient stellar processes. I showed that broad H-alpha in star-forming dwarf galaxies fades over a baseline of 5-10 years, and is likely produced by e.g., a Type II SN as opposed to an AGN. However, broad emission in dwarf galaxies with AGN/composite narrow lines is persistent and consistent across observations, suggesting an AGN origin (Baldassare et al. 2016). Finally, I analyzed X-ray and UV observations of dwarf galaxies with broad and narrow-line AGN signatures. All targets had nuclear X-ray detections at levels significantly higher than expected from X-ray binaries. With BH masses of ~105-106 MSun, inferred Eddington ratios range from 0.1-50%, akin to massive broad-line AGN at higher redshift (Baldassare et al. submitted). My dissertation work provides strong confirmation that these systems are bona fide AGN.

The connection between dark and baryonic matter in the process of galaxy formation

NASA Astrophysics Data System (ADS)

Trujillo, Sebastian

2014-01-01

Current galaxy formation theory still struggles to explain many essential galaxy properties. This thesis addresses these problems in the context of the interplay between baryons and dark matter in the concordance cosmological model. In the first part, we investigate galaxy abundance and scaling relations using a compilation of observational data along with large-scale cosmological simulations of dark matter (DM). We find that the standard cosmological model, in conjunction with halo abundance matching (HAM) and simple dynamical corrections, fits all basic statistics of galaxies more massive than the Large Magellanic Cloud (LMC). This zero-parameter model predicts the observed luminosity-velocity relation of early-and late-type galaxies, as well as the clustering of bright galaxies and the observed abundance of galaxies as a function of circular velocity. However, we find that all DM halos more massive than the LMC are much more abundant than the galaxies they host. Motivated by the model's shortcomings, in the second part we study the effect of baryons on galaxy formation using numerical simulations that include gas physics. We implement a model of star formation (SF) and stellar feedback based directly on observations of star-forming regions, where stellar feedback from massive stars includes radiation pressure, photoheating, supernovae, and stellar winds. We find that stellar radiation has a strong effect at z > 1, where it efficiently suppresses SF by dispersing cold and dense gas, preventing runaway growth of the stellar component, and yielding rising SF histories that reproduce many observations. Stellar feedback produces bulgeless discs with rotation curves and baryon fractions in excellent agreement with data. Feedback-driven blowouts reduce the central DM density of a dwarf, relieving tension between ACDM and observations. Based on these results, we begin to characterize the baryon cycle of galaxies and its imprint on studies of the circumgalactic medium (CGM). We find that feedback has a large impact on the exchange of gas and metals between the galaxy and the halo. This is evidenced in the spatial distribution of various gas phases and in the kinematics of accretion and outflows. We conclude that synergy between simulations and absorption-line studies is essential for disentangling the physics of galaxy formation in the context of ACDM.

A home for old stars

NASA Image and Video Library

2015-12-14

This image, taken with the Wide Field Planetary Camera 2 on board the NASA/ESA Hubble Space Telescope, shows the globular cluster Terzan 1. Lying around 20 000 light-years from us in the constellation of Scorpius (The Scorpion), it is one of about 150 globular clusters belonging to our galaxy, the Milky Way. Typical globular clusters are collections of around a hundred thousand stars, held together by their mutual gravitational attraction in a spherical shape a few hundred light-years across. It is thought that every galaxy has a population of globular clusters. Some, like the Milky Way, have a few hundred, while giant elliptical galaxies can have several thousand. They contain some of the oldest stars in a galaxy, hence the reddish colours of the stars in this image — the bright blue ones are foreground stars, not part of the cluster. The ages of the stars in the globular cluster tell us that they were formed during the early stages of galaxy formation! Studying them can also help us to understand how galaxies formed. Terzan 1, like many globular clusters, is a source of X-rays. It is likely that these X-rays come from binary star systems that contain a dense neutron star and a normal star. The neutron star drags material from the companion star, causing a burst of X-ray emission. The system then enters a quiescent phase in which the neutron star cools, giving off X-ray emission with different characteristics, before enough material from the companion builds up to trigger another outburst.

HIDING IN PLAIN SIGHT: RECORD-BREAKING COMPACT STELLAR SYSTEMS IN THE SLOAN DIGITAL SKY SURVEY

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

Sandoval, Michael A.; Vo, Richard P.; Romanowsky, Aaron J.

2015-07-20

Motivated by the recent, serendipitous discovery of the densest known galaxy, M60-UCD1, we present two initial findings from a follow-up search, using the Sloan Digital Sky Survey, Subaru/Suprime-Cam, and Hubble Space Telescope imaging, and SOuthern Astrophysical Research (SOAR)/Goodman spectroscopy. The first object discovered, M59-UCD3, has a similar size to M60-UCD1 (half-light radius of r{sub h} ∼ 20 pc) but is 40% more luminous (M{sub V} ∼ −14.6), making it the new densest-known galaxy. The second, M85-HCC1, has a size like a typical globular cluster (GC; r{sub h} ∼ 1.8 pc) but is much more luminous (M{sub V} ∼ −12.5). Thismore » hypercompact cluster is by far the densest confirmed free-floating stellar system, and is equivalent to the densest known nuclear star clusters. From spectroscopy, we find that both objects are relatively young (∼9 and ∼3 Gyr, respectively), with metal-abundances that resemble those of galaxy centers. Their host galaxies show clear signs of large-scale disturbances, and we conclude that these dense objects are the remnant nuclei of recently accreted galaxies. M59-UCD3 is an ideal target for follow-up with high-resolution imaging and spectroscopy to search for an overweight central supermassive black hole as was discovered in M60-UCD1. These findings also emphasize the potential value of ultra-compact dwarfs and massive GCs as tracers of the assembly histories of galaxies.« less

Observing Interstellar and Intergalactic Magnetic Fields

NASA Astrophysics Data System (ADS)

Han, J. L.

2017-08-01

Observational results of interstellar and intergalactic magnetic fields are reviewed, including the fields in supernova remnants and loops, interstellar filaments and clouds, Hii regions and bubbles, the Milky Way and nearby galaxies, galaxy clusters, and the cosmic web. A variety of approaches are used to investigate these fields. The orientations of magnetic fields in interstellar filaments and molecular clouds are traced by polarized thermal dust emission and starlight polarization. The field strengths and directions along the line of sight in dense clouds and cores are measured by Zeeman splitting of emission or absorption lines. The large-scale magnetic fields in the Milky Way have been best probed by Faraday rotation measures of a large number of pulsars and extragalactic radio sources. The coherent Galactic magnetic fields are found to follow the spiral arms and have their direction reversals in arms and interarm regions in the disk. The azimuthal fields in the halo reverse their directions below and above the Galactic plane. The orientations of organized magnetic fields in nearby galaxies have been observed through polarized synchrotron emission. Magnetic fields in the intracluster medium have been indicated by diffuse radio halos, polarized radio relics, and Faraday rotations of embedded radio galaxies and background sources. Sparse evidence for very weak magnetic fields in the cosmic web is the detection of the faint radio bridge between the Coma cluster and A1367. Future observations should aim at the 3D tomography of the large-scale coherent magnetic fields in our Galaxy and nearby galaxies, a better description of intracluster field properties, and firm detections of intergalactic magnetic fields in the cosmic web.

Must Star-forming Galaxies Rapidly Get Denser before They Quench?

NASA Astrophysics Data System (ADS)

Abramson, L. E.; Morishita, T.

2018-05-01

Using the deepest data yet obtained, we find no evidence preferring compaction-triggered quenching—where rapid increases in galaxy density truncate star formation—over a null hypothesis in which galaxies age at constant surface density ({{{Σ }}}e\\equiv {M}* /2π {r}e2). Results from two fully empirical analyses and one quenching-free model calculation support this claim at all z ≤ 3: (1) qualitatively, galaxies’ mean U–V colors at 6.5 ≲ {log}{{{Σ }}}e/{\\text{}}{M}ȯ {kpc}}-2≲ 10 have reddened at rates/times correlated with {{{Σ }}}e, implying that there is no density threshold at which galaxies turn red but that {{{Σ }}}e sets the pace of maturation; (2) quantitatively, the abundance of {log}{M}* /{\\text{}}{M}ȯ ≥slant 9.4 red galaxies never exceeds that of the total population a quenching time earlier at any {{{Σ }}}e, implying that galaxies need not transit from low to high densities before quenching; (3) applying d{log}{r}e/{dt}=1/2 d{log}{M}* /{dt} to a suite of lognormal star formation histories reproduces the evolution of the size–mass relation at {log}{M}* /{\\text{}}{M}ȯ ≥slant 10. All results are consistent with evolutionary rates being set ab initio by global densities, with denser objects evolving faster than less-dense ones toward a terminal quiescence induced by gas depletion or other ∼Hubble-timescale phenomena. Unless stellar ages demand otherwise, observed {{{Σ }}}e thresholds need not bear any physical relation to quenching beyond this intrinsic density–formation epoch correlation, adding to Lilly & Carollo’s arguments to that effect.

Compact Starburst Galaxies with Fast Outflows: Spatially Resolved Stellar Mass Profiles

NASA Astrophysics Data System (ADS)

Gottlieb, Sophia; Diamond-Stanic, Aleksandar; Lipscomb, Charles; Ohene, Senyo; Rines, Josh; Moustakas, John; Sell, Paul; Tremonti, Christy; Coil, Alison; Rudnick, Gregory; Hickox, Ryan C.; Geach, James; Kepley, Amanda

2018-01-01

Powerful galactic winds driven by stellar feedback and black hole accretion are thought to play an important role in regulating star formation in galaxies. In particular, strong stellar feedback from supernovae, stellar winds, radiation pressure, and cosmic rays is required by simulations of star-forming galaxies to prevent the vast majority of baryons from cooling and collapsing to form stars. However, it remains unclear whether these stellar processes play a significant role in expelling gas and shutting down star formation in massive progenitors of quiescent galaxies. What are the limits of stellar feedback? We present multi-band photometry with HST/WFC3 (F475W, F814W, F160W) for a dozen compact starburst galaxies at z~0.6 with half-light radii that suggest incredibly large central escape velocities. These massive galaxies are driving fast (>1000 km/s) outflows that have been previously attributed to stellar feedback associated with the compact (r~100 pc) starburst. But how compact is the stellar mass? In the context of the stellar feedback hypothesis, it is unclear whether these fast outflows are being driven at velocities comparable to the escape velocity of an incredibly dense stellar system (as predicted by some models of radiation-pressure winds) or at velocities that exceed the central escape velocity by large factor. Our spatially resolved measurements with HST show that the stellar mass is more extended than the light, and this requires that the physical mechanism responsible for driving the winds must be able to launch gas at velocities that are factors of 5-10 beyond the central escape velocity.

The ESO Nearby Abell Cluster Survey. VI. Spatial distribution and kinematics of early- and late-type galaxies

NASA Astrophysics Data System (ADS)

de Theije, P. A. M.; Katgert, P.

1999-01-01

Analysis of the data obtained in the ESO Nearby Abell Cluster Survey (ENACS) has shown that the space distribution and kinematics of galaxies with detectable emission lines in their spectra differ significantly from those of galaxies without emission lines. This result, and details of the kinematics, were considered as support for the idea that at least the spirals with emission lines are on orbits that are not isotropic. This might indicate that this subset of late-type galaxies either has `first approach'-orbits towards the dense core of their respective clusters, or has orbits that `avoid' the core. The galaxies with emission lines are essentially all late-type galaxies. On the other hand, the emission-line galaxies represent only about a third of the late-type galaxies, the majority of which do not show detectable emission lines. The galaxies without emission lines are therefore a mix of early- and late-type galaxies. In this paper we attempt to separate early- and late-type galaxies, and we study possible differences in distribution and kinematics of the two galaxy classes. For only about 10% of the galaxies in the ENACS, the morphology is known from imaging. Here, we describe our classification on the basis of the ENACS spectrum. The significant information in each spectrum is compressed into 15 Principal Components, which are used as input for an Artificial Neural Network. The latter is `trained' with 150 of the 270 galaxies for which a morphological type is available from Dressler, and subsequently used to classify each galaxy. This yields a classification for two-thirds of the ENACS galaxies. The Artificial Neural Network has two output classes: early-type (E+S0) and late-type (S+I) galaxies. We do not distinguish E and S0 galaxies, because these cannot be separated very robustly on the basis of the spectrum. The success rate of the classification is estimated from the sample of 120 galaxies with Dressler morphologies which were not used to train the ANN. The success rate is higher for early-type than for late-type galaxies (78+/-6% vs. {63+/-6%}). The weighted average success rate, irrespective of type, is {73+/-4%}. The success rate is somewhat larger for the training set, and highest for the galaxies with emission lines. Of the 3798 galaxies that were classified from their spectrum {57+/-7%} are of early type, and {43+/-7%} of late type. Using a subset of these 3798 galaxies, we constructed a composite cluster of 2594 galaxies, 399 of which have emission lines and are therefore almost exclusively spirals and irregulars. The kinematics and spatial distribution of the late-type galaxies without emission lines resemble much more those of the early-type galaxies than those of the late-type galaxies with emission lines. Yet, the late-type galaxies without emission lines may have a somewhat larger velocity dispersion and a slightly less centrally concentrated distribution than the early-type galaxies. Only the late-type galaxies with emission lines appear to have a considerably larger global velocity dispersion and a much less concentrated projected density profile than the other galaxies. Thus, the suggestion of fairly radial, and possibly `first approach' orbits applies only to spirals with emission lines. The early-type galaxies with emission lines (among which the AGN), may also have a large velocity dispersion and be concentrated towards the cluster centre. Based on observations collected at the European Southern Observatory (La Silla, Chile)

CSM interaction and dust formation in SN 2010jl .

NASA Astrophysics Data System (ADS)

Krafton, K.; Clayton, G. C.

The origin of dust in galaxies >1 Gyr old has remained an unsolved mystery for over a decade. One proposed solution is dust produced by core collapse supernovae (CCSNe). Theorists have shown that 0.1-1 M⊙ of dust must be produced per supernova for this to work as an explanation for the dust in young galaxies. SN 1987A has produced ˜1 M⊙ of dust since its detonation. However, most supernovae have been found to only produce 10-4 - 10-2 M⊙ of dust. The energetic type IIn SN 2010jl is located in UGC 5189, in a dense shell of CSM. As dust condenses in the SN ejecta, we see, (1) a sudden decrease in continuum brightness in the visible due to increased dust extinction, (2) the development of an infrared excess in the SN light curve arising from dust grains absorbing high-energy photons and re-emitting them in the infrared, and (3) the development of asymmetric, blue-shifted emission-line profiles, caused by dust forming in the ejecta, and preferentially extinguishing redshifted emission. A dense circumstellar material (CSM) may increase the dust production by supernovae. We observe signs of strong interaction between the SN ejecta and a dense CSM in SN 2010jl. SN 2010jl has been a source of much debate in the CCSN community, particularly over when and how much dust it formed. The light curve shows strong signs of dust formation after 260 days. Arguments over these subjects have been based on the evolution of the light curve and spectra. We present new optical and IR photometry, as well as optical spectroscopy, of SN 2010jl over 2000 days. We estimate dust masses using the DAMOCLES and MOCASSIN radiative transfer codes.

Under the sword of Damocles: plausible regeneration of dark matter cusps at the smallest galactic scales

NASA Astrophysics Data System (ADS)

Laporte, Chervin F. P.; Peñarrubia, Jorge

2015-04-01

We study the evolution of the dark matter (DM) halo profiles of dwarf galaxies driven by the accretion of DM substructures through controlled N-body experiments. Our initial conditions assume that early supernova feedback erases the primordial DM cusps of haloes with z = 0 masses of 109 - 1010 M⊙. The orbits and masses of the infalling substructures are borrowed from the Aquarius cosmological simulations. Our experiments show that a fraction of haloes that undergo 1:3 down to 1:30 mergers are susceptible to reform a DM cusp by z ≈ 0. Cusp regrowth is driven by the accretion of DM substructures that are dense enough to reach the central regions of the main halo before being tidally disrupted. The infall of substructures on the mean of the reported mass-concentration relation and a mass ratio above 1:6 systematically leads to cusp regrowth. Substructures with 1:6-1:8, and 1:8-1:30 only reform DM cusps if their densities are 1σ and 2σ above the mean, respectively. The merging time-scales of these dense, low-mass substructures is relatively long (5 - 11 Gyr), which may pose a time-scale problem for the longevity of DM cores in dwarfs galaxies and possibly explain the existence of dense dwarfs-like Draco. These results suggest that within cold dark matter a non-negligible level of scatter in the mass profiles of galactic haloes acted on by feedback is to be expected given the stochastic mass accretion histories of low-mass haloes and the diverse star formation histories observed in the Local Group dwarfs.

Giant Radio Jet Coming From Wrong Kind of Galaxy

NASA Astrophysics Data System (ADS)

2003-01-01

Giant jets of subatomic particles moving at nearly the speed of light have been found coming from thousands of galaxies across the Universe, but always from elliptical galaxies or galaxies in the process of merging -- until now. Using the combined power of the Hubble Space Telescope, the Very Large Array (VLA) and the 8-meter Gemini-South Telescope, astronomers have discovered a huge jet coming from a spiral galaxy similar to our own Milky Way. Radio-optical view of galaxy Combined HST and VLA image of the galaxy 0313-192. Optical HST image shows the galaxy edge-on; VLA image, shown in red, reveals giant jet of speeding particles. For more images, see this link below. CREDIT: Keel, Ledlow & Owen; STScI,NRAO/AUI/NSF, NASA "We've always thought spirals were the wrong kind of galaxy to generate these huge jets, but now we're going to have to re-think some of our ideas on what produces these jets," said William Keel, a University of Alabama astronomer who led the research team. Keel worked with Michael Ledlow of Gemini Observatory and Frazer Owen of the National Radio Astronomy Observatory. The scientists reported their findings at the American Astronomical Society's meeting in Seattle, Washington. "Further study of this galaxy may provide unique insights on just what needs to happen in a galaxy to produce these powerful jets of particles," Keel said. In addition, Owen said, "The loose-knit nature of the cluster of galaxies in which this galaxy resides may play a part in allowing this particular spiral to produce jets." Astronomers believe such jets originate at the cores of galaxies, where supermassive black holes provide the tremendous gravitational energy to accelerate particles to nearly the speed of light. Magnetic fields twisted tightly by spinning disks of material being sucked into the black hole are presumed to narrow the speeding particles into thin jets, like a nozzle on a garden hose. Both elliptical and spiral galaxies are believed to harbor supermassive black holes at their cores. The discovery that the jet was coming from a spiral galaxy dubbed 0313-192 required using a combination of radio, optical and infrared observations to examine the galaxy and its surroundings. The story began more than 20 years ago, when Owen began a survey of 500 galaxy clusters using the National Science Foundation's then-new VLA to make radio images of the clusters. In the 1990s, Ledlow joined the project, making optical-telescope images of the same clusters as part of his research for a Ph.D dissertation at the University of New Mexico. An optical image from Kitt Peak National Observatory gave a hint that this galaxy, clearly seen with a jet in the VLA images, might be a spiral. Nearly a billion light-years from Earth, 0313-192 proved an elusive target, however. Subsequent observations with the VLA and the 3.5-meter telescope at Apache Point Observatory supported the idea that the galaxy might be a spiral but still were inconclusive. In the Spring of 2002, astronauts installed the Advanced Camera for Surveys on the Hubble Space Telescope. This new facility produced a richly-detailed image of 0313-192, showing that it is a dust-rich spiral seen almost exactly edge-on. "The finely-detailed Hubble image resolved any doubt and proved that this galaxy is a spiral," Ledlow said. Infrared images with the Gemini-South telescope complemented the Hubble images and further confirmed the galaxy's spiral nature. Now, the astronomers seek to understand why this one spiral galaxy, unlike all others seen so far, is producing the bright jets seen with the VLA and other radio telescopes. Several factors may have combined, the researchers feel. "This galaxy's disk is twisted, and that may indicate that it has been disturbed by a close passage of another galaxy or may have swallowed up a companion dwarf galaxy," Keel said. He added, "This galaxy shows signs of having a very massive black hole at its core, and the jets are taking the shortest path out of the galaxy's own gas." Owen points out that 0313-192 resides in a cluster of galaxies called Abell 428. The scientists have discovered that Abell 428 is not a dense cluster, but rather a loose collection of small groups of galaxies. In order to see the large jets so common to elliptical galaxies, Owen said, "you may need pressure from a cluster's intergalactic medium to keep the particles and magnetic fields from dispersing so rapidly that the jet can't stay together." However, "A spiral won't survive in a dense cluster," Owen said. Thus, the looser collection of galaxy groups that makes up Abell 428 may be "just the right environment to allow the spiral to survive but still to provide the pressure needed to keep the jets together." In any case, the unique example provided by this jet-producing spiral galaxy "raises questions about some of our basic assumptions regarding jet production in galaxies," Owen said. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. Gemini is an international partnership managed by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation..

Hubble Helps Find Smallest Known Galaxy Containing a Supermassive Black Hole

NASA Image and Video Library

2017-12-08

This is an illustration of a supermassive black hole, weighing as much as 21 million suns, located in the middle of the ultradense galaxy M60-UCD1. The dwarf galaxy is so dense that millions of stars fill the sky as seen by an imaginary visitor. Because no light can escape from the black hole, it appears simply in silhouette against the starry background. The black hole's intense gravitational field warps the light of the background stars to form ring-like images just outside the dark edges of the black hole's event horizon. Combined observations by the Hubble Space Telescope and Gemini North telescope determined the presence of the black hole inside such a small and dense galaxy. More info: Astronomers using data from NASA’s Hubble Space Telescope and ground observation have found an unlikely object in an improbable place -- a monster black hole lurking inside one of the tiniest galaxies ever known. The black hole is five times the mass of the one at the center of our Milky Way galaxy. It is inside one of the densest galaxies known to date -- the M60-UCD1 dwarf galaxy that crams 140 million stars within a diameter of about 300 light-years, which is only 1/500th of our galaxy’s diameter. If you lived inside this dwarf galaxy, the night sky would dazzle with at least 1 million stars visible to the naked eye. Our nighttime sky as seen from Earth’s surface shows 4,000 stars. The finding implies there are many other compact galaxies in the universe that contain supermassive black holes. The observation also suggests dwarf galaxies may actually be the stripped remnants of larger galaxies that were torn apart during collisions with other galaxies rather than small islands of stars born in isolation. “We don’t know of any other way you could make a black hole so big in an object this small,” said University of Utah astronomer Anil Seth, lead author of an international study of the dwarf galaxy published in Thursday’s issue of the journal Nature. Seth’s team of astronomers used the Hubble Space Telescope and the Gemini North 8-meter optical and infrared telescope on Hawaii’s Mauna Kea to observe M60-UCD1 and measure the black hole’s mass. The sharp Hubble images provide information about the galaxy’s diameter and stellar density. Gemini measures the stellar motions as affected by the black hole’s pull. These data are used to calculate the mass of the black hole. Black holes are gravitationally collapsed, ultra-compact objects that have a gravitational pull so strong that even light cannot escape. Supermassive black holes -- those with the mass of at least one million stars like our sun -- are thought to be at the centers of many galaxies. The black hole at the center of our Milky Way galaxy has the mass of four million suns. As heavy as that is, it is less than 0.01 percent of the Milky Way’s total mass. By comparison, the supermassive black hole at the center of M60-UCD1, which has the mass of 21 million suns, is a stunning 15 percent of the small galaxy’s total mass. “That is pretty amazing, given that the Milky Way is 500 times larger and more than 1,000 times heavier than the dwarf galaxy M60-UCD1,” Seth said. One explanation is that M60-UCD1 was once a large galaxy containing 10 billion stars, but then it passed very close to the center of an even larger galaxy, M60, and in that process all the stars and dark matter in the outer part of the galaxy were torn away and became part of M60. The team believes that M60-UCD1 may eventually be pulled to fully merge with M60, which has its own monster black hole that weighs a whopping 4.5 billion solar masses, or more than 1,000 times bigger than the black hole in our galaxy. When that happens, the black holes in both galaxies also likely will merge. Both galaxies are 50 million light-years away. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington. For images and more information about Hubble, visit: www.nasa.gov/hubble NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

The Soft X-ray View of Ultra Fast Outflows

NASA Astrophysics Data System (ADS)

Reeves, J.; Braito, V.; Nardini, E.; Matzeu, G.; Lobban, A.; Costa, M.; Pounds, K.; Tombesi, F.; Behar, E.

2017-10-01

The recent large XMM-Newton programmes on the nearby quasars PDS 456 and PG 1211+143 have revealed prototype ultra fast outflows in the iron K band through highly blue shifted absorption lines. The wind velocities are in excess of 0.1c and are likely to make a significant contribution to the host galaxy feedback. Here we present evidence for the signature of the fast wind in the soft X-ray band from these luminous quasars, focusing on the spectroscopy with the RGS. In PDS 456, the RGS spectra reveal the presence of soft X-ray broad absorption line profiles, which suggests that PDS 456 is an X-ray equivalent to the BAL quasars, with outflow velocities reaching 0.2c. In PG 1211, the soft X-ray RGS spectra show a complex of several highly blue shifted absorption lines over a wide range of ionisation and reveal outflowing components with velocities between 0.06-0.17c. For both quasars, the soft X-ray absorption is highly variable, even on timescales of days and is most prominent when the quasar flux is low. Overall the results imply the presence of a soft X-ray component of the ultra fast outflows, which we attribute to a clumpy or inhomogeneous phase of the disk wind.

Understanding the physical processes driving galaxy evolution in clusters : a case study of two z~0.5 galaxy clusters

NASA Astrophysics Data System (ADS)

Moran, Sean M.

Clusters of galaxies represent the largest laboratories in the universe for testing the incredibly chaotic physics governing the collapse of baryons into the stars, galaxies, groups, and diffuse clouds that we see today. Within the cluster environment, there are a wide variety of physical processes that may be acting to transform galaxies.In this thesis, we combine extensive Keck spectroscopy with wide-field HST imaging to perform a detailed case study of two intermediate redshift galaxy clusters, Cl 0024+1654 (z=0.395) and MS 0451-03 (z=0.540). Leveraging a comprehensive multiwavelength data set that spans the X-ray to infrared, and with spectral-line measurements serving as the key to revealing both the recent star-formation histories and kinematics of infalling galaxies, we aim to shed light on the environmental processes that could be acting to transform galaxies in clusters.We adopt a strategy to make maximal use of our HST-based morphologies by splitting our sample of cluster galaxies according to morphological type, characterizing signs of recent evolution in spirals and early types separately. This approach proves to be powerful in identifying galaxies that are currently being altered by an environmental interaction: early-type galaxies that have either been newly transformed or prodded back into an active phase, and spiral galaxies where star formation is being suppressed or enhanced all stand out in our sample.We begin by using variations in the early-type galaxy population as indicators of recent activity. Because ellipticals and S0s form such a homogeneous class in the local universe, we are sensitive to even very subtle signatures of recent and current environmental interactions. This study has yielded two key results: By constructing the Fundamental Plane (FP) of Cl 0024, we observe that elliptical and S0 galaxies exhibit a high scatter in their FP residuals, which occurs only among galaxies in the cluster core, suggesting a turbulent assembly history for Cl 0024 early types. Near the Virial radius of Cl 0024, we observe a number of compact, intermediate-mass ellipticals undergoing a burst of star formation or weak AGN activity, indicated by strong [O II] emission; their locations may mark the minimum radius at which merging is effective in each cluster.While E+S0 galaxies do prove to be sensitive indicators of environmental interaction, it is the spiral galaxies that, of course, host the bulk of star formation within and around these clusters. We therefore probe for kinematic disturbances in spiral disks by measuring resolved rotation curves from optical emission lines, and constructing the Tully-Fisher relation for spirals across Cl 0024 and MS 0451. We find that the cluster Tully-Fisher relation exhibits significantly higher scatter than the field relation. In probing for the origin of this difference, we find that the central mass densities of star-forming spirals exhibit a sharp break near the cluster Virial radius, with spirals in the cluster outskirts exhibiting significantly lower densities. We argue that these results considered together demonstrate that cluster spirals are kinematically disturbed by their environment, likely due to galaxy-galaxy interactions (harassment).We then discuss our most powerful method of tracking galaxy evolution across Cl 0024 and MS 0451: identifying and studying "transition galaxies"-galaxies whose stellar populations or dynamical states indicate a recent or ongoing change in morphology or star formation rate. Such galaxies are often revealed by star formation histories that seem to be at odds with the galaxy morphologies: for example, spiral galaxies with no signs of star formation, or elliptical galaxies that do show signs of star formation.We identify and study one such class of objects, the "passive spirals" in Cl 0024. These objects exhibit no emission lines in their spectra, suggesting a lack of star formation, yet are surprisingly detected in the UV, revealing the presence of young stars. By modeling the different temporal sensitivities of UV and spectroscopic data to recent activity, we show that star formation in Cl 0024 passive spirals has decayed on timescales of less than 1 Gyr, consistent with the action of "gas starvation".We then build on and link together our previous indications of galaxy evolution at work, aiming to piece together a more comprehensive picture of how cluster galaxies are affected by their environment at intermediate redshift. To accomplish this, we document what we believe to be the first direct evidence for the transformation of spirals into S0s: through an analysis of their stellar populations and recent star formation rates, we link the passive spiral galaxies in both clusters to their eventual end states as newly generated cluster S0 galaxies. Differences between the two clusters in both the timescales and spatial location of this conversion process allow us to evaluate the relative importance of several proposed physical mechanisms that could be responsible for the transformation. Combined with other diagnostics that are sensitive to either ICM-driven galaxy evolution or galaxy-galaxy interactions, we describe a self-consistent picture of galaxy evolution in clusters.We find that spiral galaxies within infalling groups have already begun a slow process of conversion into S0s primarily via gentle galaxy-galaxy interactions that act to quench star formation. The fates of spirals upon reaching the core of the cluster depend heavily on the cluster ICM, with rapid conversion of all remaining spirals into S0s via ram-pressure stripping in clusters where the ICM is dense. In the presence of a less-dense ICM, the conversion continues at a slower pace, with galaxy-galaxy interactions continuing to play a role along with "starvation" by the ICM. We conclude that the buildup of the local S0 population through the transformation of spiral galaxies is a heterogeneous process that nevertheless proceeds robustly across a variety of different environments from cluster outskirts to cores.

Where are compact groups in the local Universe?

NASA Astrophysics Data System (ADS)

Díaz-Giménez, Eugenia; Zandivarez, Ariel

2015-06-01

Aims: The purpose of this work is to perform a statistical analysis of the location of compact groups in the Universe from observational and semi-analytical points of view. Methods: We used the velocity-filtered compact group sample extracted from the Two Micron All Sky Survey for our analysis. We also used a new sample of galaxy groups identified in the 2M++ galaxy redshift catalogue as tracers of the large-scale structure. We defined a procedure to search in redshift space for compact groups that can be considered embedded in other overdense systems and applied this criterion to several possible combinations of different compact and galaxy group subsamples. We also performed similar analyses for simulated compact and galaxy groups identified in a 2M++ mock galaxy catalogue constructed from the Millennium Run Simulation I plus a semi-analytical model of galaxy formation. Results: We observed that only ~27% of the compact groups can be considered to be embedded in larger overdense systems, that is, most of the compact groups are more likely to be isolated systems. The embedded compact groups show statistically smaller sizes and brighter surface brightnesses than non-embedded systems. No evidence was found that embedded compact groups are more likely to inhabit galaxy groups with a given virial mass or with a particular dynamical state. We found very similar results when the analysis was performed using mock compact and galaxy groups. Based on the semi-analytical studies, we predict that 70% of the embedded compact groups probably are 3D physically dense systems. Finally, real space information allowed us to reveal the bimodal behaviour of the distribution of 3D minimum distances between compact and galaxy groups. Conclusions: The location of compact groups should be carefully taken into account when comparing properties of galaxies in environments that are a priori different. Appendices are available in electronic form at http://www.aanda.orgFull Tables B.1 and B.2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/578/A61

Galaxy-galaxy and galaxy-cluster lensing with the SDSS and FIRST surveys

NASA Astrophysics Data System (ADS)

Demetroullas, C.; Brown, M. L.

2018-01-01

We perform a galaxy-galaxy lensing study by correlating the shapes of ∼2.7 × 105 galaxies selected from the VLA FIRST (Faint Images of the Radio Sky at Twenty centimetres) radio survey with the positions of ∼38.5 million Sloan Digital Sky Survey (SDSS) galaxies, ∼132 000 Brightest Cluster Galaxies (BCGs) and ∼78 000 SDSS galaxies that are also detected in the VLA FIRST survey. The measurements are conducted on angular scales θ ≲ 1200 arcsec. On scales θ ≲ 200 arcsec, we find that the measurements are corrupted by residual systematic effects associated with the instrumental beam of the VLA data. Using simulations, we show that we can successfully apply a correction for these effects. Using the three lens samples (the SDSS DR10 sample, the BCG sample and the SDSS-FIRST matched object sample), we measure a tangential shear signal that is inconsistent with 0 at the 10.2σ, 3.8σ and 9σ levels, respectively. Fitting an NFW model to the detected signals, we find that the ensemble mass profile of the BCG sample agrees with the values in the literature. However, the mass profiles of the SDSS DR10 and the SDSS-FIRST matched object samples are found to be shallower and steeper than results in the literature, respectively. The best-fitting Virial masses for the SDSS DR10, BCG and SDSS-FIRST matched samples, derived using an NFW model and allowing for a varying concentration factor, are M_{200}^SDSS-DR10 = (1.2 ± 0.4) × 10^{12} M_{⊙}, M_{200}^BCG = (1.4 ± 1.3) × 10^{13} M_{⊙} and M_{200}^SDSS-FIRST =8.0 ± 4.2 × 10^{13} M_{⊙}, respectively. These results are in good agreement (within ∼2σ) with values in the literature. Our findings suggest that for galaxies to be bright both in the radio and in the optical, they must be embedded in very dense environment on scales R ≲ 1 Mpc.

Deep Galex Observations of the Coma Cluster: Source Catalog and Galaxy Counts

NASA Technical Reports Server (NTRS)

Hammer, D.; Hornschemeier, A. E.; Mobasher, B.; Miller, N.; Smith, R.; Arnouts, S.; Milliard, B.; Jenkins, L.

2010-01-01

We present a source catalog from deep 26 ks GALEX observations of the Coma cluster in the far-UV (FUV; 1530 Angstroms) and near-UV (NUV; 2310 Angstroms) wavebands. The observed field is centered 0.9 deg. (1.6 Mpc) south-west of the Coma core, and has full optical photometric coverage by SDSS and spectroscopic coverage to r-21. The catalog consists of 9700 galaxies with GALEX and SDSS photometry, including 242 spectroscopically-confirmed Coma member galaxies that range from giant spirals and elliptical galaxies to dwarf irregular and early-type galaxies. The full multi-wavelength catalog (cluster plus background galaxies) is 80% complete to NUV=23 and FUV=23.5, and has a limiting depth at NUV=24.5 and FUV=25.0 which corresponds to a star formation rate of 10(exp -3) solar mass yr(sup -1) at the distance of Coma. The GALEX images presented here are very deep and include detections of many resolved cluster members superposed on a dense field of unresolved background galaxies. This required a two-fold approach to generating a source catalog: we used a Bayesian deblending algorithm to measure faint and compact sources (using SDSS coordinates as a position prior), and used the GALEX pipeline catalog for bright and/or extended objects. We performed simulations to assess the importance of systematic effects (e.g. object blends, source confusion, Eddington Bias) that influence source detection and photometry when using both methods. The Bayesian deblending method roughly doubles the number of source detections and provides reliable photometry to a few magnitudes deeper than the GALEX pipeline catalog. This method is also free from source confusion over the UV magnitude range studied here: conversely, we estimate that the GALEX pipeline catalogs are confusion limited at NUV approximately 23 and FUV approximately 24. We have measured the total UV galaxy counts using our catalog and report a 50% excess of counts across FUV=22-23.5 and NUV=21.5-23 relative to previous GALEX measurements, which is not attributed to cluster member galaxies. Our galaxy counts are a better match to deeper UV counts measured with HST.

The ATLAS3D project - X. On the origin of the molecular and ionized gas in early-type galaxies

NASA Astrophysics Data System (ADS)

Davis, Timothy A.; Alatalo, Katherine; Sarzi, Marc; Bureau, Martin; Young, Lisa M.; Blitz, Leo; Serra, Paolo; Crocker, Alison F.; Krajnović, Davor; McDermid, Richard M.; Bois, Maxime; Bournaud, Frédéric; Cappellari, Michele; Davies, Roger L.; Duc, Pierre-Alain; de Zeeuw, P. Tim; Emsellem, Eric; Khochfar, Sadegh; Kuntschner, Harald; Lablanche, Pierre-Yves; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Scott, Nicholas; Weijmans, Anne-Marie

2011-10-01

We make use of interferometric CO and H I observations, and optical integral-field spectroscopy from the ATLAS3D survey, to probe the origin of the molecular and ionized interstellar medium (ISM) in local early-type galaxies. We find that 36 ± 5 per cent of our sample of fast-rotating early-type galaxies have their ionized gas kinematically misaligned with respect to the stars, setting a strong lower limit on the importance of externally acquired gas (e.g. from mergers and cold accretion). Slow rotators have a flat distribution of misalignments, indicating that the dominant source of gas is external. The molecular, ionized and atomic gas in all the detected galaxies are always kinematically aligned, even when they are misaligned from the stars, suggesting that all these three phases of the ISM share a common origin. In addition, we find that the origin of the cold and warm gas in fast-rotating early-type galaxies is strongly affected by environment, despite the molecular gas detection rate and mass fractions being fairly independent of group/cluster membership. Galaxies in dense groups and the Virgo cluster nearly always have their molecular gas kinematically aligned with the stellar kinematics, consistent with a purely internal origin (presumably stellar mass loss). In the field, however, kinematic misalignments between the stellar and gaseous components indicate that at least 42 ± 5 per cent of local fast-rotating early-type galaxies have their gas supplied from external sources. When one also considers evidence of accretion present in the galaxies' atomic gas distributions, ≳46 per cent of fast-rotating field ETGs are likely to have acquired a detectable amount of ISM from accretion and mergers. We discuss several scenarios which could explain the environmental dichotomy, including preprocessing in galaxy groups/cluster outskirts and the morphological transformation of spiral galaxies, but we find it difficult to simultaneously explain the kinematic misalignment difference and the constant detection rate. Furthermore, our results suggest that galaxy mass may be an important independent factor associated with the origin of the gas, with the most massive fast-rotating galaxies in our sample (MK≲-24 mag; stellar mass of ≈8 × 1010 M⊙) always having kinematically aligned gas. This mass dependence appears to be independent of environment, suggesting it is caused by a separate physical mechanism.

The ultraviolet attenuation law in backlit spiral galaxies

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

Keel, William C.; Manning, Anna M.; Holwerda, Benne W.

The effective extinction law (attenuation behavior) in galaxies in the emitted ultraviolet (UV) regime is well known only for actively star-forming objects and combines effects of the grain properties, fine structure in the dust distribution, and relative distributions of stars and dust. We use Galaxy Evolution Explorer, XMM Optical Monitor, and Hubble Space Telescope (HST) data to explore the UV attenuation in the outer parts of spiral disks which are backlit by other UV-bright galaxies, starting with the candidate list of pairs provided by Galaxy Zoo participants. New optical images help to constrain the geometry and structure of the targetmore » galaxies. Our analysis incorporates galaxy symmetry, using non-overlapping regions of each galaxy to derive error estimates on the attenuation measurements. The entire sample has an attenuation law across the optical and UV that is close to the Calzetti et al. form; the UV slope for the overall sample is substantially shallower than found by Wild et al., which is a reasonable match to the more distant galaxies in our sample but not to the weighted combination including NGC 2207. The nearby, bright spiral NGC 2207 alone gives an accuracy almost equal to the rest of our sample, and its outer arms have a very low level of foreground starlight. Thus, this widespread, fairly 'gray' law can be produced from the distribution of dust alone, without a necessary contribution from differential escape of stars from dense clouds. Our results indicate that the extrapolation needed to compare attenuation between backlit galaxies at moderate redshifts from HST data, and local systems from Sloan Digital Sky Survey and similar data, is mild enough to allow the use of galaxy overlaps to trace the cosmic history of dust in galaxies. For NGC 2207, HST data in the near-UV F336W band show that the covering factor of clouds with small optical attenuation becomes a dominant factor farther into the UV, which opens the possibility that widespread diffuse dust dominates over dust in star-forming regions deep into the UV. Comparison with published radiative-transfer models indicates that the role of dust clumping dominates over differences in grain populations at this coarse spatial resolution.« less

Galaxy evolution at high-redshift: Millimeter-wavelength surveys with the AzTEC camera

NASA Astrophysics Data System (ADS)

Scott, Kimberly S.

Galaxies detected by their thermal dust emission at submillimeter (submm) and millimeter (mm) wavelengths comprise a population of massive, intensely star-forming systems in the early Universe. These "submm/mm- galaxies", or SMGs, likely represent an important phase in the assembly and/or evolution of massive galaxies and are thought to be the progenitors of massive elliptical galaxies. While their projected number density as a function of source brightness provides key constraints on models of galaxy evolution, SMG surveys carried out over the past twelve years with the first generation of submm/mm-wavelength cameras have not imaged a large enough area to sufficient depths to provide the statistical power needed to discriminate between competing galaxy evolution scenarios. In this dissertation, we present the results from SMG surveys carried out over the past four years using the new sensitive mm-wavelength camera AzTEC. With the improved mapping speed of the AzTEC camera combined with dedicated telescope time devoted to deep, large-area extragalactic surveys, we have tripled both the area surveyed towards blank- fields (that is, regions with no known galaxy over-densities) at submm/mm wavelengths and the total number of detected SMGs. Here, we describe the properties and performance of the AzTEC instrument while operating on the James Clerk Maxwell Telescope (JCMT) and the Atacama Submillimeter Telescope Experiment (ASTE). We then present the results from two of the blank-field regions imaged with AzTEC: the JCMT/COSMOS field, which we discovered is over- dense in the number of very bright SMGs, and the ASTE survey of the Great Observatories Origins Deep-South field, which represents one of the deepest surveys ever carried out at submm/mm wavelengths. Finally, we combine the results from all of the blank-fields imaged with AzTEC while operating on the JCMT and the ASTE to calculate the most accurate measurements to date of the SMG number counts.

Large-scale Environment of a z = 6.61 Luminous Quasar Probed by Lyα Emitters and Lyman Break Galaxies

NASA Astrophysics Data System (ADS)

Ota, Kazuaki; Venemans, Bram P.; Taniguchi, Yoshiaki; Kashikawa, Nobunari; Nakata, Fumiaki; Harikane, Yuichi; Bañados, Eduardo; Overzier, Roderik; Riechers, Dominik A.; Walter, Fabian; Toshikawa, Jun; Shibuya, Takatoshi; Jiang, Linhua

2018-04-01

Quasars (QSOs) hosting supermassive black holes are believed to reside in massive halos harboring galaxy overdensities. However, many observations revealed average or low galaxy densities around z ≳ 6 QSOs. This could be partly because they measured galaxy densities in only tens of arcmin2 around QSOs and might have overlooked potential larger-scale galaxy overdensities. Some previous studies also observed only Lyman break galaxies (LBGs; massive older galaxies) and missed low-mass young galaxies, like Lyα emitters (LAEs), around QSOs. Here we present observations of LAE and LBG candidates in ∼700 arcmin2 around a z = 6.61 luminous QSO using the Subaru Telescope Suprime-Cam with narrowband/broadband. We compare their sky distributions, number densities, and angular correlation functions with those of LAEs/LBGs detected in the same manner and comparable data quality in our control blank field. In the QSO field, LAEs and LBGs are clustering in 4–20 comoving Mpc angular scales, but LAEs show mostly underdensity over the field while LBGs are forming 30 × 60 comoving Mpc2 large-scale structure containing 3σ–7σ high-density clumps. The highest-density clump includes a bright (23.78 mag in the narrowband) extended (≳16 kpc) Lyα blob candidate, indicative of a dense environment. The QSO could be part of the structure but is not located exactly at any of the high-density peaks. Near the QSO, LAEs show underdensity while LBGs average to 4σ excess densities compared to the control field. If these environments reflect halo mass, the QSO may not be in the most massive halo but still in a moderately massive one. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

The E-MOSAICS project: simulating the formation and co-evolution of galaxies and their star cluster populations

NASA Astrophysics Data System (ADS)

Pfeffer, Joel; Kruijssen, J. M. Diederik; Crain, Robert A.; Bastian, Nate

2018-04-01

We introduce the MOdelling Star cluster population Assembly In Cosmological Simulations within EAGLE (E-MOSAICS) project. E-MOSAICS incorporates models describing the formation, evolution, and disruption of star clusters into the EAGLE galaxy formation simulations, enabling the examination of the co-evolution of star clusters and their host galaxies in a fully cosmological context. A fraction of the star formation rate of dense gas is assumed to yield a cluster population; this fraction and the population's initial properties are governed by the physical properties of the natal gas. The subsequent evolution and disruption of the entire cluster population are followed accounting for two-body relaxation, stellar evolution, and gravitational shocks induced by the local tidal field. This introductory paper presents a detailed description of the model and initial results from a suite of 10 simulations of ˜L⋆ galaxies with disc-like morphologies at z = 0. The simulations broadly reproduce key observed characteristics of young star clusters and globular clusters (GCs), without invoking separate formation mechanisms for each population. The simulated GCs are the surviving population of massive clusters formed at early epochs (z ≳ 1-2), when the characteristic pressures and surface densities of star-forming gas were significantly higher than observed in local galaxies. We examine the influence of the star formation and assembly histories of galaxies on their cluster populations, finding that (at similar present-day mass) earlier-forming galaxies foster a more massive and disruption-resilient cluster population, while galaxies with late mergers are capable of forming massive clusters even at late cosmic epochs. We find that the phenomenological treatment of interstellar gas in EAGLE precludes the accurate modelling of cluster disruption in low-density environments, but infer that simulations incorporating an explicitly modelled cold interstellar gas phase will overcome this shortcoming.

The Survival of the Core Fundamental Plane against Galactic Mergers

NASA Astrophysics Data System (ADS)

Holley-Bockelmann, Kelly; Richstone, Douglas

1999-05-01

The basic dimensional properties of the centers of elliptical galaxies, such as length scale, luminosity, and velocity dispersion, lie on a fundamental plane similar to that of elliptical galaxies as a whole. The orientation of this plane, and the distribution of core parameters within it, point to a strong correlation of core density with either core or total luminosity, and indicate that low-luminosity ellipticals are much denser than high-luminosity galaxies (Hubble Space Telescope data suggest that this relationship may be as steep as ρc~L-2). In addition, low-luminosity ellipticals have a much smaller length scale than their high-luminosity counterparts. Since we think that small galaxies are occasionally accreted by big ones, the high density of these galaxies and their likely durability against the time-varying tidal field of the bigger ones suggests that they will survive substantially intact in the cores of larger galaxies and would be easily visible. Their presence would destroy the observed correlation. Motivated by this apparent inconsistency between an observed fact and a simple physical argument, we have developed an effective simulation method and applied it to the problem of the accretion of very dense secondary companions by tenuous primaries. We have studied the accretion of objects of varying luminosity ratios, with sizes and densities drawn from the fundamental plane under the assumption that the mass distribution in the central parts of the galaxies follows the light. The results indicate that in mergers with mass ratios greater than 10, chosen with an appropriate central density dependence on luminosity, the smaller object is only stripped down to the highest density encountered in the primary during the accretion process. Thus, the form of the core fundamental plane suggests that the mass distribution in galaxy centers is different from the light distribution, or that an understanding of secondary survival requires more than the dynamics of visible stars.

The imprint of rapid star formation quenching on the spectral energy distributions of galaxies

NASA Astrophysics Data System (ADS)

Ciesla, L.; Boselli, A.; Elbaz, D.; Boissier, S.; Buat, V.; Charmandaris, V.; Schreiber, C.; Béthermin, M.; Baes, M.; Boquien, M.; De Looze, I.; Fernández-Ontiveros, J. A.; Pappalardo, C.; Spinoglio, L.; Viaene, S.

2016-01-01

In high density environments, the gas content of galaxies is stripped, leading to a rapid quenching of their star formation activity. This dramatic environmental effect, which is not related to typical passive evolution, is generally not taken into account in the star formation histories (SFHs) usually assumed to perform spectral energy distribution (SED) fitting of these galaxies, yielding a poor fit of their stellar emission and, consequently, biased estimate of the star formation rate (SFR). In this work, we aim at reproducing this rapid quenching using a truncated delayed SFH that we implemented in the SED fitting code CIGALE. We show that the ratio between the instantaneous SFR and the SFR just before the quenching (rSFR) is well constrained as long as rest-frame UV data are available. This SED modeling is applied to the Herschel Reference Survey (HRS) containing isolated galaxies and sources falling in the dense environment of the Virgo cluster. The latter are Hi-deficient because of ram pressure stripping. We show that the truncated delayed SFH successfully reproduces their SED, while typical SFH assumptions fail. A good correlation is found between rSFR and Hi-def, the parameter that quantifies the gas deficiency of cluster galaxies, meaning that SED fitting results can be used to provide a tentative estimate of the gas deficiency of galaxies for which Hi observations are not available. The HRS galaxies are placed on the SFR-M∗ diagram showing that the Hi-deficient sources lie in the quiescent region, thus confirming previous studies. Using the rSFR parameter, we derive the SFR of these sources before quenching and show that they were previously on the main sequence relation. We show that the rSFR parameter is also recovered well for deeply obscured high redshift sources, as well as in the absence of IR data. SED fitting is thus a powerful tool for identifying galaxies that underwent a rapid star formation quenching.