Listing of Contributed Talk Abstracts

Kinetic Luminosity of QSO Outflows: COS Observations

Nahum Arav (Virginia tech)

"Sub-relativistic outflows are seen as blueshifted absorption troughs in the spectra of roughly one third of all quasars. I will describe a recent breakthrough, enabled by HST/COS observations, that yield the mass flux and kinetic luminosity for the majority of these outflows. The derived values suggest that quasar absorption outflows have a profound effect on the host galaxy."

Tidal Interactions Between Dwarf Galaxies

Gurtina Besla (Columbia University)

Interactions between dwarf galaxies is a largely understudied mode of galaxy evolution that could potentially represent a major channel for the removal of baryons from low mass systems and thereby facilitate the morphological transformation from dwarf Irregular type galaxies to gas-poor dwarf Spheroidals. The ongoing tidal interactions between our nearest pair of dwarf galaxies, the Magellanic Clouds, illustrate that such interactions may be an efficient mode of gas loss, as more than 50% of the gas of the original system now resides outside the Clouds in the form of the Magellanic Bridge, Stream and Leading Arm. With the discovery of the gas-deficient tidally disrupted dwarf about the starbursting Magellanic Irregular dwarf galaxy, NGC 4449, it is becoming increasingly apparent that such interactions may be generic, in lines with theoretical expectations hierarchical structure formation. Furthermore, such interactions likely trigger significant amounts of star formation in the host dwarf galaxy and subsequent stellar outflows will contribute to the gas removal process. Such interactions are expected to occur ubiquitously in small groups of low mass galaxies and may represent a generic mode of dwarf galaxy evolution and baryon loss that is independent of proximity to a massive host.

Inner Gas Flows by Bars: ISM Turbulence & Dynamics

Eric Emsellem (ESO)

I will present the results from recent simulations, which include self-consistently stars, gas and dark matter, with implemented modelling of star formation, cooling, and (SN+HII+radiative pressure) feedback recipes, explicitly resolving ISM turbulence down to sub-pc scales. These simulations, run with RAMSES over >6000 CPUs, were designed as a realistic Milky-Way type galaxy to resolve all important scales and driving processes from which dense clouds and star-forming sub-structures arise in grand-design spiral galaxies. The formation of a bar, on a timescale of about 600 Myr, allows us to track the driven flow of gas towards the main resonances and down to the surroundings of the massive black hole. I will focus on the dynamical and (more generally) physical mechanisms associated with this gas transport toward the nucleus and central black hole, and attempt to link local star formation, turbulence and the on-going redistribution of angular momentum. The resolution of these simulations (< 0.1pc) reached for the first time in the context of a grand-design Milky-Way spiral is a pre-requisite to resolve the ISM turbulent cascade over two decades of wavelengths, and the very small structures such as clumps or the nuclear region. I will further discuss simulations performed at lower resolution which help us constraining the long-term dynamical and morphological evolution of barred systems including gas.

The WSRT HALOGAS Survey

George Heald (ASTRON)

We present the status of, and early results from, the WSRT HALOGAS (Hydrogen Accretion in LOcal GAlaxieS) Survey. This is the first systematic investigation of cold gas accretion in nearby spiral galaxies to date. It consists of deep (120 hours) WSRT observations of 20 edge-on and moderately-inclined nearby galaxies. Using these data we are able to detect neutral hydrogen down to a column density of about 10^19 cm^-2, and characterize the faint extra-planar and anomalous-velocity neutral gas with excellent spatial and velocity resolution. HALOGAS data also allow us to study the disk structure and dynamics in unprecedented detail for a sample of this size. Observations carried out so far show a variety of HI properties, ranging from accretion of (and interaction with) satellite galaxies to filaments possibly caused by star formation in the disk. The detected amount of anomalous gas indicative of accretion episodes varies significantly from galaxy to galaxy. We illustrate the range of extraplanar HI features detected in the HALOGAS sample, and compare with complementary deep observations which have been obtained at the INT (our HALOSTARS project), with GALEX, Apache Point Observatory, and at Kitt Peak.

Gas Processing in Compact Groups of Galaxies

Kelsey Johnson (University of Virginia)

Compact groups of galaxies, with their high number densities, small velocity dispersions, and an interstellar medium that has not been fully processed, provide a local analog to conditions of galaxy interactions in the earlier universe. The frequent and prolonged gravitational encounters that occur in compact groups have a pronounced effect on the gas flows and gas processing in these galaxies. We present panchromatic observations of a sample of 49 groups (with 174 individual galaxies). These data have revealed that the gas processing and evolution of galaxies in compact groups have characteristics that are not seen in "field" samples of galaxies; for example compact group galaxies exhibit a "canyon" in Mid-IR color-space, akin to the "green valley" seen in optical color magnitude diagrams for field galaxies. Curiously, Mid-IR canyon galaxies do not reside in the optical green valley, which was our initial hypothesis. Thus the timescales and gas processing in compact groups appear to be fundamentally different from field samples. We conjecture that the strong and variable torques to which the gas in compact groups is subject foster accelerated evolution not seen in other environments.

Gas Flows on GMC Scales in M51

Sharon Meidt (MPIA)

Gas kinematics on the scales of Giant Molecular Clouds (GMCs) are essential for probing the framework that links the large-scale organization of interstellar gas to cloud formation and subsequent star formation. I will present results from the first such observations outside the Local group, namely the PdBI Arcsecond Whirlpool Survey (PAWS, PI: E. Schinnerer) that maps CO(1-0) emission at 40pc resolution in the nearby grand-design spiral galaxy M51. The observed gas motions suggest a strong response to torquing by the stellar spiral pattern, and we find that dynamically distinct regions exhibit different GMC properties as well as distinct patterns of star formation. For example, the lowest azimuthally averaged star formation efficiencies coincide with zones of elevated radial gas inflow. I will discuss how GMC stabilization depends on the dynamical environment (including pressure, shear, turbulence) and describe the implications for the stable cloud mass in the presence of strong streaming motions. I will cast our findings in terms of scatter in the standard GMC relations and in star formation laws derived on larger spatial scales, and also discuss extra-planar gas flows and their relation to the on-going star formation.

The High Redshift Circumgalactic Medium

Gwen Rudie (Caltech)

We present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey, optimized for the redshift range z~2-3, which combines high-S/N HIRES spectra of 15 of the brightest QSOs in the sky at z~2.7 with galaxy redshift surveys within a few arcmin of each QSO sightline. We present quantitative results on the distribution, column density, kinematics, and absorber line widths of neutral hydrogen surrounding a subset of 886 KBSS star-forming galaxies with 2.0 < z < 2.8 and with projected distances less than 3 physical Mpc from a QSO sightline for which we have completed a full Voigt-profile fit to the Ly alpha forest. We find that the HI column density (NHI) and the multiplicity of velocity-associated HI components increase rapidly with decreasing galactocentric impact parameter and as the systemic redshift of the galaxy is approached. The strongest HI absorbers within ~100 physical kpc of galaxies have NHI ~ 3 orders of magnitude higher than those near random locations in the IGM. The circumgalactic zone of most significantly enhanced HI absorption is found within transverse distances of ~300 kpc and within 300 km/s of galaxy systemic redshifts. Taking this region as the defining bounds of the circumgalactic medium (CGM), over half of absorbers with log(NHI) > 15.5 are found within the CGM of galaxies meeting our photometric selection criteria, while their CGM occupy only 1.5% of the cosmic volume. The spatial covering fraction, multiplicity of absorption components, and characteristic NHI remain significantly elevated to transverse distances of ~2 physical Mpc from galaxies in our sample. Absorbers with log(NHI) > 14.5 are tightly correlated with the positions of galaxies, while absorbers with lower NHI are correlated with galaxy positions only on ~Mpc scales. Redshift anisotropies on these larger scales indicate coherent infall toward galaxy locations, while on scales of ~100 physical kpc, peculiar velocities 260 km/s with respect to the galaxies are indicated. The median Doppler widths of individual absorbers within 1-3 virial radii of galaxies are larger by 50% than randomly chosen absorbers of the same NHI, suggesting higher gas temperatures and/or increased turbulence likely caused by some combination of accretion shocks and galactic winds around galaxies with halo masses of 10^12 solar masses at z ~ 2-3. Metallic absorption features in the HIRES spectra currently undergoing analysis will provide unique insight into the metallically and physical state of gas in the CGM. These measurements, combined with an upcoming NIR spectroscopic observing campaign to characterize the rest-frame optical properties of these galaxies will allow for the first glimpses of the co-evolution of galaxies and the IGM, the nature of inflows, galactic outflows, and the effect of star formation on both the IGM and on the future of the galaxy itself.

Gas Flows in Nearby AGN with IFU Spectroscopy

Thaisa Storchi Bergmann (Instituto de Fisica - UFRGS, Brazil)

I present and discuss 2D measurements of the gas kinematics in the inner few 100 pc of nearby active galaxies using integral field spectroscopy at a spatial resolution of about 10 pc. Outflows observed in ionized gas emission are ubiquitous, being usually bipolar and oriented at random angles relative to the plane of the galaxies. They reach distances of a few 100 pc, velocities of a few 100 km/s and mass outflow rates in ionized gas of 1-10 M_sun yr-1. Inflows are found in approximately half of the sources, where they occur in nuclear spiral structures with mass inflow rates of the order of 10^-2 -- 10^-3 M_sun yr-1 in ionized gas, but of a few M_sun yr-1 in molecular gas. The latter is of the order of the gas outflow rates, suggesting that most mass which flows towards the nucleus to feed the supermassive black hole is expelled by the AGN.