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Listing of Poster Abstracts
| A Deep Narrow Band Imaging Search for CIV and HeII Emission from Lyman Alpha Blobs |
| Fabrizio Arrigoni Battaia (MPIA, Heidelberg) |
| The Lyman-alpha blobs ("LABs") are giant (> 100 kpc) luminous (>
10^43 erg/s) Ly-alpha emitting nebulae at high redshift. Despite significant theoretical and observational work, including new surveys, the mechanism powering their emission remains a mystery. Several scenarios, such as photoionization by an obscured AGN, gravitational cooling radiation, or a thermalized superwind, have been proposed, but discriminating between them requires additional diagnostics besides Lyman alpha emission. In this Poster we show the preliminary results of the analysis of very deep (about 20 hours) narrow band images at the wavelengths matching the CIV (1549 A) and HeII (1640 A) emission lines in the SSA22 Proto-cluster field at z=3.1 . The data were obtained with the VLT/FORS2 instrument using the SII (HeII) and OI/2500 (CIV) filters targeting a region of 7'x 7' where 13 LABs and 30 Ly-alpha Emitters (LAEs) can be observed simultaneously in a single pointing. |
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| On the Radial Velocity Offset for [OIII] Emission Line of LINER Galaxies |
| Mr.
Hyun-Jin Bae (Yonsei University) |
| Low-ionization nuclear emission-line region (LINER) galaxies constitute a major fraction of low-luminosity AGN population in the local Universe. In contrast to Seyfert galaxies, it is theoretically expected that LINERs would not have an outflow due to their low Eddington ratio. Using Keck/LRIS spectroscopy on a nearby LINER galaxy SDSS J091628.05+420818.7, we find a significant radial velocity offset for [OIII]λ5007 emission line as ~50 km/s blueshifted compared to systemic velocity of the galaxy, while other emission lines exhibit no or little offset. The observed [OIII] velocity offset possibly indicates an outflow of gas in the LINER galaxy, and it is probable that we only detected the [OIII] velocity offset because [OIII] ionization region is closer to the accretion disk, hence, more affected by an outflow. We further investigate the [OIII] velocity offset of ~4000 SDSS type 2 AGN-host galaxies to compare the strength of AGN outflow. We find that a number of both LINER and Seyfert galaxies show [OIII] velocity offset, but the fraction of LINER galaxies with velocity offset is smaller than that of Seyfert galaxies. The preliminary results imply the presence of gas outflow in LINER galaxies, although outflow strength is probably weaker compared to Seyfert galaxies. |
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| Warm, Ionized Gas Revealed in the Magellanic Bridge Tidal Remnant: Constraining the Baryon Content and the Escaping Ionizing Photons Around Dwarf Galaxies |
| Mrs.
Kat Barger (University of Wisconsin-Madison) |
| Galaxy interactions have greatly disturbed and redistributed the gas in the Magellanic System throughout the halos of the Milky Way and the Magellanic Clouds. In this talk, we will discuss the results of the highest sensitivity and kinematically resolved Hα emission-line survey of the Magellanic Bridge using the Wisconsin Hα Mapper. This census allows us to investigate the baryon content, density, kinematics, morphology, source of ionization, and fate of this tidal remnant. The Hα detections across the entire Magellanic Bridge enables us to place constraints on the fraction of ionizing photons that escape from these galaxies; this is an important parameter for determining the influence that dwarf galaxies had during the epoch of reionization and the contribution of ionizing photons they currently supply to the extragalactic background. Determining the properties of tidal debris is key for understanding the evolution of these galaxies and other tidally disturbed systems. |
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| The First Observations of Low-Redshift Damped Lyα Systems With the Cosmic Origins Spectrograph: Chemical Abundances and Affiliated Galaxies |
| Andrew Battisti (UMass at Amherst) |
| We present Cosmic Origins Spectrograph (COS) measurements of metal abundances in eight 0.083 < z < 0.321 damped Lyα (DLA) and sub-DLA absorption systems serendipitously discovered in the COS-Halos survey. We find that these systems show a large range in metallicities, with -1.10 < [Z/H] < 0.31, similar to the spread found at higher redshifts. These low-redshift systems on average have subsolar metallicities, but do show a rise in metallicity over cosmic time when compared to higher-redshift systems. We find that the average sub-DLA metallicity is higher than the average DLA metallicity at all redshifts. Nitrogen is underabundant with respect to α-group elements in all but perhaps one of the absorbers. In some cases, [N/α] is significantly below the lowest nitrogen measurements in nearby galaxies. Systems for which depletion patterns can be studied show little, if any, depletion, which is characteristic of Milky Way halo-type gas. We also identify affiliated galaxies for three of the sub-DLAs using spectra obtained from a Keck/Low Resolution Imaging Spectrometer (LRIS). None of these sub-DLAs arise in the stellar disks of luminous galaxies; instead, these absorbers may exist in galaxy halos at impact parameters ranging from 38 to 92 kpc. Multiple galaxies are present near two of the sub-DLAs, and galaxy interactions may play a role in the dispersal of the gas. Many of these low-redshift absorbers exhibit simple kinematics, but one sub-DLA has a complicated mix of at least 13 components spread over 150 km/s. We find three galaxies near this sub-DLA, which also suggests that galaxy interactions roil the gas. This study reinforces the view that DLAs have a variety of origins, and low-redshift studies are crucial for understanding absorber-galaxy connections. |
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| How Do Massive Black Holes Grow? |
| Jillian Bellovary (University of Michigan) |
| Massive black holes (MBHs) grow quickly at high redshift, but the
mechanism for this growth is not fully understood. We present a
detailed study of black hole gas accretion using cosmological
simulations by tracing the history of accreted gas to its origins. By
determining whether gas accreted by MBHs originated in major galaxy
mergers, minor mergers, or cold flows, we pinpoint the significance of
each type of gas flow and how our results vary with galaxy mass, MBH
mass, and merger history. |
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| Probing the Extension of Magnetic Fields Around Galaxies Out to $z sim 1$ |
| Martin Bernet (Swinburne University of Technology) |
| We have previously presented evidence that radio quasar sightlines with intervening strong MgII absorption display statistically enhanced Faraday Rotation Measures, |RM|, indicating the presence of magnetized plasma along the line of sight. In this work, we identify the likely host galaxies using multi-color optical imaging of the fields in order to constrain the location of this magnetized material within the intervening systems. All of the sightlines with high |RM| are found to pass within 40 kpc of a host galaxy and the |RM| distribution for impact parameters D < 40 kpc is different than for 40 < D < 120 kpc at the 2 sigma level. This correlation with D further strengthens the association of excess |RM| with these intervening systems. We also find a significant increase in the
depolarization of the radio sources between 1.4 and 20 GHz towards lower D, suggesting that the the RM screens in and around the galaxies are inhomogeneous. These results may indicate that outflowing winds carry magnetic fields to significant distances into the halos of galaxies. |
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| The Radial and Azimuthal Profiles of Mg II Absorption Around Galaxies at Intermediate Redshifts |
| Mr.
Rongmon Bordoloi (ETH Zurich) |
| MgII absorption line systems in the spectra of background sources are widely used as unbiased tracers of the gaseous environment in and around galaxies. Here, I present the radial and azimuthal profiles of MgII gas around galaxies at 0.5 < z < 0.9 using co-added spectra of more than 5000 background galaxies at z > 1. MgII absorbers exhibit a strong color dependence and the blue galaxies exhibit a correlation between equivalent width and galactic stellar mass of the host galaxy at close impact parameters. Galaxies lying in groups have more extended radial distribution of MgII gas as compared to that of non-group galaxies. These effects can be satisfactorily modeled by a simple superposition of the absorption profiles of individual member galaxies, assuming that these are the same as those of non-group galaxies. This suggests that the group environment may not significantly enhance or diminish the MgII absorption of individual galaxies. There is strong azimuthal dependence on the MgII absorption strength within 50 kpc of inclined disk-dominated galaxies, indicating that such strong absorbers must originate in cool gas entrained in star formation driven winds. This azimuthal dependence is also observed in quasar absorption line systems. I will present models that are consistent with data from both these orthogonal probes and will give joint constraints on the geometrical cross section of such highly structured MgII absorbers. |
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| Title: Effects of Starburst on Circumgalactic Medium of Galaxies:
Evidence of Presence of Hot Gas After a Burst of Star Formation |
| Sanch Borthakur (Johns Hopkins University) |
| The circum-galactic medium (CGM) of galaxies hold the clues to the
past and future evolution of their host galaxies. Here, I'll present
our work aimed at understanding the effects of starburst on the
CGM/halos of the galaxies using UV absorption spectroscopy with
background QSOs. In this study, we compare the properties of halo gas
in starburst (SB) and post-starburst (PSB) galaxies to normal galaxies
with similar stellar masses and impact parameters. We find a greater
incidence of hot gas in the CGM of SB and PSB galaxies as compared to
normal galaxies. This is evident from the higher incidence of CIV in
these systems and the simultaneous absence of other cooler
transitions. On an average, the Lyman alpha strengths in SB and PSB
galaxies are also weaker than in normal galaxies. |
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| Gas Outflow Rates in Galaxies Using Background Quasar |
| Dr.
Nicolas Bouche (Institut d'Astrophysique et de Planétologie - Toulouse) |
| Traditional galaxy spectroscopy clearly demonstrate the ubiquity of winds through the presence of blue-shifted absorption lines, but have one major limitations: they do not provide any information on the location of the out-flowing gas. On the other hand, background quasars could be more sensitive probes of galactic outflows since they can probe winds irrespectively of the galaxy luminosity and at a known impact parameter provided that one can determine the origin of the absorbing material. Using a dozen quasars passing near spectroscopically identified galaxies at z~0.1, we show that one can determine the origin of the material. For wind sight-lines, we show that strong constraints on the outflow rate can be determined. The outflow rates are typically two to three times the instantaneous SFRs. |
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| 2-D Neutral Gas Kinematics in Luminous and Ultra-Luminous Infrared Galaxies |
| Sara Cazzoli (CSIC, Madrid) |
| We use optical Integral Field Spectroscopy (IFS) data obtained with VIMOS at Very Large Telescope for studying the neutral phase of Galactic Winds (GWs) for a sample of local [U]LIRGs, via the NaI D λλ 5890,5896 absorption-line doublet. First we analyzed the spatially integrated (1-D) spectra for a subsample of 10 systems. Because of the high SNR of these spectra we were able to separate the stellar and interstellar sodium, with a Penalized Pixel Fitting method (pPXF, Cappellari et al. 2004). 2-D IFS data allow us to map the absorption feature over the spatial extent of GWs. We present the preliminary 2-D velocity and velocity dispersion maps. Future developments will include the application of technique to enhance the SNR in 2-D Data. |
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| Observational Evidence for Cold, Warm, and Hot Accretion at z=0.67 |
| Chris Churchill (New Mexico State University) |
| We present observational evidence of a cold+hot accretion flow into two galaxies at z=0.67. In the first galaxy, a solar enriched E0 with Mvir/Msol=10^13.9, the HI (observed in absorption with a COS spectrum) spans an astounding velocity range of 1600 km/s and comprises 21 components. The galaxy is probed at D=58 kpc, at D/Rvir=0.1. Most of the gas is cool (T<100,000 K) and has no metal line absorption; the metallicity is constrained to logZ<-2. One componet is hot (T=115,000 K) and shows OVI, CIV, and CIII absorption; the metallicity is -1.8. The all clouds are consistent with being in quasi-hydrodynamic equilibrium. We interept this dramatic structure as a combination of cold and hot inflow. As we will show, its collective properties are entirely inconsistent with hot-mode and cold-mode accretion predictions in cosmological simulation. In the second galaxy, a highly inclined spiral with Mvir/Msol=11.9 probed along the minor axis at D=104 kpc (D/Rvir=0.3), the HI is logN=18.3 and shows rich metal line kinematics. The galaxy has solar metallicity and the gas is modeled to have cold, warm, and hot phases with metallicities <-1.6. We show that this gas is multi-phase accretion, and is also contrary to expectations from simulations.
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| Galaxy Model for Galactic Winds In Cosmological Simulations |
| Benoit Côté (Université Laval) |
| We present a model to describe the joint evolution of starburst galaxies and the
galactic winds resulting from this evolution. This model will eventually be used to
provide a sub-grid treatment of galactic winds in cosmological simulations to
study the relative importance of various outflow driving mechanisms. The galactic
model takes into account radiative cooling, star formation, chemical enrichment
and heating from stellar winds and supernovae (SNe), and mass ejection from a
galactic wind. We use the population synthesis code Starburst99 with SNe tables
to keep track of the mechanical energy and the mass returned by stellar
populations with time. Using a semi-analytical model to drive galactic winds, we
calculate the spatial density distribution of the mass ejected into the intergalactic
medium (IGM). Our model suggests that isolated high-redshift dwarf galaxies
experience several shorts star formation episodes that provide a continuous energy
supply to drive galactic winds that can reach distances up to more than one Mpc
into the IGM, which imply metal enrichment of a large fraction of the IGM space. |
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| Chandra Diffuse X-ray Analysis of Compact Galaxy Groups |
| Mr.
Tyler Desjardins (University of Western Ontario) |
| Isolated compact groups of galaxies (CGs) present a range of dynamical states, group velocity dispersions, and galaxy morphologies with which to study galaxy evolution, particularly the properties of gas both within the galaxies and in the intragroup medium. As part of a large, multiwavelength examination of CGs, we present an archival study of diffuse X-ray emission in a subset of Hickson compact groups observed with the Chandra X-ray Observatory. We find that 7 of 9 groups in our sample exhibit detectable diffuse emission. However, unlike large scale emission in galaxy clusters, the diffuse features in the majority of the detected groups are observed to be linked to the individual galaxies in the form of both plumes and halos likely as a result of star formation or AGN activity, as well as emission in tidal features. Additionally, the emission in groups is shown to be inconsistent with relationships between X-ray luminosity and other parameters established for galaxy clusters. Finally, there is evidence for an evolutionary trend between the X-ray luminosity and the group HI to dynamical mass ratio and a difference in luminosity with HI morphology. We conclude that individual group members are largely responsible for building any hot ionized intragroup medium in dynamically young systems, and low-mass galaxy groups cannot be considered analogs to clusters as their emission is dominated by different physical processes. |
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| Cosmic Ray Driven Galactic Winds and Magnetized Galactic Halos |
| Ralf-J. Dettmar (Ruhr-University Bochum) |
| Multiwavelengths studies making use of radio-, IR-, optical, and X-ray observations of the interstellar medium in galactic halos provide evidence for a large scale exchange of matter between galactic disks and halos driven by the star formation activity in the disk. In this context, we discuss radio continuum observations of M82 and NGC 253 at several frequencies to conclude that this large scale matter transport is supported by cosmic ray pressure. The observations also provide information on the halo magnetic field structure and allow us to constrain the small scale structure of magnetic fields by comparing diffusive and advective transport processes. |
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| Galactic Outflows in Absorption and Emission: Near-UV Spectroscopy of Galaxies at z~1-2 |
| Dawn Erb (University of Wisconsin Milwaukee) |
| I will present the results of a spectroscopic study of FeII and MgII absorption and emission in ~100 star-forming galaxies at z~1-2. In addition to FeII absorption lines from outflowing cool gas, we observe FeII* in emission, and infer from the kinematics of the lines and from photoionization models that this emission likely arises from the outflowing gas. We discuss the relationship between FeII emission and absorption and the impact of line emission on measurments of outflow velocities measured from absorption lines. Through the use of composite spectra, we examine the dependence of FeII and MgII emission and absorption on stellar population properties. Unlike most other outflow-related features, the MgII line profile shows a strong dependence on stellar mass.
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| The Origin and Distribution of Cold Gas in the Halo of a Milky Way-Mass Galaxy |
| Ximena Fernandez (Columbia University) |
| We analyze an adaptive mesh refinement hydrodynamic cosmological simulation of a Milky Way-sized galaxy to study the cold gas in the halo. HI observations of the Milky Way and other nearby spirals have revealed the presence of cold halo gas in the form of clouds and other extended structures, which could be evidence for on-going accretion. We use a high-resolution simulation (136-272 pc throughout) to study the distribution of cold gas in the halo, compare it with observations, and examine its origin. The amount (10^8 Msun in HI), covering fraction, and spatial distribution of the cold halo gas around the simulated galaxy at z=0 are consistent with existing observations. We find that the origin of the gas is a mix of stripped satellite gas and cold filamentary flows. The metallicity of the gas allows us to distinguish between these two origins. We find that filamentary material accounts for at least 25-75% of the cold gas in the halo seen at any redshift analyzed here. Placing constraints on cloud formation mechanisms allows us to better understand how galaxies accrete gas and fuel star formation at z=0. |
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| Understanding the Physical Conditions in the
Circum-Galactic Medium (CGM) |
| Amanda Ford (University of Arizona) |
| I examine the physical conditions of the intergalactic medium (IGM) in
close proximity to galaxies within cosmological hydrodynamic
simulations. I will demonstrate the links between these conditions
and the emergent observable properties of the circum-galactic medium,
particularly at low redshift where recent COS data has allowed unprecedented
access to CGM properties. I discuss the extent and strength of metals and
HI in the neighborhoods of galaxies, as well as the typical temperatures, densities and ionization conditions of gas giving rise to absorption features. In addition, I demonstrate the sensitivity of these observables to models of galactic super-winds and discuss how different feedback prescriptions leave unique, observable signatures within the CGM.
We find metallic absorption significantly in excess of the average IGM
even at distances of ~1Mpc from individual galaxies, but that excess
drops with impact parameter more rapidly in low-ionization lines than
high-ionization lines. This absorption is particularly enhanced within
roughly +/-300km/sec and +/-300kpc of galaxies. We find also that
many metal species, including OVI, are photoionized, even in the CGM. |
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| New HST/COS Observations of the Magellanic Stream: Gas Fragmentation and Inflow in the Galactic Halo |
| Andrew Fox (STScI) |
| The Magellanic Stream (MS) is a massive (~10^8 M_sun in HI), extended (~200 degrees long), low-metallicity (O/H=0.1-0.2 solar) tail of material stripped out of the Magellanic Clouds as they orbit the Milky Way. Gaseous tidal streams like the MS may play an important role in bringing fresh fuel into galaxies. However, the MS appears to be fragmenting and evaporating as it interacts with the hot Galactic corona, and it remains unclear what fraction of the MS will survive to reach the disk to fuel future star formation. I will present recent results from an ongoing observing campaign on the MS using UV (HST/COS) spectroscopy, paying particular attention to the chemical and physical conditions in the gas. Toward the AGN NGC 7469, lying 84 degrees away from the SMC near the tip of the MS, the MS shows a low metallicity of 0.1 solar and a high ionization level [N(HII)/N(HI)>~19]. Altogether, these results give insight into the physical processes occurring when cold accreting streams pass through hot ambient gas. |
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| Investigating Environmental Dependencies of Gas-Fueling in GAMA Galaxies Using Radiation Transfer Modelling |
| Mr.
Meiert Grootes (Max-Planck Institut fuer Kernphysik) |
| Present and past gas-fuelling of galaxies is expected
to depend on both the properties of the galaxies themselves,
as well as their local and larger-scale environments. In the case of
galaxies in groups a potential factor determining the local
environment is the mass of the parent halo of the group, which
can be probed by measuring the spectroscopically determined
velocity dispersion of the member galaxies of groups. In particular,
the r 19.8 mag spectroscopic depth of the Galaxy And Mass Assembly survey
(GAMA) has allowed a catalogue of 14388 galaxy groups to be constructed
by Robotham et al. 2011), allowing halo masses to be measured with
unprecidentedly high statistics all the way from
massive X-ray bright clusters to groups with dynamical masses of
less than 10^12 M_solar. Here we use star-formation rates (SFRs)
of rotationally-supported disk galaxies as a proxy for gas fuelling
to investigate the dependence of gas-fuelling on group
halo mass for local Universe groups. The SFRs are derived from NUV
measurements of the GAMA groups taken in the GAMA multiwavelength survey,
incorporating corrections for dust attenuation of the NUV light made using
a
novel radiation transfer technique on an galaxy-by-galaxy basis to further
enhance the statistical precision of the analysis.
We thus characterise gas fuelling in group member galaxies spanning
a wide range of stellar masses and a wide range of inferred virialised
states of the in situ intergalactic medium. The results are discussed
in the context of predictions of semi-analytic models for galaxy growth
and
feedback in the local Universe. |
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| A Molecular Cloud In The Disk-Halo Interface |
| Audra Hernandez (University of Wisconsin-Madison) |
| Identified by their HI emission within the galactic halo, intermediate-velocity clouds (IVCs) have radial velocities which fail to be explained by simple models of galactic rotation.
Their origins remain unclear, however IVCs may be the result of extragalactic infall or the returning flows of the galactic fountain. We present FUSE observations of the molecular cloud IV21 (IVC135+54-45). This unusual molecular cloud is located in the galactic disk-halo interface and is one of the three molecular clouds with known peculiar radial velocities. We present early results on the measurements of cloud abundances, densities, and pressures. These measurements will further be used to search for time-dependent chemical changes on what seems to be an evolving system, including the formation of H2 from atomic hydrogen, for comparisons with dynamical models of cloud infall.
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| Vertical Structure of a Supernova-Driven, Tubulent, Magnetised ISM |
| Dr.
Alex Hill (CSIRO CASS/ATNF) |
| Supernovae drive the circulation of interstellar material both within galaxies and into galactic haloes. I present 3D MHD simulations of a modelled ISM with parameterized heating and cooling in which supernovae drive turbulence and establish a vertically-stratified, multi-phase medium. The resulting turbulent and thermal pressures support the disk of each component, producing relative scale heights in line with observations. This feedback naturally allows ionizing radiation from O stars in the disk to photoionize the warm ionized medium, and some fraction of the ionizing photons escape from the disk into the Galactic halo. Cold and warm ($T lesssim 10^4$~K) gas in high velocity clouds can thus be photoionized by Lyman continuum radiation emitted in the disk, consistent with observations that the H-alpha-emitting mass in the Smith Cloud is comparable to the H I-emitting mass. |
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| Triggered Star Formation in ALFALFA Starbursts |
| Ms.
Anne Jaskot (University of Michigan) |
| Quantifying the HI gas supply is of fundamental importance in understanding what triggers the high levels of star formation in starburst galaxies. The ALFALFA survey has now measured HI masses and velocities for thousands of galaxies, from which a volume-limited subsample has been imaged in R and H-alpha through the ALFALFA H-alpha program. We have identified starbursts as objects with H-alpha equivalent widths greater than 80 Angstroms. Although the high star formation intensities in the starbursts suggest a large total gas mass, their HI gas masses are quantitatively identical to the non-starbursts. The wide, single-peaked HI velocity profiles and the asymmetric optical morphologies of the starbursts
do differ from the non-starbursts, however, and support a merger origin for the bursts. During the merger, the galaxies likely experienced an influx of gas, but the excess gas probably ended up in molecular or ionized form rather than HI.
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| Enhanced (Obscured) Nuclear Activity in Gas-Rich, Star-Forming Galaxies |
| Dr.
Stephanie Juneau (CEA Saclay) |
| While it is clear that gas fuels both star formation and nuclear activity in galaxies, the connection between the growth of their stellar content and that of their central supermassive black hole remains elusive. What are the governing physical processes? Do stars and SMBHs grow in lock-step? Using a sample of actively star-forming galaxies at intermediate redshifts (0.3
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| Evidence for Outflows and Infall in Galaxy Halos as Traced by MgII Absorption |
| Glenn Kacprzak (Swinburne University of Technology) |
| We will discuss the series of observations that likely explain the
origins of MgII absorption systems. We will present how the
orientation of foreground absorbing galaxies influences the MgII
absorption strengths and gas covering fractions as probed with
background quasars/galaxies. We will show the bi-model distribution of
galaxy positions angles, relative to the background source,
demonstrating that the absorption arises along the projected galaxy
minor and major axis. This suggests that the absorption arises from
outflows along the minor axis and accretion along the major axis. For
quasars/galaxies probing along the galaxy major axis, we show how the
disk inclination determines the absorption strengths and kinematics
signatures -- as seen for cold accretion in cosmological simulations.
We present some of the first clues, including unpublished results,
regarding the origins of MgII absorption lines systems: the holy grail
that has been long overdue. |
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| The MaGICC Volume: How Stellar Feedback Affects Properties of Galaxies at High-z |
| Mr.
Rahul Vasudev Nair Kannan (Max Planck Institute for Astronomy, Heidelberg) |
| The MaGICC project attempts to see what kind of galaxies form, when stellar feedback is tuned so that the galaxies match the stellar mass - halo mass relation. This feedback is purely thermal (no kinetic feedback), and ejects gas from galaxies, thus regulating star formation. We study how this prescription works in a large uniform cosmological volume at moderate numerical resolution. The simulations match the observed stellar mass function evolution from z ~ 4-2. Using parameters derived from high resolution simulations, we still match the Stellar mass - halo mass relation upto a halo mass of 2x10^12 Msun, even at moderate resolutions. We also see a prominent star forming main sequence and limited quenching of galaxies even without AGN feedback.
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| Probing Galaxies Through Quasar Absorption Lines with HST/COS
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| Dr.
Brian Keeney (University of Colorado) |
| The COS GTO team has expended 80 HST orbits to investigate the mass,
extent, metallicity, and kinematics of the "circumgalactic medium"
(CGM) of low-z late-type galaxies. We will present results from our
studies of 13 very low-redshift galaxy/absorber associations targeted
by the COS GTO team, as well as 31 serendipitous galaxy/absorber
associations from the STIS archive, focusing on the extent and content
of a galaxy's CGM as a function of galaxy luminosity. We use
photoionization modelling of individual CGM clouds to ascertain that
the CGM of low-z galaxies contains a large collection of warm,
photoionized clouds with a total mass of ~10^8 Msun. These clouds are
likely embedded in a hot diffuse halo, which itself has a mass of
~10^9 Msun (~30% of the stellar mass in these systems). The
combination of this hot and warm gas could account for a few percent
of the cosmic baryon budget if present around all late-type galaxies.
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| Gas Accretion & Starvation in the Virgo Cluster |
| Jeffrey Kenney (Yale University) |
| Clusters and their outskirts encompass a wide range of environmental conditions and their galaxies experience a wide range of gaseous inflow and outflow phenomena. Virgo is the nearest cluster, so processes in its member galaxies can be observed at high resolution with a wealth of available data. Most of the spiral galaxies with the largest star formation rates in Virgo are HI-rich galaxies with very extended HI distributions, located in the cluster outskirts. We propose that the disks of these galaxies are actively accreting gas, which enhances their SFRs. Of course most cluster galaxies (located closer to the cluster center) are gas-deficient and have reduced SFRs. While ram pressure stripping is undoubtedly responsible for producing the many cluster galaxies with truncated gas disks, the origin of anemic galaxies, with extended but low surface brightness disks of gas and star formation, has been less clear. We propose that these disks are starved, with their gas reservoirs at large radii (perhaps like those seen in the gas-rich galaxies, although on average less extreme) removed by either tidal forces or ram pressure stripping, which stops accretion onto the disks.
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| Turbulence in CIV Absorbers at 1.5 < z < 3.5 |
| Dr.
Tae-Sun Kim (University of Wisconsin-Madison) |
| Using 17 QSO spectra taken with the Ultraviolet and Visible Echelle Spectrograph (UVES) at the VLT, we determined thermal and non-thermal motions of CIV absorbers at 1.5 < z < 3.5. These CIV absorbers are thought to arise around/inside high-redshift galaxies. We selected a sample of HI+CIV pairs that exhibited the same kinematic structure, i.e. a well-aligned HI+CIV pairs. From the Voigt profile fitting analysis, we derived the line width (or the b-parameter which constrains the gas kinematic temperature) and the column densities. Of 42 selected HI+CIV pairs with HI column densities between 10^12.5 and 10^15.5 cm^(-2), the mean temperature is 28800 K and the mean velocity from non-thermal motion or turbulence is 6.34 km/sec. The non-thermal energy density is only about 10% of the thermal energy density, which implies that the CIV absorbers in our sample are dominated by thermal energy. The CIV absorbers do not show any correlations between derived physical parameters, i.e. the size vs turbulence. |
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| The Distribution of OVI in the Galactic Halo: Confronting Simulations with Absorption-Line Observations |
| Ms.
Elizabeth Klimek (New Mexico State University) |
| The Galaxy is embedded in a corona of hot (T=10^6 K) diffuse gas, the nature and origin of which are poorly understood. In order to better understand the physical conditions of this gas, past surveys using the Far Ultraviolet Spectroscopic Explorer (FUSE) built up a large database of absorption line spectra of highly ionized species such as OVI. From these spectra, Savage et al. (2003) and Sembach et al. (2003) have determined the column density and kinematic distribution of the OVI-bearing gas. This data can be compared to cosmological simulations of Milky Way-like galaxies at redshift zero in order to assess how well current simulations are able to reproduce the structure and kinematics of the gaseous halo component of large, star-forming spiral galaxies.
We present quantitative comparisons between the distribution of OVI column densities surrounding Milky Way-like galaxies simulated with the Eulerian Gasdynamics plus N-body Adaptive Refinement Tree (ART) code and the distribution of OVI as determined by quasar absorption line observations from past FUSE surveys. To do this we have generated mock absorption line observations along lines of sight looking outward from the position of the Solar circle, situated within the disk of the simulated galaxies. In generating the mock spectra, we have mimicked the instrumentation characteristics, such as the resolution, signal-to-noise, pixel sampling, and threshold sensitivity, of the spectrograph aboard FUSE. In this way we are able to make meaningful comparisons between the velocity and spatial distributions and statistical comparisons of the column density and velocity width distributions of OVI-bearing gas around the simulated galaxies and the Milky Way. We present these comparisons here. |
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| The Role of Shocks in Suppressing and Triggering Star Formation in Tidal Debris: A Spectroscopic and Imaging Survey of Halpha-Bright Clumps in Stephan's Quintet. |
| Dr.
Iraklis Konstantopoulos (Penn State University) |
| Compact Galaxy Groups represent the tail end of clustering in the universe, with a typical membership of about four galaxies and low overall masses. When the dice are rolled in a certain way, compact groups are dominated by interactions, which trigger the morphological evolution of their member galaxies and enrich the inter-galactic medium. Stephan's Quintet provides an ideal laboratory for the study of these processes, as it hosts a multi-body interaction that has developed an intricate network of tidal debris. We combine high S/N optical spectroscopy from Gemini with narrow-, medium- and broad-band HST imaging to understand the role of large-scale shocks in forcing the collapse of tidally stripped gas, and to trace the history of inter-galactic star formation. Exploring a sample of ~50 Ha-bright knots, we find mostly HII-region like characteristics. Among them, however, we find five spectra featuring broad spectral lines, indicative of shock-ionisation. We decompose them to multiple components, with all five knots exhibiting at least one component broadened to a few 100 km/s. We also examine the physical and photometric attributes of these knots -- seemingly shocked gaseous filaments -- and discuss the importance of these findings in the context of triggering and suppressing star formation by shocks.
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|
| A Chandra/Multi-Wavelength Study of Gas Flow in M82 |
| Dr.
K.D. Kuntz (JHU) |
| A deep Chandra study of M82 reveals unprecedented detail of the inner flow. The X-ray structures are well correlated with the H alpha filaments seen in the HST images, and in many cases the H alpha lies further from the core than does the X-ray. Interestingly, the bulk of the filaments are perpendicular to the flow, rather than streaming.
Comparison of a new XMM-Newton mosaic with HI maps reveals previously unknown interaction zones in the outer flow similar to the well known "Cap", and suggest that the gas flow is broader than previously suspected. |
|
| Streams of Ionized and Neutral Gas in the Halo of the Milky Way
|
| Nicolas Lehner (University of Notre Dame) |
| How does the Milky Way get its gas has been a long-standing problem. In our Milky Way, streams of neutral and ionized gas in its halo can be studied with the high-velocity clouds (HVCs). The distances of the HVCs are key for placing them in the Galactic halo and unraveling their role and their most basic properties. I will show how COS observations of AGN and stars in the Galactic halo have allowed us to produce a major leap forward in our understanding of the mass flows in the Galactic halo. We knew that most of the neutral HVCs are within about 15 kpc, and we now know that most of the ionized HVCs are too. Most of the traditional HI HVCs seen in 21-cm emission must have ionized envelopes extending far from the HI contours. Accounting for the total mass budget of the HVCs, I will conclude the HVCs are close enough and have enough mass to support the star formation in the disk, essentially solving the missing fuel problem for continuing star formation in the Milky Way. |
|
| 3D Kinematics of a z ~ 1.3 Lensed "Clumpy" Galaxy |
| Dr.
Marie Lemoine-Busserolle (Gemini Observatory North) |
| The study of the physical properties of high-redshift galaxies has become one of the major goals of extragalactic astronomy. In particular the mass-assembly history of galaxies have been the focus of many studies at redshifts 1 to 3. The study of lensed galaxies allows to probe a low mass regime of galaxies not accessible in standard observation. Indeed, the natural magnification due to massive galaxy clusters allows to spatially resolve and constrain the dynamics of young star forming galaxies 1 to 3 magnitudes fainter than those selected in blank fields. In the purpose of probing the dynamics of intermediate and high-redshift galaxies, we have designed a research program to carry out a near-infrared spectroscopic follow up of spatially resolved distant galaxies. Here, we present the results of the 3D kinematics of a z ∼ 1.3 ”clumpy” galaxy discovered as an arc behind the lens cluster Abell 370 (z = 0.374) observed with SINFONI/VLT. |
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| Evidence for a Transition in the Link Between Neutral Hydrogen Content, Stellar Mass and Star Formation in Massive Gas-Rich Galaxies |
| Ms.
Jenna Lemonias (Columbia University) |
| We examine star-forming and structural properties of a sample of massive (10.0 < log M*/Msun < 11.25) HI-rich galaxies to reveal a complex relationship between gas content, star formation rates (SFRs) and stellar mass. For the first time we study where gas-rich galaxies fall in relation to the star-forming (SF) sequence. We find that despite their elevated gas fractions, gas-rich galaxies follow the general trend of decreasing SFR with increasing stellar mass. Our results also indicate that galaxies with log M*/Msun ~ 10.0 cluster around the SF sequence regardless of gas content. We explore whether the decline in SFR with stellar mass is due to a decline in gas fraction within the gas-rich sample. By comparing the gas-rich sample to a sample of galaxies with constant gas fraction, we show that this is not the case. We take this as evidence that the link between cold gas and star formation changes in this mass range in a way that cannot be captured by a single scaling relation or star formation law. Recent gas accretion, quenching of star formation, and long-lived extended HI disks could all contribute to this transition. The latter scenario suggests that HI disks in massive galaxies might be larger than expected based on optical indicators. |
|
| A Gas Flow Into the Milky Way (And Another Out of M31?) |
| Felix J Lockman (NRAO) |
| A cloud containing several million solar masses of gas is now
interacting with and losing mass to the Milky Way halo, and is on a
trajectory that will take it into the disk in about 30 Myr. New
observations of this object, the Smith Cloud, have been made in the
21cm line with the Green Bank Telescope (GBT) and show that it is more
extensive than previously thought and may have components that even
now are crossing the Galactic Plane.
In a separate experiment, measurements with the GBT of the area
between the galaxies M31 and M33 confirm the presence of HI clouds not
linked to the high velocity cloud population of either galaxy, nor to
any known stellar system. They could be tracing a past interaction
between these galaxies that produced a tidal tale now largely
dissipated.
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|
| Insights into Elliptical Galaxy Gas Flows from X-ray Spectroscopy |
| Dr.
Michael Loewenstein (University of Maryland, CRESST, NASA/GSFC) |
| The abundances of heavy elements in the X-ray emitting hot ISM in
elliptical galaxies are determined by the star formation history, and
the details of the interplay of the gas with stars in the galaxy and
with the intergalactic environment. We derive global abundances, and
abundance patterns, in a sample of ellipticals from spectral analysis
of Suzaku and XMM-Newton X-ray Observatory data. Applying basic
chemical evolution considerations enable us to evaluate the
contributions to enrichment from Type Ia supernovae, stellar mass
loss, and inflow. We find that accretion of subsolar metallicity
external gas has reduced the overall ISM metallicity and diluted the
effectiveness of SNIa to skew the pattern towards low alpha-to-Fe
ratios. This evidence of heating and circulation of accreted gas
helps reconcile the dynamic history of ellipticals with the mostly
passive evolution of their stellar populations. Elliptical galaxies
must experience periods of outflow and inflow, and episodes of
ejection of metal-rich gas and accretion of (relatively) metal-poor
gas dilute the impact of SNIa explosions in enriching the hot ISM.
|
|
| The Evolving Mg II Gas Radius of Galaxies |
| Dr.
Britt Lundgren (Yale University) |
| The prolific, intervening quasar absorption features of Mg II provide sensitive probes of disk-halo processes in galaxies over a wide range in redshift. But, despite the tens of thousands of Mg II absorbers now available from the SDSS spectroscopic quasar sample, a long-held controversy over their origins remains largely intact due to the difficulty of detecting their host galaxies at high redshifts and on small angular separations from the background quasar. The growing overlap of deep galaxy surveys and spectroscopically observed quasars is finally enabling highly complete analyses of Mg II-selected galaxies at z>0.5. I will present recent results from a clustering analysis of z~1 Mg II absorption systems within the DEEP2 Survey (Lundgren et al. 2011) along with new, deep HST WFC3/IR grism observations of z~1.5 Mg II host galaxies. These analyses provide complimentary (both direct and indirect) methods of constraining the gas radius evolution of Mg II host galaxies, each revealing evidence to support a shrinking gas radius for Mg II absorbing galaxies from z~1.5 to z~0.3 . |
|
| Cold Flow Disks and Gas Around Galaxies |
| Ari Maller (City University of New York) |
| High resolution hydrodynamical simulations are now showing that a cold flow disk exists around galaxies below a certain halo mass. The cold flow disk can extend out to 100kpc and gives rise to quasar absorptions systems. These systems can be identified based on their alignment with the disk of a galaxy and based on the kinematics of the gas. Studying such absorption systems thus provide a unique method for testing the hot/cold flow model of galaxy formation and understanding the build up of angular momentum in galaxies. |
|
| Mapping the Circumgalactic and Circum-QSO Medium with the Palomar Cosmic Web Imager |
| Prof.
Christopher Martin (California Institute of Technology) |
| The Palomar Cosmic Web Imager (PCWI) is an wide-field integral field spectrograph designed to detect low surface brightness line emission from the CGM and IGM. Using it we have discovered and mapped extended line emission from gas surrounding galaxies and QSOs at low and high redshift. We discuss the nature of this gas, its source of power and ionization, and radiative transfer effects. Our goal is to discriminate gas outflowing from starburst winds, orbiting in an extended CGM, or inflowing from the cosmic web, and to link these gas properties with the central galaxies and local environments. |
|
| 3-D AMR MHD Simulations of High Velocity Clouds |
| Chris Matthews (University of Notre Dame) |
| High Velocity Clouds (HVCs) are observed to cover a significant fraction of the sky, and could be the primary source for replenishing the star forming gas in our galaxy. Understanding the nature of these objects is important, and direct observation can only provide so much insight. In this poster we present the results of our high resolution numerical simulations focused on determining the importance of interface capturing on the survivability of HVCs. These MHD simulations were performed in 3D using the RIEMANN code for astrophysical fluid dynamics. Using AMR we are able to provide very high resolution at the cloud interface, reducing the numerical diffusion, and providing a more physical description of the evolution of the cloud as it falls through the stratified galactic halo. In addition we employ photoelectric heating and metalicity dependent radiative cooling in order to test their effects on the survivability of the cloud and the production of the high and low stage ions which are seen in the observations. These results help us understand the fate of the HVCs, as well as place constraints on their possible origins (galactic fountain, filament inflow, halo condensations). |
|
| Searching for Cooling Flow Byproducts in Galaxy Cluster Cores |
| Michael McDonald (MIT) |
| We present new results from a combined analysis of X-ray, far-UV, H-alpha, and CO(1-0) data for the nearby cool core cluster, Abell 1795. We find significant amounts of cold, molecular gas in the core of this cluster, distributed along a pair of thin filaments extending from the cluster center to the cooling radius. The unique and exciting aspect of this study is that it provides, for the first time, a spatially-resolved quantification of the extent of the so-called "cooling flow problem". We find that, in the highest-density regions of the ICM (i.e. filaments, cores), the amount of cooling predicted by the classical X-ray cooling rate is consistent with both the spectroscopic X-ray cooling rates and the amount of cooling byproducts. The fact that the total mass in cold molecular gas, warm ionized gas, and young stars is consistent with the local cooling rate over timescales of ~ Gyr for this system suggests that the cooling flow problem may be confined to the lower-density regions of the ICM. We speculate on what these results may mean in the context of our current understanding of cool core clusters, and how future observations will enable a more complete understanding of the cooling ICM in cluster cores. |
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| HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) in the Magellanic Clouds
|
| Margaret Meixner (STScI) |
| We are conducting a uniform survey of the Large Magellanic Cloud (LMC, 8×8.5 degrees), Small Magellanic Cloud (SMC, 5×5 degrees), and the Magellanic bridge (4×3 degrees) in SPIRE 250, 350, 500 um and PACS 100 and 160 um bands in order to produce a HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE), the interstellar medium (ISM) and massive stars. The life cycle of baryonic matter in a galaxy is driven by the exchange of material between the ISM and stars. Dust is present at these key transition phases of matter: in the ISM, in the circumstellar environments of newly forming stars and in stellar ejecta of dying stars. The Herschel HERITAGE images are providing key insights into the life cycle of galaxies because the far-infrared and submm emission from dust grains is an effective tracer of the coldest ISM dust, the most deeply embedded young stellar objects (YSOs), and the dust ejected over the lifetime of massive stars. The ISM dust map will directly measure dust on a scale size of individual regions (~10pc, ~5–20 K) with column densities >0.85×10^{21} and >6×10^{21} H-atoms cm^{−2} for the LMC and SMC, respectively. Dust emission per beam will be detected for regions with >0.1 Msun at ~25 K, >5 Msun of 10 K. HERITAGE will complete 1) the census of massive YSOs down to >4 Msun Class 0 sources and 2) the inventory of dust injected into the ISM by massive evolved stars and supernova remnants (SNRs). HERITAGE will create an archival data set that promises a lasting legacy to match current LMC and SMC surveys at other wavelengths. This poster provides an overview of the HERITAGE project.
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| X-ray Properties of the Starburst-Driven Outflow in NGC 253 |
| Ikuyuki Mitsuishi (University of Tokyo/ ISAS/JAXA) |
| X-ray properties of hot gas for 4 regions in NGC 253 characterized by multiwavelength observations were investigated by imaging and spectral analysis. In the nuclear region where the most intense starburst activity is suggested by radio observations, we detected complex Fe K line structure which is resolved into three lines (Fe I, Fe XXV and Fe XXVI). Especially, the Fe I and Fe XXVI lines are the first clear detections. Considering the spatial correlation between intensities of Fe XXV and CO lines and observed luminosity, thermal energy and Fe mass, it is indicated that X-ray emitting gas in the nuclear region is produced by 10-1000 SNRs associated with the starburst activity (Mitsuishi et al. 2011 ApJL).
In spectra of other three regions outside the nuclear region, various emission lines such as O, Ne, Mg and Si are successfully observed. We extracted abundance patterns of these elements and found that every abundance pattern in all regions is consistent with each other within the statistical error, suggesting that all of these hot gas have the same origin. Furthermore, these abundance patterns are similar to those of the product of type II supernova associated with the starburst activity even in the halo region located ~10 kpc away from the nuclear region (Mitsuishi et al. in prep).
We extracted density and temperature distributions of hot gas from the disk to the halo up to 8 kpc and found that temperature and density drop sharply in the disk region. On the other hand, no temperature gradient and shallower density gradient are observed in the halo region. We also examined polytropic relationship between temperature and density and this indicates that the hot plasma expands adiabatically in the disk region while it freely expands in the halo region. Finally, assuming that hot gas cools through a radiative cooling process and moves in the halo region with a constant velocity, the constant velocity on the order of 100 km / s is needed to reproduce the observed temperature profile (Mitsuishi Dthesis, Mitsuishi et al. in prep). |
|
| Radio Jets and Outflows of Cold Gas |
| Raffaella Morganti (ASTRON) |
| Massive gas outflows are considered a key component in the process of galaxy formation and evolution. It is, therefore, not surprising that a lot of effort is going in quantifying their impact via detailed observations. This contribution presents recent results obtained from HI and CO observations of different objects where the AGN - and in particular the radio jet - is likely playing an important role in producing the gas outflows.
The results are reinforcing the conclusion that these outflows have a complex and multiphase structure where cold gas in different phases (atomic and molecular) is involved and likely represent a major component. These results will also provide important constraints for establishing how the interaction between AGN/radio jet and the surrounding ISM occurs and how efficiently the gas should cool to produce the observed properties
of the outflowing gas. HI likely represents an intermediate phase in this process, while the molecular gas would be the final stage. Whether the estimated outflow masses match what expected from simulations of galaxy formation, it is still far from clear. |
|
| Measuring AGN Feedback Parameters from Seyfert Galaxy Outflows |
| Dr.
Francisco Mueller-Sanchez (UCLA) |
| We present results of an ongoing program to study AGN outflows using integral field spectroscopy and adaptive optics at Keck Observatory and VLT. These data enable us to study at very high angular resolution (~0.08”) the 2D kinematics of Brgamma and the high ionization line [SiVI] in nearby AGN. The spatially resolved kinematics can be modeled as a combination of an outflow bicone and a rotating disk coincident with the molecular gas. High-ionization emission is seen in both components, suggesting it is leaking out of a clumpy torus. While Seyfert 2s are viewed nearly edge-on, intermediate-type Seyferts are viewed at intermediate angles, consistent with unified schemes. The outflow rate is 2–3 orders of magnitude greater than the accretion rate, implying that the outflow is mass loaded by the surrounding interstellar medium. In half of the AGN measured so far, the kinetic energy of the outflows appears sufficient to provide the eagerly-sought “AGN feedback” invoked to explain fundamental galaxy properties such as the M–sigma relation. |
|
| Searching for the Warm Neutral Medium in Absorption with 21-SPONGE |
| Ms.
Claire Murray (UW Madison Astronomy Dept) |
| In order to constrain the fraction of thermally unstable gas in the interstellar medium, it is necessary to measure the temperature of the warm neutral medium (WNM). However, only a handful of direct measurements of the WNM exist to date. 21-SPONGE is a large EVLA project undertaking the first statistical survey of the temperature distribution of the WNM. After completion, we will produce absorption spectra in the direction of 59 radio continuum sources, with matching emission spectra from the ongoing GALFA-HI survey at Arecibo. We present the first 11 completed sources here, and reach one-sigma levels of 6E-4-1E-3, allowing us to sample excitation temperatures of T<8000K. Our results will allow us to assess the fraction of thermally unstable gas, determine the low column density tail of the cold neutral medium (CNM), and constrain the inputs of numerical simulations as well as provide observational constraints on their outputs. |
|
| High-z IGM As Probed By O VI Absorbers |
| Sowgat Muzahid (Inter-University Centre for Astronomy & Astrophysics ) |
| I will present the results of a detailed study of the largest sample of intervening O VI systems in the redshift range 1.9 < z < 3.1 detected in high resolution (R ~ 45,000) spectra of 18 bright QSOs observed with VLT/UVES. The observed properties of the O VI absorbers
favour the idea of multiphase photoionized and/or non-equilibrium cooling gas correlated over large scale.
%
The detail comparison of the properties of O VI systems in our sample with that of low redshift (z < 0.5) samples reveals that (i) the O VI components at low-z are systematically wider than at high-z with an enhanced non-thermal contribution to their b-parameter, (ii) range in gas temperature estimated from a subsample of well aligned absorbers are similar at both high and low-z, and (iii) Omega_{O VI} estimated in our high-z sample, is very similar to low-z estimations. All these leads to a speculation that the O VI absorbers at high and low-z may not originate from the similar physical conditions.
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|
| Secular Evolution of Galaxies |
| Preethi Nair (STScI) |
| The role of bars in driving secular evolution of galaxies is still highly debated. Studies on the fraction of barred galaxies in the local universe, their evolution with redshift, and their role in building bulges and triggering AGN have not yielded consistent results. Recently, Nair & Abraham (2010) using their sample of ∼14,000 visually classified galaxies were able to reconcile the disparity in local bar fractions. In this work, I will extend the analysis to high-redshift, using a sample of ∼20,000 equally detailed visual classifications from the zCOSMOS survey (Lilly et. al. 2007). In addition, I will present results on the impact of stellar bars on the color, star formation rate, and metallicity evolution of galaxies and contrast it to the role of close pairs in galaxy evolution. |
|
| Moving Mesh Cosmology: Tracing Cosmological Gas Accretion |
| Mr.
Dylan Nelson (Harvard CfA) |
| We re-evaluate the nature of gas accretion onto halos and the "cold accretion mode" using cosmological hydrodynamic simulations run with the moving mesh code AREPO. We introduce passive, Lagrangian tracer particles in order to trace the origin and thermodynamic history of accreting gas, as well as make quantitative comparisons to an otherwise identical simulation run with the SPH code GADGET-3. Previous work comparing these two numerical methods has shown systematic differences in the properties of galaxies and in the thermodynamic structure of halos. The superior treatment of fluid instabilities, more accurate shock capture, and differences in dissipative heating all affect the stability and thermodynamic evolution of gas as it falls in to collapsed galaxies. We compare the relative role of different modes of gas accretion and discuss implications for the idea of galaxy formation fueled by smooth flows of cold, cosmological gas. |
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| Spatially Resolved Halpha Maps and Sizes of 57 Strongly Star-Forming Galaxies at z~1 from 3D-HST: Evidence for Rapid Inside-Out Assembly of Disk Galaxies. |
| Ms.
Erica Nelson (Yale University) |
| We investigate the build-up of galaxies at z~1 using maps of Halpha and
stellar continuum emission for a sample of 57 galaxies with rest-frame Halpha
equivalent widths >100 Angstroms in the 3D-HST grism survey. We find that the
Halpha 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 Halpha effective radius
r_e(Halpha) is 4.2+-0.1 kpc but the sizes span a large range, from compact
objects with r_e(Halpha) ~ 1.0 kpc to extended disks with r_e(Halpha) ~ 15 kpc.
Comparing Halpha sizes to continuum sizes, we find
=1.3+-0.1 for the full sample. That is, star formation, as
traced by Halpha, 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 Halpha sizes, we derive star formation
rate surface densities. We find that they range from ~0.05 Msun yr^{-1}
kpc^{-2} for the largest galaxies to ~5 Msun 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. |
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| Looking Behind the Neutral Gas Curtain: Analogs of the Galaxies That Re-Ionized the Universe. |
| Dr.
Daniel Nestor (UCLA) |
| It generally assumed that star forming galaxies were responsible for generating the ionizing radiation that reionized the Universe. However, observations typically have not detected Lyman-continuum (LyC) radiation escaping from galaxies, indicating that all LyC radiation is absorbed by neutral gas local to the galaxy. For ionizing radiation to escape from galaxies requires the removal of such gas. In recent years, several groups have reported possible detections of LyC radiation escaping from galaxies at z~3, suggesting an evolving escape fraction for LyC radiation. We have now completed a large spectroscopic followup to our detailed imaging of galaxies with putative LyC detections in the SSA22 protocluster at z=3.09. I will discuss the interesting new results from this combined dataset, including the segregation of Ly-alpha emitting gas from the LyC producing regions.
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|
| Molecular Hydrogen in Large Simulations |
| Ms.
Sarah Nickerson (University of Zürich) |
| Here we present a model of molecular hydrogen evolution to be implemented in the RAMSES adaptive mesh gridcode. The process of star formation unfolds on the scale of molecular clouds, which is currently still treated as subgrid physics in large galactic discs and cosmological simulations. Molecular hydrogen is a well-known tracer of star formation. We use the statistics of the atomic-to-molecular transition in molecular cloud populations to predict the molecular hydrogen content of a wider region. |
|
| Using ~200 MgII Absorbers to Understand Galactic Winds and IGM Accretion |
| Nikki Nielsen (New Mexico State University) |
| Recent results indicate that MgII absorption observed in quasar
spectra probe inflows, filaments, and outflowing galactic winds
associated with galaxies. Simulations have provided predictions of
winds and of cold-mode and hot-mode gas accretion and how they depend
on the virial mass of a galaxy; however, they require observations for
confirmation. Hot accretion is predicted to dominate in massive
galaxies (log M/Msun >= 11.8), while winds and cold accretion
(filaments and co-planer gas) dominate in less massive galaxies (log
M/Msun < 11.8). Combining the study of quasar absorption line analysis
with galaxy luminosities and virial masses and radii, we can test
predictions from simulations.
We present a sample of ~200 galaxies (0.05
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| Probing the Structure and Kinematics of the Transition Layer Between the Magellanic Stream and the Halo in HI |
| Lou Nigra (Adler Planetarium) |
| Understanding the destination of cool gas flows is crucial to understanding galaxy evolution. The detailed hydrodynamic interaction governing mass transfer between that gas and the circumgalactic environment is an important factor. We provide an unprecedented observational look at these processes at work on our prominent local example of a cool gas stream, the Magellanic Stream (MS), to its circumgalactic medium, the Halo. We present results based on 21 cm (HI) observations from the Green Bank Telescope (GBT) of a cloud in the northern MS that, through special data reduction, averaging and modeling techniques, reach unprecedented 3-sigma column density sensitivity of ~1x10^17 cm^(-2) while essentially retaining the 9.1' GBT resolution. Our method reveals an extensive envelope of diffuse neutral gas with FWHM of approximately 60 km/s associated in velocity with the cloud's warm, ~8000 K core having FWHM of approximately 20 km/s. The envelope extends to 3.5 times the core radius with neutral mass 7 times that of the core. Rather than tracing a conduction-dominated evaporative boundary layer between the cloud's core and Halo gas, the envelope's characteristics are best explained by a turbulent mixing layer driven by shear instabilities at the interface as seen in various prior numerical studies. |
|
| Deep HI Observations of NGC 5055 from the HALOGAS Survey |
| Maria Patterson (New Mexico State University) |
| We present results from Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) Survey HI observations of the galaxy NGC 5055. The survey consists of some of the most sensitive HI observations of nearby spiral galaxies to date, allowing for a systemic investigation of cold gas accretion onto galaxies in the local Universe. We have performed a detailed tilted-ring analysis of NGC 5055 to characterize the HI morphology and kinematics in this galaxy. NGC 5055 is a moderately-inclined SAbc galaxy in the HALOGAS sample with a very extended gaseous disk and a large pronounced warp. The HALOGAS observations reveal faint emission in the form of HI spurs, streams, and anomalous velocity gas, which were undetected in previous data. We compare these HI features with stellar streams seen in recent deep optical imaging and with extended UV emission from GALEX. We also characterize anomalous velocity "beard” gas in the inner region of the galaxy, which may suggest a lagging halo component associated with the optical star forming disk. |
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| Metals Flowing Out of Galaxies at z~2-3: Clues from the CGM and IGM
|
| Molly Peeples (UCLA) |
| I will describe comparisons between cosmological-scale simulations and observations of heavy elements around galaxies and in the intergalactic medium, with a focus on what constraints these data place on outflow models. I will be showing are an updated set of SPH simulations from Oppenheimer et al. (2010) in which we vary the scaling of the velocities and mass-loading factors of star-formation driven winds. I will compare these simulations to the Steidel et al. (2010) observations of, e.g., CIV, SiIV, and HI in the circumgalactic medium of galaxies at z~2.2 and show predictions for both other ions and how these distributions vary with star formation rate. I will also describe a comparison between the simulations and observations of CIV absorption in paired quasar sightlines from Martin et al. (2010), which are less sensitive to peculiar velocities along the line of sight than isolated sightline studies. |
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| Probing the Flows of Gas Around HI-Selected Galaxies |
| Celine Peroux (Laboratoire d'Astrophysique de Marseille) |
| One way to study gas flows processes is to relate the cold gas, metals
and the stars in galaxies. The quasar absorbers, the galaxies probed
by the absorption they produce in a background quasar spectrum, allow
for an efficient HI-selection of galaxies. However, studying the
stellar content of these systems has proven very challenging until
now. Our group has recently taken advantage afforded by the 3D
spectroscopy at infra-red wavelengths made possible by the SINFONI
instrument on VLT to successfully detect a small sample of galaxies
responsible for DLAs. For each system, we have retrieved and analysed
data from HST/STIS (for neutral gas content), VLT/UVES, Keck/HIRES or
Magellan/MIKE (metallicity, kinematics and dust content of HI gas),
VLT/SINFONI (SFR and kinematics of HII gas) and the VLT/X-Shooter
(metallicity of HII gas). Together, all these data allow to probe the
flow of gas around those galaxies and thus current theories on the
formation and evolution of galaxies.
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|
| Is the HI in Galaxies Opaque? |
| Stephan Peters (Kapteyn Institute) |
| The 21-cm line of HI is known to be optically thick along many sight lines in our own (edge-on) Galaxy, and evidence is accumulating that flat-topped HI profiles characteristic of this effect are common in M31 and M33 where hydrogen mass correction factors of order 1.3 to 1.4 have been proposed (Braun, 2012, ApJ, accepted). Such self-obscuration of the HI emission not only biases the total hydrogen masses, it also raises questions about the use of the HI velocity profile structure for studies of the gas kinematics. Nowhere are the answers to such questions more urgent than in the study of highly-inclined galaxies, where techniques have been proposed to progressively "peel off" the edges of the observed HI in order to expose the detailed velocity dispersion of the ISM over large segments of the galaxy disk in r and z (O'Brien et al., 2010, A&A, 515, A62). In this poster we present an analysis of synthesis observations of the HI in the edge-on galaxy ESO 274-G001 with a view towards elucidating the role of optical depth in an edge-on system. |
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| Galaxy Feedback with Future X-ray Missions
|
| Dr.
Andrew Ptak (NASA/GSFC) |
| We will discuss the prospects for constraining the effects of both AGN and starburst-driven feedback in galaxies with advanced capabilities planned or proposed for future X-ray missions. Future calorimeter missions like Astro-H and mission concepts being developed by NASA and ESA will have better than 6 eV spectral resolution, allowing galactic outflows to be detected through Doppler shifts and broadening of X-ray lines. Missions under consideration will also be able to spatially resolve outflows (with better than 10" resolution), allowing their energetics, abundance distributions and ionization states to be mapped and compared to theoretical expectations. These missions will also enable spatially-resolved high-resolution spectroscopy of clusters of galaxies, directly mapping turbulence and testing AGN energy injection models. X-ray absorption line studies would detect or tightly limit the baryon mass hidden in the WHIM. eRostia and future wide-field X-ray mission concepts will be able to survey large solid angles comparable to wide-area ground-based surveys. This will result in the X-ray detection of large numbers of AGN, many of which are likely to be obscured and missed in optical surveys. When correlated with other multi-wavelength surveys these X-ray AGN samples will give a more complete picture of how AGN activity evolves as a function of parameters such as environment, galaxy type, and host galaxy star-formation rate. The mission concepts under consideration would improve on eRosita with higher spatial resolution and effective area which will allow these studies to be extended to redshifts > 6.
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| The Covering Factor of the Optically-Thick Circumgalactic Medium in the COSMOS Field |
| Joseph Ribaudo (Utica College) |
| We use a combination of QSO UV spectroscopy and deep galaxy imaging to estimate the covering factor of optically-thick H I in the circumgalactic medium of 0.6 < z < 1.0 galaxies in the COSMOS field. We use GALEX spectroscopy of 28 QSOs over this 2 square degree field to identify 9 strong H I absorbers [log N(H I)>17.5] and 19 absorber-free sight lines. We use HST and ground-based imaging surveys to identify galaxies with impact parameters < 200 kpc from the QSO lines-of-sight. We find the covering factor of strong H I absorbers about galaxies drops steeply for impact parameters >25 kpc. The normalization and shape of the H I-derived covering factor with galaxy impact parameter derived here is distinct from that seen by studies of Mg II absorption. This difference is likely due to a combination of the section of gas through H I absorption and the different H I column density regimes probed by the two methods. |
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| Kinematics and Feedback in Star Forming Regions: Investigating the Main Modes of Star Formation. |
| Dr.
Javier Rodriguez (Instituto de Astrofísica de Canarias (IAC)) |
| We use the OSIRIS instrument at the GTC, the 10.4 m telescope at La Palma, Spain, to investigate the main modes of star formation in a variety of star forming galaxies, from the local to the distant universe. In this context, we are currently carrying out a pilot project involving Hα Tunable Filter imaging along with long slit spectroscopic observations of a sample of local ULIRGs. In the 1st place, we investigate the kinematics of the population of young "Super Star Clusters" (SSCs) observed in these objects. We aim to test the idea that these SSCs may represent nascent globular clusters formed in shocks induced as tidal tails collide during merger events (e.g. Rodriguez Zaurín et al., 2007). So far we have found line splitting (evidence of distorted kinematics) coinciding with the location of one of the SSCs for which spectroscopic information is available. Secondly, we also aim to investigate the presence of the so called "positive feedback", a very efficient star forming process present in high stellar density environments (e.g. Tenorio-Tagle et al 2007, Silich et al 2009). A priori, one would expect high metallicities associated to the star forming regions where such feedback is present. In addition, at least two components, a broad and a narrow component, would be required to adequately model the emission line profiles from those regions (Tenorio-Tagle et al 2010). Along with the already mentioned observations of the local ULIRGs, we have recently obtained spectra for several SSCs in M82. So far, we find that some line profiles are best fitted with two gaussians and the line ratios are consistent with the theoretical predictions (Muñoz-Tuñon et al 2012, in prep, Rodríguez-Zaurin et al, 2012, in prep). These studies in the local universe will be used as a test-bench for future studies at high-z. At the moment, we are using the data from the SHARDs survey (PI: P.G. Pérez-González. http://guaix.fis.ucm.es/~pgperez/SHARDS/team.html) to select galaxies that actively form starts up to z~1.5. Follow up spectroscopic observations are planned for the next generation of instruments soon available at GTC, such as EMIR (http://guaix.fis.ucm.es/emir/). |
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| Extremely High Velocity Outflows in Active Galaxies |
| Dr.
Paola Rodriguez Hidalgo (York University) |
| Outflows in Active Galactic Nuclei (AGN) bring information about the physical and chemical properties of the AGN inner environments. Moreover, they are fundamental constituents of AGN: they might be ubiquitous, they might connect the Super-Massive Black Hole (SMBH) environment with the host galaxy via ''feedback'', and they might play a role in blowing out the gas and dust from young galaxies and distributing metal-rich gas to the intergalactic medium. Of special interest are the cases with extremely large velocities (v > 0.1c) because they present the biggest challenge to theoretical models and can help constrain the acceleration mechanisms proposed to be driving these outflows.
Despite our progress in understanding their characteristics and their frequency, the geometry and the physics of the outflow phenomenon in active galactic nuclei remains unknown. I will report on the progress of a multi-wavelength campaign, which aims to characterize the chemical and physical properties of some of the fastest UV/optical outflows found in quasars.
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| The Propertries of Two Low Redshift O VI Absorbers and Their Associated Galaxies Toward 3C 263 |
| Blair Savage (University of Wisconsin) |
| Ultraviolet observations of the QSO 3C 263 (zem = 0.652) with COS and FUSE reveal O VI absorption systems at z = 0.06342 and 0.14072. WIYN multi-object spectrograph observations provide information about the galaxies associated with the absorbers. The multi-phase system at z = 0.06342 containing H I, C II, Si II, Si III, C IV, and O VI traces cool photoionized gas and warm collisionally ionized gas associated with a L ~ 0.31L* compact spiral emission line galaxy with an impact parameter of 63 kpc. The photoionized gas in the absorber is well modeled with log U ~ -2.6, log N(H) ~18.1, log L(kpc) ~ -0.1, log n(H) ~ -3.3, log T(K) ~ 4.07, log P/k ~ 1.1, and [Si/H] = -0.14±0.23. The collisionally ionized gas with log N(O VI) =14.59±0.07 and log N(C IV) =14.14±0.05 probably arises in cooling shock heated transition temperature gas with log T ~ 5.5. The absorber is likely tracing circumgalactic gas enriched by gas ejected from the compact spiral emission line galaxy. The simple system at z = 0.14072 only contains O VI and broad and narrow H I. The O VI absorption with log N(O VI) = 13.60±0.09 and b = 33.4±11.9 km s-1 is likely associated with the broad H I λ1216 absorption with log N(H I) = 13.47±0.10 and b = 86.7±15.4 km s-1. The difference in Doppler parameters implies the detection of a very large column of warm gas with log T = 5.61(+0.16, -0.25), log N(H) = 19.54(+0.26, -0.44) and [O/H] = -1.48 (+0.46, -0.26). This absorber is possibly associated with a 1.6L* absorption line galaxy with an impact parameter of 617 kpc found among 6 luminous galaxies near the redshift of the absorber within 3.4 Mpc of the line of sight although an origin in warm filament gas or in the halo of a fainter galaxy is more likely. |
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| Simulations of the Origin and Fate of the Galactic Center Cloud G2
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| Dr.
Marc Schartmann (MPE / USM Munich) |
| We investigate the origin and fate of the recently discovered
gas cloud G2 close to the Galactic Center.
Our hydrodynamical simulations focussing on the dynamical evolution of the cloud in combination with currently available observations favor two scenarios: a compact cloud
which started around the year 1995 and an extended spherical shell of gas, with an
apocenter distance within the disk(s) of young stars.
The former is able to explain the detected signal of G2 in the position-velocity diagram of
the year 2008.5 and 2011.5 data.
The latter can account for both, G2's signal as well as the fainter extended tail-like structure G2t seen at larger distances to the black hole and smaller velocities.
In contrast, gas stripped from a compact cloud by hydrodynamical interactions is not able to explain the location of the detected G2t emission in the observed position-velocity diagrams. This might be a severe problem for the so-called Compact Source Scenario and favors the Spherical Shell Scenario. From these first idealised simulations we expect a rise of the current activity of Sgr A* shortly after the closest approach and a constant feeding through a nozzle-like structure over a long period. The near future evolution of the cloud will be a sensitive probe of the conditions of the gas distribution in the milli-parsec environment of the massive black hole in the Galactic Center and will also give us invaluable information of the feeding of black holes and the activation of the central source.
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| Enrichment of the Circumgalactic Medium of Massive Galaxies At z = 2-3: A Test for Stellar Feedback and Galactic Outflows |
| Sijing Shen (UC Santa Cruz) |
| We present a detailed study of the metals in the circumgalactic medium (CGM) of a massive galaxy at z = 2-3, using results from the "Eris" suite of cosmological hydrodynamic “zoom-in” simulations. The reference run adopts a star formation recipe based on a high gas density threshold, a blastwave scheme for supernova feedback that produces large-scale galactic outflows, a metal-dependent radiative cooling. We investigate the origin and of the metals in the CGM. Our study shows that there are three sources of heavy elements: the main host, its satellite progenitors and its dwarf companions, and the latter two contribute significantly to the metal budget. We also present a new comparison with observations on the kinematics, thermal and ionization state, and spatial distribution of the CGM metals. Synthetic spectra generated by drawing sight lines through the simulated volume are found to be in good agreement with the interstellar absorption line strengths of Lya,C II, C IV, Si II, and Si IV as a function of galactocentric impact parameter observed in the high-redshift galaxy-galaxy pair sample of Steidel et al. (2010). We discuss the contribution from inflows and outflows on the line width and the impacts of local UV radiation field, gas self-shielding and different feedback schemes.
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| Intermediate and High Velocity Clouds Towards the LMC and SMC - CaII and NaI Observations |
| Dr.
Jonathan Smoker (European Southern Observatory) |
| High velocity clouds were originally discovered nearly 50 years ago. Originally observed in H,{sc i}, they comprise parcels of gas with velocities not compatible with Galactic rotation; in practice this means HVCs have $|v_{
m LSR}|>$90--100,km,s$^{-1}$ if they lie at at high Galactic latitudes.
IHVCs are important to study as they may provide fuel for star formation in the Milky Way, put constraints on $Lambda$ Cold Dark Matter theory, and provide information on close encounters and/or winds from the SMC and LMC.
We present interstellar absorption-line spectroscopy of early-type stars in CaK and NaD towards the Large and Small Magellanic Clouds (taken from the ESO archive) to investigate the large- and small-scale structure in foreground Intermediate and High Velocity Clouds (IHVCs). The data include FLAMES-GIRAFFE observations of 403
stars in CaK towards four open clusters and 60 targets observed with FEROS in CaK and NaI D. The scales probed are from $sim$12 arcsec to several degrees. Many IHVC components are observed in CaK and their velocities are compared with those predicted from an outflow of gas from the LMC. As in previous work, CaK structure is present in the IHVCs on small scales. Very few sightlines show IHVC absorption in NaI, indicative of the Routly-Spitzer effect. For these objects we perform CLOUDY modelling to put weak constraints on the gas density and CaI/HI ratio.
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| Probing External Influences On Galaxy H2/HI Ratios |
| David Stark (University of North Carolina -- Chapel Hill) |
| We present the results of a study that explores the potential role of
external factors in driving the global gas content of galaxies. Using
a galaxy sample spanning the dwarf to giant mass regime, early- to
late-type morphologies, and quiescent to bursting star formation, we
find a link between molecular-to-atomic gas ratios and enhanced
central star formation events, likely linked to externally triggered
gas inflows. We find that most star forming galaxies display a
roughly linear relationship between H2/HI and centrally enhanced star
formation. However, a distinct population of low mass early-type
galaxies show systematic deviations from the main galaxy population.
Additional evidence suggests these galaxies are merger remnants, and
are accreting fresh gas from their environment.
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| Gas Flow in Barred Galaxies with a SMBH |
| Peter Teuben (University of Maryland) |
| TBA |
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| The Astrophysics Source Code Library (ASCL) |
| Peter Teuben (University of Maryland) |
| TBA |
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| Detection of Outflowing Gas in Disks in an Assembling Galaxy Cluster at z=0.37
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| Kim-Vy Tran (Texas A&M University) |
| We present maps of extraplanar and fast-moving gas indicative of galactic winds obtained with Integral Field Units on the Very Large Telescope. The three observed disk-dominated galaxies are in an assembling galaxy cluster at z=0.37 and thus provide a window into how galaxies lose their multi-phase gas in over-dense environments. Using Halpha to map the relative velocities and distribution of the warm gas, we find Halpha velocities of up to 1000 km/s. Our multi-wavelength observations indicate that these galaxies are dominated by star formation, i.e. the observed winds are driven by star formation. We estimate that the ionized gas mass loss is ~0.1 Msun/year but expect that a significantly larger amount of neutral and molecular gas are entrained in these winds.
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| COS-Halos: Flows of Mass and Metallicity in the Circumgalactic Medium with COS |
| Jason Tumlinson (STScI) |
| We have been systematically surveying the diffuse gaseous halos of z < 0.4 galaxies with COS, and relating these to galaxy properties measured with spectroscopy from Keck and Magellan. This poster describes the design and content, and highlights of the major results. Other presentations by our team will describe specific results on the masses, metallicities, kinematics, and galaxy trends in the CGM. |
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| The VLT LBG Redshift Survey |
| Pimpunyawat Tummuangpak (Durham University) |
| We have completed the largest spectroscopic survey of Lyman-break galaxies (LBGs) at z ~ 3, using the uniquely wide field of view of the VLT VIMOS multi-object spectrograph. The survey now contains > 2100 galaxy redshifts over the range 2 < z < 3.6 and is being used to investigate gas outflows from galaxies and large-scale structure at z ~ 3. These results are having an immediate impact on theories of galaxy formation and producing new tests of the standard cosmological model. In particular, we find new evidence for gas outflows from star-forming galaxies as required by theoretical galaxy formation models; and evidence for gravitational infall of galaxies into clusters at a rate that is consistent with the standard cosmology. Building on the observational work, we present an analysis of the clustering of gas and galaxies (and the associated velocity fields) using the GIMIC SPH simulations. The simulations highlight the coherent motion of gas and galaxies within the large scale structure and the effects of this on clustering measurements. |
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| Associating Lyman Alpha Absorbers with Galaxy Filaments |
| Bart Wakker (University of Wisconsin-Madison) |
| Studies of the photoionized Lyman alpha forest have shown that at
z=0 it contains about 30% of the baryons in the universe. Other
studies have shown that many Lyman alpha lines associate with the
extended outskirts of galaxies. About half of the lines originate
within about 400 kpc from galaxies. Other lines are thought to
occur in voids. In the study we present here, we look instead at
the properties of Lyman alpha absorbers in relation to galaxy
filaments. We observed 20 QSOs in an ~10x10 area of the sky,
sampling directions that are projected both on and off a prominent
filament of galaxies at cz~3000 km/s. Lyman alpha absorption near
3000 km/s having b=35-60 km/s is seen in 8 of 10 directions
projected onto the filament, in 3 of 6 directions along the edge of
the filament, and in 0 of 5 directions off the filament. For 1 of
the 8 detections on the filament OVI absorption is also seen, and
an analysis gives T~1.4E5 K and N(H)~4E19 for that absorber. If 80%
of the filament is covered with H at this column density, a
hydrogen mass on the order of 2x10^13 Msun is implied. This can be
compared to the few x10^12 Msun for the ~30 galaxies in the
filament.
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| Insight into Gas Processing in Compact Groups of Galaxies |
| Lisa May Walker (University of Virginia) |
| Compact groups of galaxies provide a unique environment to study the evolution of galaxies amid continuous gravitational encounters. In order to understand how the compact group environment affects galaxy evolution, it is important to study the gas and dust processes in these groups. HI observations of compact groups allow us to measure the HI mass of each group in our survey, as well as determining whether there is a significant amount of HI in the intragroup medium. We will compare our HI masses with dynamical masses to understand how the ratio of HI mass to dynamical mass scales with MIR star formation. Ultimately, these observations will provide information about gas processing and the ISM in an environment akin to that in the early universe. |
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| Cool Gas Outflows and Circumgalactic Cool Gas: Scaling and Associations with Star Formation |
| Dr.
Benjamin Weiner (Steward Observatory) |
| Outflows driven by star formation or AGN are increasingly recognized as a critical term in the gas budget of a galaxy, and possibly a regulator of the star formation rate. Open questions include the amount of mass loading, the distance to which winds can drive gas, and whether outflows are capable of evacuating or heating the ISM of galaxies to quench star formation. I will discuss results from studying Mg II absorption in deep galaxy redshift surveys and in lower-redshift environments with SDSS, that address the SFR-wind strength connection and the connection of star formation with associated Mg II absorbers. Our preliminary results suggest that circumgalactic Mg II is not that strongly dependent on star formation/passive nature of the associated galaxy, in contrast to the strong correlation between circumgalactic O VI and star formation recently shown by COS-Halos. This suggests we don't yet fully understand the phases of the CGM and how its evacuation is linked to star formation quenching. |
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| The CGM of L* Galaxies: Metallicities and Baryonic Content
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| Jessica Werk (University of California, Santa Cruz / UCO Lick) |
| With our HST/COS large program, "COS-Halos" we have mapped the gaseous halos of ~50 low-redshift galaxies, providing an unprecedented view of the hydrogen and ionized metal distribution around passively evolving and star-forming galaxies. These data have firmly established a physical association between properties of gas in galactic halos and basic, global properties of the stellar component (e.g. color, star formation rate). The origin(s) of these 100-kpc-scale correlations between gas and stars remains an open question, however, and may bear on the origin of galaxy bimodality and the fueling of star-formation. I will present, for the first time, constraints on the ionization parameters and halo metallicities for the galaxies in our sample that allow us to test models of galaxy accretion and feedback, and to measure the baryonic content of the gaseous halos of L* galaxies. The results may surprise you. |
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| Starburst Feedback from Super Star Cluster to Galaxy Scales |
| Dr.
Mark Westmoquette (ESO) |
| Starburst feedback is one of the primary drivers of gas flows in galaxies, and is important for many reasons within the context of galaxy evolution. In this talk I will discuss recent results from a number of high spatial and spectral resolution optical/near-IR integral field spectroscopic studies of the ionized gas environment in a sample of local starbursts. These studies are allowing us to build up an overall picture of how starburst-driven outflows evolve from pc-kpc scales. I will concentrate on two aspects: (1) how power (radiative and mechanical) is fed from star clusters into their immediate environment; and (2) how the ionized gas flows evolve structurally and energetically towards the larger-scales by examining nearby examples such as M82, NGC253 and a number of nearby ULIRGs. |
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| Star Formation Quenching in Satellite Galaxies and Implications for Gas Depletion
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| Dr.
Andrew Wetzel (Yale University) |
| Satellite galaxies in groups/clusters are more likely to have quiescent star formation rates than galaxies in the field, as driven by the lack of gas accretion in satellites after infall, combined with additional possible gas stripping in the dense group/cluster environment. Their lack of gas accretion makes satellite galaxies unique laboratories to study gas depletion and its impact on star formation. Using galaxy group/cluster catalogs from SDSS, I examine the SFR distribution of satellite galaxies and its dependence on satellite mass, halo mass, and halo-centric radius. Using a high-resolution cosmological simulation to track satellite orbits, I constrain the mechanisms and timescales of satellite star formation quenching that fit these observed dependencies. Star formation in satellites evolves environmentally unaffected for 2 - 4 Gyr after infall, after which SFR rapidly fades with a e-folding time of < 1 Gyr. More massive satellites quench more rapidly, but the quenching timescales have no dependence on group/cluster mass. I compare these quenching timescales with observed atomic/molecule gas depletion timescales, and I discuss the implications for rapid gas consumption/stripping in satellite galaxies. |
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| Scaling Relations of Star-Forming Regions: from KPC-Size Clumps to HII Regions |
| Emily Wisnioski (Swinbure University of Technology) |
| We present the properties of 8 star-forming regions, or `clumps,' in 3 galaxies at z=1.5 resolved with integral field spectroscopy that are driving large-scale winds. Within turbulent discs clumps are measured with average sizes of 1.5 kpc and average Jeans masses of 4.2 x $10^9$ Msun, in total accounting for 20-30\% of the stellar mass of the discs. These findings lend observational support to models that predict larger clumps will form as a result of higher disc velocity dispersions driven-up by cosmological gas accretion. As a consequence of the changes in global environment, it may be predicted that star-forming regions at high redshift should not resemble star-forming regions locally. Yet despite the increased sizes and dispersions, clumps and HII regions are found to follow tight scaling relations over the range z=0-2 for halpha size, velocity dispersion, luminosity, and mass when comparing >2000 HII regions locally and 30 clumps at z>1. We discuss these results in the context of the existing simulations of clump formation and evolution, with an emphasis on the processes that drive-up the turbulent motions in the interstellar medium. Our results indicate that while the turbulence of discs may have important implications for the size and luminosity of regions which form within them, the same processes govern their formation from high redshift to the current epoch. |
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| Cold Flows and Reservoirs in Galaxy Formation |
| Mr.
Rory Woods (McMaster University) |
| Over the past decade, the picture of galaxy formation has undergone a number of changes. Of great importance is the view of gas accretion into galaxies, which has changed focus from shock heating of accreting gas (hot mode gas) to cold flows along dark matter filaments (cold mode gas). These flows are seen in simulations to penetrate the hot halo and allow gas to reach the inner disk without shock heating. We present a numerical study of four galaxies from the McMaster Unbiased Galaxy Simulations (MUGS, Stinson et al. 2010). We have performed detailed tracking of gas particles which suggests that cold and hot mode gas accretion contribute roughly equally between redshifts of about 4-2. However, hot mode accretion builds up a much larger gas reservoir in the halo. Thus, at late times, star formation is dominated by hot mode gas that was accreted much earlier. In some cases, the reservoir allows the current star formation rate to surpass the overall gas accretion rate. In our tested galaxies, this leads to an overall stellar mass that is usually dominated by gas that accreted in the hot mode. |
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| Warm Ionized Gas in Early-Type Galaxies: Ionization, Metallicity, and Origin |
| Renbin Yan (New York University) |
| Early-type galaxies frequently contain warm ionized gas and have spectra similar to low-ionization nuclear emission-line regions (LINERs). Their ionization mechanism has been hotly debated. Some authors treat them as AGNs, others argue they are not AGNs but powered by shocks or hot old stars. We will present evidence from line ratio gradient that convincingly rules out AGN (and shocks) as the dominant ionization mechanism and suggests the ionizing sources follow the stellar density profile. Hot evolved stars are the favorite candidates but bring new puzzles.
We will also present a gas-phase metallicity calibration in these early-type galaxies, using the line emission. We will show how the metallicity of the warm gas depends on stellar mass and stellar age, and what it can tell us about the origin of the warm gas in these galaxies.
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| Thermal Instability-Driven Turbulent Mixing in Galactic Disks |
| Dr.
Chao-Chin Yang (University of California, Santa Cruz) |
| Observations show that open clusters and moving groups in the Solar neighborhood are extremely chemically homogenous, with typical star-to-star abundance variations of only ~0.01 dex. On a larger scale, radial metallicity gradients in majority of nearby disk galaxies are relatively shallow, if not flat, especially towards large galactocentric distances. The physical mechanism behind these phenomena, however, remains unclear. We conduct magnetohydrodynamical simulations of a local shearing sheet of a thin, thermally unstable, gaseous disk driven by a background stellar spiral potential, with the metals modeled as passive scalar fields. By Fourier and statistical analyses, we quantify the redistribution of metals and its variation within each gravitationally bound structure. We find that turbulence driven by thermal instability is very efficient at mixing metals, regardless of the presence or absence of stellar spiral potentials or magnetic fields. This in turn helps explain the chemical homogeneity of star clusters and radial metallicity gradients in disk galaxies. |
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| Warm Gas in the Virgo Cluster: The Distribution of Lya Absorbers. |
| Joo Heon Yoon (Columbia University) |
| We present the first systematic study of the warm gas (T=10^4-5 K)
distribution across a galaxy cluster using COS to observe multiple
QSOs in the background of the Virgo Cluster. We detect over 25
Ly-alpha absorbers (N_HI = 10^13.1-15.4 cm^-2) with an impact
parameter range of 0.23-1.05 R_vir. With these absorbers, we examine
the covering fraction of the warm gas and its relation to
substructures and galaxies and find the following. 1) Warm gas is
predominantly in the outskirts of the cluster and Ly-alpha absorption
strength increases with impact parameter. This indicates warm gas is
suppressed within the virial radius where the hot ICM is present. 2)
Ly-alpha absorbing warm gas traces cold HI emitting gas closely near
the substructures of the Virgo Cluster. 3) Including the absorbers
associated with the surrounding substructures, the warm gas covering
fraction is consistent with 100% for N_HI > 10^13.1 cm^-2 and this is
in agreement with cosmological simulations. We find that the observed
warm gas is most likely part of large-scale gas flows feeding the
cluster both ICM and galaxies. We discuss the gaseous filaments
around the Virgo Cluster and examine the association of the Ly-alpha
absorbers with the close-by, gas-rich galaxies. |
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| Cold Gas Accretion & the Evolution of Early-Type Galaxies |
| Lisa Young (New Mexico Tech) |
| Cold gas accretion onto early-type (elliptical and lenticular) galaxies can initiate small amounts of late star formation activity. The red sequence galaxies can thus be shuttled down into the green valley or even the blue cloud, and they should return to the red sequence as the star formation ceases. And while there are significant numbers of early-type galaxies rich in molecular gas, not all of them share the history described above. Some of them may be quenched or stripped disk galaxies, or they may have recycled their internally generated gas. With extensive observations of atomic and molecular gas in the Atlas3D sample of early-type galaxies, we now have the tools to assess the relative importance of these different processes that drive galaxies around in the color-magnitude diagram.
The critical new ingredient is the cold gas kinematics. Specifically, the molecular gas distribution and kinematics indicate whether the gas had an external origin and, if so, how long ago it happened. Stellar populations also constrain the star formation histories of the early-type galaxies. We attempt to synthesize this information and present a "big picture" of how cold gas accretion (or the lack thereof) drives the recent evolution of early-type galaxies. |
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| Discovery of An Ionization Cone in NGC 5253 |
| Ms.
Jordan Zastrow (University of Michigan) |
| Mechanical and radiative feedback processes in nuclear starbursts are closely linked. Outflows generated by the starbursts evacuate low-density regions in the ISM that facilitate the escape of ionizing radiation from the starburst region. Here, we report on the discovery of a prominent ionization cone extending from the central starburst in NGC 5253. We identify the ionization cone by its high excitation in the ratio maps of [S III] λ9069, [S II] λ6716, and Hα obtained with the Maryland-Magellan Tunable Filter at Las Campanas Observatory. The high-excitation line ratios throughout the ionization cone indicate that the gas is optically thin, which suggests the escape of ionizing photons from the starburst. The ionization cone subtends an estimated 3% of 4π steradians. This narrow morphology implies that the escape is happening through a small region of the galaxy. In addition, an echelle spectrum along the galaxy's minor axis reveals complex ionized gas kinematics that are consistent with outflow activity. This ionization cone provides us with observational constraints for the interplay between gas flows and radiative feedback in the ISM which leads to the escape of ionizing radiation. This result may have direct implications on our understanding of re-ionization at high redshift and on the difficulty in detecting Lyman continuum emission from starbursts and Lyman break galaxies. |
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| Equilibrium Star Formation In A Constant Q Disk |
| Zheng Zheng (Johns Hopkins University) |
| We developed a model for deriving the distribution of the ISM and star formation in galaxies based on recent work on the star formation law and the assumption that the two-fluid stability parameter Q of the galactic disk is a constant. The model predicts the gas surface mass density and star formation intensity of the galaxy given the rotation curve, stellar surface mass density and the gas velocity dispersion. This model is tested on a sample of 13 galaxies selected from the THINGS sample and 3 galaxies from SINGG/SUNGG survey. Four forms of two-fluid Q are also tested in our sample galaxies and all of them are close to constant. Our model works very well in most regions of galaxies and it shows that galaxies do indeed have a fairly constant two-fulid stability parameter Q. This suggests that the ISM and star formation distributions arrange themselves to maintain a constant equilibrium, most likely by internal secular means. |
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| HALOGAS: Observations and Modeling of the Nearby Spiral Galaxy NGC 4565 |
| Laura Zschaechner (University of New Mexico) |
| We present 21-cm observations and models of the neutral hydrogen in NGC 4565, a nearby, edge-on spiral galaxy, as part of the Westerbork Hydrogen Accretion in LOcal GAlaxies (HALOGAS) survey. These models provide insight concerning both the morphology and kinematics of HI above, as well as within the disk. NGC 4565 exhibits a strongly warped, highly inclined, and asymmetric disk with a flaring layer. We also observe evidence for a bar, as well as radial inflow within the bar. Our models give no indication of an extended HI halo. However, we find evidence for a lag within the inner third of the disk (10 kpc), peaking with a magnitude of -30 +5/-10 km/s/kpc in the approaching half, and -40 +5/-10 km/s/kpc in the receding half. Although this lag is not seen throughout the entire disk, it is among the steepest observed thus far. The magnitude of this lag declines rapidly in both halves, and is zero for all radii greater than 4.75' (15 kpc). This follows trends seen in NGC 891 and NGC 4244 where lags are seen to decrease with radius. We also see indications of radial motions at intermediate to large radii that are not associated with the bar. These could however, be due to spiral structure, and require further study to determine their nature. Finally, there are two companion galaxies, one of which is clearly interacting. |
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