Abstracts

Thermal OH as a Tracer for the Molecular ISM in the Galaxy

Ron Allen, STScI

A recently-published "mini-survey" covering about 16 square degrees in the outer Galaxy has revealed faint but ubiquitous emission from the main line of OH at 1667 MHz. The distribution of this OH emission in velocity and angular position resembles much more that of the 21-cm line of atomic hydrogen than it does the distribution of 3 mm CO(1-0) in the same area.
This talk will explore what might be needed to consider using the 18-cm OH emission as an alternative tracer for the molecular ISM on the large scale in the Galaxy.

Dark Matter and ISM in the THINGS galaxies

Erwin de Blok, ASTRON Dwingeloo

After a short introduction about The HI Nearby Galaxy Survey, I discuss the shapes of the dark matter halo profiles derived from the kinematics of these galaxies. I compare them with the Einasto mass density profiles which have recently become popular as a description of the halos found in cosmological N-body simulations. In the second half of the talk I discuss the velocity dispersions of the HI based on high signal-to-noise stacked profiles. I show that the profiles can be decomposed in two components: a narrow one, with a dispersion of ~4 km/s, tentatively associated with the warm neutral medium; and a broad one of ~15 km/s which can be associated with the warm neutral medium.

Measuring Distances to Galaxies Using Water Vapor Megamasers

Jim Braatz, NRAO

Water vapor masers have been detected in over 150 galaxies, most of them with active nuclei. In at least 20 percent of megamasers, the emission originates in an edge-on, circumnuclear disk surrounding the AGN. Spectacular VLBI observations show these megamasers in Keplerian rotation within a parsec of the dynamical center of the galaxy. Megamasers provide gold-standard masses of supermassive black holes, and in some cases we can use the masers to measure geometric distances to the host galaxies. The megamaser distance to NGC 4258 provides a fundamental anchor for the extragalactic distance scale. Other megamaser galaxies measure H_0 directly. In this talk I will describe the method and latest results from measurements of maser distances to galaxies.

SHIELD: The Survey of HI in Extremely Low-mass Dwarfs

John M. Cannon, Macalester University

SHIELD is an ongoing multi-wavelength investigation of the properties of 12 extremely low-mass galaxies. These systems populate the very faint end of the HI mass function derived by the ALFALFA blind HI survey. This talk will provide the motivation for SHIELD and will present preliminary results from ongoing observing campaigns with the EVLA, HST, Spitzer, and WIYN.

HI properties of massive galaxies

Barbara Catinella, MPA-Garching

Quantifying how the gas content varies with star formation and structural properties of galaxies is of paramount importance for constraining models of galaxy formation. Equally important is to perform such studies on large and unbiased samples of galaxies, in order to obtain results that are truly representative of the local population. The ongoing GALEX Arecibo SDSS Survey (GASS) is designed to provide such a representative sample for massive galaxies, with the aim of understanding the role played by gas in the transition between blue, star-forming galaxies and red, passively-evolving systems.

I will discuss how the atomic hydrogen (HI) content of massive systems depends on their structural and star formation properties, and how these scaling relations can be used to identify objects that might be transitioning between blue, star-forming cloud and red sequence. I will also talk about dynamical scaling relations, and show a relation between baryonic mass and velocity that holds for massive systems, regardless of morphology.

Lastly, I will discuss the relevance of these scaling relations for the future surveys that will be carried out with the Square Kilometer Array and its pathfinders. As an example, I will compare the properties of GASS galaxies with those of a unique sample of very HI-rich disks at redshift z~0.2 detected with Arecibo.

Cosmic Flows Project, Voyage to the Great Attractor

Helene Courtois, University of Lyon

The outstanding unsolved questions in astronomy are requiring enormous datasets. \u201cCosmic Flows\u201d is focused on producing observed galaxy distances for 30,000 galaxies with systematic errors below 2%, almost ten times the number currently known and a five-fold improvement in systematics. The resultant velocity field will provide input for constrained numerical cosmological simulations \u201cCLUES\u201d. The observed and the simulated universe are then comparatively studied. This synergy of observations and theory distinguishes this program, and should lead to fundamental discoveries regarding the sources of deviations from the expansion of the universe. Specifically, the program should give a definitive answer to an outstanding problem in cosmology: the cause of the motion of 630 km/s of the CMB. On the path to this goal we are learning new informations of the large coherent flows of galaxies away from voids and towards the Great Attractor region. "Cosmic Flows" is bringing together unique expertise in radio, optical, theoretical astrophysics and computation. We tackle a frontier question: Where are the Dark Energy and Dark Matter that dominate the cosmology?

Disk-halo Connection and Gas Accretion

Filippo Fraternalli, University of Bologna

The relatively constant rate of star formation in galaxies like the Milky Way implies the need for continuum accretion of fresh gas. I present evidence that this accretion comes from the cooling of the virial-temperature coronae, that are thought to surround galaxy
disks. This cooling is triggered by the passage of high-metallicity gas clouds ejected from the disks by supernovae. The prediction of this model is compared to neutral hydrogen surveys of some local galaxies including the Milky Way. The gas accretion rates required to reproduce the data are always of the order of 1 M_Sun/yr, remarkably close to the star formation rates in these galaxies.

Dark Matter Mini Halos

HI observations at z=0 have been effectively applied to the derivation of cosmological parameters and the characterization of the large-scale distribution of matter within the framework of the Lambda-CDM scenario. A major area of discrepancy between that scenario and observations regards the abundance of low mass haloes. A possible (partial?) solution to the problem, provided by local HI data from the ALFALFA survey, will be presented.

 

The ALFALFA Census of Gas-Bearing Galaxies at z=0

Martha Haynes, Cornell University

Capitalizing on the huge collecting area of the Arecibo telescope and the survey capability of the 7-beam Arecibo L-band Feed Array (ALFA), the Arecibo Legacy Fast ALFA (ALFALFA) extragalactic HI 21cm line survey aims to produce a census of HI-bearing objects found over 7000 square degrees of the high galactic latitude sky out to z < 0.06. Observations are 95% complete and a catalog is available for more than 50% of the final survey area. The ALFALFA population is among the least clustered known and includes many enigmatic extragalactic objects, "dark galaxy" candidates and possible very low mass "mini-halos". Most surprisingly, ALFALFA detects many more high HI mass objects than predicted by previous derivations of the HI mass and velocity functions, a result of particular importance since it directly impacts, in a positive sense, estimates of the expected HI detection rate at high z with the SKA and its pathfinders. With its completion, ALFALFA will provide the first robust census of gas-bearing halos over a cosmologically significant volume at the present epoch.

 

Mapping the HI Neighborhood Around Starburst Dwarf Galaxies

Megan Johnson, NRAO

Dwarf galaxies are believed to be the building blocks of larger galaxies. However, there are some studies that indicate the dwarf galaxies observed in the nearby universe may have formed later, after the most massive galaxies coalesced. Dwarf galaxy formation and
evolution is important for our understanding of cosmology. If dwarf galaxies mimic their more massive counterparts, then starburst dwarfs may be present day merger remnants and provide information on the building block hypothesis. The origins of starburst dwarf irregular
(dIm) galaxies are not well known. The role of interactions and mergers as mechanisms to create these systems has been hypothesized, but not well studied. We present deep HI maps around three starburst dwarf galaxies NGC 1569, NGC 4163 and NGC 4214.  The purpose of these maps is to determine if there are tenuous HI structures around these objects that would indicate a recent interaction or merger.  We detect HI filamentary structures that appear to be connected with NGC 1569 and indicate a recent interaction with nearby dwarf irregular UGCA 92. However, our map of NGC 4163 and NGC 4214 does not show any tenuous HI at our 1-sigma sensitivity limit of  ~ 2 x 10^17 for a 25 km/s line width.

Puddling and Quenching: How Does HI Content Depend on Galaxy Mass

Sheila Kannappan, University of North Carolina

Drawing on a volume-limited subsample of ALFALFA, as well as on new GBT 21cm data for the broadly representative Nearby Field Galaxy Survey, I will argue that down to baryonic masses ~10^9 Msun, galaxy HI-to-stellar mass ratios fall into three regimes: puddled (gas-dominated), normal (ranging from mildly quenched to modestly gas-rich), and permanently quenched (M_HI < 0.01M*). I will also suggest that much of the apparently continuous dependence of HI-to-stellar mass ratios on galaxy mass seen in flux-limited samples may actually reflect selection bias combined with the discretized mass dependence inherent in the rise and fall of the puddled, normal, and quenched populations.

 

Anomalous HI features in M101: Tidal Debris or Cold Accretion?

Katie M. Keating, U.S. Naval Research Laboratory

We present a wide (8.5 x 6.7 degree, 785 x 615 kpc), deep (1-sigma N_HI = 10^(16.8-17.5) cm^-2) HI map of the M101 galaxy group. Of particular interest in this data set are a few HI structures in M101 itself. We find a 120 kpc long loop of HI moving at -50 km/s with respect to the main body of the galaxy with an HI mass of 3 x 10^7 M_sun. We also find 2 extraplanar HI clouds with masses ~ 10^8 M_sun. These features may be signatures of cold accretion of fresh HI gas or tidal interaction with the nearby companion galaxies NGC 5477 and NGC 5474.

 

Gas Accretion, Starvation & Ram Pressure Stripping in the Virgo Cluster

Jeff Kenney, Yale University

Clusters and their outskirts encompass a wide range of environmental conditions. 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. There is a wealth of evidence that ram pressure stripping is responsible for producing the many cluster galaxies with truncated gas disks. However the origin of anemic galaxies, with extended but low surface brightness disks of gas and star formation, has been less clear. We propose that many of 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.HI scaling relations, and large-scale characterisation of the HI content of galaxies.

HI Scaling Relations, and Large-scale Characterisation of the HI Content of Galaxies

Virginia Kilborn, Swinburne University

We are investigating the relationship between the HI content of galaxies and the optical and infrared wavelengths. We use a sample of optically identified HIPASS galaxies to compare the HI mass of the galaxies to their various optical and infrared diameters and fluxes, to investigate the HI scaling relationships of galaxies in the southern sky. We are interested in selecting the most outlying galaxies from the relationship - ie the most gas-rich and gas-poor
galaxies in the sky, to study accretion and stripping mechanisms in spiral galaxies. This project will work towards the scientific preparation for the upcoming ASKAP HI All-Sky Survey, Wallaby. In particular, we will produce a catalogue of galaxies we expect to detect with Wallaby, using the 6dF catalog and the available optical and infrared data of the southern sky.

 

On the HI Bridge between M31 and M33

Felix J. Lockman, NRAO and Spencer Wolfe, West Virginia University

The Green Bank Telescope is being used to search for 21cm HI emission over a large area between the galaxies M31 and M33 in an attempt to study at 9.1' angular resolution the very extensive, very weak HI ``bridge'' between the two systems detected by Braun & Thilker (B&T) in 2004.

We report on two phases of this project. In the first, an area of about 50 square degrees was mapped to a 5-sigma detection limit of NHI=1.5x10^{18}. In a second phase we are mapping a smaller area, 12 square degrees, but an order of mangitude deeper, to a 5-sigma limit of <2x10^{17}.

At several locations we detect weak HI emission that has a velocity similar to that of M31 and M33. Some of the gas is clumped with column densities an order of magnitude greater than detected by B&T with their 49' resolution. These concentrations have about 10^5 solar masses on scales <2 kpc. In two directions we have detected HI lines at a few 10^{17} cm^{-2}. The measurements also cover two of M31's dwarf galaxies, And II and And XV, but in neither case is there evidence for associated HI at the 5-sigma level of 14 000 solar masses for And II, and 9300 solar masses for And XV.

The Carnegie Hubble Program (CHP)

Barry Madore, Carnegie Institute for Science

By moving the calibration and application of the Cepheid Period-Luminosity relation into the mid-infrared using space-based platform provided by SPITZER tied into the direct trigonometric parallaxes to a number of Milky Way Cepheids provided by HST we have
been able to eliminate many of the systematic errors enumerated by the HST Key Project when they completed their redetermination of the Hubble constant over a decade ago. We are now recalibrating the Tully-Fisher relation, and other so-called secondary distance
indicators using this mid-infrared base. An updated value of the Hubble constant based on these observations and its immediate consequences for interpreting WMAP data will be presented for the first time.

The Baryonic Tully-Fisher Relationship

Stacy McGaugh, University of Maryland

The luminosity-linewidth relation is a powerful tool for measuring the extragalactic distance scale. Yet the physics underpinning why it works so well remains unclear. I argue that the Tully-Fisher relation is a physical relation between a galaxy's baryonic mass and its rotation velocity. The intrinsic scatter of this relation is small, suggesting that it might be fundamental: a Natural Law in the same sense as Kepler's Laws.

As time permits, I will also discuss an application of Renzo's rule to infer the mass distribution of the stellar disk of the Milky Way from the terminal velcoity curve.

 

The TF relationship to z=1.7

Sarah Miller, Oxford University

I will present new measures of the rotation curves of disk galaxies to z~1.7, using deep exposures from both DEIMOS and LRIS spectrographs on the Keck telescopes, in combination with multi-band HST imaging. Contrary to previous studies, we show that the stellar mass Tully-Fisher relation is tightly in place at z~1 with similar scatter to that found locally. Furthermore, I will discuss evidence that there is little change in this relation beyond z~1 to z~1.7, and explore the implications for galaxy-scale baryonic and dark matter interaction in a universe with a strikingly similar stellar mass Tully-Fisher relation over two-thirds of its age.

 

AGES: The Arecibo Galaxy Environment Survey

Robert Minchin, NAIC

The Arecibo Galaxy Environment Survey (AGES) is the deepest wide-area HI survey to date, reaching a noise level of 0.7 mJy/beam at a velocity resolution of 10 km/s. It is covering 200 square degrees of sky across a number of fields selected to sample the whole gamut of galactic environments, from the Local Void, through isolated galaxies and galaxy pairs, to groups and clusters. In addition, AGES observes a large blind volume outside of the targeted environments. I will give an overview of the survey design, the progress of the survey and scientific accomplishments so far, in particular with regard to the HI mass function in low-density environments. Looking to the future, I will discuss how AGES science could feed into surveys with future instruments.

From Gas to Stars and from Stars to Gas: Dwarf Galaxy Evolution with VLA-ANGST

Juergen Ott, NRAO

The VLA-ANGST survey is a VLA project to map the HI content of a volume filled sampe of nearby galaxies at high spatial and spectral resolution. The sample is based on the HST "ACS Nearby Galaxy Survey Treasury" (ANGST) survey that aims to study the resolved, stellar population of a volume limited sample of nearby galaxies with the resolving power and sensitivity of the HST. Major data products include spatially resolved maps of star formation as a function of look-back time (typically up to 500 Myr). We find that the energy output of the underlying stellar population is large enough to create the typical morphologies of large scale rings, shells and cavities. The majority of the structures, however, is not created by single star forming events but rather by the combined feedback from many generations of stars. HI with narrow linewidths may indicate the presence of cold gas that potentially be fueling star formation. We find that the narrow components are close to the peaks of the HI column density but typically do not coincide. This, as well as the fraction of cold to warm gas, is similar to molecular clouds in more massive galaxies. We may thus be able to study the basic ingredient for star formation, the cold, dense gas, that is otherwise inaccessible in dwarfs, due to the low metallicities and hence extremely weak molecular line strengths.

The velocity width function of galaxies from the ALFALFA survey and
implications for dark matter

Manolis Papastergis, Cornell University

We use the largest HI-selected sample to date, extracted over 40% of the final area of the ALFALFA survey, to measure the abundance of galaxies as a function of their velocity width ("velocity width function"). The velocity width of a galaxy is (up to a projection on the line-of-sight) a good proxy for the total dynamical mass of a system; atomic hydrogen can trace the galactic rotation curve out to large galactocentric radii, where the dynamics are dominated by the dark matter halo. The resulting distribution can therefore be compared to predictions based on the cold dark matter (CDM) model.

We confirm previous results that indicate a substantial discrepancy between the observational distribution and the theoretical one expected in a CDM universe, at low widths. In particular, the difference between the observed and simulated velocity width functions is a factor of ~8 in abundance at the resolution limit of the simulations (w = 50 km/sec), increasing to a factor of ~100 when extrapolated to the ALFALFA limit of w = 20 km/sec. We identify possible solutions to this discrepancy, including a keV warm dark matter (WDM) scenario, as well as the fact that HI disks in low-mass galaxies are usually not extended enough to probe the full amplitude of the galactic rotation curve. In this latter case, we show that for low-mass systems galaxy velocities derived from HI linewidths must severely underestimate the maximum circular velocity of the host CDM halo. We furthermore statistically derive the galaxy HI velocity vs. halo maximum velocity relationship that must hold in a CDM universe; observational verification of the presented relationship would provide an important test of the validity of the established dark matter model.

Early Results for the HALOGAS Survey: HI Observations of NGC 5055

Maria Patterson, New Mexico State Univ.

We present an overview and early results from the WSRT Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) Survey. 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. The data are comprised of deep (120 hours) WSRT observations of a neutrally-selected sample of 20 edge-on and moderately-inclined nearby galaxies. These data are sensitive enough to detect faint (10^ 19 cm^-2) neutral hydrogen in the galaxy outskirts and to search for halo gas and possible accreting gas clouds. Detailed tilted-ring modeling of the galaxies is underway to carefully characterize the HI morphology and kinematics for each target. A preliminary analysis of the sample shows galaxies with a variety of HI characteristics ranging from accretion of (and interaction with) satellite galaxies to filaments possibly caused by star formation in the disk. We describe the data and modeling for NGC 5055, in particular. NGC 5055 is a moderately-inclined SAbc galaxy in the sample with a very extended gaseous disk and a large pronounced warp. The HALOGAS observations of this galaxy 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, which may indicate a significant accretion history for this galaxy.

A GBT survey of the diffuse HI in and around the THINGS galaxies

D.J. Pisano, West Virginia University

Abstract: One of the key questions in astronomy today is how galaxies accrete their gas from the intergalactic medium and then convert that gas into stars. The HI Nearby Galaxies Survey (THINGS), conducted with the VLA, has made great strides towards answering these questions, but it lacked sensitivity to the extended, diffuse HI in and around galaxies. I will present the early results from our GBT HI survey of 20 THINGS galaxies over a four square degree region around each galaxy. The survey is able to detect HI down to N(HI)=10^18 per square cm over 20 km/s linewidths. Using the GBT and VLA data, we will be i) studying star formation and low HI column density in the outskirts of galaxy disks, ii) probing HI at and beyond the nominal "edges" of galaxy disks, and iii) searching for low column density tidal features and infall from the "cosmic web".

The Interpretation of Global CO and HI Spectra in Spiral Galaxies (Poster)

David Rebolledo & Tony Wong, University of Illinois; Michele Thornley, Bucknell University

Differences in the shape and width of global CO and HI spectra of spiral galaxies are systematically investigated using a nearby sample for which high-resolution CO and HI maps are available. Asymmetries in the observed spectra tend to be dominated by flux rather than kinematic asymmetries, although strong outer warps can have a significant effect on HI spectra. Relative CO and HI line widths are well reproduced by axisymmetric models built from simple functional fits to the radial profile and rotation curve, although absolute line widths are sensitive to errors in the rotation curve fit. We find that CO line widths can be wider than HI widths in galaxies where the rotation curve declines in the outer parts, while they can be narrower in galaxies where the CO does not adequately sample the flat part of the rotation curve. Limited coverage of the CO emission by the telescope beam can mimic the latter effect. A physically based prescription linking the CO and HI radial profiles with the stellar disk is consistent with these findings, but any prescription which leads to CO being more centrally concentrated than HI would yield similar results. The final goal of this study is to understand the usefulness of the CO line width as an alternative to HI in the Tully-Fisher relation.

 

Visualization of Structures and Cosmic Flows in the Nearby Universe

Daniel Pomarede, CEA

A visualization of three-dimensional structures and cosmic flows is presented using informations from the Extragalactic Distance Database V8k catalog and the Cosmicflows-1 survey of galaxies peculiar velocities. Structures within a volume bounded at 8000 km/s on the Cardinal Supergalactic Axes are explored in terms of both the display of the positions of the 30124 galaxies of the catalog and its reconstructed density field, corrected to account for growing incompleteness with distance. With the intend to identify the most prominent structures, including voids, galaxy clusters, filaments and walls, a cosmography of the Local Universe is presented and discussed. This cosmography also benefits from the more precise distance measures provided in the context of the Cosmicflows-1 observational program. Using recent results obtained on the reconstruction of cosmic flows with the Wiener Filter approach, three-dimensional visualizations of the coherent flows of galaxies in the nearby universe are presented. The three major components of the Milky Way motion, namely the expulsion from the Local Void, the infall toward the Virgo Cluster, and the bulk flow of the Local Filament toward the Great Attractor are illustrated using different visualization techniques and analyzed in the light of the cosmography derived from the V8k distance catalog.

 

Constraints on galaxy formation from the Tully-Fisher relation and weak gravitational lensing of SDSS disk galaxies

Reina Reyes, KICP/Univ. of Chicago

I will present new scaling relations of disk galaxies based on a well-defined sample selected from the Sloan Digital Sky Survey (SDSS) at z~0.1. By combining (i) the relation between stellar mass and "optical" rotation velocity, which is measured at the luminous part of the disk (i.e., the Tully-Fisher relation) and (ii) the relation between stellar mass and dark matter halo mass, derived from weak lensing, we constrain the total (luminous and dark matter) mass profile of disk galaxies over two orders of magnitude (<10 kpc to 100 kpc). Results serve as constraints on disk galaxy formation models, and in particular, the extent of halo contraction due to baryon infall-- an open issue on both theoretical and observational fronts.

 

The GALFA-HI Compact Cloud Catalog: Isolated clouds in different environments

Destry Saul, Columbia University

The GALFA-HI Compact Cloud Catalog consists of nearly 2000 clouds smaller than 20' spanning the Arecibo sky and Galactic velocities. Using position, velocity, and linewidth boundaries, we have separated the catalog into five populations of clouds, two of which appear to be associated with the disc of the Galaxy, and three that are not. I will discuss the properties of each population, and the work being done to identify the origins of these clouds.

Calibration of the Mid-Infrared Tully-Fisher Relation

Jenny Sorce, University of Lyon

Spitzer Space Telescope IRAC ch.1 data present tremendous advantages for the Tully-Fisher relation (TFR) because of a homogeneous data set, reduced extinctions, and low sky values, resulting in small corrections and uncertainties.  The resulting TFR requires a color adjustment to drop the scatter from 0.49 to 0.42 magnitudes.

Probing External Influences On Galaxy H2/HI Ratios

David Stark, University of North Carolina

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.

AGES HI Detections in Virgo

Rhys Taylor, NAIC

I describe the final results of the Arecibo Galaxy Environment Survey in two regions of the Virgo Cluster, covering a total of 25 square degrees. This blind HI survey reaches a sensitivity of 2E7 Msolar at 17Mpc. 364 sources are detected, of which 114 are cluster members. I descibe our source extraction techniques and give a brief overview of the structure of the cluster. I describe the early-type galaxies detected in HI within the cluster as well as those detections without any obvious optical counterparts. I comment on the likelihood that these are features are tidal debris or so-called "dark galaxies". I compare the HI mass function from AGES and ALFALFA within the Virgo Cluster, and show that AGES detects significantly more low-mass objects.

Galaxy Distances, Then and Now

Brent Tully, University of Hawaii

The distance scale has always been a central problem in astronomy. Thirty-five years ago, the Hubble Constant controversy raged because of the challenge that was posed to the standard cosmological model of the time. Today, the most interesting questions concern departures from linear cosmic expansion.

A blind ultra-deep HI imaging survey of two volumes at z=0.2

M.A.W. Verheijen, ASTRON, Dwingeloo

Two galaxy clusters at z=0.2 and the large scale structure in which they are embedded, have been observed with the Westerbork radio telescope. Some 160 individual galaxies with M(HI)>2x10^9 Msun have been detected in HI emission, clearly outlining the large scale structure within the surveyed volumes, as well as the detailed substructure around the clusters. I will discuss the global HI properties of the galaxies in the various substructures, and for the first time present an HI-based luminosity-linewidth relation for a sample of normal spiral galaxies at z=0.2 to be compared with the Ursa Major sample at zero redshift.

Star Formation as a Function of Circular Velocity in Bulgeless Disk Galaxies

Linda C. Watson, CfA Cambridge

I will present results from our study of the atomic gas and star formation properties of twenty bulgeless disk galaxies (Sd-Sdm Hubble types) using HI emission line data from the VLA/EVLA, CO(1-0) data from the IRAM 30m, H-alpha data from the MDM Observatory, and PAH emission data derived from Spitzer IRAC observations. I will highlight three galaxies that have kinematically distinct outer HI disks. These components may be due to recent interactions, which is surprising given the bulgeless morphology of the galaxies in our sample. We study star formation above and below the circular velocity threshold of 120 km/s (stellar mass ~ 10^10 M_sun), where Dalcanton et al. found that the vertical dust structure and disk stability of edge-on bulgeless disk galaxies transitions from diffuse dust lanes with large scale heights and gravitationally stable disks at circular velocity less than 120 km/s to narrow dust lanes with small scale heights and gravitationally unstable disks at circular velocity greater than 120 km/s. I will discuss the trends we find between circular velocity, star formation efficiency, mid-plane pressure, and disk stability in light of recent star formation models.

HI Studies with the future FAST telescope

Ming Zhu, National Astronomical Observatory of China

The Five hundred meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project that is currently under construction, with the aim to build the largest single dish radio telescope in the world. It has an Arecibo-type dish located on an unique Karst depression. Unlike the Arecibo, FAST has an active main reflector which corrects spherical aberration on the ground to achieve full polarization and wide band without involving complex feed systems, and it is equipped with a light focus cabin driven by cables and servomechanism plus a parallel robot as the secondary adjustable system to carry the receivers. In this talk I will give a general introduction to the FAST technology and its major science goals, and discuss how to use FAST to study the HI properties of galaxies.