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Photodissociation regions (PDRs), where the (far-)ultraviolet light from hot young stars interact with the gas in surrounding molecular clouds, provide laboratories for understanding the nature and role of feedback by star formation on the interstellar medium. While the general nature of PDRs is well understood - at least under simplified conditions - the detailed dynamics and chemistry of these regions, including gas clumping, evolution over time etc. can be very complex. We present interferometric observations of the 21 cm atomic hydrogen line, combined with [CII] 158 $μ$m observations, towards the nearby reflection nebula IC 63. We find a clumpy HI structure in the PDR, and a ring morphology for the HI emission at the tip of IC 63. We further unveil kinematic substructure, of the order of 1~km~s$^{-1}$, in the PDR layers and several legs that will disperse IC 63 in $, 13 pages, 12 figures, accepted in AJ

The heavy element content ("metallicity") of the Universe is a record of the total star formation history. Gas-phase metallicity in galaxies, as well as its evolution with time, is of particular interest as a tracer of accretion and outflow processes. However, metallicities from the widely-used electron temperature (Te) method are typically ~2 times lower than the values based on the recombination line method. This "abundance discrepancy factor" (ADF) is well known and is commonly ascribed to bias due to temperature fluctuations. We present a measurement of oxygen abundance in the nearby (3.4 Mpc) system, Mrk 71, using a combination of optical and far-IR emission lines to measure and correct for temperature fluctuation effects. Our far-IR result is inconsistent (~2.5σ significance) with the metallicity from recombination lines and instead indicates little to no bias in the standard Te method, ruling out the long-standing hypothesis that the ADF is explained by temperature fluctuations for this object. Our results provide a framework to accurately measure metallicity across cosmic history, including with recent data reaching within the first billion years with JWST and the Atacama Large Millimeter Array (ALMA).

Many galaxy properties are known to correlate with the environment in which the galaxies are embedded. Their cold, neutral gas content, usually assessed through 21cm HI observations, is related to many other galaxy properties as it is the underlying fuel for star formation. With its high sensitivity and broad sky coverage the blind Arecibo Galaxy Environment Survey (AGES) survey brings significant improvement to the census of HI properties of galaxies in a wide range of environments, from voids to the core of a massive cluster. Here we present an HI census over a volume of ~44000 Mpc$^{3}$ towards the merging cluster Abell 1367 and the large-scale structure (LSS) surrounding the cluster out to cz = 20000 km/s. The survey is sensitive down to a column density of N$_{HI}$ = 1.5 x 10$^{17}$ cm$^{-2}$ for emission filling the beam and a line width of 10 km/s. As an approximate mass sensitivity limit, a member of A1367 (at a distance of 92 Mpc), containing M$_{HI}$ = 2.7x10$^{8}$ M$_{\odot}$ distributed over a top-hat profile of 50 km/s width would be detected at 4$\sigma$. The results are analysed in combination with optical spectroscopy data from SDSS which we use to estimate the local galaxy density based on the Voronoi-Delaunay method. In total we detect 457 HI sources, 213 of which are detected for the first time by the AGES survey, 134 of which are presented in this article for the first time. 225 of the detections are in the cluster and 232 in the remaining volume surveyed. Here we present the full catalogue of HI detections and their basic properties, including optical ones. We concentrate on the difference between the cluster and the foreground and background LSS, revealing a continuous correlation of HI detected fraction (and HI deficiency) with local galaxy density, independent of global environment., Comment: A&A accepted. 18 pages, 9 figures, 6 page appendix

Using data from the Arecibo Galaxy Environment Survey, we report the discovery of five HI clouds in the Leo I group without detected optical counterparts. Three of the clouds are found midway between M96 and M95, one is only 10$^{\prime}$ from the south-east side of the well-known Leo Ring, and the fifth is relatively isolated. HI masses range from 2.6$\times$10$^{6}$ - 9.0$\times$10$^{6}$M$_{\odot}$ and velocity widths (W50) from 16 - 42 km/s. Although a tidal origin is the most obvious explanation, this formation mechanism faces several challenges. For the most isolated cloud, the difficulties are its distance from neighbouring galaxies and the lack of any signs of disturbance in the HI discs of those systems. Some of the clouds also appear to follow the baryonic Tully-Fisher relation between mass and velocity width for normal, stable galaxies which is not expected if they are tidal in origin. Three clouds are found between M96 and M95 which have no optical counterparts, but have otherwise similar properties and location to the optically detected galaxy LeG 13. While overall we favour a tidal debris scenario to explain the clouds, we cannot rule out a primordial origin. If the clouds were produced in the same event that gave rise to the Leo Ring, they may provide important constraints on any model attempting to explain that structure, Comment: 16 pages (plus 4 page appendix), 1 table, 7 figures, accepted for publication in AJ

Probing the evolution of galaxies through the neutral hydrogen window has until recently been limited to studies of environmentally driven evolution in the local universe. Detailed imaging studies of galaxies in Virgo and volume limited surveys of clusters out to z = 0.08 show that ram pressure stripping is one of the mechanisms that drives galaxy evolution even at considerable distances from the dense cluster cores. Hydrodynamical simulations show that indeed the effects of the ICM are felt out to the virial radius due to the complex structure of the ICM. Westerbork and Arecibo have begun to observe galaxies at cosmologically interesting distances (z = 0.2). Soon the EVLA will be able to make a complete census of all H I emission in cones of 40'×40' probing an instantaneous velocity range from z = 0 to 0.53, with a resolution of a few arcsec. If prime focus feeds were to be installed at the EVLA those studies could easily be extended out to z = 1 in the coming decade, making the EVLA a prime pathfinder for H I studies with the SKA.

We extend our published work on the neutral hydrogen content of early-type galaxies in the Virgo cluster using the catalogue of detected sources from the ALFALFA survey, by showing the 21cm spectra of all the detected galaxies and discussing a deeper analysis of the ALFALFA datacubes, searching for lower S/N sources. A view of the multiphase interstellar medium of M86 is also presented, by comparing images of the cold, warm and hot phases., To appear in the Proceedings of the Conference "The Evolution of Galaxies through the Neutral Hydrogen Window", R. Minchin & E. Momjian eds

In this paper we describe results from the Arecibo Galaxy Environments Survey (AGES). The survey reaches column densities of ~3x10^18 cm^-2 and masses of ~10^7 M_O, over individual regions of order 10 sq deg in size, out to a maximum velocity of 18,000 km s^-1. Each surveyed region is centred on a nearby galaxy, group or cluster, in this instance the NGC7448 group. Galaxy interactions in the NGC7448 group reveal themselves through the identification of tidal tails and bridges. We find ~2.5 times more atomic gas in the inter-galactic medium than in the group galaxies. We identify five new dwarf galaxies, two of which appear to be members of the NGC7448 group. This is too few, by roughly an order of magnitude, dwarf galaxies to reconcile observation with theoretical predictions of galaxy formation models. If they had observed this region of sky previous wide area blind HI surveys, HIPASS and ALFALFA, would have detected only 5% and 43% respectively of the galaxies we detect, missing a large fraction of the atomic gas in this volume. We combine the data from this paper with that from our other AGES papers (370 galaxies) to derive a HI mass function with the following Schechter function parameters alpha=-1.52+/-0.05, M^*=5.1+/-0.3x10^9 h_72^-2 M_O, phi=8.6+/-1.1x10-3 h_72^3 Mpc^-3 dex-1. Integrating the mass function leads to a cosmic mass density of atomic hydrogen of Omega_HI=5.3+/-0.8x10^-4 h_72^-1. Our mass function is steeper than that found by both HIPASS and ALFALFA (alpha=1.37 and 1.33 respectively), while our cosmic mass density is consistent with ALFALFA, but 1.7 times larger than found by HIPASS.

This proceeding concentrates on the BAO signature of dark energy, and how the SKA dark energy case has been complicated by the emergence of HI structure experiments modeled after the Epoch of Reionization observatories. The purpose of the conference talk was to review the current status of the Murchison Widefield Array (MWA), and show the applications of HI structure observations for both reionization and dark energy measurements. Since the status of the MWA is changing weekly, please see the website www.haystack.mit.edu/ast/arrays/mwa/ for the current status. This proceedings will instead concentrate on HI structure observations, their applicability to reionization and cosmography, and the implications for the SKA and future HI structure observations of dark energy., Proceeding from The Evolution of Galaxies through the Neutral Hydrogen Window, Arecibo, 2008, AIP Conference Proceedings, Volume 1035

There are three distinct regimes in which radio observations of the redshifted 21 cm line of HI can contribute directly to cosmology in unique ways. The regimes are naturally divided by redshift, from high to low, into: inflationary physics, the Dark Ages and reionization, and galaxy evolution and Dark Energy. Each measurement presents its own set of technical, theoretical, and observational challenges, making “what we need to know” not so much an astrophysical question at this early stage as a comprehensive experimental question. A wave of new pathfinder projects are exploring the fundamental aspects of what we need to know (and what we should expect to learn in the coming years) in order to achieve the goals of the Square Kilometer Array (SKA) and beyond.

We present the results of Spitzer and Galex observations of gas/dust and star formation activities in the extreme outer disk of Virgo galaxy NGC 4254 and its surrounding regions. These observations were motivated in part by the potential existence of a “dark galaxy” in the vicinity. In the intergalactic VIRGOHI 21 region where the free-floating HI gas is found, neither UV nor mid-IR shows corresponding emission, thus providing stringent upper limits on the stellar mass and star formation rate in these clouds.On the other hand, we find clearly discernible excess ultraviolet emission in parts of the extended disk of NGC 4254, which is yet unseen in the optical and infrared. These UV emission appears different from the so-called “XUV disks” of other nearby galaxies in both their distribution pattern and physical origin, which we suggest is directly related to the gas concentration of VIRGOHI 21.

Above redshift 6, the dominant source of neutral hydrogen in the Universe shifts from localized clumps in and around galaxies and filaments to a pervasive, diffuse component of the intergalactic medium (IGM). This transition tracks the global neutral fraction of hydrogen in the IGM and can be studied, in principle, through the redshifted 21 cm hyperfine transition line. During the last half of the reionization epoch, the mean (global) brightness temperature of the redshifted 21 cm emission is proportional to the neutral fraction, but at earlier times (10

We show data from the Survey of Ionization in Neutral Gas Galaxies (SINGG) and Survey of Ultraviolet emission in Neutral Gas Galaxies (SUNGG) which survey the star formation properties of HI selected galaxies as traced by H-alpha and ultraviolet emission, respectively. The correlations found demonstrate a strong relationship between the neutral ISM, young massive stars, and the evolved stellar populations. For example the correlation between R band surface brightness and the HI cycling time is tighter than the Kennicutt-Schmidt Star Formation Law. Other scaling relations from SINGG give strong direct confirmation of the downsizing scenario: low mass galaxies are more gaseous and less evolved into stars than high mass galaxies. There are strong variations in the H-alpha to UV flux ratios within and between galaxies. The only plausible explanations for this result are that either the escape fraction of ionizing photons or the upper end of the IMF varies with galaxy mass. We argue for the latter interpretation, although either result has major implications for astrophysics. A detailed dissection of the massive star content in the extended HI disk of NGC2915 provides a consistent picture of continuing star formation with a truncated or steep IMF, while other GALEX results indicate that star formation edges seen in Halpha are not always apparent in the UV. These and other recent results settle some old questions but open many new questions about star formation and its relation to the ISM., To appear in AIP Conference Proceedings, "The Evolution of Galaxies through the Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, Puerto Rico, eds. R. Minchin & E. Momjian. 7 pages

The Arecibo Galaxy Environment Survey (AGES) is carrying out blind H I surveys of a number of different environments in the local Universe in order to determine what effect this has on the H I content and morphology. Whe complete, it will cover 200 square degrees in 13 regions, spanning the whole gamut of galaxy environments from the Local Void through to the Virgo Cluster. Results so far indicate that the faint‐end slope of the H I Mass Function (HIMF) is strongly influenced by the environment; far fewer small galaxier, relative to the number of large galaxies, are found in less dense environments. However, so far only a small number of fields have been analysed, not including the densest and least‐dense environments.

We only see a small fraction of the matter in the universe, but the rest gives itself away by the impact of its gravity. The distortions from pure Hubble flow (or peculiar velocities) that this matter creates have the potential to be a powerful cosmological tool, but are also a nuisance for extragalactic astronomers who wish to use redshifts to estimate distances to local galaxies. We provide a quick overview of work on the local peculiar velocity field, discussing both simple spherical infall models, non-parametric modeling using redshifts surveys, and full velocity and density field reconstruction from peculiar velocities. We discuss results from a multiattractor model fit to data from the SFI++ sample of peculiar velocities - the best peculiar velocity data currently available. We also talk about the future of samples for the study of the local velocity field, especially the 2MASS Tully-Fisher (2MTF) survey., Comment: To appear in AIP Conf. Proc., "The Evolution of Galaxies through the Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, eds. R. Minchin & E. Momjian. 6 pages, 1 figure

The HI content of the newly discovered satellites of the Milky Way has not been previously studied. We use HIPASS (HI Parkes All Sky Survey), LAB (Leiden/Argentine/Bonn), and GALFA (Galactic Arecibo L‐band Feed Array) survey data to explore HI in the environment of the newly discovered dwarf galaxies and add this information to what was previously known about HI in the dwarf spheroidal and lower mass dwarf irregular galaxies of the Local Group. All of the new satellites discovered in the Sloan Digital Sky Survey data have limits on their HI masses which range from 105 M⊙. The most favored explanation for the lack of HI in dwarf galaxies at small galactocentric distances is ram pressure stripping of the gas in the dwa...

The H I 21 cm transition provides a valuable and unique probe of the roles that gas plays in galaxy evolution and cosmology, and our understanding of these roles is far from complete. This talk discussed the synergy obtained by combining 21 cm observations with ultraviolet measurements of QSO absorption lines. In some respects, QSO absorption spectroscopy provides a much more sensitive tool for the study of intergalactic and interstellar gases—QSO absorption is six orders of magnitude more sensitive to NHI than 21 cm emission, and absorption spectroscopy reveals a rich array of metals including low‐, intermediate‐, and high‐ionization stages and even various molecules—but the UV absorption data only probes the pencil beam to the background QSO. This brief contribution provides an example of how the combination of UV absorption spectroscopy and 21 cm emission provides a more complete picture of the nature of the gas.

The baryonic Tully‐Fisher relation (BTF) and its implications for dark matter in spiral galaxies are reviewed in the context of next‐generation neutral hydrogen (HI) instruments and surveys. Spanning 5 decades in disk mass, the BTF is among the tightest known galaxy scaling relations. Recent work by McGaugh [1,2] suggests that the scatter in the BTF is minimal for a specific choice of disk mass‐to‐light ratio Υ*. Mass models of nearby spirals with these Υ* imply halo concentrations that are systematically lower than predicted by collisionless simulations of halo assembly. HI observations of statistically complete galaxy samples in cosmologically relevant volumes will be required to elucidate the origin of both the BTF and corresponding constraints on the dark matter distributions in disk galaxies.

Starting in the 1970s, the Arecibo 305m telescope has made seminal contributions in the field of extragalactic spectroscopy. With the Gregorian upgrade completed in the late 1990s, the telescope acquired a field of view. Population of that field of view with a seven-feed array at L-band (ALFA) increased by nearly one order of magnitude its survey speed. As a result, much of the extragalactic astronomy time of the telescope is now allocated to survey projects, which are briefly discussed. The next technical development stage for the 305m telescope is foreseen as that of a 40 beam system that would take advantage of phased array technology: AO40. This would further speed up the survey performance of the telescope. It is shown how the figure of merit for survey speed of AO40 would be comparable with that of SKA-precursor facilities, planned for operation in the next decade. A number of scientifically desirable new surveys that would become possible with AO40 are briefly discussed., Comment: To appear in AIP Conference Proceedings, "The Evolution of Galaxies through the Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, Puerto Rico, eds. R. Minchin & E. Momjian. 6 pages including 1 figure

A sample of HI data from the Arecibo Legacy Fast ALFA survey is described. Several unusual HI candidates have been detected in the vicinity of the Virgo Cluster, all at cz⊙

Massive low surface brightness galaxies have disk central surface brightnesses at least one magnitude fainter than the night sky, but total magnitudes and masses that show they are among the largest galaxies known. Like all low surface brightness (LSB) galaxies, massive LSB galaxies are often in the midst of star formation yet their stellar light has remained diffuse, raising the question of how star formation is proceeding within these galaxies. We have undertaken a multi-wavelength study to clarify the structural parameters and stellar and gas content of these enigmatic systems. The results of these studies, which include HI, CO, optical, near UV, and far UV images of the galaxies will provide the most in depth study done to date of how, when, and where star formation proceeds within this unique subset of the galaxy population., Comment: to be published in proceeding of IAU 244 - Dark Galaxies and Lost Baryons IAU Symposium

We present a pair of high‐resolution SPH (smoothed particle hydrodynamics) simulations that explore the nature of cool gas infall into galaxies, and the physical conditions necessary to support the type of gaseous halos that seem to be required by observations. Observations of local X‐ray absorbers, high‐velocity clouds, and distant quasar absorption line systems suggest that a significant fraction of baryons may reside in multi‐phase, low‐density, extended, ∼100 kpc, gaseous halos around normal galaxies. The two simulations are identical other than their initial gas density distributions: one is initialized with a standard hot gas halo that traces the cuspy profile of the dark matter, and the other is initialized with a cored hot halo with a high central entropy, as might be expected in models with early pre‐heating feedback. Galaxy formation proceeds in dramatically different fashions in these two cases. While the standard cuspy halo cools rapidly, primarily from the central region, the cored halo is qu...

We present the result from our color bimodality study of spirals in a single cluster environment using the VIVA (VLA Imaging Survey of Virgo in Atomic gas) sample. The goal is to investigate whether HI gas stripping in the cluster plays a role in moving galaxies from the blue cloud to the red sequence. We explore the dependence of the color‐magnitude relation on HI properties such as morphology and deficiency, and how the relation compares to the SDSS sample. We find that severely gas stripped galaxies with small HI disks are redder compared to gas rich galaxies with extended HI disks with a few exceptions. Among the most gas deficient systems, the ones showing signatures of recent stripping appear to be bluer than the galaxies that are likely to have been stripped a while ago. In particular, five out of seven galaxies with one‐sided extended HI tails, which are thought to be falling into the cluster for the first time, are found somewhere between the blue cloud and the red sequence in the region known as “green valley”. These imply that galaxies become redder due to quenching of star formation as they lose gas in high density regions (e.g. clusters). While not the only effect, it appears that HI stripping in the cluster environment is one of the contributors to color evolution.

We revisit the composition of neutral hydrogen, i.e. atomic (HI) and molecular (H2), in the local Universe, with focus on the H2-to-HI mass ratio R in various galaxies and the H2-mass function (MF). First, we derive the H2-MF from the CO-luminosity function (LF) of the FCRAO Extragalactic CO Survey, using a variable CO-to-H2 conversion fitted to nearby observations. This implies a universal H2 density Omega(H2)=(6.9±2.7)*10^-5/h and Omega(H2)/Omega(HI)=0.26±0.11, which could, however, suffer from incompleteness of the CO-sample. Therefore, a second approach derives the H2-MF from a HI-sample with well described completeness (HIPASS). This premisses an estimation of R, for which we introduce a set of phenomenological models based on a sample of 245 galaxies drawn from the literature. Our best model in terms of statistical scatter describes R as a function of galaxy type and cold gas mass. This model leads to an H2-MF that matches the one derived from the CO-LF, thus supporting that model and settling completeness uncertainties.

There have been many observational programs exploring the connection between the HI distribution and the presence of star formation in galaxies. Since the molecular phase of the ISM is most closely associated with star formation, the results of these investigations depend greatly on the type of galaxy being observed. For low mass, low metallicity galaxies, where the molecular gas in only found associated with the densest concentrations of HI, the correlation between HI maxima and star formation is very good. For high mass, high metallicity galaxies, star formation correlates strongly with densest concentrations of molecular gas, and the majority of the HI gas can be unrelated to star formation. Understanding the HI/star formation connection requires observations of the quality being produced by the THINGS program. The THINGS sample is especially promising due to the abundance and quality of the ancillary observational databases. As a forward look, I pose the question: How many galaxies do we need to obser...

How large disk galaxies have evolved in, and out of, the blue cloud of actively star-forming galaxies as a function of environment and time is an outstanding question. Some of the largest disks become systems like M31, M33 and the Milky Way today. In denser environments, it appears they transform onto the red sequence. Tracking disk systems since z, 6 pages, 3 figures; to appear in The Evolution of Galaxies through the Neutral Hydrogen Window, eds. R. Minchin and E. Momjian, AIPC, in press

We present the preliminary results of our high‐sensitivity, high‐resolution Very Large Array observations in the 21 cm line of fields centered on the Virgo cluster region spirals NGC 4307, NGC 4356, NGC 4411B, and NGC 4492. The selected targets are part of a subset of spiral galaxies identified in a previous statistical study of the three‐dimensional distribution of the atomic hydrogen in this region of the sky, as objects with a substantial dearth of HI that apparently reside on the cluster outskirts. Our VLA measurements have been used to emphasize the substantial uncertainties affecting the Tully‐Fisher radial distance estimates to these objects.

In this paper, we review the Billion Galaxy Survey that will be carried out at radio--optical wavelengths to micro--nanoJansky levels with the telescopes of the next decades. These are the Low-Frequency Array, the Square Kilometer Array and the Large Synoptic Survey Telescope as survey telescopes, and the Thirty Meter class Telescopes for high spectral resolution+AO, and the James Webb Space Telescope (JWST) for high spatial resolution near--mid IR follow-up. With these facilities, we will be addressing fundamental questions like how galaxies assemble with super-massive black-holes inside from the epoch of First Light until the present, how these objects started and finished the reionization of the universe, and how the processes of star-formation, stellar evolution, and metal enrichment of the IGM proceeded over cosmic time. We also summarize the high-resolution science that has been done thus far on high redshift galaxies with the Hubble Space Telescope (HST). Faint galaxies have steadily decreasing sizes at fainter fluxes and higher redshifts, reflecting the hierarchical formation of galaxies over cosmic time. HST has imaged this process in great structural detail to z, Comment: 8 pages, LaTeX2e requires 'aip' style (included), 8 postscript figures. To appear in the proceedings of the `The Evolution of Galaxies through the Neutral Hydrogen Window' conference, Arecibo Observatory Feb 1-3, 2008; Eds. R. Minchin & E. Momjian, AIP Conf Proc

We present the detection of enormous disks/rings of neutral hydrogen (HI) gas around several nearby radio‐loud early‐type galaxies. Goal of our study was to use HI observations to look for evidence of galaxy mergers or interactions (tails, bridges, disks, etc.) that could be related to the triggering of the radio source in a complete sample of nearby radio galaxies. One case, B2 0648+27, was studied in great detail to be a product of a major merger—it is a direct link between (Ultra‐) Luminous Infra‐Red Galaxies and Radio Galaxies, for which we trace the different stages of merger, starburst and AGN activity. We detect other large‐scale HI disks and rings only around the host galaxies of several low‐power compact radio sources as well as the powerful FR‐II radio galaxy NGC 612; the hosts of extended FR‐I radio sources seem to be devoid of large‐scale HI. This suggest a fundamental difference in the host galaxy properties—and perhaps also the triggering mechanism—of different types of radio sources.

We present results from a targeted survey undertaken with the 305m Arecibo radiotelescope to detect HI‐line emission from disk galaxies at redshift z>0.16. The targets for the observations, selected from the Sloan Digital Sky Survey database, are non‐interacting disk galaxies in relatively isolated fields. HI profiles of adequate quality for flux and velocity width measurement were obtained for ∼30 galaxies in the redshift range 0.17–0.26 (i.e. 2–3 Gyr lookback time). The HI masses of these objects are 3−8×1010 M⊙. Our results prove, for the first time, the feasibility of single‐dish HI observations above redshift z = 0.2. In particular, this sample includes the highest redshift detections of HI emission from individual galaxies to date.

Substantial star formation often occurs in the tidal debris of interacting galaxy pairs and groups. However, the packaging of the star formation is varied. Sometimes stars form in clusters reminiscent of the predecessors of globular clusters, and other times they form primarily in a tidal clump that is the size and mass of a dwarf galaxy. I report on a few recent projects that I have done with collaborators. We have been trying to identify the factors that determine whether star clusters or tidal dwarfs form in the debris of interacting pair. We have also undertaken a multiwavelength program to study Hickson compact groups. We suggest that Hickson compact groups can be on one of two evolutionary sequences depending on whether gas is converted within the galaxies or outside of the galaxies.

Roughly half of all stars are formed in galaxies with stellar masses greater than logM*>10. This same population contains “red and dead” galaxies where star formation has effectively shut down, in some cases for many gigayears. We briefly review recent observational constraints on the distribution of specific star formation and stellar mass of this population and discuss how measurements of cold gas properties might provide insight into its evolution. We highlight several new results and describe GASS—the GALEX Arecibo SDSS survey—an on‐going large survey designed to obtain deep measurements of the HI properties of massive galaxies, providing a crucial link between past, present and possible future evolution of galaxies straddling the “transition mass” in galaxy properties.

The Arecibo L‐Band Feed Array (ALFA) Zone of Avoidance (ZOA) team is mapping the distribution of low‐Galactic‐latitude galaxies and large‐scale structures through detection of galaxies'21‐cm emission with ALFA. This ZOA survey finds new HI galaxies which lie hidden behind the Milky Way, and also provides redshifts for partially‐obscured galaxies known at other wavelengths. Two precursor regions which straddle the Galactic plane have been observed to date, totalling 140 square degrees, with 72 HI galaxies detected. Detections through the inner Galaxy generally have no cataloged counterparts in any other waveband, due to the heavy extinction and stellar confusion. Detections through the outer Galaxy are more likely to have 2MASS counterparts, and we provide redshifts for these galaxies. A third region, through the Taurus molecular cloud, has also been observed. The full ALFA ZOA survey will reveal more previously unknown galaxies and map low‐latitude large‐scale structures.

In recent years, HST revolutionized the field of star formation in nearby galaxies. Due to its high angular resolution it has now become possible to construct star formation histories of individual stellar populations on scales of a few arcseconds spanning a range of up to ~600 Myr. This method will be applied to the ANGST galaxies, a large HST volume limited survey to map galaxies up to distances of 3.5-4.0 Mpc (excluding the Local Group). The ANGST sample is currently followed--up by high, ~6'' resolution VLA observations of neutral, atomic hydrogen (HI) in the context of VLA-ANGST, an approved Large VLA Project. The VLA resolution is well matched to that of the spatially resolved star formation history maps. The combination of ANGST and VLA-ANGST data will provide a new, promising approach to study essential fields of galaxy evolution such as the triggering of star formation, the feedback of massive stars into the interstellar medium, and the structure and dynamics of the interstellar medium., to appear in the proceedings to the conference: "The Evolution of Galaxies through the Neutral Hydrogen Window", Arecibo, PR, USA

We present an overview for the reionization search at GMRT. The forecast sensitivities are promising for an early detection. RFI mitigation has been successful. Several hundred hours of telescope time have already been invested in this ongoing effort, and analysis of the data is in progress., Comment: 7 pages, invited talk at Arecibo conference "The Evolution of Galaxies through the Neutral Hydrogen Window"

While we know a great about the evolution of the stellar content of galaxies, our understanding of the evolution of the gaseous content is relatively shallow. Despite a handful of notable recent observations we know little about the H I content of galaxies at intermediate or high redshift. We are just beginning to realize how little we know about the gas content of galactic halos, and the role of H I in the star formation process remains controversial. This contribution describes what it is that we need to know in order to have a better understanding of the role of H I in the formation and evolution of galaxies.

The history and timescale of the conversion of gas into stars within galaxies define their evolution through cosmic time. HI‐selected surveys of galaxies in the local universe, in combination with optical and infrared observations provide important pieces of information on the gaseous, stellar, and star‐forming properties of galaxies. I present here an overview of some of the past, current and future work on stars and star‐formation in HI‐selected systems.

As a sub‐set of activities within the THINGS (The HI Nearby Galaxy Survey) collaboration we have used the HI maps of the complete set of galaxies observed in the THINGS survey with the VLA to search for the presence of high velocity clouds. Detections were made in 9% of the cases, with a lower detection limit of just under 105 solar masses. Given the column density limit of the survey, and assuming that these clouds would have underlying structures comparable to those HVC's around the Milky Way which are known not to be galactic fountain objects (e.g. Complex C) we estimate that our detections would account for about 10% of the total HI masses that could be associated with the newly detected cloudlets. We draw some tentative conclusions about the rate of infall of HI onto the disks of the galaxies observed.

The next generation of radio arrays are being designed under the umbrella of the “Square Kilometer Array” (SKA) project. The leading concept for a “mid‐frequency” (0.3–10 GHz) array is a large wide‐field Radio Synoptic SKA (RSSKA), which is being developed for presentation to the upcoming Astronomy and Astrophysics Decadal Survey. The RSSKA is targeted at obtaining HI observations of a billion galaxies to redshift z>1.5 over 10000 square degrees, and synoptic mapping of the radio sky for transient detection and monitoring. In this talk I discuss the motivation for and the design challenges facing the RSSKA. Also suggested is a path forward from our current generation of facilities, such as the VLA and Arecibo, towards construction and operation of the RSSKA.

Extragalactic HI astronomy is half a century old. Its maturity dramatically increased in the 1970s, with the commissioning of new powerful facilities. Its contributions to Cosmology are important, from the observation of galaxy rotation curves that showed the presence of dark matter in galaxies, to the measurement of cosmological parameters and the mapping of the large scale structure of the Universe. The Arecibo telecope has played a key role in these developments. It is also currently engaged in a number of experiments that utilize its L-band feed array to map thousands of square degrees of the sky and obtain the most sensitive large-scale view of the low z HI Universe., Comment: To appear in AIP Conference Proceedings, "The Evolution of Galaxies through the Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, Puerto Rico, eds. R. Minchin & E. Momjian. 7 pages including 2 figures

We present the results of our 21cm GBT‐VLA study discovering a significant diffuse neutral intra‐group medium (IGM) (on an average 39% of the total HI mass) in a sample of 22 Hickson Compact Groups (HCGs). HCGs are dense concentrations of galaxies where strong tidal interactions constantly change gas distribution and morphology of the member galaxies. HCGs have been found to be deficient in HI, although our new GBT detections have reduced the previously estimated deficiency values considerably. The GBT detected broad HI wings rather than discrete features, suggesting the presence of a fainter HI component over a large velocity range. Here we present the comparison between the HI detected by the GBT (single dish) and the VLA (interferometer), which resulted in our discovery. Comparing the instrumental properties of the two instruments, we conclude that the excess HI is in the form of a diffuse neutral intra‐group medium, that is most likely being fed by the inter‐stellar medium of the individual galaxies. We also found correlations between the percentage of excess gas in these systems to their HI deficiency, Hubble type of the central or dominant galaxy and their evolutionary stage, all of which advocates the gradual dispersion of the tidally stripped neutral gas into the IGM with group evolution.

Numerous studies suggest that stronger Lyα absorbers are more closely associated with galaxies, while weaker absorbers arise in the intragroup medium surrounding concentrations of galaxies near the absorber redshift. What can absorbers tell us about the properties of the intragroup medium in varying galactic environments? I start by looking at the galactic environments of absorbers within the most recent HI surveys. Limited absorber data are available within current ALFALFA and AGES fields.

The new L‐band system of the EVLA and the array's enhanced capabilities will make it possible to carry out observations below 1200 MHz and down to 940 MHz; a frequency range where the VLA has severe limitations and/or simply cannot observe. To test whether astronomical science can be delivered at such frequencies, we carried out observations on two HI absorbers using the B‐configuration at 1139 and 1082 MHz. Although below 1150 MHz the band is dominated by RFI from aeronautical navigation, we were able to obtain results consistent with the expected performance of the array with its current capabilities. Once completed, the EVLA will provide much improved sensitivity at the lowest L‐band frequencies, making the array a major instrument in studies of redshifted HI and other spectral lines down to 940 MHz.