Search

In this paper, we present data from the Blind Ultra-Deep HI Environmental Survey (BUDHIES), which is a blind 21-cm HI spectral line imaging survey undertaken with the Westerbork Synthesis Radio Telescope (WSRT). Two volumes were surveyed, each with a single pointing and covering a redshift range of 0.164 < z < 0.224. Within these two volumes, this survey targeted the clusters Abell 963 and Abell 2192, which are dynamically different and offer unique environments to study the process of galaxy evolution within clusters. With an integration time of 117x12h on Abell 963 and 72x12h on Abell 2192, a total of 166 galaxies were detected and imaged in HI. While the clusters themselves occupy only 4 per cent of the 73,400 Mpc$^3$ surveyed by BUDHIES, most of the volume consists of large-scale structures in which the clusters are embedded, including foreground and background overdensities and voids. We present the data processing and source detection techniques and counterpart identification based on a wide-field optical imaging survey using the Isaac Newton Telescope (INT) and deep ultra-violet GALEX imaging. Finally, we present HI and optical catalogues of the detected sources as well as atlases of their global HI properties, which include integrated column density maps, position-velocity diagrams, global HI profiles, and optical and UV images of the HI sources.

We study complete sample of spiral galaxies brighter than M$_{\mathrm{B}} \sim$-18.4 in three Abell clusters: A85 ($z=\,$0.055), A496 ($z=\,$0.033) and A2670 ($z=\,$0.076). This work is based on a large volume limited, blind Hi-survey (21cm, NRAO-VLA), on optical imaging (CFHT) and on the search for dynamical substructures. Our goal is to explore the effects of local environment on the HI gas properties and this, in turn, on the star formation activity and quenching of individual galaxies. We report significant differences among the HI properties of these clusters and we discuss the role played by the large scale structure and by the dynamical evolution of each cluster accounting for the observational evidence.

We present JVLA-C observations of the HI gas in JO204, one of the most striking jellyfish galaxies from the GASP survey. JO204 is a massive galaxy in the low-mass cluster Abell 957 at z=0.04243. The HI map reveals an extended 90 kpc long ram-pressure stripped tail of neutral gas, stretching beyond the 30 kpc long ionized gas tail and pointing away from the cluster center. The HI mass seen in emission is (1.32 $ \pm 0.13) \times 10^{9} \rm M_{\odot}$, mostly located in the tail. The northern part of the galaxy disk has retained some HI gas, while the southern part has already been completely stripped and displaced into an extended unilateral tail. Comparing the distribution and kinematics of the neutral and ionized gas in the tail indicates a highly turbulent medium. Moreover, we observe associated HI absorption against the 11 mJy central radio continuum source with an estimated HI absorption column density of 3.2 $\times 10^{20}$ cm$^{-2}$. The absorption profile is significantly asymmetric with a wing towards higher velocities. We modelled the HI absorption by assuming that the HI and ionized gas disks have the same kinematics in front of the central continuum source, and deduced a wider absorption profile than observed. The observed asymmetric absorption profile can therefore be explained by a clumpy, rotating HI gas disk seen partially in front of the central continuum source, or by ram-pressure pushing the neutral gas towards the center of the continuum source, triggering the AGN activity., Comment: 16 pages, 10 figures, accepted for publication in MNRAS

We present 12CO (2-1) data of three Virgo spirals - NGC 4330, NGC 4402 and NGC 4522 obtained using the Submillimeter Array. These three galaxies show clear evidence of ram pressure stripping due to the cluster medium as found in previous HI imaging studies. Using high-resolution CO data, we investigate how the properties of the inner molecular gas disc change while a galaxy is undergoing HI stripping in the cluster. At given sensitivity limits, we do not find any clear signs of molecular gas stripping. However, both its morphology and kinematics appear to be quite disturbed as those of HI. Morphological peculiarities present in the molecular and atomic gas are closely related with each other, suggesting that molecular gas can be also affected by strong ICM pressure even if it is not stripped. CO is found to be modestly enhanced along the upstream sides in these galaxies, which may change the local star formation activity in the disc. Indeed, the distribution of H$\alpha$ emission, a tracer of recent star formation, well coincides with that of the molecular gas, revealing enhancements near the local CO peak or along the CO compression. FUV and H$\alpha$ share some properties in common, but FUV is always more extended than CO/H$\alpha$ in the three galaxies, implying that the star-forming disc is rapidly shrinking as the molecular gas properties have changed. We discuss how ICM pressure affects dense molecular gas and hence star formation properties while diffuse atomic gas is being removed from a galaxy., Comment: 18 pages, 10 figures, 4 tables, accepted for publication in MNRAS; high resolution figures available at http://mnras.oxfordjournals.org/content/early/2016/12/07/mnras.stw3162.full.pdf+html

In a hierarchical Universe clusters grow via the accretion of galaxies from the field, groups and even other clusters. As this happens, galaxies can lose their gas reservoirs via different mechanisms, eventually quenching their star-formation. We explore the diverse environmental histories of galaxies through a multi-wavelength study of the combined effect of ram-pressure stripping and group "processing" in Abell 963, a massive growing cluster at $z=0.2$ from the Blind Ultra Deep HI Environmental Survey (BUDHIES). We incorporate hundreds of new optical redshifts (giving a total of 566 cluster members), as well as Subaru and XMM-Newton data from LoCuSS, to identify substructures and evaluate galaxy morphology, star-formation activity, and HI content (via HI deficiencies and stacking) out to $3\times R_{200}$. We find that Abell 963 is being fed by at least 7 groups, that contribute to the large number of passive galaxies outside the cluster core. More massive groups have a higher fraction of passive and HI-poor galaxies, while low-mass groups host younger (often interacting) galaxies. For cluster galaxies not associated with groups we corroborate our previous finding that HI gas (if any) is significantly stripped via ram-pressure during their first passage through the intra-cluster medium, and find mild evidence for a starburst associated with this event. In addition, we find an overabundance of morphologically peculiar and/or star-forming galaxies near the cluster core. We speculate that these arise as groups pass through the cluster (post-processing). Our study highlights the importance of environmental quenching and the complexity added by evolving environments., Comment: 21 pages and 21 figures (including appendix). Accepted for publication in MNRAS. v2: minor changes to match published version

We present the results of our investigations into options for the computing platform for the imaging pipeline in the CHILES project, an ultra-deep HI pathfinder for the era of the Square Kilometre Array. CHILES pushes the current computing infrastructure to its limits and understanding how to deliver the images from this project is clarifying the Science Data Processing requirements for the SKA. We have tested three platforms: a moderately sized cluster, a massive High Performance Computing (HPC) system, and the Amazon Web Services (AWS) cloud computing platform. We have used well-established tools for data reduction and performance measurement to investigate the behaviour of these platforms for the complicated access patterns of real-life Radio Astronomy data reduction. All of these platforms have strengths and weaknesses and the system tools allow us to identify and evaluate them in a quantitative manner. With the insights from these tests we are able to complete the imaging pipeline processing on both the HPC platform and also on the cloud computing platform, which paves the way for meeting big data challenges in the era of SKA in the field of Radio Astronomy. We discuss the implications that all similar projects will have to consider, in both performance and costs, to make recommendations for the planning of Radio Astronomy imaging workflows., Comment: Accepted Astronomy and Computing

An understanding of the mass build-up in galaxies over time necessitates tracing the evolution of cold gas (molecular and atomic) in galaxies. To that end, we have conducted a pilot study called CO Observations with the LMT of the Blind Ultra-Deep H I Environment Survey (COOL BUDHIES). We have observed 23 galaxies in and around the two clusters Abell 2192 (z = 0.188) and Abell 963 (z = 0.206), where 12 are cluster members and 11 are slightly in the foreground or background, using about 28 total hours on the Redshift Search Receiver (RSR) on the Large Millimeter Telescope (LMT) to measure the $^{12}$CO J = 1 --> 0 emission line and obtain molecular gas masses. These new observations provide a unique opportunity to probe both the molecular and atomic components of galaxies as a function of environment beyond the local Universe. For our sample of 23 galaxies, nine have reliable detections (S/N$\geq$3.6) of the $^{12}$CO line, and another six have marginal detections (2.0 < S/N < 3.6). For the remaining eight targets we can place upper limits on molecular gas masses roughly between $10^9$ and $10^{10} M_\odot$. Comparing our results to other studies of molecular gas, we find that our sample is significantly more abundant in molecular gas overall, when compared to the stellar and the atomic gas component, and our median molecular gas fraction lies about $1\sigma$ above the upper limits of proposed redshift evolution in earlier studies. We discuss possible reasons for this discrepancy, with the most likely conclusion being target selection and Eddington bias., Comment: MNRAS, submitted

Voids represent a unique environment for the study of galaxy evolution, as the lower density environment is expected to result in shorter merger histories and slower evolution of galaxies. This provides an ideal opportunity to test theories of galaxy formation and evolution. Imaging of the neutral hydrogen, central in both driving and regulating star formation, directly traces the gas reservoir and can reveal interactions and signs of cold gas accretion. For a new Void Galaxy Survey (VGS), we have carefully selected a sample of 59 galaxies that reside in the deepest underdensities of geometrically identified voids within the SDSS at distances of ~100 Mpc, and pursued deep UV, optical, Halpha, IR, and HI imaging to study in detail the morphology and kinematics of both the stellar and gaseous components. This sample allows us to not only examine the global statistical properties of void galaxies, but also to explore the details of the dynamical properties. We present an overview of the VGS, and highlight key results on the HI content and individually interesting systems. In general, we find that the void galaxies are gas rich, low luminosity, blue disk galaxies, with optical and HI properties that are not unusual for their luminosity and morphology. We see evidence of both ongoing assembly, through the gas dynamics between interacting systems, and significant gas accretion, seen in extended gas disks and kinematic misalignments. The VGS establishes a local reference sample to be used in future HI surveys (CHILES, DINGO, LADUMA) that will directly observe the HI evolution of void galaxies over cosmic time., Comment: 7 pages, 5 figures. Proceedings of IAU Symposium 308 "The Zeldovich Universe: Genesis and Growth of the Cosmic Web", 23-28 June 2014, Tallinn, Estonia

We present optical imaging and spectroscopy and HI imaging of the Virgo Cluster galaxy IC 3418, which is likely a "smoking gun" example of the transformation of a dwarf irregular into a dwarf elliptical galaxy by ram pressure stripping. IC 3418 has a spectacular 17 kpc length UV-bright tail comprised of knots, head-tail, and linear stellar features. The only H-alpha emission arises from a few HII regions in the tail, the brightest of which are at the heads of head-tail UV sources whose tails point toward the galaxy ("fireballs"). Several of the elongated tail sources have H-alpha peaks outwardly offset by 80-150 pc from the UV peaks, suggesting that gas clumps continue to accelerate through ram pressure, leaving behind streams of newly formed stars which have decoupled from the gas. Absorption line strengths, measured from Keck DEIMOS spectra, together with UV colors, show star formation stopped 300+/-100 Myr ago in the main body, and a strong starburst occurred prior to quenching. While neither H-alpha nor HI emission are detected in the main body of the galaxy, we have detected 4x10^7 M_sun of HI from the tail with the VLA. The gas consumption timescale in the tail is relatively long, implying that most of the stripped gas does not form stars but joins the ICM. The velocities of tail HII regions, measured from Keck LRIS spectra, extend only a small fraction of the way to the cluster velocity, suggesting that star formation does not happen in more distant parts of the tail. Stars in the outer tail have velocities exceeding the escape speed, but some in the inner tail should fall back into the galaxy, forming halo streams. One likely fallback stream is identified., Comment: 19 pages, 16 figures, accepted for publication in the Astrophysical Journal

We present the optical spectroscopy for the Blind Ultra Deep HI Environmental Survey (BUDHIES). With the Westerbork Synthesis Radio Telescope, BUDHIES has detected HI in over 150 galaxies in and around two Abell clusters at z~0.2. With the aim of characterizing the environments of the HI-detected galaxies, we obtained multi-fiber spectroscopy with the William Herschel Telescope. In this paper, we describe the spectroscopic observations, report redshifts and EW[OII] measurements for ~600 galaxies, and perform an environmental analysis. In particular, we present cluster velocity dispersion measurements for 5 clusters and groups in the BUDHIES volume, as well as a detailed substructure analysis., Comment: v2: Typos and small corrections after proofs added. 14 pages (plus small appendix), 12 figures. Accepted for publication in MNRAS. Adobe Acrobat Reader is required to correctly display the (3D) animated figures (Fig. 9). Full data tables and supporting videos are also available at the BUDHIES project website: http://www.astro.rug.nl/budhies/

We present first results from the Blind Ultra Deep HI Environmental Survey (BUDHIES) of the Westerbork Synthesis Radio Telescope (WSRT). Our survey is the first direct imaging study of neutral atomic hydrogen gas in galaxies at a redshift where evolutionary processes begin to show. In this letter we investigate star formation, HI-content, and galaxy morphology, as a function of environment in Abell 2192 (at z=0.1876). Using a 3-dimensional visualization technique, we find that Abell 2192 is a cluster in the process of forming, with significant substructure in it. We distinguish 4 structures that are separated in redshift and/or space. The richest structure is the baby cluster itself, with a core of elliptical galaxies that coincides with (weak) X-ray emission, almost no HI-detections, and suppressed star formation. Surrounding the cluster, we find a compact group where galaxies pre-process before falling into the cluster, and a scattered population of "field-like" galaxies showing more star formation and HI-detections. This cluster proves to be an excellent laboratory to understand the fate of the HI gas in the framework of galaxy evolution. We clearly see that the HI gas and the star formation correlate with morphology and environment at z=0.2. In particular, the fraction of HI-detections is significantly affected by the environment. The effect starts to kick in in low mass groups that pre-process the galaxies before they enter the cluster. Our results suggest that by the time the group galaxies fall into the cluster, they are already devoid of HI., Comment: 6 pages, 4 figures. Accepted for publication in ApJL. An animated version of Figure 2 is available at: http://www.nottingham.ac.uk/~ppxyj/Jaffe_ApJL_2012_Fig2_movie.mpeg. (v2. minor corrections/typos added)

In this contribution, we present some preliminary observational results from the completed ultra-deep survey of 21cm emission from neutral hydrogen at redshifts z=0.164-0.224 with the Westerbork Synthesis Radio Telescope. In two separate fields, a total of 160 individual galaxies has been detected in neutral hydrogen, with HI masses varying from 1.1x10^9 to 4.0x10^10 Msun. The largest galaxies are spatially resolved by the synthesized beam of 23x37 arcsec^2 while the velocity resolution of 19 km/s allowed the HI emission lines to be well resolved. The large scale structure in the surveyed volume is traced well in HI, apart from the highest density regions like the cores of galaxy clusters. All significant HI detections have obvious or plausible optical counterparts which are usually blue late-type galaxies that are UV-bright. One of the observed fields contains a massive Butcher-Oemler cluster but none of the associated blue galaxies has been detected in HI. The data suggest that the lower-luminosity galaxies at z=0.2 are more gas-rich than galaxies of similar luminosities at z=0, pending a careful analysis of the completeness near the detection limit. Optical counterparts of the HI detected galaxies are mostly located in the 'blue cloud' of the galaxy population although several galaxies on the 'red sequence' are also detected in HI. These results hold great promise for future deep 21cm surveys of neutral hydrogen with MeerKAT, APERTIF, ASKAP, and ultimately the Square Kilometre Array., Comment: 10 pages, 9 figures, Proceedings of ISKAF2010 Science Meeting: A New Golden Age for Radio Astronomy, June 10-14 2010, Assen, the Netherlands. Edited by J. van Leeuwen. Movies of rendered rotating data cubes are available at http://www.astro.rug.nl/~verheyen/BUDHIES/index.html

We review and discuss aspects of Cosmic Voids that form the background for our Void Galaxy Survey (see accompanying paper by Stanonik et al.). Following a sketch of the general characteristics of void formation and evolution, we describe the influence of the environment on their development and structure and the characteristic hierarchical buildup of the cosmic void population. In order to be able to study the resulting tenuous void substructure and the galaxies populating the interior of voids, we subsequently set out to describe our parameter free tessellation-based watershed void finding technique. It allows us to trace the outline, shape and size of voids in galaxy redshift surveys. The application of this technique enables us to find galaxies in the deepest troughs of the cosmic galaxy distribution, and has formed the basis of our void galaxy program., Comment: 10 pages, 4 figures, proceedings "Galaxies in Isolation" (May 2009, Granada, Spain), eds. L. Verdes-Montenegro, ASP (this is a colour, extended and combined version; accompanying paper to Stanonik et al., arXiv:0909.2869, in same volume)

We present results of a study of large-scale neutral hydrogen (HI) gas in nearby radio galaxies. We find that the early-type host galaxies of different types of radio sources (compact, FR-I and FR-II) appear to contain fundamentally different large-scale HI properties: enormous regular rotating disks and rings are present around the host galaxies of a significant fraction of low power compact radio sources, while no large-scale HI is detected in low power, edge-darkened FR-I radio galaxies. Preliminary results of a study of nearby powerful, edge-brightened FR-II radio galaxies show that these systems generally contain significant amounts of large-scale HI, often distributed in tail- or bridge-like structures, indicative of a recent galaxy merger or collision. Our results suggest that different types of radio galaxies may have a different formation history, which could be related to a difference in the triggering mechanism of the radio source. If confirmed by larger studies with the next generation radio telescopes, this would be in agreement with previous optical studies that suggest that powerful FR-II radio sources are likely triggered by galaxy mergers and collisions, while the lower power FR-I sources are fed in other ways (e.g. through the accretion of hot IGM). The giant HI disks/rings associated with some compact sources could - at least in some cases - be the relics of much more advanced mergers., Comment: 5 pages, 3 figures - to appear in PoS, "The Modern Radio Universe: From Planets to Dark Energy Conference", Manchester UK, eds: Beswick, Diamond & Schilizzi

A pilot study with the powerful new backend of the Westerbork Synthesis Radio Telescope (WSRT) of two galaxy clusters at z=0.2 has revealed neutral hydrogen emission from 39 galaxies. The volume probed for each cluster is 1.7x10^4 Mpc^3, with spatial and velocity resolutions of 54x86 kpc^2 and 19.7 km/s, covering both clusters and the large scale structure in which they are embedded. The spatial distribution of the HI detected galaxies is very different for the two clusters. In Abell 963, most of the gas-rich galaxies are located to the northeast, at 1-3 Mpc from the cluster center in projection. Their velocities are slightly redshifted with respect to the cluster mean. This could be a gas-rich group falling in from the front. Abell 2192 is less massive and more diffuse, with the gas rich galaxies more uniformly spread over a large region around the cluster. The HI masses of the detected galaxies range from 5x10^9 to 4x10^10 Msun. Some HI-rich galaxies are spatially resolved and rudimentary rotation curves are derived, showing the prospect for Tully-Fisher studies of different galaxy populations in these environments. Only one galaxy is detected within a 1 Mpc radius from the center of the Butcher-Oemler cluster Abell 963, and none of the blue B-O galaxies which are all located within the central Mpc. The HI detected galaxies outside the central Mpc are of similar colour and magnitude as the non-detected B-O galaxies, indicating that the blue B-O galaxies are gas-poor compared to their counterparts in the field., Comment: 7 pages, 4 figures. to appear in the New Astronomy Review proceedings of "The Fate of Gas in Galaxies", held in Dwingeloo, July 2006

We present HI observations of 54 galaxies in the Pegasus cluster. The observations include single dish HI measurements, obtained with the Arecibo telescope for all 54 galaxies in the sample, as well as HI images, obtained with the VLA for 10 of these. The Arecibo profiles reveal an overall HI deficiency in the cluster, with ~40% of the galaxies in the core of the cluster showing modest deficiencies of typically a factor of 2-3. The HI morphology of some galaxies shows that the HI disk is smaller than the optical disk and slightly offset from the stars. We find a correlation between HI deficiency and the ratio of the HI disk size to optical disk size. More HI deficient galaxies have relatively smaller HI disks, a configuration that is usually attributed to an interaction between the ISM of the galaxy and the hot ICM. Such a result is surprising since the Pegasus cluster has a low level of X-ray emission, and a low velocity dispersion. The low velocity dispersion, coupled with the lack of a dense hot ICM indicate that ram pressure stripping should not play a significant role in this environment. In addition, two of the galaxies, NGC7604 and NGC7648, are morphologically peculiar. Their peculiarities indicate contradictory scenarios of what is triggering their unusual star formation. Halpha imaging, along with long-slit spectroscopy of NGC7648 reveal morphological features which point to a recent tidal interaction. On the other hand, Halpha imaging,along with VLA HI mapping, of NGC7604 reveal morphological features suggestive of a ram pressure event. Our data indicate that ISM-ICM interactions may play a role in a wider variety of environments than suggested by simple ram pressure arguments., Comment: Accepted for publication in AJ. Postscript version of paper and additional online material available at http://www.physics.unc.edu/~llevy/pegasus

We report the discovery of a large HI cloud in the central regions of the Virgo cluster. It is 110 x 25 kpc in size and contains 3.4 x 10^8 Msol of HI. The morphology and kinematics of this cloud strongly suggest that it consists of HI removed from the galaxy NGC 4388 by ram-pressure stripping. It is more likely the result of an interaction of the ISM of NGC 4388 with the hot halo of the M86 group and not with the ICM centred on M87. The large extent of the plume suggests that gas stripped from cluster galaxies can remain neutral for at least 10^8 yr. Locally, the column density is well above 10^20 cm^-2, suggesting that the intra-cluster HII regions known to exist in Virgo may have formed from gas stripped from cluster galaxies. The existence of the HI plume suggests that stripping of infalling spirals contributes to the enrichment of the ICM. The HI object in the Virgo cluster recently reported by Minchin et al. may have a similar origin and may therefore not be a ``dark galaxy''., Comment: Accepted for publication in A&A. 5 pages, 2 figures. Version with high-resolution figures at http://www.astron.nl/~oosterlo/n4388

We discuss HI and optical evidence for ongoing ICM-ISM interactions in 6 HI-deficient Virgo cluster spiral galaxies. One of the clearest cases is the highly inclined Virgo galaxy NGC 4522, which has a normal stellar disk but a truncated gas disk, and lots of extraplanar gas right next to the gas truncation radius in the disk. Unusually strong HI, H-alpha and radio continuum emission are all detected from the extraplanar gas. The radio continuum polarized flux and spectral index peak on the side opposite the extraplanar gas, suggesting ongoing pressure by the ICM. Four other HI-deficient edge-on Virgo spirals show evidence of extraplanar ISM gas or exhibit asymmetries in their disk HI distributions, but contain much less extraplanar HI than NGC 4522. Comparison with recent simulations suggests this difference may be evolutionary, with large surface densities of extraplanar gas observed only in early phases of an ICM-ISM interaction. In NGC 4569, the H-alpha image shows 2 effects of ICM pressure on the galaxy ISM. An anomalous arm of HII regions, possibly extraplanar, emerges from the edge of a truncated H-alpha disk. This resembles the arms seen in simulations which are formed by the combined effects of wind pressure plus rotation. An extended nebulosity near the minor axis, also in the NW, is interpreted as a starburst outflow bubble disturbed by ICM wind pressure., Comment: 6 pages, 4 figures, to appear in the ASP proceedings of IAU Symposium 217, "Recycling Intergalactic and Interstellar Matter", eds. Pierre-Alain Duc, Jonathan Braine, Elias Brinks. A version with high resolution figures is available at ftp://pegasus.astro.yale.edu/pub/kenney/iau2003-kenney-paper.ps.gz

We present the results of HI line and radio continuum observations of five nearby E+A galaxies. These galaxies have spectra that are dominated by a young stellar component but lack the emission lines characteristic of significant, on-going star formation. They are selected from a unique sample of 21 E+A's identified by Zabludoff et al.(1996) in their spectroscopic search for E+A galaxies using the Las Campanas Redshift Survey, where over 11,000 nearby galaxies were examined. The five E+A galaxies span a range of environments: three are in the field and two are in clusters. Only one system was detected in HI emission, the field E+A galaxy EA1, with a total flux of 0.30 +/- 0.02 Jy km/s and an HI mass of (3.5 +/- 0.2) 10^9 h^(-2) M_sun. The HI morphology and kinematics of EA 1 suggest a galaxy-galaxy interaction, with a dynamical age of about 6 x 10^8 h^(-1) yr inferred from the HI tail lengths and velocities. This age estimate is consistent with the interpretation drawn from optical spectroscopy that starbursts in E+A galaxies began (and subsequently ended) within the last 10^9 yr. Our HI detection limits are such that if the other E+A's in our sample had the HI properties of EA 1, we would have detected (or marginally detected) them. We conclude that E+A galaxies have a range of HI properties. None of the galaxies were detected in radio continuum emission, with upper limits to the radio power of about 10^21 h^(-2) W/Hz. Our limits exclude the possibility that these E+A's are dust-enshrouded massive starburst galaxies, but are insufficient to exclude modest star formation rates of less than a few h^(-2) M_sun per yr., Comment: 21 Latex pages, including 5 figures and 6 tables. Uses Aastex. To appear in AJ, April 2001; minor changes to text and Figure 4

The cluster environment is the site of important transformations in galaxies at a relatively recent cosmological epoch: the galactic morphological types and star formation activity have evolved significantly during the last few Gyrs. How is this related to the galactic gas content? The first part of this paper briefly presents the optical observations of galaxies in distant clusters, while the second part focuses on the link between the HI content and the star formation activity, presenting the results of a multiwavelength study of the cluster A2670 (z=0.08) where 42 galaxies have been detected in HI. We show the star formation properties of the HI-normal and HI-deficient galaxies and discuss their dependence on the location within the cluster. Finally, we compare A2670 with clusters at intermediate redshift and with the Coma cluster., Comment: 6 pages, 4 Postscript figures. To appear in "Gas and Galaxy Evolution", ASP Conf. Series, eds. J.E. Hibbard, M.P. Rupen and J.H. van Gorkom

We analyze the properties of a sample of galaxies identified in a 21cm, H I-line survey of selected areas in the Perseus-Pisces supercluster and its foreground void. Twelve fields were observed in the supercluster, five of them (target fields) centered on optically bright galaxies, and the other seven (blank fields) selected to contain no bright galaxies within 45 min. of their centers. We detected nine previously uncatalogued, gas-rich galaxies, six of them in the target fields. We also detected H I from seven previously catalogued galaxies in these fields. Observations in the void covered the same volume as the 12 supercluster fields at the same H I-mass sensitivity, but no objects were detected. Combining out H I data with optical broadband and H alpha imaging, we conclude that the properties of H I-selected galaxies do not differ substantially from those of late-type galaxies found in optical surveys. In particular, the galaxies in our sample do not appear to be unusually faint for their H I mass, or for their circular velocity. We find tentative evidence for a connection between optical surface brightness and degree of isolation, in the sense that low surface brightness galaxies tend to be more isolated. The previously catalogued, optically bright galaxies in our survey volume dominate the total H I mass density and cross section; the uncatalogued galaxies contribute only approximately 19 percent of the mass and approximately 12 percent of the cross section. Thus, existing estimates of the density and cross section of neutral hydrogen, most of which are based on optically selected galaxy samples, are probably accurate. Such estimates can be used to compare the nearby universe to the high-redshift universe probed by quasar absorption lines.