The Effect of Cluster Environment on Galaxy Evolution in the Pegasus I Cluster

We present neutral hydrogen observations of 54 galaxies in the Pegasus Cluster. The observations include single-dish H I measurements, obtained with the Arecibo telescope for all 54 galaxies in the sample, as well as H I images obtained with the Very Large Array (VLA) for 10 of these. The Arecibo profiles reveal an overall H I deficiency in the cluster, with similar to 40% of the galaxies in the core of the cluster showing modest deficiencies of typically a factor of 2-3. The HI morphology of so me 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 interstellar medium (ISM) of the galaxy and the hot intracluster med ium (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. Hα imaging, along with long-slit spectroscopy of NGC7648 reveal morphological features which point to a recent tidal interaction. On the other hand, Hα imaging of NGC7604 reveals a strong episode of star formation concentrated into an asymmetric arc, preferentially located on one side of the galaxy. VLA HI mapping shows the HI also highly concentrated into that region, 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

BUDHIES I: characterizing the environments in and around two clusters at z~0.2

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

The Effect of Cluster Environment on Galaxy Evolution in the Pegasus I Cluster

We present neutral hydrogen observations of 54 galaxies in the Pegasus Cluster. The observations include single-dish H I measurements, obtained with the Arecibo telescope for all 54 galaxies in the sample, as well as H I images obtained with the Very Large Array (VLA) for 10 of these. The Arecibo profiles reveal an overall H I 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 H I morphology of some galaxies shows that the H I disk is smaller than the optical disk and slightly offset from the stars. We find a correlation between H I deficiency and the ratio of the H I disk size to optical disk size. More H I-deficient galaxies have relatively smaller H I disks, a configuration that is usually attributed to an interaction between the interstellar medium (ISM) of the galaxy and the hot intracluster medium (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, NGC 7604 and NGC 7648, are morphologically peculiar. Their peculiarities indicate contradictory scenarios of what is triggering their unusual star formation. Hα imaging, along with long-slit spectroscopy of NGC 7648, reveal morphological features that point to a recent tidal interaction. On the other hand, Hα imaging of NGC 7604 reveals a strong episode of star formation concentrated into an asymmetric arc, preferentially located on one side of the galaxy. VLA H I mapping shows that H I is also highly concentrated into that region, 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

A Search for HI in E+A Galaxies

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

Gas Reservoirs and Star Formation in a Forming Galaxy Cluster at zbsime0.2

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

Early Science with the Large Millimeter Telescope: COOL BUDHIES I - a pilot study of molecular and atomic gas at z~0.2

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, submitte

Concordance in measurable residual disease result after first and second induction cycle in acute myeloid leukemia : An outcome- and cost-analysis

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