The Ursa Major Cluster of Galaxies. IV ; HI synthesis observations

In this data paper we present the results of an extensive 21cm-line synthesis imaging survey of 43 spiral galaxies in the nearby Ursa Major cluster using the Westerbork Synthesis Radio Telescope. Detailed kinematic information in the form of position-velocity diagrams and rotation curves is presented in an atlas together with HI channel maps, 21cm continuum maps, global HI profiles, radial HI surface density profiles, integrated HI column density maps, and HI velocity fields. The relation between the corrected global HI linewidth and the rotational velocities Vmax and Vflat as derived from the rotation curves is investigated. Inclination angles obtained from the optical axis ratios are compared to those derived from the inclined HI disks and the HI velocity fields. The galaxies were not selected on the basis of their HI content but solely on the basis of their cluster membership and inclination which should be suitable for a kinematic analysis. The observed galaxies provide a well-defined, volume limited and equidistant sample, useful to investigate in detail the statistical properties of the Tully-Fisher relation and the dark matter halos around them.Comment: 32 pages, including 2 sample pages of HI atlas. For full atlas (104 pages, 11 MB) see http://www.nrao.edu/library/preprints/00173.ps.gz . Accepted for publication in Astronomy and Astrophysic

The Multi-Wavelength Tully-Fisher relation with spatially resolved HI kinematics

In this paper we investigate the statistical properties of the Tully-Fisher relation for a sample of 32 galaxies with measured distances from the Cepheid period-luminosity relation and/or TRGB stars. We take advantage of panchromatic photometry in 12 bands (from FUV to 4.5 $\mu$m) and of spatially resolved HI kinematics. We use these data together with three kinematic measures ($W^{i}_{50}$, $V_{max}$ and $V_{flat}$) extracted from the global HI profiles or HI rotation curves, so as to construct 36 correlations allowing us to select the one with the least scatter. We introduce a tightness parameter $\sigma_{\perp}$ of the TFr, in order to obtain a slope-independent measure of the goodness of fit. We find that the tightest correlation occurs when we select the 3.6 $\mu$m photometric band together with the $V_{flat}$ parameter extracted from the HI rotation curve.Comment: 16 pages, 16 figures, accepted for publication in MNRAS, minor changes due to proof correction

Galaxy evolution in dense environments; a concise HI perspective

Observing the neutral Hydrogen in galaxy clusters provides crucial insights in the physical processes that influence the evolution of gas-rich galaxies as they migrate from the lower-density filaments through the cluster outskirts into to the higher-density central regions. The morphology-density relation, the Buther-Oemler effect, and the observed HI deficiencies in the central regions of galaxy clusters suggest that infalling galaxies experience a strong transformation of their morphologies, star formation rates, and gas content. The physical mechanisms that trigger and govern these transformations may depend strongly on environment. This contribution aims to illustrate that the morphological and kinematic characteristics of the cold gas provide a sensitive tool to determine which mechanisms dominate in which environments.Comment: 7 pages, 6 figures, To appear in `Outskirts of Galaxy Clusters; intense life in the suburbs', IAU Colloquium No. 195, 2004, A. Diaferio e

The H I angular momentum-mass relation

We study the relationship between the H I specific angular momentum ($\rm j_{g}$) and the H I mass ($\rm M_{g}$) for a sample of galaxies with well-measured H I rotation curves. We find that the relation is well described by an unbroken power law $\rm j_{g}$ ∝ $\rm M_{g}$α over the entire mass range (107-1010.5 M⊙), with α = 0.89 ± 0.05 (scatter 0.18 dex). This is in reasonable agreement with models which assume that evolutionary processes maintain H I discs in a marginally stable state. The slope we observe is also significantly different from both the j ∝ M2/3 relation expected for dark matter haloes from tidal torquing models and the observed slope of the specific angular momentum-mass relation for the stellar component of disc galaxies. Our sample includes two H I-bearing ultra-diffuse galaxies, and we find that their angular momentum follows the same relation as other galaxies. The only discrepant galaxies in our sample are early-type galaxies with large rotating H I discs, which are found to have significantly higher angular momentum than expected from the power-law relation. The H I discs of all these early-type galaxies are misaligned or counter-rotating with respect to the stellar discs, consistent with the gas being recently accreted. We speculate that late-stage wet mergers, as well as cold flows play a dominant role in determining the kinematics of the baryonic component of galaxies as suggested by recent numerical simulations

The Ursa Major Cluster of Galaxies. III. Optical observations of dwarf galaxies and the luminosity function down to M_R=-11

Results are presented of a deep optical survey of the Ursa Major Cluster, a spiral-rich cluster of galaxies at a distance of 18.6 Mpc which contains about 30% of the light but only 5% of the mass of the nearby Virgo Cluster. Fields around known cluster members and a pattern of blind fields along the major and minor axes of the cluster were studied with mosaic CCD cameras on the Canada-France-Hawaii Telescope. The dynamical crossing time for the Ursa Major Cluster is only slightly less than a Hubble time. Most galaxies in the local Universe exist in similar moderate density environments. The Ursa Major Cluster is therefore a good place to study the statistical properties of dwarf galaxies since this structure is at an evolutionary stage representative of typical environments yet has enough galaxies that reasonable counting statistics can be accumulated. The main observational results of our survey are: (i) The galaxy luminosity function is flat, with a logarithmic slope alpha = -1.1 for -17 < M_R < -11, from a power-law fit. The error in alpha is likely to be less than 0.2 and is dominated by systematic errors, primarily associatedd with uncertainties in assigning membership to specific galaxies. This faint end slope is quite different to what was seen in the Virgo Cluster where alpha=-2.26. (ii) Dwarf galaxies are as frequently found to be blue dwarf irregulars as red dwarf spheroidals in the blind cluster fields. The density of red dwarfs is significantly higher in the fields around luminous members than in the blind fields. The most important result is the failure to detect many dwarfs. If the steep luminosity function claimed for the Virgo Cluster were valid for Ursa Major then in our blind fields we should have found about 1000 galaxies with -17 < M_R <-11 where we have found two dozen.Comment: 15 pages, 8 figs, TeX, MNRAS in press, Fig 3 at higher resolution available from the author

The anomalous properties of Markarian 1460

We present and discuss optical, near-infrared and HI measurements of the galaxy Markarian 1460 at a distance of 19 Mpc in the Ursa Major Cluster. This low-luminosity (M_B = -14) galaxy is unusual because (i) it is blue (B-R=0.8) and has the spectrum of an HII galaxy, (ii) it has a light profile that is smooth and well fit by an r^{1/4} and not an exponential function at all radii larger than the seeing, and (iii) it has an observed central brightness of about mu_B = 20 mag arcsec^{-2}, intermediate between those of elliptical galaxies (on the bright mu_B side) and normal low-luminosity dwarf irregular (on the low mu_B side) galaxies. No other known galaxy exhibits all these properties in conjunction. On morphological grounds this galaxy looks like a normal distant luminous elliptical galaxy, since the fundamental plane tells us that higher luminosity normal elliptical galaxies tend to have lower surface-brightnesses. Markarian 1460 has 2 X 10^7 M_sun of HI and a ratio M(HI)/L_B of 0.2, which is low compared to typical values for star-forming dwarf galaxies. From the high surface brightness and r^{1/4} profile, we infer that the baryonic component of Markarian 1460 has become self-gravitating through dissipative processes. From the colours, radio continuum, HI and optical emission line properties, yet smooth texture, we infer that Markarian 1460 has had significant star formation as recently as about 1 Gyr ago but not today.Comment: MNRAS in pres

WSRT Ultra-Deep Neutral Hydrogen Imaging of Galaxy Clusters at z=0.2, a Pilot Survey of Abell 963 and Abell 2192

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 42 galaxies. The WSRT probes a total combined volume of 3.4x10^4 Mpc^3 at resolutions of 54x86 kpc^2 and 19.7 km/s, surveying both clusters and the large scale structure in which they are embedded. In Abell 963, a dynamically relaxed, lensing Butcher-Oemler cluster with a high blue fraction, most of the gas-rich galaxies are located between 1 and 3 Mpc in projection, northeast from the cluster core. Their velocities are slightly redshifted with respect to the cluster, and this is likely a background group. None of the blue galaxies in the core of Abell 963 are detected in HI, although they have similar colors and luminosities as the HI detected galaxies in the cluster outskirts and field. Abell 2192 is less massive and more diffuse. Here, the gas-rich galaxies are more uniformly distributed. The detected HI masses range from 5x10^9 to 4x10^10 Msun. Some galaxies are spatially resolved, providing rudimentary rotation curves useful for detailed kinematic studies of galaxies in various environments. This is a pilot for ultra-deep integrations down to HI masses of 8x10^8 Msun, providing a complete survey of the gas content of galaxies at z=0.2, probing environments ranging from cluster cores to voids.Comment: 5 pages, 6 figures + 1 Plate, accepted for publication in the Astrophysical Journal Letter

The DiskMass Survey. X. Radio synthesis imaging of spiral galaxies

We present results from 21 cm radio synthesis imaging of 28 spiral galaxies from the DiskMass Survey obtained with the VLA, WSRT, and GMRT facilities. We detail the observations and data reduction procedures and present a brief analysis of the radio data. We construct 21 cm continuum images, global HI emission-line profiles, column-density maps, velocity fields, and position-velocity diagrams. From these we determine star formation rates (SFRs), HI line widths, total HI masses, rotation curves, and azimuthally-averaged radial HI column-density profiles. All galaxies have an HI disk that extends beyond the readily observable stellar disk, with an average ratio and scatter of R_{HI}/R_{25}=1.35+/-0.22, and a majority of the galaxies appear to have a warped HI disk. A tight correlation exists between total HI mass and HI diameter, with the largest disks having a slightly lower average column density. Galaxies with relatively large HI disks tend to exhibit an enhanced stellar velocity dispersion at larger radii, suggesting the influence of the gas disk on the stellar dynamics in the outer regions of disk galaxies. We find a striking similarity among the radial HI surface density profiles, where the average, normalized radial profile of the late-type spirals is described surprisingly well with a Gaussian profile. These results can be used to estimate HI surface density profiles in galaxies that only have a total HI flux measurement. We compare our 21 cm radio continuum luminosities with 60 micron luminosities from IRAS observations for a subsample of 15 galaxies and find that these follow a tight radio-infrared relation, with a hint of a deviation from this relation at low luminosities. We also find a strong correlation between the average SFR surface density and the K-band surface brightness of the stellar disk.Comment: 22 pages + Appendix, 16 figures + Atlas, 5 tables. Accepted for publication in Astronomy & Astrophysic

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