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The Arecibo Legacy Fast ALFA Survey. III. H I Source Catalog of the Northern Virgo Cluster Region
We present the first installment of H I sources extracted from theArecibo Legacy Fast ALFA (ALFALFA) extragalactic survey, initiated in2005. Sources have been extracted from three-dimensional spectral datacubes exploiting a matched filtering technique and then examinedinteractively to yield global H I parameters. A total of 730 H Idetections are cataloged within the solid angle11h44m6.5,(2) high-velocity clouds in the Milky Way or its periphery, and (3)signals of lower S/N (to ~4.5) which coincide spatially with an opticalobject of known similar redshift. Although this region of the sky hasbeen heavily surveyed by previous targeted observations based on opticalflux- or size-limited samples, 69% of the extracted sources are newlyreported H I detections. The resulting positional accuracy of H Isources is dependent on S/N: it averages 24" (20" median) for allsources with S/N>6.5 and is of order ~17" (14" median) for signalswith S/N>12. The median redshift of the sample is ~7000 kms-1, and its distribution reflects the known locallarge-scale structure including the Virgo Cluster and the void behindit, the A1367-Coma supercluster at cz~7000 km s-1, and athird, more distant overdensity at cz~13,000 km s-1. Distanceuncertainties in and around the Virgo Cluster perturb the derived H Imass distribution. Specifically, an apparent deficiency of the lowest HI mass objects can be attributed, at least in part, to the incorrectassignment of some foreground objects to the cluster distance. Severalextended H I features are found in the vicinity of the Virgo Cluster. Asmall percentage (6%) of H I detections have no identifiable opticalcounterpart, more than half of which are high-velocity clouds in theMilky Way vicinity; the remaining 17 objects do not appear connected toor associated with any known galaxy. Based on these initial results,ALFALFA is expected to fulfill, and even exceed, its predictedperformance objectives in terms of the number and quality of H Idetections.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| HI-observations of galaxies in the Virgo cluster of galaxies. I - The data
New H I-data for a large number of bright galaxies inside the 10 degradius area of the Virgo cluster of galaxies have been obtained with the100 m radiotelescope at Effelsberg. A total of 234 galaxies was observedfor the first time. Among them, 53 have been detected providing newaccurate radial velocities. Data from the literature have been compiled.Together with the new data, they form a (nearly homogeneous) set of H Iobservations for more than 450 galaxies.
| Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area.
The present catalog of 2096 galaxies within an area of about 140 sq degapproximately centered on the Virgo cluster should be an essentiallycomplete listing of all certain and possible cluster members,independent of morphological type. Cluster membership is essentiallydecided by galaxy morphology; for giants and the rare class of highsurface brightness dwarfs, membership rests on velocity data. While 1277of the catalog entries are considered members of the Virgo cluster, 574are possible members and 245 appear to be background Zwicky galaxies.Major-to-minor axis ratios are given for all galaxies brighter than B(T)= 18, as well as for many fainter ones.
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