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|Redshift and Optical Properties for S Statistically Complete Sample of Poor Galaxy Clusters|
From the poor cluster catalog of White et al. (1996), we define a sampleof 71 optically-selected poor galaxy clusters. The surface-densityenhancement we require for our clusters falls between that of the looseassociations of Turner & Gott [AJ, 91,204(1976)] and the Hicksoncompact groups [Hickson, ApJ, 255, 382(1982)]. We review the selectionbiases and determine the statistical completeness of the sample. Forthis sample, we report new velocity measurements made with the ARC 3.5-mDual-Imaging spectrograph and the 2.3-m Steward Observatory MX fiberspectrograph. Combining our own measurements with those from theliterature, we examine the velocity distributions, velocity dispersions,and ID velocity substructure for our poor cluster sample, and compareour results to other poor cluster samples. We find that approximatelyhalf of the sample may have significant ID velocity substructure. Theoptical morphology, large-scale environment, and velocity field of manyof these clusters are indicative of young, dynamically evolving systems.In future papers, we will use this sample to derive the poor clusterx-ray luminosity function and gas mass function, and will examine theoptical/x-ray properties of the clusters in more detail.
|Central Parts of Some Irregular Type-II Candidate Galaxies|
|A VLA 20 CM survey of poor groups of galaxies|
The paper reports on VLA 20 cm observations of an extensive sample ofgalaxies in 139 poor groups. These groups, composed of galaxies down tothe limit of the Zwicky et al. (CGCG) catalog, were chosen using apercolation algorithm set at a high surface-density threshold.Approximately 50 percent of the groups have measured redshifts. Thesegroups were surveyed using a 'snapshot' mode of the VLA with aresolution of about 13 arcsec. Analysis of the resulting radio andoptical properties reveals that the presence of a nearby companiongalaxy has an important role in generating radio emission in a galaxy.CCD observations of two radio-loud, disturbed galaxies with companionsare presented and are used to discuss models of radio-source production.Nine tailed radio galaxies are found in the poor groups, which is muchmore than had been expected from previous work on rich clusters and fromtheoretical models. The paper discusses previous statistical biases andproposes a method for bending head-tail sources in poor groups. From theconfinement of extended radio features associated with tailed sources,the presence of a substantial intracluster medium that should radiatesignificantly at soft-X-ray energies is predicted.
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