No abstract

A catalog of 732 optically selected, nearby poor clusters of galaxies covering the entire sky north of −3 • declination is presented. The poor clusters, called WBL clusters, were identified as concentrations of 3 or more galaxies with photographic magnitudes brighter than 15.7, possessing a galaxy surface overdensity of 10 4/3 . These criteria are consistent with those used in the identification of the original Yerkes poor clusters, and this new catalog substantially increases the sample size of such objects. These poor clusters cover the entire range of galaxy associations up to and including Abell clusters, systematically including poor and rich galaxy systems spanning over three orders of magnitude in the cluster mass function. As a result, this new catalog contains a greater diversity of richness and structures than other group catalogs, such as the Hickson or Yerkes catalogs. The information on individual galaxies includes

No abstract

No abstract

We present the first X-ray luminosity function (XLF) for an optically selected sample of 49 nearby poor clusters of galaxies and a sample of 67 Abell clusters with z Յ 0.15. We have extended the measured cluster XLF by more than a factor of 10 in X-ray luminosity. Our poor cluster sample was drawn from an optical catalog of groups with 0.01 Յ z Յ 0.03 composed of Zwicky galaxies. The X-ray emission was measured from the ROSAT all-sky survey. About 45% of the poor clusters were detected, with 0.5-2.0 keV luminosities from 1.7 to 65 ϫ 10 41 h Ϫ2 ergs s Ϫ1 . These are among the X-ray brightest, optically selected poor clusters in the northern hemisphere. For this sample, the poor cluster XLF was found to be a smooth extrapolation of the rich cluster XLF. A new Hydro/N-body simulation of a hot ϩ cold dark matter model with ⍀ total ϭ 1, ⍀ ϭ 0.2, and a baryon fraction of 7.5% was used to model and understand our observational selection effects. We found that the observed cluster gas mass function was consistent with our model.