X-ray sources in clusters of galaxies.

The properties of clusters of galaxies identified with X-ray sources from the 2A catalog are investigated. Forty-one associations are found, of which 34 form a statistically complete sample which is thoroughly analyzed in this paper. The luminosity function for cluster X-ray sources is presented, and it is shown that all Abell-type clusters are expected to be X-ray sources with luminosities of at least the order of 10 to the 36th power W in the 2-10-keV range. X-ray luminosity is found to depend strongly on richness and Bautz-Morgan class. It is shown that powerful X-ray clusters contain many fewer spiral galaxies than less luminous clusters and that the dependence of X-ray luminosity on the velocity dispersion of the cluster galaxies is weak. Powerful X-ray clusters are demonstrated to contain radio sources both more frequently and with steeper spectra than in other types of cluster. No evidence is found for hot gas on the scale of superclusters. It is concluded that the evidence favors thermal bremsstrahlung from a hot intracluster gas to produce the observed X-ray emission.