Optical properties of X-ray clusters of galaxies

A strong correlation of X-ray luminosity with optical classification of galaxy clusters is found by studying all 21 clusters that Kellogg et al. (1973) have suggested may be identified with X-ray sources. No strong correlation of X-ray luminosity with cluster richness is observed, although there is a greater probability for the richer clusters (richness 2) to be X-ray sources. Centers are measured for the clusters that have small X-ray error boxes (<1 square degree). A number of the X-ray error boxes do not include the centers of the clusters, but in almost all cases they do include an active radio galaxy or a giant cD galaxy. Core radii of the galaxy distributions have also been measured in four clusters for which X-ray core radii are available; the galaxy distributions have smaller core radii than the X-ray distribution by factors of 2 to 5. Subject headings: galaxies, clusters of - X-ray sources