The Extended Medium Sensitivity Survey Distant Cluster Sample: X-Ray Data and Interpretation of the Luminosity Evolution

We describe the X-ray properties of a cluster of galaxies subsample of the Einstein Extended Medium Sensitivity Survey. A summary of this sample and its implications has been presented previously; this paper gives the full details. The cluster subsample is 98.4% identified and contains 93 X-ray-selected clusters to a redshift of 0.58. We derive the cluster X- ray luminosity function at three cosmic epochs. While our luminosity function agrees with previous determinations at the lowest redshifts, we find that the volume density of high-luminosity clusters is greater now than it was in the past. The normalization, shape, and time dependence of the luminosity function can be described by a simple hierarchical formation model with parameters which also describe the temperature function of an independent sample of low-redshift clusters. In this model the comoving hot gas density remains constant with time at least to redshifts of order 0.35.