A Cluster Deficit in the ROSAT NEP Survey

Abstract

We have used data from the deepest region of the ROSAT All-Sky Survey, the North Ecliptic Pole (NEP) region, to produce a complete and unbiased X-ray selected sample of distant clusters to understand the nature of cluster evolution and determine implications for large scale structure models. In this contribution results are presented from a comparison between the number of the observed clusters in the NEP survey and the number of expected clusters assuming no-evolution models. There is a deficit by a factor of 2.5-4 of high luminosity, high redshift clusters with respect to the present. The evolution goes in the same direction as the original EMSS result, and the results from the CfA-IfA 160 deg^{2} survey by Vikhlini et al. 1998.