The X-ray evolution of clusters of galaxies

The WARPS survey currently contains 48 X-ray selected clusters and groups of galaxies, detected serendipitously in ROSAT PSPC archival pointed observations. The survey includes the highest redshift X-ray selected cluster known (z=0.8325). The redshift range is large enough for evolutionary effects to be studied within the sample. Here we describe the X-ray luminosity function and Log(N)-Log(S) results for the initial complete sample of 29 spectroscopically confirmed clusters. We find that the X-ray luminosity function does not evolve at z-0.5 for cluster luminosities of similar to 10(44) erg s(-1), but that there is a hint of positive evolution at lower luminosities from the number of groups & clusters found in the faintest available X-ray cluster sample (the UK deep survey).