An X-ray flux-limited sample of clusters of galaxies : evidence for evolution of the luminosity function.

An X-ray flux-limited sample of clusters of galaxies is presented. Over 90 per cent of the clusters have been well-observed with both imaging and spectroscopic detectors. We have determined both the local luminosity function and the space density of clusters as a function of temperature. A significant deficit in the numbers of high-luminosity clusters is found in the redshift range z ~ 0.1-0.2 compared with numbers of nearby clusters. This indicates that the X-ray luminous clusters are undergoing strong evolution at the present time. A simple stochastic merging model which reproduces the rapid evolution seen in the data is investigated. The 'temperature function' is used to put limits on the large-scale mass spectrum of the Universe.