Recent Dynamical Evolution of Galaxy Clusters

Evidence is presented for a recent evolution of the relaxation processes inclusters of galaxies, using large optical and X-ray cluster samples. Thecriteria of the cluster relaxation used are the cluster ellipticity, the ICMtemperature and X-ray cluster luminosity. We find evidence of varying strengthand significance of all three indicators evolving with redshift for z <0.15.This result supports the view that clusters have mostly stopped undergoingmergers and accreting matter, as expected in a low-Omega_matter Universe, andare now in the process of gravitational relaxation, which reduces theirflattening, their ICM temperature (shock heated during the merging phase), andtheir X-ray luminosity. These results support similar recent claims of Melott,Chambers and Miller (2001).Comment: 4 pages, 4 figures accepted for publication in ApJ Let