Dynamical Evolution of Galaxy Clusters

We consider a sample of about 50 distant galaxy clusters at <z>0.15 (<z>=0.3), each cluster having at least 10 galaxies with available redshift in the literature. We select member galaxies and evaluatein a homogeneous way cluster velocity dispersions and optical virial masses. We apply the same procedures already successfully applied on a sample of nearby clusters in order to properly analyze the possible dynamical evolution of galaxy clusters. Moreover, we compare our results to those obtained from X-ray analyses. We do not find any evidence for an evolution of cluster properties. In particular, we find that in distant clusters the fraction of strongly substructured systems, the shape of galaxy distribution, velocity dispersion profiles and velocity anisotropies in galaxy orbits are similar to those found in nearby clusters. We do not find any evidence of a possible evolution of the relations between X--ray properties (luminosity and temperature) and velocity dispersion. We conclude that the redshift of cluster formation should be higher than that of the sample we analyze.