Evolution of the Internal Dynamics of Galaxy Clusters

We consider a sample of 51 distant galaxy clusters at 0.15 about0.3), each cluster having at least 10 galaxies with available redshift in theliterature. We select member galaxies, analyze the velocity dispersionprofiles, and evaluate in a homogeneous way cluster velocity dispersions andvirial masses. We apply the same procedures already recently applied on asample of nearby clusters (z<0.15, Girardi et al. 1998b) in order to properlyanalyze the possible dynamical evolution of galaxy clusters. We remark problemsinduced by the poor sampling and the small spatial extension of the sampledcluster region in the computation of velocity dispersion. We do not find anysignificant difference between nearby and distant clusters. In particular, weconsider the galaxy spatial distribution, the shape of the velocity dispersionprofile, and the relations between velocity dispersion and X-ray luminosity andtemperature. Our results imply little dynamical evolution in the range ofredshift spanned by our cluster sample, and suggest that the typical redshiftof cluster formation is higher than that of the sample we analyze.Comment: 18 pages, 9 eps figures, ApJ in pres