Dynamics of the X-ray clusters Abell 222, Abell 223 and Abell 520

Abstract

We present the results of a dynamical analysis of three rich, X-ray luminous galaxy clusters, Abell 222, Abell 223 and Abell 520, that are at intermediate redshifts. Our study is based on radial velocities for 71 cluster members, respectively 30 for A222, 20 for A223 and 21 for A520, measured from spectra obtained at the Canada-France-Hawaii Telescope, the European Southern Observatory, and the Pic du Midi Observatory, and supplemented with radial velocities from the literature. A222 galaxies have slightly higher velocities than those of A223, with bi-weighted mean velocity of V_{bi} = 64242 +/- 194 km/s for A222, and of V_{bi} = 63197 +/- 266 km/s for A223. The velocity dispersions of the two clusters are about the same: sigma_{bi} = 1013 +/- 150 km/s and sigma_{bi} = 1058 +/- 160 km/s for A222 and A223, respectively. For A520 we obtain V_{bi} = 60127 +/- 284 km/s with sigma_{bi} = 1250 +/- 189 km/s. We also give mass and mass-luminosities ratio estimates for each cluster separately. We argue that these clusters are presently undergoing strong dynamical evolution and that A222 and A223 will probably merge in the future. We have applied a Principal Component Analysis to a sample of 51 CFHT spectra to produce a spectral classification for these galaxies. This classification has allowed us to show that the morphological and kinematical segregations were already established in these intermediate redshift clusters.