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

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 A 222, 20 for A 223 and 21 for A 520, 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. A 222 galaxies have slightly higher velocities than those of A 223, with bi-weighted mean velocity of Vbi = 64242 ± 194 km s−1 for A 222, and of Vbi = 63197 ± 266 km s−1 for A 223. The velocity dispersions of the two clusters are about the same: σbi = 1013±150 km s−1 and σbi = 1058±160 km s−1 for A 222 and A 223, respectively. For A 520 we obtain Vbi = 60127±284 km s−1 with σbi = 1250±189 km s−1. 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 A 222 and A 223 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.