A merger scenario for the dynamics of Abell 665

We present new redshift measurements for 55 galaxies in the vicinity of the rich galaxy cluster Abell 665. When combined with results from the literat ure, we have good velocity measurements for a sample of 77 confirmed cluste r members from which we derive the cluster's redshift z = 0.1829 +/- 0.0005 and line-of-sight velocity dispersion sigma = 1390(-110)(+120) km s(-1). O ur analysis of the kinematical and spatial data for the subset of galaxies located within the central 750 kpc reveals only subtle evidence for substru cture and non-Gaussianity in the velocity distribution. We find that the br ightest cluster member is not moving significantly relative to the other ga laxies near the center of the cluster. On the other hand, our deep ROSAT hi gh-resolution image of A665 shows strong evidence for isophotal twisting an d centroid variation, thereby confirming previous suggestions of significan t substructure in the hot X-ray-emitting intracluster gas. In light of this evident substructure, we have compared the optical velocity data with N-bo dy simulations of head-on cluster mergers. We find that a merger of two sim ilar mass subclusters (mass ratios of 1:1 or 1:2) seen close to the time of core-crossing produces velocity distributions that are consistent with tha t observed.