We present new redshift measurements for 55 galaxies in the vicinity of the rich galaxy cluster Abell 665 .
When combined with results from the literature , we have good velocity measurements for a sample of 77 confirmed cluster members from which we derive the cluster ’ s redshift z = 0.1829 \pm 0.0005 and line-of-sight velocity dispersion \sigma = 1390 ^ { +120 } _ { -110 } km s ^ { -1 } .
Our analysis of the kinematical and spatial data for the subset of galaxies located within the central 750 kpc reveals only subtle evidence for substructure and non-Gaussianity in the velocity distribution .
We find that the brightest cluster member is not moving significantly relative to the other galaxies near the center of the cluster .
On the other hand , our deep ROSAT high resolution image of A665 shows strong evidence for isophotal twisting and centroid variation , thereby confirming previous suggestions of significant substructure in the hot X-ray–emitting intracluster gas .
In light of this evident substructure , we have compared the optical velocity data with N-body simulations of head-on cluster mergers .
We find that a merger of two similar 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 that observed .