The Cluster of Galaxies Surrounding Cygnus A. II. New Velocities and a Dynamic Model

We have spectroscopically identified 77 new members of the Cygnus A cluster, bringing to 118 the total number of galaxies consistent with cluster membership. We use these data, combined with the results from X-rays, to deduce a dynamical model for the system. The data are consistent with a cluster-cluster merger viewed at a projection angle of 30°-45°, 0.2-0.6 Gyr prior to core passage. We estimate the richness of the combined cluster system at an Abell richness class 2 or greater, suggesting the merger of two richness class ~1 clusters.