Abstract

We present 387 velocities covering an area 1.8° × 1.8°, including 229 new galaxy velocities obtained from 309 spectra, of which 317 appear to be cluster members according to our analysis. Based on this extended velocity sample we reanalyzed the velocity structure of the cluster. We found a strongly decreasing velocity dispersion profile that, as well as the mean velocity, shows significant radial scatter. Inside the 2.5h-1 50 Mpc radius, the velocity dispersion has a value of 1306± 73 km s-1, while further out than 3h-1 50 Mpc it falls below 800 km s-1. The global dispersion is 1085 ± 51 km s-1. We found a remarkable velocity substructure, which we interpret as a tidal outgoing arm reaching from the center to the northernmost extensions surveyed. The arm could be produced by a recent merger with another cluster, that moved from the front and SW direction and scattered from the main cluster core into the arm. This model allows us to derive an epoch for the collision between the more massive core and the front edge of the incoming cluster of 4 × 109h-1 50 yr ago and of ?2 × 109h-1 50 yr for the merging of both cores. Formation of the dumb-bell is a later merger process of the two BCMs, consistent with theoretical estimates. The collision picture is also consistent with the distorted x-ray image. The very northernmost parts of the arm could, alternatively, be interpreted as ongoing infall of a few outlying loose groups. The suggestion of a faint galaxy system within 400h-1 50 kpc, satellite to the central dumb-bell, is maintained in spite of the large central velocity dispersion value; however, confirmation requires data for further compact faint members. From several mass estimators we derived a cluster dynamical mass value of 5 × 1015h-1 50. ??, but this value should be seen in the merger context described. © 1996 American Astronomical Society.