The kinematics of dense clusters of galaxies. I. The data

We have measured redshifts in the fields of the 31 R ≥ 1 Abell clusters with 0.02≤z≤0.05 and | b^II\ > 30°. At least ten of the fields are severely contaminated by superimposed velocity peaks. We derive the mean velocities and velocity dispersions of the 25 dense peaks in the sample. The abundance of peaks, 6.6 × 10^-6h³ Mpc^-3, is consistent with the mean number density of R≥1 Abell clusters {Bahcall & Soneira [ApJ, 270, 20 (1983)]}. The range of velocity dispersions is 304-1346 km s^-1. The median dispersion is 718 km s^-1. The subset of eight systems with cD galaxies has a median velocity dispersion of 792 km s^-1, close to that of non-cD systems (626 km s^-1). When these data are combined with 16 cD cluster velocity dispersions from our previous study {Zabludoff et al. [ApJS, 74, 1 (1990) (ZHG)] and Dunn [Proceedings of NATO Conference ( 1991 )]}, eight of 25 cD galaxies have peculiar motions larger than half the cluster velocity dispersions. These findings further support the conclusions of Beers & Geller [ApJ, 274, 491 (1983)], ZHG, and Dunn (1991), who argue that cD galaxies do not lie in the global kinematic center, but in local potential minima. If so, systems with speeding cD's are probably a guide to substructure in dynamically evolving systems.