CONSTRAINTS ON CANNIBALISM FROM THE VELOCITIES OF MULTIPLE NUCLEI IN BRIGHTEST CLUSTER GALAXIES

Redshifts and stellar velocity dispersions are presented for a sample of multiple-nucleus brightest cluster galaxies (39 objects in 17 clusters) with 0.05 < z < 0.07. These are combined with an earlier set of z < 0.05 observations to produce an extended sample containing 72 objects previously identified as multiple nuclei (including the 31 primaries). The velocity distribution of the secondaries with respect to the central brightest cluster galaxy has a rms dispersion of 751 km/s. The observed velocities increase with projected radius, indicating that the secondaries have a range in orbit size. They also increase with cluster x-ray luminosity. There is a deficit of slow-moving nuclei in the richest clusters, possibly indicative of dynamical evolution, but the new data do not support the former suggestion that the most luminous central galaxies have fewer low-velocity secondaries. We find no evidence for a low-velocity bound population of merger candidates; the velocities are in accord with the expected distribution. The 95% confidence level upper limit on the number of secondaries in the combined sample which could be part of a bound population implies that brightest cluster galaxies have increased their luminosities by no more than 1.5 L * due to the process of galactic cannibalism over a typical cluster lifetime.