The Distribution of Cluster Members in the Vicinity of a Central Dominant Galaxy

The projected distribution of cluster members within 250 h^-1^ kpc of a central dominant galaxy is investigated by stacking CCD images of 29 clusters of galaxies. The radial distribution of the projected galaxy number density is well described by an exponential profile with an e-folding length of approximately 100 h^-1^ kpc. The shape of the profile is characteristic of the effects of dynamical friction and suggests that this force may have played a significant role in cluster evolution. However, there is no evidence for the luminosity segregation that might be expected to accompany such evolution. The central density for the core profile appears to be only weakly correlated with the overall cluster richness. The dynamics of this projected profile are investigated for a range of credible mass distributions, and existing redshift measurements are shown to be consistent with an isotropic velocity distribution. The high central density associated with this cusped distribution explains the presence of at least 50% of the observed "multiple nuclei" projected within 10 h^-1^ kpc of the center of the dominant galaxy. In view of the bias aperture containing maximum luminosity, and uncertainties in the effective limiting magnitude to which existing surveys of multiple nuclei have been made, this population could be responsible for most of the observed occurrences of multiple nuclei. However, calculations indicate that the high density and low velocities of galaxies in the cluster core may lead to a sufficiently high rate of collisions between cluster members and the central dominant galaxy to produce a significant population of multiple nuclei which are in the process of merging with the underlying central galaxy.