The Galaxy Cluster Core

Abstract

We have examined the dependence of brightest cluster galaxy (BCG) characteristics (metric luminosity, central structure, position relative to the cluster potential) on the central cluster environment (shape and normalization of the luminosity function and density profile) and vice versa. We find no significant dependence between the luminosity function of the core cluster galaxies and the above BCG properties. Moreover, there is no apparent segregation in cluster galaxy luminosity as a function of radial separation from the BCG. However, comparison with other studies on larger (> 1 Mpc) scales suggests that the cluster core is populated by less luminous galaxies (M*global < M*core) and the fraction of dwarf galaxies is lower (α global < α core). Tidal stripping, ram-pressure stripping and galaxy disruption can be invoked as possible explanations. We also find that the galaxy number density in the immediate vicinity of the BCG increases with BCG intrinsic luminosity. The lack of a significant deficit of bright galaxies, however, suggests this effect is not the result of dynamical friction. The insensitivity of the central density profile (where we have used the BCG as the marker of the cluster center) to the kinematic offset of the BCG from the cluster velocity distribution suggests that this excess galaxy population may be bound to the BCG.