Are Luminous [CLC]c[/CLC]D Halos Formed by the Disruption of Dwarf Galaxies?

From a total sample of 45 Abell clusters observed by the Einstein X-rayobservatory, we present the results on the galaxy luminosity function (LF) fora group of seven clusters that were identified by the morphology of their LFs.The LFs were derived using photometric data to a completeness limit ~5.5magnitudes below M*. We found that a single Schechter function with an average$\alpha \approx -1.0$ gives a good fit to these individual LFs within themagnitude range. These seven clusters have common properties, which indicatethey form a homogeneous class of dynamically evolved clusters that can becharacterized by the presence of a dominant cD galaxy, high richness,symmetrical single-peaked X-ray emission, and high gas mass. On the other hand,steep faint-end slopes (-2.0 < \alpha < -1.4) are usually detected in poorerclusters. Our result gives a direct indication that the faint-end slope of thegalaxy LF is subject to environmental effects. We propose that the flatness ofthe faint-end slope in these clusters results from the disruption of a largefraction of dwarf galaxies during the early stages of cluster evolution. Thestars and gas from the disrupted galaxies are redistributed throughout thecluster potential during violent relaxation. This heuristic scenario canexplain the origin of the luminous haloes of cD galaxies and a large fractionof the gas content in the intracluster medium as a by-product. The correlationbetween the cluster gas mass determined from the modeling of the X-ray emissionand the cD halo optical luminosity is presented to support the proposed model.Comment: 11 pages,Latex,2 Postscript figures, 2 Postscript tables, accepted for publication in Apj