The Luminosity Function of Galaxies in Clusters

By means of statistical analyses, we compute the luminosity function of galaxies in clusters and explore its dependence on cluster global properties. The data consist of two different samples of southern clusters with published redshifts, taken from the Abell cluster catalog and the APM cluster catalog. Galaxy assignment to the clusters and their corresponding apparent magnitudes were derived from the Edinburgh-Durham Southern Galaxy Catalogue. We have considered two limiting absolute magnitudes, M < -16 and M < -17, comprising 16 and 55 clusters, respectively. The galaxy luminosity function in clusters derived in this work shows a large excess of faint galaxies compared with previous field determinations. In spite of their different identification procedures, we obtain similar galaxy luminosity functions in Abell and APM clusters. A Schechter function with parameters M * ≃ -20.0 ± 0.1 and α ≃ -1.4 ± 0.1 provides a satisfactory fit to the galaxy luminosity function of the sample of 55 clusters. We also find a flatter galaxy luminosity function in poor clusters (α ≃ -1.2). We have computed errors through a Monte Carlo procedure that considers different possible background corrections and errors in the photometry. Besides providing reliable values of the uncertainties in the luminosity function fitting parameters, this method poses confident limits on the effects of possible systematics. Our results strongly argue against a universal galaxy luminosity function. The high relative frequency of faint galaxies in rich clusters reported in this work may provide constraints on models for the origin and evolution of galaxies.