THE LUMINOSITY FUNCTION OF GALAXIES IN CLUSTERS

By means of statistical analyses, we compute the luminosity function o f galaxies in clusters and explore its dependence on cluster global pr operties. The data consist of two different samples of southern cluste rs with published redshifts, taken from the Abell cluster catalog and the APM cluster catalog. Galaxy assignment to the clusters and their c orresponding apparent magnitudes were derived from the Edinburgh-Durha m Southern Galaxy catalogue. We have considered two limiting absolute magnitudes, M <-16 and M <-17, comprising 16 and 55 clusters, respecti vely. The galaxy luminosity function in clusters derived in this work shows a large excess of faint galaxies compared with previous field de terminations. In spite of their different identification procedures, w e obtain similar galaxy luminosity functions in Abell and APM clusters . A Schechter function with parameters Msimilar or equal to-20.0+/-0. 1 and alpha similar or equal to-1.4+/-0.1 provides a satisfactory st t o the galaxy luminosity function of the sample of 55 clusters. We also find a flatter galaxy luminosity function in poor clusters (alpha sim ilar or equal to-1.2). We have computed errors through a Monte Carlo p rocedure that considers different possible background corrections and errors in the photometry. Besides providing reliable values of the unc ertainties in the luminosity function fitting parameters, this method poses confident limits on the effects of possible systematics. Our res ults strongly argue against a universal galaxy luminosity function. Th e high relative frequency of faint galaxies in rich clusters reported in this work may provide constraints on models for the origin and evol ution of galaxies.