Optical luminosity functions of the Abell galaxy cluster ABCG 209 at z = 0.21

Abstract

We derive the luminosity functions in three bands (BVR) for the rich galaxy cluster ABCG 209 at z = 0.21. The data cover an area of ∼78 arcmin2 in the B and R bands, while a mosaic of three pointings was obtained in the V band, covering an area of approximately 160 arcmin2. The galaxy sample is complete to B = 22.8 (Ngal = 339), V = 22.5 (Ngal = 1078) and R = 22.0 (Ngal = 679). Although the fit of a single Schechter function cannot be rejected in any band, the luminosity functions are better described by a sum of two Schechter functions for bright and faint galaxies, respectively. There is an indication for a presence of a dip in the luminosity functions in the range V = 20.5-21.5 and R = 20.0-21.0. We find a marked luminosity segregation, in the sense that the number ratio of bright-to-faint galaxies decreases by a factor 4 from the center to outer regions. Our analysis supports the idea that ABCG 209 is an evolved cluster, resulting from the merger of two or more sub-clusters.