Environmental effects on the bright end of the galaxy luminosity function in galaxy clusters

Abstract

The dependence of the luminosity function of cluster galaxies on the evolutionary state of the parent cluster is still an open issue, in particular as concern the formation/evolution of the brightest cluster galaxies. We plan to study the bright part of the LFs of a sample of very unrelaxed clusters ("DARC" clusters showing evidence of major, recent mergers) and compare them to a reference sample of relaxed clusters spanning a comparable mass and redshift range. Our analysis is based on the SDSS DR7 photometric data of ten, massive, and X-ray luminous clusters (0.2<z<0.3), always considering physical radii (R_200 or its fractions). We consider r' band LFs and use the color-magnitude diagrams (r'-i',r') to clean our samples as well to consider separately red and blue galaxies. We find that DARC and relaxed clusters give similar LF parameters and blue fractions. The two samples differ for their content of bright galaxies BGs, M_r<-22.5, since relaxed clusters have fewer BGs, in particular when considering the outer cluster region 0.5R_200<R<R_200 (by a factor two). However, the cumulative light in BGs is similar for relaxed and DARC samples. We conclude that BGs grow in luminosity and decrease in number as the parent clusters grow hierarchically in agreement with the BG formation by merging with other luminous galaxies.Comment: 11 pages, 12 figures and 9 table