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

Context. The dependence of the luminosity function (LF) of cluster galaxies on the evolutionary state of the parent cluster is still an open question, in particular concerning the formation/evolution of the brightest cluster galaxies. Aims: We 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 that span a comparable mass and redshift range. Methods: 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 (R200 or its fractions). We considered r' band LFs and used the color-magnitude diagrams (r' - i', r') to clean our samples to consider red and blue galaxies separately. Results: We find that DARC and relaxed clusters give similar LF parameters and blue fractions. The two samples differ in their content of bright galaxies BGs, Mr' < -22.5. Relaxed clusters have fewer BGs, in particular when considering the outer cluster region 0.5R200 < R < R200 (by a factor two). However, the cumulative light in BGs is similar for relaxed and DARC samples. Conclusions: We conclude that BGs grow in luminosity and decrease in number as the parent clusters grow hierarchically, which agrees with a BG formation by merging with other luminous galaxies.