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