Recent arrival of faint cluster galaxies on the red sequence: luminosity functions from 119 deg2 of CFHTLS

The global star formation rate has decreased significantly since z similar to 1, for reasons that are not well understood. Red-sequence galaxies, dominating in galaxy clusters, represent the population that have had their star formation shut off, and may therefore be the key to this problem. In this work, we select 127 rich galaxy clusters at 0.17 <= z <= 0.36, from 119 deg(2) of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) optical imaging data, and construct the r'-band red-sequence luminosity functions (LFs). We show that the faint end of the LF is very sensitive to how red-sequence galaxies are selected, and an optimal way to minimize the contamination from the blue cloud is to mirror galaxies on the redder side of the colour-magnitude relation. The LFs of our sample have a significant inflexion centred at M-r' similar to -18.5, suggesting a mixture of two populations. Combining our survey with low-redshift samples constructed from the Sloan Digital Sky Survey, we show that there is no strong evolution of the faint end of the LF (or the red-sequence dwarf-to-giant ratio) over the redshift range 0.2 less than or similar to z less than or similar to 0.4, but from z similar to 0.2 to similar to 0 the relative number of red-sequence dwarf galaxies has increased by a factor of similar to 3, implying a significant build-up of the faint end of the cluster red sequence over the last 2.5 Gyr.