RASS-SDSS galaxy cluster survey

II. A unified picture of the cluster luminosity function

¹ Max-Planck-Institut fur extraterrestrische Physik, 85748 Garching, Germany e-mail: popesso@mpe.mpg.de
² European Southern Observatorty, Karl Scharzschildstr. 2, 85748 Garching b. München, Germany

Received: 20 August 2004
Accepted: 1 December 2004

Abstract

We constructed the composite luminosity function (LF) of clusters of galaxies in the five SDSS photometric bands u, g, r, i and z from the RASS-SDSS galaxy cluster catalog. Background and foreground galaxies are subtracted using both a local and a global background correction to take in account the presence of large scale structures and field to field variations, respectively. The composite LF clearly shows two components: a bright-end LF with a classical slope of –1.25 in each photometric band, and a steeper faint-end LF () in the dwarf galaxy region. The observed upturn of the faint galaxies has a location ranging from in the g band to in the z band. To study the universality of the cluster LF we compare the individual cluster LFs with the composite luminosity function. In agreement with the composite LF, a single Schechter component is not a good fit for the majority of the clusters. We fit a Schechter function to the bright-end of the individual cluster LFs in the magnitude region brighter than the observed upturn of the dwarf galaxies. The bright-end of the galaxy clusters shows the same shape in all the systems. To study the behavior of the individual faint-end LF we define the Dwarf to Giant galaxy Ratio (DGR) of the single clusters. The distribution of DGR has a spread much larger than the statistical errors. The DGR clearly anti-correlates with both X-ray and optical cluster luminosities. This anti-correlation is most likely due to the choice of a fixed metric aperture for all the clusters. Therefore, because of this effect, the different cluster physical sizes must be taken into account before comparing the LF of different clusters.