RASS-SDSS galaxy cluster survey

VI. The dependence of the cluster SFR on the cluster global properties

¹ European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching, Germany e-mail: ppopesso@eso.org
² INAF - Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy
³ Max-Planck-Institut fur extraterrestrische Physik, 85748 Garching, Germany

Received: 4 April 2006
Accepted: 1 September 2006

Abstract

We aim at quantifying the relationships between star formation in cluster galaxies and global cluster properties. Using a subsample of 79 nearby clusters from the RASS-SDSS galaxy cluster catalogue of Popesso et al. (2005, A&A, 433, 431), we perform a regression analysis between the cluster integrated star formation rate (), the cluster total stellar mass (), the fractions of star forming (f_SF) and blue (f_b) galaxies and other cluster global properties, namely its richness (N_gal, i.e. the total number of cluster members within the cluster virial radius, corrected for incompleteness), velocity dispersion (), virial mass (M₂₀₀), and X-ray luminosity (L_X). All cluster global quantities are corrected for projection effects before the analysis. Galaxy s and stellar masses are taken from the catalog of Brinchmann et al. (2004), which is based on SDSS spectra. We only consider galaxies with in our analysis, and exclude AGNs. We find that both  and  are correlated with all the cluster global quantities. A partial correlation analysis shows that all the correlations are induced by the fundamental one between and N_gal, hence there is no evidence that the cluster properties affect the mean  or  per galaxy. The relations between  and , on the one side, and both N_gal and M₂₀₀, on the other side, are linear, i.e. we see no evidence that different clusters have different  or different  per galaxy and per unit mass. The fraction f_SF does not depend on any cluster property considered, while f_b does depend on L_X. We note that a significant fraction of star-forming cluster galaxies are red (~25% of the whole cluster galaxy population). We conclude that the global cluster properties are unable to affect the  properties of cluster galaxies, but the presence of the X-ray luminous intra-cluster medium can affect their colors, perhaps through the ram-pressure stripping mechanism.