RASS-SDSS galaxy cluster survey - VI. The dependence of the cluster SFR on the cluster global properties

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 (Sigma SFR), the cluster total stellarmass (M-star), 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 (sigma(v)), virial mass (M-200), and X-ray luminosity (L-X). All cluster global quantities are corrected for projection effects before the analysis. Galaxy SFRs and stellar masses are taken from the catalog of Brinchmann et al. (2004), which is based on SDSS spectra. We only consider galaxies with M-r <= -20.25 in our analysis, and exclude AGNs. We find that both SSFR and M-star are correlated with all the cluster global quantities. A partial correlation analysis shows that all the correlations are induced by the fundamental one between SSFR and Ngal, hence there is no evidence that the cluster properties affect the mean Sigma SFR or M-star per galaxy. The relations between SSFR and M-star, on the one side, and both N-gal and M-200, on the other side, are linear, i.e. we see no evidence that different clusters have different SFR or different M-star per galaxy and per unit mass. The fraction f(SF) does not depend on any cluster property considered, while fb does depend on L-X. We note that a significant fraction of star-forming cluster galaxies are red (similar to 25% of the whole cluster galaxy population). We conclude that the global cluster properties are unable to affect the SF 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.