Star-formation rates of cluster galaxies: nature vs nurture

Abstract

We analyzed 17 galaxy clusters, and investigated, for the first time, the dependence of the SFR and sSFR as a function of projected distance (as a proxy for environment) and stellar mass for cluster galaxies in an intermediate-to-high redshift range ($0.4 < z < 0.9$). We used up to nine flux points (BVRIZYJHKs magnitudes), its errors and redshifts to compute M$_{\rm{star}}$, SFR and sSFR through spectral energy distribution fitting technique. We use a z-dependent sSFR value to distinguish star-forming (SF) from quiescent galaxies. To analyse the SFR and sSFR history we split our sample in two redshift bins: galaxies at $0.4 < z < 0.6$ and $0.6 < z < 0.9$. We separate the effects of environment and stellar mass on galaxies by comparing the properties of star-forming and quiescent galaxies at fixed environment (projected radius) and fixed stellar mass. For the selected spectroscopic sample of more than 500 galaxies, the well-known correlation between SFR and $M_{\rm star}$ is already in place at $z \sim 0.9$, for both SF and quenched galaxies. Our results are consistent with no evidence that SFR (or sSFR) depends on environment, suggesting that for cluster galaxies at an intermediate-to-high redshift range, mass is the primary characteristic that drives SFR.