A Multi-Wavelength Study of Low Redshift Clusters of Galaxies II. Environmental Impact on Galaxy Growth

Galaxy clusters provide powerful laboratories for the study of galaxy evolution, particularly the origin of correlations of morphology and star formation rate (SFR) with density. We construct visible to MIR spectral energy distributions (SEDs) of cluster galaxies and use them to measure stellar masses and SFRs in eight low redshift clusters, which we examine as a function of environment. A partial correlation analysis indicates that SFR depends strongly on R/R200 (> 99.9% confidence) and is independent of projected local density at fixed radius. SFR also shows no residual dependence on stellar mass. We therefore conclude that interactions with the intra-cluster medium drive the evolution of SFRs in cluster galaxies. A merged sample of galaxies from the five most complete clusters shows 〈SFR〉 ∝ (R/R200) for galaxies with R/R200 ≤ 0.4. A decline in the fraction of SFGs toward the cluster center contributes most of this effect, but it is accompanied by a reduction in SFRs among star-forming galaxies (SFGs) near the cluster center. The increase in the fraction of SFGs toward larger R/R200 and the isolation of SFGs with reduced SFRs near the cluster center are consistent with ram pressure stripping as the mechanism to truncate star formation in galaxy clusters. We conclude that stripping drives the properties of SFGs over the range of radii we examine. We also find that galaxies near the cluster center are more massive than galaxies farther out in the cluster at ∼ 3.5σ, which suggests that cluster galaxies experience dynamical relaxation during the course of their evolution. Subject headings: galaxies:clusters:general, galaxies:evolution, galaxies:star formation, infrared radiation The National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson AZ 85719