Disentangling Morphology, Star Formation, Stellar Mass, and Environment in Galaxy Evolution

We present a study of the spectroscopic and photometric properties ofgalaxies in six nearby clusters. We perform a partial correlation analysis onour dataset to investigate whether the correlation between star formation ratesin galaxies and their environment is merely another aspect of correlations ofmorphology, stellar mass, or mean stellar age with environment, or whether starformation rates vary independently of these other correlations. We find aresidual correlation of ongoing star formation with environment, indicatingthat even galaxies with similar morphologies, stellar masses, and mean stellarages have lower star formation rates in denser environments. Thus, the currentstar formation gradient in clusters is not just another aspect of themorphology-density, stellar mass-density, or mean stellar age-densityrelations. Furthermore, the star formation gradient cannot be solely the resultof initial conditions, but must partly be due to subsequent evolution through amechanism (or mechanisms) sensitive to environment. Our results constitute atrue ``smoking gun'' pointing to the effect of environment on the laterevolution of galaxies.Comment: 31 pages, including 5 figures; accepted for publication in Ap