SPATIALLY RESOLVED GALAXY STAR FORMATION AND ITS ENVIRONMENTAL DEPENDENCE. II. EFFECT OF THE MORPHOLOGY–DENSITY RELATION

Abstract

In this second of a series of papers on spatially resolved star formation, we investigate the impact of the density-morphology relation of galaxies on the spatial variation of star formation (SF) and its dependence on environment. We find that while a density-morphology relation is present for the sample, it cannot solely explain the observed suppression of SF in galaxies in high-density environments. We also find that early-type and late-type galaxies exhibit distinct radial star formation rate (SFR) distributions, with early types having an SFR distribution that extends further relative to the galaxy scale length, compared to late types at all densities. We find that a suppression of SF in the highest density environments is found in the highest star-forming galaxies for both galaxy types. This suppression occurs in the innermost regions in late types (r {<=} 0.125 Petrosian radii), and further out in radius in early types (0.125 Petrosian radii < r {<=} 0.25 Petrosian radii). When the full sample is considered no clear suppression of SF is detected, indicating that the environmental trends are driven only by the highest SF galaxies. We demonstrate that the density-morphology relation alone cannot account for the suppression of SF in the highest densitymore » environments. This points to an environmentally governed evolutionary mechanism that affects the SF in the innermost regions in both early- and late-type galaxies. We suggest that this is a natural consequence of the 'downsizing' of SF in galaxies.« less