The Zurich Environmental Study (ZENS) of Galaxies in Groups along the Cosmic Web: III. Galaxy Photometric Measurements and the Spatially-Resolved Color Properties of Early- and Late-Type Satellites in Diverse Environments

Abstract

We present photometric measurements for the 769 z~0 galaxies in the first-epoch data of the Zurich Environmental Study (ZENS). The main thrust of ZENS is to study the dependence of galaxy properties on the mass of the host group M_GROUP, the group-centric distance R/R_200, and the large-scale structure overdensity delta_LSS. For the galaxies and, if possible, for their bulge and disk components, the photometric measurements consist of resolved (B-I) colors, color gradients, color dispersions, and color maps, as well as stellar masses and star-formation rates. We classify ZENS galaxies into quiescent, moderately star-forming, and strongly star-forming systems using a combination of spectral features and broad-band NUV-optical colors. This optimally distinguishes quiescent systems from dust-reddened star-forming galaxies, which contribute up to 50% to the (B-I) "red sequence" at ~10^10 Msun. Our photometric database is made available for public use in the global ZENS catalog. We study how (B-I) colors, color gradients and color dispersion of bulge-dominated and disk-dominated satellites depend on M_GROUP, R/R_200 and delta_LSS at fixed stellar mass. We find that delta_LSS does not have an impact on either the colors, the color gradients or the color scatter of either disk- or bulge-dominated satellites. The latter are rather insensitive to any environment. The strongest environmental effects are found for disk-dominated satellites with group-centric distance. At constant galaxy mass, these satellites are redder in the group cores compared with the outskirts; at M>~10^10 Msun, they also have shallower color gradients within 0.6R_200 than at larger group-centric distances. Our results support a picture where galaxies undergo a relatively fast quenching of their star formation in the outer disks on timescales <~2 Gyr, as they progressively move deeper inside the group potential.