C. M. Carollo, A. Cibinel, S. J. Lilly, F. Miniati, P. Norberg, J. D. Silverman, J. van Gorkom, E. Cameron, A. Finoguenov, A. Pipino, C. S. Rudick, T. Lu, Y. Peng
The Zurich Environmental Study (ZENS) is designed to compare the dependence of z=0 galaxy structural and stellar populations diagnostics at constant stellar mass on four measures of the environment: the mass of the host group halos; the projected distance from the center of the halo; the rank of galaxies as central or satellites; and the filamentary LSS density on which the groups reside. The complete ZENS sample contains 1630 galaxies in 141~10^{12.5-14}M_sun 2PIGG groups at z~0.06. We outline the survey motivation and describe novel approaches to quantify the environments of galaxies. We introduce a set of self-consistency checks to define the group centers and to rank galaxies as centrals or satellites, and describe an Nth-nearest-neighbor approach to determine the LSS density field using groups as tracers. We publish the ZENS catalogue of galaxy and group properties, which combines the environmental diagnostics presented here with structural and SED measurements described in subsequent papers. In a suite of follow-up articles we investigate which measures of environment most strongly affect the galaxy properties. In this paper, we highlight the following: a) For ~40% of <10^13.5 M_sun groups there is no self-consistent identification of a central galaxy and ~10-20% of groups may be dynamically young systems; b) Properties of central galaxies in the relaxed and unrelaxed groups are similar indicating that central galaxies are not regulated by their environment but exclusively by their stellar mass; c) Satellites with M>10^10 M_sun in relaxed and unrelaxed groups, as well as centrals, have similar size, color and star formation rate distributions, but at lower galaxy masses satellites are ~0.1mag bluer in unrelaxed groups. This indicates that physical processes occurring in dynamically-relaxed group halos are important to quench star formation in low mass satellites.[Abridged]
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http://arxiv.org/abs/1206.5807
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