The Padova-Millennium Galaxy and Group Catalogue (PM2GC): the group-finding method and the PM2GC catalogues of group, binary and single field galaxies

Abstract

We present the construction and describe the properties of the Padova-Millennium Galaxy and Group Catalogue (PM2GC), a galaxy catalogue representative of the general field population in the local Universe. We characterize galaxy environments by identifying galaxy groups at 0.04<=z<=0.1 with a Friends-of-Friends (FoF) algorithm using a complete sample of 3210 galaxies brighter than MB = -18.7 taken from the Millennium Galaxy Catalogue (MGC, Liske et al. (2003)), a 38deg^2 photometric and spectroscopic equatorial survey. We identified 176 groups with at least three members, comprising in total 1057 galaxies and representing ~43 per cent of the general field population in that redshift range. The median redshift and velocity dispersion of our groups are 0.0823 and 192 km s^-1, respectively. 88 per cent of the groups have fewer than ten members, and 63 per cent have fewer than five members. Nongroup galaxies were subdivided into "inary" systems of two bright close companions, and "single" galaxies with no companion, in order to identify different environments useful for future scientific analysis. We performed a detailed comparison with the 2PIGG catalogue to validate the effectiveness of our method and the robustness of our results. Galaxy stellar masses are computed for all PM2GC galaxies, and found to be in good agreement with Sloan Digital Survey Data Release 7 (SDSS-DR7) mass estimates. The catalogues of PM2GC groups, group properties and galaxy properties in all environments are publicly available on theWorld Wide Web.Comment: 14 pages, 7 figures, 6 tables. MNRAS accepted, in press. Tables 2, 3, 4, 5, 6 early available or on request to autho