AN OPTICAL GROUP CATALOG TO<i>z</i>= 1 FROM THE zCOSMOS 10 k SAMPLE

Abstract

We present a galaxy group catalog spanning the redshift range 0.1 lsim z lsim 1 in the ~ 1.7 deg2 COSMOS field, based on the first ~10,000 zCOSMOS spectra. The performance of both the Friends-of-Friends (FOF) and Voronoi-Delaunay method (VDM) approaches to group identification has been extensively explored and compared using realistic mock catalogs. We find that the performance improves substantially if groups are found by progressively optimizing the group-finding parameters for successively smaller groups, and that the highest fidelity catalog, in terms of completeness and purity, is obtained by combining the independently created FOF and VDM catalogs. The final completeness and purity of this catalog, both in terms of the groups and of individual members, compares favorably with recent results in the literature. The current group catalog contains 102 groups with N &gt;= 5 spectroscopically confirmed members, with a further ~700 groups with 2