The DEEP2 Galaxy Redshift Survey: The Voronoi-Delaunay Method catalog of galaxy groups

TL;DR

This paper presents a publicly available catalog of galaxy groups from the DEEP2 survey, optimized using mock catalogs and the Voronoi-Delaunay Method, with detailed analysis of its completeness, purity, and classification accuracy.

Contribution

It introduces a new galaxy group catalog from DEEP2, optimized with mock catalogs and the Voronoi-Delaunay Method, including an assessment of its reliability and dependence on cosmology.

Findings

The catalog contains 1165 groups in EGS and 1295 at z>0.6.

The group-finder achieves 72% completeness and 61% purity.

Approximately 70% of true group galaxies are correctly classified.

Abstract

We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the DEEP2 Galaxy Redshift Survey, including the Extended Groth Strip (EGS). The catalog contains 1165 groups with two or more members in the EGS over the redshift range 0<z<1.5 and 1295 groups at z>0.6 in the rest of DEEP2. 25% of EGS galaxies and 14% of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay Method, after it has been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. (2005). In the optimization effort, we have taken particular care to ensure that the mock catalogs resemble the data as closely as possible, and we have fine-tuned our methods separately on mocks constructed for the EGS and the rest of DEEP2. We have also probed the effect of the assumed cosmology on our inferred group-finding efficiency by performing our optimization on three different mock catalogs with different background cosmologies, finding large differences in the group-finding success we can achieve for these different mocks. Using the mock catalog whose background cosmology is most consistent with current data, we estimate that the DEEP2 group catalog is 72% complete and 61% pure (74% and 67% for the EGS) and that the group-finder correctly classifies 70% of galaxies that truly belong to groups, with an additional 46% of interloper galaxies contaminating the catalog (66% and 43% for the EGS). (Abridged)