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