With a large, unique spectroscopic survey in the fields of 28 galaxy-scale
strong gravitational lenses, we identify groups of galaxies in the 26
adequately-sampled fields. Using a group finding algorithm, we find 210 groups
with at least five member galaxies; the median number of members is eight. Our
sample spans redshifts of 0.04 β€zgrpββ€ 0.76 with a median of 0.31,
including 174 groups with 0.1<zgrpβ<0.6. Groups have radial velocity
dispersions of 60 β€Οgrpββ€ 1200 km sβ1 with a median of 350
km sβ1. We also discover a supergroup in field B0712+472 at z= 0.29
consisting of three main groups. We recover groups similar to βΌ 85% of
those previously reported in these fields within our redshift range of
sensitivity and find 187 new groups with at least five members. The properties
of our group catalog, specifically 1) the distribution of Οgrpβ, 2)
the fraction of all sample galaxies that are group members, and 3) the fraction
of groups with significant substructure, are consistent with those for other
catalogs. The distribution of group virial masses agrees well with theoretical
expectations. Of the lens galaxies, 12 of 26 (46%) (B1422+231, B1600+434,
B2114+022, FBQS J0951+2635, HE0435-1223, HST J14113+5211, MG0751+2716,
MGJ1654+1346, PG 1115+080, Q ER 0047-2808, RXJ1131-1231, and WFI J2033-4723)
are members of groups with at least five galaxies, and one more (B0712+472)
belongs to an additional, visually identified group candidate. There are groups
not associated with the lens that still are likely to affect the lens model; in
six of 25 (24%) fields (excluding the supergroup), there is at least one
massive (Οgrpββ₯ 500 km sβ1) group or group candidate projected
within 2β² of the lens.Comment: 87 pages, 8 figures, a version of this was published in Ap