2006ApJ...641..169M

We present the first results from our spectroscopic survey of strong gravitational lens environments. Six of the eight lens galaxies in our sample belong to a poor group of galaxies, three of which are newly discovered here (those associated with BRI 0952-0115, MG 1654+1346, and B2114+022). For the three previously known groups (surrounding MG 0751+2716, PG 1115+080, and B1422+231), we more than double the number of group members. The group velocity dispersions range from 110⁺¹⁷⁰_–80to 470⁺¹⁰⁰_–90km/s. The higher velocity dispersions of the richer groups (MG 0751, PG 1115, and B1422) are consistent with those of nearby X-ray-luminous groups; the lower velocity dispersions of the other groups are more typical of dynamically younger groups. The lens galaxy is the brightest member in fewer than half of the groups. The brightest group galaxy is an early-type galaxy that, at least for the poorer groups, lies outside the group centroid and on an orbit indistinguishable from other group members. In at least three cases, MG 0751, PG 1115, and B1422, the group environment significantly affects the lens potential. These happen to be the quadruply imaged lenses in our sample, suggesting a connection between image configuration and environment. Finally, we assess the importance of line-of-sight mass structures, showing that, in principle, the lens potential may be affected by structures lying at a wide range of spatial and redshift offsets from the lens. We quantify the real line-of-sight effects, finding that four of the eight systems have substantial interloping structures and that at least one of those (behind MG 0751) significantly affects the lens potential.