The Gravitational Lens-Galaxy Group Connection. II. Groups Associated with B2319+051 and B1600+434

We report on the results of a spectroscopic survey of the environments of the gravitational lens systems CLASS B1600+434 (z_l = 0.41,z_s = 1.59) and CLASS B2319+051 (z_l = 0.62). The B1600+434 system has a time delay measured for it, and we find that the system lies in a group with a velocity dispersion of 90 km s^-1 and at least seven members. B2319+051 has a large group in its immediate foreground with at least 10 members and a velocity dispersion of 460 km s^-1 and another in the background of the lens with a velocity dispersion of 190 km s^-1. These systems increase the sample of spectroscopically confirmed groups associated with strong lenses by 20%. We find that modeling groups as single group-sized halos produces only small corrections (κ_env,grp ∼ 0.01) to lensing models. However, the very local environments, i.e., galaxies within ∼15'' of the lensing galaxy, have stronger effects on the lens models of the systems studied here. We quantify the effects of the local environment on the lens models and find up to an ≈10% correction to the derived value of H₀ for B1600+434 compared to models that do not account for the lens environment.