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 the system to lie in a group with a velocity dispersion of 100 km/s and at least six members. B2319+051 has a large group in its immediate foreground with at least 10 members and a velocity dispersion of 460 km/s and another in the background of the lens with a velocity dispersion of 190 km/s. There are several other small groups in the fields of these lens systems, and we describe the properties of these moderate redshift groups. Furthermore, we quantify the effects of these group structures on the gravitational lenses and find a ~5% correction to the derived value of H_0 for B1600+434. 
M. W. Auger (1), C. D. Fassnacht (1), A. L. Abrahamse (1), L. M. Lubin   (1), and G. K. Squires (2) ((1) UC Davis, (2) Spitz...