Keck Spectroscopy of Three Gravitational Lens Systems Discovered in the JVAS and CLASS Surveys

We present spectra of three gravitational lens systems taken with the Low Resolution Imaging Spectrograph on the W. M. Keck telescopes. All of the systems were discovered in the JVAS and CLASS radio surveys, which were designed to find lenses suitable for measuring H0. Previous spectra of these systems had low signal-to-noise ratios, and only one of the source redshifts was secure. Our observations provide unambiguous lens and source redshifts for all of the systems, with (zl, zs) = (0.4060, 1.339), (0.5990, 1.535), and (0.4144, 1.589) for B0712+472, B1030+074, and B1600+434, respectively. The observed image splittings in the systems imply that the masses of the lensing galaxies within their Einstein rings are 5.4 × 1010, 1.2 × 1011, and 6.3 × 1010 h-1 M⊙. The resulting V-band mass-to-light ratios for B0712+472 and B1030+074, measured inside their Einstein ring radii, are ∼10 h (M/L)⊙,V, slightly higher than values observed in nearby elliptical galaxies. For B1600+434, the mass-to-light ratio is 48 h (M/L)⊙,V. This high value can be explained, at least in part, by the prominent dust lane running through the galaxy. Two of the three lens systems show evidence of variability, so monitoring may yield a time delay and thus a measurement of H0.