A Keck Survey of Gravitational Lens Systems. I. Spectroscopy of SBS 0909+532, HST 1411+5211, and CLASS B2319+051

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Abstract

We present new results from a continuing Keck program designed to study gravitational lens systems. We have obtained redshifts for three lens systems, SBS 0909+532, HST 1411+5211, and CLASS B2319+051. For all of these systems, either the source or lens redshift (or both) has been previously unidentified. Our observations provide some of these missing redshifts. We find (z_l, z_s) = (0.830, 1.377) for SBS 0909+532; (z_l, z_s) = (0.465, 2.811) for HST 1411+5211, although the source redshift is still tentative; and (z_l,1, z_l,2) = (0.624, 0.588) for the two lensing galaxies in CLASS B2319+051. The background radio source in B2319+051 has not been detected optically; its redshift is, therefore, still unknown. We find that the spectral features of the central lensing galaxy in all three systems are typical of an early-type galaxy. The observed image splittings in SBS 0909+532 and HST 1411+5211 imply that the masses within the Einstein ring radii of the lensing galaxies are 1.4 × 10^(11) and 2.0 ×10^(11) h^(-1) M_⊙, respectively. The resulting B-band mass-to-light ratio (M/L) for HST 1411+5211 is 41.3 ± 1.2 h (M/L)_⊙, a factor of ~5 times higher than the average early-type lensing galaxy. This large mass-to-light ratio is almost certainly the result of the additional mass contribution from the cluster CL 3C 295 at z = 0.46. For the lensing galaxy in SBS 0909+532, we measure (M/L)B = 4^(+11)_(-3) h (M/L)⊙, where the large errors are the result of significant uncertainty in t_he galaxy luminosity. While we cannot measure directly the mass-to-light ratio of the lensing galaxy in B2319+051, we estimate that (M/L)_B is between 3–7 h (M/L)_⊙.

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