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

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 1.4x10¹¹ and 2.0x10¹¹ h^-1 M_solar, respectively. The resulting B-band mass-to-light ratio (M/L) for HST 1411+5211 is 41.3+/-1.2 h (M/L)_solar, 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)_solar, where the large errors are the result of significant uncertainty in the 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)_solar.