A Search for Disk-Galaxy Lenses in the Sloan Digital Sky Survey

We present the first automated spectroscopic search for disk-galaxy lenses, using the Sloan Digital Sky Survey database. We follow up eight gravitational lens candidates, selected among a sample of ∼ 40000 candidate massive disk galaxies, using a combination of ground-based imaging and long-slit spectroscopy. We confirm two gravitational lens systems: one probable disk galaxy, and one probable S0 galaxy. The remaining systems are four promising disk-galaxy lens candidates, as well as two probable gravitational lenses whose lens galaxy might be an S0 galaxy. The redshifts of the lenses are zlens ∼ 0.1. The redshift range of the background sources is zsource ∼ 0.3 − 0.7. The systems presented here are (confirmed or candidate) galaxy-galaxy lensing systems, that is, systems where the multiple images are faint and extended, allowing an accurate determination of the lens galaxy mass and light distributions without contamination from the background galaxy. Moreover, the low redshift of the (confirmed or candidates) lens galaxies is favorable for measuring rotation points to complement the lensing study. We estimate the rest-frame total mass-to-light ratio within the Einstein radius for the two confirmed lenses: we find Mtot/LI = 1.5 ± 0.9 for SDSS J081230.30+543650.9, and Mtot/LI = 5.4 ± 1.5 for SDSS J145543.55+530441.2 (all in solar units). Hubble Space Telescope imaging is needed to further study the systems. Subject headings: dark matter — galaxy: fundamental parameters (M/L) — galaxy: spiral — galaxy: structure — gravitational lensing