DISCOVERY OF A VERY BRIGHT, STRONGLY LENSEDz= 2 GALAXY IN THE SDSS DR5

Abstract

We report on the discovery of a very bright z = 2.00 star-forming galaxy that is strongly lensed by a foreground z = 0.422 luminous red galaxy (LRG), SDSS J120602.09+514229.5. This system, nicknamed the "Clone," was found in a systematic search for bright arcs lensed by LRGs and brightest cluster galaxies in the Sloan Digital Sky Survey Data Release 5 sample. Follow-up observations on the Subaru 8.2 m telescope on Mauna Kea and the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory confirmed the lensing nature of this system. A simple lens model for the system, assuming a singular isothermal ellipsoid mass distribution, yields an Einstein radius of θEin = 3.82 ± 003 or 14.8 ± 0.1 h−1 kpc at the lens redshift. The total projected mass enclosed within the Einstein radius is 2.10 ± 0.03 × 1012 h−1 M☉, and the magnification factor for the source galaxy is 27 ± 1. Combining the lens model with our gVriz photometry, we find a (unlensed) star formation rate (SFR) for the source galaxy of 32 h−1 M☉ yr−1, adopting a fiducial constant SFR model with an age of 100 Myr and E(B − V) = 0.25. With an apparent magnitude of r = 19.8, this system is among the very brightest lensed z ⩾ 2 galaxies, and provides an excellent opportunity to pursue detailed studies of the physical properties of an individual high-redshift star-forming galaxy.