The CASSOWARY spectroscopy survey: a new sample of gravitationally lensed galaxies in SDSS

Abstract

Bright gravitationally lensed galaxies provide our most detailed view of galaxies at high redshift. Yet as a result of the small number of ultra-bright z~2 lensed systems with confirmed redshifts, most detailed spectroscopic studies have been limited in their scope. With the goal of increasing the number of bright lensed galaxies available for detailed follow-up, we have undertaken a spectroscopic campaign targeting wide separation (>3 arcsec) galaxy-galaxy lens candidates within the Sloan Digital Sky Survey (SDSS). Building on the earlier efforts of our CASSOWARY survey, we target a large sample of candidate galaxy-galaxy lens systems in SDSS using a well-established search algorithm which identifies blue arc-like structures situated around luminous red galaxies. In this paper, we present a new redshift catalog containing 25 lensed sources in SDSS confirmed through spectroscopic follow-up of candidate galaxy-galaxy lens systems. Included in this new sample are two of the brightest galaxies (r=19.6 and 19.7) galaxies known at z~2, a low metallicity (12 + log (O/H)~8.0) extreme nebular line emitting galaxy at z=1.43, and numerous systems for which detailed follow-up will be possible. The source redshifts span 0.9<z<2.5 (median redshift of 1.9), and their optical magnitudes are in the range 19.6<r<22.3. We present a brief source-by-source discussion of the spectroscopic properties extracted from our confirmatory spectra and discuss some initial science results. With more than 50 gravitationally lensed z>1 galaxies now confirmed within SDSS, it will soon be possible for the first time to develop generalized conclusions from detailed spectroscopic studies of the brightest lensed systems at high redshift.