Spectroscopic Gravitational Lens Candidates in the CNOC2 Field Galaxy Redshift Survey

Abstract

We present five candidate gravitational lenses discovered spectroscopically in the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2), along with one found in followup observations. Each has a secure redshift based on several features, plus a discrepant emission line which does not match any known or plausible feature and is visible in multiple direct spectral images. We identify these lines as Lyman-alpha or [OII] emission from galaxies lensed by, or projected onto, the CNOC2 target galaxies. Einstein radii estimated from the candidate deflector galaxy luminosities indicate that for two candidates the lines are probably [OII] from projected z<1 galaxies (consistent with the detection of H-beta as well as [OII] in one of them), but that in the remaining four cases the lines could be Ly-alpha from lensed z>3 galaxies. We estimate that only 1.9+-0.7 [OII]-emitting galaxies are expected to project onto target galaxies in the original CNOC2 sample, consistent with three or four of the six candidates being true gravitational lenses.

arXiv comment15 pages, 4 figures, AJ in press

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• Sloan Digital Sky Survey Spectroscopic Lens Search. I. Discovery of Intermediate-Redshift Star-Forming Galaxies Behind Foreground Luminous Red Galaxies
• The Gravitational Lens CFRS03.1077
• Magellan Spectroscopy of the Galaxy Cluster RX J1347.5-1145: Redshift Estimates for the Gravitationally Lensed Arcs
• Spectroscopic detection of quasars in the 2dF Galaxy Redshift Survey
• The 2dF gravitational lens survey