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Published May 1, 2004 | Published + Accepted Version
Journal Article Open

Keck spectroscopy of Cosmic Lens All-Sky Survey gravitational lenses


We present the optical spectra of four newly discovered gravitational lenses from the Cosmic Lens All‐Sky Survey (CLASS). These observations were carried out using the Low‐Resolution Imaging Spectrograph on the W. M. Keck‐I Telescope as part of a programme to study galaxy‐scale gravitational lenses. From our spectra, we found the redshift of the background source in CLASS B0128+437 (z_s= 3.1240 ± 0.0042) and the lensing galaxy redshifts in CLASS B0445+123 (z_1= 0.5583 ± 0.0003) and CLASS B0850+054 (z_l= 0.5883 ± 0.0006). Intriguingly, we also discovered that CLASS B0631+519 may have two lensing galaxies (zl,1= 0.0896 ± 0.0001, z_(l,2)= 0.6196 ± 0.0004). We also found a single unidentified emission line from the lensing galaxy in CLASS B0128+437 and the lensed source in CLASS B0850+054. We find the lensing galaxies in CLASS B0445+123 and CLASS B0631+519 (l, 2) to be early‐type galaxies with Einstein radii of 2.8–3.0 h^(−1) kpc. The deflector in CLASS B0850+054 is a late‐type galaxy with an Einstein radius of 1.6 h^(−1) kpc.

Additional Information

© 2004 RAS. Accepted 2004 January 14. Received 2004 January 13; in original form 2003 December 2. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This research has made use of the NASA/IPAC Extragalactic Data base (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. JPM acknowledges the receipt of a PPARC studentship. LVEK acknowledges the support from an STScI Fellowship grant. RDB is supported by NSF grant AST–0206286.

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