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Published July 21, 2005 | Published + Accepted Version
Journal Article Open

CLASS B0631+519: last of the Cosmic Lens All-Sky Survey lenses


We report on the discovery of the new gravitational lens system CLASS B0631+519. Imaging with the Very Large Array, the Multi-Element Radio-Linked Interferometer Network (MERLIN) and the Very Long Baseline Array (VLBA) reveals a doubly imaged flat-spectrum radio core, a doubly imaged steep-spectrum radio lobe and possible quadruply imaged emission from a second lobe. The maximum separation between the lensed images is 1.16 arcsec. High-resolution mapping with the VLBA at 5 GHz resolves the most magnified image of the radio core into a number of subcomponents spread across approximately 20 mas. No emission from the lensing galaxy or an odd image is detected down to 0.31 mJy (5σ) at 8.4 GHz. Optical and near-infrared imaging with the Advanced Camera for Surveys and the Near-Infrared Camera and Multi-Object Spectrometer on the Hubble Space Telescope (HST) show that there are two galaxies along the line of sight to the lensed source, as previously discovered by optical spectroscopy. We find that the foreground galaxy at z= 0.0896 is a small irregular, and that the other, at z= 0.6196 is a massive elliptical, which appears to contribute the majority of the lensing effect. The host galaxy of the lensed source is detected in the HST near-infrared imaging as a set of arcs, which form a nearly complete Einstein ring. Mass modelling using non-parametric techniques can reproduce the near-infrared observations and indicates that the small irregular galaxy has a (localized) effect on the flux density distribution in the Einstein ring at the 5–10 per cent level.

Additional Information

© 2005 RAS. Accepted 2005 May 3. Received 2005 April 28; in original form 2005 April 6. The authors would like to thank Shude Mao for useful discussions, and the referee, Stephen Warren, for comments that improved the clarity of the paper. MERLIN is a UK National Facility operated by the University of Manchester on behalf of the UK Particle Physics and Astronomy Research Council (PPARC). The VLA and VLBA are operated by the NRAO for Associated Universities Inc., under a cooperative agreement with the National Science Foundation (NSF). This research used observations with the HST, obtained at the Space Telescope Science Institute, which is operated by Associated Universities for Research in Astronomy, Inc., under National Aeronautics and Space Administration (NASA) contract NAS 5-26555; these observations are associated with HST programme 9744. The WHT is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, Caltech, under contract with NASA. This publication makes use of data products from the 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Centre/California Institute of Technology, funded by NASA and the NSF. This work was supported by the European Community's Sixth Framework Marie Curie Research Training Network Programme, Contract No. MRTN-CT-2004-505183 'ANGLES'. RDB is supported by NSF grants AST-0206286 and AST-0444059. TY, JPM, MAN and PMP acknowledge the receipt of PPARC studentships.

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Accepted Version - 0505093


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