Journal Article

CASSOWARY 20: a wide separation Einstein Cross identified with the X-shooter spectrograph*

Max Pettini, Lise Christensen, Sandro D'Odorico, Vasily Belokurov, N. Wyn Evans, Paul C. Hewett, Sergey Koposov, Elena Mason and Joël Vernet

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 4, pages 2335-2343
Published in print March 2010 | ISSN: 0035-8711
Published online March 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.16090.x
CASSOWARY 20: a wide separation Einstein Cross identified with the X-shooter spectrograph*

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We have used spectra obtained with X-shooter, the triple arm optical–infrared spectrograph recently commissioned on the Very Large Telescope of the European Southern Observatory, to confirm the gravitational lens nature of the CAmbridge Sloan Survey Of Wide ARcs in the skY (CASSOWARY) candidate CSWA 20. This system consists of a luminous red galaxy at redshift zabs= 0.741, with a very high velocity dispersion, σlens≃ 500 km s−1, which lenses a blue star-forming galaxy at zem= 1.433 into four images with a mean separation of ∼6 arcsec. The source shares many of its properties with those of UV-selected galaxies at z= 2–3: it is forming stars at a rate SFR ≃ 25 M yr−1, has a metallicity of ∼1/4 solar and shows nebular emission from two components separated by 0.4 arcsec (in the image plane), possibly indicating a merger. It appears that foreground interstellar material within the galaxy has been evacuated from the sightline along which we observe the starburst, giving an unextinguished view of its stars and H ii regions. CSWA 20, with its massive lensing galaxy producing a high magnification of an intrinsically luminous background galaxy, is a promising target for future studies at a variety of wavelengths.

Keywords: gravitational lensing; galaxies: evolution; galaxies: structure

Journal Article.  7012 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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