Journal Article

X-shooter observations of the gravitational lens system CASSOWARY 5*

Lise Christensen, Sandro D'Odorico, Max Pettini, Vasily Belokurov, N. Wyn Evans, Melinda Kellogg and Joël Vernet

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 4, pages 2616-2626
Published in print August 2010 | ISSN: 0035-8711
Published online August 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16860.x
X-shooter observations of the gravitational lens system CASSOWARY 5*

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We confirm an eighth gravitational lens system in the CAmbridge Sloan Survey Of Wide ARcs in the skY (CASSOWARY) catalogue. Exploratory observations with the X-shooter spectrograph on the Very Large Telescope of the European Southern Observatory show the system CASSOWARY 5 (CSWA 5) to consist of at least three images of a blue star-forming galaxy at z= 1.0686, lensed by an apparent foreground group of red galaxies, one of which is at z= 0.3877. The lensed galaxy exhibits a rich spectrum with broad interstellar absorption lines and a wealth of nebular emission lines. Preliminary analysis of these features shows the galaxy to be young, with an age of ∼25–50 Myr. With a star formation rate of ∼20 M yr−1, the galaxy has already assembled a stellar mass M*∼ 3 × 109 M and reached half-solar metallicity. Its blue spectral energy distribution and Balmer line ratios suggest negligible internal dust extinction. A more in-depth analysis of the properties of this system is currently hampered by the lack of a viable lensing model. However, it is already clear that CSWA 5 shares many of its physical characteristics with the general population of UV-selected galaxies at redshifts z= 1–3, motivating further study of both the source and the foreground mass concentration responsible for the gravitational lensing.

Keywords: gravitational lensing: strong; galaxies: abundances; galaxies: evolution

Journal Article.  8035 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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