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arXiv · 0909.3301

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·Joel Vernet
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Abstract

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 CASSOWARY candidate CSWA 20. This system consists of a luminous red galaxy at redshift z(abs) = 0.741, with a very high velocity dispersion sigma(lens) = 500 km/s, which lenses a blue star-forming galaxy at z(em) = 1.433 into four images with mean separation of about 6 arcseconds. The source shares many of its properties with those of UV-selected galaxies z = 2-3: it is forming stars at a rate of 25 solar masses per year, has a metallicity of about 1/4 solar, and shows nebular emission from two components separated by 0.4 arcseconds in the image plane, possibly indicating a merger. It appears that foreground interstellar material within the galaxy has been evacuated from the sight-line 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.

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Max Pettini, Lise Christensen, Sandro D'Odorico, Vasily Belokurov, N. Wyn Evans, Paul C. Hewett, Sergey Koposov, Elena Mason, Joel Vernet. 2009-11-24. CASSOWARY 20: a Wide Separation Einstein Cross Identified with the X-shooter Spectrograph. https://doi.org/10.1111/j.1365-2966.2009.16090.x

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