Journal Article

The star formation history of luminous red galaxies hosting Mg <span class="smallCaps">ii</span> absorbers*

Jean-René Gauthier and Hsiao-Wen Chen

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 418, issue 4, pages 2730-2735
Published in print December 2011 | ISSN: 0035-8711
Published online December 2011 | e-ISSN: 1365-2966 | DOI:
The star formation history of luminous red galaxies hosting Mg ii absorbers*

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We present a spectroscopic sample of z≈ 0.5 luminous red galaxies (LRGs) that are located within physical projected distances of a quasi-stellar object (QSO) sightline. Of the 37 LRGs in our sample, eight have associated Mg ii absorbers with rest-frame equivalent width Wr(2796)>0.3 Å and velocity separation km s−1 and 29 do not have associated Mg ii absorbers to a 2σ limit of Wr(2796)=0.3 Å. We perform a stellar population synthesis analysis using stacked spectra of the Mg ii absorbing and non-absorbing LRG subsamples. We find that LRGs with or without associated Mg ii absorbers share similar star formation histories and are best described by old stellar population models (≳1 Gyr). Younger stellar populations (≲1 Gyr) fail to reproduce their spectra. These findings are consistent with the lack of [O ii] emission features in the LRG spectra. The primarily old stellar populations in the LRGs indicate that starburst-driven outflows are unlikely to explain the observed Mg ii absorbers at large distances from the LRGs. In addition, the spectroscopic LRG sample allows us to derive a sensitive constraint for the cool gas covering fraction of 〈κ〉= 14 ± 6 per cent in the LRG haloes for absorbers of Wr(2796)>0.3 Å. Finally, we speculate on the origin of the observed Mg ii absorbers around the LRGs.

Keywords: galaxies: evolution; quasars: absorption lines

Journal Article.  4087 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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