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The star formation history of luminous red galaxies hosting Mg ii absorbers

Authors

  • Jean-René Gauthier,

    Corresponding author
    1. Department of Astronomy and Astrophysics, Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
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  • Hsiao-Wen Chen

    Corresponding author
    1. Department of Astronomy and Astrophysics, Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
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  • This paper includes data gathered with the 2.5-m du Pont telescope located at Las Campanas Observatory, Chile, and with the Apache Point Observatory 3.5-m telescope, which is owned and operated by the Astrophysical Research Consortium.

E-mail: gauthier@oddjob.uchicago.edu (J-RG); hchen@oddjob.uchicago.edu (H-WC)

ABSTRACT

We present a spectroscopic sample of z≈ 0.5 luminous red galaxies (LRGs) that are located within physical projected distances inline image 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 inline image 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.

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