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arXiv · 1510.01336

Characterizing the Chemically-Enriched Circumgalactic Medium of ~38000 Luminous Red Galaxies in SDSS DR12

Yun-Hsin Huang·Hsiao-Wen Chen·Sean D. Johnson·Benjamin J. Weiner
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Abstract

We report a definitive detection of chemically-enriched cool gas around massive, quiescent galaxies at z~0.4-0.7. The result is based on a survey of 37621 luminous red galaxy (LRG)-QSO pairs in SDSS DR12 with projected distance d<500 kpc. The LRGs are characterized by a predominantly old (age>~1Gyr) stellar population with 13% displaying [OII] emission features and LINER-like spectra. Both passive and [OII]-emitting LRGs share the same stellar mass distribution with a mean of ~11.4 and a dispersion of 0.2 dex. Both LRG populations exhibit associated strong MgII absorbers out to d<500 kpc. The mean gas covering fraction at d<~120 kpc is _MgII > 15% and declines quickly to _MgII ~ 5% at d<~500 kpc. No clear dependence on stellar mass is detected for the observed MgII absorption properties. The observed velocity dispersion of MgII absorbing gas relative to either passive or [OII]-emitting LRGs is merely 60% of what is expected from virial motion in these massive halos. While no apparent azimuthal dependence is seen for _MgII around passive LRGs at all radii, a modest enhancement in _MgII is detected along the major axis of [OII]-emitting LRGs at d<50 kpc. The suppressed velocity dispersion of MgII absorbing gas around both passive and [OII]-emitting LRGs, together with an elevated _MgII along the major axis of [OII]-emitting LRGs at d<50 kpc, provides important insights into the origin of the observed chemically-enriched cool gas in LRG halos. We consider different scenarios and conclude that the observed MgII absorbers around LRGs are best-explained by a combination of cool clouds formed in thermally unstable LRG halos and satellite accretion through filaments.

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Yun-Hsin Huang, Hsiao-Wen Chen, Sean D. Johnson, Benjamin J. Weiner. 2015-10-05. Characterizing the Chemically-Enriched Circumgalactic Medium of ~38000 Luminous Red Galaxies in SDSS DR12. https://arxiv.org/abs/1510.01336

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