Characterizing the chemically enriched circumgalactic medium of ∼38 000 luminous red galaxies in SDSS DR12

We report a definitive detection of chemically enriched cool gas around massive quiescent galaxies at z approximate to 0.4-0.7. The result is based on a survey of 37 621 luminous red galaxy (LRG)quasi-stellar object pairs in SDSS DR12 with projected distance d < 500 kpc. The LRGs are characterized by a predominantly old stellar population (age greater than or similar to 1 Gyr) with 13 per cent displaying [O II] emission features and LINER-like spectra. Both passive and [O II]-emitting LRGs share the same stellar mass distribution with a mean of < log (M-*/M-circle dot)> approximate to 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 less than or similar to 120 kpc is (MgII) > 15 per cent and declines quickly to (MgII) approximate to 5 per cent at d less than or similar to 500 kpc. No clear dependence on stellar mass is detected for the observed Mg II absorption properties. The observed velocity dispersion of MgII-absorbing gas relative to either passive or [O II]-emitting LRGs is merely 60 per cent of what is expected from virial motion in these massive haloes. 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 [O II]-emitting LRGs at d < 50 kpc. The suppressed velocity dispersion of MgII-absorbing gas around both passive and [O II]-emitting LRGs, together with an elevated (MgII) along the major axis of [O II]-emitting LRGs at d < 50 kpc, provides important insights into the origin of the observed chemically enriched cool gas in LRG haloes. We consider different scenarios and conclude that the observed Mg II absorbers around LRGs are best explained by a combination of cool clouds formed in thermally unstable LRG haloes and satellite accretion through filaments.