A complete census of circumgalactic Mg ii at redshift z ≲ 0.5.

This paper presents a survey of Mg  ii absorbing gas in the vicinity of 380 random galaxies, using 156 background quasi-stellar objects (QSOs) as absorption-line probes. The sample comprises 211 isolated (73 quiescent and 138 star-forming galaxies) and 43 non-isolated galaxies with sensitive constraints for both Mg  ii absorption and H α emission. The projected distances span a range from d  = 9 to 497 kpc, redshifts of the galaxies range from z  = 0.10 to 0.48, and rest-frame absolute B -band magnitudes range from M B = −16.7 to −22.8. Our analysis shows that the rest-frame equivalent width of Mg  ii , Wr (2796), depends on halo radius (R h), B -band luminosity(L B), and stellar mass (M star) of the host galaxies, and declines steeply with increasing d for isolated, star-forming galaxies. At the same time, Wr (2796) exhibits no clear trend for either isolated, quiescent galaxies or non-isolated galaxies. In addition, the covering fraction of Mg  ii absorbing gas 〈κ〉 is high with 〈κ〉 ≳ 60 per cent at <40 kpc for isolated galaxies and declines rapidly to 〈κ〉 ≈ 0 at d ≳ 100 kpc. Within the gaseous radius, the incidence of Mg  ii gas depends sensitively on both M star and the specific star formation rate inferred from H α. Different from what is known for massive quiescent haloes, the observed velocity dispersion of Mg  ii absorbing gas around star-forming galaxies is consistent with expectations from virial motion, which constrains individual clump mass to |$m_{\rm cl} \gtrsim 10^5 \, \rm M_\odot$| and cool gas accretion rate of |$\sim 0.7\!-\!2 \, \mathrm{ M}_\odot \, \rm yr^{-1}$|⁠. Finally, we find no strong azimuthal dependence of Mg  ii absorption for either star-forming or quiescent galaxies. Our results demonstrate that multiple parameters affect the properties of gaseous haloes around galaxies and highlight the need of a homogeneous, absorption-blind sample for establishing a holistic description of chemically enriched gas in the circumgalactic space. [ABSTRACT FROM AUTHOR]