2021MNRAS.502.4743H

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, W_r(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, W_r(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_ cl_ ≳10⁵M_☉ and cool gas accretion rate of ∼0.7-2 M_☉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.