A complete census of circumgalactic Mg II at redshift z ≲ 0.5
Abstract
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 MB = -16.7 to -22.8. Our analysis shows that the rest-frame equivalent width of Mg II, Wr(2796), depends on halo radius (Rh), B-band luminosity(LB), and stellar mass (Mstar) 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 Mstar 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2021
- DOI:
- 10.1093/mnras/stab360
- arXiv:
- arXiv:2009.12372
- Bibcode:
- 2021MNRAS.502.4743H
- Keywords:
-
- surveys;
- galaxies: formation;
- galaxies: haloes;
- intergalactic medium;
- quasars: absorption lines;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 20 pages, 11 figures, accepted for publication in the MNRAS