The circumgalactic medium traced by Mg II absorption with DESI: dependence on galaxy stellar mass, star formation rate and azimuthal angle

TL;DR

This study uses DESI data to analyze how Mg II absorption in the circumgalactic medium varies with galaxy mass, star formation, and orientation, revealing complex dependencies that inform galaxy evolution models.

Contribution

It provides new insights into the dependence of Mg II absorption on galaxy properties and orientation, highlighting the roles of outflows and feedback in shaping the CGM.

Findings

Mg II absorption correlates with stellar mass for star-forming galaxies below 10^10 solar masses.

Higher star formation rates increase Mg II absorption within 50 kpc impact parameter.

Mg II absorption is strongest near the minor axis in low-mass star-forming galaxies, indicating outflows.

Abstract

Understanding the circumgalactic medium (CGM) distribution of galaxies is the key to revealing the dynamical exchange of materials between galaxies and their surroundings. In this work, we use DESI EDR dataset to investigate the cool CGM of galaxies ($0.3<z<1.7$) with stacking the spectra of background QSOs to obtain Mg II absorption of foreground galaxies. The equivalent width of Mg II absorption strongly correlates to stellar mass with EW(Mg II) $\propto M_{*}^{0.5}$ for star-forming galaxies with $\log M_{*}/M_{\odot} < 10$, but is independent with mass for galaxies above this mass. At given stellar mass, EW(Mg II) is larger for galaxies of higher star formation rate with impact parameter less than $50$ kpc, while showing little dependence on galaxy size. By studying the dependence on azimuthal angle, we find EW(Mg II) is strongest at the direction near the minor axis for star-forming galaxies with $\log M_{*}/M_{\odot} < 10.0$, while no dependence on azimuthal angle is seen for luminous red galaxies. This indicates that the outflow associated with star formation enhances the Mg II absorption. However, for galaxies with $\log M_{*}/M_{\odot} > 10.0$, the EW(Mg II) at the minor axis is largely suppressed with respect to low mass galaxies. This suggests that the competing processes, such as stellar feedback and gravity, play a key role in shaping the distribution of outflowing gas.