Baryonic ecosystem IN galaxies (BEINGMgII) III. Cool gas reservoirs at 0.3≤z ≤1.6 in the dark energy survey

Abstract

We investigate the origin of intervening cool Mg ii absorption detected in the spectra of background quasars and the nature of associated galaxies across a broad redshift range of 0.3 ≤ z ≤ 1.6, and a largely unexplored galactrocentric distance of .20 kpc. Using nebular [O ii] λλ3727, 3729 emission lines identified in DESI fibre spectra centred on quasars, we detect 342 galaxies at a typical detection rate of ∼0.45% at z . 1, which increases with the Mg ii equivalent width (W2796). A significant fraction (74%) of these galaxies are associated with strong absorbers with W2796 ≥ 2 Å. These absorbers trace galaxies spanning stellar masses of 8.4 ≤ log(M?/M ) ≤ 11.6 and star formation rates (SFRs) of −1 ≤ log(SFR [M yr−1]) ≤ 2.7, located at projected galactocentric distances of 4−24 kpc. We find that the average Mg ii absorber strength increases from 2.1 Å to 2.8 Å between redshifts of z ∼ 0.4 and 1.2, indicating evolution in the cool gas content of galaxy halos. The relatively constant absorber strength with galactocentric distance implies a clumpy structure of cool gas in the circumgalactic medium (CGM). Further, we find a positive correlation between W2796 versus stellar mass (M?), and the SFR, suggesting that the distribution of metal-enriched cool gas in the CGM is closely tied to the properties of the host galaxies. The redshift evolution of gas-phase metallicity suggests that strong Mg ii absorbers trace the general population of star-forming galaxies. The velocity dispersion of the cool gas increases with halo mass, and the wide range of the line-of-sight velocity offset (−389 to 364 km s−1) between the galaxy systemic velocity and absorbers highlights the dynamical nature of CGM. However, the majority of this gas remains gravitationally bound to the dark matter halos, consistent with a picture of gas recycling via galactic fountains.