2023MNRAS.519.3319G

Quasar-galaxy pairs at small separations are important probes of gas flows in the disc-halo interface in galaxies. We study host galaxies of 198 Mg II absorbers at 0.39 ≤ z_abs ≤ 1.05 that show detectable nebular emission lines in the Sloan Digital Sky Survey (SDSS) spectra. We report measurements of impact parameter (5.9 ≤ D [kpc] ≤ 16.9) and absolute B-band magnitude (-18.7 ≤ M_B ≤ -22.3 mag) of host galaxies of 74 of these absorbers using multiband images from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Survey, more than doubling the number of known host galaxies with D ≤ 17 kpc. This has allowed us to quantify the relationship between Mg II rest equivalent width (W₂₇₉₆) and D, with best-fitting parameters of W₂₇₉₆ (D = 0) = 3.44 ± 0.20 Å and an exponential scale length of 21.6$^{+2.41}_{-1.97}\, \mathrm{ kpc}$. We find a significant anticorrelation between M_B and D, and M_B and W₂₇₉₆, consistent with the brighter galaxies producing stronger Mg II absorption. We use stacked images to detect average emissions from galaxies in the full sample. Using these images and stacked spectra, we derive the mean stellar mass (9.4 ≤ log(M_*/M_⊙) ≤ 9.8), star formation rate (2.3 ≤ SFR [M_⊙ yr^–1] ≤ 4.5), age (2.5-4 Gyr), metallicity (12 + log(O/H) ∼ 8.3), and ionization parameter (log q [cm s^–1] ∼ 7.7) for these galaxies. The average M_* found is less than that of Mg II absorbers studied in the literature. The average SFR and metallicity inferred are consistent with that expected in the main sequence and the known stellar mass-metallicity relation, respectively. High spatial resolution follow-up spectroscopic and imaging observations of this sample are imperative for probing gas flows close to the star-forming regions of high-z galaxies.