Nature of the Galaxies On Top Of Quasars producing MgII absorption

TL;DR

This study investigates the properties of galaxies hosting MgII absorbers at redshifts 0.39 to 1.05, revealing relationships between galaxy brightness, gas absorption strength, and galaxy characteristics, and providing new measurements of host galaxy parameters.

Contribution

It significantly expands the sample of known MgII host galaxies at small impact parameters and quantifies the relationship between MgII absorption strength and galaxy properties.

Findings

Brighter galaxies produce stronger MgII absorption.

The impact parameter correlates inversely with MgII equivalent width.

Average galaxy stellar mass is lower than in previous studies.

Abstract

Quasar-galaxy pairs at small separations are important probes of gas flows in the disk-halo interface in galaxies. We study host galaxies of 198 MgII absorbers at $0.39\le z_{abs}\le1.05$ that show detectable nebular emission lines in the SDSS spectra. We report measurements of impact parameter (5.9$\le D[kpc]\le$16.9) and absolute B-band magnitude ($-18.7\le {\rm M_B}\le -22.3$ mag) of host galaxies of 74 of these absorbers using multi-band images from the DESI Legacy Imaging Survey, more than doubling the number of known host galaxies with $D\le17$ kpc. This has allowed us to quantify the relationship between MgII rest equivalent width($W_{2796}$) and D, with best-fit parameters of $W_{2796}(D=0) = 3.44\pm 0.20$ Angstrom and an exponential scale length of 21.6$^{+2.41}_{-1.97}$ $kpc$. We find a significant anti-correlation between $M_B$ and D, and $M_B$ and $W_{2796}$, consistent with the brighter galaxies producing stronger MgII 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 ($9.4\le log(M_*/M_\odot) \le 9.8$), star formation rate ($2.3\le{\rm SFR}[M_\odot yr^{-1}] \le 4.5$), age (2.5$-$4 Gyr), metallicity (12+log(O/H)$\sim$8.3) and ionization parameter (log~q[cm s$^{-1}$]$\sim$ 7.7) for these galaxies. The average $M_*$ found is less compared to those of MgII 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.