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The Co-Evolution of Galaxies and the Cool Circumgalactic Medium Probed with the SDSS and DESI Legacy Imaging Surveys

We study the evolution of galaxies and the circumgalactic medium (CGM) through cosmic time by correlating $\sim50,000$ MgII absorbers, tracers of cool gas ($\sim10^{4}$~K), detected in the SDSS quasar spectra with galaxies detected in the DESI Legacy Imaging Surveys. By doing so, we extract the properties of galaxies associated with absorbers from redshift 0.4 to 1.3 with effectively $\sim 15,000$ pairs and explore the covering fraction of MgII absorbers as a function of galaxy type, stellar mass, impact parameter, and redshift. We find that the gas covering fraction increases with stellar mass of galaxies by $\sim M_{*}^{0.4}$. However, after we normalize the impact parameter by the virial radius of dark matter halos, the gas profiles around galaxies with masses ranging from $10^{9}$ to $10^{11} \, M_{\odot}$ become weakly dependent on stellar mass. In addition, the gas distribution depends on galaxy type: the covering fraction within $0.3 \, r_{vir}$ around star-forming galaxies is 2-4 times higher than that around passive galaxies at all redshifts. We find that the covering fraction of strong absorbers ($W_{\lambda2796}>1$ Angstrom) around both types of galaxies evolves significantly with redshift, similarly to the evolution of star-formation rate of galaxies, while such an evolution is not detected for weak absorbers ($W_{\lambda2796}<1$ Angstrom). We quantify the HI mass traced by strong absorbers and find that the gas mass around galaxies evolves consistently with the star-formation rate of galaxies. This result suggests that the properties of galaxies and their CGM co-evolve through cosmic time. Finally, we discuss the origins of strong absorbers around passive galaxies and argue that its redshift evolution may trace the star-formation activity of satellite galaxies.