The Properties of the Cool Circumgalactic Gas Probed with the SDSS, WISE, and GALEX Surveys

We explore the distribution of cool (~10⁴ K) gas around galaxies and its dependence on galaxy properties. By cross-correlating about 50,000 Mg II absorbers with millions of sources from the SDSS (optical), WISE (IR), and GALEX (UV) surveys we effectively extract about 2000 galaxy-absorber pairs at z ~ 0.5 and probe relations between absorption strength and galaxy type, impact parameter and azimuthal angle. We find that cool gas traced by Mg II absorbers exists around both star-forming and passive galaxies with a similar incidence rate on scales greater than 100 kpc but each galaxy type exhibits a different behavior on smaller scales: Mg II equivalent width does not correlate with the presence of passive galaxies whereas stronger Mg II absorbers tend to be found in the vicinity of star-forming galaxies. This effect is preferentially seen along the minor axis of these galaxies, suggesting that some of the gas is associated with outflowing material. In contrast, the distribution of cool gas around passive galaxies is consistent with being isotropic on the same scales. We quantify the average excess Mg II equivalent width < δ W₀^Mg \scriptsize{II}> as a function of galaxy properties and find < δ W₀^Mg \scriptsize{II}> \propto SFR^1.2, sSFR^0.5, and M_\ast ^0.4 for star-forming galaxies. This work demonstrates that the dichotomy between star-forming and passive galaxies is reflected in the circumgalactic medium traced by low-ionized gas. We also measure the covering fraction of Mg II absorption and find it to be about 2-10 times higher for star-forming galaxies than passive ones within 50 kpc. We estimate the amount of neutral gas in the halo of langlog M _*/M _⊙rang ~ 10.8 galaxies to be a few × 10⁹ M _⊙ for both types of galaxies. Finally, we find that correlations between absorbers and sources detected in the UV and IR lead to physical trends consistent with those measured in the optical.