The Smooth Mg II Gas Distribution through the Interstellar/Extra-planar/Halo Interface

We report the first measurements of Mg II absorption systems associated with spectroscopically confirmed z ~ 0.1 star-forming galaxies at projected distances of D < 6 kpc. We demonstrate that the data are consistent with the well-known anti-correlation between rest-frame Mg II equivalent width, W_r (2796), and impact parameter, D, represented by a single log-linear relation derived by Nielsen et al. (MAGIICAT) that converges to ~2 Å at D = 0 kpc. Incorporating MAGIICAT, we find that the halo gas covering fraction is unity below D ~ 25 kpc. We also report that our D < 6 kpc absorbers are consistent with the W_r (2796) distributions of the Milky Way interstellar medium (ISM) and ISM+halo. In addition, quasar sight lines of intermediate redshift galaxies with 6 < D < 25 kpc have an equivalent width distribution similar to that of the Milky Way halo, implying that beyond ~6 kpc, quasar sight lines are likely probing halo gas and not the ISM. As inferred by the Milky Way and our new data, the gas profiles of galaxies can be fit by a single log-linear W_r (2796)-D relation out to large scales across a variety of gas-phase conditions and is maintained through the halo/extra-planar/ISM interfaces, which is remarkable considering their kinematic complexity. These low-redshift, small impact parameter absorption systems are the first steps to bridge the gap between quasar absorption-line studies and H I observations of the circumgalactic medium.