Description
Large-scale outflows and inflows are key ingredients in galaxy formation, as they regulate the amount of gas available for future star formation. However, the kinematics of these flows have been difficult to constrain. We measure the kinematics and absorption strength of CaII and NaI absorption systems in QSO sightlines that are located exceptionally close to a foreground galaxy (a GOTOQ, or Galaxy On Top Of a Quasar) to probe the motions of cool (. 103 K) gas at the disk-halo interface. Our 22 high resolution Keck/ESI QSO spectra are sensitive to equivalent widths > 0.02 ̊A, and probe impact parameters R⊥ < 15 kpc. We find that covering fractions for both CaII and NaI increase with projected separation, from 0.61+0.09−0.10 (0.5+0.10−0.10) at R⊥ < 6 kpc to 1+0−0.04 (0.83+0.06−0.09) at R⊥ > 6 kpc for CaII (NaI), indicating more frequent absorption at larger distances from the host galaxies. This is consistent with the Thompson et al. (2016) theory that cold gas clouds are more likely to form at ∼ 1-10 kpc distances in the presence of star formation-driven outflows. We also find most of this gas is bound to its respective dark matter halo, with two exceptions where we present evidence for unbound CaII-absorbing gas. Overall, this project is one of the first to report sensitive CaII and NaI absorption measurements in the disk-halo interface of nearby star-forming galaxies, and will improve models for the cold phase of galactic outflows.
