The independence of neutral and ionized gas outflows in low-z galaxies
  Using a large sample of emission line galaxies selected from the Sloan
Digital Sky Survey, we investigate the kinematics of the neutral gas in the
interstellar medium (ISM) based on the Na I$\lambda\lambda$5890,5896 (Na D)
doublet absorption line. By removing the Na D contribution from stellar
atmospheres, we isolate the line profile of the Na D excess, which represents
the neutral gas in the ISM. The kinematics traced by the Na D excess show high
velocity and velocity dispersion for a fraction of galaxies, indicating the
presence of neutral gas outflows. We find that the kinematics measured from the
Na D excess are similar between AGNs and star-forming galaxies. Moreover, by
comparing the kinematics traced by the Na D excess and those by the [O
III]$\lambda$5007 line taken from Woo et al. (2017), which traces ionized
outflows driven by AGNs, we find no correlation between them. These results
demonstrate that the neutral gas in the ISM traced by the Na D excess and the
ionized gas traced by [O III] are kinematically independent, and AGN has no
impact on the neutral gas outflows. In contrast to [O III], we find that the
measured line-of-sight velocity shift and velocity dispersion of the Na D
excess increase for more face-on galaxies due to the projection effect,
supporting that Na D outflows are radially driven (i.e., perpendicular to the
major axis of galaxies), presumably due to star formation.
