Motions and Deformations of the Inner-Galaxy Neutral Gas Layer

Abstract

Neutral gas in the inner few kpc of the Milky Way is notable for showing strong non-circular motions, large excursions from the nominal galactic plane, and an overwhelming preponderance of molecular (rather than atomic) neutral gas. Here, we discuss the coherent nature of the kpc-scale tilts seen in H I and CO emission and demonstrate the congruence of the inner-Galaxy atomic and molecular gas distributions, out more than 1 kpc in radius and 300 pc vertically from the center. We point out that features in inner-Galaxy spectra can usually not be identified with discrete, underlying material entities, but instead arise solely as the result of kinematic projection effects.