VERTICAL-DISTRIBUTION AND SUPPORT OF GALACTIC H-I

The shape of high-latitude 21 cm H I emission profiles suggests that the local neutral interstellar medium is supported in the Galactic gravitational potential primarily by turbulence, that is, by the motion of individual clouds. Composite H I spectra derived from averages over large areas of the high-latitude sky are modeled by several isothermal components whose equilibrium vertical distribution in a plausible Galactic potential successfully reproduces the observed thickness of the H I layer. The analysis implies that there are several H I populations with differing central density, velocity dispersion, and scale height. although we cannot characterize them with precision. The kinetic energy in bulk vertical motions is greater-than-or-similar-to 6 x 10(51) ergs kpc-2 for a full disk. About 10% of the local H I is not part of a relaxed distribution but is infalling or is in ordered flows.