Neutral hydrogen in the outer Galaxy

Abstract

The H I 21 cm emission-line survey data of Stark et al. (1991) have been used to study the distribution of H I in the outer Galaxy and to improve understanding of the various systematic problems which influence all studies of Galactic H I. For n(H) greater than 0.01/cu cm, the distributions are similar to those found by Burton and te Lintel Hekkert (1986) but are 'better behaved' at substantially lower values of n(H). The z distribution of gas in the H I layer is best described as complicated. The behavior of the gaseous matter is consistent with the observed distribution of H I found in external spiral galaxies. In the directions of the maximum warp the average distance of the gas away from the Galactic plane reaches about 4 kpc at R about 24 kpc, while the flaring of the layer as measured by z(rms) increases to about 3 kpc. In directions where the warp layers particularly well measured, the Galaxy is followed to R about 30 kpc. The surface density of the atomic gas decreases exponentially.