Flaring of gas in galactic disks

Abstract

The vertical distribution of gas in disk galaxies is studied using analytical and numerical methods. If the sound speed of gas or the velocity dispersion of clouds is only weakly dependent on galactic radius, then the gas flares outward, perpendicular to the galactic plane. The rate of this flaring is determined by the galactic potential and constrains the mass distribution differently from rotation curves. In principle, therefore, high resolution measurements of the widths of HI layers in external edge—on galaxies could be used in conjunction with measured rotation curves to infer the shapes and masses of dark matter halos. This paper investigates the dependence of flaring on the flattening of the halo, ratio of halo‐to‐disk mass, and extent of the halo. We conclude that flaring can in principle be used to constrain the vertical scale‐height of the non‐gaseous disk material, as well as the axis ratios of dark matter halos.