| Abstract | Interferometric H I observations of the Local Group dwarf irregular galaxy Sextans A are presented. The H I distribution shows a strong correspondence with the optical structure, the velocity field is very regular showing predominantly solid-body rotation, and the velocity dispersion is nearly constant across the galaxy. However, the velocity field is not aligned with the optical axis of symmetry. We have investigated the possibility of gas moving on elliptical orbits and find this to be a possible explanation for the misalignment. This lack of alignment of the velocity field with the optical axis of symmetry renders estimates of the inclination of the galaxy uncertain, and makes an accurate mass distribution analysis impossible. The H I distribution is dominated by two high surface density clumps, and the clumps are associated with regions of recent star formation. Measurements of the surface density support the postulate of Skillman (1987) that OB star formation in irregular galaxies requires an H I surface density (averaged over ~500 pc) of about 1 10^21^ atoms cm^-2^. About half of the neutral hydrogen associated with Sextans A lies in a low density (<10^20^ atoms cm^-2^), spatially extended, outer component. If the inner parts of the galaxy can be replenished from this source, star formation may proceed for quite some time. |
