The rotation curve and geometry of M31 at large galactocentric distances.
Abstract
New 21-cm observations of the southern end of M3l indicate (1) that the plane of H I is bent away from the conventional plane by up to 5 kpc and (2) that the rotational velocity is essentially constant over the outer 10 kpc, i.e., from 20 to 30 kpc radius. The latter implies a mass that increases linearly with R over this range and a mass-to-luminosity ratio of > 200 for this outer region. At 30 kpc the surface density is 50 M0 pc-2. Dwarf M stars, the most common type of star in the solar vicinity, of number density of a few tenths pc - are adequate to explain the required mass and the mass-to-luminosity ratio. At these distances H I is 1 percent of the total mass. Subject headings: galaxies, individual - galaxies, motions in - galaxies, stellar content of - 21-cm radiation
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1975
- DOI:
- 10.1086/153889
- Bibcode:
- 1975ApJ...201..327R