| Abstract | The results of a study of the 21 cm H I emission from the irregular galaxy DDO 154 are presented, including maps of the object. The galaxy is embedded in an H I disk at least seven times the optical diameter. The H I mass-to-light ratio is 6.1 and the H I fraction by mass is 0.3 to 0.5 within four optical radii, making DDO 154 one of the most gas-rich galaxies known. The H I gas distribution is nonaxisymmetric, and the H I disk is significantly more elliptical than the optical disk. A linearly rising rotation curve gives an adequate fit to the H I line profiles out to a radius of 15 kpc. Near this radius, the random velocities in the gas are about 10 km/s along the line of sight, comparable to those observed in much more massive spiral galaxies. The surface density of gravitational mass is nearly constant with radius outside the galaxy's optical image. |
