VLA observations of OH in galaxies. I. NGC 253 and its nuclear plume

The distribution of emission and absorption has been mapped in all four 18 cm lines of OH in the nuclear regions of NGC 253, using the VLA with a resolution of 17''.7 x 9''.5. A steep rotation curve is found over the inner 150 pc radius, yielding a nuclear mass of approx.5 x 108 M/sub sun/, the same as found from IR observations. The absorbing gas covers a range of 60--550 km s-1, wider than seen optically or as yet in H I. Clumping of the absorbing gas implies individual entities approx.20 pc in size, suggestive of giant molecular clouds in the Milky Way. The absorbing gas appears to be distributed in a toroid of mean radius 170 pc centered on the nucleus