Abstract
The prominent minor-axis dust lane across the radio galaxy Cen A has been extensively mapped in the emission lines of Hα, H I, and CO, revealing an ordered velocity field which has been interpreted as that of a warped and twisted disk of gas seen nearly edge-on. Here it is shown that the geometry of this disk can be explained as that of a near-polar structure precessing about the symmetry axis of an approximately oblate galaxy potential which, like the stellar body, is nearly round at the center, becoming flattened farther out. Both freely precessing models and those taking account of the self-gravity of the gas are presented. The broken elliptical ring of H I gas recently found to be associated with the faint outer shells of Cen A can be explained naturally as a continuation of the same precessing disk. This precessing model for the gas disk assumes that the gravitational potential of Cen A is close to axisymmetric; precession should be qualitatively similar if the figure is triaxial and tumbling about its short axis in the same sense as the rotation of the stars.
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