EVIDENCE FOR A 20-PARSEC DISK AT THE NUCLEUS OF CENTAURUS-A

We report Hubble Space Telescope NICMOS observations of the central re gion of NGC 5128 at 2.2 mu m and in Pa alpha. The continuum images sho w extended emission typical of an elliptical galaxy and a strong unres olved central source we identify as the nucleus of the galaxy. Its pos ition is consistent with ground-based IR and radio data, and with the peak of reddening found with the first wide field planetary camera. In Pa alpha, we detect a prominent elongated structure, centered on the nucleus, extended by similar or equal to 2 '' at a position angle of s imilar or equal to 33 degrees, and with a major to minor axis ratio of similar to 2. We interpret this as an inclined, similar to 40 pc diam eter, thin nuclear disk of ionized pas rather than a jet-gas cloud int eraction. We do see several weaker Pa alpha features, some of which ma y be circumnuclear gas clouds shocked by the X-ray/radio jet. The disk is one of the smallest ever observed at the nucleus of an active gala ctic nucleus (AGN). It is not perpendicular to the jet but is consiste nt with being oriented along the major axis of the bulge. If it repres ents the warped outer portion of an accretion disk around a black hole , we conclude that even on the scale of a few parsecs, the disk is dom inated by the galaxy gravitational potential and is not directly relat ed to the symmetry axis of the AGN.