Evidence for a Geometrically Thick Self-Gravitating Accretion Disk in NGC 3079

We have mapped, for the first time, the full velocity extent of the water maser emission in NGC 3079. The largely north-south distribution of emission, aligned with a kiloparsec-scale molecular disk, and the segregation of blueshifted and redshifted emission on the sky are suggestive of a nearly edge-on molecular disk on parsec scales. Positions and line-of-sight velocities of blueshifted and redshifted maser emission are consistent with a central mass of 62 x 10 super(6) M sub( )enclosed within a radius of 60.4 pc. The corresponding mean mass density of 10 super(6.8) M sub( )pc super(-3) is suggestive of a central black hole, which is consistent with the detection of hard X-ray excess (20-100 keV) and an Fe Ka line from the nucleus. Because the rotation curve traced by the maser emission is flat, the mass of the parsec-scale disk is significant with respect to the central mass. Since the velocity dispersion of the maser features does not decrease with radius and constitutes a large fraction of the orbital velocity, the disk is probably thick and flared. The rotation curve and the physical conditions necessary to support maser emission imply a Toomre Q-parameter that is