  We have made the first VLBI synthesis images of the H2O maser emission
associated with the central engine of the Seyfert galaxy NGC 1068. Emission
extends about +/-300 km/s from the systemic velocity. Images with
submilliarcsecond angular resolution show that the red-shifted emission lies
along an arc to the northwest of the systemic emission. (The blue-shifted
emission has not yet been imaged with VLBI.) Based on the maser velocities and
the relative orientation of the known radio jet, we propose that the maser
emission arises on the surface of a nearly edge-on torus, where physical
conditions are conducive to maser action. The visible part of the torus is
axially thick, with comparable height and radius. The velocity field indicates
sub-Keplerian differential rotation around a central mass of about 1e7 Msun
that lies within a cylindrical radius of about 0.65 pc. The estimated
luminosity of the central engine is about 0.5 of the Eddington limit. There is
no detectable compact radio continuum emission near the proposed center of the
torus (T_B< 5e6 K on size scales of about 0.1 pc), so that the observed
flat-spectrum core cannot be direct self-absorbed synchrotron radiation.

Astrophysics