The circumnuclear molecular gas in the Seyfert galaxy NGC 4945

We have mapped the central region of NGC 4945 in the J = 2 -> 1 transition of (CO)-C-12, (CO)-C-13, and (CO)-O-18, as well as the continuum at similar to 1.3 mm, at an angular resolution of 5 x 3 with the Submillimeter Array. The relative proximity of NGC 4945 (distance of only 3.8 Mpc) permits a detailed study of the circumnuclear molecular gas and dust in a galaxy exhibiting both an active galactic nucleus (AGN; classified as Seyfert 2) and a circumnuclear starburst in an inclined ring with radius similar to 2.5 (similar to 50 pc). We infer the systemic velocity similar to 585 km s(-1) from chanel maps and PV-diagrams. We find that all three molecular lines trace an inclined rotating disk with the major axis aligned with that of the starburst ring and large-scale galactic disk and which exhibits solid-body rotation within a radius of similar to 5 (similar to 95 pc). The rotation curve flattens beyond this radius, and the isovelocity contours exhibit an S-shaped asymmetry suggestive of a highly inclined bar, as has been invoked to produce a similar asymmetry observed on larger scales. We infer an inclination for the nuclear disk of 62 degrees +/- 2 degrees, somewhat smaller than the inclination of the large-scale galactic disk of similar to 78 degrees. The continuum emission at 1.3 mm also extends beyond the starburst ring and is dominated by thermal emission from dust. If it traces the same dust emitting in the far-infrared, then the bulk of this dust must be heated by star-formation activity rather than the AGN. We discover a kinematically decoupled component at the center of the disk with a radius smaller than 1.4 (27 pc), but which spans approximately the same range of velocities as the surrounding disk. This component has a higher density than its surroundings and is a promising candidate for the circumnuclear molecular torus invoked by AGN unification models.