A MOLECULAR RING IN THE CIRCINUS GALAXY

The Circinus galaxy, a type 2 Seyfert, is suspected to have a molecula r gas ring structure with a diameter of similar to 500 pc. We have map ped the lowest three rotational transitions of (CO)-C-12 in the centra l region of the galaxy, and upon detailed examination, the data sugges t that a fraction of the molecular gas is orbiting the galaxy's nucleu s in the form of a ring. There also appears to exist an associated mol ecular outflow which is coincident with the previously observed ionisa tion cone. In order to determine the geometry and kinematics of the ri ng, we have modelled various configurations, obtaining an initial esti mate from the MEM de-convolved data. The model takes defined ring para meters, i.e. velocities across the ring at various radii, the inclinat ion angle and the intensity of emission, and convolves these with a sy nthesised telescope beam in order to regenerate the observed spectra. The results suggest that the ring, which has the same position angle a s the main galaxy body, has an outer radius of greater than or similar to 600 pc and orbits with non-Keplerian rotation around a central dyn amical mass of approximate to 3 x 10(8)M(circle dot). We also estimate the dynamical mass within the central 560 pc to be approximate to 3 x 10(9)M(circle dot) i.e. only double the total molecular mass calculat ed from the intensity of CO emission, indicating that use of the Galac tic N-H2/I-CO conversion ratio may possibly cause us to overestimate t he molecular mass in this nucleus.