CO J=1-0, 2-1 AND 3-2 ABSORPTION AND EMISSION TOWARD THE NUCLEUS OF CENTAURUS-A - PROBING THE CIRCUMNUCLEAR DISK

High signal to noise spectra of (CO)-C-12, (CO)-C-13 and (CO)-O-18 J = 1-0, (CO)-C-12 2-1 and (CO)-C-13 3-2 have been obtained toward the nucleus of Centaurus A. The (CO)-C-12 profiles reveal the presence of two superposed emission components. The narrower component (DELTA-V approximately 70-100 km s-1) is due to CO emission from the dust lane. The broader component (DELTA-V approximately 260 km s-1) represents CO emission from the cirumnuclear disk, whose presence was previously deduced from absorption line and infrared continuum observations. Analysis of the CO data suggests excitation temperatures of about 25 K in the circumnuclear disk. In both HCO+ and CO spectra, weak absorption features are seen at red-shifted velocities, which probably represent warm and dense gas falling into the nucleus.