MOLECULAR-EXCITATION IN CENTAURUS-A - THE (CO)-C-13 J=1-0 MAP AND CO LINE RATIOS

We present a fully sampled map of the (CO)-C-13 J=1-0 emission in the dust lane of Centaurus A as well as (CO)-C-13 2-1 and for the first ti me (CO)-O-18 1-0 spectra at selected positions. The morphology of the (CO)-C-13 map is similar to the (CO)-C-12 1-0 and 2-1 maps. Maps of th e (CO)-C-12 2-1/1-0 and (CO)-C-12/(CO)-C-13 1-0 ratios show small vari ations of the ratios throughout the disk with a rise of the (CO)-C-12 2-1/1-0 ratio towards the southeast. The values found are within the r ange as found in other galaxies. Radiative transfer calculations indic ate a kinetic temperature of 10-15 K and H-2 densities on the order of 3 x 10(4) cm(-3). In the southeastern part of the dust lane, the gas appears to be warmer (20-30 K) which may be due to a greater star form ation activity. The total molecular mass is about 1.2 x 10(8) M.. The observed (CO)-C-12 2-1 intensity is consistent with the molecular gas being distributed in a thin, warped disk as modelled by Quillen et al. (1992). Comparison of the measurements with the kinematic model shows good agreement.