Molecular excitation in Centaurus A: the ^13^CO J=1-0 map and CO line ratios.

We present a fully sampled map of the ^13^CO J=1-0 emission in the dust lane of Centaurus A as well as ^13^CO 2-1 and for the first time C^18^O 1-0 spectra at selected positions. The morphology of the ^13^CO map is similar to the ^12^CO 1-0 and 2-1 maps. Maps of the ^12^CO 2-1/1-0 and ^12^CO/^13^CO 1-0 ratios show small variations of the ratios throughout the disk with a rise of the ^12^CO 2-1/1-0 ratio towards the southeast. The values found are within the range as found in other galaxies. Radiative transfer calculations indicate a kinetic temperature of 10-15K and H_2_ densities on the order of 3x10^4^cm^-3^. In the southeastern part of the dust lane, the gas appears to be warmer (20-30K) which may be due to a greater star formation activity. The total molecular mass is about 1.2 x 10^8^Msun_. The observed ^12^CO 2-1 intensity is consistent with the molecular gas being distributed in a thin, warped disk as modelled by Quillen et al. (1992ApJ...391..121Q). Comparison of the measurements with the kinematic model shows good agreement