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Astron. Astrophys. 322, 419-426 (1997)

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Molecular excitation in Centaurus A: the [FORMULA] CO J=1-0 map and CO line ratios *

W. Wild 1, 2, A. Eckart 3 and T. Wiklind 4

1 IRAM, Avda. Divina Pastora 7, E-18012 Granada, Spain
2 European Southern Observatory, Casilla 19001, Santiago 19, Chile
3 Max-Planck-Institut für extraterrestrische Physik, D-85740 Garching bei München, Germany
4 Onsala Space Observatory, S-43900 Onsala, Sweden

Received 27 September 1996 / Accepted 3 December 1996


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 C18 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 10-15 K and H2 densities on the order of [FORMULA] 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 formation activity. The total molecular mass is about [FORMULA] [FORMULA].

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. (1992). Comparison of the measurements with the kinematic model shows good agreement.

Key words: galaxies: individual: NGC 5128 – galaxies: nuclei – galaxies: ISM – radio lines: galaxies

* Based on observations collected at the European Southern Observatory, La Silla, Chile

Send offprint requests to: W. Wild, wild@iram.es

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998