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Astron. Astrophys. 327, 493-502

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Millimetre line CO (2FORMULA1) observations
of a complete sample of AGN

D. Rigopoulou1,2,3, I. Papadakis4, A. Lawrence1,5, and M. Ward6

1Physics Department, Queen Mary and Westfield College, University of London, Mile End Road, London E1 4NS, UK
2MPE für Extratterestrische Physik, Postfach 1603, D-85740 Garching, Germany
3Astrophysics Group, Blackett Laboratory, ICSTM, Prince Consort Road, London SW7 2BZ, UK
4Physics Department, University of Southampton, University Road, Southampton, UK
5Edinburgh Institute for Astronomy, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
6Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK

Received 24 February 1997 / Accepted 17 June 1997


We report on observations of the CO (2FORMULA1) transition of a complete subset of 11/39 of the Piccinotti (1982) hard X-ray selected AGN sample. All of the 11 galaxies were clearly detected. All the galaxies in our sample are strong hard-X ray sources and thus the sample is unbiased with respect to obscuring material. Six of the galaxies are Seyfert 1 type objects with the rest five being reddened Seyfert 1s, or the so called ''Narrow Line Galaxies''. Based on our high S/N detections we investigate the relation between CO and far-infrared luminosities. A strong correlation is found to exist for both Seyfert 1s and Narrow Line Galaxies similar to the one seen in normal and bright infrared galaxies. Our data also suggest that the FIR emission in Seyferts galaxies is of thermal origin, an argument which is supported by three different lines of evidence, the CO-FIR correlation, the FIR/M(H2) dependence on dust temperature and the similarities in the shapes of the CO and HI profiles. The relation between CO emission and non-thermal radio power was examined next. Seyferts were found to show an excess radio non-thermal power for a given CO luminosity (when compared to starburst galaxies) while no differences were found between Seyfert 1s and 2s in their CO and radio properties (Seyfert 2s were selected from the literature). We conclude that Seyfert 1s and Narrow Line Galaxies have very similar properties with respect to their molecular gas reservoir. By comparing our CO observations with published optical data we explore the distribution of the molecular clouds in the sample galaxies. We find that in most cases the spatial distribution of CO clouds is confined within 1-1.4 kpc around the nucleus.

Key words: galaxies: active - ISM: molecules - galaxies: Seyferts

Send offprint requests to: d.rigopoulou@ic.ac.uk

© European Southern Observatory (ESO) 1997

Online publication: October 14, 1997
Last change: April 6, 1998