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Astron. Astrophys. 341, 256-263 (1999)


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Dense gas in nearby galaxies *

XII. A survey for CO J = 3 - 2 emission

R. Mauersberger 1, C. Henkel 2, W. Walsh 3 and A. Schulz 4,5

1 Steward Observatory, The University of Arizona, Tucson, AZ 85721, USA
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
3 Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
4 Institut für Physik und Didaktik, Universität zu Köln, Gronewaldstrasse 22, D-50931 Köln, Germany
5 Institut für Astrophysik und Extraterrestrische Forschung, Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany

Received 27 July 1998 / Accepted 18 September 1998

Abstract

The [FORMULA] sub-mm line of 12CO has been observed with the Heinrich-Hertz-Telescope (HHT) toward a sample of 28 nearby galaxies, and toward Arp 220. All sources are detected. This is the largest extragalactic sample of CO 3-2 spectra published so far. The 3-2 line fluxes, [FORMULA], are compared to 1-0 and 2-1 fluxes measured with the IRAM 30-m telescope. Model calculations show that the [FORMULA] ratio can be used as a measure of the average H2 density. For most sources observed, [FORMULA] is in the range 0.2-0.7, which is predicted if kinetic temperatures are [FORMULA]K and/or H2 densities [FORMULA].

Our measurements of the [FORMULA], 2-1, and 3-2 lines toward M 82 do not support earlier claims of [FORMULA] line ratios much larger than 1. As in other active galaxies (NGC 253, Arp 220) the measured line intensity ratio is close to unity. Unlike single dish data from the lower excited CO lines, the CO 3-2 profile toward Arp 220 shows two velocity components, possibly arising from the edges of its molecular disk.

Key words: radio lines: galaxies – galaxies: spiral – galaxies: ISM – galaxies: general – ISM: molecules – surveys

* Based on observations with the Heinrich-Hertz-Telescope (HHT). The HHT is operated by the Submillimeter Telescope Observatory on behalf of Steward Observatory and the MPI für Radioastronomie.

Send offprint requests to: R. Mauersberger

© European Southern Observatory (ESO) 1999

Online publication: November 26, 1998

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