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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
Received 27 July 1998 / Accepted 18 September 1998
The 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, , are compared to 1-0 and 2-1 fluxes measured with the IRAM 30-m telescope. Model calculations show that the ratio can be used as a measure of the average H2 density. For most sources observed, is in the range 0.2-0.7, which is predicted if kinetic temperatures are K and/or H2 densities .
Our measurements of the , 2-1, and 3-2 lines toward M 82 do not support earlier claims of 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
Send offprint requests to: R. Mauersberger
Online publication: November 26, 1998