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

5. Conclusions

The main conclusions of this paper are:

1. We have searched for the line of ¹²CO toward 29 external galaxies and have detected emission from all of them. For most sources these are the first published sub-mm CO line data. The good quality of the baselines and the high signal-to-noise ratios demonstrate the suitability of the Heinrich-Hertz-Telescope for extragalactic sub-mm observations.

2. For most sources, the ratios are in the range 0.2-0.7. This implies that it is possible to detect this line in hundreds of galaxies, to investigate the spatial structure of prominent sources, and to study the excitation conditions by observing isotopic CO lines and higher rotational lines.

3. Model calculations show that the line ratio is an indicator of the average H₂ density in the regions observed. Observations of rare isotopic CO are needed for more exact evaluations.

4. Carefully calibrated and pointed mm-line data of M 82 show that the 2-1/1-0 ratio is close to unity, falsifying an often cited legend about a ratio much higher than one.

© European Southern Observatory (ESO) 1999

Online publication: November 26, 1998
helpdesk.link@springer.de