Astron. Astrophys. 341, 256-263 (1999)
The main conclusions of this paper are:
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.
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.
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
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