We are grateful to the staff of the SMTO who made these observations possible. We thank Dr. T.L. Wilson for help with the observations of M51. We also thank Seiichi Sakamoto and Malcolm Walmsley for giving impulses to the discussion. The CO(1-0) data were made available to us by Drs. N. Nakai and N. Kuno.
© European Southern Observatory (ESO) 1999
Online publication: June 30, 1999