1995A&A...298L..29G

Using the IRAM 30m telescope equipped with the MPIfR 7-channel bolometer array, we have mapped the λ 1.2mm continuum emission of the inner part of M 51. This emission traces the central molecular disk and the inner spiral arms and correlates remarkably well with the ¹²CO (2-1) line emission. The λ 1.2mm continuum to CO line intensity ratio, averaged over the 70 GHz-wide bolometer band, is 7; a similar value was derived for NGC 891. The λ 1.2mm emission arises mostly from cold dust (T_d<20K) associated with molecular clouds. Using the local Galactic value of the dust absorption cross section, corrected for the larger metallicity observed near M 51's center, we derive the gas distribution from this emission. The derived molecular masses are ∼4 times smaller than those obtained from the CO luminosity, using Strong et al.'s Galactic CO to H2 conversion factor, but close to the masses estimated from ¹³CO and from visual extinction.