1995A&A...295..317C

We have mapped 32 non-active spirals at 1300µm and measured 7 of them at 450 and 800µm. We determine gas masses, dust temperatures and IR luminosities. From a detailed analysis we find: i) The spatial extent of the cold dust is comparable to the optical size of the galaxies. About 70% of the mass is contained within half the optical radius; there the gas surface density decreases inversely proportional to the galactocentric radius. ii) The new submm data set limits on the decomposition of the FIR spectra into dust components of different temperatures. The flux ratios of 450 to 1300µm suggest two kinds of non-active spirals: those with S_450µm/S_1300µm≃40, like the Milky Way, where the coldest dust is ∼20K and accounts for most of the emission between 100 and 1300µm; on the other hand, there are galaxies with S_450µm/S_1300µm≃20 which implies that most of the interstellar dust is extremely cold (∼10K). iii) The ratio of infrared luminosity to gas mass, L_IR/M_gas, equals 5±2 in solar units. For active galaxies from the Markarian catalog this ratio is 20 times larger. Therefore L_IR/M_gas gives a clear signature for the activity stage.