Dust in spiral galaxies. I

We have mapped NGC 660 and UGC 3490 at 1300μm. It turns out that the spatial extent of the cold dust is comparable to the optical size of UGC 3490. Combining the new observations with IRAS data we derive a temperature of: 17K for the coldest dust component; its emission dominates the wavelength range from 100 to 1300μm. A second warm component of≃50K is required to explain the spectra down to 25μm. This decomposition is corroborated by a reinvestigation of FIR data for M 51 and the Milky Way. In both cases, the energy distributions peak around 200μm confirming our earlier, strongly doubted results on the dust components in spiral galaxies