Dust Temperatures in the Infrared Space Observatory Atlas of Bright Spiral Galaxies

We examine far-infrared and submillimeter spectral energy distributions for galaxies in the Infrared Space Observatory Atlas of Bright Spiral Galaxies. For the 71 galaxies where we had complete 60–180 μm data, we fitted blackbodies with λ-1 emissivities and average temperatures of 31 K or λ-2 emissivities and average temperatures of 22 K. Except for high temperatures determined in some early-type galaxies, the temperatures show no dependence on any galaxy characteristic. For the 60–850 μm range in eight galaxies, we fitted blackbodies with λ-1, λ-2, and λ-β (with β variable) emissivities to the data. The best results were with the λ-β emissivities, where the temperatures were ∼30 K and the emissivity coefficient β ranged from 0.9 to 1.9. These results produced gas-to-dust ratios that ranged from 150 to 580, which were consistent with the ratio for the Milky Way and which exhibited relatively little dispersion compared with fits with fixed emissivities.