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

Abstract

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 black-bodies 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.