Far Infrared Emission from Galactic and Extragalactic Dust

Abstract

This review examines the question of how similar far infrared and submillimeter dust properties are among galaxies including the Milky Way, and within the Milky Way. The IRAS data are examined, and no evidence is found for variations in the broad-band dust properties between 10 and 100 µm. Submillimeter data are examined in a search for a power-law index describing the emissivity of dust at λ > 100 µm. The data are consistent with a universal value of the index between 1 and 2. The evidence for large amounts of cold dust (10 to 15 K) in galaxies is reviewed and found quite soft in light of conflicting data. In most spiral galaxies, the dust-to-gas ratios are comparable to their values in the Milky Way, with a few well-documented exceptions such as the Magellanic Clouds and Blue Compact Dwarf galaxies, which have a lower ratio. No compelling evidence is found for gradients in the dust-to-gas ratio within disks of galaxies. Very small grains with fluctuating temperatures appear to be present in all galaxies examined, and to behave just like those observed in the Milky Way.