Infrared Radiation from Normal Galaxies

Abstract

We review the possible sources of thermal infrared radiation in a complete sample of optically bright normal galaxies. The sample comes primarily from the Virgo cluster but is augmented by field galaxies at the same distance. Ground based 10 µm measurements of the nuclear regions and the IRAS survey are both reviewed. We find that elliptical galaxies are very weak at thermal infrared wavelengths and that much of their emission comes from photospheres and dust shells around late-type M stars. SO galaxies, as a sample, are somewhat brighter than elliptical galaxies and in a small subset of the sample the infrared emission appears to come primarily from nuclear star-formation. Spiral galaxies are bright at thermal infrared wavelengths. On average, twenty-five per cent of the infrared radiation from spiral galaxies comes from a nuclear bursts of star formation and the remainder comes from the disk. The nuclear emission strength is independent of morphological type whereas disks of Sc galaxies are much stronger than the disks of Sa galaxies. Infrared emission from peculiar objects such as Seyfert type activity appears relatively weak in this sample.KeywordsStar FormationInfrared RadiationSpiral GalaxyElliptical GalaxyAsymptotic Giant BranchThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.