The IRAS survey showed that far

The IRAS survey showed that far - The IRAS survey showed...

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The IRAS survey showed that far-IR emission is ubiquitous among spiral and irregular galaxies, even some for which optical data suggested a very modest dust content. Some fraction of this emission is powered by young stars, making far-IR emission a very tempting indicator of star formation if we can understand it properly. For thermal emission, dust grains are heated by absorption of starlight, which operates most effectively in the blue and UV as the wavelength comes closer to the characteristic grain size. The grains cool by (approximately) black-body emission, modified by a wavelength-dependent emissivity cause largely by the fact that the grains are smaller than the blackbody peak wavelength and thus cannot radiate such wavelengths as efficiently as a perfect radiator. The peak emission typically correspond to a blackbody temperature 20-40 K; a significant range must be present to account for the far-IR spectral shapes. The recent advent of ISO 200-micron and ground-based submm measurements allows (and dictates) the inclusion of components slightly above 10 K, which are important out to 800 microns. In fact, this cold dust is dominant by mass over the much brighter dust seen out to 100 microns. The components are sometimes attributed to different regimes of heating: environments
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