Interpretation of Far Infra-Red Emission from Interstellar Grains

Abstract
We apply the Kramers–Kronig relations to grains in the interstellar medium and find that the recent UV, visual and infra-red extinction curves provide marginal evidence against silicates as the major cause of this extinction. In the far infra-red, grains contribute little to the extinction, but can be observed in thermal emission. We show that the far infra-red emission from grains in a given bandwidth sets a lower limit to the grain temperature. From observed intensities from the galactic plane at 100 µ and from Orion at 350 µ we find minimum grain temperatures which are larger than the observed brightness temperature. The emission and extinction data can be used together to constrain the allowable range of parameters for the grains.

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