Extrapolation of Galactic Dust Emission at 100 Microns to Cosmic Microwave Background Radiation Frequencies Using FIRAS

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Abstract

We present predicted full-sky maps of submillimeter and microwave emission from the diffuse interstellar dust in the Galaxy. These maps are extrapolated from the 100 μm emission and 100/240 μm flux ratio maps that Schlegel, Finkbeiner, & Davis generated from IRAS and COBE/DIRBE data. Results are presented for a number of physically plausible emissivity models. The correlation of COBE/FIRAS data with the simple Schlegel, Finkbeiner, & Davis (ν2 emissivity power law) extrapolation is much tighter than with other common dust templates such as H I column density or 100 μm emission. Despite the apparent success of the Schlegel, Finkbeiner, & Davis extrapolation, the assumed ν2 emissivity is inconsistent with the FIRAS data below 800 GHz. Indeed, no power-law emissivity function fits the FIRAS data from 200 to 2100 GHz. In this paper we provide a formalism for a multicomponent model for the dust emission. A two-component model with a mixture of "silicate" and "carbon-dominated" grains (motivated by Pollack et al.) provides a fit to an accuracy of ~15% to all the FIRAS data over the entire high-latitude sky. Small systematic differences are found between the atomic and molecular phases of the ISM. COBE/DMR has observed microwave emission that is correlated with thermal dust emission. However, this emission is higher than our model predicts by factors of 1.2, 2.4, and 20 at 90, 53, and 31 GHz, respectively. This provides evidence that another emission mechanism dominates dust emission at frequencies below ~60 GHz. Our predictions for the thermal (vibrational) emission from Galactic dust at ν < 3000 GHz are available for general use. These full-sky predictions can be made at the DIRBE resolution of 40' or at the higher resolution of 6farcm1 from the Schlegel, Finkbeiner, & Davis DIRBE-corrected IRAS maps.

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