A determination of the Spectra of Galactic components observed by WMAP

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  • 14 November 2005
Abstract
WMAP data when combined with ancillary data on free-free, synchrotron and dust allow an improved understanding of the spectrum of emission from each of these components. Here we examine the sky variation at intermediate latitudes using two approaches (a) T-T plots and (b) a cross-correlation technique. The free-free emission of the diffuse ionized gas fits a well-known spectrum over a frequency range from 0.4 to 94 GHz. The fact that its emissivity is temperature sensitive allows us to derive a mean temperature of 8000 K with a spread of ~30 per cent. The synchrotron emission steepens between GHz frequencies and the WMAP bands with significant changes across the sky. The anomalous emission associated with dust is clearly detected in most of the 15 fields studied. Fields that are only weakly contaminated by synchrotron, free-free and CMB are studied; the anomalous emission closely follows the 100 $\mu$m dust data with a temperature spectral index, in the frequency range between 20 and 40 GHz, of ~-3.1 and steepening at higher WMAP frequencies. Furthermore, the emissivity (microK/MJy sr) varies by a factor of ~2.5 from cloud to cloud. The relevance of these results for the correction of CMB data for Galactic foreground emission is discussed.

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