Microwave ISM Emission Observed by WMAP

TL;DR

This paper examines the diffuse Galactic microwave emission observed by WMAP, suggesting that much of the dust-correlated emission at low frequencies is likely due to spinning dust rather than synchrotron radiation.

Contribution

It proposes that spinning dust emission accounts for most dust-correlated microwave signals in WMAP data, challenging previous interpretations of synchrotron dominance.

Findings

Dust-correlated emission exceeds thermal dust expectations at low frequencies.

Models of spinning dust fit the full-sky WMAP data well.

A significant free-free component may exist near the Galactic center.

Abstract

We investigate the nature of the diffuse Galactic emission in the Wilkinson Microwave Anisotropy Probe (WMAP) temperature anisotropy data. Substantial dust-correlated emission is observed at all WMAP frequencies, far exceeding the expected thermal dust emission in the lowest frequency channels (23, 33, 41 GHz). The WMAP team (Bennett et al.) interpret this emission as dust-correlated synchrotron radiation, attributing the correlation to the natural association of relativistic electrons produced by SNae with massive star formation in dusty clouds, and deriving an upper limit of 5% on the contribution of Draine & Lazarian spinning dust at K-band (23 GHz). We pursue an alternative interpretation that much, perhaps most, of the dust-correlated emission at these frequencies is indeed spinning dust, and explore the spectral dependence on environment by considering a few specific objects as well as the full sky average. Models similar to Draine & Lazarian spinning dust provide a good fit to the full-sky data. The full-sky fit also requires a significant component with free-free spectrum uncorrelated with \Halpha, possibly hot (~million K) gas within 30 degrees of the Galactic center.