Microwave ISM Emission Observed by WMAP

TL;DR

This work reexamines the origin of dust-correlated microwave emission in the WMAP data by constructing a multi-component foreground model that includes free-free, soft synchrotron, vibrational dust, and a spinning-dust template scaled by $ au_{100\mu}$ and $T_{dust}$. The authors perform a sky-wide fit with CMB subtraction and masking, finding an excellent overall match to the data and identifying a spinning-dust–like residual as a major component, along with a diffuse free-free–like 'haze' uncorrelated with Hα. While the WMAP MEM results suggested a subdominant spinning-dust contribution, this analysis shows spinning dust remains a viable and significant contributor to the dust-correlated emission, compatible with several environmental templates and objects such as LDN1622. The results underline the need for polarization measurements and broader frequency coverage to disentangle spinning dust, magnetic dust, and hard synchrotron contributions in the diffuse ISM.

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.