Foreground Analysis Using Cross-Correlations of External Templates on the 7-year WMAP data

TL;DR

This study analyzes WMAP 7-year data using cross-correlation with external templates to characterize Galactic foreground emissions, revealing spectral variations, free-free and spinning dust contributions, and the nature of anomalous microwave emission.

Contribution

It introduces a cross-correlation technique applied to WMAP data with external templates, providing detailed spectral and spatial analysis of Galactic foreground components.

Findings

Synchrotron emission shows spectral steepening between GHz and WMAP bands.

Evidence of free-free and spinning dust contributions in the warm ionized medium.

Detection of anomalous microwave emission correlated with dust, fitting a power-law spectrum.

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 and high latitudes using a cross-correlation technique. In particular, we compare the observed emission in several large partitions of the sky plus 33 selected sky regions to three "standard" templates. The regions are selected using a criterion based on the morphology of these template maps. The synchrotron emission shows evidence of steepening between GHz frequencies and the \emph{WMAP} bands. There are indications of spectral index variations across the sky but the current data are not precise enough to accurately quantify this from region-to-region. The emission correlated with the $H_{\alpha}$ template shows clear evidence of deviation from a free-free spectrum. The emission can be decomposed into a contribution from both free-free and spinning dust in the warm ionised medium of the Galaxy. The derived free-free emissivity corresponds to a mean electron temperature of $\sim 6000$ K, although the value depends critically on the impact of dust absorption on the $H_{\alpha}$ intensity. The WIM spinning dust emission has a peak emission in intensity in the range 40--50 GHz. The anomalous microwave emission associated with dust is detected at high significance in most of the 33 fields studied. The anomalous emission correlates well with the Finkbeiner et al. (1999) model 8 predictions (FDS8) at 94 GHz, and is well described globally by a power-law emission model with an effective spectral index between 20 and 60 GHz of $\beta \approx -2.7$. It is clear that attempts to explain the emission by spinning dust models require multiple components, which presumably relates to a complex mix of emission regions along a given line-of-sight.