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

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 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 Hα 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 ∼ 6000 K, although the value depends critically on the impact of dust absorption on the Hα 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 β ≈ −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. An enhancement of the thermal dust contribution over the FDS8 predictions by a factor ∼ 1.2 is required with such models. Furthermore, the emissivity varies by a factor of ∼ 50% from cloud to cloud relative to the mean. The significance of these results for the correction of CMB data for Galactic foreground emission is discussed.