Template fitting of WMAP 7-year data: anomalous dust or flattening synchrotron emission?


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Anomalous microwave emission at 20–40 GHz has been detected across our Galactic sky. It is highly correlated with thermal dust emission and hence it is thought to be due to spinning dust grains. Alternatively, this emission could be due to synchrotron radiation with a flattening (hard) spectral index. We cross-correlate synchrotron, free–free and thermal dust templates with the Wilkinson Microwave Anisotropy Probe (WMAP) 7-year maps using synchrotron templates at both 408 MHz and 2.3 GHz to assess the amount of flat synchrotron emission that is present, and the impact that this has on the correlations with the other components. We find that there is only a small amount of flattening visible in the synchrotron spectral indices by 2.3 GHz, of around Δβ ≈ 0.05, and that the significant level of dust-correlated emission in the lowest WMAP bands is largely unaffected by the choice of synchrotron template, particularly at high latitudes (it decreases by only ∼7 per cent when using 2.3 GHz rather than 408 MHz). This agrees with expectation if the bulk of the anomalous emission is generated by spinning dust grains.