The quest for microwave foreground X

The Wilkinson Microwave Anisotropy Probe (WMAP) team has produced a foreground map that can account for most of the low-frequency Galactic microwave emission in the WMAP maps, tentatively interpreting it as synchrotron emission. Finkbeiner and collaborators have challenged these conclusions, arguing that the WMAP team's "synchrotron" template is in fact dominated not by synchrotron radiation but by some dust-related Galactic emission process, perhaps spinning dust grains, making dramatically different predictions for its behavior at lower frequencies. By cross-correlating this synchrotron template with 10 and 15 GHz cosmic microwave background observations, we find that its spectrum turns over in a manner consistent with spinning dust emission, falling about an order of magnitude below what the synchrotron interpretation would predict.