Probing the origin of the microwave anomalous emission

Context. The galactic anomalous microwave emission detected between 10 and 90 GHz is a major foreground to CMB fluctuations. Well correlated to dust emission at 100 µm, the anomalous emission is interstellar but its origin is still debated. Some possible explanations relate it to dust: emission of spinning, small (nanometric) grains carrying a permanent electric dipole or magnetic fluctuations in larger (submicronic) grains. Aims. To probe the origin of the anomalous emission, we compare microwave data to dust IR emission and search for specific signatures predicted by models of spinning dust. Methods. For the anomalous emission, we use the 23 GHz all-sky map deduced from WMAP data by Miville-Deschênes et al. (2008). The dust emission is traced by IRAS data. Models show that spinning dust emission is little sensitive to the intensity of the radiation field (G 0) for 10 ν 30 GHz while the corresponding mid-IR emission is proportional to G 0. To test this behaviour in our comparison, we derive G 0 from the dust temperature maps of Schlegel et al. (1998). Results. From all-sky maps, we show that the anomalous emission is better correlated to the emission of small grains (at 12 µm) than to that of big grains (at 100 µm). In addition we show that the former correlation is significantly improved when the 12 µm flux is divided by G 0 , as predicted by current models of spinning dust. Key words. anomalous emission – spinning dust emission – interstellar medium – PAH – galactic foregrounds – WMAP – IRIS