Letter to the Editor

Probing the origin of the microwave anomalous foreground

Institut d'Astrophysique Spatiale, UMR8617, Université Paris-Sud, 91405 Orsay, France e-mail: nathalie.ysard@ias.u-psud.fr

Received: 18 June 2009
Accepted: 28 July 2009

Abstract

Context. The Galactic anomalous microwave emission detected between 10 and 90 GHz is a major foreground to CMB fluctuations. Well correlated with dust emission at 100 μm, the anomalous foreground is interstellar but its origin is still debated. Possible carriers for this emission are spinning, small dust grains carrying a permanent electric dipole.

Aims. To probe the origin of the anomalous foreground, we compare microwave data to dust IR emission on an angular scale of 1°, and search for specific signatures predicted by models of spinning dust.

Methods. For the anomalous foreground, we use the 23 GHz all-sky map deduced from WMAP data by Miville-Deschênes and collaborators. The IR dust emission is traced by IRAS data. Models show that spinning dust emission is little sensitive to the intensity of the radiation field (G₀) for  GHz, while the mid-IR emission produced by the same small dust grains is proportional to G₀. To test this behaviour in our comparison, we derive G₀ from the dust temperature maps of Schlegel and collaborators.

Results. From all-sky maps, we show that the anomalous foreground is more strongly correlated with the emission of small grains (at 12 μm) than with that of large grains (at 100 μm). In addition, we show that the former correlation is significantly improved when the 12 μm flux is divided by G₀, as predicted by current models of spinning dust. The results apply to angular scales greater than 1°. Finally, from a model fit of the anomalous foreground, we deduce physical properties for Polycyclic Aromatic Hydrocarbons that are in good agreement with those deduced from mid-IR spectroscopy.