33RD INTERNATIONAL COSMIC RAY CONFERENCE, RIO DE JANEIRO 2013 THE ASTROPARTICLE PHYSICS CONFERENCE The angular power spectrum of the Galactic radio background

Abstract: We study the Galactic radio background produced by synchrotron emission of cosmic ray electrons in Galactic magnetic fields. The angular power spectrum of all-sky maps contains contributions from physical processes on a variety of scales, including the variation of emissivity on large (kpc) scales and the small-scale turbulence in the interstellar medium. Previous studies have focussed on one scale or the other but have not provided a self-consistent picture valid on all scales. We show that the angular power spectrum in the multipole range l ∼ 10 − 100 has a deficit with respect to observations at 408MHz and suggest that the shells of old supernova remnants (like the well-known ‘radio loops’) can provide the missing power. We model the emissivity from individual shells and find that the Galactic population of O(1000) shells naturally provides the missing power and brings the modelled angular power spectrum into agreement with the observed one. This has important implications for studies of the cosmic microwave background, in particular B-mode polarisation