Loops and spurs: The angular power spectrum of the Galactic synchrotron background

TL;DR

This paper introduces a comprehensive model of Galactic synchrotron radiation that combines large-scale emissivity variations with turbulence and supernova remnant effects, improving foreground subtraction for cosmological studies.

Contribution

It unifies previous models by incorporating the impact of supernova remnants ('radio loops') on the angular power spectrum of synchrotron emission.

Findings

The model accounts for intermediate and small scale power in the synchrotron background.

Inclusion of supernova remnant effects explains missing power in the angular spectrum.

Enhanced modeling aids in better foreground removal for CMB and dark matter research.

Abstract

We present a new model of the diffuse Galactic synchrotron radiation, concentrating on its angular anisotropies. While previous studies have focussed on either the variation of the emissivity on large (kpc) scales, or on fluctuations due to MHD turbulence in the interstellar medium, we unify these approaches to match the angular power spectrum. We note that the usual turbulence cascade calculation ignores spatial correlations at the injection scale due to compression of the interstellar medium by old supernova remnants -- the 'radio loops', only four of which are visible by eye in radio maps. This new component naturally provides the otherwise missing power on intermediate and small scales in the all-sky map at 408 MHz. Our model can enable more reliable subtraction of the synchrotron foreground for studies of CMB anisotropies (both in temperature and polarisation) or searches for dark matter annihilation. We conclude with some remarks on the relevance to modelling of the polarised foreground.