The C-Band All-Sky Survey (C-BASS): Template Fitting of Diffuse Galactic Microwave Emission in the Northern Sky

TL;DR

This study uses the C-BASS survey to analyze Galactic microwave emissions, finding a steepening of the synchrotron spectrum at high frequencies and supporting spinning dust as the origin of anomalous microwave emission.

Contribution

First detailed analysis of Galactic foregrounds at 4.76GHz using C-BASS, revealing spectral steepening and confirming spinning dust as the source of AME.

Findings

Galactic synchrotron spectrum steepens at high frequencies.

Synchrotron emission is well modeled by a single power-law up to tens of GHz.

AME emissivity is unaffected by the choice of synchrotron tracer.

Abstract

The C-Band All-Sky Survey (C-BASS) has observed the Galaxy at 4.76GHz with an angular resolution of $0.73^\circ$ full-width half-maximum, and detected Galactic synchrotron emission with high signal-to-noise ratio over the entire northern sky ($\delta > -15^{\circ}$). We present the results of a spatial correlation analysis of Galactic foregrounds at mid-to-high ($b > 10^\circ$) Galactic latitudes using a preliminary version of the C-BASS intensity map. We jointly fit for synchrotron, dust, and free-free components between $20$ and $1000$GHz and look for differences in the Galactic synchrotron spectrum, and the emissivity of anomalous microwave emission (AME) when using either the C-BASS map or the 408MHz all-sky map to trace synchrotron emission. We find marginal evidence for a steepening ($\left<\Delta\beta\right> = -0.06\pm0.02$) of the Galactic synchrotron spectrum at high frequencies resulting in a mean spectral index of $\left<\beta\right> = -3.10\pm0.02$ over $4.76-22.8$GHz. Further, we find that the synchrotron emission can be well modelled by a single power-law up to a few tens of GHz. Due to this, we find that the AME emissivity is not sensitive to changing the synchrotron tracer from the 408MHz map to the 4.76GHz map. We interpret this as strong evidence for the origin of AME being spinning dust emission.