The C-Band All-Sky Survey (C-BASS): Design and capabilities

TL;DR

The C-BASS project conducts a full-sky polarization survey at 5 GHz to map Galactic synchrotron emission, aiding CMB studies and Galactic magnetic field research with high-resolution, stable ground-based observations.

Contribution

It introduces a novel all-sky, full-polarization survey at 5 GHz with matched northern and southern telescopes, enhancing Galactic foreground characterization.

Findings

Northern instrument completed survey

Southern instrument underway

Data expected to improve CMB component separation

Abstract

The C-Band All-Sky Survey (C-BASS) is an all-sky full-polarisation survey at a frequency of 5 GHz, designed to provide complementary data to the all-sky surveys of WMAP and Planck, and future CMB B-mode polarization imaging surveys. The observing frequency has been chosen to provide a signal that is dominated by Galactic synchrotron emission, but suffers little from Faraday rotation, so that the measured polarization directions provide a good template for higher frequency observations, and carry direct information about the Galactic magnetic field. Telescopes in both northern and southern hemispheres with matched optical performance are used to provide all-sky coverage from a ground-based experiment. A continuous-comparison radiometer and a correlation polarimeter on each telescope provide stable imaging properties such that all angular scales from the instrument resolution of 45 arcmin up to full sky are accurately measured. The northern instrument has completed its survey and the southern instrument has started observing. We expect that C-BASS data will significantly improve the component separation analysis of Planck and other CMB data, and will provide important constraints on the properties of anomalous Galactic dust and the Galactic magnetic field.