The C-Band All-Sky Survey (C-BASS): constraining diffuse Galactic radio emission in the North Celestial Pole region

The C-Band All-Sky Survey (C-BASS) is a high-sensitivity all-sky radio survey at an angular resolution of 45 arcmin and a frequency of 5 GHz. We present a deep total intensity map of the North Celestial Pole (NCP) region of sky at an effective centre frequency of 4.7 GHz, which is limited by source confusion at a level of ~0.6 mK rms. The map contains extragalactic radio sources as well as diffuse Galactic synchrotron emission. We apply the template-fitting (cross-correlation) technique to WMAP and Planck data, using the C-BASS map as the synchrotron template, to investigate the contribution of diffuse foreground emission at frequencies ~20-40 GHz for declinations above +80deg. In particular, we investigate the anomalous microwave emission (AME) that is correlated with far-infrared emission associated with dust. We find that the AME amplitude does not change significantly ( 5 GHz in the NCP region, the best-fitting synchrotron spectral index is $\beta=-2.91\pm0.04$ from 4.7 to 22.8 GHz and $\beta=-2.85 \pm 0.14$ from 22.8 to 44.1 GHz. Free-free emission is weak, contributing ~$7\,\mu$K rms in this region at 22.8 GHz, which is ~7% of the total. The best explanation for the AME is still electric dipole emission from small spinning dust grains.