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

TL;DR

This paper presents a high-sensitivity 4.7 GHz all-sky radio map of the North Celestial Pole, analyzes diffuse foreground emissions including AME, and compares templates to better understand Galactic radio foregrounds relevant for cosmology.

Contribution

It provides the first detailed 4.7 GHz map of the NCP region and evaluates the effectiveness of C-BASS as a synchrotron template for foreground modeling.

Findings

AME accounts for about 60% of foreground emission at 22.8 GHz.

The synchrotron spectral index is approximately -2.9 between 4.7 and 22.8 GHz.

The AME is best explained by electric dipole emission from spinning dust grains.

Abstract

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 4.7 GHz. We present a total intensity 4.7 GHz map of the North Celestial Pole (NCP) region of sky, above declination +80 deg, which is limited by source confusion at a level of ~0.6 mK rms. 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. We quantify the anomalous microwave emission (AME) that is correlated with far-infrared dust emission. The AME amplitude does not change significantly (<10%) when using the higher frequency C-BASS 4.7 GHz template instead of the traditional Haslam 408 MHz map as a tracer of synchrotron radiation. We measure template coefficients of $9.93\pm0.35$ and $9.52\pm0.34$ K per unit $\tau_{353}$ when using the Haslam and C-BASS synchrotron templates, respectively. The AME contributes $55\pm2\,\mu$K rms at 22.8 GHz and accounts for ~60% of the total foreground emission. Our results suggest that a harder (flatter spectrum) component of synchrotron emission is not dominant at frequencies >5 GHz; the best-fitting synchrotron temperature spectral index is $\beta=-2.91\pm0.04$ from 4.7 to 22.8 GHz and $\beta=-2.85\pm0.14$ from 22.8 to 44.1 GHz. Free-free emission is weak, contributing ~$7\,\mu$K rms (~7%) at 22.8 GHz. The best explanation for the AME is still electric dipole emission from small spinning dust grains.