Exploring the faint source population at 15.7 GHz

TL;DR

This study investigates the faint, high-frequency radio sky at 15.7 GHz, revealing a dominance of radio galaxy cores at flux densities below 1 mJy and extending source counts down to 0.1 mJy without discovering a new source population.

Contribution

It provides the deepest high-frequency radio survey analysis to date, linking multi-wavelength data to characterize faint radio sources and extending source counts to lower flux densities.

Findings

Increase in flat-spectrum sources below 1 mJy

Majority of sources are radio galaxies with core dominance at high frequencies

No evidence of a new source population down to 0.1 mJy

Abstract

We discuss our current understanding of the nature of the faint, high-frequency radio sky. The Tenth Cambridge (10C) survey at 15.7 GHz is the deepest high-frequency radio survey to date, covering 12 square degrees to a completeness limit of 0.5 mJy, making it the ideal starting point from which to study this population. In this work we have matched the 10C survey to several lower-frequency radio catalogues and a wide range of multi-wavelength data (near- and far-infrared, optical and X-ray). We find a significant increase in the proportion of flat-spectrum sources at flux densities below 1 mJy - the median radio spectral index between 15.7 GHz and 610 MHz changes from 0.75 for flux densities greater than 1.5 mJy to 0.08 for flux densities less than 0.8 mJy. The multi-wavelength analysis shows that the vast majority (> 94 percent) of the 10C sources are radio galaxies; it is therefore likely that these faint, flat spectrum sources are a result of the cores of radio galaxies becoming dominant at high frequencies. We have used new observations to extend this study to even fainter flux densities, calculating the 15.7-GHz radio source count down to 0.1 mJy, a factor of five deeper than previous studies. There is no evidence for a new population of sources, showing that the high-frequency sky continues to be dominated by radio galaxies down to at least 0.1 mJy.