Exploring the faint source population at 15.7 GHz
  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.
