The prevalence of core emission in faint radio galaxies in the SKA
  Simulated Skies
  Empirical simulations based on extrapolations from well-established
low-frequency ($< 5$ GHz) surveys fail to accurately model the faint, high
frequency ($>10$~GHz) source population; they under-predict the number of
observed sources by a factor of two below $S_{18~\rm GHz} = 10$ mJy and fail to
reproduce the observed spectral index distribution. We suggest that this is
because the faint radio galaxies are not modelled correctly in the simulations
and show that by adding a flat-spectrum core component to the FRI sources in
the SKA Simulated Skies, the observed 15-GHz source counts can be reproduced.
We find that the observations are best matched by assuming that the fraction of
the total 1.4-GHz flux density which originates from the core varies with
1.4-GHz luminosity; sources with 1.4-GHz luminosities $< 10^{25} \rm W \,
Hz^{-1}$ require a core fraction $\sim 0.3$, while the more luminous sources
require a much smaller core fraction of $5 \times 10^{-4}$. The low luminosity
FRI sources with high core fractions which were not included in the original
simulation may be equivalent to the compact `FR0' sources found in recent
studies.
