  The power spectrum of redshifted 21 cm emission brightness temperature
fluctuations is a powerful probe of the Epoch of Reionization (EoR). However,
bright foreground emission presents a significant impediment to its unbiased
recovery from interferometric data. We build on the Bayesian power spectral
estimation methodology introduced in Sims et al. 2016 and demonstrate that
incorporating a priori knowledge of the spectral structure of foregrounds in
the large spectral scale component of the data model enables significantly
improved modelling of the foregrounds without increasing the model complexity.
We explore two astrophysically motivated parametrisations of the large spectral
scale model: (i) a constant plus power law model of the form
$q_{0}+q_{1}(\nu/\nu_{0})^{b_{1}}$ for two values of $b_{1}$: $b_{1} =
<\beta>_\mathrm{GDSE}$ and $b_{1} = <\beta>_\mathrm{EGS}$, the mean spectral
indices of the Galactic diffuse synchrotron emission and extragalactic source
foreground emission, respectively, and (ii) a constant plus double power law
model of the form $q_{0}+q_{1}(\nu/\nu_{0})^{b_{1}}+q_{2}(\nu/\nu_{0})^{b_{2}}$
with $b_{1} = <\beta>_\mathrm{GDSE}$ and $b_{2} = <\beta>_\mathrm{EGS}$. We
estimate the EoR power spectrum from simulated interferometric data consisting
of an EoR signal, Galactic diffuse synchrotron emission, extragalactic sources
and diffuse free-free emission from the Galaxy. We show that, by jointly
estimating a model of the EoR signal with the constant plus double power law
parametrisation of the large spectral scale model, unbiased estimates of the
EoR power spectrum are recoverable on all spatial scales accessible in the data
set, including on the large spatial scales that were found to be contaminated
in earlier work.

Cosmology and Nongalactic Astrophysics