Statistical recovery of the BAO scale from multipoles of the
  beam-convolved 21cm correlation function
  Despite being designed as an interferometer, the MeerKAT radio array (an SKA
pathfinder) can also be used in autocorrelation (`single-dish') mode, where
each dish scans the sky independently. Operating in this mode allows extremely
high survey speeds to be achieved, albeit at significantly lower angular
resolution. We investigate the recovery of the baryon acoustic oscillation
(BAO) scale from multipoles of the redshift-space correlation function as
measured by a low angular resolution 21cm intensity mapping survey of this
kind. Our approach is to construct an analytic model of the multipoles of the
correlation function and their covariance matrix that includes foreground
contamination and beam resolution effects, which we then use to generate an
ensemble of mock data vectors from which we attempt to recover the BAO scale.
In line with previous studies, we find that recovery of the transverse BAO
scale $\alpha_{\perp}$ is hampered by the strong smoothing effect of the
instrumental beam with increasing redshift, while the radial scale
$\alpha_\parallel$ is much more robust. The multipole formalism naturally
incorporates transverse information when it is available however, and so there
is no need to perform a radial-only analysis. In particular, the quadrupole of
the correlation function preserves a distinctive BAO `bump' feature even for
large smoothing scales. We also investigate the robustness of BAO scale
recovery to beam model accuracy, severity of the foreground removal cuts, and
accuracy of the covariance matrix model, finding in all cases that the radial
BAO scale can be recovered in an accurate, unbiased manner.
