Probing primordial non-Gaussianity with the power spectrum and
  bispectrum of future 21cm intensity maps
  After reionisation, the 21cm emission line of neutral hydrogen within
galaxies provides a tracer of dark matter. Next-generation intensity mapping
surveys, with the SKA and other radio telescopes, will cover large sky areas
and a wide range of redshifts, facilitating their use as probes of primordial
non-Gaussianity. {Previous works have shown that the bispectrum can achieve
tight constraints on primordial non-Gaussianity with future surveys that are
purposely designed for intensity mapping in interferometer mode}. Here we
investigate the constraints attainable from surveys operating in single-dish
mode, \rev{using the combined power spectrum and bispectrum signal}. In the
case of the power spectrum, single-dish surveys typically outperform
interferometer surveys. We find that the reverse holds for the bispectrum:
single-dish surveys are not competitive with surveys designed for
interferometer mode.
