Dark ages reionization & galaxy formation simulation XII: Bubbles at
  dawn
  Direct detection of regions of ionized hydrogen (HII) has been suggested as a
promising probe of cosmic reionization. Observing the redshifted 21-cm signal
of hydrogen from the epoch of reionization (EoR) is a key scientific driver
behind new-generation, low-frequency radio interferometers. We investigate the
feasibility of combining low-frequency observations with the Square Kilometre
Array and near infra-red survey data of the Wide-Field Infrared Survey
Telescope to detect cosmic reionization by imaging HII bubbles surrounding
massive galaxies during the cosmic dawn. While individual bubbles will be too
small to be detected, we find that by stacking redshifted 21-cm spectra centred
on known galaxies, it will be possible to directly detect the EoR at $z \sim
9-12$, and to place qualitative constraints on the evolution of the spin
temperature of the intergalactic medium (IGM) at $z \geq 9$. In particular,
given a detection of ionized bubbles using this technique, it is possible to
determine if the IGM surrounding them is typically in absorption or emission.
Determining the globally-averaged neutral fraction of the IGM using this method
will prove more difficult due to degeneracy with the average size of HII
regions.
