  The recent low value of Planck (2016) integrated optical depth to Thomson
scattering suggests that the reionization occurred fairly suddenly, disfavoring
extended reionization scenarios. This will have a significant impact on the
21cm power spectrum. Using a semi-numerical framework, we improve our model
from Hassan et al. (2016) to include time-integrated ionisation and
recombination effects, and find that this leads to more sudden reionisation. It
also yields larger HII bubbles which leads to an order of magnitude more 21cm
power on large scales, while suppressing the small scale ionization power.
Local fluctuations in the neutral hydrogen density play the dominant role in
boosting the 21cm power spectrum on large scales, while recombinations are
subdominant. We use a Monte Carlo Markov Chain approach to constrain our model
to observations of the star formation rate functions at z = 6,7,8 from Bouwens
et al. (2015), the Planck (2016) optical depth measurements, and the Becker &
Bolton (2013) ionising emissivity data at z~5. We then use this constrained
model to perform 21cm forecasting for LOFAR, HERA, and SKA in order to
determine how well such data can characterise the sources driving reionisation.
We find that the 21cm power spectrum alone can somewhat constrain the halo mass
dependence of ionising sources, the photon escape fraction and ionising
amplitude, but combining the 21cm data with other current observations enables
us to separately constrain all these parameters. Our framework illustrates how
21cm data can play a key role in understanding the sources and topology of
reionisation as observations improve.
