Abstract
The excursion set reionization framework is widely used, due to its speed and
accuracy in reproducing the 3D topology of reionization. However, it is known
that it does not conserve photon number. Here, we introduce an efficient,
on-the-fly recipe to approximately account for photon conservation. Using a
flexible galaxy model shown to reproduce current high-$z$ observables, we
quantify the bias in the inferred reionization history and galaxy properties
resulting from the non-conservation of ionizing photons. Using a mock 21-cm
observation, we perform inference with and without correcting for ionizing
photon conservation. We find that ignoring photon conservation results in very
modest biases in the inferred galaxy properties, for our fiducial model. The
notable exception is in the power-law scaling of the ionizing escape fraction
with halo mass, which can be biased from the true value by $\sim2.4\sigma$
(corresponding to $\sim0.2$ in the power-law index). Our scheme is implemented
in the public code $21cmFAST$.
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