Inside-out or Outside-in: The topology of reionization in the photon-starved regime suggested by Lyman-alpha forest data

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We use a set of semi-numerical simulations based on Zel'dovich approximation, friends-of-friends algorithm and excursion set formalism to generate reionization maps of high dynamic range with a range of assumptions regarding the distribution and luminosity of ionizing sources and the spatial distribution of sinks for the ionizing radiation.

• We find that ignoring the inhomogeneous spatial distribution of regions of high gas density where recombinations are important -- as is often done in studies of this kind -- can lead to misleading conclusions regarding the topology of reionization, especially if reionization occurs in the photon-starved regime suggested by Lya forest data.
• The inhomogeneous spatial distribution of recombinations significantly reduces the mean free path of ionizing photons and the typical size of coherently ionized regions.
• Reionization proceeds then much more as an outside-in process.