The Detectability of Lyman Alpha Emission from Galaxies during the Epoch of Reionization
Abstract
We study the visibility of the Lyman Alpha (Lya) emission line during the Epoch of Reionization (EoR). Combining galactic outflow models with large-scale semi-numeric simulations of reionization, we quantify the probability distribution function (PDF) of the fraction of Lya photons transmitted through the intergalactic medium (IGM), TIGM. Our study focusses on galaxies populating dark matter halos with masses of Mhalo=1e10 Msun at z=8.6, which is inspired by the recent reported discovery of a galaxy at z=8.6 with strong Lya line emission. For reasonable model assumptions, we find that winds cause TIGM>10% [50%], for the majority of galaxies, even when the Universe is ~80% [60%] neutral by volume. Thus, the observed strong Lya emission from the reported z=8.6 galaxy is consistent with a highly neutral IGM. We also investigate the implications of the recent tentative evidence for a observed decrease in the `LAE fraction' among drop-out galaxies between z=6 and z=7. If confirmed, we show that a rapid evolution in xHI will be required to explain this observation via the effects of reionization.
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