Inferences on the distribution of Lyα emission of z ∼ 7 and z ∼ 8 galaxies

Abstract

Spectroscopic confirmation of galaxies at z ∼ 7 and above has been extremely difficult, owing to a drop in intensity of Lyα emission in comparison with samples at z 6. This crucial finding could potentially signal the ending of cosmic reionization. However, it is based on small data sets, often incomplete and heterogeneous in nature. We introduce a flexible Bayesian framework, useful to interpret such evidence. Within this framework, we implement two simple phenomenological models: a smooth one where the distribution of Lyα is attenuated by a factor εs with respect to z 6 and a patchy one where a fraction εp is absorbed/non-emitted while the rest is unabsorbed. From a compilation of 39 observed z ∼ 7 galaxies, we find εs = 0.69 ± 0.12 and εp = 0.66 ± models can be used to compute fractions of emitters above any equivalent width W. For W > 25 , we find X 25z = 7 = 0.37 ± 0.11 (0.14 ± 0.06) for galaxies fainter (brighter) than M UV = -20.25 for the patchy model, consistent with previous work, but with smaller uncertainties by virtue of our full use of the data. At z 8 we combine new deep (5σ flux limit 10-17ergs -1cm-2) Keck/NIRSPEC observations of a bright Y-dropout identified by our Brightest of Reionization Galaxies Survey, with those of three objects from the literature and find that the inference is inconclusive. We compute predictions for future near-infrared spectroscopic surveys and show that it is challenging but feasible to constrain the distribution of Lyα emitters at z 8 and distinguish between models. © 2012. The American Astronomical Society. All rights reserved.