2012ApJ...747...27T

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 ε_s with respect to z ∼ 6 and a patchy one where a fraction ε_p is absorbed/non-emitted while the rest is unabsorbed. From a compilation of 39 observed z ∼ 7 galaxies, we find ε_s= 0.69±0.12 and ε_p= 0.66±0.16. The models can be used to compute fractions of emitters above any equivalent width W. For W > 25 Å, we find X ²⁵_ z = 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^–17 erg/s/cm2) 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.