INFERENCES ON THE DISTRIBUTION OF Ly{alpha} EMISSION OF z {approx} 7 AND z {approx} 8 GALAXIES

Spectroscopic confirmation of galaxies at z similar to 7 and above has been extremely difficult, owing to a drop in intensity of Ly alpha emission in comparison with samples at z similar to 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 Ly alpha is attenuated by a factor epsilon(s) with respect to z similar to 6 and a patchy one where a fraction epsilon(p) is absorbed/non-emitted while the rest is unabsorbed. From a compilation of 39 observed z similar to 7 galaxies, we find epsilon(s) = 0.69 +/- 0.12 and epsilon(p) = 0.66 +/- 0.16. The models can be used to compute fractions of emitters above any equivalent width W. For W > 25 angstrom, we find X-z=7(25) = 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 similar to 8 we combine new deep (5 sigma flux limit 10(-17) erg s(-1) cm(-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 Lya emitters at z similar to 8 and distinguish between models.