Signatures of reionization on Lyα emitters

We use a semi-analytic model of Ly alpha emitters (LAEs) to constrain the reionization history. By considering two physically motivated scenarios in which reionization ends either early [early reionization model (ERM), z(i) approximate to 7] or late [late reionization model (LRM), z(i) approximate to 6], we fix the global value of the intergalactic medium neutral fraction (e.g. chi HI = 3 x 10(-4), 0.15 at z = 6.56 for the ERM and LRM, respectively) leaving only the star formation efficiency and the effective escape fraction of Lya photons as free parameters. The ERM fits the observed LAE luminosity function (LF) at z = 5.7 and 6.56 requiring no redshift evolution or mass dependence of the star formation efficiency, and LAE star formation rates (SFR) of 3 < M-star/M-circle dot yr(-1) < 103, contributing approximate to 8 per cent of the cosmic SFR density at z = 5.7. The LRM requires a physically uncomfortable drop of approximate to 4.5 times in the SFR of the emitters from z = 6.5 to 5.7. Thus, the data seem to imply that the Universe was already highly ionized at z = 6.56. The mass-dependent Lya transmissivity is 0.36 less than or similar to T-alpha less than or similar to 0.51 (ERM) and T-alpha less than or similar to 0.26 (LRM) at z = 6.56. The LF data at z = 4.5 imply an extra Lya line damping factor of approximate to 0.25 possibly due to dust; the presence of a (clumpy) dust component with E(B -V) less than or similar to 0.28 is also required to reproduce the observed large Lya equivalent widths at the same redshift. Additional useful information can be extracted from the line profile (weighted) skewness, found to be S-W = 10 -17 angstrom for the two reionization models, which shows an interesting L-alpha-chi HI anti-correlation, holding under the model assumptions. The shortcomings of the model and strategies to overcome them are discussed.