Lyman alpha emitter evolution in the reionization epoch

Combining cosmological smoothed particle hydrodynamics (SPH) simulations with a previously developed Lya production/transmission model and the Early Reionization Model (ERM; reionization ends at redshift z similar to 7), we obtain Ly alpha and UV luminosity functions (LFs) for lyman alpha emitters (LAEs) at 5.7 <= z <= 7.6. Matching model results to observations at z similar to 5.7 requires escape fractions of Ly alpha, f(alpha) = 0.3, and UV (non-ionizing) continuum photons, f(c) = 0.22, corresponding to a colour excess, E(B -V) = 0.15. We find that (i) f(c) increases towards higher redshifts, due the decreasing mean dust content of galaxies, (ii) the evolution of f(alpha)/f(c) hints at the dust content of the interstellar medium becoming progressively inhomogeneous/clumped with decreasing redshift. Using the model assumptions, clustering of sources has little effect on the Ly alpha LF for a cosmic hydrogen neutral fraction chi(H I) <= 10(-4), a value attained at z <= 6.6 in the ERM. However, during the initial reionization phases (z greater than or similar to 7), the clustering photoionization boost becomes important. We quantify the physical properties of observed LAEs and their redshift evolution, for which we give handy analytical fitting functions. Halo (stellar) masses are in the range 10.0 < logM(h) < 11.8 (8.1 < logM(*) < 10.4) with M(h) alpha M(*)(0.64). The star formation rates are (M) over dot(*) = 3-120M(circle dot) yr(-1), mass-weighted mean ages are t(*) > 20 Myr at all redshifts, while the mean stellar metallicity increases from Z = 0.12 Z(circle dot) at z similar to 7.6 to Z = 0.22 Z(circle dot) at z similar to 5.7; both t(*) and Z positively correlate with stellar mass. The brightest LAEs are all characterized by large (M) over dot(*) and intermediate ages (approximate to 200 Myr), while objects in the faint end of the Lya LF show large age and star formation rate spreads. With no more free parameters, the spectral energy distributions of three LAE at z similar to 5.7 observed by Lai et al. (2007) are well reproduced by an intermediate age (182-220 Myr) stellar population and the above E(B -V) value. The model uncertainties, mostly related to the simplified treatment of dust and to the possible effects related to gas outflow/infall, are discussed along with their impact on the results.