Radiative Transfer Modeling of Lyα Emitters. I. Statistics of Spectra and Luminosity

We combine a cosmological reionization simulation with box size of 100 h ^-1 Mpc on a side and a Monte Carlo Lyα radiative transfer code to model Lyα Emitters (LAEs) at z ~ 5.7. The model introduces Lyα radiative transfer as the single factor for transforming the intrinsic Lyα emission properties into the observed ones. Spatial diffusion of Lyα photons from radiative transfer results in extended Lyα emission and only the central part with high surface brightness can be observed. Because of radiative transfer, the appearance of LAEs depends on density and velocity structures in circumgalactic and intergalactic media as well as the viewing angle, which leads to a broad distribution of apparent (observed) Lyα luminosity for a given intrinsic Lyα luminosity. Radiative transfer also causes frequency diffusion of Lyα photons. The resultant Lyα line is asymmetric with a red tail. The peak of the Lyα line shifts toward longer wavelength and the shift is anti-correlated with the apparent-to-intrinsic Lyα luminosity ratio. The simple radiative transfer model provides a new framework for studying LAEs. It is able to explain an array of observed properties of z ~ 5.7 LAEs in Ouchi et al., producing Lyα spectra, morphology, and apparent Lyα luminosity function (LF) similar to those seen in observation. The broad distribution of apparent Lyα luminosity at fixed UV luminosity provides a natural explanation for the observed UV LF, especially the turnover toward the low luminosity end. The model also reproduces the observed distribution of Lyα equivalent width (EW) and explains the deficit of UV bright, high EW sources. Because of the broad distribution of the apparent-to-intrinsic Lyα luminosity ratio, the model predicts effective duty cycles and Lyα escape fractions for LAEs.