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 Ly alpha radiative transfer code to model Ly alpha Emitters (LAEs) at z similar to 5.7. The model introduces Ly alpha radiative transfer as the single factor for transforming the intrinsic Ly alpha emission properties into the observed ones. Spatial diffusion of Ly alpha photons from radiative transfer results in extended Ly alpha 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) Ly alpha luminosity for a given intrinsic Ly alpha luminosity. Radiative transfer also causes frequency diffusion of Ly alpha photons. The resultant Ly alpha line is asymmetric with a red tail. The peak of the Ly alpha line shifts toward longer wavelength and the shift is anti-correlated with the apparent-to-intrinsic Ly alpha 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 similar to 5.7 LAEs in Ouchi et al., producing Ly alpha spectra, morphology, and apparent Ly alpha luminosity function (LF) similar to those seen in observation. The broad distribution of apparent Ly alpha 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 Ly alpha equivalent width (EW) and explains the deficit of UV bright, high EW sources. Because of the broad distribution of the apparent-to-intrinsic Ly alpha luminosity ratio, the model predicts effective duty cycles and Ly alpha escape fractions for LAEs.