Lyman-alpha Emitters in Cosmological Simulations I: Lyman-alpha Escape Fraction and Statistical Properties at z=3.1

We use very large cosmological Smoothed-Particle-Hydrodynamics simulations to study the properties of high redshift Lyman-alpha emitters (LAEs). We identify star-forming galaxies at z=3.1 in a cosmological volume of 100 h^-1Mpc on a side. We develop a phenomenological model of absorption, scattering and escape of Lyman-alpha photons on the assumption that the clumpiness of the inter-stellar medium in a galaxy is correlated with the larger scale substructure richness. The radiative transfer effect proposed by Neufeld (1991) allows a large fraction of Lyman-alpha photons to escape from a clumpy galaxy even if it contains a substantial amount of dust. Our model reproduces, for the first time, all of the following observed properties of LAEs at z=3.1: the angular correlation function, ultra-violet and Lyman-alpha luminosity functions, and the equivalent width distribution. A simple model that takes only dust absorption into account fails in matching the observational data, suggesting that the kind of effect we consider is needed. Our model also predicts a bimodal age distribution for LAEs. There are old, massive and dusty LAEs, similar to recently found high redshift LAEs. The large LAEs have escape fractions of Lyman-alpha photons of f_esc ~ 0.05-0.1.