Tracing early structure formation with massive starburst galaxies and their implications for reionization

Cosmological hydrodynamic simulations have significantly improved over the past several years, and we have already shown that the observed properties of Lyman-break galaxies (LBGs) at z = 3 can be explained well by the massive galaxies in the simulations. Here, we extend our study to z = 6 and show that we obtain good agreement for the LBGs at the bright-end of the luminosity function (LF). Our simulations also suggest that the cosmic star formation rate density has a peak at z = 5-6, and that the current LBG surveys at 7 = 6 are missing a significant number of faint galaxies that are dimmer than the current magnitude limit. Together, our results suggest that the universe could be reionized at z = 6 by the Pop II stars in ordinary galaxies. We also estimate the LF of Lyman-alpha emitters (LAEs) at z = 6 by relating the star formation rate in the simulation to the Ly alpha luminosity. We find that the simulated LAE LFs agree with the observed data provided that the net escape fraction of Ly alpha photon is f(Ly alpha) <= 0.1. We investigate two possible scenarios for this effect: (1) all sources in the simulation are uniformly dimmer by a factor of 10 through attenuation, and (2) one out of 10 LAEs randomly lights up at a given moment. We show that the correlation strength of the LAE spatial distribution can possibly distinguish the two scenarios. (c) 2005 Elsevier B.V. All rights reserved.