CANDELS: THE CONTRIBUTION OF THE OBSERVED GALAXY POPULATION TO COSMIC REIONIZATION

We present measurements of the specific ultraviolet luminosity density from a sample of 483 galaxies at 6 [< or ~] z [< or ~] 8. These galaxies were selected from new deep near-infrared Hubble Space Telescope imaging from the Cosmic Assembly Near-infrared-Deep Extragalactic Legacy Survey,Hubble-Ultra-Deep Field 2009, and Wide Field-Camera 3 Early Release Science programs. We investigate the contribution to re-ionization from galaxies that we observe directly, thus sidestepping the uncertainties inherent in complementary studies that have invoked assumptions regarding the intrinsic shape or the faint-end cutoff of the galaxy ultraviolet (UV) luminosity function. If faint galaxies dominated the ionizing photon budget at z = 6-7, future extremely deep observations with the James Webb Space Telescope will probe deep enough to directly observe them, providing an indirect constraint on the global ionizing photon escape fraction.