The escape of ionizing photons from supernova-dominated primordial galaxies

Abstract

In order to assess the contribution of Lyman break galaxies (LBGs) and Lyman alpha emitters (LAEs) at redshifts 3<z<7 to the ionization of intergalactic medium (IGM), we investigate the escape fractions of ionizing photons from supernova-dominated primordial galaxies by solving the three-dimensional radiative transfer. The model galaxy is employed from an ultra-high-resolution chemodynamic simulation of a primordial galaxy by Mori & Umemura (2006),which well reproduces the observed properties of LAEs and LBGs. The total mass of model galaxy is 10^{11}M_sun. We solve not only photo-ionization but also collisional ionization by shocks. In addition, according to the chemical enrichment, we incorporate the effect of dust extinction, taking the size distributions of dust into account. As a result, we find that dust extinction reduces the escape fractions by a factor 1.5-8.5 in the LAE phase and by a factor 2.5-11 in the LBG phase, while the collisional ionization by shocks increases the escape fractions by a factor ~ 2. The resultant escape fractions are 0.07-0.47 in the LAE phase and 0.06-0.17 in the LBG phase. These results are well concordant with the recent estimations derived from the flux ratio at 1500 angstrom to 900 angstrom of LAEs and LBGs. Combining the resultant escape fractions with the luminosity functions of LAEs and LBGs, we find that high-z LAEs and LBGs can ionize the IGM at z=3-5. However, ionizing radiation from LAEs as well as LBGs falls short to ionize the IGM at z>6. That implies that additional ionization sources may required at z>6.