Reionization of hydrogen and helium by early stars and quasars

摘要: We compute the reionization histories of hydrogen and helium caused by ionizing radiation fields produced stars quasars. For quasars we use a model based on halo-merger rates that reproduces all known properties quasar luminosity function at high redshifts. The less constrained are modeled with two free parameters: (i) transition redshift, ztran, above which stellar population is dominated massive, zero-metallicity below it Scalo mass function; (ii) product escape fraction photons from their host galaxies star formation efficiency, fescf*. constrain allowed range these parameters redshifts basis lack H I Gunn-Peterson trough z 6 upper limit total intergalactic optical depth for electron scattering, τes < 0.18, recent cosmic microwave background (CMB) experiments. find ionize redshift ~ 4, but cannot reionize themselves before 6. A major combinations fescf* ztran leads to an early peak in ionized because presence metal-free This sometimes results epochs, namely, II or He III overlap phase followed recombination second phase. Even if not achieved, visibility scattering CMB often coincides ionization rather than actual epoch. Consequently, does correspond directly redshift. generically values 7%, should be detectable MAP satellite.