Reionization of Hydrogen and Helium by Early Stars and Quasars

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Abstract
We compute the reionization histories of hydrogen and helium due to the ionizing radiation fields produced by stars and quasars. For the quasars we use a model based on halo-merger rates that reproduces all known properties of the quasar luminosity function at high redshifts. The less constrained properties of the ionizing radiation produced by stars are modeled with two free parameters: (i) a transition redshift, z_tran, above which the stellar population is dominated by massive, zero-metallicity stars and below which it is dominated by a Scalo mass function; (ii) the product of the escape fraction of stellar ionizing photons from their host galaxies and the star-formation efficiency, f_esc f_*. We constrain the allowed range of these free parameters at high redshifts based on the lack of the HI Gunn-Peterson trough at z<6 and the upper limit on the total intergalactic optical depth for electron scattering, tau_es7%, that should be detectable by the MAP satellite.

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