Experimental Constraints on Self-consistent Reionization Models

Abstract

A self-consistent formalism to jointly study cosmic reionization and thermal history of the IGM is presented. The model implements most of the relevant physics governing these processes, such as the inhomogeneous IGM density distribution, three different sources of ionizing photons (PopIII stars, PopII stars and QSOs), and radiative feedback. By constraining the free parameters with available data on redshift evolution of Lyman-limit systems, Gunn-Peterson and electron scattering optical depths, Near InfraRed Background (NIRB), and cosmic star formation history, we select a fiducial model, whose main predictions are: (i) H was completely reionized at z \approx 15, while HeII must have been reionized by z \approx 12. At z \approx 7, HeIII suffered an almost complete recombination as a result of the extinction of PopIII stars, as required by the interpretation of the NIRB. (ii) A QSO-induced complete HeII reionization occurs at z=3.5; a similar double H reionization does not take place due to the large number of photons above 1 Ryd from PopII stars and QSOs, even after PopIII stars have disappeared. (iii) Following reionization, the temperature of the IGM corresponding to the mean gas density is boosted to 15000 K. Observations of T_0 are consistent with the fact that He is singly ionized at z > 3.5, while they are consistent with He being doubly ionized at z < 3.5. This might be interpreted as a signature of (second) HeII reionization. (iv) Only 0.3% of the stars produced by z=2 need to be PopIII stars in order to achieve the hydrogen reionization. Such model not only relieves the tension between the Gunn-Peterson optical depth and WMAP observations, but also accounts self-consistently for all known observational constraints (abridged).