Experimental Constraints on Self-consistent Reionization Models

A self-consistent formalism to jointly study cosmic reionization and thermal history of the intergalactic medium (IGM) in a ΛCDM cosmology is presented. The model implements most of the relevant physics governing these processes, such as the inhomogeneous IGM density distribution, three different classes of ionizing photon sources (massive PopIII stars, PopII stars and QSOs), and radiative feedback inhibiting star formation in low-mass galaxies. By constraining the model free parameters with available data on redshift evolution of Lymanlimit absorption 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) Hydrogen was completely reionized at z ≈ 14, while at least 90% of HeII must have been reionized by z ≈ 11, allowing for the uncertainties in the ionizing photon efficiencies of stars. At z ≈ 8, 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 QSOinduced complete HeII reionization occurs at z = 3.5; a similar double H reionization does not take place due to the large number of photons with energies > 1 Ryd from PopII stars and QSOs, even after all PopIII stars have disappeared. (iii) Following reionization, the temperature of the IGM corresponding to the mean gas density, T0, is boosted to 2×10 K; following that it decreases with a relatively flat trend. Observations are consistent with the temperature of the HII regions at z & 3.5, while they are consistent with the temperature of the HeIII regions at z . 3.5. This might be interpreted as a signature of (second) HeII reionization. (iv) Only 0.2% of the stars produced by z = 2 need to be PopIII stars in order to achieve the first hydrogen reionization. In addition, we get useful constraints on the ionizing photon efficiencies of PopII and PopIII stars, namely, ǫPopII < 0.01, 0.0015 < ǫPopIII < 0.02. Varying the efficiencies in these two ranges does not affect the scenario described above. 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. We discuss how the results compare with recent numerical reionization studies and other theoretical arguments.