Constraints on Reionization and Source Properties from the Absorption Spectra of Z > 6.2 Quasars

We make use of hydrodynamical simulations of the intergalactic medium (IGM) to create model quasar absorption spectra. We compare these model spectra with the observed Keck spectra of three z > 6.2 quasars with full Gunn-Peterson troughs: SDSS J1148+5251 (z = 6.42), SDSS J1030+0524 (z = 6.28), and SDSS J1623+3112 (z = 6.22). We fit the probability density distributions (PDFs) of the observed Lyman α optical depths (τα) with those generated from the simulation, by adopting a template for the quasar’s intrinsic spectral shape, and exploring a range of values for the size of the quasar’s surrounding HII region, RS , the volume-weighted mean neutral hydrogen fraction in the ambient IGM, x̄HI, and the quasar’s ionizing photon emissivity, ṄQ. In order to avoid averaging over possibly large sightline–to–sightline fluctuations in IGM properties, we analyze each observed quasar independently. We find the following results for J1148+5251, J1030+0524, and J1623+3112: The best–fit sizes RS are 40, 41, and 29 (comoving) Mpc, respectively. For the later two quasars, the value is significantly larger than the radius corresponding to the wavelength at which the quasar’s flux vanishes. These constraints are tight, with only ∼ 10% uncertainties, comparable to those caused by redshift–determination errors. The best–fit values of ṄQ are 2.1, 1.3, and 0.9 × 10 s, respectively, with a factor of ∼ 2 uncertainty in each case. These values are a factor of ∼ 5 lower than expected from the template spectrum of Telfer et al. (2002). Finally, the best–fit values of x̄HI are 0.16, 1.0, and 1.0, respectively. The uncertainty in the case of J1148+5251 is large, and x̄HI is not well constrained. However, for both J1030+0524 and J1623+3112 we find a significant lower limit of x̄HI ∼ > 0.033. Our method is different from previous analyses of the GP absorption spectra of these quasars, and our results strengthen the evidence that the rapid end–stage of reionization is occurring near z ∼ 6. Subject headings: cosmology: theory – early Universe – galaxies: formation – high-redshift – evolution – quasars: spectrum