Abstract
Abstract We reconstruct the history of reionization using Gaussian process regression. Using the UV luminosity data compilation from Hubble Frontiers Fields we reconstruct the redshift evolution of UV luminosity density and thereby the evolution of the source term in the ionization equation. This model-independent reconstruction rules out single power-law evolution of the luminosity density but supports the logarithmic double power-law parameterization. We obtain reionization history by integrating ionization equations with the reconstructed source term. Using the optical depth constraint from Planck cosmic microwave background observation, measurement of UV luminosity function integrated until truncation magnitude of −17 and −15, and derived ionization fraction from high redshift quasar, galaxies, and gamma-ray burst observations, we constrain the history of reionization. In the conservative case we find the constraint on the optical depth as τ = 0.052 ± 0.001 ± 0.002 at 68% and 95% confidence intervals. We find the redshift duration between 10% and 90% ionization to be 2.05 − 0.21 − 0.30 + 0.11 + 0.37 . Longer duration of reionization is supported if UV luminosity density data with truncation magnitude of −15 is used in the joint analysis. Our results point out that even in a conservative reconstruction, a combination of cosmological and astrophysical observations can provide stringent constraints on the epoch of reionization.
Highlights
In the late matter-dominated epoch of the Universe, the neutral hydrogen and helium atoms in the Inter-Galactic Medium (IGM) were ionized by the photons emitted from the sources formed during structure formation
While we introduce the use of Gaussian process (GP) in obtaining reionization history by reconstructing the UV luminosity densities, for recombination time, we use the aforementioned analytical formalism as it has been demonstrated in Hazra et al (2020); Mason et al (2019); Paoletti et al (2021) that apart from strict monotonic histories, trec can not be constrained due to degeneracies with source terms
We present the results for three different choices of the mean function: constant UV luminosity density, single power law model and logarithmic double power law model
Summary
In the late matter-dominated epoch of the Universe, the neutral hydrogen and helium atoms in the Inter-Galactic Medium (IGM) were ionized by the photons emitted from the sources formed during structure formation. Simulation of large-scale structure formation reveals that the sources of high energetic photons needed for reionization could not have formed before z ∼ 30 [Shull et al (2012)]. While these two bounds on the reionization history are well understood, we are yet to uncover the complete history. Spectroscopy of high redshift quasars or galaxies [Mortlock et al (2011); Schenker et al (2014)] reveals the absorption by neutral hydrogen, that reveals its fraction as a function of redshift. Spectroscopy of high redshift quasars [Becker et al (2001)] shows evidence of IGM transition between its neutral and ionized state around redshift (z) 6. 21cm observation [Loeb & Furlanetto (2013); Pritchard & Loeb (2012); Bowman et al (2018)], which is beyond the scope of this paper, is the promising avenue to constrain the epoch of reionization
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