Intergalactic Lyman continuum photon budget in the past 5 billion years

• Published in: Monthly notices of the Royal Astronomical Society 2017-04, Vol.466 (1), p.838-860
• Main Authors: Gaikwad, Prakash, Khaire, Vikram, Choudhury, Tirthankar Roy, Srianand, Raghunathan
• Format: Article
• Language: English
• Subjects: Astronomy; Atoms & subatomic particles; Computer simulation; Continuums; Evolution; Ionization; Mathematical models; Matrix; Parameters; Probability; Simulation; Stars & galaxies; Symbols; Uncertainty
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw3086

Abstract We constrain the H i photoionization rate $(\Gamma _{\rm H\, {\small I}})$ at z ≲ 0.45 by comparing the flux probability distribution function and power spectrum of the Lyα forest data along 82 Quasi-Stellar Object (QSO) sightlines obtained using Cosmic Origins Spectrograph with models generated from smoothed particle hydrodynamic simulations. We have developed a module named ‘Code for Ionization and Temperature Evolution (cite)’ for calculating the intergalactic medium (IGM) temperature evolution from high to low redshifts by post-processing the gadget-2 simulation outputs. Our method, that produces results consistent with other simulations, is computationally less expensive thus allowing us to explore a large parameter space. It also allows rigorous estimation of the error covariance matrix for various statistical quantities of interest. We find that the best-fitting $\Gamma _{\rm H\,{\small I}}(z)$ increases with z and follows (4 ± 0.1) × 10−14 (1 + z)4.99 ± 0.12 s−1. At any given z, the typical uncertainties $\Delta \Gamma _{\rm H\,{\small I}} / \Gamma _{\rm H\,{\small I}}$ are ∼25 per cent that contains not only the statistical errors but also those arising from possible degeneracy with the thermal history of the IGM and cosmological parameters and uncertainties in fitting the QSO continuum. These values of $\Gamma _{\rm H\,{\small I}}$ favour the scenario where only QSOs contribute to the ionizing background at z