Measuring the photo-ionization rate, neutral fraction and mean free path of HI ionizing photons at 4.9≤z≤6.0 from a large sample of XShooter and ESI spectra

Gaikwad, Prakash; Haehnelt, Martin G; Davies, Fredrick B; Bosman, Sarah E I; Molaro, Margherita; Kulkarni, Girish; D’Odorico, Valentina; Becker, George D; Davies, Rebecca L; Nasir, Fahad; Bolton, James S; Keating, Laura C; Iršič, Vid; Puchwein, Ewald; Zhu, Yongda; Asthana, Shikhar; Yang, Jinyi; Lai, Samuel; Eilers, Anna-Christina

Abstract

We measure the mean free path (⁠λmfp,HI⁠), photo-ionization rate (⁠⟨ΓHI⟩⁠) and neutral fraction (⁠⟨fHI⟩⁠) of hydrogen in 12 redshift bins at 4.85 < z < 6.05 from a large sample of moderate resolution XShooter and ESI QSO absorption spectra. The fluctuations in ionizing radiation field are modeled by post-processing simulations from the Sherwood suite using our new code ‘EXtended reionization based on the Code for Ionization and Temperature Evolution’ (EX-CITE). EX-CITE uses efficient Octree summation for computing intergalactic medium attenuation and can generate large number of high resolution ΓHI fluctuation models. Our simulation with EX-CITE shows remarkable agreement with simulations performed with the radiative transfer code Aton and can recover the simulated parameters within 1σ uncertainty. We measure the three parameters by forward-modeling the Lyα forest and comparing the effective optical depth (⁠τeff,HI⁠) distribution in simulations and observations. The final uncertainties in our measured parameters account for the uncertainties due to thermal parameters, modeling parameters, observational systematics and cosmic variance. Our best fit parameters show significant evolution with redshift such that λmfp,HI and ⟨fHI⟩ decreases and increases by a factor ∼6 and ∼104, respectively from z ∼ 5 to z ∼ 6. By comparing our λmfp,HI⁠, ⟨ΓHI⟩ and ⟨fHI⟩ evolution with that in state-of-the-art Aton radiative transfer simulations and the Thesan and CoDa-III simulations, we find that our best fit parameter evolution is consistent with a model in which reionization completes by z ∼ 5.2. Our best fit model that matches the τeff,HI distribution also reproduces the dark gap length distribution and transmission spike height distribution suggesting robustness and accuracy of our measured parameters.

Citation

Gaikwad, P., Haehnelt, M. G., Davies, F. B., Bosman, S. E. I., Molaro, M., Kulkarni, G., …Eilers, A. (2023). Measuring the photo-ionization rate, neutral fraction and mean free path of HI ionizing photons at 4.9≤z≤6.0 from a large sample of XShooter and ESI spectra. Monthly Notices of the Royal Astronomical Society, 525(3), 4093-4120. https://doi.org/10.1093/mnras/stad2566

• Journal Article Type: Article
• Acceptance Date: Aug 22, 2023
• Online Publication Date: Sep 4, 2023
• Publication Date: 2023-11
• Deposit Date: Sep 7, 2023
• Publicly Available Date: Sep 7, 2023
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press (OUP)
• Peer Reviewed: Peer Reviewed
• Volume: 525
• Issue: 3
• Pages: 4093-4120
• DOI: https://doi.org/10.1093/mnras/stad2566
• Keywords: cosmology: large-scale structure of Universe, methods: numerical, galaxies: intergalactic medium, quasars: absorption lines
• Public URL: https://nottingham-repository.worktribe.com/output/25069824
• Publisher URL: https://academic.oup.com/mnras/article/525/3/4093/7259921