Measuring the photoionization rate, neutral fraction, and mean free path of H I ionizing photons at 4.9 ≤ z ≤ 6.0 from a large sample of XShooter and ESI spectra
Date Issued
2023
Author(s)
Gaikwad, Prakash
•
Haehnelt, Martin G.
•
Davies, Fredrick B.
•
Bosman, Sarah E. I.
•
Molaro, Margherita
•
Kulkarni, Girish
•
•
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 ($\lambda _{\rm mfp,H\, \small {I}}$), photoionization rate ($\langle \Gamma _{\rm H\, \small {I}} \rangle$), and neutral fraction ($\langle f_{\rm H\, \small {I}} \rangle$) 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 modelled 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 $\Gamma _{\rm H\, \small {I}}$ 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-modelling the Lyα forest and comparing the effective optical depth ($\tau _{\rm eff, H\, \small {I}}$) distribution in simulations and observations. The final uncertainties in our measured parameters account for the uncertainties due to thermal parameters, modelling parameters, observational systematics, and cosmic variance. Our best-fitting parameters show significant evolution with redshift such that $\lambda _{\rm mfp,H\, \small {I}}$ and $\langle f_{\rm H\, \small {I}} \rangle$ decreases and increases by a factor ~6 and ~104, respectively from z ~ 5 to z ~ 6. By comparing our $\lambda _{\rm mfp,H\, \small {I}}$, $\langle \Gamma _{\rm H\, \small {I}} \rangle$ and $\langle f_{\rm H\, \small {I}} \rangle$ evolution with that in state-of-the-art Aton radiative transfer simulations and the Thesan and CoDa-III simulations, we find that our best-fitting parameter evolution is consistent with a model in which reionization completes by z ~ 5.2. Our best-fitting model that matches the $\tau _{\rm eff, H\, \small {I}}$ distribution also reproduces the dark gap length distribution and transmission spike height distribution suggesting robustness and accuracy of our measured parameters.
Volume
525
Issue
3
Start page
4093
Issn Identifier
0035-8711
Ads BibCode
2023MNRAS.525.4093G
Rights
open.access
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