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Possible evidence for a large-scale enhancement in the Lyman-α forest power spectrum at redshift z ≥ 4

Molaro, Margherita; Iršič, Vid; Bolton, James S; Lieu, Maggie; Keating, Laura C; Puchwein, Ewald; Haehnelt, Martin G; Viel, Matteo


Margherita Molaro

Vid Iršič

Laura C Keating

Ewald Puchwein

Martin G Haehnelt

Matteo Viel


Inhomogeneous reionization enhances the 1D Lyα forest power spectrum on large scales at redshifts z ≥ 4. This is due to coherent fluctuations in the ionized hydrogen fraction that arise from large-scale variations in the post-reionization gas temperature, which fade as the gas cools. It is therefore possible to use these relic fluctuations to constrain inhomogeneous reionization with the power spectrum at wavenumbers log10(k/km−1 s) ≲ −1.5. We use the Sherwood-Relics suite of hybrid radiation hydrodynamical simulations to perform a first analysis of new Lyα forest power spectrum measurements at 4.0 ≤ z ≤ 4.6. These data extend to wavenumbers log10(k/km−1 s) ≃ −3, with a relative uncertainty of 10–20 per cent in each wavenumber bin. Our analysis returns a 2.7σ preference for an enhancement in the Lyα forest power spectrum at large scales, in excess of that expected for a spatially uniform ultraviolet background. This large-scale enhancement could be a signature of inhomogeneous reionization, although the statistical precision of these data is not yet sufficient for obtaining a robust detection of the relic post-reionization fluctuations. We show that future power spectrum measurements with relative uncertainties of ≲ 2.5 per cent should provide unambiguous evidence for an enhancement in the power spectrum on large scales.


Molaro, M., Iršič, V., Bolton, J. S., Lieu, M., Keating, L. C., Puchwein, E., …Viel, M. (in press). Possible evidence for a large-scale enhancement in the Lyman-α forest power spectrum at redshift z ≥ 4. Monthly Notices of the Royal Astronomical Society, 521(1), 1489–1501.

Journal Article Type Article
Acceptance Date Feb 22, 2023
Online Publication Date Mar 2, 2023
Deposit Date Mar 6, 2023
Publicly Available Date Mar 8, 2023
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 521
Issue 1
Pages 1489–1501
Keywords Methods: numerical, intergalactic medium, quasars: absorption lines, large-scale structure of Universe
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Copyright Statement
©The Author(s) 2023. Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( https://cr eativecommons.or g/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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