Possible evidence for a large-scale enhancement in the Lyman-α forest power spectrum at redshift z ≥ 4. Issue 1 (2nd March 2023)

• Record Type: Journal Article
• Authors: Molaro, Margherita; Iršič, Vid; Bolton, James S; Lieu, Maggie; Keating, Laura C; Puchwein, Ewald; Haehnelt, Martin G; Viel, Matteo
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 521:Issue 1(2023)
• Page Start: 1489
• Page End: 1501
• Publication Date: 2023-03-02
• Subjects: methods: numerical -- intergalactic medium -- quasars: absorption lines -- large-scale structure of Universe; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stad598
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Inhomogeneous reionization enhances the 1D Ly α 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 $\log _{10}(k/{\rm km^{-1}\, s})\lesssim -1.5$ . We use the Sherwood-Relics suite of hybrid radiation hydrodynamical simulations to perform a first analysis of new Ly α forest power spectrum measurements at 4.0 ≤ z ≤ 4.6. These data extend to wavenumbers $\log _{10}(k/{\rm km^{-1}\, s})\simeq -3$, 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 Ly α 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.