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arXiv · 2303.05167

Possible evidence for a large-scale enhancement in the Lyman-$α$ forest power spectrum at redshift $\mathbf{\textit{z}\geq 4}$

Margherita Molaro·Vid Iršič·James S. Bolton·Maggie Lieu·Laura C. Keating·Ewald Puchwein·Martin G. Haehnelt·Matteo Viel
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Abstract

Inhomogeneous reionization enhances the 1D Lyman-$α$ forest power spectrum on large scales at redshifts $z\geq4$. 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 Lyman-$α$ forest power spectrum measurements at $4.0\leq z \leq 4.6$. 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 Lyman-$α$ 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 $\lesssim 2.5$ per cent should provide unambiguous evidence for an enhancement in the power spectrum on large scales.

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Margherita Molaro, Vid Iršič, James S. Bolton, Maggie Lieu, Laura C. Keating, Ewald Puchwein, Martin G. Haehnelt, Matteo Viel. 2023-03-09. Possible evidence for a large-scale enhancement in the Lyman-$α$ forest power spectrum at redshift $\mathbf{\textit{z}\geq 4}$. https://doi.org/10.1093/mnras%2Fstad598

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