# Imprints of temperature fluctuations on the $z\sim5$ Lyman-$\alpha$ forest: a view from radiation-hydrodynamic simulations of reionization

## TL;DR

This study uses radiation-hydrodynamic simulations to examine how temperature fluctuations from reionization affect the Lyman-alpha forest power spectrum at redshift 5, revealing significant large-scale effects and subtle shape sensitivities.

## Contribution

It provides new insights into the impact of temperature fluctuations on the Lyman-alpha forest power spectrum and compares different reionization scenarios using advanced simulations.

## Key findings

- Large-scale temperature fluctuations increase power by 20-60% at specific scales.
- Shape of the power spectrum is mainly sensitive to reionization midpoint.
- Models with reionization midpoints below z=8 are inconsistent with observations.

## Abstract

Reionization leads to large spatial fluctuations in the intergalactic temperature that can persist well after its completion. We study the imprints of such fluctuations on the $z\sim5$ Ly$\alpha$ forest flux power spectrum using a set of radiation-hydrodynamic simulations that model different reionization scenarios. We find that large-scale coherent temperature fluctuations bring $\sim20-60\%$ extra power at $k\sim0.002$ s/km, with the largest enhancements in the models where reionization is extended or ends the latest. On smaller scales ($k\gtrsim0.1$ s/km), we find that temperature fluctuations suppress power by $\lesssim10\%$. We find that the shape of the power spectrum is mostly sensitive to the reionization midpoint rather than temperature fluctuations from reionization's patchiness. However, for all of our models with reionization midpoints of $z\le 8$ ($z\le 12$) the shape differences are $\lesssim20\%$ ($\lesssim40\%$) because of a surprisingly well-matched cancellation between thermal broadening and pressure smoothing that occurs for realistic thermal histories. We also consider fluctuations in the ultraviolet background, finding their impact on the power spectrum to be much smaller than temperature fluctuations at $k\gtrsim0.01$ s/km. Furthermore, we compare our models to power spectrum measurements, finding that none of our models with reionization midpoints of $z<8$ is strongly preferred over another and that all of our models with midpoints of $z\geq8$ are excluded at $2.5\sigma$. Future measurements may be able to distinguish between viable reionization models if they can be performed at lower $k$ or, alternatively, if the error bars on the high-$k$ power can be reduced by a factor of $1.5$.