Forecast for the detectability of patchy hydrogen reionization in WEAVE-QSO measurements of the Lyman-α forest power spectrum at redshift z ≥ 4

We present the first detailed forecasts for the detectability of patchy hydrogen reionization in the one-dimensional Lyα forest power spectrum to be measured by the WEAVE-QSO survey. Using the Sherwood-relics reionization simulations and a WEAVE-QSO survey configuration, we generate mock spectra in four redshift bins, z = 4.0, 4.2, 4.4, and 4.6, in which relic ionization and temperature fluctuations from patchy hydrogen reionization enhance the Lyα forest power spectrum on large scales (i.e., at wavenumber k~ 10⁻³ \, s\, km⁻¹). Our Lyα forest pipeline forecasts the power spectrum covariance by considering sample size, spectral resolution, noise subtraction, continuum placement, metal contamination, and damping wings from high-column density absorbers. Applying our covariance forecast within a Bayesian parameter inference framework, we find that the signature of patchy hydrogen reionization should be detectable at a significance of ≃ 4.5σ. The forthcoming WEAVE-QSO 1D power spectrum measurements should therefore be able to directly detect and characterize the large-scale relic imprint of patchy hydrogen reionization in the Lyα forest power spectrum at z ≥ 4.