The effect of helium reionization on the Lyman-alpha forest hydrogen flux statistics

TL;DR

This study investigates how helium reionization driven by quasars influences the Lyman-alpha forest flux statistics at high redshifts, highlighting the importance of QSO contributions to the UV background and their effects on flux distribution and power spectrum.

Contribution

It introduces Monte Carlo simulations of QSO populations to model HeIII regions and assesses their impact on Lyman-alpha flux statistics, considering uncertainties in QSO properties and luminosity functions.

Findings

X-ray selected QSO models produce broader HI optical depth distributions.

QSO-driven HeIII regions suppress small-scale flux power spectrum.

Higher QSO counts better match observed flux auto-correlation at z > 5.

Abstract

We assess the impact of QSOs on the high redshift (z > 4) Intergalactic Medium using Monte Carlo realisations of QSO populations and the HeIII regions they generate, applied to the Sherwood-Relics simulations, allowing for uncertainties in the QSO luminosity function, its evolution, and QSO spectra and ages. While QSO luminosity functions based on optical-infrared selection are unable to reproduce the broadening HI Lyman-alpha optical depth distributions at z > 5, much broader distributions are found for the higher numbers of QSOs based on x-ray selection, suggesting a large QSO contribution to the ultra-violet background at z > 5 may offer an alternative to late reionization models to account for the broad HI Lyman-alpha optical depth distributions. Realisations using QSOs based on the higher QSO counts also much better recover the measured pixel flux auto-correlation function at z > 5. The HeIII regions from QSO sources according to both types of luminosity function suppress the pixel flux power spectrum on small scales, k > 0.02 s/km, while enhancing it on larger, both by amounts of up to tens of percent at z > 4, with the magnitude increasing with the intergalactic HeIII filling factor and the boost in temperature within the HeIII regions.