Ly$\alpha$ Leaks in the Absorption Spectra of High Redshift QSOs

TL;DR

This study analyzes Lyα leaks in high-redshift QSO spectra to understand the early ionization state of the intergalactic medium, using observational data and simulations to reveal the properties and evolution of these leaks.

Contribution

The paper introduces new measurements of Lyα leak equivalent width distributions at z~6, comparing them with simulations to infer the ionization state of the IGM.

Findings

Lyα leaks are mainly caused by low density voids.

The observed leak statistics match simulations with a highly ionized IGM.

Results support a neutral hydrogen fraction of about 10^{-4} at z~6.

Abstract

Spectra of high redshift QSOs show deep Gunn-Peterson absorptions on the blue sides of the \Lya emissions lines. They can be decomposed into components called \Lya leaks, defined to be emissive regions in complementary to otherwise zero-fluxed absorption gaps. Just like \Lya absorption forests at low redshifts, \Lya leaks are both easy to find in observations and containing rich sets of statistical properties that can be used to study the early evolution of the IGM. Among all properties of a leak profile, we investigate its equivalent width in this paper, since it is weakly affected by instrumental resolution and noise. Using 10 Keck QSO spectra at $z\sim6$, we have measured the number density distribution function $n(W,z)$, defined to be the number of leaks per equivalent width $W$ and per redshift $z$, in the redshift range $5.4 - 6.0$. These new observational statistics, in both the differential and cumulative forms, fit well to hydro numerical simulations of uniform ionizing background in the $\Lambda$CDM cosmology. In this model, Ly $\alpha$ leaks are mainly due to low density voids. It supports the early studies that the IGM at $z\simeq6$ would still be in a highly ionized state with neutral hydrogen fraction $\simeq 10^{-4}$. Measurements of $n(W,z)$ at $z>6$ would be effective to probe the reionization of the IGM.