Investigating the characteristic shape and scatter of intergalactic damping wings during reionization

TL;DR

This study analyzes the shape and variability of intergalactic Lyα damping wings during reionization, revealing their dependence on neutral hydrogen density and redshift, and demonstrating how to distinguish different sources and stages of reionization.

Contribution

It provides a detailed simulation-based analysis of damping wing shapes, highlighting their dependence on neutral hydrogen density and redshift, and methods to differentiate sources during reionization.

Findings

Damping wing shape correlates with neutral hydrogen density along the line of sight.

Redshift influences the characteristic shape due to cosmic expansion.

Different source types can be distinguished by damping wing shape at various reionization stages.

Abstract

Ly$\alpha$ damping wings in the spectra of bright objects at high redshift are a useful probe of the ionization state of the intergalactic medium during the reionization epoch. It has recently been noted that, despite the inhomogeneous nature of reionization, these damping wings have a characteristic shape which is a strong function of the volume-weighted average neutral hydrogen fraction of the intergalactic medium. We present here a closer examination of this finding using a simulation of patchy reionization from the Sherwood-Relics simulation suite. We show that the characteristic shape and scatter of the damping wings are determined by the average neutral hydrogen density along the line of sight, weighted by its contribution to the optical depth producing the damping wing. We find that there is a redshift dependence in the characteristic shape due to the expansion of the Universe. Finally, we show that it is possible to differentiate between the shapes of damping wings in galaxies and young (or faint) quasars at different points in the reionization history at large velocity offsets from the point where the transmission first reaches zero.