Improving photometric redshifts of Epoch of Reionization galaxies: a new empirical transmission curve with neutral hydrogen damping wing Ly$\alpha$ absorption

TL;DR

This paper introduces a new empirical attenuation model for Epoch of Reionization galaxies that accounts for neutral hydrogen damping wing absorption, significantly improving photometric redshift estimates at z>7.

Contribution

The authors develop and calibrate a novel attenuation model incorporating proximate neutral hydrogen clouds, addressing biases in previous models and enhancing redshift accuracy.

Findings

The new model reduces photometric redshift bias at z>7.

Calibration using JWST data validates the model's robustness.

Implementation improves existing template-fitting methods.

Abstract

We present a new analytical model for the attenuation to Epoch of Reionization (EoR) galaxies by proximate neutral hydrogen gas. Many galaxy spectra in the EoR taken by JWST have shown a flux deficit at wavelengths just redward of the Lyman break, and this has been regarded as resulting from Ly$\alpha$ damping wing absorption by the increasing amount of neutral hydrogen in the line-of-sight. However, previous attenuation models for the intergalactic medium (IGM) commonly used in photometric redshift template-fitting codes assume that the Lyman break is rather sharp, which leads to systematic overestimation of photometric redshifts at $z>7$. In this letter, we build and empirically calibrate a new attenuation model that takes the increased Ly$\alpha$ damping wing absorption into account. Our model consists of the canonical IGM absorption and an additional absorption component due to dense neutral hydrogen gas clouds proximate to the galaxy, and we derive the redshift evolution of HI column density of the proximate clouds by calibrating the model using CANUCS JWST observations. The resulting total transmission curve resolves the photometric redshift bias at $z>7$, an improvement that is robust to choice of template-fitting code, template set, and photometric catalog used. The new attenuation model can be easily implemented in existing template-fitting codes, and significantly improves the photometric redshift performance in the EoR.