IGM Transmission Bias for $z$ $\geq$ 2.9 Lyman Continuum Detected Galaxies

TL;DR

This study investigates how intergalactic medium absorption biases the observed escape fraction of Lyman continuum photons in high-redshift galaxies, revealing that detections are skewed toward higher transmission sightlines and that mean transmission estimates can overstate true escape fractions.

Contribution

It provides a statistical analysis of IGM transmission bias on LyC escape fraction measurements, highlighting the dependence on survey depth, sample type, and underlying escape fraction distribution.

Findings

LyC detected galaxies are more likely in high transmission sightlines.

Using mean transmission overestimates true escape fractions for detected galaxies.

Bias is stronger in shallower surveys and for fainter galaxy samples.

Abstract

Understanding the relationship between the underlying escape fraction of Lyman continuum (LyC) photons ($f_{\rm esc}$) emitted by galaxies and measuring the distribution of observed $f_{\rm esc}$ values at high redshift is fundamental to the interpretation of the reionization process. In this paper we perform a statistical exploration of the attenuation of LyC photons by neutral hydrogen in the intergalactic medium using ensembles of simulated transmission functions. We show that LyC detected galaxies are more likely to be found in sightlines with higher-than-average transmission of LyC photons. This means that adopting a mean transmission at a given redshift leads to an overestimate of the true $f_{\rm esc}$ for LyC detected galaxies. We note, however, that mean values are appropriate for $f_{\rm esc}$ estimates of larger parent samples that include LyC non-detected galaxies. We quantify this IGM transmission bias for LyC detections in photometric and spectroscopic surveys in the literature and show that the bias is stronger for both shallower observations and for fainter parent samples (i.e. Lyman $\alpha$ emitters versus Lyman break galaxies). We also explore the effects of varying the underlying probability distribution function (PDF) of $f_{\rm esc}$ on recovered values, showing that the underlying $f_{\rm esc}$ PDF may depend on sample selection by comparing with observational surveys. This work represents a first step in improved interpretation of LyC detections in the context of understanding $f_{\rm esc}$ from high redshift galaxies.