The Low-Redshift Lyman Continuum Survey II: New Insights into LyC Diagnostics

TL;DR

This study uses low-redshift galaxy data to evaluate indirect indicators of Lyman continuum escape, revealing key physical factors influencing LyC leakage and identifying diverse galaxy properties among emitters.

Contribution

First statistical validation of multiple LyC escape diagnostics using low-redshift survey data, linking galaxy properties to LyC escape mechanisms.

Findings

Optical depth indicators based on Lyα are effective predictors.

[O III]/[O II] flux ratio and star formation rate surface density also predict LyC escape.

LyC escape depends on H I column density, ionization, and stellar feedback.

Abstract

The Lyman continuum (LyC) cannot be observed at the epoch of reionization (z {\gtrsim} 6) due to intergalactic H I absorption. To identify Lyman continuum emitters (LCEs) and infer the fraction of escaping LyC, astronomers have developed various indirect diagnostics of LyC escape. Using measurements of the LyC from the Low-redshift Lyman Continuum Survey (LzLCS), we present the first statistical test of these diagnostics. While optical depth indicators based on Ly{\alpha}, such as peak velocity separation and equivalent width, perform well, we also find that other diagnostics, such as the [O III]/[O II] flux ratio and star formation rate surface density, predict whether a galaxy is a LCE. The relationship between these galaxy properties and the fraction of escaping LyC flux suggests that LyC escape depends strongly on H I column density, ionization parameter, and stellar feedback. We find LCEs occupy a range of stellar masses, metallicities, star formation histories, and ionization parameters, which may indicate episodic and/or different physical causes of LyC escape.