# The Lyman Continuum escape fraction of emission line-selected $z\sim2.5$ galaxies is less than 15%

## TL;DR

This study investigates the Lyman Continuum escape fraction in emission line-selected galaxies at z~2.5, finding it to be less than 15%, suggesting such galaxies may not significantly contribute to cosmic reionization.

## Contribution

First to combine archival HST imaging with emission line catalogs to constrain LyC escape fraction in a large, homogeneous galaxy sample at z~2.5.

## Key findings

- No LyC emission detected from the sample.
- Upper limits on escape fraction: <5.6% for [OII] emitters, <14% for high [OIII]/[OII] ratio galaxies.
- Such galaxies are a small fraction at z~2, likely insufficient for reionization.

## Abstract

Recent work suggests that strong emission line, star-forming galaxies may be significant Lyman Continuum leakers. We combine archival HST broadband ultraviolet and optical imaging (F275W and F606W, respectively) with emission line catalogs derived from WFC3 IR G141 grism spectroscopy to search for escaping Lyman Continuum (LyC) emission from homogeneously selected $z\simeq$2.5 SFGs. We detect no escaping Lyman Continuum from SFGs selected on [OII] nebular emission (N=208) and, within a narrow redshift range, on [OIII]/[OII]. We measure 1$\sigma$ upper limits to the LyC escape fraction relative to the non-ionizing UV continuum from [OII] emitters, $f_{esc}<$5.6%, and strong [OIII]/[OII]$>$5 ELGs, $f_{esc}<$14.0%. Our observations are not deep enough to detect $f_{esc}\lesssim$10% typical of the low redshift Lyman continuum emitters. However, we find that this population represents a small fraction of the star-forming galaxy population at $z\simeq$2. Thus, unless the number of extreme emission line galaxies grows substantially to z$>$6, such galaxies may be insufficient for reionization. Deeper survey data in the rest-frame ionizing UV will be necessary to determine whether strong line ratios could be useful for pre-selecting LyC leakers at high redshift.