Lyman Continuum Emission from Spectroscopically Confirmed Ly$\alpha$ Emitters at $z\sim3.1$

TL;DR

This study investigates Lyman continuum emission from a large sample of Ly$ ext{α}$ emitters at $z ext{~}3.1$, detecting a few with high escape fractions and constraining the average escape fraction for the population, providing insights into galaxy ionizing photon escape.

Contribution

First direct measurement of LyC escape fractions in a large sample of spectroscopically confirmed Ly$ ext{α}$ emitters at $z ext{~}3.1$, including individual detections and average constraints.

Findings

Detected 5 LyC candidates with escape fractions 40-80%.

Average escape fraction upper limit is about 16%.

LyC emitters tend to have higher Ly$ ext{α}$ luminosities, EWs, and SFRs.

Abstract

We present a study of Lyman continuum (LyC) emission in a sample of $\sim$150 Ly$\alpha$ emitters (LAEs) at $z\approx3.1$ in the Subaru-XMM Deep Survey field. These LAEs were previously selected using the narrowband technique and spectroscopically confirmed with Ly$\alpha$ equivalent widths (EWs) $\ge45$ \r{A}. We obtain deep UV images using a custom intermediate-band filter $U_{\rm J}$ that covers a wavelength range of $3330 \sim 3650$ \r{A}, corresponding to 810$\sim$890 \r{A} in the rest frame. We detect 5 individual LyC galaxy candidates in the $U_{\rm J}$ band, and their escape fractions ($f_{\rm esc}$) of LyC photons are roughly between 40% and 80%. This supports a previous finding that a small fraction of galaxies may have very high $f_{\rm esc}$. We find that the $f_{\rm esc}$ values of the 5 LyC galaxies are not apparently correlated with other galaxy properties such as Ly$\alpha$ luminosity and EW, UV luminosity and slope, and star-formation rate (SFR). This is partly due to the fact that these galaxies only represent a small fraction ($\sim3$%) of our LAE sample. For the remaining LAEs that are not detected in $U_{\rm J}$, we stack their $U_{\rm J}$-band images and constrain their average $f_{\rm esc}$. The upper limit of the average $f_{\rm esc}$ value is about 16%, consistent with the results in the literature. Compared with the non-LyC LAEs, the LyC LAEs tend to have higher Ly$\alpha$ luminosities, Ly$\alpha$ EWs, and SFRs, but their UV continuum slopes are similar to those of other galaxies.