MXDFz4.4: A LyC emitter 250Myr after the epoch of reionization and a first test of Ly-alpha morphology as a tracer of LyC escape at high redshift

TL;DR

This paper reports the detection of the highest-redshift LyC emitter, MXDFz4.4 at z=4.442, and explores how Ly-alpha morphology can serve as a tracer for LyC escape, highlighting the role of starburst activity in reionization.

Contribution

It presents the first high-redshift LyC detection with detailed analysis of Ly-alpha morphology as a potential tracer for LyC escape, emphasizing the impact of recent starburst activity.

Findings

High LyC escape fractions of 50-100% in MXDFz4.4

Ly-alpha halo fraction shows promise as a LyC escape tracer at high redshift

Starburst activity influences LyC production and escape in early galaxies

Abstract

Assessing the contribution of ionizing sources to cosmic reionization is a central goal of extragalactic astrophysics. Understanding and quantifying ionizing escape remains challenging near the epoch of reionization. We present the highest-redshift Lyman continuum (LyC) emitter detected to date, MXDFz4.4 at z=4.442 in the MUSE eXtremely Deep Field, observed only ~0.25Gyr after the end of reionization. A high confidence Ly-alpha line confirms the redshift. LyC flux is detected at 10.3sigma in the F435W filter with a flux of 4.2+/-0.5nJy, corresponding to a flux measurement at 8.0sigma. After correcting for the intrinsic production of LyC photons and the IGM opacity at z=4.44, we derive high escape fractions, ranging from 50 - 100%. We apply established low-redshift tracers of LyC escape and, for the first time at high redshift, promising Ly-alpha morphological tracers such as the halo fraction. SED fitting indicates the presence of a recent burst of star formation; we explore its impact on the production and escape of ionizing photons. Ly-alpha-based tracers of LyC escape reveal a complex scenario in which the recent burst strong influences LyC production and escape, combined with a more evolved stellar population. This interpretation is supported by UV diagnostics, including the star formation rate surface density and sSFR. Our results provide cautious support for the Ly-alpha halo fraction as a LyC escape tracer at high redshift. Considering the burst-driven enhancement in LyC production and escape, we conclude that stochastic star formation in the early Universe likely plays a significant role in the contribution of galaxies to cosmic reionization.