LCEz4-M1: A Lyman Continuum Emitter Candidate at z = 4.444 in the MUSE Hubble Ultra Deep Field

Abstract High-redshift Lyman continuum emitters (LCEs) are crucial for understanding how galaxies ionize the neutral hydrogen in the epoch of reionization. However, detected LCEs at z > 4 are quite rare. Here, we report an LCE candidate at z = 4.444, dubbed LCEz4-M1, which is one of the highest-redshift LCE candidates currently known. The redshift is determined from the Ly α emission line detected in the Very Large Telescope (VLT)/MUSE spectrum. The Lyman continuum (LyC) signal is detected independently in the Hubble Space Telescope F435W image and the VLT/MUSE spectrum at significances of ≃3.7 σ and ≃2.8 σ –3.0 σ , respectively. The LyC centroid is spatially consistent with the James Webb Space Telescope (JWST)/NIRCam continuum within the astrometric uncertainty. Adopting the maximum intergalactic medium transmission, we infer conservative lower-limit escape fractions of f esc ( F435W ) = 0.8 2 − 0.17 + 0.13 and f esc ( MUSE ) = 0.7 5 − 0.28 + 0.18 . Using the combined JWST and MUSE dataset, we characterize the physical properties and morphology of LCEz4-M1. In our fiducial JWST-only spectral energy distribution fit, the galaxy is compact but has a moderate current galaxy-integrated star formation surface density, Σ SFR = 0.38 M ⊙ yr −1 kpc −2 , suggesting that it is not an extreme compact starburst under this fiducial interpretation. While we find no clear evidence for an ongoing major merger for LCEz4-M1, the presence of a faint companion ( ∼ 0 . ″ 5 ) detected in the F277W band suggests a potential minor interaction. We also find that LCEz4-M1 may lie in a locally overdense region, although the environmental interpretation remains tentative. Finally, the low star formation ratio, SFR 10 Myr /SFR 100 Myr , low Ly α equivalent width, and relatively weak rest-frame optical emission lines of LCEz4-M1 may indicate a postburst LyC leaking phase.