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$\hat{I}\pm$ emission line detected in the VLT/MUSE spectrum. The Lyman continuum (LyC) signal is detected independently in the \emph{Hubble Space Telescope} (HST) F435W image and the VLT/MUSE spectrum at significances of $\simeq 3.7\ddot{I}ƒ$ and $\simeq 2.8-3.0\ddot{I}ƒ$, respectively. The LyC centroid is spatially consistent with the JWST/NIRCam continuum within the astrometric uncertainty. Adopting the maximum IGM transmission, we infer conservative lower-limit escape fractions of $f_{\mathrm{esc}}(F435W)=0.82_{-0.17}^{+0.13}$ and $f_{\mathrm{esc}}(\mathrm{MUSE})=0.75_{-0.28}^{+0.18}$. Using the combined JWST and MUSE data set, we characterize the physical properties and morphology of LCEz4-M1. In our fiducial JWST-only SED fit, the galaxy is compact but has a moderate current galaxy-integrated star formation surface density, $\hat{I}{\pounds }_{\mathrm{SFR}}=0.38M_{\odot }\mathrm{y}{\mathrm{r}}^{-1}\mathrm{kp}{\mathrm{c}}^{-2}$, 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 ($\sim 0^{\prime \prime }5$) 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 ${\mathrm{SFR}}_{10\mathrm{Myr}}/{\mathrm{SFR}}_{100\mathrm{Myr}}$ ratio, low Ly$\hat{I}\pm$ EW, and relatively weak rest-frame optical emission lines of LCEz4-M1 may indicate a post-burst LyC-leaking phase.

11 pages, 3 figures, 1 table, Accepted for publication in ApJL