# Linking UV spectral properties of MUSE Ly-alpha emitters at z>3 to Lyman continuum escape

**Authors:** I. G. Kramarenko, J. Kerutt, A. Verhamme, P. A. Oesch, L. Barrufet, J. Matthee, I. Goovaerts, T. T. Thai  
**arXiv:** [2305.07044](https://arxiv.org/abs/2305.07044)  
**Date:** 2023-05-11  
**Summary page:** https://www.summarizepaper.com/en/paper/2305.07044v1/

## Key points

- Physical conditions leading to high escape fractions of ionizing radiation (LyC $f_{\rm{esc}}$) in star-forming galaxies are not fully understood.
- The authors use Lyman-$\alpha$ line profile properties to identify potential LyC leakers and non-leakers from a sample of 1422 MUSE-Wide and MUSE HUDF Lyman-$\alpha$ emitters.
- Spectral stacking reveals that LyC-leaker candidates show strong nebular OIII]1666, [SiIII]1883, and [CIII]1907+CIII]1909 emission lines, high equivalent widths of HeII1640 (~1-3 A), and high CIV1548,1550 to [CIII]1907+CIII]1909 ratios (CIV/CIII]>0.75).
- Stacks with non-leakers show weaker nebular emission lines, low HeII1640 equivalent widths (<1 A), and low CIV/CIII]<0.25 ratios.
- The CIV/CIII] ratio can be used as an indirect tracer of $f_{\rm{esc}}$, providing a promising tool for identifying ionizing sources among star-forming galaxies in the epoch of reionization.
- The study uses spectroscopic data from MUSE-Wide and MUSE HUDF surveys which provide large and homogeneous samples of LAEs at 2.9<z<6.7.
- The MUSE integral field spectrograph is a powerful tool for spectroscopic diagnostics of UV line emitting galaxies thanks to its large field view, high resolving power and large simultaneous spectral range.
- Future studies using new generation spectrographs such as MOONS/VLT , PFS/Subaru or HARMONI/ELT could probe these properties in greater detail opening up new paths for indirect identification on ionsing sources at EoR.

## Summary

The physical conditions that lead to high escape fractions of ionizing radiation (LyC $f_{\rm{esc}}$) in star-forming galaxies, which are likely responsible for the cosmic reionization, are not yet fully understood. In this study, the authors use the properties of the Lyman-$\alpha$ line profile associated with LyC escape to identify potential LyC leakers and non-leakers from a compiled sample of 1422 MUSE-Wide and MUSE HUDF Lyman-$\alpha$ emitters (LAEs) in the redshift range 2.9<z<6.7. They perform spectral stacking to obtain high signal-to-noise detections of rest-frame UV absorption and emission lines and find that stacks with LyC-leaker candidates show strong nebular OIII]1666, [SiIII]1883, and [CIII]1907+CIII]1909 emission lines, indicating high ionization parameters due to an elevated production rate of ionizing photons coming from young, metal-poor stars. The stacks also exhibit high equivalent widths of HeII1640 (~1-3 A), possibly indicating a hard ionizing spectrum alongside a high ionizing photon production efficiency. Additionally, SiII*1533 emission reveals the presence of neutral hydrogen off the line of sight, implying a highly anisotropic interstellar medium (ISM). The stacks also show high CIV1548,1550 to [CIII]1907+CIII]1909 ratios (CIV/CIII]>0.75), partly associated with increased ISM transparency. In contrast, stacks with non-leakers show weaker nebular emission lines, low HeII1640 equivalent widths (<1 A), and low CIV/CIII]<0.25 ratios suggesting a low ionization state of the ISM and a high neutral hydrogen content. The results suggest that the CIV/CIII] ratio can be used as an indirect tracer of $f_{\rm{esc}}$, providing a promising tool for identifying ionizing sources among star-forming galaxies in the epoch of reionization. The authors also suggest that the synergy between extreme ionizing fields produced by young stellar populations and the patchy ISM riddled with low-column-density channels creates an ideal physical environment for efficient escape of LyC photons. The study uses spectroscopic data from MUSE-Wide and MUSE HUDF surveys which provide large and homogeneous samples of LAEs at 2.9<z<6.7. The MUSE integral field spectrograph is a powerful tool for spectroscopic diagnostics of UV line emitting galaxies thanks to its large field view, high resolving power and large simultaneous spectral range. Overall this work provides new insights into physical conditions leading to high escape fractions of ionizing radiation in star forming galaxies offering promising tools for identifying ionizing sources at epochs reionization . Future studies using new generation spectrographs such as MOONS/VLT , PFS/Subaru or HARMONI/ELT could probe these properties in greater detail opening up new paths for indirect identification on ionsing sources at EoR .