Program: GN-2024A-FT-108

Our understanding of the epoch of re-ionization is limited by our ability to directly study the physical mechanisms that regulate ionizing photon (LyC) escape in galaxies where LyC escape can be directly measured. Tevealing the physics of LyC escape requires resolving the relevant physical scales, which are increasingly believed to be on the order of the size of individual compact star clusters (~10-100 pc). This work can only be performed with detailed studies of bright, highly magnified LyC leaking systems, but currently there is only one such system known. Observed properties of Lyman-alpha (LyA) velocity profiles are promising tools for identifying LyC escape, because the presence of multi-peaked LyA and "direct escape" (v=v_systemic) LyA are indicative of the conditions necessary for LyC escape (low HI column density). We propose medium resolution GMOS spectroscopy of a highly magnified (~70x) Lyman-alpha emitting (LAE) galaxy at z=4 to resolve the detailed velocity structure of its bright LyA emission. Archival, low-resolution (R~900) spectra of this source suggest the presence of multi-peaked LyA and direct escape LyA. New GMOS spectra (R~4300) will unambiguously resolve the detailed velocity structure of the LyA emission of this extraordinarily promising new strongly lensed galaxy for studying LyC escape.