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Arxiv: The Physics of Indirect Estimators of Lyman Continuum Escape and their Application to High-Redshift JWST Galaxies Published: 4/17/2023 9:00:50 PM Updated: 3/13/2024 3:47:55 PM

Paper abstract: Reliable indirect diagnostics of LyC photon escape from galaxies are requiredto understand which sources were the dominant contributors to reionization.While multiple LyC escape fraction (f_{\rm esc}) indicators have beenproposed to trace favourable conditions for LyC leakage from the interstellarmedium of low-redshift ''analog'' galaxies, it remains unclear whether theseare applicable at high redshifts where LyC emission cannot be directlyobserved. Using a library of 14,120 mock spectra of star-forming galaxies withredshifts 4.64 <= z <= 10 from the SPHINX^{20} cosmological radiationhydrodynamics simulation, we develop a framework for the physics that leads tohigh f_{\rm esc}. We investigate LyC leakage from our galaxies based on thecriteria that successful LyC escape diagnostics must i) track a high specificstar formation rate, ii) be sensitive to stellar population age in the range3.5-10~Myr representing the times when supernova first explode to when LyCproduction significantly drops, and iii) include a proxy for neutral gascontent and gas density in the interstellar medium. {\rm O}_{32},\Sigma_{\rm SFR}, M_{\rm UV}, and H\beta equivalent width select for oneor fewer of our criteria, rendering them either necessary but insufficient orgenerally poor diagnostics. In contrast, UV slope (\beta), and {\rm E(B-V)}match two or more of our criteria, rendering them good f_{\rm esc}diagnostics (albeit with significant scatter). Using our library, we build aquantitative model for predicting f_{\rm esc} based on direct observables.When applied to bright z > 6 Ly\alpha emitters observed with JWST, we findthat the majority of them have f_{\rm esc} <~ 10\%.