The great escape: understanding the connection between Ly α emission and LyC escape in simulated JWST analogues

ABSTRACT Constraining the escape fraction of Lyman Continuum (LyC) photons from high-redshift galaxies is crucial to understanding reionization. Recent observations have demonstrated that various characteristics of the Ly\, emission line correlate with the inferred LyC escape fraction (f ₄ₒ₂^ LyC) of low-redshift galaxies. Using a data set of 9600 mock Ly\, spectra of star-forming galaxies at 4. 64 z 6 from the SPHINX^20 cosmological radiation hydrodynamical simulation, we study the physics controlling the escape of Ly\, and LyC photons. We find that our mock Ly\, observations are representative of high-redshift observations and that typical observational methods tend to overpredict the Ly\, escape fraction (f ₄ₒ₂^ Ly\, ) by as much as 2 dex. We investigate the correlations between f ₄ₒ₂^ LyC and f ₄ₒ₂^ Ly\, , Ly\, equivalent width (W (Ly\, ) ), peak separation (v ₒ₄₏), central escape fraction (f ₂₄₍), and red peak asymmetry (Af^ red). We find that f ₄ₒ₂^ Ly\, and f ₂₄₍ are good diagnostics for LyC leakage, selecting for galaxies with lower neutral gas densities and less UV attenuation that have recently experienced supernova feedback. In contrast, W (Ly\, ) and v ₒ₄₏ are found to be necessary but insufficient diagnostics, while Af^ red carries little information. Finally, we use stacks of Ly\, , H\, , and F150W mock surface brightness profiles to find that galaxies with high f ₄ₒ₂^ LyC tend to have less extended Ly\, and F150W haloes but larger H\, haloes than their non-leaking counterparts. This confirms that Ly\, spectral profiles and surface brightness morphology can be used to better understand the escape of LyC photons from galaxies during the epoch of reionization.