Quantifying the Escape of Lyα at z ≈ 5-6: A Census of Lyα Escape Fraction with Hα-emitting Galaxies Spectroscopically Confirmed by JWST and VLT/MUSE

The James Webb Space Telescope provides an unprecedented opportunity for unbiased surveys of Hα-emitting galaxies at z > 4 with the NIRCam's wide-field slitless spectroscopy (WFSS). In this work, we present a census of Lyα escape fraction (f _esc,Lyα) of 165 star-forming galaxies at z = 4.9-6.3, utilizing their Hα emission directly measured from FRESCO NIRCam/WFSS data. We search for Lyα emission of each Hα-emitting galaxy in the Very Large Telescope/MUSE data. The overall f _esc,Lyα measured by stacking is 0.090 ± 0.006. We find that f _esc,Lyα displays a strong dependence on the observed UV slope (β _obs) and E(B − V), such that the bluest galaxies (β _obs ∼ −2.5) have the largest escape fractions (f _esc,Lyα ≈ 0.6), indicative of the crucial role of dust and gas in modulating the escape of Lyα photons. f _esc,Lyα is less well related to other parameters, including the UV luminosity and stellar mass, and the variation in f _esc,Lyα with them can be explained by their underlying coupling with E(B − V) or β _obs. Our results suggest a tentative decline in f _esc,Lyα at z ≳ 5, implying increasing intergalactic medium attenuation toward higher redshift. Furthermore, the dependence of f _esc,Lyα on β _obs is proportional to that of the ionizing photon escape fraction (f _esc,LyC), indicating that the escape of Lyα and ionizing photon may be regulated by similar physical processes. With f _esc,Lyα as a proxy to f _esc,LyC, we infer that UV-faint (M _UV > −16) galaxies contribute >70% of the total ionizing emissivity at z = 5-6. If these relations hold during the epoch of reionization, UV-faint galaxies can contribute the majority of UV photon budget to reionize the Universe.