2024ApJS..272...33L

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.