Disentangling the galactic and intergalactic components in 313 observed Lyman-alpha line profiles between redshift 0 and 5

Abstract

Lyman-alpha photons emitted in star-forming galaxies undergo complex radiative transfer through the interstellar, circumgalactic, and intergalactic media, imprinting characteristic signatures on their observed line profiles. We use the open-source zELDA package to disentangle the galactic and intergalactic contributions in 313 Lyα spectra observed with HST/COS and MUSE, spanning 0 < z < 6. zELDA employs artificial neural networks trained on mock Lyα spectra generated with Monte Carlo radiative transfer through thin-shell models and intergalactic transmission curves from TNG100. We find that sources at z < 0.5 exhibit minimal intergalactic attenuation, whereas at z > 3 the intergalactic medium significantly suppresses the blue peak of Lyα. After correcting for these effects, stacked intrinsic galactic Lyα line profiles display remarkably little evolution from z = 0 to z = 6. We measure the mean intergalactic Lyα escape fraction, finding values above 90% at z < 0.5 that decrease from approximately 0.85 at z = 3 to approximately 0.55 at z = 5. Our results demonstrate that zELDA enables robust reconstruction of intrinsic Lyα spectra and provides a direct probe of the interplay between galactic outflows and intergalactic transmission across cosmic time.