Papers › Disentangling the galactic and intergalactic components in 313 observed Lyman-alpha...
Disentangling the galactic and intergalactic components in 313 observed Lyman-alpha line profiles between redshift 0 and 5
Siddhartha Gurung-López, Chris Byrohl, Max Gronke, Daniele Spinoso, Alberto Torralba, Alberto Fernández-Soto, Pablo Arnalte-Mur, Vicent J. Martínez
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Lyman-Alpha (Lya) photons emitted in star-forming galaxies undergo complex radiative transfer through the interstellar (ISM), circumgalactic (CGM), and intergalactic medium (IGM), imprinting characteristic signatures on their observed line profiles. We use the open-source package zELDA (redshift Estimator for Line profiles of Distant Lyman-Alpha emitters) to disentangle the galactic and intergalactic contributions in 313 Lya spectra observed with HST/COS and MUSE, spanning 0<z<6. zELDA employs artificial neural networks trained on mock Lya spectra generated with Monte Carlo radiative transfer through thin-shell models and IGM transmission curves from the TNG100 simulation. We find that sources at z<0.5 exhibit minimal IGM attenuation, whereas at z>3 the IGM significantly suppresses the blue peak of Lya. After correcting for IGM effects, the stacked intrinsic galactic Lya line profiles display remarkably little evolution from z=0 to z=6. We measure the mean IGM Lya escape fraction, finding <fᴵᴳᴹ_(esc)> > 90% for z<0.5, decreasing from ∼0.85 at z=3 to ∼0.55 at z=5. Our measurement of the redshift evolution of the Lya IGM escape fraction agrees with independent constraints on the IGM mean optical depth. After a comparison between our <fᴵᴳᴹ_(esc)> estimation and the global Lya escape fraction from the literature, our findings indicate that the IGM might dominate Lya observability at redshift z≳5.0, after which ISM and CGM effects tend to dominate at lower z. Our results demonstrate that zELDA enables robust reconstruction of intrinsic Lya spectra and provides a direct probe of the interplay between galactic outflows and IGM transmission across cosmic time.
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