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Arxiv: Constraints on the z\sim6-13 intergalactic medium from JWST spectroscopy of Lyman-alpha damping wings in galaxies Published: 1/20/2025 9:31:45 PM Updated: 1/20/2025 9:31:45 PM

Paper abstract: JWST provides a unique dataset to study reionization's earliest stages,promising insights into the first galaxies. Many JWST/NIRSpec prism spectrareveal smooth Lyman-alpha breaks in z>5 galaxies, implying damping wingscattering by neutral hydrogen. We investigate what current prism spectra implyabout the intergalactic medium (IGM), and how best to use NIRSpec spectra torecover IGM properties. We use a sample of 99 z~5.5-13 galaxies with high S/Nprism spectra in the public archive, including 12 at z>10. We analyse thesespectra using damping wing sightlines from inhomogeneous reionizing IGMsimulations, mapping between the distance of a source from neutral IGM and themean IGM neutral fraction. We marginalise over absorption by local HI aroundgalaxies, and Lyman-alpha emission. We observe a decline in the median andvariance of flux around the Lyman-alpha break with increasing redshift,consistent with an increasingly neutral IGM, as ionized regions become smallerand rarer. At z\gtrsim9 the spectra become consistent with an almost fullyneutral IGM. We find S/N>15 per pixel is required to robustly estimate IGMproperties from prism spectra. We fit a sub-sample of high S/N spectra andinfer mean neutral fractions \overline{x}_\mathrm{HI}=0.33^{+0.18}_{-0.27},0.64^{+0.17}_{-0.23} (>0.70 excluding GNz11) at z ~ 6.5, 9.3. Wealso investigate local HI absorption, finding median column density\log_{10}N_\mathrm{HI}~10^{20.8} cm^{-2}, comparable to z~3Lyman-break galaxies, with no significant redshift evolution. We find galaxiesshowing the strongest absorption are more likely to be in close associations(<500 pkpc), implying enhanced absorption in massive dark matter halos. Futuredeep prism and grating spectroscopy of z>9 sources will provide tighterconstraints on the earliest stages of reionization, key for understanding theonset of star formation.