Probing the Reionization History and Bubble Sizes with JWST Lyman-α Fraction Measurements
Abstract
Recent James Webb Space Telescope (JWST) measurements quantify the fraction of ultraviolet-selected galaxies showing detectable Lyman-alpha (Ly-α) lines at z ∼ 6−14. These Ly-α fractions are partly shaped by Ly-α scattering from neutral hydrogen in the surrounding intergalactic medium (IGM), and so the observed Ly-α fraction evolution can inform our understanding of the reionization history and the size distribution of ionized bubbles during reionization. We compare the JWST measurements with Ly-α transmission calculations based on both the THESAN reionization simulations and a flexible semi-analytic model. In each case, we calibrate a sub-grid model for the intrinsic Ly-α emission lines emerging from the interstellar medium (ISM) and circumgalactic medium (CGM) of the host galaxies using empirical estimates of the Ly-α equivalent width (EW) distributions at z ∼ 6. We find that the reionization history and bubble sizes in THESAN yield good agreement with current JWST Ly-α fraction observations, with a reduced χ2ν= 0.4−1.2. Our semi-analytic models and THESAN Ly-α transmission calculations agree well, allowing us to explore a wide range of reionization models. We derive 1σ bounds on the average mass-weighted neutral fractions of: ⟨ xHI ⟩ = 0.38+0.14−0.38 (0.52+0.09−0.21), 0.57+0.23−0.57 (0.68+0.12−0.39), and 0.93+0.05−0.17 (0.89+0.11−0.15) at z ∼ 7, 8, and 11, based on the Ly-α fraction measurements with EW >25 mathringA (>10 mathringA).
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BibTeX
@misc{kundu2026probing,
title = {{Probing the Reionization History and Bubble Sizes with JWST Lyman-$α$ Fraction Measurements}},
author = {Aritra Kundu and Adam Lidz and Guochao Sun},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.40363},
eprint = {2609.40363},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.40363},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Probing the Reionization History and Bubble Sizes with JWST Lyman-α Fraction Measurements
AU - Aritra Kundu
AU - Adam Lidz
AU - Guochao Sun
PY - 2026
DA - 2026/09/30
PB - arXiv
DO - 10.48550/arxiv.2609.40363
UR - https://arxiv.org/abs/2609.40363
AB - Recent James Webb Space Telescope (JWST) measurements quantify the fraction of ultraviolet-selected galaxies showing detectable Lyman-alpha (Ly-α) lines at z ∼ 6−14. These Ly-α fractions are partly shaped by Ly-α scattering from neutral hydrogen in the surrounding intergalactic medium (IGM), and so the observed Ly-α fraction evolution can inform our understanding of the reionization history and the size distribution of ionized bubbles during reionization. We compare the JWST measurements with Ly-α transmission calculations based on both the THESAN reionization simulations and a flexible semi-analytic model. In each case, we calibrate a sub-grid model for the intrinsic Ly-α emission lines emerging from the interstellar medium (ISM) and circumgalactic medium (CGM) of the host galaxies using empirical estimates of the Ly-α equivalent width (EW) distributions at z ∼ 6. We find that the reionization history and bubble sizes in THESAN yield good agreement with current JWST Ly-α fraction observations, with a reduced χ^2_ν= 0.4−1.2. Our semi-analytic models and THESAN Ly-α transmission calculations agree well, allowing us to explore a wide range of reionization models. We derive 1σ bounds on the average mass-weighted neutral fractions of: ⟨ x_HI ⟩ = 0.38^+0.14_−0.38 (0.52^+0.09_−0.21), 0.57^+0.23_−0.57 (0.68^+0.12_−0.39), and 0.93^+0.05_−0.17 (0.89^+0.11_−0.15) at z ∼ 7, 8, and 11, based on the Ly-α fraction measurements with EW >25 mathringA (>10 mathringA).
ER -