Can Blue UV-Bright Galaxies Drive Reionization at Cosmic Dawn? An MUV=−19.6 Galaxy with fesc≈0.85 at z=9.244
Abstract
We revisit EBG-1, a gravitationally lensed galaxy at z = 9.244, using newly obtained deep (14 hr) JWST/NIRSpec G235M (R ∼ 1000) spectroscopy. EBG-1 is one of the bluest galaxies observed at z > 9. Along with its remarkably blue continuum of β= −2.99 ± 0.15, we find very weak nebular emission from EBG-1. We obtain a 3σ upper limit of EW < 8.4 Angstrom for C III], a marginal Hβ measurement (EW = 256.2 ± 122.2 Angstrom), and a 5σ detection of [O III] λ5007 (EW = 882.8 ± 180.6 Angstrom). These lines suggest an oxygen abundance of 12 + log(O/H) = 7.16 ± 0.25 (≃ 3% Z⊙) and log(C/O) < −0.88 (3σ), placing EBG-1 on the C/O-metallicity sequence traced by lower-redshift galaxies. To constrain the escape fraction (fesc), we compare the observed UV slope and emission-line equivalent widths with synthetic spectra generated using BEAGLE. The models favor fesc ≳ 0.75, with fesc ≈ 0.85 providing the best overall agreement with the observations. These results suggest that relatively UV-bright galaxies like EBG-1 can achieve the exceptionally high ionizing efficiencies supported by late reionization scenarios.
Related
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BibTeX
@misc{wu2026blue,
title = {{Can Blue UV-Bright Galaxies Drive Reionization at Cosmic Dawn? An $M_\rm UV=-19.6$ Galaxy with $f_\rm esc\approx0.85$ at $z=9.244$}},
author = {Yunjing Wu and Sijia Cai and Yongda Zhu and Masami Ouchi and Yuichi Harikane and Zheng Cai and Mengtao Tang and Khee-Gan Lee and John D. Silverman and Fengwu Sun and Xiaohui Fan and Zuyi Chen and Minami Nakane and Hiroto Yanagisawa and Angela Adamo and Fuyan Bian and Jaclyn B. Champagne and Dan Coe and Seiji Fujimoto and Enrico Garaldi and Tiger Yu-Yang Hsiao and Xiangyu Jin and Mingyu Li and Yongming Liang and Xiaojing Lin and Guan-Fu Liu and Junjie Mao and Masamune Oguri and Takafumi Tsukui and Feige Wang and Jinyi Yang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.24092},
eprint = {2610.24092},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.24092},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Can Blue UV-Bright Galaxies Drive Reionization at Cosmic Dawn? An M_UV=−19.6 Galaxy with f_esc≈0.85 at z=9.244
AU - Yunjing Wu
AU - Sijia Cai
AU - Yongda Zhu
AU - Masami Ouchi
AU - Yuichi Harikane
AU - Zheng Cai
AU - Mengtao Tang
AU - Khee-Gan Lee
AU - John D. Silverman
AU - Fengwu Sun
AU - Xiaohui Fan
AU - Zuyi Chen
AU - Minami Nakane
AU - Hiroto Yanagisawa
AU - Angela Adamo
AU - Fuyan Bian
AU - Jaclyn B. Champagne
AU - Dan Coe
AU - Seiji Fujimoto
AU - Enrico Garaldi
AU - Tiger Yu-Yang Hsiao
AU - Xiangyu Jin
AU - Mingyu Li
AU - Yongming Liang
AU - Xiaojing Lin
AU - Guan-Fu Liu
AU - Junjie Mao
AU - Masamune Oguri
AU - Takafumi Tsukui
AU - Feige Wang
AU - Jinyi Yang
PY - 2026
DA - 2026/10/16
PB - arXiv
DO - 10.48550/arxiv.2610.24092
UR - https://arxiv.org/abs/2610.24092
AB - We revisit EBG-1, a gravitationally lensed galaxy at z = 9.244, using newly obtained deep (14 hr) JWST/NIRSpec G235M (R ∼ 1000) spectroscopy. EBG-1 is one of the bluest galaxies observed at z > 9. Along with its remarkably blue continuum of β= −2.99 ± 0.15, we find very weak nebular emission from EBG-1. We obtain a 3σ upper limit of EW < 8.4 Angstrom for C III], a marginal Hβ measurement (EW = 256.2 ± 122.2 Angstrom), and a 5σ detection of [O III] λ5007 (EW = 882.8 ± 180.6 Angstrom). These lines suggest an oxygen abundance of 12 + log(O/H) = 7.16 ± 0.25 (≃ 3% Z_⊙) and log(C/O) < −0.88 (3σ), placing EBG-1 on the C/O-metallicity sequence traced by lower-redshift galaxies. To constrain the escape fraction (f_esc), we compare the observed UV slope and emission-line equivalent widths with synthetic spectra generated using BEAGLE. The models favor f_esc ≳ 0.75, with f_esc ≈ 0.85 providing the best overall agreement with the observations. These results suggest that relatively UV-bright galaxies like EBG-1 can achieve the exceptionally high ionizing efficiencies supported by late reionization scenarios.
ER -