Can Blue UV-Bright Galaxies Drive Reionization at Cosmic Dawn? An $M_{\rm UV}=-19.6$ Galaxy with $f_{\rm esc}\approx0.85$ at $z=9.244$
Year: 2026
Type: preprint
Abstract: We revisit EBG-1, a gravitationally lensed galaxy at $z = 9.244$, using newly obtained deep (14 hr) JWST/NIRSpec G235M ($R \sim 1000$) spectroscopy. EBG-1 is one of the bluest galaxies observed at $z > 9$. Along with its remarkably blue continuum of $β= -2.99 \pm 0.15$, 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 H$β$ measurement (EW $= 256.2 \pm 122.2$ Angstrom), and a $5σ$ detection of [O III] $λ5007$ (EW $= 882.8 \pm 180.6$ Angstrom). These lines suggest an oxygen abundance of $12 + \log(\mathrm{O/H}) = 7.16 \pm 0.25$ ($\simeq 3\% Z_{\odot}$) and $\log(\mathrm{C/O}) < -0.88$ ($3σ$), placing EBG-1 on the C/O-metallicity sequence traced by lower-redshift galaxies. To constrain the escape fraction ($f_{\rm esc}$), we compare the observed UV slope and emission-line equivalent widths with synthetic spectra generated using BEAGLE. The models favor $f_{\rm esc} \gtrsim 0.75$, with $f_{\rm esc} \approx 0.85$ 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.
Source: arXiv (Cornell University)
Authors: Wu, Yunjing, Cai, Sijia, Zhu, Yongda, Ouchi, Masami, Harikane, Yuichi, Cai, Zheng, Tang, Mengtao, Lee, Khee-Gan, Silverman, John D., Sun, Fengwu, Fan, Xiaohui, Chen, Zuyi, Nakane, Minami, Yanagisawa, Hiroto, Adamo, Angela, Bian, Fuyan, Champagne, Jaclyn B., Coe, Dan, Fujimoto, Seiji, Garaldi, Enrico, Hsiao, Tiger Yu-Yang, Jin, Xiangyu, Li, Mingyu, Liang, Yongming, Lin, Xiaojing, Liu, Guan-Fu, Mao, Junjie, Oguri, Masamune, Tsukui, Takafumi, Wang, Feige, Yang, Jinyi
Institutions: Tsinghua University, Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Westlake University, Center for Astrophysics Harvard & Smithsonian, Stockholm University, AlbaNova, Chinese Academy of Sciences, European Southern Observatory, National Astronomical Observatories, University of Michigan, Chiba University, University of Cambridge, Center for Frontier Science, Chiba University, National Astronomical Observatory of Japan, Institute for Cosmic Ray Research
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: G103270039, G256731684, Uncovering Early Cosmic Evolution with JWST and Subaru/PFS Spectroscopy and Theoretical Modeling, Investigating the first star formation and reionization process of the Universe by MWA, G5568641063, Galaxy Overdense Regions in the Distant Universe Revealed by Wide-Area Sky Survey and TAO, Elucidating the Trigger and Feedback Mechanisms of the Most Concentrated Quasars at Cosmic Noon
OpenAlex ID: W7223004791