In search of the first stars : an ultra-compact and very-low-metallicity Lyα emitter deep within the epoch of reionization

Willott, Chris J. (author), Asada, Yoshihisa (author), Iyer, Kartheik G. (author), Judež, Jon (author), Rihtaršič, Gregor (author), Martis, Nicholas S. (author), Harshan, Anishya (author), Felicioni, Giordano (author), Bradač, Maruša (author), Markov, Vladan (author), Tripodi, Roberta (author)

We present JWST observations of a gravitationally lensed, extremely metal-poor galaxy at redshift z = 8.203 ± 0.001 from the CANUCS survey. Based on the low oxygen to Balmer line ratios, we infer a gas-phase metallicity of 12 + log(O/H) = 6.85 (1.4% solar), making CANUCS-A370-z8-LAE one of the most metal-poor galaxies known at z > 7. The galaxy has a high Hβ equivalent width of 225 ± 50 Å, small half-light radius of only rhl=38‑19+3 pc, and high star formation rate density of 50–100 M⊙ yr‑1 kpc‑2. The galaxy shows high-equivalent-width Lyα emission with an inferred Lyα escape fraction of 0.21 ± 0.05. The high escape fraction of Lyα is likely due to the compact starbursting nature of the galaxy combined with its location in an overdensity traced by at least two other galaxies spectroscopically confirmed to lie within δz = 0.01 that have helped to reionize the environment. The low metallicity of CANUCS-A370-z8-LAE is best explained by a model where infalling metal-poor gas dilutes the interstellar medium, rather than being a young galaxy forming its first stellar populations.

• Language: English
• Keywords: Lyman-alpha galaxies, Emission line galaxies, reionization, metallicity
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FMF - Faculty of Mathematics and Physics
• Publication status: Published
• Publication version: Version of Record
• Publication date: 01.07.2025
• Year: 2025
• Number of pages: id. 26, 10 str.
• Numbering: Vol. 988, issue 1
• PID: 20.500.12556/RUL-171759
• UDC: 524.8
• ISSN on article: 1538-4357
• DOI: 10.3847/1538-4357/addf49
• COBISS.SI-ID: 247269891
• Publication date in RUL: 01.09.2025

Record is a part of a journal

• Title: The Astrophysical journal
• Shortened title: Astrophys. j.
• Publisher: University of Chicago Press for the American Astronomical Society
• ISSN: 1538-4357
• COBISS.SI-ID: 515079705

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.