Chris J. Willott, Yoshihisa Asada, Kartheik G. Iyer, Jon Judež, Gregor Rihtaršič, Nicholas S. Martis, Ghassan T. E. Sarrouh, Guillaume Desprez, Anishya Harshan, Lamiya Mowla, Gaël Noirot, Giordano Felicioni, Maruša Bradač, Gabe Brammer, Adam Muzzin, Marcin Sawicki, Jacqueline Antwi-Danso, Vladan Markov and Roberta Tripodi
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Abstract
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 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.
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