In Search of the First Stars: An Ultra-compact and Very-low-metallicity Lyα Emitter Deep within the Epoch of Reionization
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...
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| Main Authors: | , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/addf49 |
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| Summary: | 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 H β equivalent width of 225 ± 50 Å, small half-light radius of only ${r}_{\mathrm{hl}}=3{8}_{-19}^{+3}$ pc, and high star formation rate density of 50–100 M _⊙ yr ^−1 kpc ^−2 . The galaxy shows high-equivalent-width Ly α emission with an inferred Ly α escape fraction of 0.21 ± 0.05. The high escape fraction of Ly α 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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| ISSN: | 1538-4357 |