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Abstract Detecting the first generation of stars, Population III (Pop III), has been a long-standing goal in astrophysics, yet they remain elusive even in the JWST era. Here we present a novel NIRCam-based selection method for Pop III galaxies, and carefully validate it through completeness and contamination simulations. We systematically search ≃ 500 arcmin2across JWST legacy fields for Pop III candidates, including GLIMPSE, which, assisted by gravitational lensing, has produced JWST’s deepest NIRCam imaging thus far. We discover one promising Pop III galaxy candidate (GLIMPSE-16043) at , a moderately lensed galaxy ( ) with an intrinsic UV magnitude of . It exhibits key Pop III features: strong Hαemission (rest-frame EW 2810 ± 550 Å); a Balmer jump; no dust (UV slopeβ = −2.34 ± 0.36); and undetectable metal lines (e.g., [Oiii]; [Oiii]/Hβ < 0.44), implying a gas-phase metallicity ofZgas/Z⊙ < 0.5%. These properties indicate the presence of a nascent, metal-deficient young stellar population (<5 Myr) with a stellar mass of ≃105M⊙. Intriguingly, this source deviates significantly from the extrapolated UV–metallicity relation derived from recent JWST observations atz= 4–10, consistent with UV enhancement by a top-heavy Pop III initial mass function or the presence of an extremely metal-poor active galactic nucleus. We also derive the first observational constraints on the Pop III UV luminosity function atz ≃ 6–7. The volume density of GLIMPSE-16043 (≈10−4cMpc−3) is in excellent agreement with theoretical predictions, independently reinforcing its plausibility. This study demonstrates the power of our novel NIRCam method to finally reveal distant galaxies even more pristine than the Milky Way’s most metal-poor satellites, thereby promising to bring us closer to the first generation of stars than we have ever been before.
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This content will become publicly available on October 7, 2026
Spectral Evolution of Rotating Population III Stars
Abstract Population III (Pop III) stars, the first generation of stars formed from primordial gas, played a fundamental role in shaping the early Universe through their influence on cosmic reionization, early chemical enrichment, and the formation of the first galaxies. However, to date, they have eluded direct detection due to their short lifetimes and high redshifts. The launch of the James Webb Space Telescope (JWST) has revolutionized observational capabilities, providing the opportunity to detect Pop III stars via caustic lensing, where strong gravitational lensing magnifies individual stars to observable levels. This prospect makes it compelling to develop accurate models for their spectral characteristics to distinguish them from other stellar populations. Previous studies have focused on computing the spectral properties of nonrotating, zero-age main-sequence (ZAMS) Pop III stars. In this work, we expand upon these efforts by incorporating the effects of stellar rotation and post-ZAMS evolution into spectral calculations. We use the JWST bands and magnitude limits to identify the optimal observing conditions, both for isolated stars, as well as for small star clusters. We find that, while rotation does not appreciably change the observability at ZAMS, the subsequent evolution can significantly brighten the stars, making the most massive ones potentially visible with only moderate lensing.
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- Award ID(s):
- 2006839
- PAR ID:
- 10643493
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 992
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 68
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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