Kavli Affiliate: Anna Frebel
| First 5 Authors: Seiji Fujimoto, Rohan P. Naidu, John Chisholm, Hakim Atek, Ryan Endsley
| Summary:
Detecting the first generation of stars, Population III (PopIII), 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 PopIII galaxies,
and carefully validate it through completeness and contamination simulations.
We systematically search ~500 arcmin$^{2}$ across JWST legacy fields for PopIII
candidates, including GLIMPSE which, assisted by gravitational lensing, has
produced JWST’s deepest NIRCam imaging thus far. We discover one promising
PopIII galaxy candidate (GLIMPSE-16043) at $z=6.50^{+0.03}_{-0.24}$, a
moderately lensed galaxy (mu=2.9) with an intrinsic UV magnitude of
$M_{UV}$=-15.89. It exhibits key PopIII features: strong H$alpha$ emission
(rest-frame EW $2810pm550$AA); a Balmer jump; no dust (UV slope
$beta=-2.34pm0.36$); and undetectable metal lines (e.g., [OIII];
[OIII]/H$beta$<0.44) implying a gas-phase metallicity of Zgas/Zsun<0.5%. These
properties indicate the presence of a nascent, metal-deficient young stellar
population (<5Myr) with a stellar mass of $simeq10^{5}M_{odot}$.
Intriguingly, this source deviates significantly from the extrapolated
UV-metallicity relation derived from recent JWST observations at $z=4-10$,
consistent with UV enhancement by a top-heavy PopIII initial mass function or
the presence of an extremely metal-poor AGN. We also derive the first
observational constraints on the PopIII UV luminosity function at z~6-7. The
volume density of GLIMPSE-16043 ($approx10^{-4}$ cMpc$^{-3}$) 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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