Observing PopIII galaxies, the hosts of first-generation stars, remains challenging even with the JWST. In our paper Rusta et al. 2025 ApJ Letter, we study the evolution of PopIII galaxies by employing a locally calibrated galaxy-formation model that self-consistently follows the star formation and chemical evolution initiated by the first stars. We show that PopIII galaxies can emit metal lines in their “self-polluted” phase, while galaxies host only metal-free stars, but the gas has been chemically enriched by the first supernovae. In this phase, PopIII galaxies have [O III]/Hβ ≈ 1, which opens the pool of candidates to more easily detectable sources.
We propose novel diagnostics involving ultraviolet metal lines to select PopIII candidates in high-z JWST surveys. In JADES, we identify nine candidate galaxies with >25% of their stellar mass in metal-free stars, showcasing the effectiveness of our method.
Ultimately, the key to discovering PopIII galaxies could be to catch them during their first episodes of chemical enrichment.