Sown at Cosmic Dawn: Searching for Pop III Signatures in JWST JADES He II Selected Line Emitters

Population III (Pop III) stars, the first generation of metal-free stars, remain undetected, partly because entirely pristine galaxies represent a short-lived phase. We instead target the longer-lived self-polluted and hybrid Pop III-Pop II phases, in which surviving metal-free Pop III stars coexist with enriched gas and newly formed Pop II stars, producing strong He II alongside detectable UV metal lines. We search for this signature in 84 strong He II-emitting galaxies at z = 3-7 in the JWST/JADES GOODS-South and GOODS-North fields, combining UV emission-line diagnostics, gas-phase metallicities, AGN screening, and spatially resolved SED fitting. We find no evidence for any pristine Pop III galaxies. Instead, The Blueberry (ID 13176, z = 5.94) is our strongest candidate for a hybrid Pop III-Pop II system and is the only source with robust detections of all diagnostic UV lines. Its resolved stellar populations are extremely young, blue, and weakly attenuated, with high star formation rates, consistent with intense recent star formation. While these properties alone cannot distinguish it from a chemically enriched starburst, its robust UV metal-line ratios provide the strongest evidence in our sample for a surviving Pop III contribution within an enriched host. The Carrot (ID 13577, z = 5.57) further demonstrates the power of resolved analysis, revealing a central region substantially bluer and younger than the galaxy as a whole. Together, these results suggest that Pop III signatures may be spatially localised and diluted in integrated measurements, highlighting resolved SED fitting as a tool for identifying environments where the Universe's first stars may survive.