2025/05/06 by Hsiao, Tiger Yu-Yang, Sun, Fengwu, Lin, Xiaojing +19 · 2 citations
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2505.03873
Population III stars, the hypothetical first generation metal-free stars, have yet to be discovered. Even after three years of successful JWST operations, studies have shown that most galaxies identified to date at z > 5 exhibit a metallicity floor of Z\gtrsim2% Z\odot, possibly due to unknown selection biases toward bright galaxies or rapid metal enrichment. To address this question, we search for galaxies with low R3=[OIII] λ5008/Hβ ratios as part of the JWST Cycle-3 large treasury program, the Slitless Areal Pure-Parallel HIgh-Redshift Emission Survey (SAPPHIRES). Using deep NIRCam Wide-Field Slitless Spectrscopy (WFSS) data, we report the discovery of seven extremely metal-poor galaxy candidates in the SAPPHIRES Early Data Release field, with estimated 12+\rm log(O/H)<7.0 at z∼5-7, including two sources with Z<1% Z\odot, significantly breaking the metallicity floor observed both locally and at high redshift. These candidates appear extremely faint (∼28-30 F200W AB mag) and low-mass (\rm log(M*/M\odot)∼6.8-7.8), as expected from the mass-metallicity relation. They also exhibit very blue UV slopes (-2.6\lesssimβ\lesssim-2.0), likely due to low dust content AV\lesssim0.2 \rm mag or young stellar ages ∼5-20 \rm Myr. Compared to galaxies at similar redshift, they appear exceptionally bursty in their star formation activity. Our results highlight the power of NIRCam/WFSS in identifying extremely metal-poor galaxies, from just a single pointing, with more data to come in SAPPHIRES. This underscores the potential of pure-parallel programs towards achieving JWST's primary science goal: discovering the first pristine stars and galaxies. Deep JWST/NIRSpec follow-up observations will also be essential to confirm their nature and perform detailed chemical abundance analyses.