LATED: JWST integral field spectroscopy of a galaxy caught in chemical infancy at $z=4.8$ behind Abell 2744

Abstract

When Population III (Pop III) star formation ended remains an open question. LATED-1 is an intrinsically faint ($M_\mathrm{UV}=-16.15$) Ly$\alpha$ emitter at $z=4.80$ revealed by VLT/MUSE behind the lensing cluster Abell 2744 ($z=0.308$). Before any spectroscopic metallicity constraints, it was identified as an extremely metal-poor or metal-free galaxy candidate from JWST imaging by LATED, our novel photometric selection framework. Here we present serendipitous JWST/NIRSpec PRISM integral-field spectroscopy of this target. The spectrum reveals Ly$\alpha$, H$\beta$, and H$\alpha$ at 7.0, 5.6, and 17.7$\sigma$, as well as tentative detections of [O III]$\lambda\lambda4959,5007$ at 2.9$\sigma$, and yields $R3=\mathrm{[O\,III]\lambda5007/H\beta}=0.59^{+0.27}_{-0.21}$, upholding the earlier LATED photometric prediction of $R3<1.54$ ($2\sigma$ limit). The canonical JWST-based strong-line calibration, extrapolated to low metallicity, implies $\log (O/H)=6.45^{+0.17}_{-0.19}$, or $Z/Z_\odot=0.58_{-0.20}^{+0.28}\%$, placing LATED-1 among the most metal-poor galaxies known. Its modest magnification ($\mu=2.80$) leaves the intrinsic properties insensitive to the lens model. LATED-1 is therefore a dwarf galaxy caught in the earliest state of chemical enrichment, and a compelling target for testing whether Pop III star formation can persist to $z<5$. The result demonstrates that photometric selection, especially through the LATED methodology, can reach below one per cent solar metallicity to identify Pop III galaxy candidates for spectroscopic follow-up.