Discovery of an Extremely Metal-Poor Galaxy at <i>z</i> =3.654 Using JWST Infrared Spectroscopy

Abstract We report the discovery of an extremely metal-poor galaxy at a redshift of $z = 3.654$, identified through infrared spectroscopy using the James Webb Space Telescope (JWST). This galaxy, CAPERS-39810, exhibits a metallicity of $12 + \log(\mathrm{O/H}) = 6.73\pm0.13$, indicative of its primitive chemical composition, resembling the early stages of galaxy formation in the Universe. We use JWST NIRSpec/MSA for spectroscopic analysis, complemented by photometric data from the COSMOS2025 catalog. Our analysis employs the R3 strong-line diagnostic method to estimate metallicity, due to the lack of auroral lines in the spectrum. The galaxy's emission lines, including \hb, \oiii, \ha~and \hei, are clearly detected. The rest-frame equivalent widths of the strong hydrogen recombination lines are EW$_0$(\hb) = $184\pm48$ \AA~and EW$_0$(\ha) = $1144\pm48$ \AA. Furthermore, we perform detailed spectral energy distribution modeling to derive a galaxy logarithmic stellar mass of $8.02^{+0.22}_{-0.34}$ $M_\odot$. This discovery adds to the growing body of evidence for the existence of very low-metallicity galaxies existed at cosmic noon of $z\approx3$, which are crucial for understanding the processes of chemical enrichment and star formation in young galaxies at the cosmic noon.