Discovery of an Extremely Metal-poor Galaxy at z = 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 (Formula presented) 12+log(O/H)=6.73±0.13, 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 Hβ, [O iii], Hα and He i, are clearly detected. The rest-frame equivalent widths of the strong hydrogen recombination lines are EW0(Hβ) = 184 ± 48 Å and EW0(Hα) = 1144 ± 48 Å. Furthermore, we perform detailed spectral energy distribution modeling to derive a galaxy logarithmic stellar mass of (Formula presented) 8.02−0.34+0.22M⊙. This discovery adds to the growing body of evidence for the existence of very low-metallicity galaxies existing at cosmic noon of z ≈ 3, which are crucial for understanding the processes of chemical enrichment and star formation in young galaxies at the cosmic noon.