Discovery of an Extremely Metal-Poor Galaxy at $z=3.654$ Using JWST Infrared Spectroscopy

TL;DR

This paper reports the discovery of an extremely metal-poor galaxy at z=3.654 using JWST infrared spectroscopy, providing insights into early galaxy formation and chemical enrichment.

Contribution

First identification of an extremely metal-poor galaxy at high redshift using JWST, employing the R3 diagnostic and spectral energy distribution modeling.

Findings

Metallicity of 12 + log(O/H) = 6.73 ± 0.13 indicating primitive composition

Detected strong hydrogen emission lines with high equivalent widths

Derived stellar mass of approximately 10^8 solar masses

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(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, [O III], Ha and He I, 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.