Unveiling the Cosmic Chemistry. II. “Direct” T_e-based Metallicity of Galaxies at 3 < z < 10 with JWST/NIRSpec

We report the detection of the [O iii] auroral line in 42 galaxies within the redshift range of 3 < z < 10. These galaxies were selected from publicly available JWST data releases, including the JADES and PRIMAL surveys, and observed using both the low-resolution PRISM/CLEAR configuration and medium-resolution gratings. The measured electron temperatures in the high-ionization regions of these galaxies range from T_e([O iii]) = 12,000 to 24,000 K, consistent with temperatures observed in local metal-poor galaxies and previous JWST studies. In 10 galaxies, we also detect the [O ii] auroral line, allowing us to determine electron temperatures in the low-ionization regions, which range between T_e([O ii]) = 10,830 and 20,000 K. The direct T_e-based metallicities of our sample span from 12 + log(O/H) = 7.2 to 8.4, indicating these high-redshift galaxies are relatively metal-poor. By combining our sample with 25 galaxies from the literature, we expand the data set to a total of 67 galaxies within 3 < z < 10, effectively more than doubling the previous sample size for direct T_e-based metallicity studies. This larger data set allows us to derive empirical metallicity calibration relations based exclusively on high-redshift galaxies, using six key line ratios: R3, R2, R23, Ne3O2, O32, and O3N2. Notably, we derive a novel metallicity calibration relation for the first time using high-redshift T_e-based metallicities: R ˆ = 0.18log R2 + 0.98log R3. This new calibration significantly reduces the scatter in high-redshift galaxies compared to the R ˆ relation previously calibrated for low-redshift galaxies.