Direct T_e-based Metallicities of z=2-9 Galaxies with JWST/NIRSpec: Empirical Metallicity Calibrations Applicable from Reionization to Cosmic Noon

Abstract

We report detections of the [O iii]λ4364 auroral emission line for 16 galaxies at z = 2.1−8.7, measured from JWST/NIRSpec observations obtained as part of the Cosmic Evolution Early Release Science (CEERS) survey program. We combine this CEERS sample with 9 objects from the literature at z = 4−9 with auroral-line detections from JWST/NIRSpec and 21 galaxies at z = 1.4−3.7 with auroralline detections from ground-based spectroscopy. We derive electron temperature (T e ) and directmethod oxygen abundances for the combined sample of 46 star-forming galaxies at z = 1.4−8.7. We use these measurements to construct the first high-redshift empirical T e -based metallicity calibrations for the strong-line ratiosThese new calibrations are valid over 12+log(O/H) = 7.0 − 8.4 and can be applied to samples of starforming galaxies at z = 2 − 9, leading to an improvement in the accuracy of metallicity determinations at Cosmic Noon and in the Epoch of Reionization. The high-redshift strong-line relations are offset from calibrations based on typical z ∼ 0 galaxies or H ii regions, reflecting the known evolution of ionization conditions between z ∼ 0 and z ∼ 2. Deep spectroscopic programs with JWST/NIRSpec promise to improve statistics at the low and high ends of the metallicity range covered by the current sample, as well as improve the detection rate of [N ii]λ6585 to allow the future assessment of N-based indicators. These new high-redshift calibrations will enable accurate characterizations of metallicity scaling relations at high redshift, improving our understanding of feedback and baryon cycling in the early universe.

JWST/NIRSpec Measurements of the Relationships between Nebular Emission-line Ratios and Stellar Mass at z ∼ 3–6

“…The empirical nebular emission-line ratios presented here are commonly translated into gas-phase metallicities in order to construct galaxy metallicity scaling relations (e.g., Tremonti et al 2004;Sanders et al 2021), and yet care must be taken when doing so. Specifically, robust calibrations are required for the translation between emission-line ratio and metallicity, and the calibrations adopted for local star-forming galaxies need to be updated for distant galaxies (e.g., Bian et al 2018;Sanders et al 2023b). We defer the actual translation between line ratio and metallicity to future work, but we here review some recent attempts to use JWST to infer distant galaxy chemical abundances and the reasons why such analyses are so important for constraining models of galaxy formation.…”

“…As in the [N II] λ6583/Hα and O3N2 diagrams, the highmass z = 4.0-5.0 bin presents as an outlier toward significantly higher [O III] λ5007/Hβ and O 32 at fixed stellar mass relative to the lower-redshift samples (there is no z = 5.0-6.5 data point in a similar mass range). We require a larger sample, deeper spectroscopy, and robustly calibrated direct metallicity measurements at z = 4.0-5.0 (Sanders et al 2023b) to determine whether this offset is truly representative of star-forming galaxies at this redshift and reflective of higher-excitation physical conditions or else individually undetected AGN activity in some sources.…”

First Sample of Hα+[O iii]λ5007 Line Emitters at z > 6 Through JWST/NIRCam Slitless Spectroscopy: Physical Properties and Line-luminosity Functions

“…Bian et al 2018). Further direct gas-phase metallicity measurements through JWST/ NIRSpec observations (e.g., most recently withNakajima et al 2023 andSanders et al 2023b) are necessary for more accurate determination of the mass-metallicity relation in the highredshift universe.…”

JWST/NIRSpec Measurements of Extremely Low Metallicities in High Equivalent Width Lyα Emitters

“…If we use the empirical calibration between R3 and oxygen abundance from Bian et al (2018), which has been shown to match high-z observations 11 % Z e . The discrepancy between the absolute metallicities derived using the two different methods partially highlights the need for strong-line diagnostics calibrated from JWST data that include nitrogen lines (Laseter et al 2023;Sanders et al 2023b). We also need a detailed characterization of the star formation histories and emission line properties of individual galaxies in the sample (Z. Lewis, in preparation).…”