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 auroral-line detections from ground-based spectroscopy. We derive electron temperature (T e) and direct-method 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 ratios [O iii]/Hβ, [O ii]/Hβ, R23 = ([O iii]+[O ii])/Hβ, [O iii]/[O ii], and [Ne iii]/[O ii]. These new calibrations are valid over 12+log(O/H) = 7.4−8.3 and can be applied to samples of star-forming 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 to improve the detection rate of [N ii]λ6585 and thus 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.

CECILIA: Direct O, N, S, and Ar Abundances in Q2343-D40, a Galaxy at z ∼ 3

“…The O/H abundance measured in D40, 12+log(O/H) = 8.07 ± 0.06 dex, is indicative of a relatively metal-poor ISM. While this is lower than the average model-inferred metallicity of the KBSS galaxies reported in Strom et al (2018), D40ʼs O/H is consistent with its relatively high T e [O III] and T e [S III] and is in general agreement with emerging direct O/H abundance trends at z > 1 (e.g., Sanders et al 2024;Welch et al 2024). In the top panel, the inferred log(N/O) abundance in D40 (green circle; −1.37 ± 0.21 dex) is in good agreement with the primary N/O plateau (log(N/O) ∼ −1.43 dex; Garnett 1990;Nava et al 2006;van Zee & Haynes 2006) established by high-ionization, low-metallicity dwarf galaxies and H II regions.…”

“…However, with the NIR capabilities of the James Webb Space Telescope (JWST), direct T e measurements and abundances are now readily accessible in high-z galaxies (e.g., Arellano-Córdova et al 2022a;Schaerer et al 2022;Sanders et al 2024;Laseter et al 2024;Trump et al 2023;Topping et al 2024;Welch et al 2024). While these studies have started to uncover the chemical abundance patterns in the early Universe, the current scope of high-z chemical abundances is still fairly limited.…”

The MUSE Ultra Deep Field (MUDF). V. Characterizing the Mass–Metallicity Relation for Low-mass Galaxies at z ∼ 1–2

“…As the archive of deep, high-redshift observations with JWST grows, and the quality of the data calibrations steadily improve, emission-line calibrations are being expanded to a vastly increased parameter space in a robust, self-consistent manner. Progress is already being made in this area with revised calibrations proposed by Sanders et al (2024), Hirschmann et al (2023, and additional studies (Nakajima et al 2022;Garg et al 2023;Yang et al 2023). This rapid release of results related to the metallicities of galaxies across cosmic time should provide a consensus on these issues that was not possible before JWST (e.g., Langeroodi et al 2022;Atek et al 2023;Curti et al 2023;Heintz et al 2023;Langeroodi & Hjorth 2023;Maseda et al 2023;Matthee et al 2023;Shapley et al 2023;Sun et al 2023;Trump et al 2023;Bagley et al 2024).…”

A Comprehensive Metallicity Analysis of J0332−3557: Establishing a z ∼ 4 Anchor for Direct Gas Metallicity and C/O Abundance Investigations

“…Fortunately, the launch of JWST has considerably augmented the data set of high-redshift galaxies available for calibration purposes (e.g., Heintz et al 2023;Laseter et al 2024;Sanders et al 2024), bringing us closer to the direct calibration of strong methods in high-redshift galaxies.…”

“…The existing set of galaxies with detected auroral lines comprises approximately 20 targets within the redshift range of 1.6 < z < 3.6 (e.g., Yuan & Kewley 2009;Christensen et al 2012aChristensen et al , 2012bBayliss et al 2014;James et al 2014;Stark et al 2014;Berg et al 2018;Gburek et al 2019;Sanders et al 2020). However, the advent of the James Webb Space Telescope (JWST) has significantly expanded this data set, allowing for detections at redshifts up to approximately z ∼ 8 (e.g., Heintz et al 2023;Laseter et al 2024;Sanders et al 2024).…”