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

Measurements of chemical abundances in high-z star-forming (SF) galaxies place important constraints on the enrichment histories of galaxies and the physical conditions in the early Universe. The James Webb Space Telescope (JWST) is beginning to enable direct chemical abundance measurements in galaxies at z > 2 via the detection of the faint T _e -sensitive auroral line [O iii] λ4364. However, abundances of other elements (e.g., S and Ar) in high-z galaxies remain unconstrained owing to a lack of T _e data and wavelength coverage. Here we present multiple direct abundances in Q2343-D40, a galaxy at z = 2.9628 ± 0.0001 observed with JWST/NIRSpec as part of the CECILIA program. We report the first simultaneous measurement of T _e [O iii] and T _e [S iii] in a high-z galaxy, finding good agreement with the temperature trends in local SF systems. We measure a gas-phase metallicity of 12+log(O/H) = 8.07 ± 0.06, and the N/O abundance, log(N/O) = −1.37 ± 0.21, is indicative of primary nucleosynthesis. The S/O and Ar/O relative abundances, log(S/O) = −1.88 ± 0.10 and log(Ar/O) = −2.80 ± 0.12, are both >0.3 dex lower than the solar ratios. However, the relative Ar²⁺/S²⁺ abundance is consistent with the solar ratio, suggesting that the relative S-to-Ar abundance does not evolve significantly with redshift. Recent nucleosynthesis models find that significant amounts of S and Ar are produced in Type Ia supernovae, such that the S/O and Ar/O abundances in Q2343-D40 could be the result of predominantly core-collapse supernova enrichment. Future JWST observations of high-z galaxies will uncover whether S/O and Ar/O are sensitive to the timescales of these different enrichment mechanisms.