The Sunburst Arc with JWST. III. An Abundance of Direct Chemical Abundances

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Abstract We measure the gas-phase abundances of the elements He, N, O, Ne, S, Ar, and Fe in an individual H ii region known to be leaking Lyman-continuum photons in the Sunburst Arc, a highly magnified galaxy at redshift z = 2.37. We detect the temperature-sensitive auroral lines [S ii] λλ4070, 4076, [O iii] λ4363, [S iii] λ6314, [O ii] λλ7320, 7330, and [Ne iii] λ3343 in a stacked spectrum of five multiple images of the Lyman-continuum emitter (LCE), from which we directly measure the electron temperature in the low-, intermediate-, and high-ionization zones. We also detect the density-sensitive doublets of [O ii] λλ3727, 3730, [S ii] λλ6718, 6733, and [Ar iv] λλ4713, 4741, which constrain the density in both the low- and high-ionization gas. With these temperature and density measurements, we measure gas-phase abundances with similar rigor as studies of local galaxies and H ii regions. We measure a gas-phase metallicity for the LCE of 12 + log ( O / H ) = 7.97 ± 0.05 , and find an enhanced nitrogen abundance log ( N / O ) = − 0.6 5 − 0.25 + 0.16 . This nitrogen abundance is consistent with enrichment from a population of Wolf–Rayet stars, additional signatures of which are reported in a companion paper. Abundances of sulfur, argon, neon, and iron are consistent with local low-metallicity H ii regions and low-redshift galaxies. This study represents the most complete chemical abundance analysis of an individual H ii region at Cosmic Noon to date, which enables direct comparisons between local H ii regions and those in the distant Universe.