2025ApJ...980...33W

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 $12+\mathrm{log}({\rm{O}}/{\rm{H}})=7.97\pm 0.05$, and find an enhanced nitrogen abundance $\mathrm{log}({\rm{N}}/{\rm{O}})=-0.6{5}_{-0.25}^{+0.16}$. 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.