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

We measure the gas-phase abundances of the elements He, N, O, Ne, S, Ar, and Fe in an individual H$\text{textsc}ii$ 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 [SII]$\lambda \lambda 4069,4076$, [OII]$\lambda \lambda 7320,7330$, [SIII]$\lambda 6312$, [OIII]$\lambda 4363$, and [NeIII]$\lambda 3343$ in a stacked spectrum of 5 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 [OII]$\lambda \lambda 3727,3729$, [SII]$\lambda \lambda 6717,6731$, and [ArIV]$\lambda \lambda 4713,4741$, 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. We measure a gas-phase metallicity for the LCE of $12+\log (\text{O}\mathrm{/}\text{H})=7.97\pm 0.05$, and find an enhanced nitrogen abundance $\log (\text{N}\mathrm{/}\text{O})=-0.65_{-0.25}^{+0.16}$. 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$\text{textsc}ii$ regions and low-redshift galaxies. This study represents the most complete chemical abundance analysis of an individual H$\text{textsc}ii$ region at Cosmic Noon to date, which enables direct comparisons between local H$\text{textsc}ii$ regions and those in the distant universe.