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

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 ] λλ 4070, 4076, [O iii ] λ 4363, [S iii ] λ 6314, [O ii ] λλ 7320, 7330, and [Ne iii ] λ 3343 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 ] λλ 3727, 3730, [S ii ] λλ 6718, 6733, and [Ar iv ] λλ 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 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.

Keywords

• Strong gravitational lensing
• Chemical abundances
• Abundance ratios