Unveiling Galaxy Chemical Enrichment Mechanisms Out to z ∼ 8 from Direct Determination of O and Ar Abundances from JWST/NIRSPEC Spectroscopy

Abstract

Galaxy chemical enrichment mechanisms have primarily been constrained by [α/Fe] and [Fe/H] measurements of individual stars and integrated light from stellar populations. However, such measurements are limited at higher redshifts (z > 1). Recently, we proposed an analogous diagram of the oxygen-to-argon abundance ratio, log(O/Ar), versus Ar abundance, 12+log(Ar/H), as a new diagnostic window for emission nebulae. In this Letter, using line flux measurements including temperature-sensitive auroral lines, we present direct determination of O and Ar abundances in nine star-forming galaxies (SFGs) from JWST/NIRSPEC spectra at z ∼ 1.3–7.7 and two more with Keck/MOSFIRE spectra at z ∼ 2.2. Utilizing their positions on the log(O/Ar) versus 12+log(Ar/H) plane, we present the first inference of galaxy chemical enrichment mechanisms from an ensemble of galaxies. Seven SFGs at z ∼ 1.3–4 are consistent with the Milky Way solar neighborhood galactic chemical enrichment models that are driven by core-collapse and Type Ia supernovae in a self-regulated manner. Such enrichment mechanisms thus occur at least out to z ∼ 4. However, four higher-redshift SFGs (z ∼ 3.6–7.7) have lower log(O/Ar) values, revealing potentially different enrichment paths becoming important at z > 3.6. Such log(O/Ar) values may be caused by physical mechanisms such as rapid but intermittent star formation and/or additional enrichment sources. This new diagnostic window for SFGs enables us to reveal the unique fingerprints of galaxy chemical enrichment out to cosmic dawn.