N/O-enhanced chemical enrichment by massive stars: the interplay of optically-thick winds and rotation

Recent JWST observations have revealed a sample of high- z galaxies with highly enhanced N/O abundance ratios, (N/O) -1.1. Strong optically-thick winds of rotating massive stars going through the Wolf-Rayet (WR) phase provide a viable explanation for such N/O enhancements, supported by the direct spectroscopic WR signatures discovered in a few galaxies. Such strong winds are also needed to reproduce the single WR stars in the Small Magellanic Cloud (SMC). Here, we compute the metal yields of massive (about 20-100 M), metal-poor stars using two sets of MESA single stellar evolution models with and without optically-thick winds in a dense grid of metallicities (Z about 0.001-0.0045) and initial spins (ω Ω/Ω crit about 0-0.7). Considering an initial spin distribution based on observations of O-type stars in the SMC, we find that both sets produce strong N/O enhancements up to (N/O) about 0.1 within a few Myr after a starburst. The models with optically-thick winds undergo a rapid transition from high N/O to the `normal' state of (N/O) about-1.5 at t about 3-4 Myr driven by C/O-rich winds, while the transition is slower and weaker without optically-thick winds. The optically-thick-wind scenario can reproduce the nebular C, N, O, and He abundance patterns of three representative high- z galaxies showing direct WR signatures: RXCJ2248-ID, Sunburst Arc, and MARTA 4327, with stellar metallicities and ages similar to those inferred from SED-fitting. This can be interpreted as a coherent evolution sequence captured before (t 3 Myr), during (t about 3-4 Myr), and after (t 5 Myr) the transition. In contrast, the optically-thin-wind-only scenario ejects much less C and O via winds and cannot reproduce Sunburst Arc and MARTA 4327. The yields are available at https://zenodo.org/records/22897057.