N/O-enhanced chemical enrichment by massive stars: the interplay of optically-thick winds and rotation
Abstract
Recent JWST observations have revealed a sample of high-z galaxies with highly enhanced N/O abundance ratios, log(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 (∼ 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⋆∼ 0.001−0.0045) and initial spins (ω≡Ω/Ωcrit∼ 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 log(N/O)∼ 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 log(N/O)∼ −1.5 at t∼ 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∼ 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.
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BibTeX
@misc{liu2026noenhanced,
title = {{N/O-enhanced chemical enrichment by massive stars: the interplay of optically-thick winds and rotation}},
author = {Boyuan Liu and Michela Mapelli and Lumen Boco and Xihan Ji},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2609.26998},
eprint = {2609.26998},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.26998},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - N/O-enhanced chemical enrichment by massive stars: the interplay of optically-thick winds and rotation
AU - Boyuan Liu
AU - Michela Mapelli
AU - Lumen Boco
AU - Xihan Ji
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2609.26998
UR - https://arxiv.org/abs/2609.26998
AB - Recent JWST observations have revealed a sample of high-z galaxies with highly enhanced N/O abundance ratios, log(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 (∼ 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_⋆∼ 0.001−0.0045) and initial spins (ω≡Ω/Ω_crit∼ 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 log(N/O)∼ 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 log(N/O)∼ −1.5 at t∼ 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∼ 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.
ER -