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arXiv · 2502.04817

Potential Nitrogen Enrichment via Direct-Collapse Wolf-Rayet Stars in a $z=4.7$ Star-Forming Galaxy

Yechi Zhang·Takahiro Morishita·Massimo Stiavelli
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Abstract

We present analyses of a nitrogen-enriched star-forming galaxy, ID60001, at $z=4.6928$ based on JWST/NIRSpec MSA spectroscopy and NIRCam photometry. From rest-frame optical emission lines we derive the nitrogen-to-oxygen (N/O) abundance ratio of ID60001 to be $\log({\rm N/O})=-0.76_{-0.03}^{+0.03}$ ($[{\rm N/O}]=0.10_{-0.03}^{+0.03}$), which is significantly elevated at the corresponding metallicity $12+\log({\rm O/H})=7.75_{-0.01}^{+0.01}$ ($Z/Z_\odot = 0.12$) compared to local counterparts. We discuss possible scenarios for elevated N/O abundance in ID60001, including pristine gas inflow, Wolf-Rayet (WR) stars, and Oxygen depletion by Type II supernova winds. Based on the moderately broadened He{\sc ii}$λ$4686 emission line, galaxy morphology, and star-formation history, we conclude that the elevated N/O abundance of ID60001 is likely originated from massive ($>25\,M_\odot$) WR stars that directly collapse into a black hole. We also stress the importance of reliable electron density measurements when deriving N/O abundance with rest-frame optical emission lines.

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Yechi Zhang, Takahiro Morishita, Massimo Stiavelli. 2025-02-07. Potential Nitrogen Enrichment via Direct-Collapse Wolf-Rayet Stars in a $z=4.7$ Star-Forming Galaxy. https://arxiv.org/abs/2502.04817

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