Potential Nitrogen Enrichment via Direct-collapse Wolf–Rayet Stars in a z = 4.7 Star-forming Galaxy

Abstract We present analyses of a nitrogen-enriched star-forming galaxy, ID60001, at z = 4.6928 based on James Webb Space Telescope/NIRSpec Multi-Object 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 ( N / O ) = − 0.7 6 − 0.03 + 0.03 ( [ N / O ] = 0.1 0 − 0.03 + 0.03 ), which is significantly elevated at the corresponding metallicity 12 + log ( O / H ) = 7.7 5 − 0.01 + 0.01 ( Z / Z ⊙ = 0.12) compared to local counterparts. We discuss possible scenarios for elevated N/O abundance in ID60001, including pristine gas inflow, Wolf–Rayet (W-R) stars, and oxygen depletion by Type II supernova winds. Based on the moderately broadened He 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 ⊙ ) W-R 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.