Potential Nitrogen Enrichment via Direct-collapse Wolf–Rayet Stars in a <i>z</i> = 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">N</mml:mi> <mml:mo>/</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>0.7</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.03</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.03</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">[</mml:mo> <mml:mi mathvariant="normal">N</mml:mi> <mml:mo>/</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mo stretchy="false">]</mml:mo> <mml:mo>=</mml:mo> <mml:mn>0.1</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.03</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.03</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ), which is significantly elevated at the corresponding metallicity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>12</mml:mn> <mml:mo>+</mml:mo> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mo>/</mml:mo> <mml:mi mathvariant="normal">H</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>7.7</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.01</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.01</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ( 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 (&gt;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.