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arXiv · 2609.32045

The AURORA Survey: Determining the Production Mechanism for OI $\mathbf{λ8449}$ Emission in Star-forming Galaxies at Cosmic Noon

Leonardo Clarke·Alice E. Shapley·Zhiwei Shao·Massimo Pascale·Ryan L. Sanders·Naveen A. Reddy·Tucker Jones·Harley Katz·Natalie Lam·Shreya Karthikeyan·Callum T. Donnan·Natascha M. Förster Schreiber·Anthony J. Pahl·Danielle A. Berg
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Abstract

We analyze deep JWST/NIRSpec observations of 58 star-forming galaxies at $1.3< z <4.8$ in the AURORA survey to investigate the origin of the permitted OI $λ8449$ emission feature. Based on the detection of OI $λ8449$ in a stack of objects with non-detections, we infer that this feature is ubiquitous among star-forming galaxies at $\sim$0.5% the strength of H$α$. We additionally compare our results with measurements of this line in local HII regions from the CHAOS survey and star-forming galaxies at $z<0.1619$ in the DESI survey, finding a similar strength of OI $λ8449$ relative to H$α$ in these objects. We evaluate four production mechanisms: recombination, collisional excitation, Ly$β$ fluorescence, and stellar continuum fluorescence. Of these mechanisms, stellar continuum fluorescence (rather than Ly$β$ fluorescence) provides the most compelling explanation for the OI $λ8449$ emission based on the additional detection of the near-infrared OI $λ11290$ and OI $λ13168$ emission lines. Adopting physical conditions derived from a stacked composite spectrum, we make predictions for the contribution of the other mechanisms to OI $λ8449$, determining that recombination, collisional excitation, and Ly$β$ fluorescence contribute negligibly to this feature. While a simple HII region model using Cloudy reproduces the average observed OI $λ8449$/H$α$ ratios in the AURORA sample, future works focused on refining model density profiles will be a valuable step in better explaining the near-infrared OI emission-line strengths.

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Leonardo Clarke, Alice E. Shapley, Zhiwei Shao, Massimo Pascale, Ryan L. Sanders, Naveen A. Reddy, Tucker Jones, Harley Katz, Natalie Lam, Shreya Karthikeyan, Callum T. Donnan, Natascha M. Förster Schreiber, Anthony J. Pahl, Danielle A. Berg. 2026-09-25. The AURORA Survey: Determining the Production Mechanism for OI $\mathbf{λ8449}$ Emission in Star-forming Galaxies at Cosmic Noon. https://arxiv.org/abs/2609.32045

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