The AURORA Survey

Authors

• Danielle A. Berg, University of Texas at AustinFollow
• Ryan L. Sanders, University of KentuckyFollow
• Alice E. Shapley, University of California, Los Angeles
• Michael W. Topping, University of Arizona
• Naveen A. Reddy, University of California Riverside
• Evan D. Skillman, University of Minnesota
• Erik Aver, Gonzaga University
• Fergus Cullen, University of Edinburgh
• Callum T. Donnan, NSF's National Optical-Infrared Astronomy Research Laboratory
• James S. Dunlop, University of Edinburgh
• Tucker Jones, University of California Davis
• Ali Ahmad Khostovan, University of KentuckyFollow
• Derek J. McLeod, University of Edinburgh
• Desika Narayanan, University of Florida
• Pascal A. Oesch, University of Geneva
• Anthony J. Pahl, Carnegie Institution of Washington
• Max Pettini, Institute of Astronomy
• N. M.Förster Schreiber, Max Planck Institute for Extraterrestrial Physics
• Daniel P. Stark, University of California Berkeley

Abstract

We present the first robust helium (He) abundance measurements in star-forming galaxies at redshifts 1.6 ≲ z ≲ 3.3 using deep, moderate-resolution JWST/NIRSpec spectroscopy from the AURORA survey. We establish a high-z He sample consisting of 20 galaxies with multiple high-signal-to-noise-ratio (>5σ) He i emission-line detections, including the critical near-infrared λ10833 line. This is the first study at high redshift leveraging λ10833 to break degeneracies between temperature, electron density, optical depth, and He⁺/H⁺, enabling reliable He abundance determinations in the early Universe. We use a custom Markov Chain Monte Carlo framework incorporating direct-method electron temperature priors, extended optical depth (τ_λ3890) model grids up to densities of 10⁶ cm⁻³, and simultaneous fits of the physical conditions and He i/H i line ratios to derive ionic He⁺/H⁺ abundances. Most of the AURORA galaxies follow the extrapolated z ∼ 0 He/H–O/H trend, indicating modest He enrichment by z ∼ 2–3. However, we identify a subpopulation of four galaxies that exhibit elevated He mass fractions (ΔY > 0.03) without corresponding enhancements in N/O or α-elements (∼20% of the sample). This abundance pattern is inconsistent with enrichment from asymptotic giant branch stars, but favors early He enrichment from very massive stars (M ≳ 100M_⊙), which can eject He-rich, N-poor material via stellar winds and binary stripping in young stellar populations. We speculate that these elevated-He systems may represent an early phase of globular cluster (GC) formation where N enrichment is still lagging behind He production. This work demonstrates the power of JWST multi-line He i spectroscopy for tracing early stellar feedback, enrichment pathways, and GC progenitor signatures in the high-redshift Universe.

Document Type

Article

Publication Date

1-1-2026

Notes/Citation Information

Publisher Copyright: © 2025. The Author(s). Published by the American Astronomical Society.

Digital Object Identifier (DOI)

10.3847/1538-4357/ae18db

Archival?

Archival

Repository Citation

Berg, Danielle A.; Sanders, Ryan L.; Shapley, Alice E.; Topping, Michael W.; Reddy, Naveen A.; Skillman, Evan D.; Aver, Erik; Cullen, Fergus; Donnan, Callum T.; Dunlop, James S.; Jones, Tucker; Khostovan, Ali Ahmad; McLeod, Derek J.; Narayanan, Desika; Oesch, Pascal A.; Pahl, Anthony J.; Pettini, Max; Schreiber, N. M.Förster; and Stark, Daniel P., "The AURORA Survey" (2026). Physics and Astronomy Faculty Publications. 794.
https://uknowledge.uky.edu/physastron_facpub/794