The AURORA Survey: Robust Helium Abundances at High Redshift Reveal a Subpopulation of Helium-enhanced Galaxies in the Early Universe

Authors

• Danielle A. Berg, University of Texas at Austin
• Ryan L. Sanders, University of Kentucky
• 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 UniversityFollow
• Fergus Cullen, The University of Edinburgh
• Callum T. Donnan, National Optical-Infrared Astronomy Research Laboratory
• James S. Dunlop, The University of Edinburgh
• Tucker Jones, University of California, Riverside
• Ali Ahmad Khostovan, University of Kentucky
• Derek J. McLeod, The University of Edinburgh
• Desika Narayanan, University of Florida
• Pascal A. Oesch, University of Geneva
• Anthony J. Pahl, Observatories of the Carnegie Institution for Science
• Max Pettini, University of Cambridge
• N. M. Förster Schreiber, Max-Planck-Institut für extraterrestrische Physik
• Daniel P. Stark, University of California - Berkeley

Author ORCID Identifier

Erik Aver:  https://orcid.org/0009-0006-2077-2552

Document Type

Article

Publication Title

The Astrophysical Journal

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 (τλ3890) 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.

DOI

https://doi.org/10.3847/1538-4357/ae18db

Publication Date

12-24-2025

Comments

This is an accessible version of the article published at: Danielle A. Berg et al 2026 ApJ 996 68 (10.3847/1538-4357/ae18db).

For the published Version of Record (VoR), please visit the link above. 

Recommended Citation

Danielle A. Berg et al 2026 ApJ 996 68