2025/07/22 by Danielle A. Berg, Ryan L. Sanders, Berg, Danielle A. +35 · 2 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Scientific Research and Discoveries
paper · pdf · doi:10.48550/arxiv.2507.17057
openalex publication_date 2025/07/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
We present the first robust helium (He) abundance measurements in star-forming galaxies at redshifts 1.6\lesssim z\lesssim 3.3 using deep, moderate-resolution JWST/NIRSpec spectroscopy from the AURORA survey. We establish a High-z HeI Sample consisting of 20 galaxies with multiple high-S/N (>5σ) HeI 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 MCMC 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 HeI/HI 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 (VMSs; M\gtrsim100 M_\odot), 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 HeI spectroscopy for tracing early stellar feedback, enrichment pathways, and GC progenitor signatures in the high-z universe.