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

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$-z$ HeI Sample consisting of 20 galaxies with multiple high-S/N ($>5σ$) HeI emission-line detections, including the critical near-infrared $λ$10833 line. This is the first study at high redshift leveraging $λ$10833 to break degeneracies between temperature, electron density, optical depth, and He⁺/H⁺, enabling reliable He abundance determinations in the early universe. We use a custom MCMC framework incorporating direct-method electron temperature priors, extended optical depth (τλ3890) model grids up to densities of 10⁶~cm⁻³, and simultaneous fits of the physical conditions and HeI/HI line ratios to derive ionic He⁺/H⁺ abundances. Most of the AURORA galaxies follow the extrapolated z~0 He/H-O/H trend, indicating modest He enrichment by z~2-3. However, we identify a subpopulation of four galaxies that exhibit elevated He mass fractions ($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; M100\ M_), 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.