A Fleeting GLIMPSE of N/O Enrichment at Cosmic Dawn: Evidence for Wolf Rayet N Stars in a z = 6.1 Galaxy

Danielle A. Berg, Rohan P. Naidu, John Chisholm, Hakim Atek, Seiji Fujimoto, Vasily Kokorev, Lukas J. Furtak, Chiaki Kobayashi, Daniel Schaerer, Angela Adamo, Qinyue Fei, Damien Korber, Jorryt Matthee, Rui Marques-Chaves, Zorayda Martinez, Kristen B. W. Mcquinn, Julian B. Muñoz, Pascal A. Oesch, Daniel P. Stark, Mabel G. Stephenson, Tiger Yu-Yang Hsiao

First listed 2025-11-17 | Last updated 2025-11-17

Abstract

We present the discovery of extreme nitrogen enrichment by Wolf Rayet nitrogen stars (WN) in the metal-poor ($\sim10\%Z_\odot$), lensed, compact ($R_{\rm eff}\sim20$ pc) galaxy RXCJ2248 at $z=6.1$, revealed by unprecedentedly deep JWST/NIRSpec medium-resolution spectroscopy from the GLIMPSE-D Survey. The exquisite S/N reveals multiple high-ionization nebular lines and broad Balmer and [OIII] components (FWHM$\sim700-3000$ km s$^{-1}$). We detect broadened HeII $λ$1640 and $λ$4687 (FWHM$\sim530$ km s$^{-1}$) and strong NIII] $λ$4642 emission consistent with a population of WN stars, making RXCJ2248 the most distant galaxy with confirmed WR features to date. We measure the multi-phase nebular density across five ions, the direct-method metallicity ($12+\log(\rm O/H)= 7.749\pm0.023$), and a non-uniform elemental enrichment pattern of extreme N/O enhancement ($\log(\rm N/O)=-0.390\pm0.035$ from N$^+$, N$^{+2}$, and N$^{+3}$) and suppressed C/O relative to empirical C/N trends. We show that this abundance pattern can be explained by enrichment from a dual-burst with a low WC/WN ratio, as expected at low metallicities. Crucially, these signatures can only arise during a brief, rare evolutionary window shortly after a burst ($\sim3-6$ Myr), when WN stars dominate chemical feedback but before dilution by later yields (e.g., supernovae). The observed frequency of strong N emitters at high$-z$ implies a $\sim50$ Myr burst duty cycle, suggesting that N/O outliers may represent a brief but ubiquitous phase in the evolution of highly star-forming early galaxies. The detection in RXCJ2248, therefore, provides the first direct evidence of WN-driven chemical enrichment in the early Universe and a novel timing argument for the bursty star formation cycles that shaped galaxies at cosmic dawn.

Short digest

Deep JWST/NIRSpec GLIMPSE-D spectra of the lensed, compact z=6.1 galaxy RXCJ2248-ID3 reveal classic WN Wolf–Rayet signatures, including broadened He II λ1640 and λ4687 (FWHM ≈530 km/s) and a strong N III] λ4642 “WR bump.” Multi-component fits also uncover broad Balmer and [O III] emission (FWHM ≈700–3000 km/s), enabling precise direct-method abundances with 12+log(O/H)=7.749±0.023 and an extreme N/O enhancement of log(N/O)=-0.390±0.035 alongside suppressed C/O. The authors argue for recent WN-driven enrichment from a dual burst with a low WC/WN ratio at low Z, occurring in a brief 3–6 Myr window after a starburst. The implied ≈50 Myr burst duty cycle provides a timing argument for ubiquitous, short-lived N/O outliers shaping early chemical evolution at cosmic dawn.

Key figures to inspect

• Fig. 2: Inspect the rest-UV/optical spectra to verify simultaneous N+ (optical), N++ (N III] 1750), and N+3 (N IV] 1483,1486) along with broadened He II and the 4650 WR bump; confirm the line IDs and relative strengths that anchor the WN interpretation.
• Fig. 3: Study the multi-component fits to Hγ/Hβ/Hα+[N II] and [O III], noting the required broad components (≈700–3000 km/s); see how subtracting these changes E(B–V), Te via [O III] λ4364, and thus the direct O/H and N/O.
• Fig. 4: Compare the blue WR region to the Sunburst Arc to see the unusually strong N III λ4642 in RXCJ2248-ID3 and the narrower He II profile, consistent with low-Z WN winds and a low WC/WN ratio.
• Fig. 1: Check the MSA slit placements and wavelength coverage across the three pointings to understand which exposures secure the key blue features ([O II], [O III] λ4364) used in density/temperature diagnostics and the final coadd S/N.