JWST Survey Finds Nitrogen-Enhanced Galaxies Rise to 18% at z~7, Driven by Wolf-Rayet and AGB Enrichment Cycles

The arXiv preprint constructs the largest high-redshift sample of nitrogen-enhanced galaxies using public JWST NIRSpec and NIRCam data. Stacked spectra isolate low-metallicity Wolf-Rayet signatures in the most extreme objects and detect secondary kinematic components in 40% of targets, indicating ionised outflows. The remaining systems display broadened H-alpha without forbidden-line counterparts and weak Balmer breaks, consistent with post-burst phases 30-40 Myr after the initial star formation episode.

These patterns connect directly to open questions in cosmic dawn by showing that standard closed-box chemical evolution models underpredict primary nitrogen production on short timescales. The observed sequence—WR-driven enrichment within 10 Myr followed by AGB contributions after outflow dilution—matches recent hydrodynamical simulations that incorporate bursty, cluster-dominated star formation. This challenges assumptions of steady, continuous enrichment in early galaxies.

Future ALMA and ELT observations targeting [N II] and CNO isotope ratios will test whether the same galaxies cycle through multiple enrichment episodes. Confirmation would require measuring outflow velocities above 300 km/s and detecting carbon-enhanced phases between the WR and AGB windows.

The key limitation remains the reliance on stacked spectra for the non-outflow subset, reducing individual-object constraints on stellar population ages.