2024ApJ...966...92S

The first JWST spectroscopy of the luminous galaxy GN-z11 simultaneously established its redshift at z = 10.6 and revealed a rest-ultraviolet spectrum dominated by signatures of highly ionized nitrogen, which has so far defied clear interpretation. We present a reappraisal of this spectrum in the context of both detailed nebular modeling and nearby metal-poor reference galaxies. The N IV] emission enables the first nebular density measurement in an apparently predominantly star-forming galaxy at z > 10, revealing evidence for extremely high densities n_e ≳ 10⁵ cm^–3. With a suite of photoionization models, we establish that regardless of the ionization mechanism and accounting for depletion and this density enhancement, gas substantially enriched in nitrogen ([N/O] = +0.52 assuming the nebular emission is dominated by star formation) is required to reproduce the observed lines. We compare the GN-z11 spectrum to local UV databases and highlight a unique nearby galaxy, Mrk 996, where a high concentration of Wolf-Rayet stars and their CNO-processed ejecta produce a UV spectrum remarkably similar in some respects to that of GN-z11 and the Sunburst Arc. Collating this evidence in the context of Galactic stellar abundances, we suggest that the peculiar nitrogenic features prominent in GN-z11 may be a unique signature of intense and densely clustered star formation in the evolutionary chain of the present-day globular clusters, consistent with in situ early enrichment with nuclear-processed stellar ejecta on a massive scale. Combined with insight from local galaxies, these and future JWST data open a powerful new window into the physical conditions of star formation and chemical enrichment at the highest redshifts.