Professor Andrew Bunker

Abstract:

We investigate the unusual emission-line luminosity ratios observed in the JWST Deep Extragalactic Survey (JADES) NIRSpec spectroscopy of GN-z11, which reveal exceptionally strong emission lines and a significant detection of the rarely observed N iii] , multiplet. These features suggest an elevated N/O abundance, challenging existing models of stellar populations and nebular emission. To assess whether Wolf–Rayet (WR) stars can account for the observed line ratios, we construct a suite of stellar and nebular models incorporating high-resolution stellar spectral libraries, enabling a more accurate treatment of WR evolution and its influence on the ionizing radiation field. We find that the inclusion of WR stars is essential for reproducing the observed position of GN-z11 in the C iii]/He ii versus C iii]/C iv diagnostic plane, resolving discrepancies from previous studies. The model-derived metallicity (0.07 Z/Z 0.15), ionization parameter (−2), and stellar ages are consistent with the literature estimates. However, our models underpredict the N iii/O iii] ratio, suggesting that WR stars alone cannot fully explain the nitrogen enrichment. This suggests that additional mechanisms, such as rapid chemical enrichment in a young, metal-poor environment, may be necessary to explain the nitrogen excess. While our models successfully reproduce most observed line ratios, further refinements to the models are needed to fully characterize the stellar populations and the enrichment processes of high-redshift galaxies like GN-z11.