Abstract

Recent JWST /NIRSpec observations have revealed several interesting galaxies with particularly enhanced nitrogen abundances at redshifts of z > 6. These galaxies are featured by strong nitrogen emission lines in the rest-frame UV, similar to the ’’nitrogen-loud’’ quasars previously observed at lower redshifts. Among these nitrogen-loud galaxies, there is an AGN candidate, GN-z11, at a redshift of z = 10.6, also showing potentially exotic abundances of carbon and iron. The chemical enrichment history of the high-redshift nitrogen-loud galaxies and their connection with nitrogen-loud quasars remain unclear despite that many theories have been proposed. In this talk, I present our recent analyses on a nitrogen-loud Type-1 AGN at z = 5.55 observed within the JWST /NIRSpec IFS GTO Program, GA-NIFS. By combining the ground-based observations and JWST observations, we confirmed the nitrogen loudness of this AGN and further constrained its carbon abundance and iron abundance. We found evidence of a chemically stratified narrow-line region (NLR) in this AGN , where the denser and more highly ionized part of the NLR is more nitrogen enhanced. Our results suggest the peculiar chemical enrichment in this AGN is confined to the inner part of the NLR and potentially traces a specific stage of chemical evolution in a dense environment.