Description
Several studies reported unexpected abundances of C, N, O elements in metal-poor nebulae in the first billion years of the universe. As these elements are produced via different pathways and on different timescales, such features present a unique opportunity to learn about the early metal enrichment and beginnings of galaxy evolution. This study focuses on the galaxies exhibiting enhanced N/O abundances identified in archival JWST data using the direct temperature method. Our sample consists of robust abundance measurements at $z > 4$, where we consider both galaxies with strong rest-frame UV and optical emission lines probing different ionization regions. This allows us to investigate general trends in temperature and density of the high and low-ionization nebulae as a function of redshift. We place these high-redshift observations in the context of metal-poor galaxies by comparing them with the H II regions in the local universe and at low redshift. By comparing the measurements of C, N, O and alpha-element abundances (Ne, Ar) with photoionization modelling of different stellar populations we discuss possible mechanisms for producing the nitrogen signature and outline existing gaps in resolving this problem.
