Understand
We interpret the peculiar super-solar nitrogen abundance recently reported by the James Webb Space Telescope observations for GN-z11 ($z=10.6$) using our state-of-the-art chemical evolution models.
- The observed CNO ratios can be successfully reproduced -- independently of the adopted initial mass function, nucleosynthesis yields, and presence of supermassive ($>$1000$M_\odot$) stars -- if the galaxy has undergone an intermittent star formation history with a quiescent phase lasting $\sim$100 Myr, separating two strong starbursts.
- Immediately after the second burst, Wolf--Rayet stars (up to $120M_\odot$) become the dominant enrichment source, also temporarily ($<$1 Myr) enhancing particular elements (N, F, Na, and Al) and isotopes ($^{13}$C and $^{18}$O).
- Alternative explanations involving (i) single burst models, also including very massive stars and/or pair-instability supernovae, or (ii) pre-enrichment scenarios fail to match the data.