Rapid Chemical Enrichment by Intermittent Star Formation in GN-z11

TL;DR

This study explains the super-solar nitrogen levels in GN-z11 through a model of intermittent star formation with two bursts separated by a quiescent period, highlighting Wolf-Rayet stars' role in chemical enrichment.

Contribution

It demonstrates that intermittent star formation with specific timing can reproduce observed chemical abundances, challenging single-burst or pre-enrichment models.

Findings

Intermittent star formation explains observed CNO ratios.

Wolf-Rayet stars dominate enrichment immediately after the second burst.

Alternative models fail to match the observed data.

Abstract

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. Feedback-regulated, intermittent star formation might be common in early systems. Elemental abundances can be used to test this hypothesis and to get new insights on nuclear and stellar astrophysics.