High N/O ratio at high redshift as a result of a strong burst of star formation and differential galactic winds

TL;DR

This study demonstrates that high N/O ratios at high redshift can be explained by models with intense star formation and differential galactic winds, without needing exotic nucleosynthesis sources.

Contribution

It introduces chemical evolution models with differential winds and high star formation rates to reproduce observed high N/O ratios at high redshift.

Findings

High star formation rates are essential to match observed abundances.

Differential galactic winds mainly eject supernova products.

No need for Population III or supermassive star nucleosynthesis.

Abstract

Recent observations by JWST have revealed supersolar $^{14}$N abundances in galaxies at very high redshift. On the other hand, these galaxies show subsolar metallicity. The observed N/O ratios are difficult to reproduce in the framework of chemical evolution models for the Milky Way. Our aim is to reproduce these high N/O ratios with chemical evolution models assuming different histories of star formation triggering galactic winds coupled with detailed nucleosynthesis prescriptions for $^{14}$N, $^{12}$C, $^{16}$O and $^{56}$Fe. We compute several models for small galaxies ($10^{9}\text{ - }10^{10}\text{ M}_{\odot}$) with high star formation efficiency and strong galactic winds. These winds are assumed to be differential, carrying out mainly the products of the explosion of core-collapse supernovae. We find that only models with high star formation rates, normal initial mass function, and differential galactic winds can reproduce the observed chemical abundances. We also find that with the same assumptions about star formation and galactic winds, but with a very rapid formation resulting from fast gas infall, we can also reproduce the estimated ages of these objects. We find no necessity to invoke peculiar nucleosynthesis from Population III stars, very massive stars and supermassive stars.