Fast-rotating massive Population~III stars as possible sources of extreme N-enrichment in high-redshift galaxies

TL;DR

This study investigates how fast-rotating Population III stars and extremely metal-poor stars could explain the nitrogen enrichment observed in high-redshift galaxies, using stellar models to match observed abundance ratios.

Contribution

It introduces stellar models of massive, fast-rotating Population III stars that successfully reproduce observed nitrogen and other elemental abundances in early galaxies.

Findings

Population III stars with rapid rotation match observed N/O ratios.

Models at low metallicity reproduce observed chemical abundances.

Higher metallicity models do not align with high-redshift galaxy data.

Abstract

We present an analysis of the chemical compositions in high-redshift galaxies, with a focus on the nitrogen-enhanced galaxies GN-z11 and CEERS-1019. We use stellar models of massive stars with initial masses ranging from 9 to 120 Msol across various metallicities to deduce the chemical abundances of stellar ejecta for a few light elements (H, He, C, N, O). Our study reveals insights into the chemical processes and elemental synthesis in the early universe. We find that Population III stars, particularly at initial fast equatorial rotation and sampled from a top-heavy initial mass function, as well as stars at Z=10^{-5} with moderate rotation, align closely with observed abundance ratios in GN-z11 and CEERS-1019. These models demonstrate log(N/O) = -0.38, log(C/O) =-0.22 and log(O/H) + 12 = 7.82 at dilution factors of f = 20~100, indicating a good match with observational data. Models at higher metallicities do not match these observations, highlighting the unique role of Population III and extremely metal-poor stars in enhancing nitrogen abundance in high-redshift galaxies. Predictions for other abundance ratios, such as log(He/H) ranging from -1.077 to -1.059 and log{(^{12}C/^{13}C)} from 1.35 to 2.42, provide detailed benchmarks for future observational studies.