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

Département d’Astronomie, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
e-mail: deveshnandal@yahoo.com

Received: 6 December 2023
Accepted: 17 May 2024

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 used stellar models of massive stars with initial masses ranging from 9 to 120 M_⊙ and various metallicities to deduce the chemical abundances of stellar ejecta for a few light elements (H, He, C, N, and 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 to –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 the 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(¹²C/¹³C) from 1.35 to 2.42, provide detailed benchmarks for future observational studies.