Explaining the high nitrogen abundances observed in high-z galaxies via population III stars of a few thousand solar masses

¹ Département d’Astronomie, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
e-mail: deveshnandal@yahoo.com
² Centre for Astrophysics and Space Sciences Maynooth, Department of Theoretical Physics, Maynooth University, Maynooth, Ireland
³ Department of Physics and Astronomy, Allen Building, University of Manitoba, 30A Sifton Rd, Winnipeg, MB R3T 2N2, Canada

Received: 21 September 2023
Accepted: 30 January 2024

Abstract

The chemical enrichment of the early Universe is a crucial element in the formation and evolution of galaxies, and Population III (Pop III) stars must play a vital role in this process. In this study, we examine metal enrichment from massive stars in the early Universe’s embryonic galaxies. Using radiation hydrodynamic simulations and stellar evolution modelling, we calculated the expected metal yield from these stars. Specifically, we applied accretion rates from a previous radiation-hydrodynamic simulation to inform our stellar evolution modelling, executed with the Geneva code, across 11 selected datasets, with final stellar masses between 500 and 9000 M_⊙. Our results demonstrate that the first generation of Pop III stars within a mass range of 2000−9000 M_⊙ result in N/O, C/O and O/H ratios compatible with the values observed in very high-z galaxies GN-z11 and CEERS 1019. The ejecta of these Pop III stars are predominantly composed of ⁴He, ¹H, and ¹⁴N. Our Pop III chemical enrichment model of the halo can accurately reproduce the observed N/O and C/O ratios, and, by incorporating a hundred times more zero-metallicity interstellar material with the stellar ejecta, it accurately attains the observed O/H ratio. Thus, a sub-population of extremely massive Pop III stars, with masses surpassing approximately 2000 M_⊙, effectively reproduces the CNO elemental abundances observed in high-z JWST galaxies to date. We closely reproduced the observed Ne/O ratio in CEERS 1019 employing a model with several thousand solar masses and non-zero metallicity, and we projected a ¹²C/¹³C ratio of 7, substantially lower than the solar ratio of around 90. The significant nitrogen enrichment predicted by Pop III stars with a few thousand solar masses not only reinforces the argument for a heavy seed formation pathway for massive black holes at redshifts as high as z = 10.6 but it also accentuates the need for deeper investigations into their complex nature and pivotal role in the early Universe.