The impact of very massive stars on the chemical evolution of extremely metal-poor galaxies

TL;DR

This study explores how very massive stars, especially those ending as Pair-Instability Supernovae, influence the chemical makeup of extremely metal-poor galaxies, highlighting the role of a top-heavy initial mass function and stellar rotation.

Contribution

It introduces new rotating stellar yields and demonstrates that a bi-modal IMF with a burst of very massive stars can explain observed chemical ratios in metal-poor galaxies.

Findings

Reproduces near-solar Fe/O ratios with a burst of very massive stars.

Rotation is essential to match observed N/O ratios.

Supports a top-heavy IMF in early galaxy evolution.

Abstract

In recent observations of extremely metal-poor low-mass starburst galaxies, almost solar Fe/O ratios are reported, despite N/O ratios consistent with the low metallicity. We investigate if the peculiar Fe/O ratios can be a distinctive signature of an early enrichment produced by very massive objects dying as Pair-Instability Supernovae (PISN). We run chemical evolution models with yields that account for the contribution by PISN. We use both the recent non-rotating stellar yields from Goswami et al. 2021, and new yields from rotating very massive stars calculated on purpose in this work. We also search for the best initial mass function (IMF) that is able to reproduce the observations. We can reproduce the observations by adopting a bi-modal IMF and by including an initial burst of rotating very massive stars. Only with a burst of very massive stars can we reproduce the almost solar Fe/O ratios at the estimated young ages. We also confirm that rotation is absolutely needed to concomitantly reproduce the observed N/O ratios. These results stress the importance of very massive stars in galactic chemical evolution studies and strongly support a top-heavy initial mass function in the very early evolutionary stages of metal poor starburst galaxies.