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

¹ SISSA, Via Bonomea 265, 34136 Trieste, Italy
e-mail: sgoswami@sissa.it
² INAF-OATs, Via G. B. Tiepolo 11, 34143 Trieste, Italy
³ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, 34014 Trieste, Italy
⁴ CENTRA, Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
⁵ Dipartimento di Fisica e Astronomia, Università degli studi di Padova, Vicolo Osservatorio 3, Padova, Italy
⁶ Instituto de Astronomia Teorica y Experimental (IATE), Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina (CONICET), Argentina
⁷ IRA-INAF, Via Gobetti 101, 40129 Bologna, Italy
⁸ INFN, Sezione di Padova, Via Marzolo 8, 35131 Padova, Italy
⁹ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁰ CIERA and Department of Physics & Astronomy, Northwestern University, Evanston, IL 60208, USA
¹¹ Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy

Received: 16 August 2021
Accepted: 2 May 2022

Abstract

Context. 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.

Aims. We aim to 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 supernova (PISN).

Methods. We ran chemical evolution models with yields that account for the contribution by PISN. We used both the non-rotating stellar yields from a recent study and new yields from rotating very massive stars calculated specifically for this work. We also searched for the best initial mass function (IMF) that is able to reproduce the observations.

Results. 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.

Conclusions. 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.