Contribution of very massive stars to the sulfur abundance in star-forming galaxies: Role of pair-instability supernovae

¹ Department of Applied Physics, University of Cádiz, Campus of Puerto Real, 11510 Cádiz, Spain
e-mail: sabyasachi.goswami@uca.es
² Instituto de Astrofísica de Andalucía – CSIC, Apdo 3004, 18080 Granada, Spain
³ INAF-OATs, Via G. B. Tiepolo 11, 34143 Trieste, Italy
⁴ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, 34014 Trieste, Italy
⁵ SISSA, Via Bonomea 265, 34136 Trieste, Italy

Received: 11 October 2023
Accepted: 20 February 2024

Abstract

Context. Recent work presented increasing evidence of high non-constant S/O abundance ratios observed in star-forming metal-poor galaxies that deviated from the constant canonical S/O across a wide range of O/H abundances. Similar peculiarly high Fe/O ratios have also recently been detected.

Aims. We investigate whether these high S/O ratios at low metallicities could be explained when the process of pair-instability supernovae (PISN) in chemical modelling is included, through which a similar behaviour of the Fe/O ratios was reproduced successfully.

Methods. We used chemical evolution models that considered the stages of PISN in the previously published yields and adopted a suitable initial mass function (IMF) to characterize this evolutionary stage appropriately.

Results. The peculiarly high values and the behaviour of the observed S/O versus O/H relation can be reproduced when the ejecta of very massive stars that go through the process of PISN are taken into account. Additionally, a bimodal top-heavy IMF and an initial strong burst of star formation are required to reach the reported high S/O values.

Conclusions. We show that the role of very massive stars going through the process of PISN should be taken into account to explain the chemical enrichment of sulphur and oxygen in metal-poor star-forming regions.