Constraints on the Metallicity-dependent Explodability of Massive Stars from Galactic Chemical Evolution: Toward Alleviating the Red Supergiant Problem

TL;DR

This study integrates metallicity-dependent explodability models into galactic chemical evolution to constrain black hole formation regions and address the red supergiant problem, showing that such models align with observed abundance trends.

Contribution

It introduces a simplified metallicity-dependent explodability prescription that can alleviate the red supergiant problem while remaining consistent with chemical evolution constraints.

Findings

Explodability prescriptions reproduce key abundance trends.

GCE constrains black hole formation in mass-metallicity space.

A metallicity-dependent initial mass function improves observational agreement.

Abstract

The explodability of massive stars, namely whether they undergo core-collapse supernovae (CCSNe) or form black holes (BHs), strongly influences galactic chemical evolution (GCE). Details of the explodability are still controversial, but realistic predictions including metallicity-dependence are becoming available through stellar-evolution and explosion calculations. In the present work, we implement recently-proposed metallicity-dependent explodability prescriptions into a GCE framework. We show that the physics-motivated explodability prescriptions reproduce the key observed abundance trends. Further, within uncertainties of the explodability models, the GCE model provides strong constraints on the region of the BH formation in the mass-metallicity space. Guided by these findings, we further construct a simplified form of the metallicity-dependent explodability designed to alleviate the red supergiant (RSG) problem and explore its compatibility with GCE constraints. We find that such a solution exists, if (1) the net outflows from the system are negligible/absent, and (2) the transition of the explodability takes place at sub-solar metallicity. These results demonstrate that GCE can provide meaningful constraints on massive-star explodability and that explodability prescriptions capable of addressing the RSG problem can be constructed without violating chemical-evolution observables. We also show that a metallicity-dependent initial mass function can improve agreement with observations; this effect becomes importance once coupled with the metallicity-dependent explodability.