A population study on the effect of metallicity on ZAMS to the merger

Abstract

The formation channels of compact object binaries are crucial for interpreting gravitational wave observations and enhancing early multi-messenger alerts. Despite the key role of stellar metallicity in progenitor evolution, many models assume a uniform value for all stars in a cluster. In this study, we investigate the impact of a heterogeneous stellar metallicity distribution on the formation of compact object binaries and their resulting gravitational wave signatures. We extend the COSMIC binary population synthesis code to incorporate a fiducial mass-redshift-metallicity relation for individual Zero-Age Main Sequence stars of a stellar cluster. Focusing on low-metallicity environments at redshift $z \approx 4$, we analyse the gravitational-wave signals from binary black holes and black hole-neutron star systems in the sub-hertz regime. The resulting binary black holes have total masses from $8$-$86\,M_\odot$, while black hole--neutron star systems range from $6$-$31\,M_\odot$. We assess the detectability of the characteristic strains against the sensitivity curves of planned sub-hertz observatories.