Modelling the formation of the first two neutron star–black hole mergers, GW200105 and GW200115: metallicity, chirp masses, and merger remnant spins

The two neutron star-black hole mergers (GW200105 and GW200115) observed in gravitational waves by advanced LIGO Virgo, mark the first ever discovery of such binaries nature. We study these systems through isolated binary evolution, using a grid population synthesis models. Using both mass spin observations (chirp mass, effective remnant spin) binaries, we probe their different possible formation channels metallicity environments. Our models only support data when assuming black is non spinning. results show strong preference that GW200105 GW200115 formed from stars with sub-solar metallicities $Z\lesssim 0.005$. Only metal-rich ($Z=0.02$) are agreement GW200115. also find chirp spins jointly aid constraining models, whilst parameter does not add any further information. present observable (i.e. post selection effects) median values distribution all our which maybe used as reference for future mergers. Further, exhibits distinguishable features sub-populations. non-spinning, born holes dominate significantly merging population, ensuring electromagnetic counterparts to rare affair.