Binary black hole mergers from population III stars: Uncertainties from star formation and binary star properties

Abstract Population III (Pop. III) binary stars likely produced the first stellar-born black hole (BBH) mergers in Universe. Here, we quantify main sources of uncertainty for merger rate density evolution and mass spectrum Pop. BBHs by considering four different formation histories 11 models initial orbital properties stars. The on affects BBH up to two orders magnitude, with shorter periods leading higher rates. star history has a substantial impact both shape normalisation density: peak shifts from z ∼ 8 16 depending assumed rate, while maximum our fiducial population model spans ∼2 ∼30 Gpc−3 yr−1. typical masses are not affected only mildly influenced parameters. primary holes born tend be rather massive (30 − 40 M⊙) respect those metal-rich (8 10 M⊙). We estimate that Einstein Telescope will detect 104 per year, properties.