Constraint on the progenitor of binary black hole merger using Population III star formation channel

Abstract

The observations of gravitational waves have revealed the existence of black holes above $30 M_\odot$. A variety of channels have been proposed as their origin, including the Population III (Pop. III) star channel. In this channel, Binary Black Holes (BBHs) containing such massive BHs are naturally produced. In this paper, we examine the relative fractions of five formation channels that may contribute to the origins of BBHs: isolated binaries of either Population I or Population II stars, PopIII isolated binaries, chemically homogeneous evolution, and the dynamical evolution in globular clusters and nuclear star clusters, using the LIGO-Virgo-KAGRA gravitational-wave transient catalog (GWTC-3) events through hierarchical Bayesian inference. We find that the branching fraction of the Pop. III BBH channel is $0.11^{+0.08}_{-0.06}$ within our framework, consistent with the local merger rate density of the model of the Pop. III BBH channel we adopt. We also evaluate the contributions to the catalogue using the selection effect of each formation channel and find that Pop. III BBH could contribute at a non-negligible rate, though the adequacy of these ratios should be subject to ongoing discussion.