Divergence in Mass Ratio Distributions between Low-mass and High-mass Coalescing Binary Black Holes
Yin-Jie Li, Yuan-Zhu Wang, Shao-Peng Tang, Qiang Yuan, Yi-Zhong Fan, Da-Ming Wei
Abstract
Abstract Coalescing binary black hole (BBH) systems are likely formed via several channels, and it is challenging to understand their formation/evolutionary processes. Some features in the mass function of the primary components ( m 1 ), such as the distinct Gaussian-like peak located at ∼34 M ⊙ , have been previously found. In this work, we investigate the possible dependence of the mass ratio ( q = m 2 / m 1 ) distribution on the primary mass. We find a Bayesian odds ratio of 18.1 in favor of divergence in the mass ratio distributions between the low- and high-mass ranges over an invariable mass ratio distribution. BBHs with m 1 ≳ 29 M ⊙ have a stronger preference of being symmetric compared to those with m 1 ≲ 29 M ⊙ at a 97.6% credible level. Additionally, we find mild evidence that BBHs with m 1 located in the Gaussian-like peak have a mass ratio distribution different from that of other BBHs. Our findings may favor some formation channels, such as chemically homogeneous evolution and dynamical assembly in globular clusters/nuclear star clusters, which are more likely to provide symmetric BBHs in the high-mass range.