Mass and effective spin distributions of binary black hole events: Evidence for a population of hierarchical black hole mergers in active galactic nuclei disks

2021/10/21 by Wang, Yuan-Zhu, Fan, Yi-Zhong, Tang, Shao-Peng +2
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)

paper · doi:10.48550/arxiv.2110.10838

Abstract

The origins of the coalescing binary black holes (BBHs) detected by the advanced LIGO/Virgo are still in debate and clues may present in the mass and effective spin (χ_{\rm eff}) distributions of these merger events. Here we analyze the GWTC-1 and GWTC-2.1 BBH events, and find evidence for a primary mass dependent χ_{\rm eff} distribution. Below (above) the mass of ∼ 50M_\odot, a nearly zero (relatively high) effective spin is typical. In the joint analysis of the primary mass and χ_{\rm eff} distributions, we identify a sub-population of BBHs characterized by both a bump-like primary mass distribution extending to ∼ 100M_\odot and a relatively high χ_{\rm eff}∼ 0.3, consistent with the expectation for the ≥ 2g merger events in the disks of active galactic nuclei (AGNs). Our results suggest that the merger rate in AGN disks is around 1.7~\rm Gpc^-3\rm yr^-1.

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