Event Rates of Gravitational Waves from merging Intermediate mass Black Holes: based on a Runaway Path to a SMBH

Department of Information Systems, Osaka Institute of Technology, Hirakata City, Osaka 573-0196, Japan

^* e-mail: hisaaki.shinkai@oit.ac.jp

Published online: 9 January 2018

Abstract

Based on a dynamical formation model of a supermassive black hole (SMBH), we estimate the expected observational profile of gravitational wave at ground-based detectors, such as KAGRA or advanced LIGO/VIRGO. Noting that the second generation of detectors have enough sensitivity from 10 Hz and up, we are able to detect the ring-down gravitational wave of a BH with the mass M < 2 × 10₃M_⊙. This enables us to check the sequence of BH mergers to SMBHs via intermediate-mass BHs. We estimate the number density of galaxies from the halo formation model and estimate the number of BH mergers from the giant molecular cloud model assuming hierarchical growth of merged cores. At the designed KAGRA (and/or advanced LIGO/VIRGO), we find that the BH merger of its total mass M ∼ 60M_⊙ is at the peak of the expected mass distribution. With its signal-to-noise ratio ρ = 10(30), we estimate the event rate R ∼ 200(20) per year in the most optimistic case, and we also find that BH mergers in the range M < 150M_⊙ are R > 1 per year for ρ = 10. Thus, if we observe a BH with more than 100M_⊙ in future gravitational-wave observations, our model naturally explains its source.