Gravitational Waves from Merging Intermediate-mass Black Holes. II. Event Rates at Ground-based Detectors

Based on a dynamical formation model of a supermassive black hole (SMBH), we estimate the expected observational profile of gravitational waves 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 (especially with KAGRA owing to its location at less seismic noise), we are able to detect the ring-down gravitational wave of a BH with mass M < 2 x 10(3)M(circle dot). 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 similar to 60M(circle dot) is at the peak of the expected mass distribution. With its signal-to-noise ratio rho = 10(30), we estimate the event rate R similar to 200(20) per year in the most optimistic case, and we also find that BH mergers in the rangeM < 150M(circle dot) are R > 1 per year for rho = 10. Thus, if we observe a BH with more than 100 M-circle dot in future gravitational-wave observations, our model naturally explains its source.