Binary Intermediate-mass Black Hole Mergers in Globular Clusters

We consider the formation of binary intermediate black holes (BIMBHs) in globular clusters (GC), which could happen either in situ or due to the mergers between clusters. We simulate the evolution of the BIMBH orbit (and its subsequent merger) due to stellar ejections. We also take into account the evaporation of GCs due to the tidal field of the host galaxy and two-body relaxation. Our results show that if at least 10(-3)of all GCs become BIMBH hosts and the BIMBH masses are similar to 1% of the GC mass, at least one of the inspiraling (or merging) BIMBHs will be detected by LISA during its 4 yr mission lifetime. Most of the detected BIMBHs come (1) from heavy GCs (greater than or similar to 3 x 10(5) M-circle dot), as lower-mass GCs end up being disrupted before their BIMBHs have time to merge, and (2) from redshifts 1 z < 3, assuming that most GCs form aroundz similar to 4 and given that the merger timescale for most BIMBHs is similar to 1 Gyr. If the BIMBH to GC mass ratio is lower (similar to 10(-3)) but the fraction of BIMBH hosts among GCs is higher (greater than or similar to 10(-2)), some of their mergers will also be detected by LIGO, Virgo, and KAGRA and the proposed Einstein Telescope.