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Abstract

Supermassive black holes (SMBHs) merging in dwarf galaxies will be detectable
by the Laser Interferometer Space Antenna (LISA) in the mid-2030s. Previous
cosmological hydrodynamic simulations have shown the prediction of massive
black holes merging in dwarf galaxies, but these simulations are limited by
their resolution and cannot follow black hole pairs all the way to coalescence.
We calculate the delay time between black hole pairing and merger based on the
properties of the black holes and their host galaxies, and use these properties
to calculate gravitational wave strains for eleven different binary black holes
that merge inside dwarf galaxies from eight cosmological simulations. This
delay time calculation accounts for dynamical friction due to gas and stars,
loss-cone scattering, and hardening of the binary due to gravitational
radiation. Out of the eleven black hole mergers in the simulations, five black
hole pairs will merge within 0.8 - 8 Gyr of forming a close pair and could be
observed by LISA, and the remaining six are unresolved due to resolution
limitations of the simulation. As all five of the resolved close pairs merge
within a Hubble time, we make the broad estimate that close SMBH pairs in dwarf
galaxies will merge and be detectable by LISA, but this estimate depends on
either the presence of gas during orbital decay or a solution to the dynamical
buoyancy problem in cored potentials.