Detectability and source characterization of intermediate mass-ratio black hole coalescences with gravitational waves

Coalescences of intermediate mass ratio binaries containing stellar-mass black holes into intermediate-mass black holes (IMBHs) (M > 100M_sun) are exciting sources of gravitational waves (GWs). We consider the detectability and characterization of GWs from intermediate mass ratio binaries with mass ratios 1/40 < q < 1/10 and total mass 175M_sun < M < 300M_sun. Using multi-mode frequency domain GWs waveform models, we find that GW signals from such intermediate mass ratio binaries are greatly aided by the inclusion of subdominant GW modes in improving both detectability and characterization. We also explore the precision with which the current generation detectors will be able to measure the source properties for these binaries. We demonstrate that including subdominant modes in the waveform model can enable an informative measurement of the spin components especially for the highest mass binaries that can merge in LIGO/Virgo’s sensitive band. Finally, we show that our results are valid for face-off binaries, binaries with generic spins and binaries in the pair-instability mass gap.Thus we conclude that templates containing higher-order multipoles are crucial for both searches and accurate source characterization.