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Abstract

Over the past year, a handful of new gravitational wave models have been
developed to include multiple harmonic modes thereby enabling for the first
time fully Bayesian inference studies including higher modes to be performed.
Using one recently-developed numerical relativity surrogate model,
NRHybSur3dq8, we investigate the importance of higher modes on parameter
inference of coalescing massive binary black holes. We focus on examples
relevant to the current three-detector network of observatories, with
detector-frame masses and signal amplitudes consistent with plausible
candidates for the next few observing runs. We show that for such systems the
higher mode content will be important for interpreting coalescing binary black
holes, reducing systematic bias, and computing properties of the remnant
object. For asymmetric binaries with mass ratios $q>1$, higher modes are
critical, and their omission usually produces substantial parameter biases.
Even for comparable-mass binaries and at low signal amplitude, the omission of
higher modes can influence posterior probability distributions. We discuss the
impact of our results on source population inference and self-consistency tests
of general relativity.