Impact of subdominant modes on the interpretation of gravitational-wave signals from heavy binary black hole systems

TL;DR

This paper demonstrates that including higher harmonic modes in gravitational wave models significantly improves parameter estimation for heavy binary black hole mergers, reducing biases and enhancing understanding of source properties.

Contribution

The study evaluates the impact of higher modes on parameter inference using a numerical relativity surrogate model, highlighting their importance for asymmetric and high-mass binary black hole systems.

Findings

Higher modes are crucial for accurate parameter estimation in heavy binary black hole mergers.

Omission of higher modes can lead to significant biases in inferred source properties.

Including higher modes improves consistency tests of general relativity.

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 a detector-frame mass set to $120 M_\odot$ and with signal amplitude values that are 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. 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. Our work can be used to better understand asymmetric binary black hole merger events, such as GW190412. Higher modes are critical for such systems, and their omission usually produces substantial parameter biases.