Modeling ringdown excitations for precessing binary black holes

With the commencement of the LIGO-Virgo-KAGRA Collaboration's fourth observing run, the field of gravitational wave (GW) physics is uniquely poised to collect even more precise data from compact binary mergers. Consequently, we will soon be able to perform even more stringent tests of general relativity. One such test that will be of particular interest in the near future is examining the excitation of quasinormal modes during the ringdown phase of observed binary coalesences. Conducting this test, however, requires that we have a robust understanding of the magnitude of excitations that can occur across binary black hole parameter space. Unfortunately, models of these excitations only exist for quasicircular, nonprecessing black holes. In this work, we present a surrogate model for the remnant black hole's mass, spin, kick velocity, and complex quasinormal mode amplitudes for quasicircular, precessing systems with mass ratios up to 8 and spin magnitudes less than 0.8. The 2,500 simulations used to train this model are produced using the SXS Collaboration's SpEC code and the waveform data is extracted using SpECTRE's Cauchy-characteristic evolution module. The remnant mass, spin, and kick velocity are calculated from the waveform data directly using Poincaré charges, while the quasinormal mode amplitudes are extracted from the waveform in the superrest frame of the remnant black hole using a linear least squares fitting routine in a stable manner.