Gravitational wave surrogate model for spinning, intermediate mass ratio binaries based on perturbation theory and numerical relativity

We present BHPTNRSur2dq1e3, a reduced order surrogate model of gravitational waves emitted from binary black hole (BBH) systems in the comparable to large mass ratio regime with aligned spin (${\ensuremath{\chi}}_{1}$) on the heavier mass (${m}_{1}$). We trained this model on waveform data generated from point particle black hole perturbation theory (ppBHPT) with mass ratios varying from $3\ensuremath{\le}q\ensuremath{\le}1000$ and spins from $\ensuremath{-}0.8\ensuremath{\le}{\ensuremath{\chi}}_{1}\ensuremath{\le}0.8$. The waveforms are 13,500 ${m}_{1}$ long and include all $\ensuremath{\ell}\ensuremath{\le}4$ spin-weighted spherical harmonic modes except the (4,1) and $m=0$ modes. We find that, for binaries with ${\ensuremath{\chi}}_{1}\ensuremath{\lesssim}\ensuremath{-}0.5$, retrograde quasinormal modes are significantly excited, thereby complicating the modeling process. To overcome this issue, we introduce a domain decomposition approach to model the inspiral and merger-ringdown portion of the signal separately. The resulting model can faithfully reproduce ppBHPT waveforms with a median time-domain mismatch error of $8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$. We then calibrate our model with numerical relativity (NR) data in the comparable mass regime ($3\ensuremath{\le}q\ensuremath{\le}10$). By comparing with spin-aligned BBH NR simulations at $q=15$, we find that the dominant quadrupolar (subdominant) modes agree to better than $\ensuremath{\approx}{10}^{\ensuremath{-}3}$ ($\ensuremath{\approx}{10}^{\ensuremath{-}2}$) when using a time-domain mismatch error, where the largest source of calibration error comes from the transition-to-plunge and ringdown approximations of perturbation theory. Mismatch errors are below $\ensuremath{\approx}{10}^{\ensuremath{-}2}$ for systems with mass ratios between $6\ensuremath{\le}q\ensuremath{\le}15$ and typically get smaller at larger mass ratio. Our two models---both the ppBHPT waveform model and the NR-calibrated ppBHPT model---will be publicly available through gwsurrogate and the black hole perturbation toolkit packages.