Targeted large mass ratio numerical relativity surrogate waveform model for GW190814

Gravitational wave observations of large mass ratio compact binary mergers like GW190814 highlight the need for reliable, high-accuracy waveform templates for such systems. We present NRHybSur2dq15, a new surrogate model trained on hybridized numerical relativity (NR) waveforms with mass ratios $q\leq15$, and aligned spins $|\chi_{1z}|\leq0.5$ and $\chi_{2z}=0$. We target the parameter space of GW190814-like events as large mass ratio NR simulations are very expensive. The model includes the (2,2), (2,1), (3,3), (4,4), and (5,5) spin-weighted spherical harmonic modes, and spans the entire LIGO bandwidth (with $f_{\mathrm{low}}=20$ Hz) for total masses $M \gtrsim 9.5 \, M_{\odot}$. NRHybSur2dq15 accurately reproduces the hybrid waveforms, with mismatches below $\sim 2 \times 10^{-3}$ for total masses $10 \, M_{\odot} \leq M \leq 300 \, M_{\odot}$. This is at least an order of magnitude improvement over existing semi-analytical models for GW190814-like systems. Finally, we reanalyze GW190814 with the new model and obtain source parameter constraints consistent with previous work.