Anomalies in the gravitational recoil of eccentric black-hole mergers with unequal mass ratios

The radiation of linear momentum imparts a recoil (or "kick") to the center of mass of a merging black-hole binary system. Recent numerical relativity calculations have shown that eccentricity can lead to an approximate 25% increase in recoil velocities for equal-mass, spinning binaries with spins lying in the orbital plane ("superkick" configurations) [U. Sperhake et al. Phys. Rev. D 101, 024044 (2020)]. Here we investigate the impact of nonzero eccentricity on the kick magnitude and gravitational-wave emission of nonspinning, unequal-mass black hole binaries. We confirm that nonzero eccentricities at merger can lead to kicks which are larger by up to similar to 25% relative to the quasicircular case. We also find that the kick velocity v has an oscillatory dependence on eccentricity, which we interpret as a consequence of changes in the angle between the infall direction at merger and the apoapsis (or periapsis) direction.