Gravitational Recoil Velocities from Eccentric Binary Black Hole Mergers

The formation and growth of supermassive black holes is a key issue to unveilthe secrets of galaxy formation. In particular, the gravitational recoilproduced in the merger of unequal mass black hole binaries could have a numberof astrophysical implications, such as the ejection of black holes from thehost galaxy or globular cluster. We present estimates of the recoil velocitythat include the effect of small eccentricities. The approach is speciallysuited for the last stage of the merger, where most of the emission of linearmomentum in gravitational waves takes place. Supplementing our estimates withpost-Newtonian approximations, we obtain lower and upper bounds that constrainprevious recoil velocities estimates as well as a best estimate that agreeswith numerical simulations in the quasi-circular case. For eccentricities e <=0.1, the maximum recoil is found for mass ratios of M_1/M_2 ~ 0.38 with a bestestimate of ~ 167 (1 + e) km/s and upper and lower bounds of 79 (1 + e) km/sand 216 (1 + e) km/s respectively.Comment: 6 pages, 3 figure