The role of gravitational recoil in the assembly of massive black hole seeds (2002.04740v1)

Abstract: When two black holes merge, the asymmetric emission of gravitational waves provides an impulse to the merged system; this gravitational wave recoil velocity can be up to 4000 km s$^{-1}$, easily fast enough for the black hole to escape its host galaxy. We combine semi-analytic modeling with cosmological zoom-in simulations of a Milky Way-type galaxy to investigate the role of black hole spin and gravitational recoil in the epoch of massive black hole seeding. We sample four different spin distributions (random, aligned, anti-aligned, and zero spin), and compare the resulting merger rates, occupation fractions, and MBH-host relations with what is expected by excluding the effect of recoil. The inclusion of gravitational recoil and MBH spin in the assembly of MBH seeds can reduce the final $z=5$ MBH mass by up to an order of magnitude. The MBH occupation fraction, however, remains effectively unaltered due to episodes of black hole formation following a recoil event. While electromagnetic detections of these events are unlikely, LISA is ideally suited to detect gravitational wave signals from such events.