Massive Black Hole Recoil in High Resolution Hosts

TL;DR

This paper investigates the dynamics of recoiling massive black holes in high-resolution, non-axisymmetric galaxy potentials through N-body simulations, revealing that halo shape significantly affects black hole wandering times and retention.

Contribution

It presents the first detailed N-body simulations of recoiling black holes in realistic, high-resolution galaxy potentials, highlighting the impact of halo shape on black hole dynamics.

Findings

Halo asphericity increases wandering time of black holes.

Black holes with recoil velocities over 200 km/s often do not return to the nucleus within 1 Gyr.

In gas-rich merger remnants, black holes are retained even with recoil velocities of 500 km/s.

Abstract

The final inspiral and coalescence of a black hole binary can produce highly beamed gravitational wave radiation. To conserve linear momentum, the black hole remnant can recoil with "kick" velocity as high as 4000 km/s. We present two sets of full N-body simulations of recoiling massive black holes (MBH) in high-resolution, non-axisymmetric potentials. The host to the first set of simulations is the main halo of the Via Lactea I simulation (Diemand et al. 2007). The nature of the resulting orbits is investigated through a numerical model where orbits are integrated assuming an evolving, triaxial NFW potential, and dynamical friction is calculated directly from the velocity dispersion along the major axes of the main halo of Via Lactea I. By comparing the triaxial case to a spherical model, we find that the wandering time spent by the MBH is significantly increased due to the asphericity of the halo. For kicks larger than 200 km/s, the remnant MBH does not return to the inner 200 pc within 1 Gyr, a timescale an order of magnitude larger than the upper limit of the estimated QSO lifetime. The second set of simulations is run using the outcome of a high-resolution gas-rich merger (Mayer et al. 2007) as host potential. In this case, a recoil velocity of 500 km/s cannot remove the MBH from the nuclear region.