Dynamics of Kicked and Accelerated Massive Black Holes in Galaxies

TL;DR

This paper investigates how massive black holes behave in disk galaxies after receiving kicks or accelerations, revealing conditions for escape, oscillation, and observable galaxy asymmetries through simulations.

Contribution

It introduces a detailed simulation study of black hole dynamics post-merger or jet acceleration, highlighting escape velocities and observable galaxy features.

Findings

Black holes escape above ~600 km/s kick velocity.

Oscillations occur below escape thresholds with decreasing frequency.

Galactic asymmetries and displacements are observable due to black hole motion.

Abstract

A study is made of the behavior of massive black holes in disk galaxies that have received an impulsive kick from a merger or a sustained acceleration from an asymmetric jet. The motion of the gas, stars, dark matter, and massive black hole are calculated using the GADGET-2 simulation code. The massive black hole escapes the galaxy for kick velocities above about 600 km/s or accelerations above about 4*10^{-8} cm/s^2 over time-scales of the order of 10^8 yr. For smaller velocity kicks or smaller accelerations, the black hole oscillates about the center of mass with a frequency which decreases as the kick velocity or acceleration increases. The black hole displacements may give rise to observable nonaxisymmetries in the morphology and dynamics of the stellar and gaseous disk of the galaxy. In some cases the dynamical center of the galaxy is seen to be displaced towards the direction of the BH acceleration with a characteristic ``tongue--'' shaped extension of the velocity contours on the side of the galaxy opposite the acceleration.