Gaseous Dynamical Friction in Presence of Black Hole Radiative Feedback

TL;DR

This study uses 2D radiative hydrodynamic simulations to show that radiative feedback from massive black holes can significantly suppress gaseous dynamical friction, affecting their orbital evolution in galaxy mergers.

Contribution

It introduces a new model demonstrating how radiative feedback diminishes dynamical friction efficiency, especially for lower-mass black holes, with implications for galaxy evolution simulations.

Findings

Radiative feedback weakens dynamical friction wake formation.

Black holes can experience slight positive acceleration due to feedback.

Suppression of dynamical friction is more severe for black holes below 10^7 solar masses.

Abstract

Dynamical friction is thought to be a principal mechanism responsible for orbital evolution of massive black holes (MBHs) in the aftermath of galactic mergers and an important channel for formation of gravitationally bound MBH binaries. We use 2D radiative hydrodynamic simulations to investigate the efficiency of dynamical friction in the presence of radiative feedback from an MBH moving through a uniform density gas. We find that ionizing radiation that emerges from the innermost parts of the MBH's accretion flow strongly affects the dynamical friction wake and renders dynamical friction inefficient for a range of physical scenarios. MBHs in this regime tend to experience positive net acceleration, meaning that they speed up, contrary to the expectations for gaseous dynamical friction in absence of radiative feedback. The magnitude of this acceleration is however negligibly small and should not significantly alter the velocity of MBHs over relevant physical timescales. Our results suggest that suppression of dynamical friction is more severe at the lower mass end of the MBH spectrum which, compounded with inefficiency of the gas drag for lower mass objects in general, implies that $< 10^7$ solar mass MBHs have fewer means to reach the centers of merged galaxies. These findings provide formulation for a sub-resolution model of dynamical friction in presence of MBH radiative feedback that can be easily implemented in large scale simulations.