Self-Regulated Black Hole Growth via Momentum Deposition in Galaxy Merger Simulations

TL;DR

This paper introduces a new simulation approach for galaxy mergers that models black hole growth and feedback via momentum deposition, leading to self-regulated black hole growth without large-scale outflows.

Contribution

It presents a phenomenological model for black hole accretion and feedback that better captures the interaction with dense gas in galaxy mergers.

Findings

Black hole growth is self-regulated by feedback physics.

Black holes significantly influence nuclear gas dynamics.

Feedback sets black hole mass without large-scale galactic outflows.

Abstract

We perform hydrodynamical simulations of major galaxy mergers using new methods for calculating the growth of massive black holes (BH) in galactic nuclei and their impact on the surrounding galaxy. We model BH growth by including a subgrid model for accretion produced by angular momentum transport on unresolved scales. The impact of the BHs radiation on surrounding gas is approximated by depositing momentum into the ambient gas, which produces an outward force away from the BH. We argue that these phenomenological models for BH growth and feedback better approximate the interaction between the BH and dense gas in galaxies than previous models. We show that this physics leads to self-regulated black hole growth: during the peak of activity, the accretion rate onto the BH is largely determined by the physics of BH feedback, not the subgrid accretion model. The BH significantly modifies the gas dynamics in the galactic nucleus (< 300 pc), but does not generate large-scale galactic outflows. Integrated over an entire galaxy merger, BH feedback has little effect on the total number of stars formed, but is crucial for setting the BHs mass.