Black hole growth and AGN feedback under clumpy accretion

TL;DR

This study uses a stochastic subgrid model to show that clumpy, variable accretion significantly accelerates black hole growth, drives powerful outflows, and suppresses star formation, highlighting the importance of accretion variability in galaxy evolution.

Contribution

The paper introduces a calibrated stochastic model for clumpy black hole accretion, demonstrating its impact on black hole growth and galaxy feedback processes in cosmological simulations.

Findings

Clumpy accretion enhances black hole growth at high redshift.

Variable accretion drives stronger galactic outflows.

Increased black hole mass suppresses star formation significantly.

Abstract

High-resolution simulations of supermassive black holes in isolated galaxies have suggested the importance of short (~10 Myr) episodes of rapid accretion caused by interactions between the black hole and massive dense clouds within the host. Accretion of such clouds could potentially provide the dominant source for black hole growth in high-z galaxies, but it remains unresolved in cosmological simulations. Using a stochastic subgrid model calibrated by high-resolution isolated galaxy simulations, we investigate the impact that variability in black hole accretion rates has on black hole growth and the evolution of the host galaxy. We find this clumpy accretion to more efficiently fuel high-redshift black hole growth. This increased mass allows for more rapid accretion even in the absence of high-density clumps, compounding the effect and resulting in substantially faster overall black hole growth. This increased growth allows the black hole to efficiently evacuate gas from the central region of the galaxy, driving strong winds up to ~2500 km/s, producing outflows ~10x stronger than the smooth accretion case, suppressing the inflow of gas onto the host galaxy, and suppressing the star formation within the galaxy by as much as a factor of two. This suggests that the proper incorporation of variability is a key factor in the co-evolution between black holes and their hosts.