Environmental Dependence of Self-Regulating Black-hole Feedback in Massive Galaxies

TL;DR

This study uses simulations to explore how environmental factors like halo mass and CGM pressure influence black-hole feedback regulation in massive galaxies, revealing conditions that lead to stable or episodic star formation suppression.

Contribution

It demonstrates how environmental conditions affect the self-regulation of black-hole feedback and star formation in massive galaxies through detailed numerical simulations.

Findings

Self-regulation is effective in deep potential wells with low CGM pressure.

Higher CGM pressure leads to episodic feedback and some star formation.

Low-mass galaxies may experience explosive feedback due to lack of angular momentum.

Abstract

In the universe's most massive galaxies, kinetic feedback from a central supermassive black hole appears to limit star formation. Abundant circumstantial evidence suggests that accumulation of cold gas near the central black hole strongly boosts the feedback output, keeping the ambient medium in a state marginally unstable to condensation and formation of cold gas clouds. However, the ability of that mechanism to self-regulate may depend on numerous environmental factors, including the depth of the potential well and the pressure of the surrounding circumgalactic medium (CGM). Here we present a suite of numerical simulations that explores the dependence of cold-fuelled bipolar kinetic feedback on those environmental factors. Halo mass in this simulation suite ranges from $2 \times 10^{12} \, M_\odot$ to $8 \times 10^{14} \, M_\odot$. We include the spatially extended mass and energy input from the massive galaxy's old stellar population, which is capable of sweeping gas out of the galaxy and away from the central black hole if the confining CGM pressure is sufficiently low. Our simulations show that this feedback mechanism is tightly self-regulating in a massive galaxy with a deep central potential and low CGM pressure, permitting only small amounts of multiphase gas to accumulate and allowing almost no star formation. In a massive galaxy of similar mass but a shallower central potential and greater CGM pressure the same feedback mechanism is more episodic, producing extended multiphase gas and occasionally allowing small rates of star formation ($\sim 0.1 \, M_\odot \, {\rm yr}^{-1}$). At the low-mass end of the explored range the mechanism becomes implausibly explosive, perhaps because the ambient gas initially has no angular momentum, which would have reduced the amount of condensed gas capable of fueling feedback.