Stellar feedback-regulated black hole growth: driving factors from nuclear to halo scales

TL;DR

This study uses cosmological simulations to identify key physical factors like halo mass, stellar density, and gas disk formation that trigger rapid supermassive black hole growth, especially in galaxies around L* luminosity.

Contribution

It reveals the specific physical thresholds and galaxy properties that correlate with the transition to accelerated black hole accretion, emphasizing the role of stellar feedback inefficiency.

Findings

Black hole growth accelerates when central stellar surface density exceeds ~10^9.5 Msun/kpc^2.

Formation of long-lived, thin gas disks correlates with black hole fueling.

Halo mass ~10^12 Msun marks the onset of rapid black hole growth.

Abstract

Several recent simulations of galaxy formation predict two main phases of supermassive black hole (BH) accretion: an early, highly intermittent phase (during which BHs are under-massive relative to local scaling relations), followed by a phase of accelerated growth. We investigate physical factors that drive the transition in BH accretion in cosmological zoom-in simulations from the FIRE project, ranging from dwarf galaxies to galaxies sufficiently massive to host luminous quasars. The simulations model multi-channel stellar feedback, but neglect AGN feedback. We show that multiple physical properties, including halo mass, galaxy stellar mass, and depth of the central gravitational potential correlate with accelerated BH fueling: constant thresholds in these properties are typically crossed within ~0.1 Hubble time of accelerated BH fueling. Black hole masses increase sharply when the stellar surface density in the inner 1 kpc crosses a threshold Sigma1 ~ 10^9.5 Msun/kpc^2, a characteristic value above which gravity prevents stellar feedback from ejecting gas, and similar to the value above which galaxies are observed to quench. We further show that accelerated BH growth correlates with the emergence of long-lived, thin gas disks, as well as with virialization of the inner circumgalactic medium. The halo mass Mh ~ 10^12 Msun and stellar mass Mstar ~ 10^10.5 Msun at which BH growth accelerates correspond to ~L* galaxies. The fact that stellar feedback becomes inefficient at ejecting gas from the nucleus above this mass scale may play an important role in explaining why AGN feedback appears to be most important in galaxies above ~L*.