Baryon Cycles in the Biggest Galaxies

TL;DR

This paper reviews how supermassive black holes and large-scale atmospheres in massive galaxies interact to regulate star formation, emphasizing the role of black hole accretion energy in maintaining a marginally stable gaseous state.

Contribution

It introduces a model linking black hole accretion energy to the suppression of star formation based on galaxy velocity dispersion and supernova heating.

Findings

Massive galaxies are often near a marginal state for cold cloud formation.

Black hole accretion energy can suspend galaxy atmospheres, regulating star formation.

Star formation is closely tied to the galaxy's central velocity dispersion.

Abstract

The universe's biggest galaxies have both vast atmospheres and supermassive central black holes. This article reviews how those two components of a large galaxy couple and regulate the galaxy's star formation rate. Models of interactions between a supermassive black hole and the large-scale atmosphere suggest that the energy released as cold gas clouds accrete onto the black hole suspends the atmosphere in a state that is marginally stable to formation of cold clouds. A growing body of observational evidence indicates that many massive galaxies, ranging from the huge central galaxies of galaxy clusters down to our own Milky Way, are close to that marginal state. The gas supply for star formation within a galaxy in such a marginal state is closely tied to the central velocity dispersion (sigma_v) of its stars. We therefore explore the consequences of a model in which energy released during blackhole accretion shuts down star formation when sigma_v exceeds a critical value determined by the galaxy's supernova heating rate.