AGN jet-driven stochastic cold accretion in cluster cores

TL;DR

This study uses 3-D hydrodynamic simulations to show that stochastic cold gas accretion with isotropic angular momentum distribution can rapidly power AGN jets, effectively regulating cooling flows in galaxy cluster cores.

Contribution

First detailed 3-D simulations of cold gas angular momentum distribution in AGN feedback, revealing stochastic accretion as a key mechanism for jet power regulation.

Findings

Cold gas angular momentum is isotropic and cancels out rapidly.

Stochastic cold accretion leads to large variability in cold gas mass.

Simulation results align with observed weak correlation between cavity and Bondi powers.

Abstract

Several arguments suggest that stochastic condensation of cold gas and its accretion onto the central supermassive black hole (SMBH) is essential for active galactic nuclei (AGN) feedback to work in the most massive galaxies that lie at the centres of galaxy clusters. Our 3-D hydrodynamic AGN jet-ICM (intracluster medium) simulations, looking at the detailed angular momentum distribution of cold gas and its time variability for the first time, show that the angular momentum of the cold gas crossing $\lesssim 1$ kpc is essentially isotropic. With almost equal mass in clockwise and counter-clockwise orientations, we expect a cancellation of angular momentum on roughly the dynamical time. This means that a compact accretion flow with a short viscous time ought to form, through which enough accretion power can be channeled into jet mechanical energy sufficiently quickly to prevent a cooling flow. The inherent stochasticity, expected in feedback cycles driven by cold gas condensation, gives rise to a large variation in the cold gas mass at the centres of galaxy clusters, for similar cluster and SMBH masses, in agreement with the observations. Such correlations are expected to be much tighter for the smoother hot/Bondi accretion. The weak correlation between cavity power and Bondi power obtained from our simulations also match observations.