Chaotic cold accretion in giant elliptical galaxies heated by AGN cosmic rays

TL;DR

This study uses advanced 3D magneto-hydrodynamic simulations to explore how plasma physics, magnetic fields, and cosmic rays influence AGN feedback and cold gas formation in elliptical galaxies, revealing critical dependencies on small-scale physics.

Contribution

It demonstrates the significant impact of plasma physics, magnetic fields, and cosmic ray transport on the effectiveness of AGN feedback in elliptical galaxies, highlighting the importance of these factors in galaxy evolution models.

Findings

Magnetic fields prevent cold disk formation via magnetic braking.

Cosmic ray streaming and heating suppress cooling catastrophes.

Feedback physics on small scales critically affect large-scale galaxy evolution.

Abstract

Black hole feedback plays a central role in shaping the circumgalactic medium (CGM) of elliptical galaxies. We systematically study the impact of plasma physics on the evolution of ellipticals by performing three-dimensional non-ideal magneto-hydrodynamic simulations of the interactions of active galactic nucleus (AGN) jets with the CGM including magnetic fields, and cosmic rays (CRs) and their transport processes. We find that the physics of feedback operating on large galactic scales depends very sensitively on plasma physics operating on small scales. Specifically, we demonstrate that: (i) in the purely hydrodynamical case, the AGN jets initially maintain the atmospheres in global thermal balance. However, local thermal instability generically leads to the formation of massive cold disks in the vicinity of the central black hole in disagreement with observations; (ii) including weak magnetic fields prevents the formation of the disks because local B-field amplification in the precipitating cold gas leads to strong magnetic breaking, which quickly extracts angular momentum from the accreting clouds. The magnetic fields transform the cold clouds into narrow filaments that do not fall ballistically; (iii) when plasma composition in the AGN jets is dominated by CRs, and CR transport is neglected, the atmospheres exhibit cooling catastrophes due to inefficient heat transfer from the AGN to CGM despite Coulomb/hadronic CR losses being present; (iv) including CR streaming and heating restores agreement with the observations, i.e., cooling catastrophes are prevented and massive cold central disks do not form. The AGN power is reduced as its energy is utilized efficiently.