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