Magnetized Accretion onto and Feedback from Supermassive Black Holes in Elliptical Galaxies

We present 3D magnetohydrodynamic simulations of the fueling of supermassive black holes in elliptical galaxies from a turbulent cooling medium on galactic scales, taking M87* as a typical case. We find that the mass accretion rate is increased by a factor of similar to 10 compared with analogous hydrodynamic simulations. The scaling of M similar to r1/2 roughly holds from similar to 10 pc to similar to 10-3 pc (similar to 10 r g) with the accretion rate through the event horizon being similar to 10-2 M circle dot yr-1. The accretion flow on scales similar to 0.03-3 kpc takes the form of magnetized filaments. Within similar to 30 pc, the cold gas circularizes, forming a highly magnetized (beta similar to 10-3) thick disk supported by a primarily toroidal magnetic field. The cold disk is truncated and transitions to a turbulent hot accretion flow at similar to 0.3 pc (103 r g). There are strong outflows toward the poles driven by the magnetic field. The outflow energy flux increases with smaller accretor size, reaching similar to 3 x 1043 erg s-1 for r in = 8 r g; this corresponds to a nearly constant energy feedback efficiency of eta similar to 0.05-0.1 independent of accretor size. The feedback energy is enough to balance the total cooling of the M87/Virgo hot halo out to similar to 50 kpc. The accreted magnetic flux at small radii is similar to that in magnetically arrested disk models, consistent with the formation of a powerful jet on horizon scales in M87. Our results motivate a subgrid model for accretion in lower-resolution simulations in which the hot gas accretion rate is suppressed relative to the Bondi rate by similar to(10rg/rB)1/2 .