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

We present three-dimensional magnetohydrodynamic (MHD) 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 10 compared with analogous hydrodynamic simulations. The scaling of Ṁ r^1/2 roughly holds from 10\, pc to 10^-3\, pc (10\, rg) with the accretion rate through the event horizon being 10^-2\, M_\, yr^-1. The accretion flow on scales 0. 03-3\, kpc takes the form of magnetized filaments. Within 30\, pc, the cold gas circularizes, forming a highly magnetized (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 0. 3\, pc (10³\, rg). There are strong outflows towards the poles driven by the magnetic field. The outflow energy flux increases with smaller accretor size, reaching 310^43\, erg\, s^-1 for rᵢn=8\, rg; this corresponds to a nearly constant energy feedback efficiency of 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 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 (10rg/rB) ^1/2.