Magnetized Accretion onto and Feedback from Supermassive Black Holes in Elliptical Galaxies
Minghao Guo, James M. Stone, Eliot Quataert, Chang‐Goo Kim
Abstract
Abstract 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 ∼10 compared with analogous hydrodynamic simulations. The scaling of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> roughly holds from ∼10 pc to ∼10 −3 pc (∼10 r g ) 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 ( β ∼ 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 (10 3 r g ). There are strong outflows toward the poles driven by the magnetic field. The outflow energy flux increases with smaller accretor size, reaching ∼3 × 10 43 erg s −1 for r in = 8 r g ; this corresponds to a nearly constant energy feedback efficiency of η ∼ 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>10</mml:mn> <mml:mspace width="0.25em"/> <mml:msub> <mml:mi>r</mml:mi> <mml:mi mathvariant="normal">g</mml:mi> </mml:msub> <mml:mo stretchy="true">/</mml:mo> <mml:msub> <mml:mi>r</mml:mi> <mml:mi mathvariant="normal">B</mml:mi> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo stretchy="true">/</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> .