Fermi bubble simulations: black hole feedback in the Milky Way
  The $Fermi$ gamma-ray telescope discovered a pair of bubbles at the Galactic
center. These structures are spatially-correlated with the microwave emission
detected by the WMAP and Planck satellites. These bubbles were likely inflated
by a jet launched from the vicinity of a supermassive black hole in the
Galactic center. Using MHD simulations, which self-consistently include
interactions between cosmic rays and magnetic fields, we build models of the
supersonic jet propagation, cosmic ray transport, and the magnetic field
amplification within the $Fermi$ bubbles. Our key findings are that: (1) the
synthetic $Fermi$ gamma-ray and WMAP microwave spectra based on our simulations
are consistent with the observations, suggesting that a single population of
cosmic ray leptons may simultaneously explain the emission across a range of
photon energies; (2) the model fits the observed centrally-peaked microwave
emission if a second, more recent, pair of jets embedded in the $Fermi$ bubbles
is included in the model. This is consistent with the observationally-based
suggestion made by Su & Finkbeiner (2012); (3) the radio emission from the
bubbles is expected to be strongly polarized due to the relatively high level
of field ordering caused by elongated turbulent vortices. This effect is caused
by the interaction of the shocks driven by the jets with the preexisting
interstellar medium turbulence; (4) a layer of enhanced rotation measure in the
shock-compressed region could exist in the bubble vicinity but the level of
this enhancement depends on the details of the magnetic topology.
