Black hole feedback in a multiphase interstellar medium
  Ultrafast outflows (UFOs) from supermassive black holes (SMBHs) are thought
to regulate the growth of SMBHs and host galaxies, resulting in a number of
observational correlations. We present high-resolution numerical simulations of
the impact of a thermalized UFO on the ambient gas in the inner part of the
host galaxy. Our results depend strongly on whether the gas is homogeneous or
clumpy. In the former case all of the ambient gas is driven outward rapidly as
expected based on commonly used energy budget arguments, while in the latter
the flows of mass and energy decouple. Carrying most of the energy, the shocked
UFO escapes from the bulge via paths of least resistance, taking with it only
the low-density phase of the host. Most of the mass is however in the
high-density phase, and is affected by the UFO much less strongly, and may even
continue to flow inwards. We suggest that the UFO energy leakage through the
pores in the multiphase interstellar medium (ISM) may explain why observed
SMBHs are so massive despite their overwhelmingly large energy production
rates. The multiphase ISM effects reported here are probably under-resolved in
cosmological simulations but may be included in prescriptions for active
galactic nuclei feedback in future simulations and in semi-analytical models.
