A Galaxy-Scale Fountain of Cold Molecular Gas Pumped by a Black Hole
  We present ALMA and MUSE observations of the Brightest Cluster Galaxy in
Abell 2597, a nearby (z=0.0821) cool core cluster of galaxies. The data map the
kinematics of a three billion solar mass filamentary nebula that spans the
innermost 30 kpc of the galaxy's core. Its warm ionized and cold molecular
components are both cospatial and comoving, consistent with the hypothesis that
the optical nebula traces the warm envelopes of many cold molecular clouds that
drift in the velocity field of the hot X-ray atmosphere. The clouds are not in
dynamical equilibrium, and instead show evidence for inflow toward the central
supermassive black hole, outflow along the jets it launches, and uplift by the
buoyant hot bubbles those jets inflate. The entire scenario is therefore
consistent with a galaxy-spanning "fountain", wherein cold gas clouds drain
into the black hole accretion reservoir, powering jets and bubbles that uplift
a cooling plume of low-entropy multiphase gas, which may stimulate additional
cooling and accretion as part of a self-regulating feedback loop. All
velocities are below the escape speed from the galaxy, and so these clouds
should rain back toward the galaxy center from which they came, keeping the
fountain long-lived. The data are consistent with major predictions of chaotic
cold accretion, precipitation, and stimulated feedback models, and may trace
processes fundamental to galaxy evolution at effectively all mass scales.
