The Galactic center chimneys: The base of the multiphase outflow of the
  Milky Way
  Outflows and feedback are key ingredients of galaxy evolution. Evidence for
an outflow arising from the Galactic center (GC) has recently been discovered
at different wavelength. We show that the X-ray, radio, and infrared emissions
are deeply interconnected, affecting one another and forming coherent features
on scales of hundreds of parsecs, therefore indicating a common physical link
associated with the GC outflow. We debate the location of the northern chimney
and suggest that it might be located on the front side of the GC because of a
significant tilt of the chimneys toward us. We report the presence of strong
shocks at the interface between the chimneys and the interstellar medium, which
are traced by radio and warm dust emission. We observe entrained molecular gas
outflowing within the chimneys, revealing the multiphase nature of the outflow.
In particular, the molecular outflow produces a long, strong, and structured
shock along the northwestern wall of the chimney. Because of the different
dynamical times of the various components of the outflow, the chimneys appear
to be shaped by directed large-scale winds launched at different epochs. The
data support the idea that the chimneys are embedded in an (often dominant)
vertical magnetic field, which likely diverges with increasing latitude. We
observe that the thermal pressure associated with the hot plasma appears to be
smaller than the ram pressure of the molecular outflow and the magnetic
pressure. This leaves open the possibility that either the main driver of the
outflow is more powerful than the observed hot plasma, or the chimneys
represent a "relic" of past and more powerful activity. These multiwavelength
observations corroborate the idea that the chimneys represent the channel
connecting the quasi-continuous, but intermittent, activity at the GC with the
base of the Fermi bubbles.
