Non-Thermal Insights on Mass and Energy Flows Through the Galactic
  Centre and into the Fermi Bubbles
  We construct a simple model of the star-formation- (and resultant supernova-)
driven mass and energy flows through the inner ~200 pc (in diameter) of the
Galaxy. Our modelling is constrained, in particular, by the non-thermal radio
continuum and {\gamma}-ray signals detected from the region. The modelling
points to a current star-formation rate of 0.04 - 0.12 M\msun/year at 2{\sigma}
confidence within the region with best-fit value in the range 0.08 - 0.12
M\msun/year which - if sustained over 10 Gyr - would fill out the ~ 10^9 M\msun
stellar population of the nuclear bulge. Mass is being accreted on to the
Galactic centre (GC) region at a rate ~0.3M\msun/year. The region's
star-formation activity drives an outflow of plasma, cosmic rays, and
entrained, cooler gas. Neither the plasma nor the entrained gas reaches the
gravitational escape speed, however, and all this material fountains back on to
the inner Galaxy. The system we model can naturally account for the
recently-observed ~> 10^6 'halo' of molecular gas surrounding the Central
Molecular Zone out to 100-200 pc heights. The injection of cooler,
high-metallicity material into the Galactic halo above the GC may catalyse the
subsequent cooling and condensation of hot plasma out of this region and
explain the presence of relatively pristine, nuclear-unprocessed gas in the GC.
The plasma outflow from the GC reaches a height of a few kpc and is
compellingly related to the recently-discovered Fermi Bubbles. Our modelling
demonstrates that ~ 10^9 M\msun of hot gas is processed through the GC over 10
Gyr. We speculate that the continual star-formation in the GC over the age of
the Milky Way has kept the SMBH in a quiescent state thus preventing it from
significantly heating the coronal gas, allowing for the continual accretion of
gas on to the disk and the sustenance of star formation on much wider scales in
the Galaxy [abridged].
