A Dynamical Model for Gas Flows, Star Formation, and Nuclear Winds in
  Galactic Centres
  We present a dynamical model for gas transport, star formation, and winds in
the nuclear regions of galaxies, focusing on the Milky Way's Central Molecular
Zone (CMZ). In our model angular momentum and mass are transported by a
combination of gravitational and bar-driven acoustic instabilities. In
gravitationally-unstable regions the gas can form stars, and the resulting
feedback drives both turbulence and a wind that ejects mass from the CMZ. We
show that the CMZ is in a quasi-steady state where mass deposited at large
radii by the bar is transported inward to a star-forming, ring-shaped region at
$\sim 100$ pc from the Galactic Centre, where the shear reaches a minimum. This
ring undergoes episodic starbursts, with bursts lasting $\sim 5-10$ Myr
occurring at $\sim 20-40$ Myr intervals. During quiescence the gas in the ring
is not fully cleared, but is driven out of a self-gravitating state by the
momentum injected by expanding supernova remnants. Starbursts also drive a wind
off the star-forming ring, with a time-averaged mass flux comparable to the
star formation rate. We show that our model agrees well with the observed
properties of the CMZ, and places it near a star formation minimum within the
evolutionary cycle. We argue that such cycles of bursty star formation and
winds should be ubiquitous in the nuclei of barred spiral galaxies, and show
that the resulting distribution of galactic nuclei on the Kennicutt-Schmidt
relation is in good agreement with that observed in nearby galaxies.
