Low and high velocity clouds produced by young stellar clusters
  Intermediate and high velocity HI clouds rain onto the plane of our Galaxy.
They are observed at heights of between 500 and 1500 pc, falling onto the
Galactic plane at velocities from 50 to 140 km s$^{-1}$. To explain the origin
of these clouds, we present a galactic fountain model, driven by the wind from
a super stellar cluster (SSC). We solve the equations for a steady, radiative
de Laval nozzle flow. We consider two effects not considered previously in
astrophysical nozzle flow models: cooling functions for different
metallicities, and the direct action of the galactic gravitational field on the
gas flowing along the nozzle. For an adiabatic nozzle flow, the gravity acting
directly on the gas within the nozzle "stalls" the nozzle flow for initial wind
velocities lower than the escape velocity from the Galaxy. For the same wind
velocity, a radiative nozzle flow stalls at lower altitudes above the galactic
plane. We find that SSC winds with velocities of $v_w=500 - 800$ km s$^{-1}$
produce nozzles stall at heights of $x_m=1 - 15$ kpc. The stalled nozzle flow
then rains back onto the galactic plane at velocities in the range observed in
intermediate and high velocity HI clouds. We study a nozzle flow driven by a
wind from a SSC close to the Galactic centre. We find that for velocities
within the range expected for a SSC wind, we can produce nozzle flows that
stall above the galactic plane. These stalled flows produce cool, infalling
clouds with velocities similar to those of intermediate and high velocity HI
clouds.
