  We present the study of a set of N-body+SPH simulations of a Milky Way-like
system produced by the radiative cooling of hot gas embedded in a dark matter
halo. The galaxy and its gaseous halo evolve for 10 Gyr in isolation, which
allows us to study how internal processes affect the evolution of the system.
We show how the morphology, the kinematics and the evolution of the galaxy are
affected by the input supernova feedback energy E$_{\rm SN}$, and we compare
its properties with those of the Milky Way. Different values of E$_{\rm SN}$ do
not significantly affect the star formation history of the system, but the disc
of cold gas gets thicker and more turbulent as feedback increases. Our main
result is that, for the highest value of E$_{\rm SN}$ considered, the galaxy
shows a prominent layer of extra-planar cold (log(T)<4.3) gas extended up to a
few kpc above the disc at column densities of $10^{19}$ cm$^{-2}$. The
kinematics of this material is in agreement with that inferred for the HI halos
of our Galaxy and NGC 891, although its mass is lower. Also, the location, the
kinematics and the typical column densities of the hot (5.3<log(T)<5.7) gas are
in good agreement with those determined from the O$_{\rm VI}$ absorption
systems in the halo of the Milky Way and external galaxies. In contrast with
the observations, however, gas at log(T)<5.3 is lacking in the circumgalactic
region of our systems.
