  Using high-resolution, three-dimensional hydrodynamical simulations, we
investigate the structure of the interstellar medium in the central hundred pc
region in galaxies, taking into account self-gravity of the gas, radiative
cooling from 10 K to $10^8$ K, and energy feedback from supernovae. Similar to
the previous two-dimensional results produced by Wada and Norman, we find that
a gravitationally and thermally unstable ISM evolves, in a self-stabilizing
manner, into a quasi-stable thin disk, which is characterized by a network of
cold ($T < 100$ K), dense clumps and filaments, and hot ($T > 10^6$ K), diffuse
medium. Supernova explosions blow the diffuse gases from the disk, and as a
result, a quasi-steady diffuse halo, which is not uniform but has a plume-like
structure, is formed. The density probability distribution function (PDF) in a
quasi-steady state is well fitted by a Log-Normal function over about seven
orders of magnitude.
