The three-dimensional structure of a massive gas disk in the galactic central region

Using high-resolution, three-dimensional hydrodynamical simulations, we investigate the structure of the interstellar medium (ISM) in the central 100 pc region in galaxies, taking into account the self-gravity of the gas, radiative cooling from 10 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 a 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 plumelike structure, is formed. The density probability distribution function in a quasi-steady state is well fitted by a lognormal function over about 7 orders of magnitude.