The global structure and evolution of a self-gravitating multiphase interstellar medium in a galactic disk

Using high-resolution, two-dimensional hydrodynamical simulations, we inves tigate the evolution of a self-gravitating multiphase interstellar medium i n the central kiloparsec region of a galactic disk. We find that a gravitat ionally and thermally unstable disk evolves, in a self-stabilizing manner, into a globally quasi-stable disk that consists of cold (T < 100 K), dense clumps and filaments surrounded by hot (T > 10(4) K), diffuse medium. The q uasi-stationary, filamentary structure of the cold gas is remarkable. The h ot gas, characterized by low-density holes and voids, is produced by shock heating. The shocks derive their energy from differential rotation and grav itational perturbations due to the formation of cold dense clumps. In the q uasi-stable phase in which cold and dense clouds are formed, the effective stability parameter Q has a value in the range 2-5. The dynamic range of ou r multiphase calculations is 10(6)-10(7) in both density and temperature. P hase diagrams for this turbulent medium are analyzed and discussed.