Multi-phase gas dynamics in a weak barred potential

The structure of the interstellar medium in the central kpc region of a galaxy with a weak bar-like potential was investigated while taking into account realistic cooling and heating processes and the self-gravity of the gas. Using high-resolution hydrodynamical simulations, it has been revealed that the resonant structures (e.g. smooth spiral shocks and a nuclear ring) are very different from those seen in past numerical models where simple models of the ISM, i.e. non-self-gravitating, isothermal gas, were assumed. We find that the pc-scale filaments and clumps form large-scale spirals, which resemble those seen in real galaxies. The fine structures are different between the arms and in the nuclear region. The next-generation millimeter interferometer (ALMA) may reveal the fine structures of the cold gas in nearby galaxies. We also find a large-scale anisotropy in the gas temperature, which is caused by a non-circular velocity field of the gas. The damped-orbit model based on the epicyclic approximation explains the distribution of the hot (> 10⁴ K) and cold (< 100 K) gases appearing alternately around the galactic center. Because of the temperature anisotropy, cold gases observed by molecular lines do not necessarily represent the real gas distribution in galaxies. Position-Velocity diagrams strongly depend on the viewing angles. As a result, the rotational velocity inferred from the P-V maps could be two-times larger or smaller than the true circular velocity.