Synthetic Observations of Carbon Lines of Turbulent Flows in Diffuse Multiphase Interstellar Medium

We examine observational characteristics of multi-phase turbulent flows in the diffuse interstellar medium (ISM) using a synthetic radiation field of atomic and molecular lines. We consider the multi-phase ISM which is formed by thermal instability under the irradiation of UV photons with moderate visual extinction AV ∼ 1. Radiation field maps of C, C, and CO line emissions were generated by calculating the non-local thermodynamic equilibrium (nonLTE) level populations from the results of high resolution hydrodynamic simulations of diffuse ISM models. By analyzing synthetic radiation field of carbon lines of [C II] 158 μm, [C I] P2 −3 P1 (809 GHz), P1 −3 P0 (492 GHz), and CO rotational transitions, we found a high ratio between the lines of highand low-excitation energies in the diffuse multi-phase interstellar medium. This shows that simultaneous observations of the lines of warmand cold-gas tracers will be useful in examining the thermal structure, and hence the origin of diffuse interstellar clouds. Subject headings: ISM: clouds – ISM: molecules – radio lines: ISM