Three Dimensional Line Transfer Study of Energy Sources in Compact   Molecular Gas in Active Galaxies -- AGN/Starburst Connection --
  Recent observations suggest molecular line ratios in millimeter and submillimeter bands may be a good tool to reveal the long-standing question on the origin of energy sources in obscured active galaxies -- AGN and/or starburst. Observations of actual molecular medium show in general inhomogeneous structures as well as high-resolution hydrodynamic simulations do. In order for precise interpretation of emergent line emission from the inhomogeneous molecular gas to probe the dominant energy source of active galaxies, we study characteristic features of emergent intensities via three-dimensional non-LTE (non-local thermodynamic equilibrium) line transfer simulations. Our results succeeded in making clear 1) the necessary conditions for HCN/HCO$^{+}$-dichotomy, and 2) importance of clumpiness on intensity ratio and its interpretation. These results are obtained for the first time by our realistic three-dimensional simulations, and line transfer simulations will be a powerful tool to comprehensive studies of extragalactic interstellar medium (ISM) in forthcoming ALMA (Atacama Large Millimeter/submillimeter Array) era. 
Masako Yamada, Wada Keiichi, Kohji Tomisaka