The Structure and Dynamics of an AGN Torus: CO Line Predictions for ALMA
  from 3D Hydrodynamical Simulations with X-ray Driven Chemistry
  Many efforts have been made to model the mass distribution and dynamical
evolution of the circumnuclear gas in active galactic nuclei (AGNs). However,
chemical evolution is not included in detail in three-dimensional (3-D)
hydrodynamic simulations. The X-ray radiation from the AGN can drive the gas
chemistry and affect the thermodynamics, as well as the excitation of the
interstellar medium (ISM). Therefore, we estimate the effects (on chemical
abundances and excitation) of X-ray irradiation by the AGN, for atomic and
molecular gas in a 3-D hydrodynamic model of an AGN torus. We obtain the
abundances of various species from an X-ray chemical model. A 3-D radiative
transfer code estimates the level populations, which result in line intensity
maps. Predictions for the CO J=1-0 to J=9-8 lines indicate that mid-J CO lines
are excellent probes of density and dynamics in the central (<60 pc) region of
the AGN, in contrast to the low-J CO lines. Analysis of the X_CO/\alpha
conversion factors shows that only the higher-J CO lines can be used for gas
mass determination in AGN tori. The [C II] 158 um emission traces mostly the
hot (T_k>1000m K) central (<60 pc) region of the AGN torus. The [C II] 158 um
line will be useful for ALMA observations of high redshift (z>1) AGNs. The
spatial scales (>0.25 pc) probed with our simulations match the size of the
structures that ALMA will resolve in nearby (<45 Mpc at 0.01") galaxies.
