MOLECULAR GAS DISK STRUCTURES AROUND ACTIVE GALACTIC NUCLEI

We present new high-resolution numerical simulations of the interstellar medium (ISM) in a central R <= 32 parsecs region around a supermassive black hole (1.3 x 10(7) M-circle dot) at a galactic center. Three-dimensional hydrodynamic modeling of the ISM (Wada & Norman 2002) with the nuclear starburst now includes tracking of the formation of molecular hydrogen (H-2) out of the neutral hydrogen phase as a function of the evolving ambient ISM conditions with a finer spatial resolution (0.125 pc). In a quasi-equilibrium state, mass fraction of H-2 is about 0.4 (total H-2 mass is similar or equal to 1.5 x 10(6) M-circle dot) of the total gas mass for the uniform far ultra-violet (FUV) with G(0) = 10 in Habing unit. As shown in the previous model, the gas forms an inhomogeneous disk, whose scale height becomes larger in the outer region. H-2 forms a thin nuclear disk in the inner similar or equal to 5 pc, which is surrounded by molecular clouds swelled up toward h less than or similar to 10 pc. The velocity field of the disk is highly turbulent in the torus region, whose velocity dispersion is similar to 20 km s(-1) on average. Average supernova (SN) rate of similar or equal to 5 x 10(-5) yr(-1) is large enough to energize these structures. Gas column densities toward the nucleus larger than 10(22) cm(-2) are observed if the viewing angle is smaller than theta(upsilon) similar or equal to 50 degrees from the edge-on. However, the column densities are distributed over almost two orders of magnitude around the average for any given viewing angle due to the clumpy nature of the torus. For a stronger FUV (G(0) = 100), the total H-2 mass in an equilibrium is only slightly smaller (similar or equal to 0.35), a testimony to the strong self-shielding nature of H-2, and the molecular gas is somewhat more concentrated in a midplane. Other properties of the ISM are not very sensitive either to the FUV intensity or the SN rate. Finally, the morphology and kinematics of the circum nuclear molecular gas disks emerging from our models are similar to that revealed by recent near infrared observations using VLTI/Keck.