MOLECULAR GAS DISK STRUCTURES AROUND ACTIVE GALACTIC NUCLEI

Abstract

We present new high resolution numerical simulations of the ISM in a central R ~32 parsecs region around a supermassive black hole 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 out of the neutral hydrogen phase. In a quasi equilibrium state, mass fraction of H2 is about 0.4 (total H2 mass is ~1.5 10^6 Msun) of the total gas mass for the uniform far UV (FUV) with G_0 = 10. The gas forms an inhomogeneous disk, whose scale-height becomes larger in the outer region. H2 forms a thin nuclear disk in the inner ~ 5 pc, which is surrounded by molecular clouds swelled up toward h < 10 pc. The velocity field of the disk is highly turbulent in the torus region, whose velocity dispersion is ~ 20 km/s on average. Average supernova rate (SNR) of ~ 5 10^-5/yr 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_v ~ 50 deg 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 H2 mass in an equillibrium is only slightly smaller (~ 0.35). Finally the morphology and kinematics of the circumnuclear molecular gas disks emerging from our models is similar to that revealed by recent near infrared observations using VLTI/Keck.