Molecular Gas Disk Structures Around Active Galactic Nuclei

Details Molecular Gas Disk Structures Around Active Galactic Nuclei Molecular Gas Disk Structures Around Active Galactic Nuclei

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009apj...702...63w&link_type=abstract

The Astrophysical Journal, Volume 702, Issue 1, pp. 63-74 (2009).

Astronomy and Astrophysics

Astronomy

29

Galaxies: Seyfert, Galaxies: Starburst, Ism: Molecules, Ism: Structure, Methods: Numerical

Scientific paper

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 × 107 M sun) 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 (H2) 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 H2 is about 0.4 (total H2 mass is sime1.5 × 106 M sun) 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. H2 forms a thin nuclear disk in the inner sime5 pc, which is surrounded by molecular clouds swelled up toward h lsim 10 pc. The velocity field of the disk is highly turbulent in the torus region, whose velocity dispersion is sime20 km s-1 on average. Average supernova (SN) rate of sime5 × 10-5 yr-1 is large enough to energize these structures. Gas column densities toward the nucleus larger than 1022 cm-2 are observed if the viewing angle is smaller than θ v sime 50° 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 equilibrium is only slightly smaller (sime0.35), a testimony to the strong self-shielding nature of H2, 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.

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