Molecular gas structure around an AGN with nuclear starburst: 3-D Non-LTE calculations of CO lines

Abstract

We have performed three-dimensional, non-LTE radiative transfer calculations for 12CO and 13CO lines, applying them to our high-resolution hydrodynamic models of the `torus' around a SMBH in an active galactic nucleus. The hydrodynamic simulations reveal inhomogeneous and turbulent gas structure on a sub-pc scale in a circum-nuclear starburst region. Thick disks interlaced with filaments, clumps and holes are naturally formed due to the interplay among energy feedback from supernovae, self-gravity of the gas, galactic rotation, and radiative cooling. The intensity maps of the molecular lines for the circum-nuclear disks show a clumpy structure reflecting the intrinsic inhomogeneity and turbulent motion of the gas disk. The fine structure of the `torus' could be resolved in the nearby active galaxies using ALMA. We also found that the X-factor is not uniformly distributed in the central 100 pc region. The X-factor derived for 12CO(J=1-0) intensity depends strongly on the intensity, whereas the X for 12CO(3-2) is nearly constant over two orders of magnitude of the intensity. The suggested conversion factor for the molecular gas mass is X_CO (3-2) ~ 0.27 x 10^{20} cm^{-2} (K km s^{-1})^{-1}.