Circumnuclear Multi-phase Gas in the Circinus Galaxy II: The Molecular
  and Atomic Obscuring Structures Revealed with ALMA
  We used the Atacama Large Millimeter/Submillimeter Array (ALMA) to map the
CO(3-2) and [CI](1-0) lines, as well as their underlying continuum emission,
from the central $\sim 200$ pc region of the Circinus galaxy that hosts the
nearest type 2 Seyfert-class active galactic nucleus (AGN), with a spatial
resolution of $\sim 6-15$ pc. The lines and continuum-emitting regions consist
of a circumnuclear disk (CND; 74 pc $\times$ 34 pc) and spiral arms. The
distribution of the continuum emission revealed a temperature-dependent dust
geometry and possibly polar dust elongation in the torus region. The molecular
mass of the CND is $M_{\rm H2} \sim 3 \times 10^6~M_\odot$ with a beam-averaged
H$_2$ column density of $\sim 5 \times 10^{23}$ cm$^{-2}$ toward the AGN
position, which contributes significantly to the nuclear obscuration. The
[CI](1-0)/CO(3-2) ratio at the AGN position is unusually high, suggesting an
X-ray dominated region-type chemistry. We decomposed the observed velocity
fields into rotational and dispersion components, and revealed multi-phase
dynamic nature in the $r \lesssim 10$ pc torus region, i.e., the diffuse atomic
gas is more spatially extended along the vertical direction of the disk than
the dense molecular gas. Through comparisons with our model predictions based
on the radiation-driven fountain scheme, we indicate that atomic outflows are
the driver of the geometrical thickness of the atomic disk. This supports the
validity of the radiation-driven fountain scheme in the vicinity of this AGN,
which would explain the long-lasting mystery, the physical origin of the AGN
torus.
