Study of the Inner Structure of the Molecular Torus in IRAS 08572+3915
  NW with Velocity Decomposition of CO Rovibrational Absorption Lines
  Understanding the inner structure of the clumpy molecular torus surrounding
the active galactic nucleus is essential in revealing the forming mechanism.
However, spatially resolving the torus is difficult because of its size of a
few parsecs. Thus, to probe the clump conditions in the torus, we performed the
velocity decomposition of the CO rovibrational absorption lines
($\Delta{v}=0\to 1,\ \Delta{J}=\pm 1$) at $\lambda\sim 4.67\,\mathrm{\mu{m}}$
observed toward an ultraluminous infrared galaxy IRAS 08572+3915 NW with the
high-resolution spectroscopy ($R\sim 10{,}000$) of Subaru Telescope.
Consequently, we found that each transition had two outflowing components,
i.e., (a) and (b), both at approximately $\sim -160\,\mathrm{km\,s^{-1}}$, but
with broad and narrow widths, and an inflowing component, i.e., (c), at
approximately $\sim +100\,\mathrm{km\,s^{-1}}$, which were attributed to the
torus. The ratios of the velocity dispersions of each component lead to those
of the rotating radii around the black hole of
$R_\mathrm{rot,a}:R_\mathrm{rot,b}:R_\mathrm{rot,c}\approx 1:5:17$, indicating
the torus where clumps are outflowing in the inner regions and inflowing in the
outer regions if a hydrostatic disk with $\sigma_V\propto
R_\mathrm{rot}^{-0.5}$ is assumed. Based on the kinetic temperature of
components (a) and (b) of $\sim 720\,\mathrm{K}$ and $\sim 25\,\mathrm{K}$
estimated from the level population, the temperature gradient is
$T_\mathrm{kin}\propto R_\mathrm{rot}^{-2.1}$. Magnetohydrodynamic models with
large density fluctuations of two orders of magnitude or more are necessary to
reproduce this gradient.
