A Massive Molecular Torus inside a Gas-Poor Cirnumnuclear Disk in the
  Radio Galaxy NGC 1052 Discovered with ALMA
  We report ALMA observations of NGC 1052 to quest mass accretion in a gas-poor
active galactic nucleus (AGN). We detected CO emission representing a rotating
ring-like circumnuclear disk (CND) seen edge-on with the gas mass of $5.3
\times 10^{5}$ M$_{\odot}$. The CND has smaller gas mass than that in typical
Seyfert galaxies with circumnuclear star formation and is too gas-poor to drive
mass accretion onto the central engine. The continuum emission casts molecular
absorption features of CO, HCN, HCO$^+$, SO, SO$_2$, CS, CN, and H$_2$O, with
H$^{13}$CN and HC$^{15}$N and vibrationally-excited (v$_2 = 1$) HCN and
HCO$^+$. Broader absorption line widths than CND emission line widths imply
presence of a geometrically thick molecular torus with a radius of $2.4 \pm
1.3$ pc and a thickness ratio of $0.7 \pm 0.3$. We estimate the H$_2$ column
density of $(3.3 \pm 0.7) \times 10^{25}$ cm$^{-2}$ using H$^{12}$CN,
H$^{13}$CN, and HCO$^{+}$ absorption features and adopting abundance ratio of
$^{12}$C-to-$^{13}$C and a HCO$^{+}$-to-H$_2$, and derived the torus gas mass
of $(1.3 \pm 0.3) \times 10^7$ M$_{\odot}$, which is $\sim 9$\% of the central
black-hole mass. The molecular gas in the torus is clumpy with the estimated
covering factor of $0.17^{+0.06}_{-0.03}$. The gas density of clumps inside the
torus is inferred to be $(6.4 \pm 1.3) \times 10^7$ cm$^{-3}$, which meets the
excitation conditions of H$_2$O maser. Specific angular momentum in the torus
exceeds a flat-rotation curve extrapolated from that of the CND, indicating a
Keplerian rotation inside a 14.4-pc sphere of influence.
