  We present new observations with the IRAM Interferometer, in its
longest-baseline configuration, of the CO(2-1) line and the 1.3mm dust
radiation from the Arp 220 nuclear region. The dust source in the West nucleus
has a size of 0.19 x 0.13 arcsec and a 1.3mm brightness temperature of 90K.
This implies that the dust ring in the West nucleus has a high opacity, with
tau = 1 at 1.1mm. Not only is the dust ring itself optically thick in the submm
and far-IR, but it is surrounded by the previously-known, rapidly rotating
molecular disk of size 0.5 arcsec that is also optically thick in the mid-IR.
The molecular ring is cooler than the hot dust disk because the CO(2-1) line is
seen in absorption against the dust disk. The dust ring is massive (1E9 solar
masses), compact (radius 35pc), and hot (true dust temperature 170K). It
resembles rather strikingly the dust ring detected around the quasar APM
08279+52, and is most unlike the warm, extended dust sources in starburst
galaxies. Because there is a strong temperature gradient from the hot dust ring
to the cooler molecular disk, the heating must come from a concentrated source,
an AGN accretion disk that is completely invisible at optical wavelengths, and
heavily obscured in hard X-rays.
