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We have used the Submillimeter Array (SMA) to make the first interferometricobservations (beam size ~1") of the 12CO J=6-5 line and 435 micron (690 GHz)continuum emission toward the central region of the nearby ULIRG Arp 220. Theseobservations resolve the eastern and western nuclei from each other, in boththe molecular line and dust continuum emission. At 435 micron, the peakintensity of the western nucleus is stronger than the eastern nucleus, and thedifference in peak intensities is less than at longer wavelengths. Fitting asimple model to the dust emission observed between 1.3 mm and 435 micronsuggests that dust emissivity power law index in the western nucleus is nearunity and steeper in the eastern nucleus, about 2, and that the dust emissionis optically thick at the shorter wavelength. Comparison with single dishmeasurements indicate that the interferometer observations are missing ~60% ofthe dust emission, most likely from a spatially extended component to whichthese observations are not sensitive. The 12CO J=6-5 line observations clearlyresolve kinematically the two nuclei. The distribution and kinematics of the12CO J=6-5 line appear to be very similar to lower J CO lies observed atsimilar resolution. Analysis of multiple 12CO line intensities indicates thatthe molecular gas in both nuclei have similar excitation conditions, althoughthe western nucleus is warmer and denser. The excitation conditions are similarto those found in other extreme environments, including M82, Mrk 231, and BR1202-0725. Simultaneous lower resolution observations of the 12CO, 13CO, andC18O J=2-1 lines show that the 13CO and C18O lines have similar intensities,which suggests that both of these lines are optically thick, or possibly thatextreme high mass star formation has produced in an overabundance of C18O.

SMA CO(J=6-5) and 435 micron interferometric imaging of the nuclear region of Arp 220