SMA12CO(J= 6 – 5) AND 435 μm INTERFEROMETRIC IMAGING OF THE NUCLEAR REGION OF Arp 220

Abstract

We have used the Submillimeter Array (SMA) to make the first interferometric observations (beam size ∼1'' or ∼400 pc) of the 12CO J = 6 − 5 line and 435 μm (690 GHz) continuum emission toward the central region (half power field of view 17'') of the nearby ultra-luminous infrared galaxy (ULIRG) Arp 220. These observations resolve the eastern and western nuclei from each other, in both the molecular line and dust continuum emission. At 435 μm, the peak intensity of the western nucleus is stronger than the eastern nucleus, and the difference in peak intensities is less than at longer wavelengths. Fitting a simple model to the dust emission observed between 1.3 mm and 435 μm suggests that dust emissivity power law index in the western nucleus is near unity and steeper in the eastern nucleus, about 2, and that the dust emission is optically thick at the shorter wavelength. Comparison with single dish measurements indicate that the interferometer observations are missing ∼60% of the dust emission, most likely from a spatially extended component to which these observations are not sensitive. The 12CO J = 6 − 5 line observations clearly resolve kinematically the two nuclei. The distribution and kinematics of the 12CO J = 6 − 5 line appear to be very similar to lower J CO lies observed at similar resolution. Analysis of multiple 12CO line intensities indicates that the molecular gas in both nuclei have similar excitation conditions, although the western nucleus is warmer and denser. The excitation conditions are similar to those found in other extreme environments, including the nearby starburst galaxy M82, the active galactic nucleus (AGN) hosting ULIRG Mrk 231, and the high-z QSO BR 1202–0725. Simultaneous lower resolution observations of the 12CO, 13CO, and C18O 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 that extreme high mass star formation has produced in an overabundance of C18O.