SMA¹²CO(<i>J</i>= 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\nobservations (beam size ~1") of the 12CO J=6-5 line and 435 micron (690 GHz)\ncontinuum emission toward the central region of the nearby ULIRG Arp 220. These\nobservations resolve the eastern and western nuclei from each other, in both\nthe molecular line and dust continuum emission. At 435 micron, the peak\nintensity of the western nucleus is stronger than the eastern nucleus, and the\ndifference in peak intensities is less than at longer wavelengths. Fitting a\nsimple model to the dust emission observed between 1.3 mm and 435 micron\nsuggests that dust emissivity power law index in the western nucleus is near\nunity and steeper in the eastern nucleus, about 2, and that the dust emission\nis optically thick at the shorter wavelength. Comparison with single dish\nmeasurements indicate that the interferometer observations are missing ~60% of\nthe dust emission, most likely from a spatially extended component to which\nthese observations are not sensitive. The 12CO J=6-5 line observations clearly\nresolve kinematically the two nuclei. The distribution and kinematics of the\n12CO J=6-5 line appear to be very similar to lower J CO lies observed at\nsimilar resolution. Analysis of multiple 12CO line intensities indicates that\nthe molecular gas in both nuclei have similar excitation conditions, although\nthe western nucleus is warmer and denser. The excitation conditions are similar\nto those found in other extreme environments, including M82, Mrk 231, and BR\n1202-0725. Simultaneous lower resolution observations of the 12CO, 13CO, and\nC18O J=2-1 lines show that the 13CO and C18O lines have similar intensities,\nwhich suggests that both of these lines are optically thick, or possibly that\nextreme high mass star formation has produced in an overabundance of C18O.\n