High Resolution Observations of Molecular Lines in Arp 220: Kinematics,
  Morphology, and Limits on the Applicability of the Ammonia Thermometer
  We observe Arp 220, the nearest Ultra-Luminous Infrared Galaxy (ULIRG), over
4 GHz in the K and Ka bands. We provide constraints for the
kinematics,morphology, and identify molecular species on scales resolving both
nuclei (0.6" or 230 pc). We detect multiple molecular species, including
hydroxyl in both cores. We tentatively detect H2O at 21.84 GHz in both nuclei,
indicating the likely presence of maser emission. The observed frequency range
also contains metastable ammonia transitions from (J,K) = (1,1) to (5,5), as
well as the (9,9) inversion line, which, together are a well-known thermometer
of dense molecular gas. Furthermore, the non-metastable (4,2) and (10,9) and
possibly the (3,1) lines are also detected. We apply a standard temperature
analysis to Arp 220. However, the analysis is complicated in that standard LTE
assumptions do not hold. There are indications that a substantial fraction of
ammonia could be in the non-metastable transitions as opposed to only the
metastable ones. Thus, the non-metastable transitions could be essential to
constraining the temperature. We compare all of these data to ALMA observations
of this source, confirming the outflow previously observed by other tracers in
both nuclei.
