Description
The origin of the enormous luminosities of the two opaque nuclei of Arp 220, the prototypical ultra-luminous infrared galaxy, remains a mystery because we lack observational tools to explore the innermost regions around the nuclei. We explore the potential of imaging vibrationally excited molecular emission at high angular resolution to better understand the morphology and physical structure of the dense gas in Arp 220 and to gain insight into the nature of the nuclear powering sources. The Atacama Large Millimeter/submillimeter Array (ALMA) provided simultaneous observations of HCN, HCO^+^, and vibrationally excited HCN v_2_=1f emission. Their J=4-3 and 3-2 transitions were observed at a matching resolution of ~0.5", which allows us to isolate the emission from the two nuclei.
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