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Published online by Cambridge University Press: 03 August 2017
Using the IRAM interferometer we have mapped HCN(1 → 0), HCO+(1 → 0), and 3.5 mm continuum emission from Arp 220, the prototype infrared ultraluminous galaxy. The extended molecular emission and velocity gradient are aligned with the optical dust lane. The HCN and HCO+ lines are exceptionally strong, suggesting a connection between the dense molecular gas they trace and Arp 220's enhanced infrared emission. The inferred gas density and filling factor imply the nucleus of Arp 220 may be a giant molecular cloud.