2009ApJ...700L.104S

We report ∼100 pc (0".3) resolution observations of (sub)millimeter HCO⁺ and CO lines in the ultraluminous infrared galaxy Arp 220. The lines peak at two merger nuclei, with HCO⁺ being more spatially concentrated than CO. Asymmetric line profiles with blueshifted absorption and redshifted emission are discovered in HCO⁺(3-2) and (4-3) toward the two nuclei and in CO(3-2) toward one nucleus. We suggest that these P Cygni profiles are due to ∼100 km/s outward motion of molecular gas from the nuclei. This gas is most likely outflowing from the inner regions of the two nuclear disks rotating around individual nuclei, clearing the shroud around the luminosity sources there.