P-Cygni Profiles of Molecular Lines toward Arp 220 Nuclei
  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.
