  For the first time we study the Eastern nucleus in greater detail and search
for the more extended emission in the molecular gas in different CO line
transitions of the famous ULIRG Arp 220. Furthermore we present a model of the
merger in Arp 220 on large scales with the help of the CO data and an optical
and near-infrared composite HST image of the prototypical ULIRG. Using the
Plateau de Bure Interferometer (PdBI) we obtained CO(2-1) and (1-0) data at
wavelengths of 1 and 3 mm in 1994, 1996, 1997 and 2006 at different beam sizes
and spatial resolutions. The simulations of the merger in Arp 220 were
performed with the Identikit modeling tool. The model parameters that describe
the galaxy merger best give a mass ratio of 1:2 and result in a merger of
~6x10^8 yrs. The low resolution CO(1-0) PdBI observations suggest that there
are indications for emission ~10" towards the south, as well as to the north
and to the west of the two nuclei.
