  Integral field optical spectroscopy with the INTEGRAL system has been used to
investigate for the first time the two-dimensional kinematic and ionization
properties of the extended, warm ionized gas in Arp 220 over an area of 28 kpc
by 15 kpc. The structure of the ionized gas is divided into well identified
regions associated with the X-ray emitting plumes and extended lobes. Changes
in the ionization state of the gas along the major axis of the plumes are
detected, in particular in the outer regions of the northwestern plume where
the transition between the main stellar body of the galaxy and a broad, low
surface brightness tidal tail is located. If the plumes are produced by a
starburst-driven galactic wind, the efficiency in the conversion of mechanical
to radiation energy is a factor of at least 10 smaller than in galactic winds
developed in edge-on spirals with well defined rotation and outflowing axis.
The kinematic properties of the lobes are to a first order in agreement with
the predictions of the merger scenario according to which the lobes are
tidal-induced gas condensations produced during the merging process. The
largest velocity gradients and velocity deviations from the systemic velocity
are not associated with the plumes, but with the outer stellar envelope and
broad tidal tails at distances of up to 7.5 kpc, indicating that the large
scale kinematics of the extended ionized gas in Arp 220, is most likely
dominated by the tidal-induced motions, and not by galactic winds associated
with nuclear starbursts.
