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 75 \farcs 0 \times 40 \farcs 0 ( i.e .
28 \times 15 kpc ) .
The structure of the ionized gas is divided into well identified regions associated with the X-ray emitting plumes and extended lobes , previously studied in detail by McDowell and collaborators .
The overall ionization state of the warm gas in the plumes and lobes as traced by the [ NII ] /H \alpha line is consistent with high velocity shocks expanding in a neutral ambient medium .
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 with an average velocity of +8 km s ^ { -1 } ( E lobe ) and - 79 km s ^ { -1 } ( W lobe ) 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 of 50 km s ^ { -1 } kpc ^ { -1 } and velocity deviations of up to +280 km s ^ { -1 } and - 320 km s ^ { -1 } 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 .