We present the results of interferometric spectral line observations of Arp 220 at 3.5 mm and 1.2 mm from the Plateau de Bure Interferometer ( PdBI ) , imaging the two nuclear disks in H ^ { 13 } CN ( 1 - 0 ) and ( 3 - 2 ) , H ^ { 13 } CO ^ { + } ( 1 - 0 ) and ( 3 - 2 ) , and HN ^ { 13 } C ( 3 - 2 ) as well as SiO ( 2 - 1 ) and ( 6 - 5 ) , HC ^ { 15 } N ( 3 - 2 ) , and SO ( 6 _ { 6 } -5 _ { 5 } ) .
The gas traced by SiO ( 6 - 5 ) has a complex and extended kinematic signature including a prominent P Cygni profile , almost identical to previous observations of HCO ^ { + } ( 3 - 2 ) .
Spatial offsets 0.1 ^ { \prime \prime } north and south of the continuum centre in the emission and absorption of the SiO ( 6 - 5 ) P Cygni profile in the western nucleus ( WN ) imply a bipolar outflow , delineating the northern and southern edges of its disk and suggesting a disk radius of \sim 40 pc , consistent with that found by ALMA observations of Arp 220 .
We address the blending of SiO ( 6 - 5 ) and H ^ { 13 } CO ^ { + } ( 3 - 2 ) by considering two limiting cases with regards to the H ^ { 13 } CO ^ { + } emission throughout our analysis .
Large velocity gradient ( LVG ) modelling is used to constrain the physical conditions of the gas and to infer abundance ratios in the two nuclei .
Our most conservative lower limit on the [ H ^ { 13 } CN ] / [ H ^ { 13 } CO ^ { + } ] abundance ratio is 11 in the WN , cf .
0.10 in the eastern nucleus ( EN ) .
Comparing these ratios to the literature we argue on chemical grounds for an energetically significant AGN in the WN driving either X-ray or shock chemistry , and a dominant starburst in the EN .