Arp 220 outflow regions. (a): Composite view of the isolated outflow regions: southeast outflow (red), hour-glass outflow (blue), northwest outflow (green). (b): Channel map between −650 and −300 km s⁻¹ in the H₂ transition with respect to the systemic redshift of the E nucleus. The white curve indicates the edges of the SEO mask. (c): Sum of channel maps <  − 200 and > 200 km s⁻¹ in the H₂ transition with respect to the systemic redshift of the W nucleus. The white curve indicates the edges of the HG region. (d): Sum of H₂ and Paα channel maps between −800 and −450 km s⁻¹ with respect to the systemic redshift of the E nucleus. The white curve indicates the edges of the NWB region.