Arp 220 line ratios: top r₂₁ and r₃₂, (2nd row) R₁₀ and R₂₁, (3rd row) and H₁₀, bottom CS / HNCO. The ellipse in the bottom left corner of each map represents the synthesized beam size. The black contours represent the high-resolution ¹²CO J = 2 − 1 emission published in Downes & Eckart (2007) to guide the eye to the positions of the two nuclei of Arp 220. Note that the resolution of our observations do not spatially resolve the two nuclei.