Map of the C¹⁸O(1−0) integrated intensity superposed on the contours of H₂CO absorption toward the AMC. The C¹⁸O(1−0) and H₂ CO data were smoothed to the same effective resolution and cell size of 10′ and 2.5′, respectively. Contour levels of the H₂CO intensity map are −0.4 to − 1.8 in steps of −0.15 K km s⁻¹. The white circle presents the location of the W 40 H II region (radius ∽3′) and the black circle in the bottom-right illustrates the resolution of 10′.