Upper panel: velocity-galactic longitude map obtained in a strip along b = +011 (corresponding to clump A) showing . Contour levels start at 0.7 K and the contour spacing is 0.7 K. The dotted lines indicate the location of NGC 3503 . Lower panel: mean velocity map of Component 1. Contours levels go from  − 26 to  − 24 km s^-1 , with interval of 0.2 km s^-1 . The dotted ellipse depicts approximately the region of clump A.