Upper panel: excitation temperature T_ex determined for the J = 1 → 0 transition of ¹²CO and ¹³CO. Lower panel:total column density of ¹³CO, . Position offsets are relative to the position of M8E-IR (marked with an asterisk) given in Sect. 2. The contour levels are from 10 to 100% in steps of 10% peak emission (Table 1). The values of T_mb and that of ∫ for the J = 1 → 0 transition used to calculate T_ex and were extracted from maps convolved to the same resolution of 24′′.