Fermi-LAT map (in colours) from Fig. 1 with¹³CO moment 0 map overlaid as grey contours. The ¹³CO map was integrated between −20 and −8 km s⁻¹. The contours are [−4,4,5,8,12,16,20] times the rms value of 0.5 K km s⁻¹. The dashed black ([FTK-MC]J2108) and white dotted ([FTK-MC]HS) ellipses indicate the two regions where the physical parameters were determined. The cross (×) and the plus sign (+) cross indicate the central position of J2108 and HS, respectively.