X_CO map of the mIVC at the locations of detected ¹²CO(1 → 0) emission. The contours mark the modelled dust optical depth from Planck from 1 × 10^-6 to 9 × 10^-6 in steps of 2 × 10^-6. The values range between 0.5 × 10²⁰ cm^-2 (K km s^-1)^-1 ≲ X_CO ≲ 11 × 10²⁰ cm^-2 (K km s^-1)^-1. We note that the X_CO map is derived at the angular resolution of the Planck data, which is shown at the bottom-left.