Example of the steps in the method to estimate the spatial association between two emission lines. The top panels shows the channel maps of the 1 km s^-1 integrated intensity (in K km s^-1 ) of the [C II] 158 μm (left) and [C I] 609 μm (right) lines. The contour lines correspond to the threshold of 10% of their global peak intensities (136.4 K km s^-1 and 54.6 K km s^-1 for [C II] and [C I], respectively). The middle panels are the binary images obtained after applying the intensity threshold to the original channel maps. The bottom panel shows the result of multiplying the two binary images, which corresponds to the region where the emission of both [C II] and [C I] lines are associated in a particular velocity channel (in this case 15.5–16.5 km s^-1).