Example of the method used to estimate the oxygen column density and the molecular hydrogen volume density over the OI-emitting region. The solid red contours and the blue dashed contours are maps of , respectively. The solid, thick black contour and the black dashed contour correspond to the observed values of the same quantities. The dot marks the intersection between these two contours, which gives the pair of values of and N_O (4.4 × 10⁴ cm^–3 and 5.6 × 10¹⁶ cm^–2) that reproduce both observables.