Comparison of τ (250 μm) and τ (J) estimates: the τ (250 μm) map (panel a), the ratio k₋₃ = 10⁻³ × τ (250 μm)∕τ (J) (panel b), and the same ratio as a correlation plot (panel c). The last two panels are limited to data in the area indicated in the first panel, also excluding pixels for which τ (J) is not defined because of masked stars. Selected 30′′ radius regions (see panel a) are marked in panel c with different colours: a point source SE of the southern clump (cyan) and the northern and southern τ (250 μm) peaks (red and blue circles, respectively). The black line in panel c is a least squares fit to the data, only excluding the SE point source. Fits to the northern clump and to data τ (J) <6 are shown in red and magenta, respectively.