Panel a: Spitzer c2d visual extinction map overlaid with the Herschel H₂ column density contours. The contours increase from 4 × 10²¹ cm⁻² to 1.2 × 10²² cm⁻² by 4 × 10²¹ cm⁻². The color bar represents the visual extinction in units of magnitude. Panel b: map of the ratios (N_{H_2,av}/) between the H₂ column densities derived from the visual extinction map and those derived from the Herschel SED fitting. The color bar represents the H₂ column density ratio. The beam size is shown in the lower right of each panel.