Left panel: [HDCO]/[H₂CO] map using the column density maps of HDCO and H₂CO derived as described in Sect. 4.1. Middle panel: map of [D₂CO]/[H₂CO], using the column density maps of D₂CO and H₂CO derived as described in Sect. 4.1. Right panel: map of the ratio [D₂ CO]/[HDCO], using the column density maps of HDCO and D₂CO derived as described in Sect. 4.1. In all panels the black contours represent increasing 10% steps of the peak of the Herschel N(H₂) map, presented by Spezzano et al. (2016). The beams are shown in the bottom right corners of the figures, in yellow for Herschel/SPIRE and in white for the 30 m telescope.The black cross marks the dust continuum peak, and only values above the 3σ detection level are considered.