Radial intensity profiles of the central UCH ii region showing the measurements done at 70 μm (blue points) and 160 μm (green points) taking advantage of the PACS highest resolution, compared with the 3-band temperature (T_3B) and the 4-band temperature (T_4B) data given by the black arrow. The 160 μm profile decreases less in the inner part of the envelope (pink line) than in its outer part (yellow line). Since 160 μm emission is sensitive to dust temperature and density, this behaviour is probably related to the two different slopes found for the density profile of the envelope characterised in Sect. 3.4.1. The slope change indeed occurs at similar R_Infall radius.