Left: overlay of the 4.5 μm Spitzer/IRAC image (contours) on the LBT/LUCI image of the H₂ line emission (continuum subtracted). Contours are drawn in 5 logarithmic steps from 1 to 60 MJy/sterad. The angular resolution of the contour maps is indicated by the circle in the bottom left. Middle: same as left panel, for the overlay of the HCO⁺(1–0) line OVRO map by Molinari et al. (2002), corrected for primary beam attenuation, on our LBT/LUCI K_s-filter image. The HCO⁺ map has been obtained by averaging the emission between –28.76 and –20.78 km s^-1. Contour levels range from 57 to 342 in steps of 95 mJy/beam. The dashed circle denotes the primary beam of the OVRO interferometer. Right: same as left panel, for the overlay of the WISE 3.4 μm map on the LBT/LUCI H-filter image. Contours are drawn in 6 logarithmic steps from 1 to 76 MJy/sterad. Labels C1, C2, and C3 have the same meaning as in Fig 1.