Spatial and spectral distribution of gas and dust around the UCH II region W3 C. The colour maps show the integrated intensity in the combined NOEMA and 30 m data for ¹³CO 2−1 (top-left), C¹⁸O 2−1 (top-centre),c-C₃H₂ 6−5 (middle-left), and H₂CO 3_0,3 −2_0,2 (middle-centre), and the NOEMA-only continuum (top-right). The velocity integration ranges are given in the text. The grey contours indicate 5σ for the continuum map (σ_rms = 0.95 mJy beam⁻¹). The beam is shown in the lower-left corner of each map. c-C₃H₂ and H₂CO are shown using a square-root intensity scheme to emphasise the extended emission. The middle-right panel shows the fractional intensity of the continuum and gas emission as a function of radius from the centre of W3 C, averaged over θ. The centre was determined by hand and is indicated on the maps with a cyan +. The region containing emission related to the hot core W3 IRS4 and cold filament, indicated with a red polygon on the maps, is excluded from the radial analysis, while the maximum radius is indicated with a white dashed circle. The radius of peak emission for each tracer is indicated with a circle on the relevant maps. Gas spectra at three representative positions, indicated in the maps with red crosses which are numbered in the continuum panel, are shown in the lower panels.