XCLASS fitting for H₂CO in the filament. The panels show: integrated intensity (between −55.3 and −29.8 km s⁻¹) in the H₂CO 3_0,3 −2_0,2 (top-left) and 3_2,2−2_2,1 (bottom-left) transitions; example spectra (black) and  XCLASS model fits (red) for H₂CO 3_0,3 −2_0,2 (top-middle-left) and 3_2,2−2_2,1 (bottom-middle-left); column density in p-H₂CO (top-middle-right); excitation temperature (top-right); peak velocity (bottom-middle-right); FWHM (bottom-right). The data for the two lines were resampled to a common spherical beam with a FWHM of 0.8′′, as shown in the top-right panel, and converted to the T_MB scale. The grey contours in the maps show the continuum smoothed to the same resolution as the line data, starting at 5σ (σ = 0.81 mJy beam⁻¹) and increasing to 45σ in 10σ steps. The spectra are extracted at the continuum peak (coordinates in Table 2), which is indicated in the left-hand panels with a red marker. A scale-bar is shown in the lower-left panel. The model results are only displayed for pixels where the integrated intensity for H₂CO 3_0,3 −2_0,2 is above 5σ_mom0, with grey used to indicate those regions that do not meet this requirement. The white dashed contours in the map of excitation temperature indicate 3σ_mom0 for H₂CO 3_2,2 −2_2,1.