Integrated intensity (0th moment, integrating between −55.3 and −29.8 km s⁻¹) maps of H₂CO 3_0,3 −2_0,2 imaged with the SDI algorithm (see text for more details) and uniform weighting for NOEMA only (left) andmerged NOEMA and 30 m data (right). The black-solid and white-dashed contours indicate 5σ and −5σ, where σ = 12.5 and 12.6 mJy beam⁻¹ km s⁻¹ for the NOEMA only and the merged data respectively. The black circle, dashed circle and crosses indicate the positions of W3 IRS4,W3 C and the two cold cores, as indicated in Fig. 2.