Integrated intensity (0th moment) maps of OCS 18−17 (left, between −55.3 and −29.8 km s⁻¹) and C¹⁸O 2−1 (middle and right, between −81.8 and −0.8 km s⁻¹) for data images with the Clark (top) and SDI (bottom) clean algorithms. All are imaged with uniform weighting. The OCS map is from only NOEMA data while the C¹⁸O is merged NOEMA and 30 m data. The C¹⁸O maps are without (middle) and with (right) primary beam correction, where in the latter case the data have been truncated at the FWHM of the primary beam. The black contours indicate 5σ, where σ = 13.8 (OCS, Clark), 12.6 (OCS, SDI), 19.0 (C¹⁸O before primary-beam correction, Clark), and 20.0 mJy beam⁻¹ km s⁻¹ (C¹⁸O before primary-beam correction, SDI). 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.