Moment-zero map of the CH₃CN (19₄–18₄) emission (colours and black contours) for a direct comparison with the CH₃OH (14_1,13–14_0,14) A⁺ emission of Fig. 1 (white contours). These CH₃CN and CH₃OH transitions have similar excitation energies (E_up) of 281.9 K and 260.2 K, respectively, and the line emission has been integrated over the same velocity range. The upper wedge quantifies the line intensity from its peak to the maximum negative in the map; black contours are drawn at levels of 10, 50, and 100 times the 1 σ rms of 2.5 mJy beam⁻¹ km s⁻¹. We note that the white and black contours should be used for a direct comparison between the spatial morphology of the CH₃OH and CH₃CN emissions, respectively, because they correspond to relative levels of comparable rms (at variance with the colour map which depends on the maximum in the map). The synthesized ALMA beam is shown in the bottom left corner.