From top to bottom: spatial coverage of the observations in SiO and H¹³CO⁺ (HCO⁺ has uniform sampling of ). Emission integrated over velocity from  − 230 to 270 kms^-1 for the region measured in HCO⁺. The solid contour levels start at 1.9 K kms^-1 (3σ) and increase in steps of 12.53 K kms^-1 (20σ). Emission integrated over velocity from  − 140 to 190 kms^-1 for the region measured in SiO. The solid contours start at 1.09 K kms^-1 (3σ) and increase in steps of 5.46 K kms^-1 (15σ). Emission integrated over velocity from  − 100 to 120 kms^-1 for the region measured in H¹³CO⁺. The solid contours start at 0.89 K kms^-1 (3σ) and increase in steps of 2.97 K kms^-1 (10σ). In all plots, the dashed line shows the coverage of the survey in each molecule. For a better display of the observations, we choose the velocity integration range in each spectral line to cover only the emission visible in the respective longitude-velocity diagram.