Integrated intensities (moment zero maps). Contour levels for HCN, HCO⁺ and HNC (1 − 0) go from 0 to 6 Jy kms⁻¹ beam⁻¹ with a step of 0.5 Jy kms⁻¹ beam⁻¹. For HCN (3 − 2) and HCO ⁺(3 − 2) the levels range from 2 to 30 Jy kms⁻¹ beam⁻¹ with a step of 2 Jy kms⁻¹ beam⁻¹. For HOC⁺(3 − 2), the contours are from 0.4 to 0.6 Jy kms⁻¹ beam⁻¹ with a step of 0.04 Jy kms⁻¹ beam⁻¹. We highlight the different scales between the (1 − 0) and the (3 − 2) lines. The crosses in the centre of each panel indicate the location of the nuclear source. The synthesised beam is shown in the bottom-left corner of each panel. North is up, and east is to the left.