Spectra of the strong absorption of HCO⁺, HCN and HNC transitions observed in 2011 with ATCA (full black line). The dotted spectra correspond to the higher spectral resolution PdBI observations with the narrow-band correlator (see Table 1). The J = 1–0 spectra observed in our previous ATCA 7 mm survey (Muller et al. 2011) are superimposed in light grey. The intensity is normalized to the total continuum flux (NE plus SW images).