IRAM Plateau de Bure spectra (continuum subtracted) of IC 860 (left panel) and Zw049.057 (right panel). The systemic velocities of HCN, HCO⁺ and HCN-VIB J = 3–2 are marked with dashed vertical lines. The self- and continuum absorption leads to double-peaked HCN and HCO⁺ν = 0 spectra while the HCN-VIB lines are singled peaked close to systemic velocity (see Sect. 4.2). The spectra also show prominent, single peaked lines of HOC⁺, CH₂NH, CH₃OH and HC₃N. Fluxes are in mJy beam^-1.