Pixel-by-pixel integrated line intensities for HCN, HNC, N₂H⁺, HCO⁺(1–0) as function of Σ_mol, Σ_SFR, Σ_*, galactocentric radius, P_DE and σ_CO for both detected emission (> 3σ, colored by galactocentric distance) as well as all data (gray). Pixels with detected emission are colored by galactocentric radius. We show the binned average for all data (black solid line) and significant data (black dashed line). We add Spearman correlation coefficients using all data in the top left corner of each panel, but note that those coefficients strongly depend on the S/N of the line and a decrease in coefficients from brighter to fainter lines is expected (i.e. from HCN to N₂H⁺). All p-values are below 5%.