EMPIRE versus ALMOND: HCN(1 − 0) average spectra. The blue and red lines show average HCN brightness temperatures within r_gal ≤ 5 kpc obtained from spatially and spectrally matched ALMOND and EMPIRE observations, respectively, across the three galaxies NGC 628, NGC 2903, NGC 4321 from top to bottom. The grey dashed line shows (homogenised) CO(2 − 1) intensities from PHANGS–ALMA (Leroy et al. 2021b), scaled down by a factor of 20. The grey-shaded area indicates the velocity-integration window constructed using the highly significant CO(2 − 1) data. The resulting integrated intensities are quoted in the text.