NGC 4321 data used in this study, each at the native resolution of the respective observations indicated in the bottom left of each panel. Top left: HCN(1–0) moment-zero map presented in this work. Top right: CO(2–1) moment-zero map from PHANGS–ALMA (Leroy et al. 2021b). Bottom left: Extinction-corrected Hα flux density from PHANGS–MUSE (Emsellem et al. 2022). Bottom right: 21 μm flux density from MIRI-F2100W (PHANGS–JWST; Lee et al. 2023). In each panel, white-to-black-gradient contours show HCN moment-zero signal-to-noise ratio levels of (2, 3, 5, 10, 20, 30, 50, 100) as in Fig. 1. The yellow-coloured outline shows the FOV of the respective observations.