Top: PAWS map of the CO(1–0) line intensity in M 51, highlighting the areas where we have mapped HCN(1–0) and which will be the focus of this paper. Middle panels: zoom on the targeted regions with HCN(1–0) intensity in grayscale, indicating the set of circular apertures centred on HCN peaks, with a diameter of 3″ (FWHM of synthesised beam); the large, thick circles indicate the truncation radius of R = 35″ (the same as the shaded areas in the top panel). Bottom panels: background grayscale map shows the 33 GHz radio continuum, tracing star formation for the same three regions, with contours showing CO emission (red) and HCN emission (cyan); CO contours correspond to [40, 80, 120] K km s⁻¹ for the north, and [100, 150, 200] K km s⁻¹ for the ring and the south, whereas HCN contours represent values of [1.5, 3] K km s⁻¹ for the north, [5.5, 8] K km s⁻¹ for the ring, and [3.5, 10] K km s⁻¹ for the south.