Star formation rate surface density at ∼100 pc scales as a function of dense gas fraction (F_dense = Σ_dense/Σ_mol, left) and dense gas surface density (Σ_dense, right). The filled circles show results for 3″ apertures (∼100 pc) centred on HCN peaks, while the small open circles in the background represent all detections across our fields of view (above 3σ simultaneously for Σ_SFR, F_dense, and Σ_dense). Open circles with a downward arrow indicate upper limits. The blue triangles and gray squares correspond to measurements at comparable scales for NGC 3627 (Murphy et al. 2015) and M 31 (Brouillet et al. 2005, and new SFRs described in the text).