Star formation rate, molecular gas density, and depletion timescale along the single-arm spiral. The top panel shows the SFR surface density Σ_SFR (red) and the molecular gas mass surface density Σ_mol (blue) as function of distance to the AGN measured along the spiral arm. While the Σ_mol has high values all across the spiral, the SF is clumped, resulting in variations of Σ_SFR by more than one order of magnitude. The bottom panel shows the molecular gas mass depletion timescale, with the dashed line marking the typical $t_{\mathrm{dep}}^{\mathrm{mol}}=1.7\mathrm{Gyr}$ measured by resolved observations in nearby spiral galaxies (Utomo et al. 2018). In the single arm spiral, it is nearly constant with a median $⟨t_{\mathrm{dep}}^{\mathrm{mol}}⟩=3.9\mathrm{Gyr}$ indicating that star formation in the single-arm spiral is remarkably inefficient.