Top panel: angular frequency plot based on the rotation curve of M 51 calculated in Meidt et al. (2013): Ω (solid black), Ω ± κ/ 2 (dotted black), Ω ± κ/ 4 (dashed black). The red circle indicates the crossing of the estimated corotation radius of the bar (CR_bar = (22 ± 2.5)′′) with the angular frequency curve Ω, which implies a bar pattern speed of  km s^-1 kpc^-1 (horizontal red line). The blue circle shows the analogous crossing of the suggested corotation radius of the spiral (CR_sp = (102 ± 10)′′), implying a pattern speed for the spiral of  km s^-1 kpc^-1 (horizontal blue line). Middle panel: torque profile weighted by the PAWS gas distribution (same as Fig. 4, reproduced here for comparison). As a result of the smaller field of view of PAWS, the profile stops at R = 85′′. Bottom panel: torque profile weighted by the gas emission traced by THINGS (solid line) and HERACLES (dashed line).