Spiral pattern speed Ω_s and disc angular velocity Ω_d computed by Roca-Fàbrega et al. (2014) are indicated with light blue and violet lines, respectively. With the long, vertical dashed red line, we show the position of the co-rotation radius located at the Galactocentric distance R = 8.31 kpc. Outer and inner Lindblad resonances extracted by the Roca-Fàbrega et al. (2014) simulation are also drawn with dotted magenta and dotted purple lines, respectively.