Defining the spiral arms. Panel a: Illustration of the selected regions highlighting the spiral arms of NGC 4030, having as reference the HST photometric frame in the filter F450W, after modelling and subtracting the contribution of the underlying main body with KINEMETRY. Panel b: Stellar velocity dispersion residual map (Δσ_⋆) of NGC 4030 with the spiral arms overlaid. Panel c: Radial profiles of Δσ_⋆ amidst (blue) and beyond (red) the delineated spiral arms, as well as across the entire galaxy (grey). The upper horizontal axis displays the distance from the centre in kpc.