Δv values from a double-Gaussian fit at different azimuth angles ϕ. We define ϕ as the azimuth angle with respect to the bar as visualised in Fig. 7. We computed spectroscopic observations at a fixed inclination of θ = 60° and at a redshift of z = 0.05. We show all snapshots of gSa and gSb simulations, which indicate a bar. With a red line we show the value of three times the bin-width of the SDSS. A Δv larger than this value is one criteria for a DP detection (see Sect. 2.3).