Present-day oxygen (upper left panel), europium (upper right panel), iron (lower left panel), and barium (lower right panel) abundance gradients for different azimuths as predicted by Model A (see Table 1 for model details). In each panel, the coloured dashed vertical lines indicate the location of the co-rotation radii for the three spiral structures characterised by different pattern speeds. Model predictions are compared with Cepheids data provided by Kovtyukh et al. (2022) and Luck & Lambert (2011) for oxygen and europium, and by Genovali et al. (2014) for iron and by Luck (2018) for barium. The data trends (black dashed lines) are computed by calculating the running median in bins of 0.5 kpc, with a 40% overlap, and a minimum number of stars per bin of two for O, Fe, and Eu, and one for Ba; this lower minimum for Ba is chosen because of the low number of measurements in the sample. The shaded regions on the plot represent the standard deviation of these trends. For the sake of visualisation, we focus on the abundance range [–0.5, 0.6] dex, excluding stars with [Ba/H] > 0.6 dex.