Top row: 2D histogram of intensity gradients’ amplitude, i.e., ﹩\mathrm{log}(| {\rm{\nabla }}I| )﹩, and velocity’s convergence using A2 simulation at t_r ≃ 0.0 Myr (left) and t_r ≃ 3.4 Myr (right). Here, p gives the volume fraction of each data point. Bottom row: 2D histogram of intensity gradients’ orientation and velocity’s convergence using A2 simulation. Note that the orientation is measured in typical Cartesian coordinates, i.e., with respect to the right horizontal direction. Bin size is 200 for the 2D histograms.