Same as in Fig. 1. However, from t = 10.084 Gyr, we continue the fiducial SIDM simulation (blue) with collisionless DM, employing three different sets of numerical choices. Noteably, we do not show the core formation and early collapse phase but focus on the late stage of the collapse. We also display the fiducial CDM simulation from Fig. (black). The simulation labelled ‘CDM’ (yellow), was run with a variable time step and our wider opening criterion (ErrTolForceAcc = 5 × 10⁻⁴). In contrast, the simulation named ‘CDM, Δt_CDM’ (purple) employs a fixed time step for all particles set to the value of the smallest time step required by gravity (Δt ≈ 3 × 10⁻⁴ Gyr). Again, the wider opening criterion (ErrTolForceAcc = 5 × 10⁻⁴) is used. For the simulation titled ‘CDM, Δ_CDM + α’ (green), we also employed the fixed small time step of Δt ≈ 3 × 10⁻⁴ Gyr, but we did use a more accurate opening criterion for the gravity computations (ErrTolForceAcc = 1 × 10⁻⁴).