Upper panel: evolution of the galactic core center-of-mass position as a function of time during the simulation run. The blue, orange, and green curves represent the position in x, y, and z, respectively. Lower panel: as above but in this case referring to the velocity vector components. After an initial period of time at rest while the halo is building up, the entire system starts accelerating (at approximately t = 300) and continues to gain speed with a constant acceleration. The sign of the x and y components has been reversed for better visualization in the figure.