Decay of the galactocentric distance of a tracer particle of mass m_t = 10⁻³M in models with γ = 0 (top left panel) and 1 (bottom left) and the data collapse after a N^1/2 scaling (mid panels) to the time-averaged scaling radius, r_s, and the evolution of the corresponding mass enclosed with in a sphere of radius 5ϵ centred around m_t. The horizontal dotted and dashed lines have the same meaning as in Fig. 3.