2D histograms of the projected radial particle velocities, υ_rad, as a function of particle radius (for the selected particles, see Fig. 4). Because the polynomial fits to the particle tracks also approximate the particle accelerations, instead of using values averaged over a track, the particle velocities and radii were determined for each detection of a track individually and the results were weighted by the number of detections of the respective track (residence time weighting). The histogram data thus represent the weighted number of detections, Ñ_det. Also shown are the approximate escape speeds at the suspected source regions, υ_esc (dotted line), and the corresponding maximum fall-back fractions, ϕ_fb (gray area).