α – c plane (left panels) and α − r_10%/r_50% plane (right panels) of observed GCs compared with N-body simulations. Shaded areas mark the 3σ limit of the simulations. Clusters falling within these limits and not overlapping with other models are considered to be well-represented by these models. The error bar in panel a) is representative for the uncertainties in α for the observed clusters. The labeled clusters are discussed in Sect. 5.