a) Effective radii as a function of mass of the merger objects (stars) and of UCDs with observed velocity dispersions (crosses for compact UCDs with r_eff < 10 pc, circles for extended UCDs and NGC 2419). b) Global line-of-sight velocity dispersion σ as a function of the mass of the same objects as in the above figure. The solid and the dotted line show the scaling relation for objects with an effective radius of 10 pc and 30 pc, respectively (see Eq. (8)). The dashed grey curve indicates the general trend of σ for an increasing r_eff (as parameterized by Dabringhausen et al. 2008, see Fig. 1).