Left: isotropic distribution function f(ℰ) for the same set of Sérsic models as in Fig. 1. Only for the distribution function is positive over the entire range of binding energies, and hence physical. For models with , the distribution function is negative for binding energies larger than some critical value, and hence these models cannot be supported by an isotropic velocity distributions. For these models, the (positive part of) the distribution function is shown as a dotted line. Middle: density of states function g(ℰ). Right: differential energy distribution N(ℰ).