Structural properties of Dark Matter Halos

Using the results of a high mass resolution (${256}^3$ particles) N-body simulation of a cluster-forming region, we study the statistic ${\sigma }_v-M$ for low mass halos ($\mathrm{M}<{10}^{12}{\mathrm{M}}_{\text{sun}}$), and we compare it with three theoretical models. At the final redshift halos are well described by the Truncated Isothermal Sphere model recently introduced by Shapiro, Iliev & Raga (1999). We speculate that this is a consequence of the action of tidal fields on galaxy formation within clusters.