The Distribution of Dark Matter in Spirals

In the past years a wealth of observations allowed to unravel the structural properties of the Dark Matter Halos around spirals. First, their rotation curves follow an Universal profile (URC) that can be described in terms of an exponential thin stellar disk and a dark halo with a constant density core, whose relative importance increases with galaxy luminosity. Careful studies of individual objects reveal that dark halos have a core, whose size $r_0$ correlates with the central density $\rho_0$. These properties are in serious discrepancy with the cuspy density distribution predicted by N-body simulations in collisionless $\Lambda$CDM Cosmology.