The constant density region of the dark halos of spiral galaxies

From the kinematics of 137 spirals we find that the DM halo density profiles are self-similar at least out to R_opt and show core radii much larger that the corresponding disk scale-lenghts. The luminous regions of spirals consist of stellar disks embedded in dark halos with roughly constant density. With respect to previous work, the present evidence is obtained by means of a robust method and for a large and complete sample of normal spirals.