Velocity peaks and caustic rings

Abstract

The late infall of cold dark matter onto an isolated galaxy produces flows with definite local velocity vectors throughout the galactic halo. It also produces caustic rings, which are places in the halo where the dark matter density is very large. The self-similar model of halo formation predicts that the caustic ring radii $a_n$ follow the approximate law $a_n \simeq 1/n$. I interpret bumps in the rotation curves of NGC 3198 and of our own galaxy as due to caustic rings of dark matter. In this model of our halo the annual modulation effect in direct searches for WIMPs has the opposite sign from that predicted by the isothermal sphere model.