Evidence for universal structure in galactic halos

The late infall of dark matter onto a galaxy produces structure (such as caustics) in the distribution of dark matter in the halo. We argue that such structure is likely to occur generically on length scales proportional to (Formula presented) where (Formula presented) is the age of the universe and (Formula presented) is the rotation velocity of the galaxy. A set of 32 extended galactic rotation curves is analyzed. For each curve, the radial coordinate is rescaled according to (Formula presented) where we choose (Formula presented) km/s. A linear fit to each rescaled rotation curve is subtracted, and the residuals are binned and averaged. The sample shows significant features near (Formula presented) kpc and (Formula presented) kpc. This is consistent with the predictions of the self-similar caustic ring model of galactic halos.