Structure in the motions of the fastest halo stars

We analyzed the catalog published by Beers et al. ( 2000, ApJ, 119, 2866) of 2106 non-kinematically selected metal poor stars in the solar neighborhood, with the goal of quantifying the amount of substructure in the motions of the fastest halo stars. We computed the two-point velocity correlation function for a subsample of halo stars within 1 - 2 kpc of the Sun, and found statistical evidence of substructure with a similar amplitude to that predicted by high resolution CDM simulations. The signal is due to a small kinematic group whose dynamical properties are compared to the stellar stream previously discovered by Helmi et al. ( 1999). If real, this high velocity moving group would provide further support for the idea that substructures remain as fossils from the formation of the Galaxy as expected in the CDM scenario.