Structure in the motions of the fastest halo stars

¹ Dipartimento di Fisica Generale, via Pietro Giuria 1, 10125 Torino, Italy e-mail: paola.re.fiorentin@to.infn.it
² INAF - Osservatorio Astronomico di Torino, Strada dell'Osservatorio 20, 10025 Pino Torinese, Italy
³ Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands

Received: 21 February 2005
Accepted: 2 April 2005

Abstract

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.