The virgo stellar overdensity: Mapping the infall of the sagittarius tidal stream onto the milky way disk

The recently discovered Virgo stellar overdensity, which extends over ∼ 1000 deg2 perpendicular to the Galactic disk plane (7 kpc < Z < 15 kpc, R ∼ 7 kpc), is the largest clump of tidal debris ever detected in the outer halo and is likely related to the accretion of a nearby dwarf galaxy by the Milky Way. We carry out N-body simulations of the Sagittarius stream to show that this giant stellar overdensity is a confirmation of theoretical model predictions in which the leading arm of the Sagittarius stream crosses the Milky Way plane in the solar neighborhood. Radial velocity measurements are needed to confirm this association and to further constrain the shape of the Milky Way dark matter halo through a new generation of theoretical models. If the identification of the Virgo overdensity and the Sagittarius leading arm is correct, we predict highly negative radial velocities for the stars of the Virgo overdensity. The detection of this new portion of the Sagittarius tidal stream would represent an excellent target for ongoing and future kinematic surveys and for dark matter direct detection experiments in the proximity of the Sun. © 2007. The American Astronomical Society. All rights reserved.