The Origin of the Virgo Overdensity
The Virgo stellar structure - discovered as an overdensity of stars in photometric surveys - encompasses some 3000 square degrees and is located in the Milky Way halo. Using proper motions and radial velocities of members of this overdensity, we have determined that its orbit is on a very disruptive path through the Galaxy. N-body simulations suggest that the entire cloud-like Virgo structure is the tidal remnant from a disrupted massive (109 Msun) dwarf galaxy. The model also suggests that the progenitor of the Virgo overdensity is responsible for other stellar overdensities (i.e., the Pisces Overdensity, debris near NGC 2419 and near SEGUE 1) and NGC 2419 itself.
Likely orbits of the Virgo overdensity members are shown below.
Image Credits: (header) NASA, ESA, J. Hester and A. Loll (Arizona State University)