Selecting Sagittarius : a study of Sagittarius dwarf members throughout the Milky Way galactic halo

Wrapping around the Milky Way, the Sagittarius (Sgr) stream is the most dominant substructure in the halo. Its progenitor, the Sgr dwarf galaxy, has been assumed to be a non-rotating, pressure-supported dwarf spheroidal galaxy. However, to date, no such model for the interaction of Sgr with the Milky Way has been able to reproduce all of the observational features of the stream. We have obtained spectra of over 21,000 stars in the stream and the core of Sgr, providing the most comprehensive spectral observations ever taken for this system. Our analysis demonstrates that Sgr is unlikely to have originated as a disk galaxy. Using careful selection criteria, we have identified several hundred likely members of the Sgr stream. From the most probable members identified, we characterize the chemical and dynamical nature and, through comparison to theory, provide a new mapping of this extended system of Sgr stars.1 page(s