Lessons from the Sagittarius dSph Tidal Stream

Abstract

As the most prominent and extensive halo substructure in the Milky Way, the Sagittarius (Sgr) tidal stream gives us an important tool for exploring a number of problems in galactic astronomy. Here we will focus on four distinct applications of the Sgr stream: (1) Because stellar orbits are a product of the gravitational potential, tidal streams offer a unique probe of the distribution of dark matter. The Sgr stream allows us to probe the shape of the Milky Way potential to ∼ 50 kpc. (2) The particular orientation of the Sgr stream allows measurement of the Local Standard of Rest velocity in a way independent of the solar Galactocentric distance via the proper motions of stream stars. (3) Because tidal stream stars tend to be stripped from the outermost parts of the parent object, the chemical properties of stars along a tidal stream enable us not only to reconstruct the net enrichment history of the parent body, but the original radial distribution of chemical abundances. (4) By determining those stars and clusters that are in the stream now, we can assess what types of stars and clusters get contributed to large, MW-like galaxies through the accretion process. Although now well studied for nearly two decades, the Sgr stream is still offering us surprises.