Inhomogeneous chemical evolution of dwarf spheroidal galaxies

Stellar abundance pattern of n-capture elements such as barium is used as a powerful tool to infer how star formation proceeded in dwarf spheroidal (dSph) galaxies. It is found that the abundance correlation of barium with iron in stars belonging to dSph galaxies orbiting the Milky Way, i.e., Draco, Sextans, and Ursa Minor have a feature similar to that in Galactic metal-poor stars. The common feature of these two correlations can be realized by our inhomogeneous chemical evolution model based on the supernova-driven star formation scenario if dSph stars formed from gas with a velocity dispersion of similar to26 km s(-1). This velocity dispersion together with the stellar luminosities strongly suggest that dark matter dominated dSph galaxies. The tidal force of the Milky Way links this velocity dispersion with the currently observed value less than or similar to 10 km s(-1) by stripping the dark matter in dSph galaxies. As a result, the total mass of each dSph galaxy is found to have been originally similar to25 times larger than at present. In this model, supernovae immediately after the end of the star formation can expel the remaining gas over the gravitational potential of the dSph galaxy.