Title:The Stellar populations and spatial structures of dark dwarf satellites
Author(s):Sakurako Okamoto, Nobuo Arimoto
Abstract:

Dwarf galaxies like dSphs around the Milky Way may be the building blocks of the universe. Most of them are considered to be dynamically and chemically simple system with the high M/L ratio. Recent analyses of the colour-magnitude diagrams (CMD) and high dispersion spectroscopic abundances, however, reveal the fact that some bright dSphs are composed of multiple stellar populations. Here, we present the deep CMDs of "classical" and "ultra faint" dSphs, such as Sextans, Draco, Ursa Minor, Ursa Major I, Bootes, Canes Venatici I dSph taken by Subaru/Suprime-Cam to study their stellar populations and spatial structures. The massive one of these dSphs shows the relatively younger stars (~ 10Gyr) are more spatially concentrated to the galaxy center than old stars (~ 14Gyr), which indicates that the star formation in the central region continued at least a few Gyr, consistent with the different spatial distributions of red and blue HB stars. On the other hands, the CMD of the faintest one which is newly discovered by SDSS shows a single epoch of star formation as a metal-poor globular cluster. These different duration of past star formation must be influenced by their initial conditions and the past orbit with their host and the unexpected gas accretion, if any. The relation between the star formation history and the present properties of each galaxy is important to understand the formation of dwarf galaxies in general.