The Faintest Galaxies

摘要

We investigate the nature of ultra faint dwarf spheroidal galaxies (UF dSphs) in a general cosmological context, simultaneously accounting for various "classical" dSphs and Milky Way (MW) properties. including their metallicity distribution function (MDF). Our model successfully reproduces both the observed [Fe/H]-luminosity relation and the mean MDF of UFs. According to our results. UFs are the living fossils of H_2-cooling minihalos Mrmed at z＞ 8.5, i.e. before the end of reionization. They are the oldest and the most dark matter-dominated (M/L ＞ 100) dSphs in the MW system, with total masses of M=10~(7-8)M.. The model allows us to interpret the different shapes of UF and classical dSph MIA's along with the frequency of extremely metal-poor stars in these objects. We discuss the "missing satellites problem" by comparing UF star formation efficiencies with those derived for minihalos in the Via Lactea simulation.