The chemical compositions of the stars in Milky Way ( MW ) satellite galaxies reveals the history of gas flows and star formation ( SF ) intensity .
This talk presented a Keck/DEIMOS spectroscopic survey of the Fe , Mg , Si , Ca , and Ti abundances of nearly 3000 red giants in eight MW dwarf satellites .
The metallicity and alpha-to-iron ratio distributions obey the following trends : ( 1 ) The more luminous galaxies are more metal-rich , indicating that they retained gas more efficiently than the less luminous galaxies .
( 2 ) The shapes of the metallicity distributions of the more luminous galaxies require gas infall during their SF lifetimes .
( 3 ) At \mathrm { [ Fe / H ] } < -1.5 , [ \alpha /Fe ] falls monotonically with increasing [ Fe/H ] in all MW satellites .
One interpretation of these trends is that the SF timescale in any MW satellite is long enough that Type Ia supernovae exploded for nearly the entire SF lifetime .