The m etallicity distribution ofthe halo and the satellitesofthe M ilky way in the hierarchicalm erging paradigm

Aim s. To accountforthe observed dierentialm etallicity distribution (DM D)ofthe M ilky W ay halo,a sem i-analyticalm odel ispresented in thefram ework ofthehierarchicalm erging paradigm forstructureform ation. M ethods. Itisassum ed thatthe M ilky W ay halo iscom posed ofa num berofsub-haloeswith propertieseitherasobserved in thedwarfsatellite galaxiesoftheLocalgroup (shape ofm etallicity distribution,eective yield)orderived from calculationsof structureform ation (sub-halo distribution function). Results. W ith reasonable assum ptions for the param eters involved,wend that the overallshape and eective yield ofthe G alactichalo DM D can bereproduced in thefram ework ofsuch a sim plem odel.Thelow m etallicity tailoftheDM D presentsa deciency ofstarswith respectto thesim ple m odelpredictions(akin to theG -dwarfproblem in thesolarneighborhood);itis suggested thatan early infallphasecan accountforthatproblem ,aswellasfortheobserved DM Dsofdwarfsatellite galaxies. Conclusions. Accretion ofgalaxiessim ilar(butnotidentical)to theprogenitorsofpresentday dwarfsatellitesoftheM ilky W ay m ay wellhaveform ed the G alactic halo.