Cosmic stellar relics in the galactic halo

Stellar archaeology of the most metal-poor stars represents a promising way to explore primordial star formation. Due to their low metallicities, metal-poor stars are expected to form out of gas enriched by members of the first stellar generation. Therefore, despite the fact that metal-poor stars are observed in the Galactic halo or in nearby dwarf galaxies, satellites of the Milky Way (MW), these objects might well be living fossils of the first star formation episodes in the Universe. One of the most important observational constraints is provided by the distribution of stellar metallicities in the halo of the Galaxy, the so-called Metallicity Distribution Function (MDF). Using a Monte Carlo method based on the semi-analytical Press & Schechter formalism, we have developed a new code GAMETE (Galaxy MErger Tree & Evolution) to reconstruct the merger tree of the Galaxy and follow the evolution of gas and stars along the hierarchical tree. Our appoach allows to compare the observational properties of the MW with model results, exploring the imprint of undetectable high redshift processes. By matching model predictions to the observed MDF of metal poor stars in the Galactic halo we: (i) study the metal enrichment history of the MW environment; (ii) set limits on the primordial Initial Mass Function (IMF) and the critical metallicity for low mass star formation, Z(cr); (iii) investigate the statistical impact of second generation stars in up-to-date observed samples.