Tracing the accretion history of the Milky Way with halo stars

The ΛCDM model predicts a hierarchical formation for galaxies. Many substructures were found in the Galactic halo, identified as clumps in kinematic spaces. If they also feature different chemical properties, they are then associated to independent merger debris. Our aim is to explore to what extent different clumps in the energy-angular momentum space (E − Lz) with different metallicity distribution functions (MDF) trace the accretion history of the Galaxy. By means of N-body simulations, we confirm that accreted stars from a massive merger redistribute in a wide range of E and Lz, due to dynamical friction, thus not being associated to a single clump. Since satellite stars with different metallicities can be deposited in different regions of the E − Lz space, a single accretion can manifest with different MDFs. This method can bias the merger tree of the Galaxy towards increasing the number of accretions and decreasing the masses of the progenitor galaxies.