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Driven by gravity, galaxies continuously grow through accretion of smaller systems. Stellar streams are nice illustrations of this hierarchical build-up, but the accreted stars quickly disperse. I will present advanced dynamical models that can convert the observed positions and velocities of the accreted stars to phase-space quantities like energy and angular momentum which remain conserved. In addition, these models can include the observed chemical properties of stars which are also conserved. The resulting population-dynamical models allow us then to uncover even those accretion events which are now fully dispersed. At the same time, these models also accurately constrain the total mass distribution, including a central black hole and dark matter halo. I will illustrate how these models make optimally use of observations to unveil the colourful past and dark side of galaxies: from unveiling their complex orbital distribution, to uncovering the satellite accretion history, to dark-matter dominated dwarf spheroidal galaxies having suffered interactions and even mergers. By the end, I aim to have demonstrated that these models provide a unique bridge between the studies of resolved stars in the Milky Way and integrated-light of high-redshifts galaxies. Together with direct coupling to state-of-the-art galaxy formation simulations, these population-dynamical models enable us to uncover the hierarchical build-up of galaxies in a cosmological context. |
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