Reconstructing the Merger History of the Milky Way Using Gaia

The current model for galaxy formation, Λ-CDM, predicts that galaxies are built from the accumulation and disruption of other small galaxies. Such merger events are expected to leave imprints on the kinematics of the affected stars. Due to this, the hypothesis proposed by this model can be tested in the Milky Way by studying the dynamics of individual stars for which full phase information is available – three-dimensional positions and velocities. Previous observational surveys have only been able to retrieve this for a small fraction of stars in the solar neighborhood, severely limiting the conclusions that can be drawn. However, with the recent second data release (DR2) of the Gaia Archive, observational data from millions of stars has been made available, allowing more thorough comparisons between the observations and galaxy formation models. This project involved the acquisition and analysis of recent data sets from Gaia DR2, and sought to identify structures present in phase space that are debris from previous merging events in our galaxy. Such identified structures can be cross-correlated with well known surviving objects, such as the globular cluster ωCen, which has long been hypothesized to be the core of a dwarf galaxy that was disrupted by the Milky Way tidal field.