Mapping the Past in the Future: Science Enabled by High-Resolution Spectroscopic Stellar Surveys

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Dr. Johnston and her team investigate the formation and evolution of dwarf galaxies, the most common type of galaxies in our local universe, and the formation of the Milky Way galaxy through detailed hydrodynamic and N-body simulations. The observed chemical composition of stars and their distribution today together with simulations is used to learn about ancient accretion events in the stellar halo, and to recover the properties of progenitor objects (e.g. dwarf galaxies and star clusters) that contributed to our galaxy's formation. The research aims to reconstruct the galaxy's past through comparing simulations to the observed distribution of the abundances of the chemical elements in large samples of stellar populations in all components of our Galaxy, which will become available from ongoing and planned surveys (e.g. with the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and the HERMES spectrometer on the Anglo-Australian telescope). The chemo-dynamical formation models of the Milky Way's halo that are produced here also provide guidance on the interpretation of large data sets from stellar surveys. The models include physics on star formation, feedback and mixing, and take into account the recurrent cycle of star formation and the chemical enrichment of new star-forming regions through ejecta from dying stars. The predicted abundance distributions of the chemical elements in different stellar populations might be detected in the spectroscopic surveys of stars. The plans for the semi-analytic chemo-dynamic models include the development of multi-zoned descriptions of the galaxy with collisionless stellar orbits allowing for star formation and enrichment of gas in chemical elements. In order to derive a more complete picture about the formation and evolution of the Galactic halo, results are combined from the semi-analytic chemo-dynamical models of galaxies, the fully self-consistent cosmological N-body and hydrodynamic simulations; and the statistical analyses of structures in high dimensional spaces. The self-consistent simulations will be used to refine the descriptions of internal baryonic physics and external environmental influences that are implemented in the simpler chemo-dynamical models. This research program provides research topics for two graduate students.