The assembly history of the Milky Way halo

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This project aims to constrain the early assembly history of the Milky Way by studying the chemistry and kinematics of the stellar populations in its halo. Initially we will constrain the origin of N-rich stars in the inner halo of the Galaxy, and following that we will conduct a combined observational and theoretical approach in order to establish the nature of the in-situ halo. In the first stage we will compare the chemistry and kinematics of N-rich stars with those of various Galactic components and/or accreted systems. This will be done using latest APOGEE abundances, GAIA proper motions and Gaia-based distances. The thick and thin disk will be selected on the basis of chemistry, following previous work from our group (Mackereth et al., 2018). Stars belonging to accreted systems (Gaia Enceladus and Sequoia) will be selected using the definitions from Helmi et al (2018) and Myeong et al (2019). Orbital parameters will be obtained using the python package 'gaply' (Bovy 2015). To study the in-situ halo, a selection of high-resolution simulations of Milky Way like galaxies will be examined in search for the presence of the 'Splash' population, which has been claimed to result from the impact of an early accretion event. Once such populations are identified in the simulations we will devise tests aimed at establishing their presence in data from APOGEE and WEAVE surveys. The final part of the project will involve looking into the survey data for the predicted signatures of 'simulated splashes'. This will be based on a combination of the APOGEE DR17 data (whose public data release will happen in Summer/2021) and hopefully WEAVE (expected first light 2020).