The assembly history of the Milky Way halo

该项目旨在通过研究银河系光晕中恒星群的化学和运动学来限制银河系的早期组装历史。首先，我们将限制银河系内晕中富n恒星的起源，然后我们将采取观测和理论相结合的方法来确定原位晕的性质。在第一阶段，我们将把富n恒星的化学和运动学与各种银河系成分和/或吸积系统的恒星进行比较。这将使用最新的远地点丰度、盖亚固有运动和盖亚距离来完成。厚盘和薄盘将在化学基础上选择，遵循我们小组之前的工作（Mackereth et al., 2018）。属于吸积系统（盖亚土卫二和红杉）的恒星将使用Helmi等人（2018）和Myeong等人（2019）的定义进行选择。轨道参数将使用python包“gaply”（Bovy 2015）获得。为了研究原位晕，将对一些类似银河系的星系进行高分辨率模拟，以寻找“飞溅”群体的存在，这被认为是早期吸积事件的影响结果。一旦在模拟中确定了这些种群，我们将设计旨在在APOGEE和WEAVE调查数据中确定它们存在的测试。该项目的最后一部分将包括研究调查数据，以预测“模拟飞溅”的特征。这将基于APOGEE DR17数据（其公开数据将于2021年夏季发布）和WEAVE（预计2020年首亮）的组合。

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).