Finding stars that are likely to be from accreted satellite galaxies

Abstract: The Milky Way galaxy has through its lifetime merged with several smaller galaxies in its surroundings. Merger events like these play an important role in the formation of galaxies and are therefore of great interest to better our understanding of galaxy formation. In this project we create candidate lists of stars that are likely to originate from past merger events experienced by the Galaxy, using the method and results of Mikkola et al. (2023). Merging stars tend to follow the trajectory of their original galaxy, even as this system is pulled apart by the larger galaxy. With time the merged galaxy will no longer be spatially coherent but its stars can instead be found as overdensities in velocity space. The full 3D velocity of stars is needed to identify stars within these overdensities, but only a small number of the observed stars have measured radial velocities. Mikkola et al. (2023) therefore used a maximum-likelihood method to obtain a full 3D velocity distribution of stars in the solar neighbourhood, without using radial velocities. In this project we use this velocity distribution to identify overdensities, corresponding to the four known moving groups Gaia Sausage Enceladus (GSE), ED-2, MMH-1 and the Helmi streams, and find stars that are likely to be members of them. These lists of probable candidates can be used as a tool for future spectroscopic surveys to efficiently target stars and gain further knowledge about these moving groups, such as their detailed chemical abundances.