The outer disc of the Milky Way (MW), where orbital timescales are of the order of ~1Gyr holds valuable information about the Galaxy's past and current interactions with satellite galaxies. These interactions cause the formation of tidal arms in the outer disc which remain coherent over several Gyrs and can be witnessed at present as long thin stream-like structures with witdth ~1-10 degrees and spanning lengths of ~180degrees on the sky. The dynamic of these tracer structures is simple, following a single particle orbit which can be exploited to measure the potential and its flattening close to the midplane (Laporte et al. 2019).
In this project, we will use the Anticenter Stream (ACS, Grillmair 2006) to constrain the potential and its flattening in the midplane at ~20kpc (similarly to Koposov 2010). This will also probe the impact of baryons on the sphericalisation of dark matter halos. We will map the ACS in 6-D using the astrometric data from Gaia eDR3 combined with radial velocities from legacy surveys (APOGEE, SEGUE, LAMOST) and fit the orbit of the ACS stream. The results and robustness of the method will also be compared with self-consistent N-body simulations of the interaction of the Milky Way with Sagittarius (Laporte et al. 2018).