12 juin 2025Séminaire – Elena Asencio (University of Bonn)

« Do the stellar streams of the Milky Way point to a past Milky Way-Andromeda interaction? »

Stellar streams around the Milky Way (MW) can provide valuable insights into its history and substructure formation. Previous studies suggested that several MW streams could have a correlated origin with the disk of satellite galaxies (DoS) and the young halo globular clusters of the MW, given that many of these structures present a similar orbital pole orientation. In this work we test the validity of this hypothesis by revising the orbital pole distribution of the MW streams with the latest stream dataset (galstreams). For a sample of 91 streams at Galactocentric distances d < 100 kpc we find that the pole distribution has no preferred orbital direction. However, as we subtract the streams closer to the Galactic centre, by imposing several lower distance cuts, we find that, the larger the Galactocentric distance of the streams, the higher is the fraction of stream poles pointing in a direction similar to that of the DoS. This trend could be explained if the stream pole distribution was originally anisotropic, but precession effects displaced the orbital poles of the streams close to the Galactic centre. From the pole distribution and the estimated precession rates of the streams in the sample, we infer that the streams near the Galactic centre are indeed quite likely to be affected by precession. Finally, we corroborate with hydrodynamical simulations that, even in a scenario in which the MW substructures had a correlated origin, an overdensity in their orbital pole direction can not be appreciated until the selected sample also includes material at d ≳ 150 kpc.