Speaker
Description
Unveiling the 3D shape of the Milky Way’s dark matter halo is critical to understanding its formation history and provides a fundamental test of the ΛCDM cosmological model. Functioning as an intermediary between the Galaxy and its satellites, the shape of dark matter halo also plays a key role in deciphering the long-standing problem of a ‘plane of satellites’ vertically aligned to the Galactic disk. We create an innovative dynamical method with minimal assumptions, by applying the method to 6d phase-space data of halo stars from LAMOST+Gaia, we provide a robust determination of the 3D shape of the halo. We discover a nearly oblate dark-matter halo with its long-intermediate axis plane unexpectedly vertical to the Galactic disk, yet aligned with the satellite plane. This striking configuration suggests that the Galactic disk has flipped, torqued by minor mergers, from an original alignment with the halo and satellite plane. Such disk reorientation is non-trivial yet its physical mechanism is straightforward to comprehend and naturally originates a vertical satellite plane. Our findings offer a unified framework that links halo orientation, satellite alignment, and disk evolution, reinforcing the internal consistency of the Milky Way in 𝚲CDM model.
