IAUS379: Dynamical Masses of Local Group Galaxies

Gaia EDR3 has provided proper motions of Milky Way (MW) dwarf galaxies with an unprecedented accuracy, which allows us to investigate their orbital properties. We found that the total energy and angular momentum of MW dwarfs are much larger than that of MW K-giant stars, Sagittarius stream stars and globular clusters. It suggests that many MW dwarfs have recently infall into the Milky Way halo. We also confirmed that Milky Way dwarfs lie preferentially near their pericenters and many of them belong to a vast polar structure perpendicular to the Milky Way disk, which suggests that Milky Way dwarfs do not behave like satellite systems derived from LCDM cosmological simulations. These new results require revisiting the origin of MW dwarf galaxies, e.g., if they came recently, they were likely to have experienced gas removal due to the ram pressure induced by MW’s hot gas, and to be affected by MW tides. We will discuss the consequences of these processes on their mass estimation.