Gaia EDR3 proper motions, energies, angular momenta of Milky Way dwarf galaxies: a recent infall to the Milky Way halo

TL;DR

Gaia EDR3 data reveals that Milky Way dwarf galaxies have high energies and angular momenta, indicating recent infall into the galaxy's halo, challenging existing cosmological models and suggesting new formation and interaction scenarios.

Contribution

This study provides new orbital property measurements of MW dwarf galaxies using Gaia EDR3, highlighting their recent infall and challenging standard cosmological assumptions.

Findings

MW dwarf galaxies have higher energies and angular momenta than other MW systems.

They are near their pericenters, indicating recent infall.

Results suggest recent accretion and environmental effects on dwarf galaxies.

Abstract

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 dwarf galaxies are much larger than that of MW K-giant stars, Sagittarius stream stars and globular clusters. It suggests that many MW dwarf galaxies have had a recent infall into the MW halo. We confirmed that MW dwarf galaxies lie near their pericenters, which suggests that they do not behave like satellite systems derived from Lambda-Cold-Dark-Matter 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.