Gaia EDR3 proper motions of Milky Way dwarfs. II: Velocities, Total
  Energy and Angular Momentum
  Here we show that precise Gaia EDR3 proper motions have provided robust
estimates of 3D velocities, angular momentum and total energy for 40 Milky Way
dwarfs. The results are statistically robust and are independent of the Milky
Way mass profile. Dwarfs do not behave like long-lived satellites of the Milky
Way because of their excessively large velocities, angular momenta, and total
energies. Comparing them to other MW halo population, we find that many are at
first passage, $\le$ 2 Gyr ago, i.e., more recently than the passage of
Sagittarius, $\sim$ 4-5 Gyr ago. We suggest that this is in agreement with the
stellar populations of all dwarfs, for which we find that a small fraction of
young stars cannot be excluded. We also find that dwarf radial velocities
contribute too little to their kinetic energy when compared to satellite
systems with motions only regulated by gravity, and some other mechanism must
be at work such as ram pressure. The latter may have preferentially reduced
radial velocities when dwarf progenitors entered the halo until they lost their
gas. It could also explain why most dwarfs lie near their pericenter. We also
discover a novel large scale structure perpendicular to the Milky Way disk,
which is made by 20% of dwarfs orbiting or counter orbiting with the
Sagittarius dwarf.
