Gaia Early Data Release 3: Updated radial velocities from Gaia DR2
  Gaia's Early Third Data Release (EDR3) does not contain new radial velocities
because these will be published in Gaia's full third data release (DR3),
expected in the first half of 2022. To maximise the usefulness of EDR3, Gaia's
second data release (DR2) sources (with radial velocities) are matched to EDR3
sources to allow their DR2 radial velocities to also be included in EDR3. This
presents two considerations: (i) arXiv:1901.10460 (hereafter B19) published a
list of 70,365 sources with potentially contaminated DR2 radial velocities; and
(ii) EDR3 is based on a new astrometric solution and a new source list, which
means sources in DR2 may not be in EDR3. EDR3 contains 7,209,831 sources with a
DR2 radial velocity, which is 99.8% of sources with a radial velocity in DR2.
14,800 radial velocities from DR2 are not propagated to any EDR3 sources
because (i) 3871 from the B19 list are found to either not have an unpublished,
preliminary DR3 radial velocity or it differs significantly from its DR2 value,
and 5 high-velocity stars not in the B19 list are confirmed to have
contaminated radial velocities; and (ii) 10,924 DR2 sources could not be
satisfactorily matched to any EDR3 sources, so their DR2 radial velocities are
also missing from EDR3. The reliability of radial velocities in EDR3 has
improved compared to DR2 because the update removes a small fraction of
erroneous radial velocities (0.05% of DR2 radial velocities and 5.5% of the B19
list). Lessons learnt from EDR3 (e.g. bright star contamination) will improve
the radial velocities in future Gaia data releases. The main reason for radial
velocities from DR2 not propagating to EDR3 is not related to DR2 radial
velocity quality. It is because the DR2 astrometry is based on one component of
close binary pairs, while EDR3 astrometry is based on the other component,
which prevents these sources from being unambiguously matched. (Abridged)
