Bibcode
Fritz, T. K.; Battaglia, G.; Pawlowski, M. S.; Kallivayalil, N.; van der Marel, R.; Sohn, S. T.; Brook, C.; Besla, G.
Bibliographical reference
Astronomy and Astrophysics, Volume 619, id.A103, 18 pp.
Advertised on:
11
2018
Journal
Citations
251
Refereed citations
231
Description
A proper understanding of the Milky Way (MW) dwarf galaxies in a
cosmological context requires knowledge of their 3D velocities and
orbits. However, proper motion (PM) measurements have generally been of
limited accuracy and are available only for more massive dwarfs. We
therefore present a new study of the kinematics of the MW dwarf
galaxies. We use the Gaia DR2 for those dwarfs that have been
spectroscopically observed in the literature. We derive systemic PMs for
39 galaxies and galaxy candidates out to 420 kpc, and generally find
good consistency for the subset with measurements available from other
studies. We derive the implied Galactocentric velocities, and calculate
orbits in canonical MW halo potentials of low (0.8 ×
1012 M⊙) and high mass (1.6 ×
1012 M⊙). Comparison of the distributions of
orbital apocenters and 3D velocities to the halo virial radius and
escape velocity, respectively, suggests that the satellite kinematics
are best explained in the high-mass halo. Tuc III, Crater II, and
additional candidates have orbital pericenters small enough to imply
significant tidal influences. Relevant to the missing satellite problem,
the fact that fewer galaxies are observed to be near apocenter than near
pericenter implies that there must be a population of distant dwarf
galaxies yet to be discovered. Of the 39 dwarfs: 12 have orbital poles
that do not align with the MW plane of satellites (given reasonable
assumptions about its intrinsic thickness); 10 have insufficient PM
accuracy to establish whether they align; and 17 satellites align, of
which 11 are co-orbiting and (somewhat surprisingly, in view of prior
knowledge) 6 are counter-orbiting. Group infall might have contributed
to this, but no definitive association is found for the members of the
Crater-Leo group.
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