The dynamics of isolated Local Group galaxies
  We measured velocities of 862 individual red giant stars in seven isolated
dwarf galaxies in the Local Group: NGC 6822, IC 1613, VV 124 (UGC 4879), the
Pegasus dwarf irregular galaxy (DDO 216), Leo A, Cetus, and Aquarius (DDO 210).
We also computed velocity dispersions, taking into account the measurement
uncertainties on individual stars. None of the isolated galaxies is denser than
the densest Local Group satellite galaxy. Furthermore, the isolated dwarf
galaxies have no obvious distinction in the velocity dispersion--half-light
radius plane from the satellite galaxies of the Milky Way and M31. The
similarity of the isolated and satellite galaxies' dynamics and structural
parameters imposes limitations on environmental solutions to the
too-big-to-fail problem, wherein there are fewer dense dwarf satellite galaxies
than would be expected from cold dark matter simulations. This data set also
has many other applications for dwarf galaxy evolution, including the
transformation of dwarf irregular into dwarf spheroidal galaxies. We intend to
explore these issues in future work.
