On the many '3-kiloparsec arms' - shocked wave and nuclear rotation
  Many features near the Galactic Center have been called 3-kiloparsec arms. We
reached a point of having too many divergent data, making it difficult to be
constrained by a single physical model. Their differing characteristics suggest
different physical and dynamical objects.
  Radial velocity data on the so-called 3-kpc arms do not coincide with radial
velocities of major spiral arms near 3kpc, nor near 2 kpc, nor near 4 kpc from
the Galactic Center (Fig. 1 and 2).
  Different 3-kpc arm features may require different models: turbulence around
a shock in a Galactic density wave between 2 and 4 kpc from the Galactic Center
(Table 1), or nuclear rotation between 0 and 2 kpc from the Galactic Center
region (Table 2), or a putative radial expansion between 0 and 4 kpc from the
Galactic Center.
  Despite their naming as Near 3-kiloparsec arms or Far 3-kiloparsec arms,
these features are not major arms. Those 3-kpc arm features nearer the Galactic
Center (within 13o of Galactic longitude) may be different than those farther
out (Table 2).
  Here we show that the plethora of observed '3-kpc arm' features can be
separated in two: those with Galactic longitude of 13 degrees or more away from
the Galactic Center (Table 1 - some of which are possibly associated with the
observed major spiral arms), and those within 13 degrees from the Galactic
Center (Table 2 - some of which are possibly associated with the observed
central bars; Fig.1 and Fig.2).
