Kinematics in the Galactic Bulge with APOGEE: II. High-Order Kinematical
  Moments and Comparison to Extragalactic Bar Diagnostics
  Much of the inner Milky Way's (MW) global rotation and velocity dispersion
patterns can be reproduced by models of secularly-evolved, bar-dominated
bulges. More sophisticated constraints, including the higher moments of the
line-of-sight velocity distributions (LOSVDs) and limits on the chemodynamical
substructure, are critical for interpreting observations of the unresolved
inner regions of extragalactic systems and for placing the MW in context with
other galaxies. Here, we use SDSS-APOGEE data to develop these constraints, by
presenting the first maps of the LOSVD skewness and kurtosis of metal-rich and
metal-poor inner MW stars (divided at [Fe/H] = -0.4), and comparing the
observed patterns to those that are seen both in N-body models and in
extragalactic bars. Despite closely matching the mean velocity and dispersion,
the models do not reproduce the observed LOSVD skewness patterns in different
ways, which demonstrates that our understanding of the detailed orbital
structure of the inner MW remains an important regime for improvement. We find
evidence in the MW of the skewness-velocity correlation that is used as a
diagnostic of extragalactic bar/bulges. This correlation appears in metal-rich
stars only, providing further evidence for different evolutionary histories of
chemically differentiated populations. We connect these skewness measurements
to previous work on high-velocity "peaks" in the inner Galaxy, confirming the
presence of that phenomenon, and we quantify the cylindrical rotation of the
inner Galaxy, finding that the latitude-independent rotation vanishes outside
of lon ~ 7 deg. Finally, we evaluate the MW data in light of select
extragalactic bar diagnostics and discuss progress and challenges of using the
MW as a resolved analog of unresolved stellar populations.
