The Discrepant Kinematics of ORLs and CELs in NGC 7009 as a Function of
  Ionization Structure
  We present spatially- and velocity-resolved echelle spectroscopy for NGC 7009
obtained with the UVES spectrograph at the European Southern Observatory's Very
Large Telescope. Our objective is to analyze the kinematics of emission lines
excited by recombination and collisions with electrons to determine whether
similarities or differences could be useful in elucidating the well-known
abundance discrepancy derived from them. We construct position-velocity maps
for recombination, fluorescence, charge transfer, and collisionally-excited
lines. We find a plasma component emitting in the C II, N II, O II, and Ne II
recombination lines whose kinematics are discrepant: They are incompatible with
the ionization structure derived from all other evidence and the kinematics
derived from all of these lines are unexpectedly very similar. We find direct
evidence for a recombination contribution to [N II] 5755. Once taken into
account, the electron temperatures from [N II], [O III], and [Ne III] agree at
a given position and velocity. The electron densities derived from [O II] and
[Ar IV] are consistent with direct imaging and the distribution of hydrogen
emission. The kinematics of the C II, N II, O II, and Ne II lines does not
coincide with the kinematics of the [O III] and [Ne III] forbidden emission,
indicating that there is an additional plasma component to the recombination
emission that arises from a different volume from that giving rise to the
forbidden emission from the parent ions within NGC 7009. Thus, the chemical
abundances derived from either type of line are correct only for the plasma
component from which they arise. Apart from [N II] 5755, we find no anomaly
with the forbidden lines usually used to determine chemical abundances in
ionized nebulae, so the abundances derived from them should be reliable for the
medium from which they arise.
