Weighing the Galactic disk using the Jeans equation: lessons from
  simulations
  Using three-dimensional stellar kinematic data from simulated galaxies, we
examine the efficacy of a Jeans equation analysis in reconstructing the total
disk surface density, including the dark matter, at the "Solar" radius. Our
simulation dataset includes galaxies formed in a cosmological context using
state-of-the-art high resolution cosmological zoom simulations, and other
idealised models. The cosmologically formed galaxies have been demonstrated to
lie on many of the observed scaling relations for late-type spirals, and thus
offer an interesting surrogate for real galaxies with the obvious advantage
that all the kinematical data are known perfectly. We show that the vertical
velocity dispersion is typically the dominant kinematic quantity in the
analysis, and that the traditional method of using only the vertical force is
reasonably effective at low heights above the disk plane. At higher heights the
inclusion of the radial force becomes increasingly important. We also show that
the method is sensitive to uncertainties in the measured disk parameters,
particularly the scale lengths of the assumed double exponential density
distribution, and the scale length of the radial velocity dispersion. In
addition, we show that disk structure and low number statistics can lead to
significant errors in the calculated surface densities. Finally we examine the
implications of our results for previous studies of this sort, suggesting that
more accurate measurements of the scale lengths may help reconcile conflicting
estimates of the local dark matter density in the literature.
