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Using three-dimensional stellar kinematic data from simulated galaxies, weexamine the efficacy of a Jeans equation analysis in reconstructing the totaldisk surface density, including the dark matter, at the "Solar" radius. Oursimulation dataset includes galaxies formed in a cosmological context usingstate-of-the-art high resolution cosmological zoom simulations, and otheridealised models. The cosmologically formed galaxies have been demonstrated tolie on many of the observed scaling relations for late-type spirals, and thusoffer an interesting surrogate for real galaxies with the obvious advantagethat all the kinematical data are known perfectly. We show that the verticalvelocity dispersion is typically the dominant kinematic quantity in theanalysis, and that the traditional method of using only the vertical force isreasonably effective at low heights above the disk plane. At higher heights theinclusion of the radial force becomes increasingly important. We also show thatthe method is sensitive to uncertainties in the measured disk parameters,particularly the scale lengths of the assumed double exponential densitydistribution, and the scale length of the radial velocity dispersion. Inaddition, we show that disk structure and low number statistics can lead tosignificant errors in the calculated surface densities. Finally we examine theimplications of our results for previous studies of this sort, suggesting thatmore accurate measurements of the scale lengths may help reconcile conflictingestimates of the local dark matter density in the literature.

Weighing the Galactic disk using the Jeans equation: lessons from simulations