Jeans that fit: weighing the mass of the Milky Way analogues in the
  $\Lambda{\rm CDM}$ universe
  The spherical Jeans equation is a widely used tool for dynamical study of
gravitating systems in astronomy. Here we test its efficacy in robustly
weighing the mass of Milky Way analogues, given they need not be in equilibrium
or even spherical. Utilizing Milky Way stellar halos simulated in accordance
with $\Lambda{\rm CDM}$ cosmology by Bullock and Johnston (2005) and analysing
them under the Jeans formalism, we recover the underlying mass distribution of
the parent galaxy, within distance $r/{\rm kpc}\in[10,100]$, with a bias of
$\sim12\%$ and a dispersion of $\sim14\%$. Additionally, the mass profiles of
triaxial dark matter halos taken from the SURFS simulation, within scaled
radius $0.2<r/r_{\rm max}<3$, are measured with a bias of $\sim-2.4\%$ and a
dispersion of $\sim10\%$. The obtained dispersion is not because of Poisson
noise due to small particle numbers as it is twice the later. We interpret the
dispersion to be due to the inherent nature of the $\Lambda{\rm CDM}$ halos,
for example being aspherical and out-of-equilibrium. Hence the dispersion
obtained for stellar halos sets a limit of about $12\%$ (after adjusting for
random uncertainty) on the accuracy with which the mass profiles of the Milky
Way-like galaxies can be reconstructed using the spherical Jeans equation. This
limit is independent of the quantity and quality of the observational data. The
reason for a non zero bias is not clear, hence its interpretation is not
obvious at this stage.
