On the Shoulders of Giants: Properties of the Stellar Halo and the Milky
  Way Mass Distribution
  Halo stars orbit within the potential of the Milky Way and hence their
kinematics can be used to understand the underlying mass distribution. However,
the inferred mass distribution depends sensitively upon assumptions made on the
density and the velocity anisotropy profiles of the tracers. Also, there is a
degeneracy between the parameters of the halo and that of the disk or bulge.
Here, we decompose the Galaxy into bulge, disk and dark matter halo and then
model the kinematic data of the halo BHB and K-giants from the SEGUE.
Additionally, we use the gas terminal velocity curve and the Sgr A$^*$ proper
motion. With $R_\odot = 8.5$kpc, our study reveals that the density of the
stellar halo has a break at $17.2^{+1.1}_{-1.0}$ kpc, and an exponential
cut-off in the outer parts starting at $97.7^{+15.6}_{-15.8}$kpc. Also, we find
the velocity anisotropy is radially biased with $\beta_s= 0.4\pm{0.2}$ in the
outer halo. We measure halo virial mass $M_{\text{vir}} = 0.80^{+0.31}_{-0.16}
\times 10^{12} M_{\odot}$, concentration $c=21.1^{+14.8}_{-8.3}$, disk mass of
$0.95^{+0.24}_{-0.30}\times10^{11} M_{\odot}$, disk scale length of
$4.9^{+0.4}_{-0.4}$ kpc and bulge mass of $0.91^{+0.31}_{-0.38} \times 10^{10}
M_{\odot}$. The mass of halo is found to be small and this has important
consequences. The giant stars reveal that the outermost halo stars have low
velocity dispersion interestingly suggesting a truncation of the stellar halo
density rather than a small overall mass of the Galaxy. Our estimates of local
escape velocity $v_{\rm esc} = 550.9^{+32.4}_{-22.1}$ kms$^{-1}$ and dark
matter density $\rho^{\rm DM}_{\odot} = 0.0088^{+0.0024}_{-0.0018} M_{\odot}
{\rm pc^{-3}} $ ($0.35^{+0.08}_{-0.07}$ GeV cm$^{-3}$) are in good agreement
with recent estimates. Some of the above estimates are depended on the adopted
value of $R_\odot$ and of outer power-law index of the tracer number density.
