We have compiled a new sample of 240 halo objects with accurate distance and radial velocity measurements , including globular clusters , satellite galaxies , field blue horizontal branch stars and red giant stars from the Spaghetti survey .
The new data lead to a significant increase in the number of known objects for Galactocentric radii beyond 50 kpc , which allows a reliable determination of the radial velocity dispersion profile out to very large distances .
The radial velocity dispersion shows an almost constant value of 120 km s ^ { -1 } out to 30 kpc and then continuously declines down to 50 km s ^ { -1 } at about 120 kpc .
This fall-off puts important constraints on the density profile and total mass of the dark matter halo of the Milky Way .
For a constant velocity anisotropy , the isothermal profile is ruled out , while both a dark halo following a truncated flat model of mass 1.2 ^ { +1.8 } _ { -0.5 } \times 10 ^ { 12 } M _ { \odot } and an NFW profile of mass 0.8 ^ { +1.2 } _ { -0.2 } \times 10 ^ { 12 } M _ { \odot } and c = 18 are consistent with the data .
The significant increase in the number of tracers combined with the large extent of the region probed by these has allowed a more precise determination of the Milky Way mass in comparison to previous works .
We also show how different assumptions for the velocity anisotropy affect the performance of the mass models .