  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 out to 30 kpc and then continuously declines down to 50 km/s 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_sun and an NFW profile of mass $0.8^{+1.2}_{-0.2}\times 10^{12}$ M_sun 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.
