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The Hypervelocity Star survey presents the currently largest sample of radialvelocity measurements of halo stars out to 80 kpc. We apply spherical Jeansmodeling to these data in order to derive the mass profile of the Galaxy. Werestrict the analysis to distances larger than 25 kpc from the Galactic center,where the density profile of halo stars is well approximated by a single powerlaw with logarithmic slope between -3.5 and -4.5. With this restriction, wealso avoid the complication of modeling a flattened Galactic disk. In the range25 < r < 80 kpc, the radial velocity dispersion declines remarkably little; arobust measure of its logarithmic slope is between -0.05 and -0.1. The circularvelocity profile also declines remarkably little with radius. The allowed rangeof V_c(80 kpc) lies between 175 and 231 km/s, with the most likely value 193km/s. Compared with the value at the solar location, the Galactic circularvelocity declines by less than 20% over an order of magnitude in radius. Such aflat profile requires a massive and extended dark matter halo. The massenclosed within 80 kpc is 6.9(+3.0-1.2) 10^11 Msun. Our sample of radialvelocities is large enough that the biggest uncertainty in the mass is notstatistical but systematic, dominated by the density slope and anisotropy ofthe tracer population. Further progress requires modeling observed datasetswithin realistic simulations of galaxy formation.

The Mass Profile of the Galaxy to 80 kpc