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We show that the mass of a dark matter halo can be inferred from thedynamical status of its satellite galaxies. Using 9 dark-matter simulations ofhalos like the Milky Way (MW), we find that the present-day substructures ineach halo follow a characteristic distribution in the phase space of orbitalbinding energy and angular momentum, and that this distribution is similar fromhalo to halo but has an intrinsic dependence on the halo formation history. Weconstruct this distribution directly from the simulations for a specific haloand extend the result to halos of similar formation history but differentmasses by scaling. The mass of an observed halo can then be estimated bymaximizing the likelihood in comparing the measured kinematic parameters of itssatellite galaxies with these distributions. We test the validity and accuracyof this method with mock samples taken from the simulations. Using thepositions, radial velocities, and proper motions of 9 tracers and assumingobservational uncertainties comparable to those of MW satellite galaxies, wefind that the halo mass can be recovered to within $\sim$40%. The accuracy canbe improved to within $\sim$25% if 30 tracers are used. However, the dependenceof the phase-space distribution on the halo formation history sets a minimumuncertainty of $\sim$20% that cannot be reduced by using more tracers. Webelieve that this minimum uncertainty also applies to any mass determinationfor a halo when the phase space information of other kinematic tracers is used.

Determination of Dark Matter Halo Mass from Dynamics of Satellite Galaxies