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We investigate the claim that the largest subhaloes in high resolutiondissipationless cold dark matter (CDM) simulations of the Milky Way aredynamically inconsistent with observations of its most luminous satellites. Wefind that the inconsistency is largely attributable to the large values of\sigma_8 and n_s adopted in the discrepant simulations producing satellitesthat form too early and therefore are too dense. We find the tension betweenobservations and simulations adopting parameters consistent with WMAP9 isgreatly diminished making the satellites a sensitive test of CDM. We find theVia Lactea II halo to be atypical for haloes in a WMAP3 cosmology, adiscrepancy that we attribute to its earlier formation epoch than the mean forits mass. We also explore warm dark matter (WDM) cosmologies for 1--4 keVthermal relics. In 1 keV cosmologies subhaloes have circular velocities at kpcscales ~ 60% lower than their CDM counterparts, but are reduced by only 10% in4 keV cosmologies. Since relic masses < 2-3 keV are ruled out by constraintsfrom the number of Milky Way satellites and Lyman-\alpha\ forest, WDM has aminor effect in reducing the densities of massive satellites. Given theuncertainties on the mass and formation epoch of the Milky Way, the need forreducing the satellite densities with baryonic effects or WDM is alleviated.

Massive Milky Way Satellites in Cold and Warm Dark Matter: Dependence on Cosmology