We present a new analysis of the Aquarius simulations done in combination with a semi-analytic galaxy formation model .
Our goal is to establish whether the subhalos present in \Lambda CDM simulations of Milky Way-like systems could host the dwarf spheroidal ( dSph ) satellites of our Galaxy .
Our analysis shows that , contrary to what has been assumed in most previous work , the mass profiles of subhalos are generally not well fit by NFW models but that Einasto profiles are preferred .
We find that for shape parameters \alpha = 0.2 - 0.5 and v _ { max } = 10 - 30 km/s there is very good correspondence with the observational constraints obtained for the nine brightest dSph of the Milky Way .
However , to explain the internal dynamics of these systems as well as the number of objects of a given circular velocity the total mass of the Milky Way should be \sim 8 \times 10 ^ { 11 } M _ { \odot } , a value that is in agreement with many recent determinations , and at the low mass end of the range explored by the Aquarius simulations .
Our simulations show important scatter in the number of bright satellites , even when the Aquarius Milky Way-like hosts are scaled to a common mass , and we find no evidence for a missing population of massive subhalos in the Galaxy .
This conclusion is also supported when we examine the dynamics of the satellites of M31 .