  We investigate the formation and evolution of satellite galaxies using
smoothed particle hydrodynamics (SPH) simulations of a Milky Way(MW)-like
system, focussing on the best resolved examples, analogous to the classical MW
satellites. Comparing with a pure dark matter simulation, we find that the
condensation of baryons has had a relatively minor effect on the structure of
the satellites' dark matter halos. The stellar mass that forms in each
satellite agrees relatively well over three levels of resolution (a factor of
~64 in particle mass) and scales with (sub)halo mass in a similar way in an
independent semi-analytical model. Our model provides a relatively good match
to the average luminosity function of the MW and M31. To establish whether the
potential wells of our satellites are realistic, we measure their masses within
observationally determined half-light radii, finding that the most massive
examples have somewhat higher mass-to-light ratios than those derived for the
MW dSphs from stellar kinematic data. A statistical test yields a ~9 percent
probability that the simulated and observationally derived distributions of
masses are consistent. Our results may suggest that either the MW halo is less
massive than assumed in our simulations (~1.4e12 M_sun) or that there is
substantial scatter in the satellite luminosity function or distribution of
mass-to-light ratios at fixed host halo mass. Alternatively, feedback processes
not properly captured by our simulations may have reduced the central densities
of (sub)halos, or the subhalos may have initially formed with lower
concentrations as would be the case, for example, if the dark matter were made
of warm, rather than cold particles.
