  We propose a simple model for the formation of dwarf spheroidal galaxies, in
which stars are assumed to have formed from isothermal gas in hydrostatic
equilibrium inside extended dark matter halos. After expelling the leftover
gas, the stellar system undergoes a dynamical relaxation inside the dark matter
halo. These models can adequately describe the observed properties of three
(Draco, Sculptor, and Carina) out of four Galactic dwarf spheroidal satellites
studied in this paper. We suggest that the fourth galaxy (Fornax), which cannot
be fitted well with our model, is observed all the way to its tidal radius. Our
best fitting models have virial masses of ~10^9 M_Sun, halo formation redshifts
consistent with the age of oldest stars in these dwarfs, and shallow inner dark
matter density profiles (with slope gamma -0.5...0). The inferred temperature
of gas is ~10^4 K. In our model, the "extratidal" stars observed in the
vicinity of some dwarf spheroidal galaxies are gravitationally bound to the
galaxies and are a part of the extended stellar halos. The inferred virial
masses make Galactic dwarf spheroidals massive enough to alleviate the "missing
satellites" problem of LCDM cosmologies.
