A possible formation scenario for dwarf spheroidal galaxies - I. Fiducial model

We perform numerical simulations to study a formation scenario for dwarf spheroidal (dSph) galaxies in which their stellar populations are the products of the dissolution of open star clusters and stellar associations within cosmological dark matter haloes. This paper shows that this process gives rise to objects which resemble the observed dSph satellites of the Milky Way without invoking external influences. The presence of long-lived kinematic substructures within the stellar components of these objects affects their projected velocity dispersions. We find that this in turn affects mass estimates based on the projected velocity dispersion profiles which may overestimate the actual dark matter halo mass depending on the amount of substructure which is present. Our models make predictions about the detailed kinematic and photometric properties of the dSphs which can be tested using future observations.