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The LambdaCDM simulations predict the presence of far more satellite galaxies than is observed around the Milky Way, and the concept of failed dwarfs has been advanced to rescue the "theory". In this picture, studies of high velocity clouds are debated, but their individual distances are quite uncertain, and they don't indeed seem to have stars (e.g. Simon & Blitz 2002).

The dwarf spheroidal companions of the Milky Way are very important in another way : the smallest ones are dark matter dominated. New data on the Draco system (Kleyna et al. 2002) show that this galaxy is more extended than previously thought; Stoehr et al. (2002) produce a good fit with LambdaCDM. But for Ursa Minor there is a subpopulation of stars with low velocity dispersion. Such a cold clump will survive easily in a cored halo potential, but breaks up rather rapidly in a cusped halo potential (Kleyna et al. 2003).

Finally, modelling the trail of the Sagitarius dwarf galaxy (e.g. Ibata et al. 2001) suggests that the dark halo around the Milky Way is nearly spherical.