Wide-field surveys have been highly successful in testing ΛCDM in the linear regime to the extent that future surveys have been proposed to explore the nature of dark energy (Seo & Eisenstein 2003). We can now extend this powerful methodology to resolved studies of galaxy formation and evolution over cosmic time.
Computer simulations of how the Big Bang unfolded over 13.7 Gyr to yield present-day galaxies can involve up to 10 billion particles. These computations yield structures that look a good deal like real galaxies and clusters of galaxies, adding to the evidence that our picture for the evolution of the universe is on the right track. But close examination of nearby galaxies shows discrepancies with what the simulations might lead one to expect. For example, CDM models predict higher concentrations of dark matter than is believed to exist in the high surface-brightness cores of galaxies. Some of the best evidence to date has come from attempts to construct self-consistent models of the Galactic bulge (for a progress report, see Binney ). A key conclusion is that baryons dominate everywhere within the Solar Circle, in sharp conflict with almost all CDM simulations.
A more sensitive test of the CDM model however requires that we greatly increase the kinematic samples in galaxy cores beyond the Galaxy (Gilmore et al 2006). Thus, future wide-field and pencil-beam Galactic surveys will be necessary in order to continue to challenge CDM calculations in the non-linear regime.