Are the inner cores of galaxy clusters dominated by dark matter

One of the basic assumptions used in the study of the dark matter in clusters of galaxies (essentially any nonluminous mass source: massive neutrinos, axions, blackholes, bricks) is that this matter has a distribution similar to the galaxies--galaxies are ''good'' tracers of the dark matter. Unfortunately, when using galaxies, determination of the distribution of the dark matter in the cores of the cluster is very uncertain. Furthermore, the assumption that galaxies are good tracers will be violated at small enough scales where galaxies begin to interact. Therefore, new types of tracers are necessary