DOES THE BARYON FRACTION IN CLUSTERS IMPLY AN OPEN UNIVERSE

Clusters are the largest objects in the universe where one can measure both the total baryonic mass and the total mass. Under the assumption that the baryonic mass fraction of clusters should be equal to the universal value, it has been argued that comparing the baryonic mass fraction of clusters to the value derived by nucleosynthesis constraints requires an open universe. We test these arguments using numerical simulations. We find that the cluster total masses are underestimated and that the baryons are more concentrated in clusters. These two effects together reconcile the observed cluster baryonic mass fraction with a flat universe.