Dark Matter in Galaxy Clusters
		• Dynamical estimates of cluster masses – Virial Theorem as we have discussed, but… • Very few clusters exist that can be well done! • E.g, which are cluster members? • Must measure many velocities – Case of Coma • Regular rich cluster, looks like isothermal sphere • Crossing time arguments OK • Virial mass issue for Coma first by Zwicky (1937) • Surface distribution, velocities in next figure…