Components of Clusters.

The present model of a cluster of galaxies comprises $\sim 100$-$1000$s of galaxies which inhabit a hot ($\sim 10^{6-7}$ K) gas, both of which reside in the potential well of a dark matter halo. Each of these components will now be briefly introduced.

Figure 1.1: The Coma Cluster of Galaxies. Credit: Omar Lopez-Cruz and Ian Shelton NOAO/AURA/NSF