What gravitational requirement infers dark matter presence via the ICM?

A gravitational potential well deep enough to trap hot gas

The existence of dark matter within galaxy clusters is strongly inferred by analyzing the state of the intracluster medium (ICM). The ICM is superheated, achieving temperatures in the range of tens of millions of degrees Celsius. For gas at such extreme kinetic energies to remain gravitationally bound within the cluster structure, rather than escaping into intergalactic space, the cluster must possess a tremendously deep gravitational potential well. Calculations based solely on the visible baryonic matter (stars and gas luminosity) do not provide sufficient gravitational pull. Therefore, the necessity of a potential well deep enough to confine this high-temperature gas serves as direct evidence for the presence of the immense, unseen mass supplied by dark matter.