Sunyaev-Zel'dovich-effect

The Sunyaev-Zel’dovich effect describes a tiny transfer of thermal or kinetic energy from the hot intra-cluster medium of a galaxy cluster to the cold cosmic microwave background. It is a tool for detecting clusters of galaxies out to very high redshift, and provides a diagnostic of the relationship between temperature and mass of clusters. In addition, the kinetic Sunyaev-Zel’dovich effect arises due to a minuscule transfer of kinetic energy from the galaxy cluster’s electrons to the CMB photons, if the cluster is not at rest in a frame in which the CMB appears isotropic.