The evolution of X-ray emitting gas in clusters of galaxies

The bremsstrahlung cooling process in X-ray clusters is studied using a simple model. Only for a restricted range of initial conditions can the atmospheres in rich clusters of galaxies have undergone substantial cooling without leaving excessive present X-ray luminosities. From observational data it is then found that it is unlikely that clusters can have gone through a high-temperature cooling phase since z = 3. It is concluded either that clusters of galaxies must have formed with little gas in their cores or that such gas was dispersed before cooling occurred. (author)