On the evolution of quasars in clusters and central cluster of galaxies.

Radio-loud quasars are generally found in groups and clusters of galaxies, the richness of which increases with redshift. They are surrounded by dense cooling intracluster gas. We show that Compton cooling of this gas by radiation from the quasar can provide a self-sustaining source of fuel for the most powerful objects. Recent evidence from X-ray observations of clusters that shows strong evolution at the present epoch through the accretion and merger of subclusters is related here to the demise of powerful quasars. The disruption of the intracluster gas in the core of a subcluster containing a quasar leads to the switching off of the quasar. We speculate that the merger of subclusters also leads to the recent evolution of radio-quiet QSO due to disruption of the gas supply.