Thermal Instability, Star Formation and AGN Feedback in Clusters

Paul Nulsen, Harvard-Smithsonian Center for Astrophysics

The most likely cause for the suppression of copious star formation in clusters with short central cooling times is AGN feedback. In order for feedback to function, the AGN should be fed by cooled or cooling gas. Results will be presented relating star formation to thermal properties of the the intracluster gas, in particular, its cooling time. Star formation is only found in systems that are thermally unstable in the presence of suppressed thermal conduction. This builds the case that the stars are formed from cooled intracluster gas. It also suggests that cooled gas is a source of the fuel for AGN feedback.