For this paper: postscript 4 Discussion and Conclusion... Abstract... References...

Acknowledgements 

I thank my collaborators, Simon White and Rashid Sunyaev (MPA), for allowing me to present results from our work. Also I am very grateful to Hans Böhringer and Roland Egger for many helpful discussions and to Joachim Trümper (MPE) for supporting the ROSAT observation. I further thank Alastair Edge, Andrew Fabian, Mike Jones and Richard Saunders for useful discussion. The ROSAT project has been supported by the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF/DARA) and by the Max-Planck-Society.