Vol. 545
In section 1. Letters

Discovery of an X-ray cavity near the radio lobes of Cygnus A indicating previous AGN activity

by G. Chon, H. Böhringer, M. Krause, J. Trümper, A&A 545, L3

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The energy injected by quasars in the surrounding environment has profound implications for the evolution of their host galaxy and, ultimately, for their own survival. This process, known in galaxy evolution field as “quasar feedback”, has been advocated to explain many properties of massive galaxies that could not be understood any other way. It is therefore a crucial ingredient of theoretical models. In spite of its importance, little direct observational evidence of such energy deposition has been available so far. This paper represents a major step forward by reporting the identification of a cavity in the distribution of the X-ray emitting plasma of Cyg A (a FRII galaxy showing powerful jets), filled with synchrotron emitting plasma. This cavity is likely to be the fossil record of a previous, much more active quasar phase, so its study will allow better understanding of the feedback process evolution.