The Many Routes to AGN Feedback
  The energy released by Active Galactic Nuclei (AGN) in the form of radiation,
winds, or radio plasma jets, is known to impact on the surrounding interstellar
medium. The result of these processes, known as AGN (negative) feedback, is
suggested to prevent gas, in and around galaxies, from cooling, and to remove,
or at least redistribute, gas by driving massive and fast outflows, hence
playing a key role in galaxy evolution. Given its importance, a large effort is
devoted by the astronomical community to trace the effects of AGN on the
surrounding gaseous medium and to quantify their impact for different types of
AGN. This review briefly summarizes some of the recent observational results
obtained in different wavebands, tracing different phases of the gas. I also
summarize the new insights they have brought, and the constraints they provide
to numerical simulations of galaxy formation and evolution. The recent addition
of deep observations of cold gas and, in particular, of cold molecular gas, has
brought some interesting surprises and has expanded our understanding of AGN
and AGN feedback.
