Feedback from Active Galactic Nuclei in Galaxy Groups
  The co-evolution between supermassive black holes and their environment is
most directly traced by the hot atmospheres of dark matter halos. Cooling of
the hot atmosphere supplies the central regions with fresh gas, igniting active
galactic nuclei (AGN) with long duty cycles. Outflows from the central engine
tightly couple with the surrounding gaseous medium and provide the dominant
heating source preventing runaway cooling by carving cavities and driving
shocks across the medium. The AGN feedback loop is a key feature of all modern
galaxy evolution models. Here we review our knowledge of the AGN feedback
process in the specific context of galaxy groups. Galaxy groups are uniquely
suited to constrain the mechanisms governing the cooling-heating balance.
Unlike in more massive halos, the energy supplied by the central AGN to the hot
intragroup medium can exceed the gravitational binding energy of halo gas
particles. We report on the state-of-the-art in observations of the feedback
phenomenon and in theoretical models of the heating-cooling balance in galaxy
groups. We also describe how our knowledge of the AGN feedback process impacts
on galaxy evolution models and on large-scale baryon distributions. Finally, we
discuss how new instrumentation will answer key open questions on the topic.
