Datensatz

Zusammenfassung

Active galactic nuclei (AGN) feedback stands for the dramatic impact that a supermassive black hole can make on its environment. It has become an essential element of models that describe the formation and evolution of baryons in massive virialized halos in the universe. The baryons’ radiative losses in the cores of these halos might lead to massive cooling of the gas and vigorous star formation on the order of ∼10–1000 M_⊙ yr⁻¹, whereas observations show that the star formation rates are considerably less (i.e., ∼1–10 M_⊙ yr⁻¹). It has now become clear from an observational, theoretical, and simulation perspective that the activity of central supermassive black holes compensates for gas cooling losses and prevents very high star formation rates in massive galaxies, which otherwise would be much brighter than observed today. While AGN feedback is important over a broad range of halo masses, the most massive objects like galaxy groups and clusters truly provide outstanding laboratories for understanding the intrinsic details of AGN feedback. Partly, this is because in the nearby massive objects, we can directly see what AGN feedback is doing to its surrounding hot halo in exquisite details, as opposed to less massive or distant systems. Yet another reason is that in the most massive objects, the magnitude of AGN feedback has to be extremely large, providing the most stringent constraints on the models. In a nutshell, the AGN feedback paradigm in groups and clusters postulates that (i) a supermassive black hole in the center of a halo can release a vast amount of energy, (ii) this energy can be intercepted and thermalized by the gaseous atmosphere of the halo, and (iii) the system self-regulates so that the black hole energy releases scales with the properties of the halo. A combination of multiwavelength observations, in particular X-ray and radio wavebands, provides compelling evidence of the AGN feedback importance. Similarly, theoretical arguments suggest that self-regulation might be a natural property of a system consisting of the gaseous atmosphere and a black hole at the bottom of the potential well.