Abstract
One of the major current problems in black hole demography is to understand the feedback phenomena of AGNs. Throughout the Universe, the history of star formation parallels the growth of black hole mass. Is this a problem of simultaneous feeding, or feedback, and is the latter really effective, positive or negative? However, the small number of very massive galaxies can only be explained by the feedback effect of AGNs, i.e. the suppression of star formation. Cosmological simulations without AGN feedback overestimate the mass function of galaxies on the higher-mass side.
There are two modes of feedback: winds from the disk, for non-radio quasars, or radio jets, for the less frequent and less luminous ones. The wind is emitted by quasars with high accretion and near-Eddington luminosity, when radiation pressure compensates for, and exceeds, the force of gravity. Efficient feedback diagnostics are observed particularly in galaxy clusters, where hot intragalactic gas cools and feeds an AGN in the central galaxy. The radio jet emits bubbles in the X-ray gas, hollowing out cavities and moderating the cooling of the gas and the feeding of the AGN. Recently, streams of molecular gas are frequently observed in galaxies hosting AGNs and star-forming outbreaks. Statistical relationships of their energy and momentum properties show that they are conservers of energy rather than momentum, and are therefore very effective at repelling cold gas and stopping star formation. Simulations show that there is feedback, both positive and negative.
