Observational Evidence of Active Galactic Nuclei Feedback

Abstract

Radiation, winds and jets from the active nucleus of a massive galaxy can interact with its interstellar medium leading to ejection or heating of the gas. This can terminate star formation in the galaxy and stifle accretion onto the black hole. Such Active Galactic Nucleus (AGN) feedback can account for the observed proportionality between central black hole and host galaxy mass. Direct observational evidence for the radiative or quasar mode of feedback, which occurs when the AGN is very luminous, has been difficult to obtain but is accumulating from a few exceptional objects. Feedback from the kinetic or radio mode, which uses the mechanical energy of radio-emitting jets often seen when the AGN is operating at a lower level, is common in massive elliptical galaxies. This mode is well observed directly through X-ray observations of the central galaxies of cool core clusters in the form of bubbles in the hot surrounding medium. The energy flow, which is roughly continuous, heats the hot intracluster gas and reduces radiative cooling and subsequent star formation by an order of magnitude. Feedback appears to maintain a long-lived heating/cooling balance. Powerful, jetted radio outbursts may represent a further mode of energy feedback which affect the cores of groups and subclusters. New telescopes and instruments from the radio to X-ray bands will come into operation over the next few years and lead to a rapid expansion in observational data on all modes of AGN feedback.

ALMA observations of cold molecular gas filaments trailing rising radio bubbles in PKS 0745−191

“…The prevalence of short central radiative cooling times in cluster atmospheres and strong correlations with detections of cold gas, star formation and Hα emission suggest that cooling is long-lived Fabian 2012). Studies of the fraction of cool core clusters with radio bubbles and central radio sources suggest that the duty cycle of AGN activity in BCGs is at least 70% (Dunn & Fabian 2006, 2008Bîrzan et al 2012).…”

“…10; Rafferty et al 2006;Sanders et al 2014). The AGN has inflated two large radio bubbles detected as cavities in the X-ray emission where the radio lobes have displaced the cluster's hot atmosphere (McNamara & Nulsen 2007;Fabian 2012;.…”

The jet feedback mechanism (JFM) in stars, galaxies and clusters

“…The processes that were considered favorable until the year 2012 are summarized by Fabian (2012) and . list the following heating mechanisms that were studied (references are given there): shocks, sound waves, and cosmic rays leakage.…”

“…There is a large body of literature on feedback processes during the epoch of galaxy formation, including feedback from stars, mainly through supernovae, and from AGN, by radiation and/or jets/outflows (e.g., Cattaneo et al 2009;Alexander & Hickox 2012;Fabian 2012;Kormendy & Ho 2013;Heckman & Best 2014;King & Pounds 2015; Tadhunter 2016 for reviews, and, e.g., Wagner et al 2016;Bongiorno et al 2016;Weinberger et al 2016 for recent papers on the AGN-JFM). In this section I review only the AGN-JFM, and concentrate only on processes that are related to other objects that are reviewed here, in particular to cooling flows in clusters of galaxies.…”

Implications of coronal line emission in NGC 4696*

“…The X-ray-emitting hot intracluster medium (ICM) at the centres of cool core clusters of galaxies can have cooling times shorter than a Hubble time (see, e.g., Fabian 2012). Heating, most likely from active galactic nuclei (AGN) feedback, prevents catastrophic cooling.…”