Heating Hot Atmospheres with Active Galactic Nuclei

Abstract

High resolution X-ray spectroscopy of the hot gas in galaxy clusters has shown that the gas is not cooling to low temperatures at the predicted rates of hundreds to thousands of solar masses per year. X-ray images have revealed giant cavities and shock fronts in the hot gas that provide a direct and relatively reliable means of measuring the energy injected into hot atmospheres by active galactic nuclei (AGN). Average radio jet powers are near those required to offset radiative losses and to suppress cooling in isolated giant elliptical galaxies, and in larger systems up to the richest galaxy clusters. This coincidence suggests that heating and cooling are coupled by feedback, which suppresses star formation and the growth of luminous galaxies. How jet energy is converted to heat and the degree to which other heating mechanisms are contributing, eg. thermal conduction, are not well understood. Outburst energies require substantial late growth of supermassive black holes. Unless all of the approximately 10E62 erg required to suppress star formation is deposited in the cooling regions of clusters, AGN outbursts must alter large-scale properties of the intracluster medium.Comment: 60 pages, 12 figures, to appear in 1997 Annual Reviews of Astronomy and Astrophysics. This version supersedes the April 2007 version in Reviews in Advance (references and minor corrections were added), and is similar to the one scheduled to appear in Volume 45 of ARA

Interplay Among Cooling, Agn Feedback, and Anisotropic Conduction in the Cool Cores of Galaxy Clusters

“…Moreover, it is difficult for the Bondi accretion to explain higher-power jets, for which other mechanisms are required (e.g., McNamara et al 2011). As has been discussed by various authors, the simple Bondi accretion has many theoretical difficulties (e.g., Pizzolato & Soker 2005;McNamara & Nulsen 2007;Gaspari et al 2011Gaspari et al , 2013Hobbs et al 2012;Yang et al 2012b). Despite these shortcomings, Bondi accretion cannot be ruled out as it could still play a role in some systems, particularly in low-power jets (Russell et al 2014) or in systems where cold gas is depleted (Gaspari et al 2015).…”

“…This implies that the radiative losses in cluster cores are balanced by some heating mechanisms, the most promising among which is feedback from active galactic nuclei (AGNs; see McNamara & Nulsen 2007, for a review). This scenario is supported by the occurrence of AGN jet-inflated X-ray cavities within all CC clustersand the fact that the cavity power (which approximates the AGN jet power) correlates with the core X-ray luminosity, suggestingthat a feedback cycle is at work (Rafferty et al 2006).…”

The Co-Evolution of Galaxies and Black Holes: Current Status and Future Prospects

“…The most direct evidence comes from observations of the cavities evacuated in the hot gas in the cores of galaxy clusters by radio sources (e.g., Fabian et al 2006;Birzan et al 2004;McNamara & Nulsen 2007). The sizes of the cavities and the measured gas pressure allows the amount of P ΔV work done by the radio source to be calculated, while the sound-crossing time of the cavity gives a characteristic time scale.…”

Constraints on Feedback in the Local Universe: The Relation Between Star Formation and Agn Activity in Early-Type Galaxies

“…This theoretical picture has been supported by numerous observations. The strongest evidence comes from the brightest cluster galaxies (BCGs) of cool core clusters, whose powerful radio jets have swept out cavities in the intracluster medium (ICM; Rosner & Tucker 1989;Allen et al 2001;McNamara & Nulsen 2007), while in some individual galaxies, energy transportation into the ISM via AGN-driven outflows is observed to remove gas from the central regions of the galaxy (Crenshaw et al 2003;Nesvadba et al 2007;Alexander et al 2010;Morganti et al 2013). All these show the negative effect of AGN feedback by removing/heating up the gas and eventually suppressing the star formation and regulating the galaxy growth.…”