Active galactic nucleus feedback in clusters of galaxies

Abstract

Observations made during the last ten years with the Chandra X-ray Observatory have shed much light on the cooling gas in the centers of clusters of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of the hot intracluster medium in cluster centers can feed the supermassive black holes found in the nuclei of the dominant cluster galaxies leading to AGN outbursts which can reheat the gas, suppressing cooling and large amounts of star formation. AGN heating can come in the form of shocks, buoyantly rising bubbles that have been inflated by radio lobes, and the dissipation of sound waves.clusters of galaxies | active galactic nuclei | X-ray observations | Chandra X-ray Observatory C handra observations of cavities in cluster centers in the last decade have brought the issue of feedback to the center stage in astrophysics. Feedback from AGN driven by supermassive black holes in the cores of massive galaxies is now seen as a necessary ingredient to adequately describe the formation and evolution of galaxies and the clusters in which they sometimes reside. The energy injected by AGN is required to produce a galaxy luminosity function in simulations (e.g. ref. 1) that matches observations. This feedback may set the upper limit to the observed masses of galaxies and contributes to cluster preheating and the observed "entropy floors" seen in cluster centers. It may affect scaling relations, such as the relationship between X-ray luminosity and temperature and potentially affects cluster properties that are used for constraining cosmological models, such as the gas mass fraction (e.g. ref.2). Data from the Chandra X-ray Observatory over the last 10 years reveal AGN at work in the centers of clusters, inflating bubbles that rise buoyantly through the intracluster medium (ICM), sometimes producing shocks and sound waves.Many of the most spectacular Chandra images of AGN feedback are of interactions in the centers of cooling flow (sometimes referred to as "cool core") clusters of galaxies. Under the assumption of hydrostatic equilibrium, the X-ray-emitting gas in a cluster is the most dense at the cluster center. The gas will cool as it radiates, and the cooling time is inversely proportional to the density of the gas. Therefore, gas will cool at cluster centers before it cools at larger radii. If the cooling time is shorter than the cluster age, the central gas will cool, lose pressure, and outer gas must flow in to maintain hydrostatic equilibrium (see ref. 3 for a review). Data from earlier X-ray observatories such as Einstein (4), the Roentgen Satellite (ROSAT) (5), and the Advanced Satellite for Cosmology and Astrophysics (ASCA) (6) were used to give estimates of the gas inflow rates of typically hundreds or thousands of solar masses per year. The classic "cooling flow problem" has been that sufficient quantities of cool gas and/or star formation were not detected to match the predictions from the X-ray data.Chandra and XMM-Newton observations have shown that while the gas temperature drops in the ...

A thermally stable heating mechanism for the intracluster medium: turbulence, magnetic fields and plasma instabilities

“…Observationally, a large majority of cool‐core clusters harbour radio sources at their centres, and the AGN energy output inferred from radio‐emitting plasma outflows and cavities is often similar to the X‐ray cooling rate of the central gas (e.g. Blanton et al 2010). However, it may not be necessary for the energy source to be fine‐tuned or tightly self‐regulating.…”

Constraining radio mode feedback in galaxy clusters with the cluster radio AGNs properties to z ∼ 1

“…A number of studies of low redshift clusters have shown that local instabilities due to active galactic nuclei (AGN) outbursts reheat the intracluster medium (ICM) and regulate the cooling in the cluster centre through radio-mode nikhel.gupta@unimelb.edu.au AGN feedback (e.g. McNamara et al 2005;Rafferty et al 2006;Blanton et al 2010;Ogrean et al 2010;Ehlert et al 2011;Bîrzan et al 2012;Gitti et al 2012;Bharadwaj et al 2014;Voit et al 2015;?). There is some evidence of the evolution of AGN feedback in massive field galaxies up to z ∼ 1.3 (Simpson et al 2013), suggesting that the balance between radiative cooling and AGN feedback was achieved in the early universe.…”

Nonlinear excitation of the ablative Rayleigh-Taylor instability for all wave numbers

“…It occurs when a heavy fluid is accelerated against a light fluid and is manifested by the formation of upward rising bubbles of the light fluid and downward sinking spikes of the heavy fluid. Examples include the oceanic meridional overturning circulation [3], buoyant magnetic flux-tubes in the solar corona [4], current sheet reconnection [5], and jet-driven lobes in the intergalactic cluster medium [6]. RTI also plays a central role in the evolution of supernova (SN) explosions [7].…”