The dance of heating and cooling in galaxy clusters: three-dimensional simulations of self-regulated active galactic nuclei outflows

Abstract

It is now widely accepted that heating processes play a fundamental role in galaxy clusters, struggling in an intricate but fascinating 'dance' with its antagonist, radiative cooling. Lastgeneration observations, especially X-ray, are giving us tiny hints about the notes of this endless ballet. Cavities, shocks, turbulence and wide absorption lines indicate that the central active nucleus is injecting a huge amount of energy in the intracluster medium. However, which is the real dominant engine of self-regulated heating? One of the models we propose is massive subrelativistic outflows, probably generated by a wind disc or just the result of the entrainment on kpc scale by the fast radio jet. Using a modified version of the adaptive mesh refinement code FLASH 3.2, we have explored several feedback mechanisms that self-regulate the mechanical power. Two are the best schemes that answer our primary question, that is, quenching cooling flow and at the same time preserving a cool core appearance for a long-term evolution (7 Gyr): one is more explosive (with efficiencies ∼ 5 × 10 −3 -10 −2 ), triggered by central cooled gas, and the other is gentler, ignited by hot gas Bondi accretion (with = 0.1). These three-dimensional simulations show that the total energy injected is not the key aspect, but the results strongly depend on how energy is given to the intracluster medium. We follow the dynamics of the best models (temperature, density, surface brightness maps and profiles) and produce many observable predictions: buoyant bubbles, ripples, turbulence, iron abundance maps and hydrostatic equilibrium deviation. We present an in-depth discussion of the merits and flaws of all our models, with a critical eye towards observational concordance.

A Mechanism for Stimulating Agn Feedback by Lifting Gas in Massive Galaxies

“…The metal-rich columns of gas extending tens to hundreds of kiloparsecs in elevation are thought to trace hot flows lifted outward by radio bubbles (Simionescu et al 2008;Kirkpatrick et al 2009Kirkpatrick et al , 2011Werner et al 2010;Werner et al (2011)). This phenomenon is also seen in hydrodynamic simulations where metal-enriched gas in the central galaxy is propelled outward in the updraft of rising bubbles (Pope et al 2010;Gaspari et al 2011). Estimated flow rates of several tens of solar masses per year would be sufficient to account for the observed molecular gas masses.…”

Modeling Active Galactic Nucleus Feedback in Cool-Core Clusters: The Balance Between Heating and Cooling

“…The total amount of cold gas in the last stage is larger in our simulations likely because our model cluster is much more massive than that in Cattaneo & Teyssier (2007). Gaspari et al (2011) studied the momentum-driven AGN feedback with mass-loaded outflows, and also found that the results are not very sensitive to the efficiency in their coldregulated feedback model. Vernaleo & Reynolds (2006) finds that simple hydro jets cannot prevent a cooling catastrophe because most of the energy channels out of the cool core.…”

“…Previous simulations on AGN feedback in cool-core clusters have been focusing on how AGN deposits its energy and whether cooling can be balanced (e.g., Soker et al 2001;Vernaleo & Reynolds 2006;Gaspari et al 2011). It has been found that momentum-driven AGN feedback can indeed suppress cooling over a few Gyr timescale (e.g., Cattaneo & Teyssier 2007;Gaspari et al 2011), and Gaspari et al (2012) has also seen the formation of multiphase gas, suggesting that momentumdriven AGN feedback is a very successful model.…”

“…It has been found that momentum-driven AGN feedback can indeed suppress cooling over a few Gyr timescale (e.g., Cattaneo & Teyssier 2007;Gaspari et al 2011), and Gaspari et al (2012) has also seen the formation of multiphase gas, suggesting that momentumdriven AGN feedback is a very successful model.…”

An examination of magnetized outflows from active galactic nuclei in galaxy clusters

“…Accretion rate calculations can vary from the simple Bondi rate (Bondi 1952) to estimates of viscous angular momentum transport (Debuhr et al 2010) to fully stochastic models (Pope 2007). If the resolution and computing resources permit it, large-scale jets can be placed on the simulation grid with many modifications, including simple fluxes at cell boundaries (Gaspari et al 2011), limited-lifetime jets (Morsony et al 2010), extended jets (Cattaneo & Teyssier 2007), wide-angle jets (Sternberg, Pizzolato & Soker 2007) and precessing jets (Sternberg & Soker 2008;Falceta-Gonçalves et al 2010a). Since jets eventually inflate bubbles, it is easier computationally to simply place already formed bubbles (e.g.…”