Subgrid Modeling of AGN‐driven Turbulence in Galaxy Clusters

Scannapieco, Evan; Brüggen, M.

doi:10.1086/591228

Cited by 87 publications

(91 citation statements)

References 96 publications

(146 reference statements)

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“…Our MHD simulations confirm the findings of previous hydrodynamic simulations that AGN-driven turbulence is local and non-volume-filling (Scannapieco & Brüggen 2008;Heinz et al 2010;Gaspari et al 2011;Vazza et al 2013). It is also in agreement with a recent study by Reynolds et al (2015), which showed that the generation of volume-filling turbulence by AGNsrequires that the g-waves are not trapped only within a small area.…”

Section: Hbi With Agnsupporting

confidence: 92%

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

Yang

Reynolds

2016

ApJ

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Feedback from the active galactic nuclei (AGNs) is one of the most promising heating mechanisms to circumvent the cooling-flow problem in galaxy clusters. However, the role of thermal conduction remains unclear. Previous studies have shown that anisotropic thermal conduction in cluster cool cores (CCs) could drive the heat-flux-driven buoyancy instabilities (HBIs) that reorient the field lines in the azimuthal directions and isolate the cores from conductive heating from the outskirts. However, how the AGN interacts with the HBI is still unknown. To understand these interwined processes, we perform the first 3D magnetohydrodynamic simulations of isolated CC clusters that include anisotropic conduction, radiative cooling, and AGN feedback. We find the following: (1) For realistic magnetic field strengths in clusters, magnetic tension can suppress a significant portion of HBI-unstable modes, and thus the HBI is either completely inhibited or significantly impaired, depending on the unknown magnetic field coherence length. (2) Turbulence driven by AGN jets can effectively randomize magnetic field lines and sustain conductivity at ∼1/3 of the Spitzer value; however, the AGN-driven turbulence is not volumefilling. (3) Conductive heating within the cores could contribute to ∼10% of the radiative losses in Perseus-like clusters and up to ∼50% for clusters twice the mass of Perseus. (4) Thermal conduction has various impacts on the AGN activity and intracluster medium properties for the hottest clusters, which may be searched by future observations to constrain the level of conductivity in clusters. The distribution of cold gas and the implications are also discussed.

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Section: Hbi With Agnsupporting

confidence: 92%

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

Yang

Reynolds

2016

ApJ

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“…This closure is based on ideas of Woodward et al (2006) and features a nonlinear term in addition to a linear eddy-viscosity term. In general, the turbulence energy cascade is an important source of SGS turbulence energy production in turbulent flows, and it should not be neglected even if other subresolution sources are emphasized in particular astrophysical applications (e.g., Scannapieco & Brüggen 2008;Joung et al 2009). Our proposed closure for the transfer of energy by the turbulent cascade complements theses models.…”

Section: Resultsmentioning

confidence: 99%

A fluid-dynamical subgrid scale model for highly compressible astrophysical turbulence

Schmidt

Federrath

2011

A&A

110

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Context. Compressible turbulence influences the dynamics of the interstellar and the intergalactic medium over a vast range of length scales. In numerical simulations, phenomenological subgrid scale (SGS) models are used to describe particular physical processes below the grid scale. In most cases, these models do not cover fluid-dynamical interactions between resolved and unresolved scales, or the employed SGS model is not applicable to turbulence in the highly compressible regime. Aims. We formulate and implement the Euler equations with SGS dynamics and provide numerical tests of an SGS turbulence energy model that predicts the turbulent pressure of unresolved velocity fluctuations and the rate of dissipation for highly compressible turbulence. Methods. We tested closures for the turbulence energy cascade by filtering data from high-resolution simulations of forced isothermal and adiabatic turbulence. Optimal properties and an excellent correlation are found for a linear combination of the eddy-viscosity closure that is employed in LES of weakly compressible turbulence and a term that is nonlinear in the Jacobian matrix of the velocity. Using this mixed closure, the SGS turbulence energy model is validated in LES of turbulence with stochastic forcing. Results. It is found that the SGS model satisfies several important requirements: 1. The mean SGS turbulence energy follows a power law for varying grid scale. 2. The root mean square (rms) Mach number of the unresolved velocity fluctuations is proportional to the rms Mach number of the resolved turbulence, independent of the forcing. 3. The rate of dissipation and the turbulence energy flux are constant. Moreover, we discuss difficulties with direct estimates of the turbulent pressure and the dissipation rate on the basis of resolved flow quantities that have recently been proposed. Conclusions. In combination with the energy injection by stellar feedback and other unresolved processes, the proposed SGS model is applicable to a variety of problems in computational astrophysics. By computing the SGS turbulence energy, the treatment of star formation and stellar feedback in galaxy simulations can be improved. Furthermore, we expect that the turbulent pressure on the grid scale affects the stability of gas against gravitational collapse. The influence of small-scale turbulence on emission line broadening, e.g., of O VI, in the intergalactic medium is another potential application.

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“…Churazov et al 2004;Gaspari et al 2011bGaspari et al , 2012b, the evolution of filaments and bubbles (e.g. Scannapieco & Brüggen 2008), or the reacceleration of cosmic rays (e.g. Brunetti & Lazarian 2007).…”

Section: Introductionmentioning

confidence: 99%

The relation between gas density and velocity power spectra in galaxy clusters: High-resolution hydrodynamic simulations and the role of conduction

Gaspari

Churazov

Nagai

et al. 2014

A&A

122

147

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Exploring the power spectrum of fluctuations and velocities in the intracluster medium (ICM) can help us to probe the gas physics of galaxy clusters. Using high-resolution 3D plasma simulations, we study the statistics of the velocity field and its intimate relation with the ICM thermodynamic perturbations. The normalization of the ICM spectrum (related to density, entropy, or pressure fluctuations) is linearly tied to the level of large-scale motions, which excite both gravity and sound waves due to stratification. For a low 3D Mach number M ∼ 0.25, gravity waves mainly drive entropy perturbations, which are traced by preferentially tangential turbulence. For M > 0.5, sound waves start to significantly contribute and pass the leading role to compressive pressure fluctuations, which are associated with isotropic (or slightly radial) turbulence. Density and temperature fluctuations are then characterized by the dominant process: isobaric (low M), adiabatic (high M), or isothermal (strong conduction). Most clusters reside in the intermediate regime, showing a mixture of gravity and sound waves, hence drifting toward isotropic velocities. Remarkably, regardless of the regime, the variance of density perturbations is comparable to the 1D Mach number, M 1D ∼ δρ/ρ. This linear relation allows us to easily convert between gas motions and ICM perturbations (δρ/ρ < 1), which can be exploited by the available Chandra, XMM data and by the forthcoming Astro-H mission. At intermediate and small scales (10-100 kpc), the turbulent velocities develop a tight Kolmogorov cascade. The thermodynamic perturbations (which can be generally described by log-normal distributions) act as effective tracers of the velocity field, in broad agreement with the Kolmogorov-Obukhov-Corrsin advection theory. The cluster radial gradients and compressive features induce a flattening in the cascade of the perturbations. Thermal conduction, on the other hand, acts to damp the thermodynamic fluctuations, washing out the filamentary structures and steepening the spectrum, while leaving the velocity cascade unaltered. The ratio of the velocity and density spectrum thus inverts the downtrend shown by the non-diffusive models, as it widens up to ∼5. This new key diagnostic can robustly probe the presence of conductivity in the ICM. We produce X-ray images of the velocity field, showing how future missions (e.g. Astro-H, Athena) can detect velocity dispersions of a few 100 km s −1 (M > 0.1 in massive clusters), allowing us to calibrate the linear relation and to constrain relative perturbations down to just a few percent.

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Subgrid Modeling of AGN‐driven Turbulence in Galaxy Clusters

Cited by 87 publications

References 96 publications

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

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

A fluid-dynamical subgrid scale model for highly compressible astrophysical turbulence

The relation between gas density and velocity power spectra in galaxy clusters: High-resolution hydrodynamic simulations and the role of conduction

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