On Helium Mixing in Quasi-global Simulations of the Intracluster Medium

Abstract

The assumption of a spatially uniform helium distribution in the intracluster medium can lead to biases in the estimates of key cluster parameters if composition gradients are present. The helium concentration profile in galaxy clusters is unfortunately not directly observable. Current models addressing the putative sedimentation are one-dimensional and parametrize the presence of magnetic fields in a crude way, ignoring the weakly-collisional, magnetized nature of the medium. When these effects are considered, a wide variety of instabilities can play an important role in the plasma dynamics. In a series of recent papers, we have developed the local, linear theory of these instabilities and addressed their non-linear development with a modified version of Athena. Here, we extend our study by developing a quasi-global approach that we use to simulate the mixing of helium as induced by generalizations of the heat-flux-driven buoyancy instability (HBI) and the magneto-thermal instability (MTI), which feed off thermal and composition gradients. In the inner region of the ICM, mixing can occur on few Gyrs, after which the average magnetic field inclination angle is $\sim 45^{\circ }$ resulting in an averaged Spitzer parameter higher by about 20 % than the value obtained in homogeneous simulations. In the cluster outskirts the instabilities are rather inefficient, due to the shallow gradients. This suggests that compositions gradients in cluster cores might be shallower than one-dimensional models predict. More quantitative statements demand more refined models that can incorporate the physics driving the sedimentation process and simultaneously account for the weakly-collisional nature of the plasma.

15 pages, 9 figures, published in ApJ, animation of Figure 5 at http://tberlok.dk/movies/icm_quasi_global.html

References in corpus (18)

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• Hydrodynamic Simulation of Non-thermal Pressure Profiles of Galaxy Clusters
• Buoyancy Instabilities in Weakly Magnetized Low Collisionality Plasmas
• Anisotropic Thermal Conduction and the Cooling Flow Problem in Galaxy Clusters
• Multi-Species Measurements of the Firehose and Mirror Instability Thresholds in the Solar Wind
• Nonlinear growth of firehose and mirror fluctuations in turbulent galaxy-cluster plasmas
• Nonlinear Simulations of the Heat Flux Driven Buoyancy Instability and its Implications for Galaxy Clusters
• Saturation of the Magnetothermal Instability in Three Dimensions
• The Magnetothermal Instability in the Intracluster Medium
• Simulations of MHD Instabilities in Intracluster Medium Including Anisotropic Thermal Conduction
• PIC Simulations of the Effect of Velocity Space Instabilities on Electron Viscosity and Thermal Conduction
• Suppression of thermal conduction in a mirror-unstable plasma
• The Stability of Weakly Collisional Plasmas with Thermal and Composition Gradients
• Plasma Instabilities in the Context of Current Helium Sedimentation Models: Dynamical Implications for the ICM in Galaxy Clusters
• Linear Vlasov theory of a magnetised, thermally stratified atmosphere
• Local Simulations of Instabilities Driven by Composition Gradients in the ICM
• Surprises in astrophysical gasdynamics
• Stability Analysis of Convection in the Intracluster Medium

Cited by in corpus (9)

• Atomic data and spectral modeling constraints from high-resolution X-ray observations of the Perseus cluster with Hitomi
• Radial metal abundance profiles in the intra-cluster medium of cool-core galaxy clusters, groups, and ellipticals
• Enrichment of the hot intracluster medium: observations
• On the Kelvin-Helmholtz instability with smooth initial conditions -- Linear theory and simulations
• Suppressed heat conductivity in the intracluster medium: implications for the magneto-thermal instability
• Braginskii viscosity on an unstructured, moving mesh accelerated with super-time-stepping
• Dynamical properties and detectability of the magneto-thermal instability in the intracluster medium
• On the Helium fingers in the intracluster medium
• Effect of Composition Gradient on Magnetothermal Instability Modified by Shear and Rotation