A Heating Mechanism via Magnetic Pumping in the Intracluster Medium

Abstract

Turbulence driven by AGN activity, cluster mergers and galaxy motion constitutes an attractive energy source for heating the intracluster medium (ICM). How this energy dissipates into the ICM plasma remains unclear, given its low collisionality and high magnetization (precluding viscous heating by Coulomb processes). Kunz et al. 2011 proposed a viable heating mechanism based on the anisotropy of the plasma pressure (gyroviscous heating) under ICM conditions. The present paper builds upon that work and shows that particles can be gyroviscously heated by large-scale turbulent fluctuations via magnetic pumping. We study how the anisotropy evolves under a range of forcing frequencies, what waves and instabilities are generated and demonstrate that the particle distribution function acquires a high energy tail. For this, we perform particle-in-cell simulations where we periodically vary the mean magnetic field $\text{B}(t)$. When $\text{B}(t)$ grows (dwindles), a pressure anisotropy $P_{\perp }>P_{\parallel }$ ($P_{\perp }<P_{\parallel }$) builds up ($P_{\perp }$ and $P_{\parallel }$ are, respectively, the pressures perpendicular and parallel to $\text{B}(t)$). These pressure anisotropies excite mirror ($P_{\perp }>P_{\parallel }$) and oblique firehose ($P_{\parallel }>P_{\perp }$) instabilities, which trap and scatter the particles, limiting the anisotropy and providing a channel to heat the plasma. The efficiency of this mechanism depends on the frequency of the large-scale turbulent fluctuations and the efficiency of the scattering the instabilities provide in their nonlinear stage. We provide a simplified analytical heating model that captures the phenomenology involved. Our results show that this process can be relevant in dissipating and distributing turbulent energy at kinetic scales in the ICM.

24 pages, 17 figures, submitted to ApJ

References in corpus (8)

• Turbulent Heating in Galaxy Clusters Brightest in X-rays
• Electron Heating by the Ion Cyclotron Instability in Collisionless Accretion Flows. I. Compression-Driven Instabilities and the Electron Heating Mechanism
• Ultraviolet Morphologies and Star-Formation Rates of CLASH Brightest Cluster Galaxies
• Nonlinear mirror instability
• Dissipation in intercluster plasma
• Magnetic pumping as a source of particle heating and power-law distributions in the solar wind
• Proton fire hose instabilities in the expanding solar wind
• Stochastic Electron Acceleration by the Whistler Instability in a Growing Magnetic Field

Cited by in corpus (6)

• Recent Progress in Modeling the Macro- and Micro-Physics of Radio Jet Feedback in Galaxy Clusters
• Nonlinear aspects of stochastic particle acceleration
• Thermal conductivity with bells and whistlers: suppression of the magnetothermal instability in galaxy clusters
• Electron Re-acceleration via Ion Cyclotron Waves in the Intracluster Medium
• Electron Heating in the Trans-Relativistic Perpendicular Shocks of Tilted Accretion Flows
• Constraints on dark matter annihilation and turbulent reacceleration set by high-frequency observations of the radio halo in the Coma cluster