Evolution of Kinetic and Magnetic Energy in Intra Cluster Media

TL;DR

This paper investigates the evolution of kinetic and magnetic energies in the intra-cluster medium using simulations and analytical models, revealing how magnetic fields influence plasma turbulence and energy spectra.

Contribution

It introduces a combined simulation and analytical approach to understand magnetic and kinetic energy spectra in ICM turbulence, highlighting the role of small-scale magnetic energy in dynamo processes.

Findings

Magnetic fields are amplified through plasma motion and cascade to diffusivity scales.

Kinetic energy spectrum follows a $k^{-3}$ power law, while magnetic energy follows a $k^{-1/2}$ law.

Small-scale magnetic energy plays a significant role in dynamo action.

Abstract

Intra Cluster Media (ICMs) located at galaxy clusters is in the state of hot, tenuous, magnetized, and highly ionized X-ray emitting plasmas. This overall collisionless, viscous, and conductive magnetohydrodynamic (MHD) turbulence in ICM is simulated using hyper and physical magnetic diffusivity. The results show that fluctuating random plasma motion amplifies the magnetic field, which cascades toward the diffusivity scale passing through the viscous scale. The kinetic eddies in the subviscous scale are driven and constrained by the magnetic tension which finally gets balanced with the highly damping effect of the kinetic eddies. However, the saturated kinetic energy spectrum is deeper than that of the incompressible or compressible hydrodynamics fluid. To explain this unusual field profile we set up two simultaneous differential equations for the kinetic and magnetic energy spectrum using an Eddy Damped Quasi Normal Markovianized (EDQNM) approximation. The analytic solution tells us that the magnetic energy in addition to the viscous damping effect constrains the plasma motion leading to the power spectra: kinetic energy spectrum $E_V^k\sim k^{-3}$ and corresponding representative magnetic energy spectrum $E_M^k\sim k^{-1/2}$. Also the comparison of simulation results with different resolutions and magnetic diffusivities implies the role of small scale magnetic energy in dynamo.