Statistics of Gas Density, Velocity, and Magnetic Fields in Cool-Core Galaxy Clusters

TL;DR

This study uses 3D MHD simulations to analyze the statistical properties and anisotropies of gas density, velocity, and magnetic fields in cool-core galaxy clusters, revealing scale-dependent anisotropy influenced by magnetic field strength.

Contribution

It provides new insights into the anisotropic turbulence and magnetic field behavior in galaxy clusters, and evaluates the effectiveness of the SIG method for magnetic field tracing.

Findings

Velocity fluctuations follow a 1/2 slope scaling relation.

Magnetic and velocity fluctuations are more anisotropic perpendicular to magnetic fields.

SIG method reliably traces magnetic fields regardless of magnetization level.

Abstract

Understanding turbulence within the Intracluster Medium (ICM) of galaxy clusters is pivotal for comprehending their evolution and dynamics. Employing 3D magnetohydrodynamic (MHD) simulations of galaxy cluster mergers, we examine the statistical properties of gas density, magnetic fields, and velocity, particularly emphasizing the central regions spanning 400 kpc. The simulations are designed to resemble massive cool-core clusters such as Perseus, while varying the initial plasma $\beta$ values (100, 200, and 500). Our findings indicate that while the statistical histogram distributions of gas density and velocity appear similar across different $\beta$ scenarios, their spatial distributions and morphological patterns exhibit noticeable differences. Through the application of the second-order structure function, we identified a scaling relation in velocity fluctuations, characterized by a slope of 1/2 and predominantly dominated by solenoidal components. Furthermore, our analysis reveals a pronounced anisotropy in both velocity and magnetic field fluctuations, with more significant fluctuations along the direction perpendicular to the magnetic fields. This anisotropy is scale-dependent, becoming more pronounced at smaller scales, and exhibits a decreasing trend in scenarios where the magnetic field is relatively weak, particularly at $\beta=500$. This suggests that the anisotropic nature of these fluctuations is predominantly regulated by the magnetic fields. Additionally, we test the efficacy of the Synchrotron Intensity Gradient (SIG) method for tracing magnetic fields in these environments. The SIG shows a global agreement with the magnetic field across all three $\beta$ scenarios, confirming the SIG's insensitivity to the medium's magnetization level.