Multiscale analysis of turbulence evolution in the density-stratified intracluster medium

Shi, Xun; Nagai, Daisuke; Lau, Erwin T.

doi:10.1093/mnras/sty2340

Cited by 33 publications

(39 citation statements)

References 57 publications

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“…Zhang et al 2016), this final reversal may never be reached. Thus, in this scenario, an increasing turbulence amplitude with radius is the generic state of the ICM, in accordance with the previous numerical results of ICM turbulence (Lau et al 2009;Battaglia et al 2012;Nelson et al 2014;Shi et al 2018).…”

Section: Global Variations Of Gas Density and Gravitational Potentialsupporting

confidence: 92%

“…The inclusion of gravitational potential flattening may help maintain the positive dependence of turbulence amplitude on cluster radius for a longer time (t ∼ Gyr), during which turbulence kinetic energy decays at a time scale characterized by the buoyancy time 1/N BV . This is potentially the underlying physics for the faster turbulence decay in the inner ICM regions discovered by Shi et al (2018), and that for the increasing turbulence amplitude observed in cosmological numerical simulations.…”

Section: Discussionmentioning

confidence: 76%

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Turbulence decay in the density-stratified intracluster medium

Shi

Zhang

2019

Monthly Notices of the Royal Astronomical Society

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Turbulence evolution in a density-stratified medium differs from that of homogeneous isotropic turbulence described by the Kolmogorov picture. We evaluate the degree of this effect in the intracluster medium (ICM) with hydrodynamical simulations. We find that the buoyancy effect induced by ICM density stratification introduces qualitative changes to the turbulence energy evolution, morphology, and the density fluctuation -turbulence Mach number relation, and likely explains the radial dependence of the ICM turbulence amplitude as found previously in cosmological simulations. A new channel of energy flow between the kinetic and the potential energy is opened up by buoyancy. When the gravitational potential is kept constant with time, this energy flow leaves oscillations to the energy evolution, and leads to a balanced state of the two energies where both asymptote to power-law time evolution with slopes shallower than that for the turbulence kinetic energy of homogeneous isotropic turbulence. We discuss that the energy evolution can differ more significantly from that of homogeneous isotropic turbulence when there is a time variation of the gravitational potential. Morphologically, ICM turbulence can show a layered vertical structure and large horizontal vortical eddies in the central regions with the greatest density stratification. In addition, we find that the coefficient in the linear density fluctuation -turbulence Mach number relation caused by density stratification is in general a variable with position and time.

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Section: Global Variations Of Gas Density and Gravitational Potentialsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 76%

Turbulence decay in the density-stratified intracluster medium

Shi

Zhang

2019

Monthly Notices of the Royal Astronomical Society

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“…This result is particularly important since it indicates that, in the inner regions of relaxed clusters, turbulence is dominated by buoyancy forces and regulated by the Brunt-Väisälä frequency. Recently Shi et al (2018), from an adiabatic simulation of a single cluster, obtained similar values for the Froude number in the cluster inner high density region. Turbulent velocities were extracted by applying a wavelet analysis, so that their result provides an independent confirmation of our values for the Froude number.…”

Section: An Individual Study Of a Very Relaxed Clustermentioning

confidence: 59%

A Multifiltering Study of Turbulence in a Large Sample of Simulated Galaxy Clusters

Valdarnini

2019

ApJ

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We present results from a large set of N-body/SPH hydrodynamical cluster simulations aimed at studying the statistical properties of turbulence in the ICM. The numerical hydrodynamical scheme employs a SPH formulation in which gradient errors are strongly reduced by using an integral approach. We consider both adiabatic and radiative simulations. We construct clusters subsamples according to the cluster dynamical status or gas physical modeling, from which we extract small-scale turbulent velocities obtained by applying to cluster velocities different multiscale filtering methods. The velocity power spectra of non-radiative relaxed clusters are mostly solenoidal and exhibit a peak at wavenumbers set by the injection scales ≃ r 200 /10, at higher wavenumbers the spectra are steeper than Kolgomorov. Cooling runs are distinguished by much shallower spectra, a feature which we interpret as the injection of turbulence at small scales due to the interaction of compact cool gas cores with the ICM. Turbulence in galaxy clusters is then characterized by multiple injection scales, with the small scale driving source acting in addition to the large scale injection mechanisms. Cooling runs of relaxed clusters exhibit enstrophy profiles with a power-law behavior over more than two decades in radius, and a turbulent-to-thermal energy ratio < ∼ 1%. In accord with Hitomi observations, in the core of a highly relaxed cluster we find low level of gas motions. In addition, the estimated cluster radial profile of the sloshing oscillation period is in very good agreement with recent Fornax measurements, with the associated Froude number satisfying F r < ∼ 0.1 within r/r 200 < ∼ 0.1. Our findings suggest that in cluster cores ICM turbulence approaches a stratified anisotropic regime, with weak stirring motions dominated by gravity buoyancy forces and strongly suppressed along the radial direction. We conclude that turbulent heating cannot be considered the main heating source in cluster cores.

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“…The exact scaling would depend on dynamical circumstances analogous to the scaling for B itself. Nonetheless, we would expect from dynamical "similarity" arguments that L int would usually increase towards the cluster outskirts (e.g., Shi et al 2018). As discussed in the main text, we express this behavior in terms of a density scaling as a convenient proxy.…”

Section: A2 Some Power Spectrum Issuesmentioning

confidence: 99%

Characterizing the Uncertainty in Cluster Magnetic Fields Derived from Rotation Measures

Johnson

Rudnick

Jones

et al. 2020

ApJ

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Magnetic fields play vital roles in intracluster media (ICMs), but estimating their strengths and distributions from observations is a major challenge. Faraday rotation measures (RMs) are widely applied to this task, so it is critical to understand inherent uncertainties in RM analysis. In this paper, we seek to characterize those uncertainties given the types of information available today, independent of the specific technique used. We conduct synthetic RM observations through the ICM of a galaxy cluster drawn from an MHD cosmological simulation in which the magnetic field is known. We analyze the synthetic RM observations using an analytical formalism based on commonly used model assumptions allowing us to relate model physical variables to outcome uncertainties. Despite the simplicity of some assumptions, and unknown physical parameters, we are able to extract an approximate magnitude of the central magnetic field within an apparently irreducible uncertain factor ≈ 3. Principal, largely irreducible, uncertainties come from the unknown depth along the line of sight of embedded polarized sources, the lack of robust coherence lengths from area-constrained polarization sampling, and the unknown scaling between ICM electron density and magnetic field strength. The RM-estimated central magnetic field strengths span more than an order of magnitude including the full range of synthetic experiments.

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Multiscale analysis of turbulence evolution in the density-stratified intracluster medium

Cited by 33 publications

References 57 publications

Turbulence decay in the density-stratified intracluster medium

Turbulence decay in the density-stratified intracluster medium

A Multifiltering Study of Turbulence in a Large Sample of Simulated Galaxy Clusters

Characterizing the Uncertainty in Cluster Magnetic Fields Derived from Rotation Measures

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