Characterizing the turbulent multiphase haloes with periodic box simulations

Abstract

ABSTRACT Turbulence in the intracluster medium (ICM) is driven by active galactic nuclei (AGNs) jets, by mergers, and in the wakes of infalling galaxies. It not only governs gas motion but also plays a key role in the ICM thermodynamics. Turbulence can help seed thermal instability by generating density fluctuations, and mix the hot and cold phases together to produce intermediate temperature gas (104–107 K) with short cooling times. We conduct high resolution (3843–7683 resolution elements) idealized simulations of the multiphase ICM and study the effects of turbulence strength, characterized by fturb (0.001–1.0), the ratio of turbulent forcing power to the net radiative cooling rate. We analyse density and temperature distribution, amplitude and nature of gas perturbations, and probability of transitions across the temperature phases. We also study the effects of mass and volume weighted thermal heating and weak ICM magnetic fields. For low fturb, the gas is distribution is bimodal between the hot and cold phases. The mixing between different phases becomes more efficient with increasing fturb, producing larger amounts of the intermediate temperature gas. Strong turbulence (fturb ≥ 0.5) generates larger density fluctuations and faster cooling, The rms logarithmic pressure fluctuation scaling with Mach number $\sigma _{\ln {\bar{P}}}^2\approx \ln (1+b^2\gamma ^2\mathcal {M}^4)$ is unaffected by thermal instability and is the same as in hydro turbulence. In contrast, the density fluctuations characterized by $\sigma _s^2$ are much larger, especially for $\mathcal {M}\lesssim 0.5$. In magnetohydrodynamic runs, magnetic fields provide significant pressure support in the cold phase but do not have any strong effects on the diffuse gas distribution, and nature and amplitude of fluctuations.