Characterising the turbulent multiphase halos with periodic box simulations

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 (10 4 -10 7 K) with short cooling times. We conduct high resolution (384 3 -768 3 resolution elements) idealised simulations of the multiphase ICM and study the effects of turbulence strength, characterised by 𝑓 turb (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 𝑓 turb , the gas is distribution is bimodal between the hot and cold phases. The mixing between different phases becomes more efficient with increasing 𝑓 turb , producing larger amounts of the intermediate temperature gas. Strong turbulence ( 𝑓 turb ≥ 0.5) generates larger density fluctuations and faster cooling, and ultimately supersonic gas motions. The rms logarithmic pressure fluctuation scaling with Mach number 𝜎 2 ln P ≈ ln 1 + 𝑏 2 𝛾 2 M 4 is unaffected by thermal instability and is the same as in hydro turbulence. In contrast, the density fluctuations characterised by 𝜎 2 𝑠 are much larger, especially for M 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.

Velocity structure functions in multiphase turbulence: interpreting kinematics of Hα filaments in cool-core clusters

“…We analyse the second-order velocity structure functions (VSF 2 ) in these simulations and study the effects of varying spatial resolution, the introduction of magnetic fields, and the effect of projection along the line of sight (LOS) on it. In the second part of the study, we analyse high-resolution (768 3 resolution elements) idealised simulations of multiphase turbulence in the intracluster medium (ICM) from Mohapatra et al (2021a). We compare the VSF 2 for both the hot (𝑇 ∼ 10 7 K) and cold (𝑇 ∼ 10 4 K) phases and find that their amplitude depends on the density contrast between the phases.…”

Velocity structure functions in multiphase turbulence: interpreting kinematics of H$α$ filaments in cool core clusters

“…We also quantify the effects of magnetic fields and projection along the LOS on the VSFs. In the second part, we analyse the high resolution multiphase ICM turbulence simulations from Mohapatra et al (2021a) (hereafter M21). In these runs we study the VSFs of the hot and cold phases separately.…”

“…We analyse the second-order velocity structure functions (VSF 2 ) in these simulations and study the effects of varying spatial resolution, the introduction of magnetic fields, and the effect of projection along the line of sight (LOS) on the VSF 2 . In the second part of the study, we analyse high-resolution (768 3 resolution elements) idealised simulations of multiphase turbulence in the intracluster medium (ICM) from Mohapatra et al (2021a). We compare VSF 2 for both the hot (𝑇 ∼ 10 7 K) and cold (𝑇 ∼ 10 4 K) phases.…”