Hot and turbulent gas in clusters

Schmidt, Wolfgang; Engels, Jan Frederik; Niemeyer, J. C.; Almgren, Ann S.

doi:10.1093/mnras/stw632

Cited by 26 publications

(66 citation statements)

References 61 publications

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“…Also, we justified using the Smagorinsky model by assuming that the local equilibrium condition holds, where the kinetic energy transfer rate down the turbulent cascade is equal on all scales. While the assumption is approximately true on average in the regimes we investigated (Schmidt et al 2016), a fully-consistent turbulence model involves tracking the sub-grid kinetic energy via an additional transport equation that includes all of the necessary, higher-order, sub-grid scale terms (Schmidt 2015). However, the dynamic model mitigates the issue by inherently calculating the deviations from local equilibrium.…”

Section: Discussionmentioning

confidence: 99%

“…In order for this to be possible, the local equilibrium condition must be approximately true in the regime of interest. We are specifically interested in cosmological-scale gas, and Schmidt et al (2016) show that the local equilibrium condition holds -on average -in a cosmological-scale volume. Introducing the dynamic model on top of these approximations further supports our model assumption, because the dynamic model inherently accounts for the deviations from local equilibrium.…”

Section: Diffusivitymentioning

confidence: 99%

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Dynamic localized turbulent diffusion and its impact on the galactic ecosystem

Rennehan

Babul

Hopkins

et al. 2018

Monthly Notices of the Royal Astronomical Society

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Modelling the turbulent diffusion of thermal energy, momentum, and metals is required in all galaxy evolution simulations due to the ubiquity of turbulence in galactic environments. The most commonly employed diffusion model, the Smagorinsky model, is known to be over-diffusive due to its strong dependence on the fluid velocity shear. We present a method for dynamically calculating a more accurate, locally appropriate, turbulent diffusivity: the dynamic localised Smagorinsky model. We investigate a set of standard astrophysically-relevant hydrodynamical tests, and demonstrate that the dynamic model curbs over-diffusion in non-turbulent shear flows and improves the density contrast in our driven turbulence experiments. In galactic discs, we find that the dynamic model maintains the stability of the disc by preventing excessive angular momentum transport, and increases the metal-mixing timescale in the interstellar medium. In both our isolated Milky Way-like galaxies and cosmological simulations, we find that the interstellar and circumgalactic media are particularly sensitive to the treatment of turbulent diffusion. We also examined the global gas enrichment fractions in our cosmological simulations, to gauge the potential effect on the formation sites and population statistics of Population III stars and supermassive black holes, since they are theorised to be sensitive to the metallicity of the gas out of which they form. The dynamic model is, however, not for galaxy evolution studies only. It can be applied to all astrophysical hydrodynamics simulations, including those modelling stellar interiors, planetary formation, and star formation.

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Section: Discussionmentioning

confidence: 99%

Section: Diffusivitymentioning

confidence: 99%

Dynamic localized turbulent diffusion and its impact on the galactic ecosystem

Rennehan

Babul

Hopkins

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…However, compressible turbulence in astrophysical systems is often found in the intermediate regime (q ∼ w). An important example is the intracluster medium in clusters of galaxies [41,42]. is publicly available on Github.…”

Section: Discussionmentioning

confidence: 99%

Kinetic and internal energy transfer in implicit large-eddy simulations of forced compressible turbulence

Schmidt

Grete

2019

Phys. Rev. E

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We revisit the problem of how energy transfer through the turbulent cascade operates in compressible hydrodynamic turbulence. In general, there is no conservative compressible cascade since the kinetic and internal energy reservoirs can exchange energy through pressure dilatation. Moreover, statistically stationary turbulence at high Mach number can only be maintained in nearly isothermal gas, i.e. if excess heat produced by shock compression and kinetic energy dissipation is continuously removed from the system. We mimic this process by a linear cooling term in numerical simulations of turbulence driven by stochastic forcing. This allows us to investigate turbulence statistics for a broad range of Mach numbers. We compute the rate of change of kinetic and internal energy in wavenumber shells caused by advective, compressive, and pressure dilatation effects and constrain power-law fits to compressible turbulence energy spectra to a range of wavenumbers in which the total energy transfer is close to zero. The resulting scaling exponents are significantly affected by the forcing. Depending on the root mean square Mach number, we find a nearly constant advective component of the cross-scale flux of kinetic energy at intermediate wavenumbers for particular mixtures of solenoidal and compressive modes in the forcing. This suggests the existence of a natural, Mach number dependent mixture of forcing modes. Our findings also support an advection-dominated regime at high Mach numbers with specific scaling exponents (Burgers scaling for the pure velocity fluctuation u and Kolmogorov scaling for the mass-weighted variable v = ρ 1/3 u). * wolfram.schmidt@uni-hamburg.de †

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“…Global refinement by overdensity and vorticity made the simulations extremely resource-intensive, limiting their resolution to 78 kpc. To improve on that and to increase the mass resolution at least for a selected cluster, we centred the box at the density peak of the most massive halo (halo 1 in Table 4 in Schmidt et al 2016; the halo mass is M halo = 6.68 × 10 14 M , its maximal radial extent R halo = 3.24 Mpc, and R500 = 1.04 Mpc). Further analysis revealed that this cluster is the result of a major merger at low redshift.…”

Section: Numerical Methods and Modelsmentioning

confidence: 99%

“…In this article, we revisit the problem of major mergers of cool-core clusters from the perspective of dynamical processes in numerical simulations. We consider the limiting case of gas dynamics with radiative cooling and a homogeneous UV background based on the simulations reported in Schmidt et al (2016), as summarised in the next section. Since no local feedback is applied, gravitational heating, shock compression, and turbulent dissipation are the major sources of thermal energy.…”

Section: Introductionmentioning

confidence: 99%

Viscosity, pressure and support of the gas in simulations of merging cool-core clusters

Schmidt

Byrohl

Engels

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Major mergers are considered to be a significant source of turbulence in clusters. We performed a numerical simulation of a major merger event using nested-grid initial conditions, adaptive mesh refinement, radiative cooling of primordial gas, and a homogeneous ultraviolet background. By calculating the microscopic viscosity on the basis of various theoretical assumptions and estimating the Kolmogorov length from the turbulent dissipation rate computed with a subgrid-scale model, we are able to demonstrate that most of the warm-hot intergalactic medium can sustain a fully turbulent state only if the magnetic suppression of the viscosity is considerable. Accepting this as premise, it turns out that ratios of turbulent and thermal quantities change only little in the course of the merger. This confirms the tight correlations between the mean thermal and non-thermal energy content for large samples of clusters in earlier studies, which can be interpreted as second self-similarity on top of the self-similarity for different halo masses. Another long-standing question is how and to which extent turbulence contributes to the support of the gas against gravity. From a global perspective, the ratio of turbulent and thermal pressures is significant for the clusters in our simulation. On the other hand, a local measure is provided by the compression rate, i.e. the growth rate of the divergence of the flow. Particularly for the intracluster medium, we find that the dominant contribution against gravity comes from thermal pressure, while compressible turbulence effectively counteracts the support. For this reason it appears to be too simplistic to consider turbulence merely as an effective enhancement of thermal energy.

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Hot and turbulent gas in clusters

Cited by 26 publications

References 61 publications

Dynamic localized turbulent diffusion and its impact on the galactic ecosystem

Dynamic localized turbulent diffusion and its impact on the galactic ecosystem

Kinetic and internal energy transfer in implicit large-eddy simulations of forced compressible turbulence

Viscosity, pressure and support of the gas in simulations of merging cool-core clusters

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