Turbulent gas motions in galaxy cluster simulations: the role of smoothed particle hydrodynamics viscosity

By Klaus Dolag, Franco Vazza, Gianfranco Brunetti, G. Tormen. 2005

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Smoothed particle hydrodynamics (SPH) employs an artificial viscosity to properly capture hydrodynamic shock waves. In its original formulation, the resulting numerical viscosity is large enough to suppress structure in the velocity field on scales well above the nominal resolution limit, and to damp the generation of turbulence by fluid instabilities. This could artificially suppress random gas motions in the intracluster medium (ICM), which are driven by infalling structures during the hierarchical structure formation process. We show that this is indeed the case by analysing results obtained with an SPH formulation where an individual, time-variable viscosity is used for each particle, following a suggestion by Morris & Monaghan. Using test calculations involving strong shocks, we demonstrate that this scheme captures shocks as well as the original formulation of SPH, but, in regions away from shocks, the numerical viscosity is much smaller. In a set of nine high-resolution simulations of cosmological galaxy cluster formation, we find that this low-viscosity formulation of SPH produces substantially higher levels of turbulent gas motions in the ICM, reaching a kinetic energy content in random gas motions (measured within a 1-Mpc cube) of up to 5‐30 per cent of the thermal energy content, depending on cluster mass. This also has significant effects on radial gas profiles and bulk cluster properties. We find a central flattening of the entropy profile and a reduction of the central gas density in the low-viscosity scheme. As a consequence, the bolometric X-ray luminosity is decreased by about a factor of 2. However, the cluster temperature profile remains essentially unchanged. Interestingly, this tends to reduce the differences seen in SPH and adaptive mesh refinement simulations of cluster formation. Finally, invoking a model for particle acceleration by magnetohydrodynamics waves driven by turbulence, we find that efficient electron acceleration and thus diffuse radio emission can be powered in the clusters simulated with the low-viscosity scheme provided that more than 5‐10 per cent of the turbulent energy density is associated with fast magneto-sonic modes.

Subfields: Astronomy and Astrophysics, Computational Mechanics

View Paper: https://www.semanticscholar.org/paper/637fb0b445947875dc5de933b15a605417c5f04a

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Citations in the corpus

Systematics in the X-ray cluster mass estimators (2006, background): “Since some years, veloci¨ty fields have been studied in simulated cluster as bulk motion (see e.g. Norman & Bryan 1999) or turbulent motions (see e.g. Dolag et al. 2005; Vazza et al. 2006).”
Resolving the Formation of Protogalaxies. I. Virialization (2007, methodology): “For galaxy clusters, cosmological virialization has been studied extensively (Norman & Bryan 1999; Nagai & Electronic address: jwise, tabel@slac.stanford.edu Kravtsov 2003a; Nagai et al. 2003b; Schuecker et al. 2004; Dolag et al. 2005).”
Turbulent Motions and Shocks Waves in Galaxy Clusters simulated with AMR (2009, background): “However, it is unclear if the observed inner turbulence profile can be reconciled with wit SPH findings, where an increase of the ratio between turbulent energy and the total one is observed with decreasing radius,for r/Rvir 0.1 (Dolag et al.2005).”
An improved SPH scheme for cosmological simulations (2015, methodology): “Most commonly, the so called Balsara switch (Balsara 1995) is used to reduce viscosity in shear flows, while further attempts were made to reduce AV where it is unwanted (Morris & Monaghan 1997; Dolag et al. 2005).”
Moving mesh cosmology: numerical techniques and global statistics (2011, background): “Indeed, a number of numerical studies have analysed turbulence in the intracluster medium (Dolag et al. 2005b; Vazza et al. 2009; Iapichino et al. 2011; Valdarnini 2011).”
RESIDUAL GAS MOTIONS IN THE INTRACLUSTER MEDIUM AND BIAS IN HYDROSTATIC MEASUREMENTS OF MASS PROFILES OF CLUSTERS (2009, background): “The magnitude and effects of gas motions in such simulations depends on the specific treatment of artificial viscosity (Dolag et al. 2005).”
Relativistic neutron star merger simulations with non-zero temperature equations of state. I. Variation of binary parameters and equation of state (2006, methodology): “Comparisons of this viscosity scheme with the one used in the old code version (Oechslin et al. 2004) show less particle noise and a smaller numerical viscosity (see also similar work by Dolag et al. 2005 in a cosmological context).”
Total mass biases in X-ray galaxy clusters (2008, background): “It has been shown that the level of kinetic energy in random gas motion could be as high as ∼30% of the gas thermal energy (Dolag et al. 2005; Vazza et al. 2006), when the numerical viscosity scheme is generalized as in Morris & Monaghan (1997) to properly treat fluid turbulence.”
Inviscid smoothed particle hydrodynamics (2010, methodology): “The widely used code GADGET-2 (Springel 2005) employs a fixed α chosen at the start of the simulation (though Dolag et al. 2005 have implemented into GADGET-2 the improved method described in Section 2.3).”
Massive and refined - II. The statistical properties of turbulent motions in massive galaxy clusters with high spatial resolution (2010, methodology): “More recent works, performing high-resolution Lagrangian (Dolag et al. 2005, Vazza et al. 2006; Valdarnini 2010) and Eulerian re-simulations of galaxy clusters extracted from large cosmolog-F ical volumes found that a sizable amount of pressure support (i.e. ∼ 10 − 30 percent of the total pressure i”
Constraints on the distribution and energetics of fast radio bursts using cosmological hydrodynamic simulations (2014, methodology): “We produce maps of the electron density using SMAC (Dolag et al. 2005a), taking the ionisation state of the medium into account.”
The population of dark matter subhaloes: mass functions and average mass-loss rates (2007, unknown): “See Dolag et al. (2005) for further details.”
Compressible turbulence in galaxy clusters: physics and stochastic particle re-acceleration (2007, background): “Numerical simulations suggest that turbulent motions may store an appreciable fraction, 5–30%, of the thermal energy of the ICM (e.g., Sunyaev, Bryan & Norman 2003; Dolag et al. 2005; Vazza et al. 2006).”
Chemical enrichment of galaxy clusters from hydrodynamical simulations (2007, background): “The description of turbulence requires not only sampling a wide enough dynamical range, where the energy cascade takes place, but also a good knowledge of the plasma viscosity, which determine the scale at which turbulent energy is dissipated (e.g. Dolag et al. 2005).”
IMPACT OF CLUSTER PHYSICS ON THE SUNYAEV–ZEL'DOVICH POWER SPECTRUM (2010, background): “This kinetic support is largely sourced by infalling and merging structures, which can further generate turbulent gas motions at the boundary between the bulk flow and the thermalized ICM (Dolag et al. 2005; Kim 2007; Vazza et al. 2009).”
Shocking results without shocks: Subsonic turbulence in smoothed particle hydrodynamics and moving-mesh simulations (2011, methodology): “…the culprit lies simply in the artificial viscosity parameterization, and that schemes that dynamically reduce the viscosity away from shocks (e.g. Morris 1997; Dolag et al. 2005; Cullen & Dehnen 2010) do much better and have no problem to reproduce a Kolmogorov cascade also in the subsonic regime.”
Evidence for non-hydrostatic gas from the cluster X-ray to lensing mass ratio (2007, background): “…energy input from active galactic nuclei, pressure support from turbulence and residual bulk motions, and variations in the merging history may contribute substantially to this systematic bias (Dolag et al. 2005; Faltenbacher et al. 2005; Rasia et al. 2006; Nagai et al. 2007; Ameglio et al. 2007).”
Moving mesh cosmology: the hydrodynamics of galaxy formation (2011, background): “…have an impact on the level of turbulence injected by curved shocks that are associated with galaxy or subhalo motions through the ICM, producing a bias in the amount of non-thermal pressure support in galaxy clusters (see also e.g. Dolag et al. 2005; Iapichino et al. 2011; Vazza et al. 2011a).”