21 research outputs found
Temperature Structure of the Intra-Cluster Medium from SPH and AMR simulations
Analyses of cosmological hydrodynamic simulations of galaxy clusters suggest
that X-ray masses can be underestimated by 10% to 30%. The largest bias
originates by both violation of hydrostatic equilibrium and an additional
temperature bias caused by inhomogeneities in the X-ray emitting intra-cluster
medium (ICM). To elucidate on this large dispersion among theoretical
predictions, we evaluate the degree of temperature structures in cluster sets
simulated either with smoothed-particle-hydrodynamics (SPH) and
adaptive-mesh-refinement (AMR) codes. We find that the SPH simulations produce
larger temperature variations connected to the persistence of both
substructures and their stripped cold gas. This difference is more evident in
no-radiative simulations, while it is reduced in the presence of radiative
cooling. We also find that the temperature variation in radiative cluster
simulations is generally in agreement with the observed one in the central
regions of clusters. Around R_500 the temperature inhomogeneities of the SPH
simulations can generate twice the typical hydrostatic-equilibrium mass bias of
the AMR sample. We emphasize that a detailed understanding of the physical
processes responsible for the complex thermal structure in ICM requires
improved resolution and high sensitivity observations in order to extend the
analysis to higher temperature systems and larger cluster-centric radii.Comment: 13 pages, 12 figures, 4 table
A fast and accurate method for computing the Sunyaev-Zeldovich signal of hot galaxy clusters
New generation ground and space-based CMB experiments have ushered in
discoveries of massive galaxy clusters via the Sunyaev-Zeldovich (SZ) effect,
providing a new window for studying cluster astrophysics and cosmology. Many of
the newly discovered, SZ-selected clusters contain hot intracluster plasma (kTe
> 10 keV) and exhibit disturbed morphology, indicative of frequent mergers with
large peculiar velocity (v > 1000 km s^{-1}). It is well-known that for the
interpretation of the SZ signal from hot, moving galaxy clusters, relativistic
corrections must be taken into account, and in this work, we present a fast and
accurate method for computing these effects. Our approach is based on an
alternative derivation of the Boltzmann collision term which provides new
physical insight into the sources of different kinematic corrections in the
scattering problem. This allows us to obtain a clean separation of kinematic
and scattering terms which differs from previous works. We briefly mention
additional complications connected with kinematic effects that should be
considered when interpreting future SZ data for individual clusters. One of the
main outcomes of this work is SZpack, a numerical library which allows very
fast and precise (<~0.001% at frequencies h nu <~ 20kT_g) computation of the SZ
signals up to high electron temperature (kT_e ~ 25 keV) and large peculiar
velocity (v/c ~ 0.01). The accuracy is well beyond the current and future
precision of SZ observations and practically eliminates uncertainties related
to more expensive numerical evaluation of the Boltzmann collision term. Our new
approach should therefore be useful for analyzing future high-resolution,
multi-frequency SZ observations as well as computing the predicted SZ effect
signals from numerical simulations.Comment: 20 pages, 11 figures, 3 tables, accepted by MNRAS; SZpack download:
www.Chluba.de/SZpac
nIFTy galaxy cluster simulations – I. Dark matter and non-radiative models
We have simulated the formation of a galaxy cluster in a É… cold dark matter universe using 13 different codes modelling only gravity and non-radiative hydrodynamics (RAMSES, ART, AREPO, HYDRA and nine incarnations of GADGET). This range of codes includes particle-based, moving and fixed mesh codes as well as both Eulerian and Lagrangian fluid schemes. The various GADGET implementations span classic and modern smoothed particle hydrodynamics (SPH) schemes. The goal of this comparison is to assess the reliability of cosmological hydrodynamical simulations of clusters in the simplest astrophysically relevant case, that in which the gas is assumed to be non-radiative. We compare images of the cluster at z = 0, global properties such as mass and radial profiles of various dynamical and thermodynamical quantities. The underlying gravitational framework can be aligned very accurately for all the codes allowing a detailed investigation of the differences that develop due to the various gas physics implementations employed. As expected, the mesh-based codes RAMSES, ART and AREPO form extended entropy cores in the gas with rising central gas temperatures. Those codes employing classic SPH schemes show falling entropy profiles all the way into the very centre with correspondingly rising density profiles and central temperature inversions. We show that methods with modern SPH schemes that allow entropy mixing span the range between these two extremes and the latest SPH variants produce gas entropy profiles that are essentially indistinguishable from those obtained with grid-based methods