Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOn the Origin of Cores in Simulated Galaxy Clusters
107
0
0.0
(
0
)
Authors
N. L. Mitchell
Ask ChatGPT about the research
No Arabic abstract
(Abridged) The thermal state of the intracluster medium results from a competition between gas cooling and heating. The heating comes from two distinct sources: gravitational heating from the collapse of the dark matter halo and thermal input from galaxy/black hole formation. However, a long standing problem has been that cosmological simulations based on smoothed particle hydrodynamics (SPH) and Eulerian mesh codes predict different results even when cooling and galaxy/black hole heating are switched off. Clusters formed in SPH simulations show near powerlaw entropy profiles, while those formed in mesh simulations develop a core and do not allow gas to reach such low entropies. Since the cooling rate is closely connected to the minimum entropy of the gas, the differences are of potentially key importance. In this paper, we investigate the origin of this discrepancy. By comparing simulations run using the GADGET-2 SPH code and the FLASH adaptive Eulerian mesh code, we show that the discrepancy arises during the idealised merger of two clusters. The difference is not sensitive to the resolution of our simulations, nor is it is due differences in the gravity solvers, Galilean non-invariance of the mesh code, or an effect of unsuitable artificial viscosity in the SPH code. Instead, we find that the difference is inherent to the treatment of eddies and fluid instabilities. These are suppressed in the SPH simulations, while the cluster mergers generate strong vortices in the mesh simulations that efficiently mix the fluid and erase the low entropy gas. Consequently, particles in the SPH simulations retain a close connection to their initial entropy, while this connection is much weaker in the mesh simulations. We discuss the potentially profound implications of these results.
rate research
Read More
We present a pilot study on the origin and assembly history of the ICL for four galaxy clusters at 0.44<z<0.57 observed with the Hubble Space Telescope from the Cluster Lensing and Supernova Survey with Hubble (CLASH) sample. Using this sample of clusters we set an empirical limit on the amount of scatter in ICL surface brightness profiles of such clusters at z=0.5 and constrain the progenitor population and formation mechanism of the ICL by measuring the ICL surface brightness profile, the ICL color and color gradient, and the total ICL luminosity within 10<r<110 kpc. The observed scatter is physical, which we associate with differences in ICL assembly process, formation epoch, and/or ICL content. Using stellar population synthesis models we transform the observed colors to metallicity. For three of the four clusters we find clear negative gradients that, on average, decrease from super solar in the central regions of the BCG to sub-solar in the ICL. Such negative color/metallicity gradients can arise from tidal stripping of L* galaxies and/or the disruption of dwarf galaxies, but not major mergers with the BCG. We also find that the ICL at 110 kpc has a color comparable to m*+2 red sequence galaxies and a total luminosity between 10<r<110 kpc of 4-8 L*. This suggests that the ICL is dominated by stars liberated from galaxies with L>0.2 L* and that neither dwarf disruption nor major mergers with the BCG alone can explain the observed level of luminosity and remain consistent with either the observed evolution in the faint end slope of the luminosity function or predictions for the number of BCG major mergers since z=1. Taken together, the results of this pilot study are suggestive of a formation history for these clusters in which the ICL is built-up by the stripping of >0.2 L* galaxies, and disfavor significant contribution to the ICL by dwarf disruption or major mergers with the BCG.
We use XMM-Newton data to carry out a detailed study of the Si, Fe and Ni abundances in the cool cores of a representative sample of 26 local clusters. We have performed a careful evaluation of the systematic uncertainties related to the instruments, the plasma codes and the spectral modeling finding that the major source of uncertainty is in the plasma codes. Our Si, Fe, Ni, Si/Fe and Ni/Fe distributions feature only moderate spreads (from 20% to 30%) around their mean values strongly suggesting similar enrichment processes at work in all our cluster cores. Our sample averaged Si/Fe ratio is comparable to those measured in samples of groups and high luminosity ellipticals implying that the enrichment process in ellipticals, dominant galaxies in groups and BCGs in clusters is quite similar. Although our Si/Fe and Ni/Fe abundance ratios are fairly well constrained, the large uncertainties in the supernovae yields prevent us from making a firm assessment of the relative contribution of type Ia and core-collapsed supernovae to the enrichment process. All that can really be said with some certainty is that both contribute to the enrichment of cluster cores.
Clusters of galaxies are embedded in halos of optically thin, gravitationally stratified, weakly magnetized plasma at the systems virial temperature. Due to radiative cooling and anisotropic heat conduction, such intracluster medium (ICM) is subject to local instabilities, which are combinations of the thermal, magnetothermal and heat-flux-driven buoyancy instabilities. If the ICM rotates significantly, its stability properties are substantially modified and, in particular, also the magnetorotational instability (MRI) can play an important role. We study simple models of rotating cool-core clusters and we demonstrate that the MRI can be the dominant instability over significant portions of the clusters, with possible implications for the dynamics and evolution of the cool cores. Our results give further motivation for measuring the rotation of the ICM with future X-ray missions such as ASTRO-H and ATHENA.
We argue that the recently reported Kolmogorov-like magnetic turbulence spectrum in the cool core of the Hydra A galaxy cluster can be understood by kinetic energy injection by active galaxies that drives a turbulent non-helical magnetic dynamo into its saturated state. Although dramatic differences exist between small-scale dynamo scenarios, their saturated state is expected to be similar, as we show for three scenarios: the flux rope dynamo, the fluctuation dynamo, and the explosive dynamo. Based on those scenarios, we develop an analytical model of the hydrodynamic and magnetic turbulence in cool cores. The model implies magnetic field strengths that fit well with Faraday rotation measurements and minimum energy estimates for the sample of cool core clusters having such data available. Predictions for magnetic fields in clusters for which the appropriate observational information is still missing, and for yet unobserved quantities like the hydrodynamical turbulence velocity and characteristic length-scale are provided. The underlying dynamo models suggest magnetic intermittency and possibly a large-scale hydrodynamic viscosity. We conclude that the success of the model to explain the field strength in cool core clusters indicates that in general cluster magnetic fields directly reflect hydrodynamical turbulence, also in clusters without cool cores.
We explore the morphological and dynamical evolution of galaxy clusters in simulations using scalar and vector-valued Minkowski valuations and the concept of fundamental plane relations. In this context, three questions are of fundamental interest: 1. How does the average cluster morphology depend on the cosmological background model? 2. Is it possible to discriminate between different cosmological models using cluster substructure in a statistically significant way? 3. How is the dynamical state of a cluster, especially its distance from a virial equilibrium, correlated to its visual substructure? To answer these questions, we quantify cluster substructure using a set of morphological order parameters constructed on the basis of the Minkowski valuations (MVs). The dynamical state of a cluster is described using global cluster parameters: in certain spaces of such parameters fundamental band-like structures are forming indicating the emergence of a virial equilibrium. We find that the average distances from these fundamental structures are correlated to the average amount of cluster substructure for our cluster samples during the time evolution. Furthermore, significant differences show up between the high- and the low-Omega models. We pay special attention to the redshift evolution of morphological characteristics and find large differences between the cosmological models even for higher redshifts.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
