Simulations of binary galaxy cluster mergers: Modeling real clusters and exploring parameter spaces.
详细信息
文摘
We present an investigation of controlled N-body/hydrodynamics high-resolution simulations of binary galaxy cluster mergers, performed using the FLASH code. In addition to analyzing the quantities directly from the simulation, we produce simulated X-ray observations of the cluster ICM and perform standard analyses of the surface brightness distribution and spectra of the X-ray photons emitted from the hot cluster gas. Several lines of evidence have suggested that the galaxy cluster Cl 0024＋17, an apparently relaxed system, is actually a collision of two clusters, the interaction occurring along our line of sight. We present a high-resolution N-body/hydrodynamics simulation of such a collision. We analyze mock X-ray observations of our simulated clusters to generate radial profiles of the surface brightness and temperature to show that at later times the simulated surface brightness profiles are better fit by a superposition of two beta-model profiles than a single profile, in agreement with the observations of Cl 0024＋17. We determine from our fitted profiles that if the system is modeled as a single cluster, the hydrostatic mass estimate is a factor &sim；2-3 less than the actual mass, but if the system is modeled as two galaxy clusters in superposition, a hydrostatic mass estimation can be made which is accurate to within &sim；10%. Additionally, recent lensing observations of Cl 0024＋17 suggest the presence of a ring-like dark matter structure, which has been interpreted as the result of such a collision. To determine the conditions under which such a feature would form, we vary the initial velocity anisotropy of the dark matter particles. Our simulations show a ring feature does not occur even when the initial particle velocity distribution is highly tangentially anisotropic. Only when the initial particle velocity distribution is circular do our simulations show such a feature, which is consistent with the halo velocity distributions seen in cosmological simulations. Lastly, we present a fiducial set of galaxy cluster merger simulations, where the initial mass ratio and the impact parameter have been varied. By projecting the simulated quantities along the axes of the computational domain, we produce maps of X-ray surface brightness, temperature, projected mass density, and simulated X-ray observations. From these observations we compute the observed X-ray luminosity and fitted spectral temperature, and fit beta-model profiles to compute estimated hydrostatic masses. From this information we determine the effect of mergers viewed along different projections on these observed quantities. We also construct simulated maps of galaxies, and test the power of a commonly employed substructure statistic to probe for the existence of substructure along the different projections during the merger. Finally, we comment on other aspects of our simulations, such as comparisons to existing merging clusters； and the mixing of the intracluster medium due to merging, and resulting cluster entropy and cooling time profiles.