Hierarchical clustering and galaxy cluster scaling laws

Research output: ThesisDoctoral Thesis


The dependency of the morphology of the hot gaseous component of clusters of galaxies on the hierarchical nature of the structure formation in our universe is examined. The indicators of morphology examined are the universal density profile of Navarro, Frenk, and White (1995), the mass-temperature relationship, and the biasing of the gas with respect to the dark matter. The study is done using high resolution numerical simulations of clusters of galaxies. The simulations model the collisionless (dark matter) component as well as the baryonic matter using an N-body code with smoothed particle hydrodynamics (SPH) parallelised using Pthreads. The clusters are evolved from initial conditions smoothed by top-hat filtering and low-pass filtering of the initial perturbation spectrum. The evolution takes place in a 40h-1 Mpc volume. The mean dark matter density profiles from each of the models is found to be fit well by the universal profile. A discontinuous form described in the text finds r~r-1.8 in the inner regimes of the clusters, independent of the model. The density in the outer regimes is found to depend on the degree of smoothing, becoming more shallow with increased smoothing. The mass-temperature relation is found to depend on the initial conditions, as well. All models reproduce the T~M2/3 relation, but the coefficient of proportionality is found to decrease with increased smoothing of the initial conditions. This is traced to an increase in the isothermal radius of the clusters. The gas in the clusters is found to be anti- biased with respect to the dark matter. This anti-bias is reduced with smoothing of the initial conditions. In particular for the clusters formed hierarchically from unsmoothed initial conditions, there is a strong positive bias in the outer radii of the clusters. A description of the method of parallelisation is given as well as results of tests of SPH involving cooling near a steep density gradient and the drag on a cold clump moving through a hot media. The tests are done for a variety of implementations of SPH which vary both the method of symmetrising the equations of motion and the form of the artificial viscosity. Both of these are found to not have significant effects.
Original languageEnglish
Publication statusPublished - 1999




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