Simulations of the Formation and Evolution of X-ray Clusters

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Session 41 -- Computational Astrophysics II
Display presentation, Wednesday, 1, 1994, 9:20-6:30

[41.10] Simulations of the Formation and Evolution of X-ray Clusters

G.L.Bryan (NCSA), A.Klypin (NMSU), M.L.Norman (NCSA)

We describe results from a set of $\Omega = 1$ Cold plus Hot Dark Matter (CHDM) and Cold Dark Matter (CDM) simulations. We examine the formation and evolution of X-ray clusters in a cosmological setting with sufficient numbers to perform statistical analysis. We find that CDM, normalized to COBE, seems to produce too many large clusters, both in terms of the luminosity ($dn/dL$) and temperature ($dn/dT$) functions. The CHDM simulation produces fewer clusters and the temperature distribution (our numerically most secure result) matches observations where they overlap. The computed cluster luminosity function drops below observations, but we are almost surely underestimating the X-ray luminosity. Because of the lower fluctuations in CHDM, there are only a small number of bright clusters in our simulation volume; however we can use the simulated clusters to fix the relation between temperature and velocity dispersion, allowing us to use collisionless N-body codes to probe larger length scales with correspondingly brighter clusters. The hydrodynamic simulations have been performed with a hybrid particle-mesh scheme for the dark matter and a high resolution grid-based piecewise parabolic method for the adiabatic gas dynamics. This combination has been implemented for massively parallel computers, allowing us to achive grids as large as $512^3$.

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