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Session 21 - Galaxies and Clusters of Galaxies.
Oral session, Monday, June 10
Humanities 3650,

[21.09] The Ellipticity and Orientation of Clusters of Galaxies in N-Body Experiments

R. J. Splinter (U. Kentucky), A. M. Linn, A. L. Melott, C. Buck, J. Tinker (U. Kansas)

There exists a large literature on clusters, their ellipticity, and possible alignment of axes, in both data and numerical simulations. Much of the theoretical work is difficult to interpret due to differences in procedure from observations, or simulations variation of several parameters,

Therefore, in this study using simulations of 128^3 particles we studied the ellipticity and orientation of clusters of galaxies in N-body simulations of differing power-law initial spectra (P(k)\propto k^n ,n = +1, 0, -1, -2), and density parameters (Ømega_0 = 0.2 to 1.0), in a controlled way, based on nearly 3000 simulated clusters.

We computed the axial ratio and the principal axes using the inertia tensor of each cluster. We compared the orientation of a cluster to the orientation of neighboring clusters as a function of distance (correlation). In addition, we looked at whether a cluster's major axis lies along the line connecting it to a neighboring cluster, also as a function of distance (alignment). We found that differences in Ømega had no measurable effect on mean ellipticity, cluster angle correlations, or cluster alignment. However, there are systematic effects due to the primordial spectral index, n. Our results suggest that cluster property may probe the primordial power spectrum independently of the parameters of the background cosmology.

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