Andreas Skielboe, Radoslaw Wojtak, Kristian Pedersen, Eduardo Rozo, Eli S. Rykoff
Measurements of galaxy cluster kinematics are important in understanding the dynamical state and evolution of clusters of galaxies, as well as constraining cosmological models. While it is well established that clusters exhibit non-spherical geometries, evident in the distribution of galaxies on the sky, azimuthal variations of galaxy kinematics within clusters have yet to be observed. Here we measure the azimuthal dependence of the line of sight velocity dispersion profile in a stacked sample of 1,743 galaxy clusters from the Sloan Digital Sky Survey (SDSS). The clusters are drawn from the SDSS DR8 redMaPPer catalog. We find that the line of sight velocity dispersion of galaxies lying along the major axis of the central galaxy (CG) is larger than those that lie along the minor axis. This is the first observational detection of anisotropic kinematics of galaxies in clusters. We show that the result is consistent with predictions from numerical simulations. Furthermore we find that the degree of projected anisotropy is strongly dependent on the line of sight orientation of the galaxy cluster, opening new possibilities for assessing systematics in optical cluster finding.
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http://arxiv.org/abs/1208.4598
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