2008/08/14 by Ole Host, Steen H. Hansen, Rocco Piffaretti +4 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Dark Matter and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1088/0004-637x/690/1/358
published as Astrophys.J.690:358-366,2009 · 10 pages, 8 figures, submitted to ApJ
arxiv created 2008/08/14 · openalex publication_date 2008/12/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/30
The internal dynamics of a dark matter structure may have the remarkable property that the local temperature in the structure depends on direction. This is parameterized by the velocity anisotropy β which must be zero for relaxed collisional structures, but has been shown to be nonzero in numerical simulations of dark matter structures. Here, we present a method for inferring the radial profile of the velocity anisotropy of the dark matter halo in a galaxy cluster from X-ray observables of the intracluster gas. This nonparametric method is based on a universal relation between the dark matter temperature and the gas temperature which is confirmed through numerical simulations. We apply this method to observational data and we find that β is significantly different from zero at intermediate radii. Thus, we find a strong indication that dark matter is effectively collisionless on the dynamical timescale of clusters, which implies an upper limit on the self-interaction cross-section per unit mass σ/ m ≲ 1 cm 2 g −1 . Our results may provide an independent way to determine the stellar mass density in the central regions of a relaxed cluster, as well as a test of whether a cluster is in fact relaxed.