IDM2008 - Identification of Dark Matter 2008 18-22 August 2008 AlbaNova
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Measurement of the dark matter velocity anisotropy profile in galaxy clusters (15'+5')

 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 parametrized by the velocity anisotropy beta which must be zero for relaxed collisional structures, but has been shown to be non-zero in numerical simulations of dark matter structures. Here, we present a method to infer 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 non-parametric 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 beta is significantly different from zero at intermediate radii. Thus we find a strong indication that dark matter is effectively collisionless on the dynamical time-scale of clusters, which implies an upper limit on the self-interaction cross-section per unit mass sigma/m~1cm^2/g. Extrapolating our analysis to radii smaller than what can be probed by numerical simulations at present, we find observational indications that $\beta$ increases to about 0.3.

Id: 426
Place: AlbaNova
Room: Oskar Klein auditorium
Starting date:
 20-Aug-2008 13:30
Duration: 20'
Contribution type: Talk
Primary Authors: Mr. HOST, Ole (Dark Cosmology Centre, NBI, Copenhagen)
Co-Authors: Dr. HANSEN, Steen H (Dark Cosmology Centre, NBI, Copenhagen)
Presenters: Mr. HOST, Ole
Material: Slides

Included in session: Dark matter cosmology / structure formation
Included in track: Dark matter cosmology / structure formation