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IDM2008 - Identification of Dark Matter 2008
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: slide Slides
 
Included in session: Dark matter cosmology / structure formation
Included in track: Dark matter cosmology / structure formation
 

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