Measuring the dark matter velocity anisotropy to the cluster edge. (arXiv:1904.04260v1 [astro-ph.CO])

Measuring the dark matter velocity anisotropy to the cluster edge. (arXiv:1904.04260v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Svensmark_J/0/1/0/all/0/1">Jacob Svensmark</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hansen_S/0/1/0/all/0/1">Steen H. Hansen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Martizzi_D/0/1/0/all/0/1">Davide Martizzi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Moore_B/0/1/0/all/0/1">Ben Moore</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Teyssier_R/0/1/0/all/0/1">Romain Teyssier</a>

Dark matter dominates the properties of large cosmological structures such as
galaxy clusters, and the mass profiles of the dark matter have been measured
for these equilibrated structures for years using X-rays, lensing or galaxy
velocities. A new method has been proposed, which should allow us to measure a
dynamical property of the dark matter, namely the velocity anisotropy. For the
gas a similar velocity anisotropy is zero due to frequent collisions, however,
the collisionless nature of dark matter allows it to be non-trivial. Numerical
simulations have for years found non-zero and radially varying dark matter
velocity anisotropies. Here we employ the method proposed by Hansen and
Pifaretti (2007), and developed by H{o}st et al. (2009) to measure the dark
matter velocity anisotropy in the bright galaxy cluster Perseus, to near 5
times the radii previously obtained. We find the dark matter velocity
anisotropy to be in good agreement with the results of numerical simulations,
however, still with large error-bars. At half the virial radius we find the
velocity anisotropy to be non-zero at 1.7$,sigma$, thus confirming the
collisionless nature of dark matter.

Dark matter dominates the properties of large cosmological structures such as
galaxy clusters, and the mass profiles of the dark matter have been measured
for these equilibrated structures for years using X-rays, lensing or galaxy
velocities. A new method has been proposed, which should allow us to measure a
dynamical property of the dark matter, namely the velocity anisotropy. For the
gas a similar velocity anisotropy is zero due to frequent collisions, however,
the collisionless nature of dark matter allows it to be non-trivial. Numerical
simulations have for years found non-zero and radially varying dark matter
velocity anisotropies. Here we employ the method proposed by Hansen and
Pifaretti (2007), and developed by H{o}st et al. (2009) to measure the dark
matter velocity anisotropy in the bright galaxy cluster Perseus, to near 5
times the radii previously obtained. We find the dark matter velocity
anisotropy to be in good agreement with the results of numerical simulations,
however, still with large error-bars. At half the virial radius we find the
velocity anisotropy to be non-zero at 1.7$,sigma$, thus confirming the
collisionless nature of dark matter.

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