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Article overview
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Power law pseudo phase-space density profiles of dark matter halos: fluke of physics? | | Arpit Arora
; Liliya L. R. Williams
; | | Date: |
8 Apr 2019 | | Abstract: | It has been known for nearly 20 years that the pseudo phase-space density
profile of equilibrium simulated dark matter halos, $
ho(r)/sigma^3(r)$, is
well described by a power law over 3 decades in radius, even though both the
density $
ho(r)$, and the velocity dispersion $sigma(r)$ deviate
significantly from power laws. The origin of this scale-free behavior is not
understood. It could be a dynamical attractor that represents an emergent
property of self-gravitating collisionless systems, or it could be a mere
coincidence. To address the question we work with the second derivative of the
Jean’s equation, which, under the assumptions of (i) Einasto density profile,
(ii) linear velocity anisotropy - density slope relation, and (iii)
$
ho/sigma^3propto r^{-alpha}$, can be transformed from a differential
equation to a cubic algebraic equation. Relations (i)-(iii) are all observed in
numerical simulations, and are well parametrized by a total of 4 or 6 model
parameters. Taking advantage of the fact that the algebraic Jean’s equation
puts relations (i)-(iii) on the same footing, we study the (approximate)
solutions of this equation in the 4 and 6 dimensional spaces. We argue that the
distribution of best solutions in these parameter spaces is inconsistent with
$
ho/sigma^3propto r^{-alpha}$ being an attractor, and conclude that the
scale-free nature of this quantity is likely to be a fluke. | | Source: | arXiv, 1904.3772 | | Services: | Forum | Review | PDF | Favorites | |
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