Density profiles of collisionless equilibria. I. Spherical isotropic systems

Bric I. Barnes, Liliya L.R. Williams, Arif Babul, Julianne J. Dalcanton

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24 Scopus citations


We investigate the connection between collisionless equilibria and the phase-space relation between density ρ and velocity dispersion found in simulations of dark matter halo formation, F = ρ/σ3 ∝ r. Understanding this relation will shed light on the physics relevant to collisionless collapse and on the subsequent structures formed. We show that empirical density profiles that provide good fits to N-body halos also happen to have nearly scale-free ρ/σ3 distributions when in equilibrium. We have also done a preliminary investigation of variables other than r that may match or supersede the correlation with F. In the same vein, we show that ρ/σm, where m = 3, is the most appropriate combination to use in discussions of the power-law relationship. Since the mechanical equilibrium condition that characterizes the final systems does not by itself lead to power-law F distributions, our findings prompt us to posit that dynamical collapse processes (such as violent relaxation) are responsible for the radial power-law nature of the ρ/σ3 distributions of virialized systems.

Original languageEnglish (US)
Pages (from-to)797-803
Number of pages7
JournalAstrophysical Journal
Issue number2 I
StatePublished - Jun 1 2006


  • Dark matter
  • Galaxies: kinematics and dynamics
  • Galaxies: structure


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