2006/06/30 by R. N. Henriksen · 1 citation
Physics and Astronomy · #Cosmology #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #Dark matter #Dispersion (optics) #Galaxies: Formation, Evolution, Phenomena #Halo #Instability #Parameter space #Phase space #Power law #Scalar field dark matter #Velocity dispersion #astro-ph
paper · pdf · doi:10.1086/508802
published as Astrophys.J.653:894-904,2006 · 31 pages, 4 figures
arxiv created 2006/09/05 · openalex publication_date 2006/12/13 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Simulated dark matter profiles are often modeled as an NFW density profile rather than a single power law. Recently, attention has turned to the rather rigorous power-law behavior exhibited by the "pseudo-phase-space density" of the dark matter halo, which is defined dimensionally in terms of the local density and velocity dispersion of the dark matter particles. The non-power-law behavior of the density profile is generally taken to exclude simple scale-free infall models; however, the power-law behavior of the "pseudodensity" is a counter indication. We argue in this paper that both behaviors may be at least qualitatively understood in terms of a dynamically evolving self-similarity, rather than as the form for self-similar infall that is fixed by cosmological initial conditions. The evolution is likely due to collective relaxation such as that provided by the radial-orbit instability on large scales. We deduce, from a distribution function given by first-order coarse-graining, both the NFW-type density profile and the power-law pseudodensity profile. The results are not greatly sensitive to variations of about 3 in the power of the velocity dispersion used in the definition of the phase-space pseudodensity. We suggest that the power 2 may create the more physical quantity, whose deviations from a power law are a diagnostic of incomplete relaxation.