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Title:
Is the Concentration of Dark Matter Halos at Virialization Universal?
Authors:
Ricotti, Massimo; Pontzen, Andrew; Viel, Matteo
Affiliation:
AA(Department of Astronomy, University of Maryland, College Park, MD 20742.), AB(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK.), AC(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK; INAF-Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, I-34131 Trieste, Italy.)
Publication:
The Astrophysical Journal, Volume 663, Issue 2, pp. L53-L56. (ApJL Homepage)
Publication Date:
07/2007
Origin:
UCP
Astronomy Keywords:
Cosmology: Theory, Galaxies: Formation, Methods: n-Body Simulations, Methods: Numerical, Methods: Statistical
DOI:
10.1086/520113
Bibliographic Code:
2007ApJ...663L..53R

Abstract

Several recent studies suggest a correlation between dark matter halo mass and the shape of the density profile. We reanalyze simulations from Ricotti in which such a correlation was first proposed. We use a standard analysis of the halo density profiles and compare the old simulations to new ones performed with Gadget2, including higher resolution runs. We confirm Ricotti's result that, at virialization, the central log slopes alpha, at 5%-10% of the virial radius, are correlated with the halo mass and that the halo concentration is a universal constant. Our results do not contradict the majority of published papers: when using a split power law to fit the density profiles, due to the alpha-c degeneracy, the fits are consistent with halos having a universal shape with alpha=1 or 1.5 and concentrations that depend on the mass, in agreement with results published elsewhere. Recently, several groups have found no evidence for convergence of the inner halo profile to a constant power law. The choice of the split power-law parameterization used in this Letter is motivated by the need to compare our results to previous ones and is formally valid because we are not able to resolve regions where the slope of the fitting function reaches its asymptotic constant value. Using a nonparameterized technique, we also show that the density profiles of dwarf galaxies at z~10 have a log slope shallower than 0.5 within 5% of the virial radius.
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