Dark Matter Halo Profiles in Scale-Free Cosmologies

Physics

Scientific paper

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Methods: N-Body Simulations, Cosmology: Theory, Galaxies: Haloes, Dark Matter

Scientific paper

We performed a set of cosmological N-body simulations of scale-free models (i.e. P(k) ∝ kn) and investigated the central logarithmic slope of relaxed dark matter halo density profiles α and its dependence on the spectral index n of the linear matter power spectrum P(k). The simulations are started and stopped according to a set of clear, reproducible and physically motivated criteria, allowing to compare haloes across models with different spectral indices. In each simulation we identify samples of well resolved haloes in dynamical equilibrium and we analyse their mass profiles. Using a "generalized" Navarro, Frenk & White profile in which the central logarithmic slope α is allowed to vary while the r-3 asymptotic form at large radii is preserved, we obtain best-fit central slopes for haloes in the different models. We find a strong correlation between α and n, such that α becomes shallower as n becomes steeper. When normalising the mass profiles by r-2, the radius at which the logarithmic slope of the density profile is -2, we find that the differences between the models are no longer present. This becomes clearly visible when plotting the maximum slope γ = 3(1 - ρ /bar {ρ }) as a function of r/r-2: We observe a similar behaviour for haloes forming in different n models. This traces back to the concentration of the haloes, in steep-n cosmologies we find smaller concentration than in shallow-n cosmologies. Also, we do not find evidence for a convergence to a unique central asymptotic slope on the scale we can resolve.

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