The diversity and similarity of simulated cold dark matter haloes

Abstract

We study the mass, velocity dispersion and anisotropy profiles of Λ cold dark matter (ΛCDM) haloes using a suite of N‐body simulations of unprecedented numerical resolution. The Aquarius Project follows the formation of six different galaxy‐sized haloes simulated several times at varying numerical resolution, allowing numerical convergence to be assessed directly. The highest resolution simulation represents a single dark matter halo using 4.4 billion particles, of which 1.1 billion end up within the virial radius. Our analysis confirms a number of results claimed by earlier work, and clarifies a few issues where conflicting claims may be found in the recent literature. The mass profile of ΛCDM haloes deviates slightly but systematically from the form proposed by Navarro, Frenk & White. The spherically averaged density profile becomes progressively shallower inwards and, at the innermost resolved radius, the logarithmic slope is γ≡− d ln ρ/d ln r≲ 1. Asymptotic inner slopes as steep as the recently claimed ρ∝r−1.2 are clearly ruled out. The radial dependence of γ is well approximated by a power law, γ∝rα (the Einasto profile). The shape parameter, α, varies slightly but significantly from halo to halo, implying that the mass profiles of ΛCDM haloes are not strictly universal: different haloes cannot, in general, be rescaled to look identical. Departures from similarity are also seen in velocity dispersion profiles and correlate with those in density profiles so as to preserve a power‐law form for the spherically averaged pseudo‐phase‐space density, ρ/σ3∝r−1.875. The index here is identical to that of Bertschinger's similarity solution for self‐similar infall on to a point mass from an otherwise uniform Einstein–de Sitter universe. The origin of this striking behaviour is unclear, but its robustness suggests that it reflects a fundamental structural property of ΛCDM haloes. Our conclusions are reliable down to radii below 0.4 per cent of the virial radius, providing well‐defined predictions for halo structure when baryonic effects are neglected, and thus an instructive theoretical template against which the modifications induced by the baryonic components of real galaxies can be judged.

Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

“…See Diemand & Moore (2011) for a review of cusp structure. CDM simulation papers widely agree that CDM halos are expected to have cuspy centers rather than isothermal-like cores (e. g., Moore et al 1998Moore et al , 2001Klypin et al 2001Klypin et al , 2011Navarro et al 2004Navarro et al , 2010Colín et al 2004;Hayashi et al 2004;Diemand et al 2005Diemand et al , 2008Klypin, TrujilloGomez, & Primack 2011).…”

Optimized Dark Matter Searches in Deep Observations of Segue 1 with MAGIC

“…This dependence is less pronounced for the decaying DM, since J dec ∝ ρ. Motivated by the numerical simulations, we model the DM density distribution assuming the Einasto profile [42], with scale radius r s = 0.15 kpc, scale density ρ s = 1.1×10 8 M ⊙ kpc −3 and slope α = 0.30 [19,43].…”

Orbit-based dynamical models of the Sculptor dSph galaxy

“…Navarro, Frenk & White (1996) showed that simulated dark halos have a universal internal density distribution, now known as the NFW profile. Although there have been some revisions, the general form has remained, and the inner regions of simulated dark halos are found to be cusped with logarithmic slopes in the range −1.2 to −0.75 (Navarro et al 2010). CDM simulations have also revealed the existence of a universal spin distribution and of relations between the characteristic parameters of a ⋆ E-mail:breddels@astro.rug.nl dark halo such as concentration and mass (e.g Bullock et al 2001).…”