Article

# The diversity and similarity of simulated cold dark matter haloes

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Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305, USA
(Impact Factor: 5.11). 02/2010; 402(1):21 - 34. DOI: 10.1111/j.1365-2966.2009.15878.x

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.

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Available from: Aaron D. Ludlow, Jan 05, 2014
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• "−0 . 39 , when excluding the inner 40 kpc / h . While the total density profile is in agreement with a NFW profile ( α = 1 ) , the inner DM profile is shallower than simulations . Even considering recent simulations ( Stadel et al . 2009 ; Navarro et al . 2010 ) the minimum slope obtained , α −0 . 8 at 120 pc , ( Stadel et al . 2009 ) is larger than the results of observations , and the scatter in the slope from cluster to cluster is much larger than what found in simulations ( see figure 2 , gray points ) . If some part of the scatter can be explained , as previously reported , in terms of t"
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ABSTRACT: The present paper is an extension and continuation of Del Popolo (2012a) which studied the role of baryon physics on clusters of galaxies formation. In the present paper, we studied by means of the SIM introduced in Del Popolo (2009), the total and DM density profiles, and the correlations among different quantities, observed by Newman et al. (2012a,b), in seven massive and relaxed clusters, namely MS2137, A963, A383, A611, A2537, A2667, A2390. As already found in Del Popolo 2012a, the density profiles depend on baryonic fraction, angular momentum, and the angular momentum transferred from baryons to DM through dynamical friction. Similarly to Newman et al. (2012a,b), the total density profile, in the radius range 0.003–0.03r200, has a mean total density profile in agreement with dissipationless simulations. The slope of the DM profiles of all clusters is flatter than -1. The slope, α, has a maximum value (including errors) of α = −0.88 in the case of A2390, and minimum value α = −0.14 for A2537. The baryonic component dominates the mass distribution at radii < 5–10 kpc, while the outer distribution is dark matter dominated. We found an anti-correlation among the slope α, the effective radius, Re, and the BCG mass, and a correlation among the core radius rcore, and Re. Moreover, the mass in 100 kpc (mainly dark matter) is correlated with the mass inside 5 kpc (mainly baryons).
Journal of Cosmology and Astroparticle Physics 07/2014; 2014(07):019. DOI:10.1088/1475-7516/2014/07/019 · 5.81 Impact Factor
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• "With even higher resolution of the numerical simulations, the asymptotic flat Einasto profile [43] is shown to better fit the simulation results at the central most part [44] [45], "
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• "The DM mass distribution within halos is well described by a near-universal density profile, the so-called NFW profile [30], which has the form of a double-power-law with the logarithmic slope c d log q/d log r transitioning at the scale radius r s from c = À3 at large radii to c = À1 in the center. More recent higher resolution simulations, however, have found a central slope shallower than c = À1, indicating that the density profile may be better described by a functional form with a central slope gradually flattening to c = 0, e.g. the Einasto profile [31] [32]. "
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ABSTRACT: We present a review of the current state of the art of cosmological dark matter simulations, with particular emphasis on the implications for dark matter detection efforts and studies of dark energy. This review is intended both for particle physicists, who may find the cosmological simulation literature opaque or confusing, and for astro-physicists, who may not be familiar with the role of simulations for observational and experimental probes of dark matter and dark energy. Our work is complementary to the contribution by M. Baldi in this issue, which focuses on the treatment of dark energy and cosmic acceleration in dedicated N-body simulations. Truly massive dark matter-only simulations are being conducted on national supercomputing centers, employing from several billion to over half a trillion particles to simulate the formation and evolution of cosmologically representative volumes (cosmic scale) or to zoom in on individual halos (cluster and galactic scale). These simulations cost millions of core-hours, require tens to hundreds of terabytes of memory, and use up to petabytes of disk storage. The field is quite internationally diverse, with top simulations having been run in China, France, Germany, Korea, Spain, and the USA. Predictions from such simulations touch on almost every aspect of dark matter and dark energy studies, and we give a comprehensive overview of this connection. We also discuss the limitations of the cold and collisionless DM-only approach, and describe in some detail efforts to include different particle physics as well as baryonic physics in cosmological galaxy formation simulations, including a discussion of recent results highlighting how the distribution of dark matter in halos may be altered. We end with an outlook for the next decade, presenting our view of how the field can be expected to progress. (abridged)
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