A toy model to test the accuracy of cosmological<i>N</i>-body simulations

Labini, Francesco Sylos

doi:10.1051/0004-6361/201321037

Cited by 5 publications

(3 citation statements)

References 36 publications

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“…Indeed, the collapse in an expanding universe involves several additional parameters that can play a role in the dynamics (e.g. how precisely the background density is modelled) and additional numerical issues (notably concerning the control of numerical accuracy without energy conservation -see Joyce & Sylos Labini 2012;Sylos Labini 2013b).…”

Section: Introductionmentioning

confidence: 99%

Generation of angular momentum in cold gravitational collapse

Benhaiem

Joyce

Labini

et al. 2016

A&A

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During the violent relaxation of a self-gravitating system, a significant fraction of its mass may be ejected. If the time-varying gravitational field also breaks spherical symmetry, this mass can potentially carry angular momentum. Thus, starting initial configurations with zero angular momentum can, in principle, lead to a bound virialised system with non-zero angular momentum. Using numerical simulations we explore here how much angular momentum can be generated in a virialised structure in this way, starting from configurations of cold particles that are very close to spherically symmetric. For the initial configurations in which spherical symmetry is broken only by the Poissonian fluctuations associated with the finite particle number N, with N in range 10 3 to 10 5 , we find that the relaxed structures have standard "spin" parameters λ ∼ 10 −3 , and decreasing slowly with N. For slightly ellipsoidal initial conditions, in which the finite-N fluctuations break the residual reflection symmetries, we observe values λ ∼ 10 −2 , i.e. of the same order of magnitude as those reported for elliptical galaxies. The net angular momentum vector is typically aligned close to normal to the major semi-axis of the triaxial relaxed structure and of the ejected mass. This simple mechanism may provide an alternative, or complement, to the so-called tidal torque theory for understanding the origin of angular momentum in astrophysical structures.

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Section: Introductionmentioning

confidence: 99%

Generation of angular momentum in cold gravitational collapse

Benhaiem

Joyce

Labini

et al. 2016

A&A

Self Cite

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“…It has been used in determinations of the matter density, cluster mass and size, and the galaxy peculiar velocity field [3][4][5][6] and, more recently, as a crucial test to the accuracy of cosmological N-body simulations in the nonlinear regime [7,8].…”

Section: Introductionmentioning

confidence: 99%

Generalized Layzer-Irvine equation: The role of dark energy perturbations in cosmic structure formation

Avelino

Gomes

2013

Phys. Rev. D

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We derive, using the spherical collapse model, a generalized Layzer-Irvine equation which can be used to describe the gravitational collapse of cold dark matter in a dark energy background. We show that the usual Layzer-Irvine equation is valid if the dark matter and the dark energy are minimally coupled to each other and the dark energy distribution is homogeneous, independently of its equation of state. We compute the corrections to the standard Layzer-Irvine equation which arise in the presence of dark energy inhomogeneities assuming a minimal coupling between dark matter and dark energy. We show that, in the case of a dark energy component with a constant equation-of-state parameter consistent with the latest observational constraints, these corrections are expected to be small, even if the dark energy has a negligible sound speed. However, we find that, in more general models, the impact of dark energy perturbations on the dynamics of clusters of galaxies, which will be constrained by ESA's Euclid mission with unprecedented precision, might be significant.

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“…Beyond issues of numerical convergence, it is important to understand the limits imposed on the accuracy of results by the use of a finite number of particles to represent the theoretical continuum density field, and the associated introduction of a smoothing scale ε in the gravitational force that imposes a lower limit on the spatial resolution. The question of the suitable value of the ratio ε/ , where is the initial inter-particle distance, has been the subject of long-standing controversy (see, e.g., Joyce & Sylos Labini 2013;Sylos Labini 2013b;Baushev & Barkov 2018 and references therein). The use of a softening length that is fixed in physical coordinates rather than in comoving coordinates should mitigate the resolution effects, but a more detailed study is needed to proof that this is the case.…”

Section: Cosmological Halosmentioning

confidence: 99%

Properties of self-gravitating quasi-stationary states

Labini

Capuzzo-Dolcetta

2020

A&A

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Initially far out-of-equilibrium, self-gravitating systems form quasi-stationary states (QSS) through a collisionless relaxation dynamics. These may arise from a bottom-up aggregation of structures or in a top-down frame; their quasi-equilibrium properties are well described by the Jeans equation and are not universal. These QSS depend on initial conditions. To understand the origin of such dependence, we present the results of numerical experiments of initially cold and spherical systems characterized by various choices of the spectrum of initial density fluctuations. The amplitude of such fluctuations determines whether the system relaxes in a top-down or bottom-up manner. We find that statistical properties of the resulting QSS mainly depend upon the amount of energy exchanged during the formation process. In particular, in the violent top-down collapses the energy exchange is large and the QSS show an inner core with an almost flat density profile and a quasi Maxwell-Boltzmann (isotropic) velocity distribution, while their outer regions display a density profile ρ(r) ∝ r−α (α > 0) with radially elongated orbits. We show analytically that α = 4, in agreement with numerical experiments. In the less violent bottom-up dynamics, the energy exchange is much smaller, the orbits are less elongated, and 0 < α(r) ≤ 4, where the density profile is well fitted by the Navarro-Frenk-White behavior. Such a dynamical evolution is shown by both nonuniform spherical isolated systems and by halos extracted from cosmological simulations. We consider the relation of these results with the core-cusp problem and conclude that this can be solved naturally if galaxies form through a monolithic collapse.

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A toy model to test the accuracy of cosmologicalN-body simulations

Cited by 5 publications

References 36 publications

Generation of angular momentum in cold gravitational collapse

Generation of angular momentum in cold gravitational collapse

Generalized Layzer-Irvine equation: The role of dark energy perturbations in cosmic structure formation

Properties of self-gravitating quasi-stationary states

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