scholarly journals DISTRIBUTION FUNCTION OF DARK MATTER WITH CONSTANT ANISOTROPY

2008 ◽  
Vol 17 (08) ◽  
pp. 1283-1294 ◽  
Author(s):  
DING MA ◽  
PING HE
Keyword(s):  
Dark Matter ◽  
Asymptotic Behavior ◽  
Density Profile ◽  
Anisotropy Parameter ◽  
Outer Part ◽  
Distribution Functions ◽  
Dark Matter Halos ◽  
Spherical Models ◽  
Two Parameters ◽  
Inner Parts

N-body simulations of dark matter halos show that the density is cusped near the center of the halo. The density profile behaves as r–γ in the inner parts, where γ ≃ 1 for the NFW model and γ ≃ 1.5 for the Moore model, but in the outer parts the two models agree with each other in the asymptotic behavior of the density profile. The simulations also show information about the anisotropy parameter β(r) of the velocity distribution: β ≈ 0 in the inner part and β ≈ 0.5 (radially anisotropic) in the outer part of the halo. We provide some distribution functions F(E, L) with the constant anisotropy parameter β for the two spherical models of dark matter halos: a new generalized NFW model and a generalized Moore model. There are two parameters α and ∊ for those two generalized models to determine the asymptotic behavior of the density profile. In this paper, we concentrate on the situation of β(r) = 1/2 from the viewpoint of the simulation.

scholarly journals Triaxial versus Spherical Dark Matter Halo Profiles

2006 ◽  
Vol 23 (3) ◽  
pp. 125-128 ◽  
Author(s):  
Alexander Knebe ◽  
Volkmar Wießner
Keyword(s):  
Dark Matter ◽  
Mass Distribution ◽  
Density Profile ◽  
Simple Formula ◽  
Dark Matter Halo ◽  
Spherically Symmetric ◽  
Dark Matter Halos ◽  
Spherical Shells ◽  
Arbitrary Axis ◽  
Inner Parts

AbstractWhen analyzing dark matter halos forming in cosmological n-body simulations, it is common practice to obtain the density profile utilizing spherical shells. However, it is also known that the systems under investigation are far from spherically symmetric but, rather, follow a triaxial mass distribution. In this study we present an estimator for the error introduced by spherically averaging an elliptical mass distribution. We systematically investigate the differences arising when using a triaxial density profile under the assumption of spherical symmetry. We show that the variance in the density can be as large as 50% in the outer parts of dark matter halos for extreme (but still credible) axis ratios of 0.55: 0.67: 1. The inner parts are less affected but still show a scatter at the 16% level for these prolate systems. For more moderate ellipticities, i.e. axis ratios of 0.73: 0.87: 1, the error is smaller but still as large as 10–20% depending on distance. We further provide a simple formula that allows estimation of this variance as a function of radius for arbitrary axis ratios. We conclude that highly prolate and/or oblate systems are better fit by analytical profiles that take into account the triaxial nature of cosmological objects.

scholarly journals The Structure of Dark Matter Halos in Dwarf Galaxies

1996 ◽  
Vol 171 ◽  
pp. 175-178 ◽  
Author(s):  
A. Burkert
Keyword(s):  
Dark Matter ◽  
Density Distribution ◽  
Density Profile ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Dark Matter Halos ◽  
Density Structure ◽  
Rotation Curves ◽  
Low Mass ◽  
Inner Parts

Some dwarf galaxies have HI rotation curves that are completely dominated by a surrounding dark matter (DM) halo (e.g. Carignan & Freeman 1988). These objects represent ideal candidates for an investigation of the density structure of low-mass DM halos as the uncertainties resulting from the subtraction of the visible component are small, even in the innermost regions. Flores & Primack (1994) and Moore (1994) compared the observed DM rotation curves with the profiles, predicted from cosmological cold dark matter (CDM) calculations. They found an interesting discrepancy: whereas the calculations lead to a DM density distribution which diverges as ρ ∼ r−1 in the inner parts, the observed rotation curves indicate shallow DM cores which can be described by an isothermal density profile with finite central density.

scholarly journals Density profile asymptotes at the centre of dark matter halos

2003 ◽  
Vol 404 (3) ◽  
pp. 809-814 ◽  
Author(s):  
J. P. Mücket ◽  
M. Hoeft
Keyword(s):  
Dark Matter ◽  
Density Profile ◽  
Dark Matter Halos

The Role of the Radial Orbit Instability in Dark Matter Halo Formation and Structure

2006 ◽  
Vol 2 (S235) ◽  
pp. 124-124
Author(s):  
J. M. Meyer ◽  
J. J. Dalcanton ◽  
T. R. Quinn ◽  
L. L. R. Williams ◽  
E. I. Barnes ◽  
...  
Keyword(s):  
Dark Matter ◽  
Density Profile ◽  
Dark Matter Halo ◽  
Dark Matter Halos ◽  
Radial Orbit ◽  
Profile Changes ◽  
Analytic Models ◽  
The Universe ◽  
Scale Length

AbstractFor nearly a decade, N-body simulations have revealed a nearly universal dark matter density profile. This density profile appears to be robust to changes in the overall density of the universe and the underlying power spectrum. Despite its universality, however, the physical origin of this profile has not yet been well understood. Semi-analytic models have suggested that scale lengths in dark matter halos may be determined by the onset of the radial orbit instability. We have tested this theory using N-body simulations of collapsing dark matter halos. The resulting halo structures are prolate in shape, due to the mild aspect of the instability. We find that the radial orbit instability sets a scale length at which the velocity dispersion changes rapidly from isotropic to radially anisotropic. Preliminary analysis suggests that this scale length is proportional to the radius at which the density profile changes shape, as is the case in the semi-analytic models; however, the coefficient of proportionality is different by a factor of ~2. We conclude that the radial orbit instability may be a key physical mechanism responsible for the nearly universal profiles of simulated dark matter halos.

scholarly journals Structural Evolution of Substructure

2003 ◽  
Vol 208 ◽  
pp. 403-404
Author(s):  
Eric Hayashi ◽  
Julio F. Navarro
Keyword(s):  
Dark Matter ◽  
Gravitational Potential ◽  
Density Profile ◽  
Outer Region ◽  
Structural Evolution ◽  
Dark Matter Halos ◽  
Initial Profile ◽  
Host System ◽  
Elliptical Orbits ◽  
Mass Profiles

The evolution of substructure in dark matter halos is investigated in a series of simulations of N = 105 satellite halos on elliptical orbits in the gravitational potential of a much larger host system. The bound mass of the satellite decreases with each pericentric passage and most of the mass is lost from the outer region of the satellite halo. We parameterize the change in its density profile by modifying the initial profile by a factor proportional to (1 + r-3), which results in reasonable fits to the mass profiles of tidally stripped subhalos.

scholarly journals DISTRIBUTION FUNCTION IN THE CENTER OF THE DARK MATTER HALO

2009 ◽  
Vol 18 (03) ◽  
pp. 477-484
Author(s):  
DING MA ◽  
PING HE
Keyword(s):  
Dark Matter ◽  
Distribution Function ◽  
Phase Space ◽  
Velocity Dispersion ◽  
Anisotropy Parameter ◽  
Dark Matter Halo ◽  
Phase Space Density ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Space Density

N-body simulations of dark matter halos show that the density profiles of the halos behave as ρ(r) ∝ r-α(r), where the density logarithmic slope α ≃ 1–1.5 in the center and α ≃ 3–4 in the outer parts of the halos. However, some observations are not in agreement with simulations in the very central region of the halos. The simulations also show that the velocity dispersion anisotropy parameter β ≈ 0 in the inner part of the halo and the so-called pseudo–phase-space density ρ/σ3 behaves as a power law in radius r. With these results in mind, we study the distribution function and the pseudo–phase-space density ρ/σ3 of the center of dark matter halos and find that they are closely related.

scholarly journals New Model of Density Distribution for Fermionic Dark Matter Halos

2018 ◽  
Vol 63 (9) ◽  
pp. 769 ◽  
Author(s):  
A. V. Rudakovskyi ◽  
D. O. Savchenko
Keyword(s):  
Dark Matter ◽  
Density Distribution ◽  
Density Profile ◽  
Initial Phase ◽  
Matter Density ◽  
Dark Matter Halos ◽  
New Model ◽  
Dwarf Spheroidal Galaxies ◽  
The Core ◽  
Dirac Distribution

We formulate a new model of density distribution for halos made of warm dark matter (WDM) particles. The model is described by a single microphysical parameter – the mass (or, equivalently, the maximal value of the initial phase-space density distribution) of dark matter particles. Given the WDM particle mass and the parameters of a dark matter density profile at the halo periphery, this model predicts the inner density profile. In the case of initial Fermi–Dirac distribution, we successfully reproduce cored dark matter profiles from N-body simulations. We calculate also the core radii of warm dark matter halos of dwarf spheroidal galaxies for particle masses mFD = 100, 200, 300, and 400 eV.

scholarly journals The differential energy distribution of the universal density profile of dark halo

2003 ◽  
Vol 208 ◽  
pp. 397-398
Author(s):  
Asao Habe ◽  
Chiaki Hanyu
Keyword(s):  
Dark Matter ◽  
Energy Distribution ◽  
Density Distribution ◽  
Density Profile ◽  
Analytical Formula ◽  
Dark Halo ◽  
Dark Matter Halos ◽  
Physical Reason

We study the differential energy distribution of dark matter halos, carrying out cosmological N-body simulation. From our simulation, we give an analytical formula of the differential energy distribution of dark matter in the halos. Density distribution from the analytical formula is consistent with the Navarro, Frenk, and White (NFW) profile. We find that a parameter in our analytical formula of differential energy distribution is related with the slope of inner cusp of dark halo. We discuss physical reason of form of the analytical formula.

scholarly journals Dark matter density profile and galactic metric in Eddington-inspired Born–Infeld gravity

2014 ◽  
Vol 29 (09) ◽  
pp. 1450049 ◽  
Author(s):  
Tiberiu Harko ◽  
Francisco S. N. Lobo ◽  
M. K. Mak ◽  
Sergey V. Sushkov
Keyword(s):  
Dark Matter ◽  
Gravitational Field ◽  
Density Profile ◽  
Galactic Center ◽  
Matter Density ◽  
Dark Matter Halos ◽  
Field Equations ◽  
Metric Tensor ◽  
Dark Matter Density ◽  
Gravitational Field Equations

We consider the density profile of pressureless dark matter in Eddington-inspired Born–Infeld (EiBI) gravity. The gravitational field equations are investigated for a spherically symmetric dark matter galactic halo, by adopting a phenomenological tangential velocity profile for test particles moving in stable circular orbits around the galactic center. The density profile and the mass distribution, as well as the general form of the metric tensor is obtained by numerically integrating the gravitational field equations, and in an approximate analytical form by using the Newtonian limit of the theory. In the weak field limit, the dark matter density distribution is described by the Lane–Emden equation with polytropic index n = 1, and is nonsingular at the galactic center. The parameter κ of the theory is determined so that the theory could provide a realistic description of the dark matter halos. The gravitational properties of the dark matter halos are also briefly discussed in the Newtonian approximation.

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