scholarly journals The True Surface Mass density of Cold Dark Matter Halos

2007 ◽  
Vol 3 (S244) ◽  
pp. 358-359
Author(s):  
Janne Holopainen ◽  
E. Zackrisson ◽  
A. Knebe ◽  
P. Nurmi ◽  
P. Heinämaki ◽  
...  
Keyword(s):  
Dark Matter ◽  
Analytical Model ◽  
Light Propagation ◽  
Cold Dark Matter ◽  
Mass Density ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Surface Mass ◽  
Symmetric Density ◽  
Surface Mass Density

AbstractThe cold dark matter (CDM) scenario generically predicts the existence of triaxial dark matter halos which contain notable amounts of substructure. However, analytical halo models with smooth, spherically symmetric density profiles are routinely adopted in the modelling of light propagation effects through such objects. In this paper, we report the biases introduced by this procedure by comparing the surface mass densities of actual N-body halos against the widely used analytical model suggested by Navarro, Frenk and White (1996) (NFW). We conduct our analysis in the redshift range of 0.0 − 1.5.In cluster sized halos, we find that triaxiality can cause scatter in the surface mass density of the halos up to σ+= +60% and σ−= −70%, where the 1-σ limits are relative to the analytical NFW model given value. Subhalos can increase this scatter to σ+= +70% and σ−= −80%. In galaxy sized halos, the triaxial scatter can be as high as σ+= +80% and σ−= −70%, and with subhalos the values can change to σ+= +40% and σ−= −80%.We have developed an analytical model for the surface mass density scatter as a function of distance to the halo centre, halo redshift and halo mass. The analytical description enables one to investigate the reliability of results obtained with simplified halo models. Additionally, it provides the means to add simulated surface density scatter to analytical density profiles. We have tested our model on the calculation of microlensing optical depths for MACHOs in CDM halos.

scholarly journals Lensing Diagnostics of Halo Substructure

2004 ◽  
Vol 220 ◽  
pp. 85-90
Author(s):  
Shude Mao
Keyword(s):  
Dark Matter ◽  
Numerical Simulations ◽  
Cold Dark Matter ◽  
Mass Density ◽  
Broad Band ◽  
Mass Range ◽  
Dark Matter Halos ◽  
Gravitational Lenses ◽  
Surface Mass ◽  
Surface Mass Density

The Cold Dark Matter (CDM) hierarchical structure formation theory predicts substructures in dark matter halos. the number of predicted subhalos seems to exceed the observed number of luminous satellite galaxies. Gravitational lenses can be used to probe luminous or dark substructures. Image positions and flux ratios in broad-band (including radio and optical) and emission lines can all be used to probe substructures on different mass scales. the observed gravitational lenses appear to require a few percent of the mass surface density in substructures within the mass range of 104M⊙ − 109M⊙. Numerical simulations predict roughly the same mass fraction in substructures within the virialised region. But at typical image positions (a few percent of the virial radius), the predicted surface mass density in substructures appears to be lower than required. Both observations and numerical simulations are somewhat uncertain at present so it is not yet clear whether the discrepancy is severe.

scholarly journals The signature of primordial black holes in the dark matter halos of galaxies

2020 ◽  
Vol 633 ◽  
pp. A107 ◽  
Author(s):  
M. R. S. Hawkins
Keyword(s):  
Black Holes ◽  
Dark Matter ◽  
Surface Brightness ◽  
Mass Density ◽  
Stellar Surface ◽  
Primordial Black Holes ◽  
Dark Matter Halos ◽  
Surface Mass ◽  
Surface Mass Density ◽  
The Individual

Aims. The aim of this paper is to investigate the claim that stars in the lensing galaxy of a gravitationally lensed quasar system can always account for the observed microlensing of the individual quasar images. Methods. A small sample of gravitationally lensed quasar systems was chosen where the quasar images appear to lie on the fringe of the stellar distribution of the lensing galaxy. As with most quasar systems, all the individual quasar images were observed to be microlensed. The surface brightness of the lensing galaxy at the positions of the quasar images was measured from Hubble Space Telescope frames, and converted to stellar surface mass density. The surface density of smoothly distributed dark matter at the image positions was obtained from lensing models of the quasar systems and applied to the stellar surface mass density to give the optical depth to microlensing. This was then used to assess the probability that the stars in the lensing galaxy could be responsible for the observed microlensing. The results were supported by microlensing simulations of the star fields around the quasar images combined with values of convergence and shear from the lensing models. Results. Taken together, the probability that all the observed microlensing is due to stars was found to be ∼3 × 10−4. Errors resulting from the surface brightness measurement, the mass-to-light ratio, and the contribution of the dark matter halo do not significantly affect this result. Conclusions. It is argued that the most plausible candidates for the microlenses are primordial black holes, either in the dark matter halos of the lensing galaxies, or more generally distributed along the lines of sight to the quasars.

scholarly journals Satellite galaxies in the Illustris-1 simulation: anisotropic locations around relatively isolated hosts

2019 ◽  
Vol 489 (1) ◽  
pp. 459-469 ◽  
Author(s):  
Tereasa G Brainerd ◽  
Masaya Yamamoto
Keyword(s):  
Dark Matter ◽  
Mass Density ◽  
Stellar Mass ◽  
Stellar Surface ◽  
Surface Mass ◽  
Degree Of Anisotropy ◽  
Surface Mass Density ◽  
The Mean ◽  
Satellite Galaxies ◽  
Stellar Masses

ABSTRACT We investigate the locations of satellite galaxies in the z = 0 redshift slice of the hydrodynamical Illustris-1 simulation. As expected from previous work, the satellites are distributed anisotropically in the plane of the sky, with a preference for being located near the major axes of their hosts. Due to misalignment of mass and light within the hosts, the degree of anisotropy is considerably less when satellite locations are measured with respect to the hosts’ stellar surface mass density than when they are measured with respect to the hosts’ dark matter surface mass density. When measured with respect to the hosts’ dark matter surface mass density, the mean satellite location depends strongly on host stellar mass and luminosity, with the satellites of the faintest, least massive hosts showing the greatest anisotropy. When measured with respect to the hosts’ stellar surface mass density, the mean satellite location is essentially independent of host stellar mass and luminosity. In addition, the satellite locations are largely insensitive to the amount of stellar mass used to define the hosts’ stellar surface mass density, as long as at least 50–70 per cent of the hosts’ total stellar mass is used. The satellite locations are dependent upon the stellar masses of the satellites, with the most massive satellites having the most anisotropic distributions.

scholarly journals Structure of Dark Matter Halo

1999 ◽  
Vol 183 ◽  
pp. 155-155
Author(s):  
Toshiyuki Fukushige ◽  
Junichiro Makino
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Temperature Inversion ◽  
Dark Matter Halo ◽  
Temperature Structure ◽  
Galactic Halos ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Order Of Magnitude ◽  
Special Purpose Computer

We performed N-body simulation on special-purpose computer, GRAPE-4, to investigate the structure of dark matter halos (Fukushige, T. and Makino, J. 1997, ApJL, 477, L9). Universal profile proposed by Navarro, Frenk, and White (1996, ApJ, 462, 563), which has cusp with density profiles ρ ∝r−1in density profile, cannot be reproduced in the standard Cold Dark Matter (CDM) picture of hierarchical clustering. Previous claims to the contrary were based on simulations with relatively few particles, and substantial softening. We performed simulations with particle numbers an order of magnitude higher, and essentially no softening, and found that typical central density profiles are clearly steeper than ρ ∝r−1, as shown in Figure 1. In addition, we confirm the presence of a temperature inversion in the inner 5 kpc of massive galactic halos, and give a natural explanation for formation of the temperature structure.

scholarly journals Are the most super-massive dark compact objects harbored at the center of dark matter halos?

2014 ◽  
Vol 23 (12) ◽  
pp. 1442020 ◽  
Author(s):  
C. R. Argüelles ◽  
R. Ruffini
Keyword(s):  
Dark Matter ◽  
Mass Density ◽  
Compact Objects ◽  
Fermion Mass ◽  
Dark Matter Halos ◽  
Core Mass ◽  
Density Profiles ◽  
Equilibrium Configurations ◽  
Isothermal System ◽  
The One

We study an isothermal system of semi-degenerate self-gravitating fermions in general relativity (GR). The most general solutions present is mass density profiles with a central degenerate compact core governed by quantum statistics followed by an extended plateau, and ending in a power law behavior r-2. By fixing the fermion mass m in the keV regime, the different solutions depending on the free parameters of the model: the degeneracy and temperature parameters at the center, are systematically constructed along the one-parameter sequences of equilibrium configurations up to the critical point, which is represented by the maximum in a central density (ρ0) versus core mass (Mc) diagram. We show that for fully degenerate cores, the Oppenheimer–Volkoff (OV) mass limit [Formula: see text] is obtained, while instead for low degenerate cores, the critical core mass increases showing the temperature effects in a nonlinear way. The main result of this work is that when applying this theory to model the distribution of dark matter (DM) in big elliptical galaxies from miliparsec distance-scales up to 102Kpc, we do not find any critical core-halo configuration of self-gravitating fermions, able to explain both the most super-massive dark object at their center together with the DM halo simultaneously.

scholarly journals Structure of Dark Halos: Model-independent Information from HI Rotation Curves

1997 ◽  
Vol 14 (1) ◽  
pp. 11-14 ◽  
Author(s):  
Penny D. Sackett
Keyword(s):  
Mass Density ◽  
Large Radius ◽  
Dark Matter Halos ◽  
Rotation Curves ◽  
Surface Mass ◽  
Independent Information ◽  
The Galaxy ◽  
Flat Rotation Curves ◽  
Surface Mass Density ◽  
Model Independent

AbstractAlthough the approximately flat rotation curves of gas in the outskirts of spirals are generally taken as strong evidence for spherical, isothermal dark matter halos, this conclusion is often incorrect and always model-dependent. A re-examination of the old and (nearly) model-independent inversion technique for determining the surface mass density of galaxies from their kinematics is presented. The method is shown to be relatively insensitive to noise in the kinematics. Due to incomplete kinematical knowledge at large radius, however, the surface mass density is reliable only in the inner half of the galaxy, a result that also applies to traditional rotation curve fitting techniques.

scholarly journals Formation of dwarf galaxies and small-scale problems of CDM

2006 ◽  
Vol 2 (S235) ◽  
pp. 385-388
Author(s):  
Oleg Y. Gnedin
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Galactic Halo ◽  
Dwarf Galaxies ◽  
Small Scale ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Gas Cooling ◽  
Low Efficiency ◽  
The Universe

AbstractThe concordance cosmological model based on cold dark matter makes definitive predictions for the growth of galaxies in the Universe, which are being actively studied using numerical simulations. These predictions appear to contradict the observations of dwarf galaxies. Dwarf dark matter halos are more numerous and have steeper central density profiles than the observed galaxies. The first of these small-scale problems, the “missing satellites problem”, can be resolved by accounting for the low efficiency of gas cooling and star formation in dwarf halos. A newly-discovered class of HyperVelocity Stars will soon allow us to test another generic prediction of CDM models, the triaxial shapes of dark matter halos. Measuring the proper motions of HVS will probe the gravitational potential out to 100 kpc and will constrain the axis ratios and the orientation of the Galactic halo.

scholarly journals The Structure of Cold Dark Matter Halos

1996 ◽  
Vol 171 ◽  
pp. 255-258 ◽  
Author(s):  
Julio F. Navarro
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Large Range ◽  
Disk Galaxies ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Halo Structure ◽  
Disk Rotation ◽  
Disk Mass ◽  
The Masses

High resolution N-body simulations show that the density profiles of dark matter halos formed in the standard CDM cosmogony can be fit accurately by scaling a simple “universal” profile. Regardless of their mass, halos are nearly isothermal over a large range in radius, but significantly shallower than r–2 near the center and steeper than r–2 in the outer regions. The characteristic overdensity of a halo correlates strongly with halo mass in a manner consistent with the mass dependence of the epoch of halo formation. Matching the shape of the rotation curves of disk galaxies with this halo structure requires (i) disk mass-to-light ratios to increase systematically with luminosity, (ii) halo circular velocities to be systematically lower than the disk rotation speed, and (iii) that the masses of halos surrounding bright galaxies depend only weakly on galaxy luminosity. This offers an attractive explanation for the puzzling lack of correlation between luminosity and dynamics in observed samples of binary galaxies and of satellite companions of bright spiral galaxies, suggesting that the structure of dark matter halos surrounding bright spirals is similar to that of cold dark matter halos.

scholarly journals Understanding the cosmic web

2014 ◽  
Vol 11 (S308) ◽  
pp. 47-56 ◽  
Author(s):  
Marius Cautun ◽  
Rien van de Weygaert ◽  
Bernard J. T. Jones ◽  
Carlos S. Frenk
Keyword(s):  
Time Evolution ◽  
Qualitative Agreement ◽  
Mass Density ◽  
Good Qualitative Agreement ◽  
Subsequent Evolution ◽  
Density Profiles ◽  
Surface Mass ◽  
Analysis Tools ◽  
Surface Mass Density ◽  
Hierarchical Pattern

AbstractWe investigate the characteristics and the time evolution of the cosmic web from redshift, z=2, to present time, within the framework of the \nexus{} algorithm. This necessitates the introduction of new analysis tools optimally suited to describe the very intricate and hierarchical pattern that is the cosmic web. In particular, we characterising filaments (walls) in terms of their linear (surface) mass density, which is very good in capturing the evolution of these structures. At early times the cosmos is dominated by tenuous filaments and sheets, which, during subsequent evolution, merge together, such that the present day web is dominated by fewer, but much more massive, structures. We show also that voids are more naturally described in terms of their boundaries and not their centres. We illustrate this for void density profiles, which, when expressed as a function of the distance from void boundary, show a universal profile in good qualitative agreement with the theoretical shell-crossing framework of expanding underdense regions.

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