scholarly journals Dark Matter: Observational Aspects

1987 ◽  
Vol 117 ◽  
pp. 243-261
Author(s):  
Jaan Einasto ◽  
Mihkel Joeveer ◽  
Enn Saar
Keyword(s):  
Dark Matter ◽  
Correlation Function ◽  
Dwarf Galaxies ◽  
Galactic Disk ◽  
Clusters Of Galaxies ◽  
Available Information ◽  
The Universe

A review of observational work on dark matter in USSR is given. Dynamically the dark matter can be located (i) in the galactic disk and/or in dwarf galaxies, (ii) in coronas of galaxies and in clusters of galaxies, and (iii) distributed smoothly in voids. The possible amount of matter in all three forms is discussed. Physically dark matter can be baryonic or non-baryonic, in the latter case either hot, warm or cold. Available information on the nature of dark matter is indirect, coming from theories of the formation of structure in the Universe. Two constraints to the formation scenarios are discussed, the galaxian correlation function and their morphology.

scholarly journals Large-Scale Structure in the Universe: Spatial Distribution and Peculiar Velocities

1987 ◽  
Vol 124 ◽  
pp. 335-348
Author(s):  
Neta A. Bahcall
Keyword(s):  
Dark Matter ◽  
Spatial Distribution ◽  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Clusters Of Galaxies ◽  
Large Scale Structures ◽  
Peculiar Velocities ◽  
Scale Structures ◽  
The Universe

The evidence for the existence of very large scale structures, ∼ 100h−1Mpc in size, as derived from the spatial distribution of clusters of galaxies is summarized. Detection of a ∼ 2000 kms−1 elongation in the redshift direction in the distribution of the clusters is also described. Possible causes of the effect are peculiar velocities of clusters on scales of 10–100h−1Mpc and geometrical elongation of superclusters. If the effect is entirely due to the peculiar velocities of clusters, then superclusters have masses of order 1016.5M⊙ and may contain a larger amount of dark matter than previously anticipated.

scholarly journals NIKA: a mm camera for Sunyaev-Zel’dovich science in clusters of galaxies

2020 ◽  
Vol 228 ◽  
pp. 00016
Author(s):  
J.F. Macías-Pérez ◽  
R. Adam ◽  
P. Ade ◽  
P. André ◽  
A. Andrianasolo ◽  
...  
Keyword(s):  
Dark Matter ◽  
Angular Resolution ◽  
High Redshift ◽  
Radial Pressure ◽  
Pressure Profile ◽  
Field Of View ◽  
Dual Band ◽  
Clusters Of Galaxies ◽  
The Universe

Clusters of galaxies, the largest bound objects in the Universe, constitute a cosmological probe of choice, which is sensitive to both dark matter and dark energy. Within this framework, the Sunyaev-Zel’dovich (SZ) effect has opened a new window for the detection of clusters of galaxies and for the characterization of their physical properties such as mass, pressure and temperature. NIKA, a KID-based dual band camera installed at the IRAM 30-m telescope, was particularly well adapted in terms of frequency, angular resolution, field-of-view and sensitivity, for the mapping of the thermal and kinetic SZ effect in high-redshift clusters. In this paper, we present the NIKA cluster sample and a review of the main results obtained via the measurement of the SZ effect on those clusters: reconstruction of the cluster radial pressure profile, mass, temperature and velocity.

scholarly journals Gravitational lenses as probes of the distribution of dark matter in the universe

1986 ◽  
Vol 119 ◽  
pp. 545-546
Author(s):  
R. Cowsik ◽  
P. Ghosh
Keyword(s):  
Dark Matter ◽  
Gravitational Lensing ◽  
Clusters Of Galaxies ◽  
Gravitational Lenses ◽  
The Universe ◽  
Individual Galaxies

Studies of the characteristic properties of gravitational lensing by clusters of galaxies suggest that the dark matter in them is probably smoothly distributed on the scale of the cluster itself, rather than being clumped into halos around individual galaxies.

scholarly journals Tidal Dwarf Galaxies and Missing Baryons

2010 ◽  
Vol 2010 ◽  
pp. 1-7 ◽  
Author(s):  
Frederic Bournaud
Keyword(s):  
Dark Matter ◽  
Spiral Galaxies ◽  
Dwarf Galaxies ◽  
High Redshift ◽  
Rotation Curves ◽  
Cosmological Problem ◽  
Flat Rotation Curves ◽  
Mass Size ◽  
Merger Rate ◽  
The Universe

Tidal dwarf galaxies form during the interaction, collision, or merger of massive spiral galaxies. They can resemble “normal” dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the “missing baryons,” known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem for which it is important to ascertain if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today. In this paper, “dark matter” is used to refer to the nonbaryonic matter, mostly located in large dark halos, that is, CDM in the standard paradigm, and “missing baryons” or “dark baryons” is used to refer to the baryons known to exist but hardly observed at redshift zero, and are a baryonic dark component that is additional to “dark matter”.

scholarly journals Dark Matter in Groups and Clusters of Galaxies

2000 ◽  
Vol 174 ◽  
pp. 360-372 ◽  
Author(s):  
Jaan Einasto ◽  
Maret Einasto
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Dynamical Evolution ◽  
Constant Term ◽  
Stellar Populations ◽  
Clusters Of Galaxies ◽  
Baryonic Matter ◽  
Dark Matter Halos ◽  
Hot Gas ◽  
The Universe

AbstractWe compare the characteristics of stellar populations with those of dark halos. Dark matter around galaxies, and in groups, clusters and voids is discussed. Modern data suggest that the overall density of matter in the Universe is ΩM = 0.3 ± 0.1, about 80 % of this matter is nonbaryonic dark matter, and about 20 % is baryonic, mostly in the form of hot intra-cluster and intragroup gas, the rest in stellar populations of galaxies. All bright galaxies are surrounded by dark matter halos of external radii 200 − 300 kpc; halos consist mostly of non-baryonic matter with some mixture of hot gas. The Universe is dominated by dark energy (cosmological constant) term. Dark matter dominates in the dynamical evolution of galaxies in groups and clusters.

TYPICAL SCALES IN THE CLUSTERING OF THE UNIVERSE

1995 ◽  
Vol 04 (04) ◽  
pp. 417-428
Author(s):  
LI-ZHI FANG ◽  
ZU-GAN DENG ◽  
XIAO-YANG XIA
Keyword(s):  
Correlation Function ◽  
Clusters Of Galaxies ◽  
High Confidence ◽  
Scale Free ◽  
Density Perturbations ◽  
Point Correlation ◽  
Point Correlation Function ◽  
Periodic Components ◽  
The Universe ◽  
Characteristic Scales

The cosmic density perturbations are not completely scale-free, i.e. preferential scales should exist in the clustering of the universe. Observations do show the existence of the typical scales, namely, the distribution of various objects cannot be described by a simple fractal law. However, the standard two-point correlation function statistic is ineffective in detecting the typical scales. A better method based on identifying the periodic components in two-point correlation functions was developed. Using this method, the typical scales have been systematically searched for in samples of galaxies, clusters of galaxies, quasars and absorption lines of quasars. It showed the existence of typical scales in the range of 20–130 h−1 Mpc with high confidence. In particular, two typical scales, 60−1 Mpc and 130−1 Mpc, have been detected in all the samples being analysed. Such “universal” scales are probably the characteristic scales in the primordial fluctuations of the universe. Other theoretical implications of the detected typical scales have also been reviewed.

scholarly journals Possible Inhomogeneities in the Universe on Scales of 100–300 MPC from Observations with the 6-Meter Telescope

1988 ◽  
Vol 130 ◽  
pp. 129-137
Author(s):  
A. I. Kopylov ◽  
D. Yu. Kuznetsov ◽  
T. S. Fetisova ◽  
V. F. Shvartsman
Keyword(s):  
Correlation Function ◽  
Hubble Constant ◽  
Galactic Latitude ◽  
Clusters Of Galaxies ◽  
Space Correlation ◽  
Point Space ◽  
Topology Of The Universe ◽  
The Universe

In 1986 the programme “The Northern Cone of Metagalaxy” has been finished with the 6-meter Telescope. In the course of the programme redshifts of all very rich compact clusters of galaxies inside the cone with galactic latitude and indirect estimates of redshifts ZLB < 0.28 have been measured. The total volume of the investigated region is V ≈ 500·106 Mpc3 (we accept Hubble constant H=50 km/s Mpc−1). A number of possible indications of existence of inhomogeneities in the Universe on scales greater than 100 Mpc are obtained: 1) the void of 400 Mpc in size; 2) the flat stratum of 150 Mpc thickness and 1000 Mpc diameter; 3) two-point space correlation function ξ (R = 200–300 Mpc) = 0.5±0.2. We found no indications that topology of the Universe is non-Euclidean on scales of 20–200 Mpc.

scholarly journals Dragging Force on Galaxies Due to Streaming Dark Matter

1990 ◽  
Vol 124 ◽  
pp. 645-649
Author(s):  
Tetsuya Hara ◽  
Shigeru Miyoshi
Keyword(s):  
Dark Matter ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Rest Frame ◽  
Background Radiation ◽  
Clusters Of Galaxies ◽  
Microwave Background ◽  
The Galaxy ◽  
Microwave Background Radiation ◽  
The Universe

It has been reported that galaxies in large regions (~102Mpc), including some clusters of galaxies, may be streaming coherently with velocities up to 600km/sec or more with respect to the rest frame determined by the microwave background radiation.) On the other hand, it is suggested that the dominant mass component of the universe is dark matter. Because we can only speculate the motion of dark matter from the galaxy motions, much attention should be paid to the correlation of velocities between the observed galaxies and cold dark matter. So we investigate whether such coherent large-scale streaming velocities are due to dark matter or only to baryonic objects which may be formed by piling up of gases due to some explosive events.

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.

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