scholarly journals Measuring the Density Fluctuation From the Cluster Gas Mass Function

1999 ◽  
Vol 183 ◽  
pp. 267-267
Author(s):  
K. Shimasaku
Keyword(s):  
Density Fluctuation ◽  
Mass Function ◽  
Baryon Density ◽  
Density Parameter ◽  
Clusters Of Galaxies ◽  
Fluctuation Spectrum ◽  
The Mean ◽  
Image Position ◽  
The Universe

We derive the gas mass function of clusters of galaxies to measure the density fluctuation spectrum on cluster scales. The baryon abundance confined in rich clusters is computed from the gas mass function and compared with the mean baryon density in the universe which is predicted by the BBN. This baryon fraction and the slope of the gas mass function put constraints on σ8 and the slope of the fluctuation spectrum. Adopting the density parameter of baryons Ωbh2 = 0.0175 ± 0.0075 and assuming that , we find for h = 0.7 ± 0.1. Our value of σ8 is independent of Ω0 and thus we can estimate Ω0 by combining σ8 as obtained in this study with those from Ω0-dependent analyses to date. Constraints are also derived for CDM and CHDM models.

scholarly journals Catalogue of Clusters that are Members of Superclusters

1983 ◽  
Vol 104 ◽  
pp. 185-186
Author(s):  
M. Kalinkov ◽  
K. Stavrev ◽  
I. Kuneva
Keyword(s):  
Standard Deviation ◽  
Correlation Coefficient ◽  
The Other ◽  
Clusters Of Galaxies ◽  
Number Of Clusters ◽  
Abell Clusters ◽  
The Mean ◽  
Abell Cluster ◽  
Image Position

An attempt is made to establish the membership of Abell clusters in superclusters of galaxies. The relation is used to calibrate the distances to the clusters of galaxies with two redshift estimates. One is m10, the magnitude of the ten-ranked galaxy, and the other is the “mean population,” P, defined by: where p = 40, 65, 105 … galaxies for richness groups 0, 1, 2 …, and r is the apparent radius in degrees given by: The first iteration for redshift, z1, is obtained from m10 alone: The standard deviation for Eq. (1) is 0.105, the number of clusters with known velocities is 342 and the correlation coefficient between observed and fitted values is 0.921. With zi from Eq. (1), we define Cartesian galactic coordinates Xi = Rih−1 cosBi cosLi, Yi = Rih−1 cosBi sinLi, Zi = Rih−1 sinBi for each Abell cluster, i = 1, …, 2712, where Ri is the distance to the cluster (Mpc), and Ho = 100 h km s−1 Mpc−1.

scholarly journals From 2-D to 3-D by Maximum Entropy Method

1988 ◽  
Vol 130 ◽  
pp. 559-559
Author(s):  
Ofer Lahav ◽  
Donald Lynden-Bell ◽  
Steve F. Gull
Keyword(s):  
Maximum Entropy Method ◽  
Entropy Method ◽  
Number Density ◽  
True Number ◽  
Spread Function ◽  
Redshift Survey ◽  
The Mean ◽  
Image Position ◽  
Distance Indicators ◽  
The Universe

We present a method of estimating distances to clusters of galaxies from twodimensional catalogues. The angular diameters (or magnitudes) of galaxies are used as distance indicators. The mapping from 2-D to 3-D is done by using a ‘diameter function’ (analogous to a luminosity function), which is based on a redshift survey from a section of the sky. The problem is formulated as follows. The number of galaxies with a metric diameter D in a volume element d3r is: where n(r) is the ‘true’ number density of galaxies at position r, n& is the mean number density of galaxies in the universe and ϕ(D)dD is the diameter function. We assume that within a narrow cone n(r) = n(r) and then express N(> θ), the number of galaxies greater than a certain angular diameter θ. In a discrete form we write the relation as: where ni is the density at the i – th distance bin and Pik is our ‘point spread function’, which is a function of the diameter function and Galactic obscuration. We express (2) in terms of χ2 statistics over the measurements, and require it to be less than a certain value. The entropy of the image is expressed as:

scholarly journals Trinity Relations in the Universe

1988 ◽  
Vol 130 ◽  
pp. 512-512
Author(s):  
Yasushi Suto ◽  
Roman Juskiewicz ◽  
Joseph Silk
Keyword(s):  
Perturbation Theory ◽  
Linear Perturbation ◽  
Mean Square ◽  
Mass Excess ◽  
Microwave Background ◽  
The Mean ◽  
Linear Perturbation Theory ◽  
Image Position ◽  
Density Irregularity ◽  
The Universe

On large scales where linear perturbation theory is valid, the mean square values of the mass excess , the peculiar velocity ν and the microwave background anisotropy due to the Sachs-Wolfe effect, are simply expressed in terms of the present-day power spectrum of the density irregularity P(k):

scholarly journals 47. Cosmology

1976 ◽  
Vol 16 (3) ◽  
pp. 137-157
Author(s):  
M. S. Longair
Keyword(s):  
Deceleration Parameter ◽  
Hubble Constant ◽  
Density Parameter ◽  
Massive Galaxies ◽  
A Value ◽  
The Mean ◽  
Points Of View ◽  
The Universe

A major procedural advance in the determination of the H0 and Ω has been that the problem is now being attacked from many different points of view and to some extent the observations are converging on preferred values of H0 and Ω (Ω = density parameter = 8πGρ0/3H0 where ρ0 is the mean density of matter in the Universe and H0 is the Hubble constant; Ω = 2q0 where q0 is the deceleration parameter). The classical approaches through the redshift-magnitude relation for the most massive galaxies in clusters suggest a value of H0 = 60 km s-1 Mpc (see the review by Tammann in IAU Symp. 63).

Ω0 from Clusters of Galaxies

2005 ◽  
Vol 201 ◽  
pp. 330-339
Author(s):  
Alain. Blanchard ◽  
Rachida. Sadat ◽  
Jim. Bartlett
Keyword(s):  
Power Spectrum ◽  
High Density ◽  
Rich Source ◽  
Low Density ◽  
Clusters Of Galaxies ◽  
Number Density ◽  
The Mean ◽  
Source Of Information ◽  
The Universe ◽  
Parameter Density

Clusters constitute a very rich source of information for cosmology. Their present day abundance can be used to found the normalization and the shape of the power spectrum. Clusters can also be used to determine the parameter density of the universe Ω − 0. The evolution of their number density is a powerful cosmological global test of the mean density of the Universe. It is fashionable to claim that the abundance of clusters does not change very much with clusters redshift and therefore favor a low density universe. This is an overstatement and analyses based on the most recent data rather favor a high density universe. The baryon fraction in clusters is an alternative method to derive the mean density of the Universe. Here again, taking into account several biases in the baryon fraction is derived from data, the actual baryon fraction seen in clusters can be reconcilied with a high density universe.

scholarly journals Measurements of The Primordial D/H Abundance Towards Quasars

2000 ◽  
Vol 198 ◽  
pp. 125-134
Author(s):  
David Tytler ◽  
John M. O'Meara ◽  
Nao Suzuki ◽  
Dan Lubin ◽  
Scott Burles ◽  
...  
Keyword(s):  
Neutral Hydrogen ◽  
Big Bang ◽  
Baryon Density ◽  
Light Nuclei ◽  
Clusters Of Galaxies ◽  
Big Bang Nucleosynthesis ◽  
Measurement And Analysis ◽  
Similar Density ◽  
Analysis Errors ◽  
The Universe

Big Bang Nucleosynthesis (BBN) is the synthesis of the light nuclei, Deuterium (D or 2H), 3He, 4He and 7Li during the first few minutes of the universe. In this review we concentrate on recent data which give the primordial deuterium (D) abundance.We have measured the primordial D/H in gas with very nearly primordial abundances. We use the Lyman series absorption lines seen in the spectra of quasars. We have measured D/H towards three QSOs, while a fourth gives a consistent upper limit. All QSO spectra are consistent with a single value for D/H: 3.325+0.22−0.25X10−5. From about 1994 − 1996, there was much discussion of the possibility that some QSOs show much higher D/H, but the best such example was shown to be contaminated by H, and no other no convincing examples have been found. Since high D/H should be much easier to detect, and hence it must be extremely rare or non-existent.The new D/H measurements give the most accurate value for the baryon to photon ratio, η, and hence the cosmological baryon density: ωb = 0.0190 ± 0.0009 (1σ) A similar density is required to explain the amount of Lyα absorption from neutral Hydrogen in the intergalactic medium (IGM) at redshift z ≃ 3, and to explain the fraction of baryons in local clusters of galaxies. The D/H measurements lead to predictions for the abundances of the other light nuclei, which generally agree with measurements. The remaining differences with some measurements can be explained by a combination of measurement and analysis errors or changes in the abundances after BBN. The measurements do not require physics beyond the standard BBN model. Instead, the agreement between the abundances is used to limit the non-standard physics.

scholarly journals Determination of Cosmological Parameters by Cosmic Microwave Background

1999 ◽  
Vol 183 ◽  
pp. 88-97
Author(s):  
Naoshi Sugiyama
Keyword(s):  
Cosmic Microwave Background ◽  
Gravitational Lensing ◽  
Microwave Radiometer ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
Linear Structure ◽  
Baryon Density ◽  
Density Parameter ◽  
Microwave Background ◽  
The Universe

After the sensational discovery of Cosmic Microwave Background (CMB) anisotropies by Differential Microwave Radiometer (DMR) boarded on the Cosmic Background Explore (COBE) (Smoot et al. 1992), the number of observational data of temperature fluctuations have been rapidly increasing (see e.g., White, Scott and Silk 1994) together with the understanding of physical processes of evolution of CMB anisotropies. Nowadays, CMB anisotropies are becoming one of the key observational object in the modern cosmology. CMB anisotropies provide us direct information at last scattering surface, i.e., redshift z ≈ 1000. Since the shape of the angular power spectrum of CMB anisotropies is highly sensitive to geometry of the universe, cosmological models and cosmological parameters, i.e., density parameter Ω0, Hubble constant h which is normalized by 100km/s/Mpc, cosmological constant Λ, baryon density ΩB and so on, CMB anisotropies are expected to be a new tool to understand our universe. Moreover, we can obtain information of thermal history of the universe after recombination (through the formation of secondary fluctuations and damping of primary fluctuations), physics of clusters of galaxies (through the Sunyaev-Zeldovich effect) and non-linear structure of the universe (through the gravitational lensing effect) from CMB anisotropies.

Beyond the Schwarzschild Metric

2018 ◽  
Author(s):  
David M. Wittman
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Gravitational Waves ◽  
Test Particle ◽  
Direct Detection ◽  
Relativistic Effects ◽  
Big Bang ◽  
Clusters Of Galaxies ◽  
General Relativistic ◽  
The Universe

General relativity explains much more than the spacetime around static spherical masses.We briefly assess general relativity in the larger context of physical theories, then explore various general relativistic effects that have no Newtonian analog. First, source massmotion gives rise to gravitomagnetic effects on test particles.These effects also depend on the velocity of the test particle, which has substantial implications for orbits around black holes to be further explored in Chapter 20. Second, any changes in the sourcemass ripple outward as gravitational waves, and we tell the century‐long story from the prediction of gravitational waves to their first direct detection in 2015. Third, the deflection of light by galaxies and clusters of galaxies allows us to map the amount and distribution of mass in the universe in astonishing detail. Finally, general relativity enables modeling the universe as a whole, and we explore the resulting Big Bang cosmology.

An Overall Approach for Microcrack and Inhomogeneity Toughening in Brittle Solids

1999 ◽  
Vol 15 (2) ◽  
pp. 57-68
Author(s):  
Huang Hsing Pan
Keyword(s):  
Poisson Ratio ◽  
Crack Density ◽  
Mean Field ◽  
Analytic Form ◽  
Density Parameter ◽  
Brittle Solids ◽  
The Matrix ◽  
Microcrack Toughening ◽  
Average Quantity ◽  
The Mean

ABSTRACTBased on the weight function theory and Hutchinson's technique, the analytic form of the toughness change near a crack-tip is derived. The inhomogeneity toughening is treated as an average quantity calculated from the mean-field approach. The solutions are suitable for the composite materials with moderate concentration as compared with Hutchinson's lowest order formula. The composite has the more toughened property if the matrix owns the higher value of the Poisson ratio. The composite with thin-disc inclusions obtains the highest toughening and that with spheres always provides the least effective one. For the microcrack toughening, the variations of the crack shape do not significantly affect the toughness change if the Budiansky and O'Connell crack density parameter is used. The explicit forms for three types of the void toughening and two types of the microcrack toughening are also shown.

scholarly journals Background Light from Population III Stars

1987 ◽  
Vol 117 ◽  
pp. 414-414
Author(s):  
Jonathan C. McDowell
Keyword(s):  
Dark Matter ◽  
Background Radiation ◽  
Large Fraction ◽  
Rest Mass ◽  
Critical Density ◽  
Density Parameter ◽  
Extragalactic Background Light ◽  
Background Light ◽  
Far Ultraviolet ◽  
The Universe

It has been proposed (e.g. Carr, Bond and Arnett 1984) that the first generation of stars may have been Very Massive Objects (VMOs, of mass above 200 M⊙) which existed at large redshifts and left a large fraction of the mass of the universe in black hole remnants which now provide the dynamical ‘dark matter’. The radiation from these stars would be present today as extragalactic background light. For stars with density parameter Ω* which convert a fraction ϵ of their rest-mass to radiation at a redshift of z, the energy density of background radiation in units of the critical density is ΩR = εΩ* / (1+z). The VMOs would be far-ultraviolet sources with effective temperatures of 105 K. If the radiation is not absorbed, the constraints provided by measurements of background radiation imply (for H =50 km/s/Mpc) that the stars cannot close the universe unless they formed at a redshift of 40 or more. To provide the dark matter (of one-tenth closure density) the optical limits imply that they must have existed at redshifts above 25.

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