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1.
The dynamical masses of dwarf-spheroidals, spiral and elliptical galaxies, dwarf irregular binaries, groups of galaxies and clusters are shown to lie in a band about the M ∼ ρR3 line. The value of ρ is approximately the same as that estimated for unseen matter in the solar neighbourhood. The clusters themselves lie about theM ∼ R -3 line derived for a self-gravitating neutrino gas; their masses are distributed around the maximum Jeans-mass, MJmax. corresponding to mv - 10 eV in an expanding universe. The present day length scales of clusters and the dispersion in the velocities observed within them are understood in terms of a 100-fold expansion subsequent to the initial growth of the fluctuations at MJmax. These systematics on theR-M plane imply that the initial condensations in the expanding universe are on the scale of the rich clusters of galaxies, these condensations were triggered dominantly by the gravitation of the neutrinos and the constant density of al systems arises naturally due to the embedding of these systems in the large scale neutrino condensations. If the neutrino density falls off asr -2 beyond the cluster edge till the distributions from different clusters overlap, then the mean density of the neutrinos approximately equals the closure density of the universe.  相似文献   

2.
Chandra X-ray observations of rich, dynamically relaxed galaxy clusters allow the properties of the X-ray gas and the total gravitating mass to be determined precisely. Here, we discuss how Chandra observations may be used as a powerful tool for cosmological studies. By combining Chandra X-ray results on the X-ray gas mass fractions in clusters with independent measurements of the Hubble constant and the mean baryonic matter density of the universe, we obtain a tight constraint on the mean total matter density of the universe, Οm, and an interesting constraint on the cosmological constant, ΟΛ. Using these results, together with the observed local X-ray luminosity function of the most X-ray luminous galaxy clusters, a mass-luminosity relation determined from Chandra and ROSAT X-ray data and weak gravitational lensing observations, and the mass function predicted by numerical simulations, we obtain a precise constraint on the normalization of the power spectrum of density fluctuations in the nearby universe,σ8. We compare our results with those obtained from other, independent methods. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
The visible and invisible matters in the universe have rather different density distributions. The formar is obvious clustered on the scales of galaxies, clusters and superclusters, while the latter is rather more uniform. Here we discuss the possibility of this difference forming during the stage of Jeans clustering. For a two-component universe, so long as the growth and decay time-scales of gravitational perturbation satisfy a certain relation, the perturbation will grow in one component and decay in the other. Specific calculations are made for the development of inhomogeneity in a universe consisting of two collisionless gases. It is found that as long as the densities of the Jeans lengths of the two components satisfy the relations ?1 ? ?2λ1j ? λ2j, then, whether the initial perturbation is in component 1 or component 2, the result will be component 1 having a large degree of inhomogeneity and component 2, a small one. If the invisible matter is mainly neutrino with a finite rest-mass, then the above result can be used to explain the quasi-uniform distribution of the invisible matter.  相似文献   

4.
A new paradigm in cosmology is presented: A geometrical phase transition from the Minkowski space to an anti-deSitter space at its maximum of extension instead of a big bang with inflation. This scenario implies an open universe with a negative cosmological constant which replaces completely the cold dark matter in galaxy clusters. Baryonic matter and radiation are created from the gravitational field over a very long period of about 30 billion years. The contracting universe runs then after a further period of 13 billion years through a minimum with T max ≃ 1.8 × 1012 K and a particle density n max ≃ 5 × 1038 cm-3 due to Hagedorn’s theory of a hadron gas. After the run through the minimum the universe expands like a big bang universe and reaches due to the negative cosmological constant after 44 billion years its maximal extension. Then it contracts again, and so on: An open ever-oscillating universe.  相似文献   

5.
A sample of 11 thousand galaxies with radial velocities V LG < 3500 km/s is used to study the features of the local distribution of luminous (stellar) and dark matter within a sphere of radius of around 50 Mpc around us. The average density of matter in this volume, ?? m,loc = 0.08 ± 0.02, turns out to be much lower than the global cosmic density ?? m,glob = 0.28 ± 0.03. We discuss three possible explanations of this paradox: 1) galaxy groups and clusters are surrounded by extended dark halos, the major part of the mass of which is located outside their virial radii; 2) the considered local volume of the Universe is not representative, being situated inside a giant void; and 3) the bulk of matter in the Universe is not related to clusters and groups, but is rather distributed between them in the form of massive dark clumps. Some arguments in favor of the latter assumption are presented. Besides the two well-known inconsistencies of modern cosmological models with the observational data: the problem of missing satellites of normal galaxies and the problem of missing baryons, there arises another one??the issue of missing dark matter.  相似文献   

6.
The distribution of X-ray sources in our galaxy is obtained, assuming that the absolute X-ray luminosities of these sources are the same. The distribution is found to be in good correlation with the distribution of interstellar gas. The density of X-ray sources is nearly proportional to the square density of gas. This indicates that X-ray sources are comparatively young. The relation between the densities of X-ray sources and gas allows us to estimate the X-ray intensities of various objects such as Magellanic Clouds and Andromeda nebula, and also to obtain the average X-ray luminosity of spiral galaxies. The latter should increase as the age of a galaxy decreases, since the amount of gas decreases as the galaxy evolves. Under the assumptions that the gas density is inversely proportional to the age and that galaxies older thant 0/30 are visible in X-rays, wheret 0 is the present age of the universe, the contribution of X-ray sources in distant galaxies to the background component is calculated. The intensity and the spectrum of the background component of X-rays thus obtained are in fair agreement with observed ones in the energy range between 1 and 4 keV but significantly deviate from the latter at high energies.  相似文献   

7.
We have performed a series ofN-body experiments including the effects of a massive dominant background which follows Schuster's density law in order to simulate clusters of galaxies in which a smoothly distributed dark component is present. The existence of this background is inferred from the weak luminosity segregation observed in clusters which, however, show several characteristics of well-relaxed systems. The comparison of the velocity dispersion profiles of three clusters of galaxies (Coma, Perseus, and Virgo) with those obtained in the numerical experiments allows us to place some constraints on both the distribution and amount of distributed dark material in these clusters. The profiles are rather insensitive to variations in the ratio of the background mass to the mass attached to galaxies (M b/Mg), but exhibit a strong dependence on their relative concentration. We conclude that highly concentrated background models are not consistent with observations. We find a maximum value for the ratio of the gravitational radius of the galaxies and the background (R g/Rb) (approximately 0.6) and using previous results (Navarroet al., 1986) we conclude that virial theorem masses underestimate the total mass (M b+M g) of the clusters. As a final result, we derive a minimum value for theM b/Mg ratio. All these conclusions could apply in general if Coma, Perseus, and Virgo constitute a fair sample of the rich clusters of galaxies in the Universe.  相似文献   

8.
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9.
We study the mass distribution in six nearby  ( z < 0.06)  relaxed Abell clusters of galaxies A0262, A0496, A1060, A2199, A3158 and A3558. Given the dominance of dark matter in galaxy clusters, we approximate their total density distribution by the Navarro, Frenk & White (NFW) formula characterized by virial mass and concentration. We also assume that the anisotropy of galactic orbits is reasonably well described by a constant and that galaxy distribution traces that of the total density. Using the velocity and position data for 120–420 galaxies per cluster we calculate, after removal of interlopers, the profiles of the lowest order even velocity moments, dispersion and kurtosis. We then reproduce the velocity moments by jointly fitting the moments to the solutions of the Jeans equations. Including the kurtosis in the analysis allows us to break the degeneracy between the mass distribution and anisotropy and constrain the anisotropy as well as the virial mass and concentration. The method is tested in detail on mock data extracted from the N -body simulations of dark matter haloes. We find that the best-fitting Galactic orbits are remarkably close to isotropic in most clusters. Using the fitted pairs of mass and concentration parameters for the six clusters, we conclude that the trend of decreasing concentration for higher masses found in the cosmological N -body simulations is consistent with the data. By scaling the individual cluster data by mass, we combine them to create a composite cluster with 1465 galaxies and perform a similar analysis on such sample. The estimated concentration parameter then lies in the range  1.5 < c < 14  and the anisotropy parameter in the range  −1.1 < β < 0.5  at the 95 per cent confidence level.  相似文献   

10.
The present-day large increase of the amount of data relevant to cosmology, as well as their increasing accuracy, leads to the idea that the determination of cosmological parameters has been achieved with a rather good precision, may be of the order of 10%. There is a large consensus around the so-called concordance model. Indeed this model does fit an impressive set of independent data, the most impressives been: CMB Cl curve, most current matter density estimations, Hubble constant estimation from HST, apparent acceleration of the Universe, good matching of the power spectrum of matter fluctuations. However, the necessary introduction of a non zero cosmological constant is an extraordinary new mystery for physics, or more exactly the come back of one of the ghost of modern physics since its introduction by Einstein. Here, I would like to emphasize that some results are established beyond reasonable doubt, like the (nearly) flatness of the universe and the existence of a dark non-baryonic component of the Universe. But also that the evidence for a positive cosmological constant may not be as strong as needed for its existence to be considered as established beyond doubt. In this respect, I will argue that an Einstein-De Sitter universe might still be a viable option. Some observations do not fit the concordance picture. I discuss several of the claimed observational evidences supporting the concordance model and will focus more specifically on the observational properties of clusters which offer powerful constraints on various quantities of cosmological interest. They are particularly interesting in constraining the cosmological density parameter, nicely complementing the CMB result, which by its own does not request a non vanishing cosmological constant, contrary to what is sometimes claimed. Early, local, estimations based on the M/L ratio are now superseded by new tests that have been proposed during the last ten years which are globalin nature. Here, I will briefly discuss three of them: 1) the evolution of the abundance of clusters with redshift 2) the baryon fraction measured in local clusters 3) apparent evolution of the baryon fraction with redshift. I will show that these three independent tests lead to high matter density for the Universe in the range 0.6 — 1. I therefore conclude that the dominance of vacuum to the various density contributions to the Universeis presently a fascinating possibility, but it is still premature to consider it as an established scientific fact.  相似文献   

11.
We present results from N-body simulations of the clustering properties of the universe in a cubic box of size 260h−1 Mpc, within a cold dark matter (CDM) cosmology with skewed distributions for initial adiabatic density perturbations δM. We consider two non-Gaussian models, Chi-squared and Lognormal, where the primordial gravitational potential is obtained from a non-linear transformation on a Gaussian random field. Our procedure yields for each model two primordial density distributions with opposite skewness δ3M. The gravitational evolution and the present statistical properties of our simulations are strongly sensitive to the sign of the initial skewness. Skew-positive simulations produce a highly lumpy distribution with little power on large scales. Skew-negative simulations, on the contrary, evolve towards a cellular structure with high power on large scales, showing, in many respects, better agreement with observations than the standard CDM model. Giving up the random-phase hypothesis for primordial perturbations seems then a viable possibility to reproduce the large-scale properties of the universe; such a possibility is further motivated by many physical models either within the inflationary dynamics or phase transitions in the early universe.  相似文献   

12.
The most recently celebrated cosmological implications of the cosmic microwave background studies with WMAP (2006), though fascinating by themselves, do, however, create some extremely hard conceptual challenges for the present‐day cosmology. These recent extremely refined WMAP observations seem to reflect a universe which was extremely homogeneous at the recombination age and thus is obviously causally closed at the time of the cosmic recombination era. From the very tiny fluctuations apparent at this early epoch the presently observable nonlinear cosmic density structures can, however, only have grown up, if in addition to a mysteriously high percentage of dark matter an even higher percentage of dark energy is admitted as drivers of the cosmic evolution. The required dark energy density, on the other hand, is nevertheless 120 orders of magnitude smaller then the theoretically calculated value. These are outstanding problems of present day cosmology onto which we are looking here under new auspices. We shall investigate in the following, up to what degree a universe simply abolishes all these outstanding problems in case it reveals itself as an universe of constant total energy. As we shall show basic questions like: How could the gigantic mass of the universe of about 1080 proton masses at all become created? – Why is the presently recognized and obviously indispensable cosmic vacuum energy density so terribly much smaller than is expected from quantum theoretical considerations, but nevertheless terribly important for the cosmic evolution? – Why is the universe within its world horizon a causally closed system? –, can perhaps simply be answered, when the assumption is made that the universe has a constant total energy with the consequence that the total mass density of the universe (matter and vacuum) scales with . Such a scaling of matter and vacuum energy abolishes the horizon problem, and the cosmic vacuum energy density can easily be reconciled with its theoretical expectation values. In this model the mass of the universe increases linearly with the world extension Ru and can grow up from a Planck mass as a vacuum fluctuation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
In this paper we present anisotropic, homogeneous two-fluid cosmological models in a Bianchi I space-time. These classes of cosmological models picture two different scenarios of cosmic history; viz., when the radiation and matter content of the universe are in interactive phase and another when the two are non-interacting. The universe is highly anisotropic in the initial stages, however, anisotropy tapers out to insignificance in due course of cosmic evolution. In every model the anisotropy of the space-time is determined by the density parameter Ω0 at the present epoch. For Ω0=1, the anisotropy is washed out before long. An interesting class of models, having an inflationary epoch in finite future, is discovered.   相似文献   

14.
By constructing different parameters which are able to give us the information about our universe during inflation, (specially at the start and the end of the inflationary universe) a brief idea of brane world inflation is given in this work. What will be the size of the universe at the end of inflation, i.e., how many times will it grow than the original size is been speculated and analysed thereafter. Different kinds of fluids are taken to be the matter inside the brane. It is observed that in the case of highly positive pressure giving gas like polytropic, the size of the universe at the end of inflation is comparatively smaller. Whereas for negative pressure creators (like Chaplygin gas) this size is much bigger. Except these two cases, inflation has been studied for barotropic fluid and linear red shift parametrization ω(z)=ω 0+ω 1 z too. For them the size of the universe after inflation is much more high. We also have seen that this size does not depend upon the potential energy at the end of the inflation. On the contrary, there is a high impact of the initial potential energy upon the size of inflation.  相似文献   

15.
Based on the spectra of 4 high-redshift quasars (resolution 2A) obtained by us [1–5] using IPCS on the RGO Cassegrain spectrograph of the AAT, we point out the following. 1. Auto-correlation peaks at in PKS 0805+046 and PKS 1442+101 suggest that the large number of absorption lines shortward of Lα in high redshift quasars are due to absorption by hydrogen clouds. 2. The distribution of absorption lines and the correlation function of indicate that PKS 0528-250 may be an exception, requiring further observation. 3. Absorption redshift systems containing metallic lines may be produced by either matter ejected from the quasar, or an associated galaxy cluster or an intervening galaxy. 4. The randomness in the column density and the dispersion velocity deduced from the curve of growth of the pair supports the hypothesis that the pure Lα absorption comes from primitive hydrogen clouds in the early, exploding universe. 5. The number of hydrogen clouds per unit redshift interval is determined by the data of absorption lines of quasars with Z > 3.  相似文献   

16.
The present paper outlines a cosmological paradigm based upon Dirac’s large number hypothesis and continual creation of matter in a closed static (nonexpanding) universe. The cosmological redshift is caused by the tired-light phenomenon originally proposed by Zwicky. It is shown that the tired-light cosmology together with continual matter creation has a universal Hubble constant H 0=(512π 2/3)1/6(GC 0)1/3 fixed by the universal rate C 0 of matter creation, where G is Newton’s gravitational constant. It is also shown that a closed static universe has a finite age τ 0=(243π 5/8GC 0)1/3 also fixed by the universal rate of matter creation. The invariant relationship H 0 τ 0=3π 261/2 shows that a closed static universe is much older (≈one trillion years) than any expanding universe model based upon Big-Bang cosmology. It is this property of a static universe that resolves any cosmic age crisis provided that galaxy formation in the universe is a continual recurring process. Application of Dirac’s large number hypothesis gives a matter creation rate C 0=4.6×10?48 gm?cm?3?s?1 depending only on the fundamental constants of nature. Hence, the model shows that a closed static universe has a Hubble constant H 0=70 km?s?1?Mpc?1 in good agreement with recent astronomical determinations of H 0. By using the above numerical value for H 0 together with observational data for elongated cellular-wall structures containing superclusters of galaxies, it is shown that the elongated cellular-wall configurations observed in the real universe are at least one hundred billion years old. Application of the microscopic laws of physics to the large-scale macroscopic universe leads to a static eternal cosmos endowed with a matter-antimatter symmetry. It is proposed that the matter-antimatter asymmetry is continuously created by particle-antiparticle pair annihilation occurring in episodic cosmological gamma-ray bursts observed in the real universe.  相似文献   

17.
In this paper we discuss the properties of the quasi-steady state cosmological model (QSSC) developed in 1993 in its role as a cyclic model of the universe driven by a negative energy scalar field. We discuss the origin of such a scalar field in the primary creation process first described by F. Hoyle & J. V. Narlikar forty years ago. It is shown that the creation processes which take place in the nuclei of galaxies are closely linked to the high energy and explosive phenomena, which are commonly observed in galaxies at all redshifts. The cyclic nature of the universe provides a natural link between the places of origin of the microwave background radiation (arising in hydrogen burning in stars), and the origin of the lightest nuclei (H, D, He3 and He4). It also allows us to relate the large scale cyclic properties of the universe to events taking place in the nuclei of galaxies. Observational evidence shows that ejection of matter and energy from these centers in the form of compact objects, gas and relativistic particles is responsible for the population of quasi-stellar objects (QSOs) and gamma-ray burst sources in the universe. In the later parts of the paper we briefly discuss the major unsolved problems of this integrated cosmological and cosmogonical scheme — the understanding of the origin of the intrinsic redshifts, and the periodicities in the redshift distribution of the QSOs.  相似文献   

18.
We present an XMM observation of the moderately distant (z=0.41)galaxy cluster CL 0939+4713 (Abell 851), an exceptionally rich cluster. The formation and evolution of clusters depends sensitively on cosmological parameters like the mean matter density in the universe Οm. Therefore it is important to determine the dynamical state of clusters at different redshifts, i.e. at different evolutionary states. The X-ray morphology alone is not the best indicator of the dynamical state, but it should be complemented with all other information available, e.g. the temperature map or the galaxy distribution. The combination of all findings gives a detailed picture of the state of a cluster. This analysis, of this relatively distant cluster, can be used as a basis for comparisons at lower and higher redshifts. The capability of XMM to perform spatially resolved spectroscopy can be used also to determine the distribution of the metal abundances. Not only the overall value of metallicity but also its spatial distribution gives important indications on the metal enrichment processes. The X-ray image shows pronounced substructure. There are two main subclusters which have also some internal structure. This is an indication that the cluster is a dynamically young system. This conclusion is supported by the temperature distribution: a hot region is found between the two main subclusters indicating that the cluster is in the process of a major merger, in which the two subclusters will probably collide in a few hundreds of Myr. The intra-cluster gas of CL 0939+4713 shows variations of the metal abundances. The optically richer subcluster has a somewhat higher metallicity. This finding together with the absence of post-starburst galaxies in this region gives interesting hints on the metal enrichment processes favouring recent enrichment processes like ram-pressure stripping or tidal stripping. Throughout this paper we use H 0 =50 km s-1Mpc-1 and q 0 =0.5; all errors are 90% confidence levels. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
Multispectral faint galaxy counts, including the deepest Hubble DeepField, are interpreted with the help of our evolution model PEGASE(Fioc and Rocca-Volmerange, 1997). The best fits correspond to galaxyformations at high redshifts, a pure luminosity evolution andclassical luminosity functions. The adopted cosmology is a flatuniverse with the matter density parameter ΩM =0.3 and acosmological constant ΩΛ =0.7. A solution with ΩM=0.01 (open universe) is also acceptable. But a flat universe withΩM =1 is clearly excluded. The star formation histories for galaxytypes are derived from scenarios of evolution. The comparison with resultsalready published in the litterature, arises puzzling problems needinga further analysis of star formation tracers, specifically for bright galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

20.
A correlation analysis is made of the spatial distribution of galaxies in the Coma, Bridge, and A1367 clusters, which form the Coma supercluster. The scale of the clustering of galaxies and the variation in their density distribution with the main parameters of the galaxies– luminosity, morphological type, and observed H I deficiency in the 21 cm line– are evaluated. The mass-to-luminosity ratios are computed for the spiral galaxies in the Coma, Bridge, and A1367 clusters. It is suggested that a larger fraction of hypothetical dark matter may be concentrated in the spiral galaxies which predominantly populate the subclusters previously identified by us within these clusters than in the spiral galaxies observed in the peripheral regions of the clusters.  相似文献   

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