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1.
We investigate a spatially flat cold dark matter model (with the matter density parameter with a primordial feature in the initial power spectrum. We assume that there is a bump in the power spectrum of density fluctuations at wavelengths , which corresponds to the scale of superclusters of galaxies . There are indications for such a feature in the power spectra derived from redshift surveys and also in the power spectra derived from peculiar velocities of galaxies. We study the mass function of clusters of galaxies, the power spectrum of the cosmic microwave background (CMB) temperature fluctuations, the rms bulk velocity and the rms peculiar velocity of clusters of galaxies. The baryon density is assumed to be consistent with the big bang nucleosynthesis value. We show that with an appropriately chosen feature in the power spectrum of density fluctuations at the scale of superclusters, the mass function of clusters, the CMB power spectrum, the rms bulk velocity and the rms peculiar velocity of clusters are in good agreement with the observed data. 相似文献
2.
S. Basilakos M. Plionis M. Rowan-Robinson 《Monthly notices of the Royal Astronomical Society》2001,323(1):47-55
We study the possibility of correctly identifying, from the smooth galaxy density field of the PSC z flux-limited catalogue, high-density regions (superclusters) and recovering their true shapes in the presence of a bias introduced by the coupling between the selection function and the constant radius smoothing. We quantify such systematic biases in the smoothed PSC z density field and after applying the necessary corrections we study supercluster multiplicity and morphologies using a differential geometry definition of shape. Our results strongly suggest that filamentary morphology is the dominant feature of PSC z superclusters. Finally, we compare our results with those expected in three different cosmological models and find that the Λ cold dark matter (CDM) model (ΩΛ =1−Ωm =0.7) performs better than Ωm =1 CDM models. 相似文献
3.
Recent spectroscopic observations of galaxies in the Fornax Cluster reveal nearly unresolved 'star-like' objects with redshifts appropriate to the Fornax Cluster. These objects have intrinsic sizes of ≈100 pc and absolute B -band magnitudes in the range −14< M B <−11.5 mag and lower limits for the central surface brightness μ B ≳23 mag arcsec−2 , and so appear to constitute a new population of ultracompact dwarf galaxies (UCDs). Such compact dwarfs were predicted to form from the amalgamation of stellar superclusters (by Kroupa) , which are rich aggregates of young massive star clusters (YMCs) that can form in collisions between gas-rich galaxies. Here we present the evolution of superclusters in a tidal field. The YMCs merge on a few supercluster crossing times. Superclusters that are initially as concentrated and massive as knot S in the interacting Antennae galaxies evolve to merger objects that are long-lived and show properties comparable to the newly discovered UCDs. Less massive superclusters resembling knot 430 in the Antennae may evolve to ω Cen-type systems. Low-concentration superclusters are disrupted by the tidal field, dispersing their surviving star clusters while the remaining merger objects rapidly evolve into the μ B − M B region populated by low-mass Milky Way dSph satellites. 相似文献
4.
《New Astronomy》2019
The recent hypothesis of a giant supercluster binary-like structure formed by the Corona Borealis and its close companion Abell 2142 (supercluster) belongs to a little known area of investigation as the dynamics of gravitationally interacting galaxy supercluster pairs. From the observational point of view this structure approximates the configuration of a binary-like system in linear orbit interconnected by a huge filamentary structure which, if confirmed, it would be the first case to date observed at z ≥ 0.07. Given the importance to disentangle this issue, a follow-up analysis has been performed on the region constrained by the common envelop of the two superclusters in order to search for new hints to confirm their mutual gravitational interaction. Observational signatures of that interaction have been found mapping the inner peculiar motions where the observed negative peculiar velocities measured within the A2142 (supercluster) region suggest a general matter flow toward the Corona Borealis supercluster. Besides, analyzing the effects on both superclusters due to the mutual impact of the external tidal forces, turns out that their inner dynamics remain unperturbed up to the turnaround radii. Outside, where the binding forces are overlapped by the tidal ones, the outskirts of both superclusters should be unstable and subject to fragmentation. Such a scenario indicates that both superclusters interact with comparable and reciprocal tidal perturbations leaving the whole system in a substantial dynamical equilibrium. The origin of such a dynamical dichotomy would be explained either by a much more massive Corona Borealis supercluster than that estimated in the present work or by a selection effect biasing the small sample of peculiar velocities due to the remoteness of the system worsened by the large uncertainty on their measurements. 相似文献
5.
Observations have been conducted using the Ooty Radio Telescope in order to place constraints on the evolutionary scenario
leading to the formation of the present day superclusters. The experiment attempted to detect 21 cm emission from massive
neutral hydrogen condensates at a redshift ofz = 3.3. In an Einstein de-Sitter universe with baryon density Ω = 0.05, about ten condensates were expected in the volume
surveyed if superclusters, having H I masses ≃5 × 1015
M
⊙, were the first objects to separate out of the Hubble expansion. The sensitivity of our experiment rules out the existence
of these condensates atz = 3.3 unless their lifetimes are less than one-tenth the dispersion in their epoch of formation or the proto-superclusters
subtend angles greater than 6 arcmin. The result indicates that superclusters form at z > 3.3 if indeed they were the first
objects to condense out of the Hubble flow.
An erratum to this article is available at . 相似文献
6.
We show that present day observational techniques make it possible to detect diffuse gas masses down to ～1010 M ⊙ in cosmic voids with linear sizes of ～1 Mpc or larger. The observations consist of searches for absorption lines, similar in character to those produced in galactic interstellar clouds, in the spectra of high-redshift objects located beyond previously identified voids adjoining nearby superclusters. 相似文献
7.
We present results of the study of peculiar motions of 57 clusters and groups of galaxies in the regions of the Corona Borealis (CrB), Bootes (Boo), Z5029/A1424, A1190, A1750/A1809 superclusters of galaxies and the galaxy clusters located beyond massive structures (0.05 < z < 0.10). Using the SDSS (Data Release 8) data, a sample of early-type galaxies was compiled in the systems under study, their fundamental planes were built, and relative distances and peculiar velocities were determined. Within the galaxy superclusters, significant peculiar motions along the line of sight are observed with rms deviations of 652 ± 50 kms?1—in CrB, 757 ± 70 kms?1—in Boo. In the most massive A2065 cluster in the CrB supercluster, no peculiar velocity was found. Peculiar motions of the other galaxy clusters can be caused by their gravitational interaction both with A2065 and with the A2142 supercluster. It has been found that there are two superclusters projected onto each other in the region of the Bootes supercluster with a radial velocity difference of about 4000 kms?1. In the Z 5029/A1424 supercluster near the rich Z5029 cluster, the most considerable peculiar motions with a rms deviations of 1366 ± 170 kms?1 are observed. The rms deviations of peculiar velocities of 20 clusters that do not belong to large-scale structures is equal to 0 ± 20 kms?1. The whole sample of the clusters under study has the mean peculiar velocity equal to 83 ± 130 kms?1 relative to the cosmic microwave background. 相似文献
8.
Corrado Massa 《Astrophysics and Space Science》2007,310(3-4):209-210
The generalized Buchdahl inequality in the presence of a positive cosmological constant gives rise to a constraint on the
mass density of celestial bodies. We find that such a constraint implies an upper bound on the mass and radius of spherical
celestial bodies born from macroscopic superstrings. We obtain a maximal mass of about 1015 solar masses and a maximal radius of about 80 million light years, not far from the observed mass and size of the largest
structures in the universe, viz. the superclusters of galaxies. 相似文献
9.
We calculated the spatial two-point correlation function of cD clusters in Abell's statistical sample using estimated redshifts and found that positive correlation exists on all scales except around 70 Mpc and 170 Mpc (H0 = 100 km s−1 Mpc−1). In particular, positive correlation persists on the super large scale around 300 Mpc. This is particularly interesting in view of the known relationships among cD clusters, radio sources and superclusters. 相似文献
10.
We propose a simple mechanism for driving the recently detected non-decelerating expansion of the observable Universe. It
is based on the assumption of the predominance of the vacuum energy over the inert matter and a fractal structuring of the
latter. The Newton’s universal gravitational force ensures the attraction between celestial bodies at small and medium astronomical
distances, but gives rise to the repulsive interaction between mutually very separated cosmic subsystems, like clusters and
superclusters, and thus to the observed accelerating expansion and the fractal structuring. 相似文献
11.
O. J. Eggen 《Astrophysics and Space Science》1988,142(1-2):145-151
Summary Distinguishing wide binaries from contiguous members of young disk population superclusters is not possible with present definitions.
Members of old disk population groups have non-parallel space motions and the question, ‘when is a wide binary’ is more easily
approached.
Presented by H. A. Abt.
Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
12.
Y. Gao 《Astrophysics and Space Science》1987,138(2):369-379
The formation of galaxies, clusters, and superclusters is discussed in the cosmic string model and the constraints are given for the corresponding loops which form these structures by the accretion of the loops. The alignment of position angles of galaxies with that of their parent cluster and of clusters with that of the supercluster they lie on, appears naturally. Various different observations and statistical results of position angles are (at least qualitatively) explained in the cosmic string theory of formation of the large-scale structure. 相似文献
13.
P. J. E. Peebles 《Astrophysics and Space Science》1974,31(2):403-410
A new view of the nature of the large-scale distribution of matter is suggested by the fact that the covariance function for the distribution varies smoothly, like a power law, over a wide range of separations. This leads one to ask whether superclusters are entities distinguishable in some natural and fundamental way from clusters, or from groups, or even from individual galaxies. I discuss here an attempt to find an acceptable model for clustering consistent with the picture of a continous hierarchy.Research supported in part at Princeton by the National Science Foundation. 相似文献
14.
Miralda-Escudé J 《The Astrophysical journal》2000,536(1):L1-L4
Radio galaxies are uniquely useful as probes of large-scale structure since their uniform identification with giant elliptical galaxies out to high redshift means that the evolution of their bias factor can be predicted. As the initial stage in a project to study large-scale structure with radio galaxies, we have performed a small redshift survey, selecting 29 radio galaxies in the range of 0.19相似文献
15.
The data on the peculiar velocities of 1493 RFGC flat spiral galaxies processed using the POTENT method allowed the density distribution of matter, including dark matter, on 75-Mpc scales to be reconstructed. Well-known attractors (the Great Attractor, the Perseus—Pisces and Coma superclusters) and voids are separated from the distribution. In general, the density distribution is close to that of IRAS galaxies, suggesting that the luminous-to-dark matter density ratio is constant. The masses of the main attractors were estimated. 相似文献
16.
H. T. Macgillivray R. J. Dodd B. V. McNally J. F. Lightfoot H. G. Corwin Jr. S. R. Heathcote 《Astrophysics and Space Science》1982,83(1-2):373-380
Geometric properties (positions, orientations and shapes) are generated in three dimensional space for galaxies in a simulated distant supercluster filament according to the galaxy orientations and filament inclinations described in Papers I (MacGillivrayet al., 1981) and II (MacGillivray and Dodd, 1982), and the distributions for projected galaxy shapes and position angles examined. The results may be used to assist the interpretation of the observed geometrical properties for galaxies in real external superclusters. 相似文献
17.
In the nearest neighbour method of the random distribution of N objectson a sphere surface the variable (N-1) sin2(α/2) isproposed to be used instead of the angular distance α. Thenboth the expected mean and variance equal to one for large N, and both theStudent's test and F-test are especially simple. An illustrative applicationshows that the superclusters – collected in the All-Sky Catalogues ofSuperclusters of Abell-ACO Clusters – need not be distributedrandomly. 相似文献
18.
A computational model is developed for the origin of protogalactic eddies at the fronts of large-scale pancake shocks. Possible effects of orientation of spiral galaxies in their pairs, groups, clusters and superclusters are discussed. 相似文献
19.
The characteristics of two stars, 25 Sex and HD 21699, as additional candidates for the sample of magnetic stars belonging to superclusters, are discussed. For 25 Sex, which was already accepted as a probable member of the Hyades supercluster in a previous study, arguments supporting the view that this star indeed is a magnetic star are presented. In the case of HD 21699, the radial velocity derived from our observations is not inconsistent with membership. But from the determinations of its proper motion found in the literature, this star cannot be regarded as a probable member of the α Per cluster. On the basis of recent evolutionary models, all the well established Ap cluster members appear to be close to the end of their main-sequence life. This suggests that A stars possibly become magnetic at the end of core hydrogen burning. 相似文献
20.
J. P. Mücket 《Astronomische Nachrichten》1987,308(1):1-7
The evolution of small-scale density perturbations on the background of increasing large-scale perturbations of supercluster size will be considered. In the case that the characteristic length scales of both perturbation modes differ significantly, the interaction between both modes has to be taken into account already within lowest order of approximation. It will be shown that in this case an effective amplification for the smaller-scale perturbations occurs. For these perturbations the characteristic times of evolution decreases in dependence on the considered mass-scales more or less rapidly. Therefore, the growth of adiabatic density perturbations on mass-scales up to galaxy masses seems to be triggered by the density evolution of superclusters which the smaller-mass perturbations are embedded in. A model for the formation of observed condensed matter distribution will be proposed. 相似文献