Showing papers on "Structure formation published in 1987"
TL;DR: In this paper, the behavior of a flat, cold dark matter universe is investigated on scales larger than 10 Mpc using a model in which galaxies are required to form only near high peaks of the smoothed linear density field.
Abstract: The behavior of a flat, cold dark matter universe is investigated on scales larger than 10 Mpc using a model in which galaxies are required to form only near high peaks of the smoothed linear density field. N-body techniques complemented by the statistical analysis of peaks in Gaussian random fields developed by Bardeen et al. (1986) are used in an ensemble of 25 simulations of comoving regions. Galaxies are located in the mass distributions by assuming their abundance to be proportional to the local number density of peaks given by the analytic formalism. These techniques are used to find Abell clusters in the models and to construct both magnitude-limited and volume-limited galaxy catalogs. The properties of the predicted clusters, voids, and filaments are discussed. The results demonstrate that observed large-scale structures can be produced by the gravitational amplification of random-phase density fluctuations in a flat universe. 43 references.
215 citations
80 citations
TL;DR: In this paper, a review of when and how galaxies form is given, and the results of two numerical simulations of inhomogeneous galaxy formation are presented, which are used to predict the abundance of primeval galaxies in observational surveys.
Abstract: The appearance of protogalaxies expected by current theories of structure formation is discussed. A review of when and how galaxies form is given, and the results of two numerical simulations of inhomogeneous galaxy formation are presented. These models are used to predict the abundance of primeval galaxies in observational surveys.
75 citations
TL;DR: In this paper, the compatibility of inflation with the cosmic string theory for galaxy formation was examined, and a class of models where the inflaton is coupled to the string-producing field was proposed.
51 citations
TL;DR: Cluster formation is only marginally different from that in the cold-dark-matter and strings model, but galaxy masses are lower and the mass spectrum of galaxies is flatter than with cold dark matter, and the density profile about an individual loop is less steep, in better agreement with observations.
Abstract: Galaxy and structure formation in a neutrino-dominated universe with cosmic strings is investigated. Strings survive neutrino-free streaming to seed galaxies and clusters. The effective maximum Jeans mass is about 1.5\ifmmode\times\else\texttimes\fi{}${10}^{14}$${n}_{50}^{\mathrm{\ensuremath{-}}4}$${M}_{\ensuremath{\bigodot}}$, lower than in the adiabatic scenario. Hence cluster formation is only marginally different from that in the cold-dark-matter and strings model, but galaxy masses are lower. The mass spectrum of galaxies is flatter than with cold dark matter, and the density profile about an individual loop is less steep, in better agreement with observations.
35 citations
TL;DR: In this article, it was shown that the amount of mass accreted into the wake of a point mass or small loop of cosmic string is approximately independent of the peculiar velocity of the perturber, so that the spherical accretion model correctly gives the mass that has become nonlinear.
Abstract: In an expanding universe, a rapidly moving cosmic string or point mass causes matter to accrete into a wake behind the perturber. Analytic solutions for the structure and evolution of these wakes are derived using the Zel'dovich approximation. At early times the wakes are narrow and their evolution is self-similar. It is found that the amount of mass accreted into the wake of a point mass or small loop of cosmic string is approximately independent of the peculiar velocity of the perturber, so that the spherical accretion model correctly gives the mass that has become nonlinear. Initially the accretion wake of a moving point mass is a thin cylinder, but it becomes increasingly spherical as matter is accreted from larger comoving volumes. The accretion wakes of long strings have the form of thin sheets. Less matter is swept up in the sheets than in the wakes of small loops, but the long strings may be important for large-scale structure. The cosmic string scenario of structure formation predicts that galaxy halos should be nearly round, while Abell clusters should be prolate. 22 references.
19 citations
TL;DR: In this paper, the effects of Population III stars on the surrounding space by radiative ionizations and shock waves are investigated, and the galaxy formation near wakes and sheets (secondary systems) after heat-up of the universe is briefly discussed.
Abstract: S M0 ) within the first systems has begun to contract due to Hz cooling, and Population III stars with ~asses of 10- 1 ~ 1il'M0 may be formed by the fragmentation within such systems. The large scale mesh· like traces of moving cosmic strings are superimposed on the structure of the universe and these patterns have simultaneously begun to be luminous at this epoch. The ratio of the accumulated matter in the wakes to the total matter at z "" 10 z is about 10- 3 • The effects of such Population III stars on the surrounding space by radiative ionizations and shock waves are investigated. The second, third and succeeding baryonic sheets are formed after the isothermal plane shocks. Under moderate parameters, the remaining interwake medium could have been heated up until now. From these sheets, the secondary systems are formed, which may correspond to the globular clusters or dwarf galaxies. The galaxy formation (z:::::8) near wakes and sheets (secondary systems) after heat-up of the universe is briefly discussed.
9 citations
TL;DR: In this paper, 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.
Abstract: 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.
3 citations
01 Jan 1987
TL;DR: In this paper, the angular correlation function of galaxies, w gg (θ), was used as a direct test of large scale power in cosmic density fluctuation spectra.
Abstract: We show that the angular correlation function of galaxies, w gg (θ), may be used as a direct test of large scale power in cosmic density fluctuation spectra. Groth and Peebles (1986) found a break in w(θ) from a power-law at θ ∼ 3° in an analysis of the Shane-Wirtanen galaxy counts. Maddox and Efstathiou (1987) find evidence for a similar break in w(θ) in the Southern Sky Survey. Testing for a break is a powerful probe of the linear regime of fluctuation spectra. The CDM model has such a break; almost all candidate Gaussian theories with enough large scale power to explain the clustering of clusters do not.
3 citations
TL;DR: In the cosmic string theory, this effect is too weak to change the initial two-point correlation function of clusters and it can, however, lead to a steepening of the galaxy correlation function, provided the dark matter is cold as mentioned in this paper.
2 citations
TL;DR: In this article, a series of N-body experiments including the effects of a massive dominant background which follows Schuster's density law was performed in order to simulate clusters of galaxies in which a smoothly distributed dark component is present.
Abstract: 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 (Mb/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 (Rg/Rb) (approximately 0.6) and using previous results (Navarroet al., 1986) we conclude that virial theorem masses underestimate the total mass (Mb+Mg) of the clusters. As a final result, we derive a minimum value for theMb/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.
01 Jan 1987
TL;DR: In this article, EHMO electronic structure calculations were performed for the neutral and singly positive charged tin clusters in the size range of N = 2-17 atoms, where the bond lengths, binding energies, energy gaps, and ionization potentials for various clusters were determined.
Abstract: EHMO electronic structure calculations were performed for the neutral and singly positive charged tin clusters in the size range of N=2-17 atoms. From calculation we determined the bond lengths, binding energies, energy gaps, and ionization potentials for various clusters. It also enabled us to compare the calculated values for ionization potentials with those obtained experimentally for various clusters. Moreover our calculations were extended to include the thermodynamic properties of tin clusters like cohesive Enthalpy, structure formation Enthalpy, fragmentation Enthalpy, and free Energies. These later values enabled us to judge for the formation stability of the clusters studied at various temperatures. The results and the method, used enabled us to study not only small clusters (N = 2-17) but also very large ones up to SnN (N = 1000) using a reasonably very cheap method compared to literature.
TL;DR: The relation between the mean separation of clusters of galaxies and their mean richness is well represented by the Bahcall-Soneira relation, which is well explained by the cosmic string picture.
Abstract: The relation between the mean separationd of clusters of galaxies and their mean richnessN is found to be well represented byd=34N2/3 Both this observed result and the Bahcall-Soneira relation(that is, the spatial correlations of clusters of galaxies are increased with their richness) are well explained by the cosmic string picture, lending support to the cosmic-string theory