Showing papers on "Structure formation published in 1990"

Global texture and the microwave background.

Abstract: The metric perturbation produced by a collapsing ``knot'' of global texture in a flat background is calculated. This is used to calculate the energy shift for photons traversing such knots, leading to a prediction for the microwave anisotropy pattern produced in the global-texture scenario for large-scale structure formation. The metric is also used to calculate the velocity field induced in nonrelativistic matter, on scales well inside the horizon. This would produce an early generation of small gravitationally bound objects. At larger scales, the texture field would induce coherent velocity fields on a scale comparable to that seen in galaxy surveys.

Detecting the largest magnets : the universe and the clusters of galaxies

Abstract: Recently, a large sample of rotation measures of galaxies and quasars at various redshifts has been published. This data set is used to test for the existence of an uniform component of a cosmic/intergalactic magnetic field outside clusters of galaxies. From a total of 309 galaxies and quasars with a known redshift and a small intrinsic rotation measure value, an upper limit of about 2 rad/sq m is obtained for such a cosmic/intergalactic contribution out to a redshift z of 3.6. From this result, and a mean density of 0.00001/cu cm, an upper limit of 6 x 10 to the -12th G follows for the strength of such a cosmic/intergalactic magnetic field outside clusters of galaxies, or an upper limit of 6 x 10 to the -11th G for a mean density of 10 to the -6th/cu cm. 27 refs.

The Formation and evolution of cosmic strings : proceedings of a workshop supported by the SERC and held in Cambridge, 3-7 July, 1989

Abstract: Superconducting cosmic strings and electroweak magnetism J. APPLETON Harmonic analysis of more than cosmic strings R. BROWN Are the small ?? real ??? A. ALBRECHT Covariant mechanics of simple and conducting strings and membranes B. CARTER New results on gravitational radiation of cosmic strings R. DURRER String mechanics at high energy densities S. JAM Srings and phase transitions ED COPELAND, R. GREGORY, R. BRANDENBERGER and W. PERKINS, Decaying strings D. MITCHELL String-driven inflation J. BARNES Cosmic string an momentum R. SCHERRER Static string configurations A. VILENTION Searching for cosmic strings M. HANDMARSH Rings R. DAVIS and P. SHALLOT The new picture for cosmic string seeded structure formation A. STEBBING String network D. BENNETT String loop product and observable effects F. BOUCHET Evolution of cosmic string networks N. TURSK Cosmological applications of superstring models Q. SHAFI Cosmic strings and module spaces P. RUBACK Strings and phase transitions R. RIVER String-seeded galaxy formation linear theory and N-body simulations E. BERTSCHINGER Quantum field theory around conical defects J. S. DOWLER Cosmic strings: an overview T. KIBBLE On the evolution of cosmic strings P. SHELLAND and B. ALLEN Axion string radiation P. SHELLAND and R. DAVIS.

New measurements of distances to spirals in the great attractor - Further confirmation of the large-scale flow

Abstract: H-alpha rotation curves and CCD photometry have been obtained for 117 Sb-Sc spiral galaxies in the direction of the large-scale streaming flow. By means of the Tully-Fisher relation, these data are used to predict distances to these galaxies and, by comparison with their observed radial velocities, their peculiar motions relative to a smooth Hubble flow. The new data confirm the results of the earlier studies of a coherent flow pattern in a large region called the 'great attractor'. For the first time, evidence is found for backside infall into the great attractor. Taken as a whole, the data sets for E, S0, and spiral galaxies support the model proposed by Lynden-Bell et al. (1988) of a large, extended overdensity centered at about 45/h Mpc that perturbs the Hubble flow over a region less than about 100/h Mpc in diameter. Observation of the full 's-wave' in the Hubble flow establishes this scale for the structure, providing a strong constraint for models of structure formation, like those based on hot or cold dark matter. 24 refs.

Dark matter in the universe

Abstract: What is the quantity and composition of material in the universe This is one of the most fundamental questions we can ask about the universe, and its answer bears on a number of important issues including the formation of structure in the universe, and the ultimate fate and the earliest history of the universe. Moreover, answering this question could lead to the discovery of new particles, as well as shedding light on the nature of the fundamental interactions. At present, only a partial answer is at hand: most of the material in the universe does not give off detectable radiation, i.e., is dark;'' the dark matter associated with bright galaxies contributes somewhere between 10% and 30% of the critical density (by comparison luminous matter contributes less than 1%); baryonic matter contributes between 1.1% and 12% of critical. The case for the spatially-flat, Einstein-de Sitter model is supported by three compelling theoretical arguments -- structure formation, the temporal Copernican principle, and inflation -- and by some observational data. If {Omega} is indeed unity--or even just significantly greater than 0.1--then there is a strong case for a universe comprised of nonbaryonic matter. There are three well motivated particle dark-matter candidates: an axionmore » of mass 10{sup {minus}6} eV to 10{sup {minus}4} eV; a neutralino of mass 10 GeV to about 3 TeV; or a neutrino of mass 20 eV to 90 eV. All three possibilities can be tested by experiments that are either being planned or are underway. 71 refs., 6 figs.« less

Evolution of Clusters in a Hybrid Hot Dark Matter Universe

Abstract: The evolution of clusters of galaxies in a cosmological model where the large-scale structure is formed by gravitational instability in a hot dark matter universe with initial adiabatic Harrsion-Zel'dovich fluctuations, but with a lower than usual normalization, is analyzed. The normalization of the power spectrum is possibly too low to form galaxies, so that small-scale structures may be formed by some other short-range process. The analysis is based on the statistics of peaks in a random Gaussian field and the spherical infall model. While the typical mass, virial temperature, and X-ray luminosity change little with redshift, the evolution of the comoving number density of clusters is dramatic. The evolution is especially severe for high values of the Hubble constant and for low values of the present number density of clusters (low normalizations). 38 refs.

Implications of Abundance Measurements of the Intracluster Medium

Abstract: The potential implications of future measurements of the heavy-element abundances in intracluster gas are considered in the framework of the cold-dark-matter scenario of structure formation in the early universe (Blumenthal et al., 1984). Particular attention is given to the correlation between the M(gas)/M(stellar) ratio and the gas temperature in groups and clusters of galaxies found by Jones et al. (1989) and its relationship to the efficiency of galaxy formation. Quantitative predictions for the correlation between Fe abundance and gas temperature are presented in graphs and discussed in detail.