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  • ASTROPHYSICS  (40)
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  • 1
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    Cosmological shells and blast waves (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is argued that cosmic explosions could have produced significant amounts of large-scale structure in the cosmic microwave background (CMB). Observations appear to indicate the presence of bubblelike structures with radii suggesting that positive energy perturbations were more prevalent than negative energy perturbations, since the latter would produce a prevalence of clusterlke irregularities. Energy input from processes occurring during galaxy formation and releasing about 10 to the 61st-62nd ergs per event would not overly disturb the CMB. The merging of bubbles typically resulting in bubbles with radii of roughly (10-20)/h x Mpc also would not affect the CMB. If much larger bubbles of radii 50-100 Mpc exist, a different energy input is likely to be the cause.
    Keywords: ASTROPHYSICS
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  • 2
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    Galaxy distances and deviations from the Hubble flow - Summary remarks (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A summary is presented of the issues addressed by the papers delivered at this conference. Papers addressing classical cosmological topics, including the distances to nearby objects, the intermediate scale distance determination, the local peculiar velocity, the local Hubble constant and other age parameters, and the density parameter from Virgo infall are reviewed. Papers discussing new cosmological developments, including large-scale inhomogeneities, large-scale deviations from Hubble flow, and the origin of the velocity and density inhomogeneities are briefly summarized. Prospects for the next 10 years are examined.
    Keywords: ASTROPHYSICS
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  • 3
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    The universe at moderate redshift (1992)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The Final Report on the universe at moderate redshift covering the period from 1 Mar. 1988 to 28 Feb. 1991 is presented. Areas of research included: galaxy formation and large-scale structure; intergalactic medium and background radiation fields; quasar statistics and evolution; and gravitational lenses.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-193771 , NAS 1.26:193771
    Format: application/pdf
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  • 4
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    Superclustering in the explosion scenario (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A simple toy model is used to study the spatial distribution of rich clusters in a generic type of explosion scenario. The model, parameterized by the distribution of shell radii and the filling factor, places spherical shells at random and identifies each 'knot' as a cluster. The resulting cluster correlation function is close to a power law extending to the diameter of the largest spheres. Richer clusters form at the intersections of bigger shells and so have stronger correlations. Typical shell radii and filling factors are required to produce the observed number density of clusters. Models with a power-law radius distribution also reproduce the richness distribution of clusters in the Abell catalog. Supercluster multiplicity functions, void probabilities, number counts, topology statistics, and velocity correlations confirm the presence of strong superclustering and quantify the non-Gaussian nature of the model.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 336; 9-45
    Format: text
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  • 5
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    On the evolution of globular cluster systems. I - Present characteristics and rate of destruction in our Galaxy (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The current dynamic state and rate of destruction for the system of globular clusters in the Galaxy are modeled. It is found that gravitational shocks due to the central bulge of the Galaxy are very efficient in destroying clusters on highly radial orbits. This effect, extrapolated at the present unweighted destruction rate over 10 to the 10th yr, can account for the observed difference between the velocity distribution of globular clusters and other tracers of the halo population.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 335; 720-747
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  • 6
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    Would a Galactic bar destroy the globular cluster system? (1992)
    In:  Other Sources
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    Publication Date: 2019-08-14
    Description: Five different dynamical Galaxy models are presented for the Galactic potential which satisfy the observed rotation curve but contain a central bar so that the 3-kpc nonintersecting streamlines have a radial velocity of 50 km/s when viewed at 45 deg to the bar axis. The effect of the central bars on the destruction rates of globular clusters in the Galaxy is investigated. The method of Aguilar et al. (1988) is applied to these barred Galaxy models. The unknown tangential velocity components of each observed cluster are drawn randomly from an assumed distribution function. The cluster's orbit is integrated, and the bulge shocking rate is calculated. The median destruction rate of the cluster is computed by sampling a large number of such orbits. The addition of the rotating bar does not strongly affect the destruction rates of globular clusters. There is a small increase in the destruction rate for those clusters within about 2.5 kpc. Thus it is not possible to rule out the existence of a rotating bar on these grounds.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 388; 362-371
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  • 7
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    The relation of local measures of Hubble's constant to its global value (1992)
    In:  Other Sources
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    Publication Date: 2019-08-14
    Description: The distributions of fractional deviations of local values form global H0 that observers with perfect distance data would find if they surveyed specified volumes of the universe are examined here using new very large scale calculations of cold dark matter (CDM) and primordial isocurvature baryonic (PIB) scenarios for the origin of structure. It is found that the expected deviations due to large-scale motions are larger than quoted observational errors unless very large volumes are surveyed. Even perfect sampling and distances of all galaxies within a sphere extending out to the distances of the Virgo and Coma clusters would leave 45 percent and 3 percent rms uncertainties, respectively, in the global value of H0 in the CDM model. It is shown that the local versus global error in an H0 determination can be roughly estimated by the angular variance seen over the sky in the expansion rate, and that a very rough correction from the local to the global H0 value can be derived.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 103; 5 Ma
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  • 8
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    Statistics of the cosmic Mach number from numerical simulations of a cold dark matter universe (1992)
    In:  Other Sources
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    Publication Date: 2019-08-14
    Description: Results are presented of an analysis of the cosmic Mach number, M, the ratio of the streaming velocity, v, to the random velocity dispersion, sigma, of galaxies in a given patch of the universe, which was performed on the basis of hydrodynamical simulations of the cold dark matter scenario. Galaxy formation is modeled by application of detailed physical processes rather than by the ad hoc assumption of 'bias' between dark matter and galaxy fluctuations. The correlation between M and sigma is found to be very weak for both components. No evidence is found for a physical 'velocity bias' in the quantities which appear in the definition of M. Standard cold-dark-matter-dominated universes are in conflict, at a statistically significant level, with the available observation, in that they predict a Mach number considerably lower than is observed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 395; 1; p. 1-20.
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  • 9
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    A hydrodynamic treatment of the tilted cold dark matter cosmological scenario (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: A standard hydrodynamic code coupled with a particle-mesh code is used to compute the evolution of a tilted cold dark matter (TCDM) model containing both baryonic matter and dark matter. Six baryonic species are followed, with allowance for both collisional and radiative ionization in every cell. The mean final Zel'dovich-Sunyaev y parameter is estimated to be (5.4 +/- 2.7) x 10 exp -7, below currently attainable observations, with an rms fluctuation of about (6.0 +/- 3.0) x 10 exp -7 on arcmin scales. The rate of galaxy formation peaks at a relatively late epoch (z is about 0.5). In the case of mass function, the smallest objects are stabilized against collapse by thermal energy: the mass-weighted mass spectrum peaks in the vicinity of 10 exp 9.1 solar masses, with a reasonable fit to the Schechter luminosity function if the baryon mass to blue light ratio is about 4. It is shown that a bias factor of 2 required for the model to be consistent with COBE DMR signals is probably a natural outcome in the present multiple component simulations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 414; 2; p. 407-420.
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  • 10
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    A tilted cold dark matter cosmological scenario (1992)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: A new cosmological scenario based on CDM but with a power spectrum index of about 0.7-0.8 is suggested. This model is predicted by various inflationary models with no fine tuning. This tilted CDM model, if normalized to COBE, alleviates many problems of the standard CDM model related to both small-scale and large-scale power. A physical bias of galaxies over dark matter of about two is required to fit spatial observations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 399; 1; p. L11-L14.
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