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NASA NTRS1990

The Hawaii Imaging Fabry-Perot Interferometer (HIFI)

At Mauna Kea Observatory, researchers conducted optical, imaging spectrophotometric studies of selected active galaxies using both the Canada-France-Hawaii 3.6m and University of Hawaii 2.2m telecopes (Tully, Bland and Cecil 1988). To maximize spatial resolution, researchers select galaxies independent of luminosity but known to possess interesting morphologies or high-velocity, extranuclear ionized gas (Walker 1968; Rubin and Ford 1968). They study both the large-scale patterns produced in IR-luminous, starburst systems (e.g., M82, NGC 253, NGC 6240) and those with compact, but spatially extended, circumnuclear, narrow line regions (e.g., M51, NGC 1068, NGC 4151). Current studies are restricted to the optical (SII), (NII) and (OIII) lines and the brightest Balmer recombination lines. These lines are, in principle, sufficient to constrain the dynamical structure and dominant excitation mechanism of the ionized component.

Bland, Jonathan↗

NASA NTRS1986

A slice of the universe

A preliminary discussion is presented of recent results obtained as part of the extension of the Center of Astrophysics redshift survey. Several features of the results are striking. The distribution of galaxies in the sample, which contains 1100 galaxies in a 6 deg x 117 deg strip going through the Coma cluster, looks like a slice through the suds in the kitchen sink. It appears that the galaxies are on the surfaces of bubble-like structures with diameters of 25-50/h-Mpc. The largest bubble in the survey has a diameter comparable with the most recent estimates of the diameter of the void in Bootes. This topology poses serious challenges for current models for the formation of large-scale structure. The best available model for generating these structures is the explosive galaxy formation theory of Ostriker and Cowie (1981).

De Lapparent, V.↗

NASA NTRS1991

The evolution of void-filled cosmological structures

1D, 2D, and 3D simulations are used here to investigate the salient features in the evolution of void-filled cosmological structures in universes with arbitrary values of Omega. It is found that the growth of a void as a function of time decreases significantly at the time corresponding to Omega = 0.5. In models constructed in 2D and 3D, suitable initial conditions lead to cellular structure with faceted voids similar to those observed in redshift surveys. Matter compressed to planes flows more rapidly toward condensations at the intersections than would be expected for spherical infall. The peculiar streaming velocities for void diameters of 5000 km/s should be observable. The simulations provide a more physical basis and dynamics for the bubbly and Voronois tesselation models used to derive statistical properties of cellular large-scale structure.

Regos, Eniko↗

NASA NTRS1992

deltaT/T limits from the UCSB South Pole degree-scale experiment and constraints on the large-scale deviations from the Hubble flow

The limits to the cosmic microwave background radiation (CBR) temperature anisotropy derived from the results of the University of California at Santa Barbara South Pole degree-scale experiment are translated into upper bounds on large-scale deviations from the Hubble flow. The lack of measurable CBR anisotropy in this experiment implies very low upper bounds upon the rms amplitude V(R) of the streaming motion within a Gaussian window of radius R: Vmax(R is greater than 4000 km/s) less than 200 km/s, and Vmax(R is greater than 7500 km/s) is less than 100 km/s. Thus, the smoothness of the CBR at about 1-2 deg and the apparent large-amplitude (about 500 km/s) deviations from pure Hubble flow at R greater than about 4000 km/s cannot be simultaneously explained in the framework of usual large-scale structure formation models based on the assumptions involved in this calculation.

Gorski, Krzysztof M.↗

NASA NTRS1986

Molecular clouds in the Carina arm

Results from the first large-scale survey in the CO(J = 1 to 0) line of the Vela-Carina-Centaurus region of the Southern Milky Way are reported. The observations, made with the Columbia University 1.2 m millimeter-wave telescope at Cerro Tololo, were spaced every beamwidth (0.125 deg) in the range 270 deg is less than or = l is less than or = 300 deg and -1 deg less than or = b less then or = 1 deg, with latitude extensions to cover all Carina arm emission beyond absolute b = 1 deg. In a concurrent survey made with the same telescope, every half-degree in latitude and longitude was sampled. Both surveys had a spectral coverage of 330 km/s with a resolution of 1.3 km/s. The Carina arm is the dominant feature in the data. Its abrupt tangent at l is approx. = 280 deg and characteristic loop in the l,v diagram are unmistakable evidence for CO spiral structure. When the emission is integrated over velocity and latitude, the height of the step seen in the tangent direction suggests that the arm-interarm contrast is at least 13:1. Comparison of the CO and H I data shows close agreement between these two species in a segment of the arm lying outside the solar circle. The distribution of the molecular layer about the galactic plane in the outer Galaxy is determined. Between R = 10.5 and 12.5 kpc, the average CO midplane dips from z = -48 to -167 pc below the b = 0 deg plane, following a similar well-known warping of the H I layer. In the same range of radii the half-thickness of the CO layer increases from 112 to 182 pc. Between l = 270 deg and 300 deg, 27 molecular clouds are identified and cataloged along with heliocentric distances and masses. An additional 16 clouds beyond 300 deg are cataloged from an adjoining CO survey made with the same telescope. The average mass for the Carina arm clouds is 1.4x 10(6)M (solar), and the average intercloud spacing along the arm is 700 pc. Comparison of the distribution of the Carina arm clouds with that of similarly massive molecular clouds in the first and second quadrants strongly suggests that the Carina and Sagittarius arms form a single spiral arm approx. 40 kpc long wrapping two-thirds of the way around the Galaxy.

Grabelsky, D. A.↗

NASA NTRS1983

The origin of density fluctuations in the 'new inflationary universe'

Cosmological mysteries which are not explained by the Big Bang hypothesis but may be approached by a revamped inflationary universe model are discussed. Attention is focused on the isotropy, the large-scale homogeneity, small-scale inhomogeneity, the oldness/flatness of the universe, and the baryon asymmetry. The universe is assumed to start in the lowest energy state, be initially dominated by false vacuum energy, enter a de Sitter phase, and then cross a barrier which is followed by the formation of fluctuation regions that lead to structure. The scalar fields (perturbation regions) experience quantum fluctuations which produce spontaneous symmetry breaking on a large scale. The scalar field value would need to be much greater than the expansion rate during the de Sitter epoch. A supersymmetric (flat) potential which satisfies the requirement, yields fluctuations of the right magnitude, and allows inflation to occur is described.

Turner, M. S.↗

NASA NTRS1985

Massive superclusters as a probe of the nature and amplitude of primordial density fluctuations

It is pointed out that correlation studies of galaxy positions have been widely used in the search for information about the large-scale matter distribution. The study of rare condensations on large scales provides an approach to extend the existing knowledge of large-scale structure into the weakly clustered regime. Shane (1975) provides a description of several apparent massive condensations within the Shane-Wirtanen catalog, taking into account the Serpens-Virgo cloud and the Corona cloud. In the present study, a description is given of a model for estimating the frequency of condensations which evolve from initially Gaussian fluctuations. This model is applied to the Corona cloud to estimate its 'rareness' and thereby estimate the rms density contrast on this mass scale. An attempt is made to find a conflict between the density fluctuations derived from the Corona cloud and independent constraints. A comparison is conducted of the estimate and the density fluctuations predicted to arise in a universe dominated by cold dark matter.

Kaiser, N.↗

NASA NTRS1986

Isocurvature cold dark matter fluctuations

According to Preskill et al. (1983), the axion field represents a particularly attractive candidate for the dark matter in the universe. In many respects it behaves like other forms of cold dark matter, such as massive gravitinos, photinos, and monopoles. It is, however, a pseudo-Goldstone boson of very low mass, and it is only because of rapid coherent oscillations of the field that it can dominate the mass density of the universe. In the present paper it is assumed that the isocurvature mode is dominant. The linear evolution calculations conducted do not depend upon specific details of particle physics. For this reason, the conducted discussion is applicable to any cold dark matter model with isocurvature perturbations. The results of the study lead to the conclusion that scale-invariant isocurvature perturbations do not seem an attractive possibility for the origin of large-scale structure. The findings strengthen the review that primordial adiabatic perturbations were the dominant fluctuations in the early stages of the Big Bang.

Efstathiou, G.↗

NASA NTRS1985

The Ohio SETI program - The first decade

A full-time dedicated SETI program has been in operation at Ohio State University since 1973. A 50-channel narrowband filter bank is in use near the 21 cm hydrogen-line. All data is processed in real time and permanently recorded. A large portion of the northern sky has been surveyed and analyzed for large-scale structure. The only obvious nonrandom structure is caused by isolated narrowband pulses, which are anticorrelated with galactic latitude, and congregate in two specific areas. The origin of these pulses is unknown, although they may be partially due to instrumental effects.

Dixon, R. S.↗

NASA NTRS1987

Does lower Omega allow a resolution of the large-scale structure problem?

The intermediate angular scale anisotropy of the cosmic microwave background, peculiar velocities, density correlations, and mass fluctuations for both neutrino and baryon-dominated universes with Omega less than one are evaluated. The large coherence length associated with a low-Omega, hot dark matter-dominated universe provides substantial density fluctuations on scales up to 100 Mpc: there is a range of acceptable models that are capable of producing large voids and superclusters of galaxies and the clustering of galaxy clusters, with Omega roughly 0.3, without violating any observational constraint. Low-Omega, cold dark matter-dominated cosmologies are also examined. All of these models may be reconciled with the inflationary requirement of a flat universe by introducing a cosmological constant 1-Omega.

Silk, Joseph↗

NASA NTRS1987

The topology of large-scale structure. I - Topology and the random phase hypothesis

Many models for the formation of galaxies and large-scale structure assume a spectrum of random phase (Gaussian), small-amplitude density fluctuations as initial conditions. In such scenarios, the topology of the galaxy distribution on large scales relates directly to the topology of the initial density fluctuations. Here a quantitative measure of topology - the genus of contours in a smoothed density distribution - is described and applied to numerical simulations of galaxy clustering, to a variety of three-dimensional toy models, and to a volume-limited sample of the CfA redshift survey. For random phase distributions the genus of density contours exhibits a universal dependence on threshold density. The clustering simulations show that a smoothing length of 2-3 times the mass correlation length is sufficient to recover the topology of the initial fluctuations from the evolved galaxy distribution. Cold dark matter and white noise models retain a random phase topology at shorter smoothing lengths, but massive neutrino models develop a cellular topology.

Weinberg, David H.↗

NASA NTRS1989

Cosmic structure from radiation-blown bubbles

Absorbing material in an expanding universe filled with sources of radiation is subject to an instability driven by radiation pressure. In the optically thick limit, this instability takes the form of rapidly growing cavities or bubbles in the absorbing material. No matter how small they are when they begin, such bubbles grow to approach a limiting size which depends only on the ratio of photon pressure to absorber inertia. For a nonprimordial submillimeter radiation background as strong as that recently detected by the Berkely-Nagoya group, the bubbles grow to a comoving radius of about 20 Mpc, comparable in scale to the voids seen in the large-scale galaxy distribution.

Hogan, Craig J.↗

NASA NTRS1989

Dynamical evolution of domain walls in an expanding universe

Whenever the potential of a scalar field has two or more separated, degenerate minima, domain walls form as the universe cools. The evolution of the resulting network of domain walls is calculated for the case of two potential minima in two and three dimensions, including wall annihilation, crossing, and reconnection effects. The nature of the evolution is found to be largely independent of the rate at which the universe expands. Wall annihilation and reconnection occur almost as fast as causality allows, so that the horizon volume is 'swept clean' and contains, at any time, only about one, fairly smooth, wall. Quantitative statistics are given. The total area of wall per volume decreases as the first power of time. The relative slowness of the decrease and the smoothness of the wall on the horizon scale make it impossible for walls to both generate large-scale structure and be consistent with quadrupole microwave background anisotropy limits.

Press, William H.↗

NASA NTRS1990

The stability of a collisionless cosmological shell

The P3 M technique is used here to simulate the evolution of collisionless shells in an Omega = 1 universe. Starting from the spherical similarity solution, a bootstrap technique is used to follow the evolution over very large expansion factors. It is found that the overall structure follows the similarity solution for a long period during which bound clumps grow within the shell. At late times the growth of structure depends on induced velocity perturbations in material outside the shell. If such perturbations are suppressed, structure on the shell becomes self-similar. When induced motions in the background medium are included, the evolution at late times is dominated by large-scale modes as predicted by linear stability analysis. The stable final state appears to consist of one or two massive clumps on the edge of a spherical void. The possible application of these results to the origin of galaxies and large-scale structure is discussed.

White, Simon D. M.↗

NASA NTRS1991

Infrared polarization images of star-forming regions. I - The ubiquity of bipolar structure

The inefficiency of the stellar formation process leads rather generally to high residual dust densities, and so to the existence of infrared reflection nebulosity (IRN), in regions of star formation. Polarization images of several star-forming regions with mass outflows (GSS 30, S255, GL 5180, GL 2591, GGD 27, and NGC 7538) presented here: (1) establish the universality of bipolarity and of shell or cavity structure in the IRN consistent with that of CO outflow; (2) identify the source of the mass outflow in each case; (3) show that the opening angle near this central source is large; and (4) demonstrate several instances of multiple shells, probably arising from episodic mass loss. Astrometry of 2.2-micron sources with arcsecond accuracy identifies the illuminating source of each IRN uniquely with a compact H II region or a bright IR source. The polarization images provide strong evidence for large-scale dust toroids around each of these sources. The density and mass of these disks are estimated from the extinction through the disk.

Tamura, M.↗

NASA NTRS1991

Jet noise generated by large-scale coherent motion

The noise generated by large scale turbulence structures and instability waves of jets is discussed. Emphasis is placed on supersonic jets with moderate to high Reynolds numbers. This is because it is in these jets that unambiguous experimental and theoretical evidence is found indicating that large turbulence structures and instability waves are directly responsible for generating the dominant part of the noise. For subsonic jets similar large turbulence structures and instability waves do play a crucial role in the dynamics, spread, and mixing of the jet fluid. However, at subsonic convection speeds, they do not appear to be efficient noise generators. Many investigators believe that the dominant noise source of subsonic jets is, in fact, the small scale turbulence. As yet, this belief has not yet received universal acceptance. The issues involved are complicated and are not easy to resolve.

Tam, Christopher K. W.↗

NASA NTRS1992

The topology of large-scale structure. V - Two-dimensional topology of sky maps

A 2D algorithm is applied to observed sky maps and numerical simulations. It is found that when topology is studied on smoothing scales larger than the correlation length, the topology is approximately in agreement with the random phase formula for the 2D genus-threshold density relation, G2(nu) varies as nu(e) exp-nu-squared/2. Some samples show small 'meatball shifts' similar to those seen in corresponding 3D observational samples and similar to those produced by biasing in cold dark matter simulations. The observational results are thus consistent with the standard model in which the structure in the universe today has grown from small fluctuations caused by random quantum noise in the early universe.

Gott, J. R., III↗

NASA NTRS1992

The relation of local measures of Hubble's constant to its global value

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.

Turner, Edwin L.↗