Large-scale Structure Observations Research Articles

Temperature Fluctuations of the Microwave Background in Primeval Isocurvature Baryon Models

We calculate the temperature fluctuations in the microwave background in open primeval isocurvature baryon models (Peebles, 1987) with cosmological densities in the range 0.05 ≤ ω ≤ 0.2 We assume that the power spectrum of fluctuations is a power law with the index varying between – 1 ≤n≤ 0, as indicated by observations of large scale structure in the Universe. The Universe is assumed to be always fully ionized. The South Pole 13 field point experiment (Schusteret al., 1993) is compared to our theoretical predictions, and we find that the models predict larger temperature fluctuations than are observed. The observed temperature fluctuations on intermediate scales of ≲ 1°thus seem difficult to reconcile with the isocurvature baryon model.

Note On A Super-Horizon-Scale Inhomogeneous Cosmological Model

Many observations of large-scale and cosmological structures in the universe have been collected, but so far there is no consistent theoretical explanation. In the region within 100 Mpc from us, the observed two-point correlations of galaxies and clusters of galaxies can be described well by low-density homogeneous cosmological models (Bahcall & Cen 1993; Suto 1993). On the other hand, the observed anisotropies of the cosmic microwave background radiation have been explained well by comparatively high-density cosmological models such as the Einstein-de Sitter model (Bunn & Sugiyama 1994). In the intermediate scale, the angular sizes of the cores of quasars have been measured and their redshift dependence has been shown to be more consistent with the Einstein-de Sitter model than with the low-density models (Kellermann 1993). The number count-magnitude relation for remote galaxies supports low-density models with a nonzero cosmological constant (for example, Fukugita et al. 1990), but these models may be inconsistent with the observed distribution of Lyα clouds (Fukugita & Lahav 1991).

Trends in large-scale structure observations and the likelihood of early reionization

With the imminent promise of constraints on the epoch of reionization from observations of microwave background anisotropies, the question of whether or not the standard Cold Dark Matter (CDM) model permits early reionization has been subjected to detailed investigation by various authors, with the conclusion that reionization may occur at quite high redshift. However, it is widely accepted that this model is excluded, as when normalised to the COBE observations it possesses excessive galaxy clustering on scales below tens of megaparsecs. We examine the trends of observations, first in a fairly model independent way, and second by considering variants on the standard CDM model introduced to resolve the observational conflicts. We conclude that the epoch of reionization favoured by the observational data is typically considerably later than the standard CDM model suggests, and amongst models which may fit the observational data only the introduction of a cosmological constant leads to a reionization redshift close to that of standard CDM.

Large scale structure and supersymmetric inflation without fine tuning.

We explore constraints on the spectral index $n$ of density fluctuations and the neutrino energy density fraction ${\ensuremath{\Omega}}_{\ensuremath{\nu}}$ from observations of large scale structure. The best fits imply $n\ensuremath{\approx}1$ and ${\ensuremath{\Omega}}_{\ensuremath{\nu}}\ensuremath{\approx}0.1\ensuremath{-}0.3$, for Hubble constants 40-60 km ${\mathrm{s}}^{\ensuremath{-}1}$ ${\mathrm{Mpc}}^{\ensuremath{-}1}$. We present a new class of inflationary models based on realistic supersymmetric grand unified theories (GUTs) which do not have the usual "fine tuning" problems. The amplitude of primordial density fluctuations is found to be $\ensuremath{\propto}{(\frac{{M}_{X}}{{M}_{P}})}^{2}$, where ${M}_{X}$ (${M}_{P}$) denote the GUT (Planck) scale. The spectral index $n=0.98$, in excellent agreement with the observations.

Cosmic structure formation

This article reviews the prevailing paradigm for how galaxies and larger structures formed in the universe: gravitational instability. Basic observational facts are summarized to motivate the standard cosmological framework underlying most detailed investigations of structure formation. The observed universe approaches spatial uniformity on scales larger than about 10 26 cm. On these scales gravitational dynamics is almost linear and therefore relatively easy to relate to observations of large-scale structure. On smaller cosmic structure is complicated not only by nonlinear gravitational clustering but also by nonlinear nongravitational gas dynamical processes. The complexity of these phenomena makes galaxy formation one of the grand challenge problems of the physical sciences. No fully satisfactory theory can presently account in detail for the observed cosmic structure. However, as this article summarizes, significant progress has been made during the last few years.

Probing the large-scale velocity field with clusters of galaxies

What is the role of clusters of galaxies in probing the large-scale velocity field of the universe? We investigate the distribution of peculiar velocities of clusters of galaxies in the popular low-density ($\Omega=0.3$) flat Cold-Dark-Matter (CDM) cosmological model, which best fits many large-scale structure observations. An $\Omega=1$ CDM model is also studied for comparison. We find that clusters of galaxies are efficient tracers of the large-scale velocity field. The clusters exhibit a Maxwellian distribution of peculiar velocities, as expected from Gaussian initial density fluctuations. The cluster 3-D velocity distribution for the $\Omega=0.3$ model peaks at $v \sim 400$ km s$^{-1}$, and extends to high velocities of $v \sim 1200$ km s$^{-1}$. The rms peculiar velocity of the clusters is $440$ km s$^{-1}$. Approximately 10\% of all model clusters move with high peculiar velocities of $v \ge 700$ km s$^{-1}$. The observed velocity distribution of clusters of galaxies is compared with the predictions from cosmological models. The observed data exhibit a larger velocity tail than seen in the model simulations; however, due to the large observational uncertainties, the data are consistent at a $\sim 3\sigma$ level with the model predictions, and with a Gaussian initial density field. The large peculiar velocities reported for some clusters of galaxies ($v \geq 3000$ km s$^{-1}$) are likely to be overestimated, if the current model is viable.

Recurrence spectroscopy: Observation and interpretation of large-scale structure in the absorption spectra of atoms in magnetic fields.

Measurements were made of the absorption spectrum of hydrogen atoms to levels near the ionization threshold in a strong magnetic field. Taking advantage of a classical scaling law, we varied the photon energy and the magnetic-field strength simultaneously, and measured absorption versus ${\mathit{B}}^{\mathrm{\ensuremath{-}}1/3}$ at fixed scaled energy, \ensuremath{\varepsilon}=E/(B/${\mathit{B}}_{\mathrm{o}}$${)}^{2/3}$. The absorption rate has sinusoidal fluctuations which are correlated with closed classical orbits of the electron. Fourier transformation of this signal gives peaks, which we interpret as ``recurrence strength,'' as a function of the classical action of the closed orbit. Closed-orbit theory gives formulas for these recurrence strengths. We find that the formulas are in good agreement with the measurements. As the scaled energy is increased, observed recurrences proliferate, consistent with a change from orderly to chaotic motion of the electron. Bifurcation theory provides organizing principles for understanding this proliferation and for interpreting the data. New ``exotic'' orbits suddenly appear through saddle-node bifurcations. The ``main sequence'' of orbits is produced from an orbit parallel to B through a sequence of pitchfork and period-doubling bifurcations. Other recurrences are created by period-tripling and higher-order bifurcations of existing orbits. These bifurcations can have ``generic'' structure, or sometimes the structures are modified by symmetries of the system. Focusing effects associated with these bifurcations cause some recurrences to be particularly strong.

Cosmic structure formation and microwave anisotropies from global field ordering.

Spontaneous breaking of global symmetries and the consequent field ordering provide a mechanism for the formation of structure in the Universe. We compare the predictions of these theories with the cosmic microwave background (CMB) anisotropy recently detected by the Cosmic Background Explorer (COBE) and with recent observations of large-scale structure. In this paper we give a self-contained discussion of the analytical formalism, and numerical techniques required to simulate the texture, global monopole, global string, and nontopological texture scenarios. The Universe is assumed to have critical density and to be dominated by "cold" dark matter. Our main conclusions are that all of these scenarios are consistent with the reported amplitude, statistical properties, and multipole spectrum of the COBE signal, for a high bias factor $b\ensuremath{\sim}(2\ifmmode\pm\else\textpm\fi{}1){h}^{\ensuremath{-}1}$. The distinctive non-Gaussian character of the CMB anisotropies produced in these theories is investigated, and the prospects for its detection are discussed. We also compare the theories with the recent data on the large-scale galaxy distribution. Like the "standard" inflationary scenarios, if $\ensuremath{\Omega}=1$, $\ensuremath{\Lambda}=0$, these theories may have insufficient power on large scales.

Cosmological constant, COBE cosmic microwave background anisotropy, and large-scale clustering

A flat, scale-free, low-density cold dark matter model with a positive cosmological constant is one of the surviving scenarios after the COBE discovery of large-scale anisotropy in the cosmic background radiation. We calculate the expected properties of the model when normalized to the anisotropy measured by COBE, for various large-scale structure observations: the CfA and IRAS galaxy power spectra, the galaxy peculiar velocities, the bulk-flow motion, the APM galaxy angular correlation function, and the cluster mass function. Several effects due to the cosmological constant and properties of primordial fluctuations from inflation are taken into account. We find that a flat model ({OMEGA} + {OMEGA}<SUB>LAMBDA</SUB>_ = 1) with {OMEGA}h ~ 0.25-0.3 is consistent with all the above large-scale structure observations. A value of {OMEGA} &gt;~ 0.3-0.4 is also consistent with the observed age of the globular clusters and a galaxy bias of b ~ 1.5. The streaming velocity test fits the data at the 1.6 σ level and appears to be a critical test for the model.

Galaxy clustering on large scales.

I describe some recent observations of large-scale structure in the galaxy distribution. The best constraints come from two-dimensional galaxy surveys and studies of angular correlation functions. Results from galaxy redshift surveys are much less precise but are consistent with the angular correlations, provided the distortions in mapping between real-space and redshift-space are relatively weak. The galaxy two-point correlation function, rich-cluster two-point correlation function, and galaxy-cluster cross-correlation function are all well described on large scales ( greater, similar 20h-1 Mpc, where the Hubble constant, H0 = 100h km.s-1.Mpc; 1 pc = 3.09 x 10(16) m) by the power spectrum of an initially scale-invariant, adiabatic, cold-dark-matter Universe with Gamma = Omegah approximately 0.2. I discuss how this fits in with the Cosmic Background Explorer (COBE) satellite detection of large-scale anisotropies in the microwave background radiation and other measures of large-scale structure in the Universe.

Observations of large-scale structures in wakes behind axisymmetric bodies

Wakes behind disk-shaped axisymmetric bodies of varying solidity are studied using flow visualization and two-dimensional Fourier decomposition of velocity measurements. Evidence of a reverse flow region behind some of the bodies is observed to coincide with the presence of large-scale structures in the near and far wake. Fourier analysis shows that these large-scale structures are predominately helical (m= ±1) and occur at a characteristic frequency which corresponds to their wavelength as observed from flow visualization. Our measured value for this characteristic frequency agrees with vortex shedding frequencies observed for these types of wakes.

Inflation and mixed dark matter models

Recent large scale structure observations, including COBE, have prompted many authors to discuss modifications of the standard Cold Dark Matter model. Two of these, a tilted spectrum and a gravitational wave contribution to COBE, are at some level demanded by theory under the usual assumption that inflation generates the primeval perturbations. The third, whose motivation comes by contrast from observation, is the introduction of a component of hot dark matter to give the Mixed Dark Matter model. We discuss the implication of taking these modifications together. Should Mixed Dark Matter prove necessary, very strong constraints on inflationary models will ensue.

Second-order solution for determining density and velocity fields of galaxies

In this Letter, I use second-order Lagrangian perturbation theory to calculate an analytical expression relating density to velocity in a gravitating system. This solution can be used to compare peculiar velocity field measurements with observations of large-scale structure. The predictions of both linear theory and second-order theory are compared with the results of N-body simulations. While linear theory systematically overestimates the velocity flows in high-density regions, the second-order corrections calculated herein remove this systematic error.

The CFHT north Galactic pole faint galaxy survey

view Abstract Citations (26) References (48) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The CFHT North Galactic Pole Faint Galaxy Survey Infante, L. ; Pritchet, C. J. Abstract As part of a study of large-scale structure at intermediate redshifts, a catalog of faint galaxies has been derived for a 2.2 deg^2^ area (maximum angular extent ~2.5^deg^ X 2.5^deg^) near the north Galactic pole. The photometric and astrometric calibration methods for the catalog are described in detail; the data comprising the catalog are found to be complete to limiting magnitudes J ~ 24 and F ~ 23. Galaxy counts and color distributions have been obtained from the catalog. A logarithmic slope of d(log N)/dm = 0.45 was derived for the J bandpass over the magnitude interval 20 <= J <= 24 whereas d(log N)/dm = 0.37 for the F bandpass (19 <= F <= 23); these results are in good agreement with previous work. These slopes are determined primarily by the counts at the faintest magnitudes; brighter than J~22.5 and F~21.5 the logarithmic slope of the counts is 0.40 in both bands, consistent with the constant mean color that is observed for such galaxies. There is a dramatic difference in the slope of the J and F counts fainter than J ~22.5 and F ~ 21.5. It is shown that this must imply a change in the properties (number count slope or mean color) of fainter galaxies relative to those at J <~ 22, and cannot be due solely to the presence of a new population of faint blue objects. The galaxy counts in this catalog match almost perfectly onto counts over the range 15 <~ J <~ 20 from the APM survey by Maddox and collaborators, and onto the faint CCD counts by Lilly et al. and Tyson at J ~> 23. These three data sets therefore provide a well defined mean relation for galaxy counts in the J bandpass. No significant variations are seen in the mean number density of galaxies over our fields. This constraint requires that the extent of large-scale inhomogeneities ("sheets") in the galaxy distribution across the line of sight must be larger than ~25 h_100_^-1^ Mpc-in reasonable accord with observations of large-scale structure in the CfA survey. Publication: The Astrophysical Journal Supplement Series Pub Date: December 1992 DOI: 10.1086/191736 Bibcode: 1992ApJS...83..237I Keywords: Astrometry; Astronomical Photometry; Galactic Clusters; Red Shift; Sky Surveys (Astronomy); Astronomical Catalogs; Charge Coupled Devices; Galactic Evolution; Astronomy; GALAXIES: CLUSTERING; GALAXIES: PHOTOMETRY; GALAXIES: DISTANCES AND REDSHIFTS; SURVEYS full text sources ADS |

Minimal anisotropies in the cosmic microwave background.

A second-order perturbation theory approach is developed to provide a calculation of temperature an- isotropies in the cosmic microwave background. Results with zero or negligible Sachs-Wolfe effect are given for models based on specific initial conditions, these models fitting the large-scale structure observations. No fluctuations are present on the surface of last scattering, but arise at low redshift and amount to δT/T∼10 −6 . The ratio of quadrupole to intermediate angular scale anisotropy is predicted to be about a factor of 2 less than expected in the standard inflationary models of large-scale structure

Structure formation in a universe with cold plus hot dark matter

view Abstract Citations (87) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Structure Formation in a Universe with Cold Plus Hot Dark Matter van Dalen, Anthony ; Schaefer, Robert K. Abstract We examine the effect of a small admixture of hot dark matter (HDM) to the "standard" cold dark matter (CDM) model for galaxy formation. With equal amounts of HDM and CDM the growth of galactic scale density peaks in the CDM component is highly damped and galaxy formation is problematic, as has been discussed elsewhere. However, if the HDM contribution is <~ 30% then the damping is not so severe and galaxies can still form by a reasonable redshift. Further, with this amount of HDM agreement with large-scale structure observations are greatly improved over that of pure CDM. In this paper we demonstrate this by comparing the predictions of CDM and cold plus hot dark matter (CPHDM) models with the most recent observations. We will consider galactic cluster correlations, large-scale peculiar velocity flows, observationally derived power spectra, and the likelihood of finding a Great Attractor-sized object. Galaxy formation is still a computationally subtle issue, but we make some preliminary observations concerning two-point correlations and formation times. Publication: The Astrophysical Journal Pub Date: October 1992 DOI: 10.1086/171832 Bibcode: 1992ApJ...398...33V Keywords: Dark Matter; Galactic Evolution; Universe; Astronomical Models; Power Spectra; Red Shift; Transfer Functions; Astrophysics; COSMOLOGY: DARK MATTER; GALAXIES: CLUSTERING; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE full text sources ADS |

Galaxy clusters and cold dark matter - A low-density unbiased universe?

Large-scale simulations of a universe dominated by cold dark matter (CDM) are tested against two fundamental properties of clusters of galaxies: the cluster mass function and the cluster correlation function. We find that standard biased CDM models are inconsistent with these observations for any bias parameter b. A low-density, low-bias CDM-type model, with or without a cosmological constant, appears to be consistent with both the cluster mass function and the cluster correlations. The low-density model agrees well with the observed correlation function of the Abell, Automatic Plate Measuring Facility (APM), and Edinburgh-Durham cluster catalogs. The model is in excellent agreement with the observed dependence of the correlation strength on cluster mean separation, reproducing the measured universal dimensionless cluster correlation. The low-density model is also consistent with other large-scale structure observations, including the APM angular galaxy-correlations, and for lambda = 1-Omega with the COBE results of the microwave background radiation fluctuations.

The formation of cosmic structure in a texture-seeded cold dark matter cosmogony

view Abstract Citations (34) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Formation of Cosmic Structure in a Texture-seeded Cold Dark Matter Cosmogony Gooding, Andrew K. ; Park, Changbom ; Spergel, David N. ; Turok, Neil ; Gott, Richard, III Abstract We use numerical and analytic approaches to calculate the growth of density fluctuations induced by global texture in an {OMEGA} = 1 cold dark matter (CDM) cosmogony. The resulting power spectra are in good agreement with each other, with more power on large,scales than in the standard inflation plus CDM model. We calculate various related statistics, including two-point correlation functions, mass variances, and the cosmic Mach number- our results indicate that the texture plus CDM cosmogony compares more favorably than standard CDM with the observations of large-scale structure. Texture produces coherent velocity fields on large scales, in agreement with observation, although the small-scale velocity dispersions appear excessive. Also, while structure on scales corresponding to the observed "bubbles" is produced, the voids appear less empty than observed if one assumes light traces mass. Both of these problems may be cured when baryonic physics is included. The topology of the cosmic structure found in the simulations agrees well with that observed. The non-Gaussian texture induced density fluctuations lead to earlier nonlinear object formation than in Gaussian models and may also be more compatible with recent evidence that the galaxy density field is non-Gaussian on large scales. On smaller scales, the density field is strongly non-Gaussian, but this appears to be primarily due to nonlinear gravitational clustering. The velocity field on smaller scales is surprisingly Gaussian. Publication: The Astrophysical Journal Pub Date: July 1992 DOI: 10.1086/171483 Bibcode: 1992ApJ...393...42G Keywords: Astronomical Models; Background Radiation; Cosmology; Dark Matter; Power Spectra; Baryons; Galactic Clusters; Galactic Evolution; Infrared Astronomy Satellite; Probability Distribution Functions; Astrophysics; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: DARK MATTER; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE full text sources ADS |

INFLATIONARY COSMOLOGY AND LARGE SCALE STRUCTURE OF THE UNIVERSE

Scale-invariant (flat) fluctuation spectra are the most generic outcomes of inflation. However, current observations of large scale structure require more fluctuation power on large scales than flat spectra give. One such observation concerns the existence of large cosmological bubbles on the scales ~ (20–50) Mpc in the galaxy distribution. We attempt an explanation of these structures based on an inflationary model containing two scalar fields. One of these fields undergoes a first order phase transition, owing to the evolution of the other. We study the distribution of bubbles formed during the phase trnasition and show that for a wide range of choice of the free parameters in our model, a few bubbles can survive and grow to become the bubble structures observed at present.

Anisotropies of the cosmic microwave background in nonstandard cold dark matter models

Small angular scale cosmic microwave anisotropies in flat, vacuum-dominated, cold dark matter cosmological models which fit large-scale structure observations and are consistent with a high value for the Hubble constant are reexamined. New predictions for CDM models in which the large-scale power is boosted via a high baryon content and low H(0) are presented. Both classes of models are consistent with current limits: an improvement in sensitivity by a factor of about 3 for experiments which probe angular scales between 7 arcmin and 1 deg is required, in the absence of very early reionization, to test boosted CDM models for large-scale structure formation.