Primordial Density Field Research Articles

Nonlinear Evolution of Genus in a Primordial Random Gaussian Density Field

The genus statistics is studied using large $N$-body simulations for several cosmological models. We consider the effects of nonlinear gravitational evolution, smoothing the particle data in fully nonlinear regime, and the redshift-space distortion on the genus curve. Detailed comparison between the theoretical prediction in weakly nonlinear theory and the appropriate simulation results shows that the analytic formula describes the behavior of genus in weakly nonlinear regime fairly accurately. We also find that the redshift-space distortion on genus statistics is small in linear and weakly nonlinear regimes. We conclude that if weakly nonlinear theory and direct numerical simulations are combined, the normalized genus curve $G(\nu)/G(0)$ is a powerful tool to directly check the random-Gaussian paradigm of the origin of the large-scale structure in the universe.

Shear fields and the evolution of galactic scale density peaks

view Abstract Citations (46) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Shear fields and the evolution of galactic scale density peaks van de Weygaert, Rien ; Babul, Arif Abstract We present preliminary results of our investigation into the influence of shear fields on the evolution of galactic scale fluctuations in a primordial Gaussian random density field. Specifically, we study how the matter associated with a galaxy scale peak evolves, to determine whether the shear can affect the peak's ability to form a virialized structure. We find that the evolution of the mass distribution in the immediate surroundings of >= 1 σ initial density peaks is sensitive to the nature and magnitude of the shear. Its final fate and configuration spans a plethora of possibilities, ranging from accretion onto the peak to complete disruption. On the other hand, the mass defining the peak itself tends to form a virialized object, though a given galaxy scale peak need not necessarily form only one halo. Furthermore, galaxy-sized halos need not necessarily be associated with initial galaxy scale density peaks. Under certain conditions, the shear field is capable of breaking up a single primordial peak into two (and perhaps, more) distinct halos, or of promoting the growth of smaller scale peaks into galaxy-sized halos. Publication: The Astrophysical Journal Pub Date: April 1994 DOI: 10.1086/187310 arXiv: arXiv:astro-ph/9402003 Bibcode: 1994ApJ...425L..59V Keywords: Cosmology; Galactic Evolution; Galactic Halos; Galactic Structure; Shearing; Universe; Astronomical Models; Computerized Simulation; Density (Mass/Volume); Mass Distribution; Astrophysics; Astrophysics E-Print: 11 pages Plain Tex, figure available by anonymous fpt to ftp.cita.utoronto.ca in /cita/rien/peakshrlt.1.ps, CITA/93/47 full text sources arXiv | ADS |

Testing for the Gaussian nature of cosmological density perturbations through the three-point temperature correlation function

One of the crucial aspects of density perturbations that are produced by the standard inflation scenario is that they are Gaussian where seeds produced by topological defects tend to be non-Gaussian. The three-point correlation function of the temperature anisotropy of the cosmic microwave background radiation (CBR) provides a sensitive test of this aspect of the primordial density field. In this paper, this function is calculated in the general context of various allowed non-Gaussian models. It is shown that the Cosmic Background Explorer and the forthcoming South Pole and balloon CBR anisotropy data may be able to provide a crucial test of the Gaussian nature of the perturbations.

The Great Wall in the CfA survey - Its origin and imprint on the microwave background radiation

view Abstract Citations (8) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Great Wall in the CfA Survey: Its Origin and Imprint on the Microwave Background Radiation Atrio-Barandela, F. ; Kashlinsky, A. Abstract The Great Wall (GW) found in the latest CfA survey has clearly started out as an aspherical overdense region. We model its evolution after recombination and the imprint its time-dependent gravitational potential leaves in the microwave background radiation (MBR). We show that within the framework of the Zel'dovich approximation the (pre)GW region can be treated as ellipsoid. Consequently we approximate the GW as an oblate ellipsoid that started at recombination with an almost spherical shape, but with initial density contrast, δ_i_ much smaller than it had to be in the spherical model in order to reach the observed density contrast of δ_f_ ~ 5. The resultant δ_i_ is compatible with the rms value of δρ/ρ on the GW scale at recombination for models with the n < 0 power spectrum of the primordial density field. We show that the time-dependent potential of the GW will induce a detectable fluctuation in MBR. The amplitude of the resultant {DELTA}T/T would depend on {OMEGA} and the overall density contrast of the mass distribution (or bias parameter), and therefore, MBR observations in that direction can further constrain these parameters. We also discuss the possibility of similar structures located at higher redshifts producing measurable and perhaps dominant statistical MBR anisotropies by this effect. Publication: The Astrophysical Journal Pub Date: May 1992 DOI: 10.1086/171282 Bibcode: 1992ApJ...390..322A Keywords: Background Radiation; Cosmology; Galactic Evolution; Gravitation; Microwaves; Universe; Astronomical Models; Red Shift; Temperature Distribution; Astrophysics; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; GALAXIES: FORMATION; GRAVITATION full text sources ADS |

Constraints on the power spectrum of the primordial density field from large-scale data - Microwave background and predictions of inflation

view Abstract Citations (7) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Constraints on the Power Spectrum of the Primordial Density Field from Large-Scale Data: Microwave Background and Predictions of Inflation Kashlinsky, A. Abstract One of the most robust predictions of the inflationary scenario for the early universe is the Harrison-Zeldovich (n = 1) spectrum of primordial density fluctuations (PDF). The later evolution of such spectrum is also uniquely specified in terms of its transfer function T^2^(k). We show that these assumptions about the early universe can be tested by measurements of the microwave background radiation (MBR) anisotropies with present techniques from COBE and other ground and balloon-based experiments; coupled with the data from galaxy catalogs (APM) they predict MBR anisotropies whose amplitudes restrict the primordial n. We compute MBR anisotropies corresponding to the minimum of C(0), the large-scale variance of the MBR anisotropy, and show that models with the Harrison-Zeldovich spectrum predicted by inflation should have quadrupole anisotropy Q > 1.2 x 10^-5^(a_2_ >= 2 x 10^-5^) and can soon be probed by COBE. If P(k) had n = 4 on large scales, the quadrupole anisotropy would he Q >= (a few) x 10^-8^ well below the quadrupole induced by the local motion. We show that experiments with FWHM ~1^deg^ would be ideal for probing the primordial n and present numbers for an experiment with FWHM = 1.5^deg^ conducted by Lubin and colleagues-in this case one should see δT|T|_~2^deg^_>=(a few) x 10^-5^ if n= 1 or if the universe is flat. If the universe is open and n = 4, the numbers should still be detectable with the ultimate resolution of this experiment. COBE should detect anisotropies if the universe is flat or if n = 1 on large scales. The minimal anisotropies implied by the APM data are inconsistent with the upper limits from the MIT experiment if n = 1. Publication: The Astrophysical Journal Pub Date: March 1992 DOI: 10.1086/186292 Bibcode: 1992ApJ...387L...1K Keywords: Density Distribution; Power Spectra; Relic Radiation; Universe; Computational Astrophysics; Cosmic Background Explorer Satellite; Probability Density Functions; Space Density; Astrophysics; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; GALAXIES: CLUSTERING; GALAXIES: FORMATION; GRAVITATION full text sources ADS |

Lyman-alpha clouds as a relic of primordial density fluctuations

view Abstract Citations (131) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lyman-Alpha Clouds as a Relic of Primordial Density Fluctuations Bond, J. R. ; Szalay, A. S. ; Silk, J. Abstract We develop a model in which Lyα clouds are probes of primordial density fluctuations. We argue that they are pressure-driven relics whose expansion is triggered by photoionization at z ~ 4. This model finds its natural setting in the class of cold dark matter models with {OMEGA} = 1 and biased galaxy formation in which density peaks of subgalactic mass go nonlinear at z ~ 5. The more massive clouds are confined by dark matter and form dwarf galaxies, while the abundance and dimensions of the smaller clouds are comparable to those of the Lyα systems. A simple model of the photoionization history of the universe enables us to calculate the redshift evolution of the neutral hydrogen fraction in these clouds and simultaneously satisfy the Gunn-Peterson constraint on the ionization of the IGM. We present hydrodynamic computations of cloud histories in {OMEGA} = 1 CDM-dominated and baryon-dominated universes. By combining these results with the statistical properties of peaks in the Gaussian primordial density field, we determine the H I column density distribution as a function of N_H I_ and redshift, and estimate the correlation function of the clouds. The observed cloud parameters come out naturally in the CDM model and suggest that Lyα clouds are the missing link between primordial density fluctuations and the formation of galaxies. Publication: The Astrophysical Journal Pub Date: January 1988 DOI: 10.1086/165923 Bibcode: 1988ApJ...324..627B Keywords: Cosmology; Dark Matter; Intergalactic Media; Lyman Alpha Radiation; Relic Radiation; Dwarf Galaxies; Galactic Clusters; Galactic Evolution; Hydrodynamics; Photoionization; Astrophysics; COSMOLOGY; DARK MATTER; GALAXIES: CLUSTERING; GALAXIES: INTERGALACTIC MEDIUM full text sources ADS |