COBE DMR Research Articles

Cosmic Background Anisotropies in Cold Dark Matter Cosmology

view Abstract Citations (455) References (58) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cosmic Background Anisotropies in Cold Dark Matter Cosmology Sugiyama, Naoshi Abstract Cosmic microwave background (CMB) anisotropies and density fluctuations are calculated for flat cold dark matter (CDM) models with a wide range of parameters, viz., Ω0, h, and ΩB, for standard recombination and for various epochs of reionization. Tables of the power spectrum of CMB anisotropies in the form of C1 values as a function of l are presented. Although the Harrison-Zeldovich initial spectrum is assumed in these tables, we present simple approximations for obtaining the C1 values corresponding to a tilted spectrum from those with a Harrison-Zeldovich spectrum. Values of σ8 are derived for the matter density spectrum, with α(10°), fixed Qrms-PS and COBE Differential Microwave Radiometer (DMR) 2 yr normalizations. Simple modifications of the fitting formula for the density transfer function are given which are applicable for models with high baryon density. By using both numerical results and these fitting formulae, we calculate the relation between α8 and Qrms-PS and find good agreement. In addition, the velocity fields are calculated. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1995 DOI: 10.1086/192220 arXiv: arXiv:astro-ph/9412025 Bibcode: 1995ApJS..100..281S Keywords: COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: THEORY; COSMOLOGY: DARK MATTER; Astrophysics E-Print: 30 pages including 10 figures, uuencoded comressed Postscript. 3 figures are missing. A complete version is available at anonymous ftp site ftp://pac2.berkeley.edu/pub/sugiyama/sugiyama.uu Tables (39pages) are also available at ftp://pac2.berkeley.edu/pub/sugiyama/tables.ps (and tables.tex) Replaced because one new figure is added and some figures are modified full text sources arXiv | ADS | data products CDS (2) Related Materials (1) Catalog: 1996yCat..21000281S

Comments on the Comparison of the COBE DMR and Tenerife Data

Comments on the Comparison of the COBE DMR and Tenerife Data

Transient events in the COBE database simultaneous with gamma ray bursts

We are investigating the COBE DMR data at instances of known γ-ray bursts (GRBs) when any of the six DMR horn directions was coincident with the direction of a burst. The BATSE instrument on board GRO has detected 207 bursts during the eight-month period of overlap corresponding to the current release of COBE data. The odds of a GRB occurring within the DMR field of view are near one coincidence per year. Here we report on one such serendipitous observation in 1991, GRB 911226, for which a detailed analysis is currently in progress.

ITAL]COBE[/ITAL] Constraints on Baryon Isocurvature Models

We consider Bayesian constraints on standard isocurvature baryon models from the slope and normalization of the anisotropy power spectrum detected by the COBE DMR experiment in their two year maps. In conjunction with either the amplitude of matter fluctuations $\sigma_8$ {\it or} its slope, all open models are ruled out at greater than 95\% confidence, whereas cosmological constant $\Lambda$ dominated models are constrained to be highly ionized. By including the COBE FIRAS 95\% confidence upper limit on spectral distortion, we further reduce the available parameter space for $\Lambda$ models by excluding these highly ionized models. These constraints define a single class of barely viable standard models which makes definite and testable predictions for degree scale anisotropies and large scale structure.

COBE observations of the microwave counterpart of GRBs

We have used the data from the COBE satellite to search for delayed microwave emission (31 - 90 GHz) from Gamma Ray Bursts (GRBs). The large 7° beam of COBE is well matched to the large positional uncertainties in the GRB locations, although it also means that fluxes from (point source) GRB objects will be diluted. In view of this we are doing a statistical search of the GRBs which occurred during the currently released COBE DMR data (years 1990 and 1991), which overlap ∼ 200 GRBs recorded by GRO. Here we concentrate on just the top 10 GRBs (in peak counts/second). We obtain the limits on the emission by comparing the COBE fluxes before and after the GRB at the GRB location. Since it is thought that the microwave emission should lag the GRB event, we have searched the GRB position for emission in the few months following the GRB occurrence.

Cosmological Constant Cold Dark Matter Models and the COBE Two-Year Sky Maps

We compare the 2 yr COBE DMR sky maps with the predictions of cosmological constant cold dark matter (ACDM) models. Using a Bayesian analysis, we find that the most likely value of the cosmological constant in a ACDM model is Λ = 0. The data set an upper limit on A of 0.78 (0.85) at 90% confidence, and 0.86 (0.92) at 95% confidence with (without) the quadrupole anisotropy. The angular power spectrum C<SUB>l</SUB> depends only quadratically on Λ when Λ is small; the likelihood function L(Λ) is therefore quite flat near Λ = 0.

COBE DMR-normalized open inflation cold dark matter cosmogony

view Abstract Citations (66) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS COBE DMR--normalized Open Inflation, Cold Dark Matter Cosmology Gorski, Krzysztof M. ; Ratra, Bharat ; Sugiyama, Naoshi ; Banday, Anthony J. Abstract Fourier analysis on a cut sky of the two-year COBE DMR 53 and 90 GHz sky maps (in galactic coordinates) is used to determine the normalisation of an open inflation model based on the cold dark matter scenario. The normalised model is compared to measures of large-scale structure in the universe. Although the DMR data alone does not provide sufficient discriminative power to prefer a particular value of the mass density parameter, the open model appears to be reasonably consistent with observations when Omega_0 ~ 0.3 - 0.4 and merits further study. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/187861 arXiv: arXiv:astro-ph/9502034 Bibcode: 1995ApJ...444L..65G Keywords: Background Radiation; Cosmology; Dark Matter; Density Distribution; Galactic Evolution; Universe; Anisotropy; Mass Distribution; Mathematical Models; Maximum Likelihood Estimates; Microwaves; Power Spectra; Astrophysics; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: OBSERVATIONS; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; GALAXIES: FORMATION; Astrophysics E-Print: uuencoded file containing 6 postscript files (11 pgs text, 4 figures, 1 table) full text sources arXiv | ADS |

Contribution to the Three-Point Function of the Cosmic Microwave Background from the Rees-Sciama Effect

view Abstract Citations (43) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Contribution to the Three-Point Function of the Cosmic Microwave Background from the Rees-Sciama Effect Mollerach, Silvia ; Gangui, Alejandro ; Lucchin, Francesco ; Matarrese, Sabino Abstract We compute the contribution to the three-point temperature correlation function of the cosmic microwave background coming from the nonlinear evolution of Gaussian initial perturbations, as described by the Rees-Sciama (or integrated Sachs-Wolfe) effect. By expressing the collapsed three-point function in terms of multipole amplitudes, we are able to calculate its expectation value for any power spectrum and for any experimental setting on large angular scales. We also give an analytical expression for the rms collapsed three-point function arising from the cosmic variance of a Gaussian fluctuation field. In the case of COBE DMR, we find that the predicted signal is ∼3 orders of magnitude below that expected from the cosmic variance. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176363 arXiv: arXiv:astro-ph/9503115 Bibcode: 1995ApJ...453....1M Keywords: COSMOLOGY: COSMIC MICROWAVE BACKGROUND; GALAXIES: CLUSTERS: GENERAL; Astrophysics E-Print: uuencoded compressed postscript, 10 pages text, 2 pages figures full text sources arXiv | ADS |

Angular power spectrum of the microwave background anisotropy seen by the COBE differential microwave radiometer

The angular power spectrum estimator developed by Peebles (1973) and Hauser & Peebles (1973) has been modified and applied to the 2 yr maps produced by the Cosmic Background Explorer Satellite Differential Microwave Radiometer (COBE DMR)). The power spectrum of the real sky has been compared to the power spectra of a large number of simulated random skies produced with noise equal to the observed noise and primordial density fluctuation power spectra of power-law form, with P(k) proportional to k(exp n). Within the limited range of spatial scales covered by the COBE DMR, corresponding to spherical harmonic indices 3 less than or = l is less than or approximately = 30, the best-fitting value of the spectral index is n = 1.25(sup +0.39 sub -0.44) with the Harrisson-Zel'dovich value n = 1 approximately 0.5 sigma below the best fit. For 3 less than or = l less than or approximately = 19, the best fit is n = 1.46(sup +0.39 sub -0.44). Comparing the COBE DMR delta-T/T at small l to the delta-T/T at l approximately = 50 from degree scale anisotropy experiments gives a smaller range of acceptable spectral indices which includes n = 1.

Comparison of double-inflationary models with observations.

We consider double-inflationary models with two noninteracting scalar fields: a ``light'' scalar field ${\mathrm{\ensuremath{\varphi}}}_{\mathit{l}}$ with the potential 1/2${\mathit{m}}_{\mathit{l}}^{2}$${\mathrm{\ensuremath{\varphi}}}_{\mathit{l}}^{2}$ and a ``heavy'' scalar field ${\mathrm{\ensuremath{\varphi}}}_{\mathit{h}}$ with the potential \ensuremath{\lambda}/n${\mathrm{\ensuremath{\varphi}}}_{\mathit{h}}^{\mathit{n}}$, n=2,4, whose effective mass is larger than ${\mathit{m}}_{\mathit{l}}$ during inflation with ${\mathrm{\ensuremath{\varphi}}}_{\mathit{h}}$&gt;${\mathit{M}}_{\mathit{P}}$. Cold dark matter (CDM) with the initial spectrum of adiabatic perturbations produced in these models is compared with observations. These models contain two more free parameters than the standard CDM model with an initial scale-invariant spectrum. We normalize our spectra to the COBE DMR and compare the predictions with observations on the biasing factor, large-scale peculiar velocities, quasar and galaxy formation, and the Stromlo-APM counts-in-cells analysis. The model with n=4 is excluded by the data while for the n=2 model, taking cosmic variance into account, a small window of parameters compatible with observations is found.

Statistical constraints on the inflation effective potential from the COBE DMR results.

We explore constraints on various forms for the effective potential during inflation based upon a statistical comparison between inflation-generated fluctuations in the cosmic microwave background temperature and the COBE DMR results. We show that the confidence limits of fits to the angular correlation are more sensitive to the inflation generating potential than implied by the uncertainty in the spectral index alone. This is because the cosmic variance diminishes both as contributions from higher multipoles become important, and as the tensor and scalar contributions become comparable. Fits to the first year 53A+B\ifmmode\times\else\texttimes\fi{}90A+B cross correlation function using an effective potential of the form V(\ensuremath{\varphi})=\ensuremath{\lambda}${\mathrm{\ensuremath{\varphi}}}^{\mathit{x}}$/x! yield upper limits of x\ensuremath{\le}35 and x\ensuremath{\le}266 at the 1\ensuremath{\sigma} and 2\ensuremath{\sigma} confidence levels, while the same analysis produces a power law of index of n=1.${10}_{\mathrm{\ensuremath{-}}0.64}^{+0.47}$ which would imply an overestimate of x\ensuremath{\le}63 from the simple analytic relation between x and n. We also quantify new limits on the parameters for polynomial effective potentials. This work highlights the importance of a careful statistical treatment when seeking constraints on the inflation-generating effective potential.

Non-Gaussian effects in the cosmic microwave background from inflation.

The presence of non-Gaussian features in the cosmic microwave background (CMB) radiation maps represents one of the most long-awaited clues in the search for the actual structure of primordial radiation, still needing confirmation. These features could shed some light on the nontrivial task of distinguishing the real souce of the primeval perturbations leading to large scale structure. One of the simplest non-Gaussian signals to search is the (dimensionless) skewness scrS. Explicit computations for scrS are presented in the frame of physically motivated inflationary models (natural, intermediate, and polynomial potential inflation) in the hope of finding values in agreement with estimated quantities from large angle scale (e.g., COBE DMR) maps. In all the cases considered the non-Gaussian effects turn out to lie below the level of theoretical uncertainty (cosmic variance). The possibility of unveiling the signal for scrS with multiple-field models is also discussed.

Bias and high-order galaxy correlation functions in the APM galaxy survey

On large scales, the higher order moments of the mass distribution, $S_J=\xibar_J/\xibar_2^{J-1}$, e.g., the skewness $S_3$ and kurtosis $S_4$, can be predicted using non-linear perturbation theory. Comparison of these predictions with moments of the observed galaxy distribution probes the bias between galaxies and mass. Applying this method to models with initially Gaussian fluctuations and power spectra $P(k)$ similar to that of galaxies in the APM survey, we find that the predicted higher order moments $S_J(R)$ are in good agreement with those directly inferred from the APM survey {\it in the absence of bias}. We use this result to place limits on the linear and non-linear bias parameters. Models in which the extra power observed on large scales (with respect to standard CDM) is produced by scale-dependent bias match the APM higher order amplitudes only if non-linear bias (rather than non-linear gravity) generates the observed higher order moments. When normalized to COBE DMR, these models are significantly ruled out by the $S_3$ observations. The cold plus hot dark matter model normalized to COBE can reproduce the APM higher order correlations if one introduces non-linear bias terms, while the low-density CDM model with a cosmological constant does not require any bias to fit the large-scale amplitudes.

Cosmic temperature fluctuations from two years of COBE differential microwave radiometers observations

view Abstract Citations (300) References (73) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cosmic Temperature Fluctuations from Two Years of COBE Differential Microwave Radiometers Observations Bennett, C. L. ; Kogut, A. ; Hinshaw, G. ; Banday, A. J. ; Wright, E. L. ; Gorski, K. M. ; Wilkinson, D. T. ; Weiss, R. ; Smoot, G. F. ; Meyer, S. S. ; Mather, J. C. ; Lubin, P. ; Loewenstein, K. ; Lineweaver, C. ; Keegstra, P. ; Kaita, E. ; Jackson, P. D. ; Cheng, E. S. Abstract The first two years of COBE DMR observations of the CMB anisotropy are analyzed and compared with our previously published first year results. The results are consistent, but the addition of the second year of data increases the precision and accuracy of the detected CMB temperature fluctuations. The two-year 53 GHz data are characterized by RMS temperature fluctuations of DT=44+/-7 uK at 7 degrees and DT=30.5+/-2.7 uK at 10 degrees angular resolution. The 53X90 GHz cross-correlation amplitude at zero lag is C(0)^{1/2}=36+/-5 uK (68%CL) for the unsmoothed 7 degree DMR data. A likelihood analysis of the cross correlation function, including the quadrupole anisotropy, gives a most likely quadrupole-normalized amplitude Q_{rms-PS}=12.4^{+5.2}_{-3.3} uK (68% CL) and a spectral index n=1.59^{+0.49}_{-0.55} for a power law model of initial density fluctuations, P(k)~k^n. With n fixed to 1.0 the most likely amplitude is 17.4 +/-1.5 uK (68% CL). Excluding the quadrupole anisotropy we find Q_{rms-PS}= 16.0^{+7.5}_{-5.2} uK (68% CL), n=1.21^{+0.60}_{-0.55}, and, with n fixed to 1.0 the most likely amplitude is 18.2+/-1.6 uK (68% CL). Monte Carlo simulations indicate that these derived estimates of n may be biased by ~+0.3 (with the observed low value of the quadrupole included in the analysis) and {}~+0.1 (with the quadrupole excluded). Thus the most likely bias-corrected estimate of n is between 1.1 and 1.3. Our best estimate of the dipole from the two-year DMR data is 3.363+/-0.024 mK towards Galactic coordinates (l,b)= (264.4+/-0.2 degrees, +48.1+/-0.4 degrees), and our best estimate of the RMS quadrupole amplitude in our sky is 6+/-3 uK. Publication: The Astrophysical Journal Pub Date: December 1994 DOI: 10.1086/174918 arXiv: arXiv:astro-ph/9401012 Bibcode: 1994ApJ...436..423B Keywords: Background Radiation; Cosmology; Extraterrestrial Radio Waves; Microwaves; Radio Astronomy; Spaceborne Astronomy; Temperature Distribution; Universe; Anisotropy; Computerized Simulation; Cosmic Background Explorer Satellite; Microwave Radiometers; Monte Carlo Method; Astronomy; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; COSMOLOGY: OBSERVATIONS; Astrophysics E-Print: Accepted by the Astrophysical Journal. Modifications include the addition of a quadrupole- removed correlation function and an analysis of the technique bias on the power spectral index, n. The most likely, de-biased, estimate of n is between 1.1 and 1.3. 57 pages of uu-encoded postscript (incl 3 b&amp full text sources arXiv | ADS |

Spectrum of scalar ("adiabatic") perturbations in a model of double inflation.

We study numerically a model of double inflation with two massive scalar fields and no interaction potential. Such models display a non-scale-invariant spectrum when the heavy mass ${m}_{h}&gt;&gt;{m}_{l}$, the light mass. The spectrum of adiabatic perturbations is studied numerically for $10\ensuremath{\le}p\ensuremath{\equiv}\frac{{m}_{h}}{{m}_{l}}\ensuremath{\le}25$ for which there is no pronounced intermediate stage between the two inflations. In that case we find that the contribution of the light scalar field to the spectrum ${k}^{\frac{3}{2}}\ensuremath{\Phi}(k)$, where $\ensuremath{\Phi}(k)$ is a rms gravitational potential, is dominant on all scales where the transition from the upper to the lower "plateau" takes place. Normalization to COBE DMR yields ${m}_{h}\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ Mp. When the "step" is located around $10{h}_{100}^{\ensuremath{-}1}$ Mpc, we get acceptable biasing parameters $2.30\ensuremath{\le}b\ensuremath{\le}2.72$. However, the model has sensibly less power on intermediate scales than standard CDM, where the latter is known to give acceptable results. This will severely constrain the parameters of the model.

Correlated noise in the COBE DMR sky maps

The Cosmic Background Explorer Satellite Differential Radiometer (COBE DMR) sky maps contain low-level correlated noise. We obtain estimates of the amplitude and pattern of the correlated noise from three techniques: angular averages of the covariance matrix, Monte Carlo simulations of two-point correlation functions and direct analysis of the DMR maps. The results from the three methods are mutually consistent. The noise covariance matrix of a DMR sky maps is diagonal to an accuracy of better than 1%. For a given sky pixel, the dominant noise covariance occure with the ring of pixels at an angular separation of 60 deg due to the 60 deg separation of the DMR horns. The mean covariance at 60 deg is 0.45%((sup +0.18)(sub -0.14)) of the mean variance. Additionally, the variance in a given pixel is 0.7% greater than would be expected from a single beam experiment with the same noise properties. Autocorrelation functions suffer from a approximately 1.5 sigma positive bias at 60 deg while cross-correlations have no bias. Published COBE DMR results are not significantly affected by correlated noise.

Power spectrum constraints from spectral distortions in the cosmic microwave background

view Abstract Citations (164) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Power Spectrum Constraints from Spectral Distortions in the Cosmic Microwave Background Hu, Wayne ; Scott, Douglas ; Silk, Joseph Abstract Using recent experimental limits on chemical potential distortions from COBE FIRAS, and the large lever-arm spanning the damping of sub- Jeans scale fluctuations to the COBE DMR fluctuations, we set a constraint on the slope of the primordial power spectrum n. It is possible to analytically calculate the contribution over the full range of scales and redshifts, correctly taking into account fluctuation growth and damping as well as thermalization processes. Assuming conservatively that μ < 1.76 x 10^-4^, we find that the 95% upper limit on n is only weakly dependent on other cosmological parameters, e.g., n < 1.60 (h = 0.5) and n < 1.63 (h = 1.0) for {OMEGA}_0_ = 1, with marginally weaker constraints for {OMEGA}_0_ < 1 in a flat model with a cosmological constant. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/187424 arXiv: arXiv:astro-ph/9402045 Bibcode: 1994ApJ...430L...5H Keywords: Background Radiation; Cosmology; Damping; Microwave Emission; Perturbation; Cosmic Noise; Power Gain; Power Spectra; Relic Radiation; Astronomy; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: EARLY UNIVERSE; COSMOLOGY: THEORY; Astrophysics E-Print: 8pg, uuencoded-tarred (&amp full text sources arXiv | ADS |

The three-point correlation function of the cosmic microwave background in inflationary models

We analyze the temperature three–point correlation function and the skewness of the Cosmic Microwave Background (CMB), providing general relations in terms of multipole coefficients. We then focus on applications to large angular s anisotropies, such as those measured by the COBE DMR, calculating the contribution to these quantities from primordial, inflation generated, scalar perturbations, via the Sachs–Wolfe effect. Using the techniques of stochastic inflation we are able to provide a universal expression for the ensemble averaged three–point function and for the corresponding skewness, which accounts for all primordial second–order effects. These general expressions would moreover apply to any situation where the bispectrum of the primordial gravitational potential has a hierarchical form. Our results are then specialized to a number of relevant models: power–law inflation driven by an exponential potential, chaotic inflation with a quartic and quadratic potential and a particular case of hybrid inflation. In all these cases non–Gaussian effects are small: as an example, the mean skewness is much smaller than the cosmic rms skewness implied by a Gaussian temperature fluctuation field.

Gravity's rainbow (microwave anisotropy and gravitational waves)

Could COBE DMR be detecting the imprint from a spectrum of gravitational waves generated during inflation? The conventional inflationary prediction had been that the cosmic microwave anisotropy is dominated by energy density fluctuations generated during inflation and that the gravitational waves contribute negligibly. The authors report on recent work that has shown that the conventional wisdom may be wrong; specifically, gravitational waves may dominate the anisotropy in inflationary models where the spectrum of perturbations deviates significantly from scale invariance (e.g., extended and power-law inflation models and extreme versions of chaotic inflation). If gravitational waves do dominate at the large-angular scales measured by COBE DMR, the expectation and interpretation of anisotropies on small-angular scales is profoundly altered.

Tensor perturbations in inflationary models as a probe of cosmology.

In principle, the tensor metric (gravity-wave) perturbations that arise in inflationary models can, beyond probing the underlying inflationary model, provide information about the Universe: ionization history, presence of a cosmological constant, and epoch of matter-radiation equality. Because tensor perturbations give rise to the anisotropy of the cosmic background radiation (CBR) solely through the Sachs-Wolfe effect we are able to calculate analytically their contribution to the variance of the multipole moments of the CBR temperature anisotropy. In so doing, we carefully take account of the effect of tensor perturbations that entered the Hubble radius during both the matter-dominated and radiation-dominated epochs by means of a transfer function. (Previously, only those modes that entered during the matter era were properly taken into account.) The striking feature in the spectrum of multipole amplitudes is a dramatic falloff for l\ensuremath{\gtrsim} \ensuremath{\surd}1+${\mathit{z}}_{\mathrm{LSS}}$ , where ${\mathit{z}}_{\mathrm{LSS}}$ is the redshift of the last-scattering surface, which depends upon the ionization history of the Universe. Finally, using our transfer function we provide a more precise formula for the energy density in stochastic gravitational waves from inflation, and, using the Cosmic Background Explorer Differential Microwave Radiometer (COBE DMR) quadrupole normalization, we express this energy density in terms of the ``tilt'' of the spectrum of tensor perturbations alone and show that it is unlikely that the stochastic background of gravity waves can be detected directly in the foreseeable future.