Showing papers on "Dipole anisotropy published in 1990"

Local Gravity and Large-Scale Structure

Abstract: The magnitude and direction of the observed dipole anisotropy of the galaxy distribution can in principle constrain the amount of large-scale power present in the spectrum of primordial density fluctuations. This paper confronts the data, provided by a recent redshift survey of galaxies detected by the IRAS satellite, with the predictions of two cosmological models with very different levels of large-scale power: the biased Cold Dark Matter dominated model (CDM) and a baryon-dominated model (BDM) with isocurvature initial conditions. Model predictions are investigated for the Local Group peculiar velocity, v(R), induced by mass inhomogeneities distributed out to a given radius, R, for R less than about 10,000 km/s. Several convergence measures for v(R) are developed, which can become powerful cosmological tests when deep enough samples become available. For the present data sets, the CDM and BDM predictions are indistinguishable at the 2 sigma level and both are consistent with observations. A promising discriminant between cosmological models is the misalignment angle between v(R) and the apex of the dipole anisotropy of the microwave background.

Theoretical implications of the CMB spectral distortions

Abstract: The spectral distortions of the Cosmic Microwave Background (CMB) are quite informative on the processes that might (or had to) occur in the primordial plasma after the thermalization time, during an epoch which is crucial for the formation of the observed structures of the universe. Here we review the relevant processes generating CMB spectral distortions. We compare the presently available data on the spectrum with the predictions of a variety of theoretical scenarios. We also review the connections among the spectral shape of the CMB, the dipole anisotropy and the Sunyaev-Zeldovich effect.

Early results from the Cosmic Background Explorer (COBE)

Abstract: The Cosmic Background Explorer, launched 18 Nov. 1989, has nearly completed its first full mapping of the sky with all three of its instruments: A Far Infrared Absolute Spectrometer (FIRAS) covering 0.1 to 10 mm, a set of Differential Microwave Radiometers (DMR) operating at 3.3, 5.7, and 9.6 mm, and a diffuse Infrared Background Experiment (DIRBE) spanning 1 to 300 microns in ten bands. A preliminary map of the sky derived from DIRBE data is presented. Initial cosmological implications include: a limit on the comptonization parameter of 0.001, on the chemical potential parameter of 0.01, a strong limit on the existence of a hot smooth intergalactic medium, and a confirmation that the dipole anisotropy has the spectrum expected from a Doppler shift of a blackbody. There are no significant anisotropies in the microwave sky detected, other than from our own galaxy and a cos theta dipole anisotropy whose amplitude and direction agree with previous data. At shorter wavelengths, the sky spectrum and anisotropies are dominated by emission from local sources of emission within our Galaxy and Solar System. Preliminary comparison of IRAS (Infrared Astronomical Satellite) and DRIBE sky brightnesses toward the ecliptic poles shows the IRAS values to be significantly higher than found by DRIBE at 100 microns. The presence of gain and zero point errors in the IRAS total brightness data is suggested. The spacecraft, instrument designs, and data reduction methods are described.

Cosmic Background Radiation Anisotropies in the Far Infrared

Abstract: The motion of the earth with respect to the distant matter frame produces a spectral distortion in the observed background radiation given by 1 The second-order approximation in β gives (de Bernardis et al., 1989) 2 where α≅(dlnI/dln v) = (v/I)(dI/dv). The first term in cosθ of equation (2) is the usual dipole anisotropy, the second constant term is the equivalent of the transverse Doppler effect in special relativity, and the third term is the quadrupole anisotropy. It is interesting to note that the quadrupole term is zero in the Rayleigh-Jeans region of the blackbody spectrum: Q ≈ 1/2(3–α)(2–α)β2cos2θ.