Showing papers on "Dipole anisotropy published in 1986"

Anisotropy of the galaxies detected by IRAS

Abstract: We generate a catalogue of 6730 galaxies uniformly selected over most of the sky (> 9.5sr) using the IRAS point source catalogue. Our catalogue reveals a small (4–7%), but robust dipole anisotropy in the galaxy distribution that points towards l = 235°, b = 45°, within 30° of the microwave dipole anisotropy. Angular correlation analysis suggests that subsets of the catalogue have characteristic distances D* ≃50 – 100h-1 Mpc. The good agreement in direction of these dipoles suggests that the IRAS galaxies roughly trace the large scale mass distribution, that the microwave dipole velocity is mostly induced by the local supercluster (cz < 3000 km s -1), and that the indicated cosmological density is high (Ω ≈ 0.5). A full sky redshift survey is in progress to obtain a more precise estimate.

Cosmic microwave background anisotropy.

Abstract: Current hypotheses for the origin of structure in the Universe lead to predictions of the amplitudes of anisotropies in the cosmic microwave background radiation. The dipole anisotropy is related to density fluctuations on large scales and to other determinations of our motion relative to distant galaxies. Observation and theory are coming tantalizingly close to measuring the elusive anisotropy, or to revealing that our ideas about the origin of galaxies and large-scale structures are in need of substantial revision.

Anisotropy of the galaxies detected by IRAS.

Abstract: We generate a catalogue of 6730 galaxies uniformly selected over most of the sky (> 9.5sr) using the IRAS point source catalogue. Our catalogue reveals a small (4–7%), but robust dipole anisotropy in the galaxy distribution that points towards l = 235°, b = 45°, within 30° of the microwave dipole anisotropy. Angular correlation analysis suggests that subsets of the catalogue have characteristic distances D* ≃50 – 100h-1 Mpc. The good agreement in direction of these dipoles suggests that the IRAS galaxies roughly trace the large scale mass distribution, that the microwave dipole velocity is mostly induced by the local supercluster (cz < 3000 km s -1), and that the indicated cosmological density is high (Ω ≈ 0.5). A full sky redshift survey is in progress to obtain a more precise estimate.

Measurement of the microwave background radiation

Abstract: Absolute flux measurements of the 2.7 K background radiation show a blackbody spectrum with good accuracy ( ca . + 5 %) over two orders of magnitude of wavelength (12 cm to 1 mm). This is in agreement with the thermal history of matter and radiation envisaged by the hot Big Bang model. In particular, experimental limits on spectral distortion constrain processes that release energy into the early Universe. The extreme isotropy of the 2.7 K radiation on small angular scales (10" to 1°) sets interesting limits on models for the formation of mass structure. Some types of perturbations can be ruled out because the accompanying spatial fluctuations in radiation temperature are not seen (Δ T / T -4 ). Large-scale (1-90°) anisotropy of the radiation is plausible because at the time of decoupling (z « 1000), regions separated by more than a few degrees in the sky were not in causal contact. Explanation of the observed isotropy is a major feature of inflationary models. Finally, the observed dipole anisotropy is mostly due to the peculiar velocity of the Galaxy with respect to the radiation frame. An interesting question is: how much of this velocity is primordial and how much can be accounted for by local mass attractors?

Cosmological Shells and Blast Waves

Abstract: The microwave background is extremely smooth, showing possible deviations from isotropy at only two scales. The dipole anisotropy (cf. Lubin, this conference) is attributable to the motion of the Local Group with respect to the background at approximately 600 km/s. At a much smaller scale (1’) Partridge et al. (1986) may have found fluctuations attributable to the era of galaxy formation (Ostriker, Vishniac and Sunyaev, 1986). But fluctuations in the background at intermediate scales due to initial density perturbations have not been detected, implying (cf. DeZotti, this conference) embarrassment for some of the standard models for the development of large-scale structure.

The Local Gravitational Field

Abstract: In the redshift range v<3000 km s-1, the density distributions of the infrared selected IRAS galaxies and the optically selected CfA galaxies are shown to be identical. But the cosmological baseline density level of the IRAS galaxies appears to be higher by a factor ~2 than the one determined for the optical galaxies. If correct, this difference could account for the discrepancy between the determinations of Ω0 from the Virgocentric infall and from the IRAS dipole anisotropy. There are, however, a number of problems with this simple explanation.

Cosmic microwave background at its twentieth anniversary

Abstract: The role of cosmic microwave background radiation in cosmology is examined. The thermal spectrum, the large entropy in the universe, the large-scale isotropy of the radiation, and the small-scale isotropy or homogeneity of the radiation are analyzed in order to describe the properties of the universe. It is observed that the microwave background spectrum is thermal over a wide range, there is a significant detectable dipole anisotropy in the radiation, but no quadrupole anisotropy, and there is a high deree of radiation isotropy on angular scales between 1-5 degrees. 62 references.

The cosmic microwave background radiation and galaxy formation

Abstract: Observational limits on the microwave-background-radiation anisotropy on various angular scales are reviewed. Comparison is made with the predictions of the gravitational-instability theory of galaxy formation from primordial fluctuations in the very early universe. There is no entirely satisfactory theory that presently reconciles inflationary cosmology predictions of the flatness of the universe and of the scale-invariant primordial fluctuation spectrum with the limits on the amplitude of the anisotropy (δT/T), with the Virgo-cluster motion inferred from the dipole anisotropy, and with astronomical determinations of the cosmological density parameter.

Microwave and X-Ray Constraints on Local Large-Scale Overdensities

Abstract: We discuss the small scale temperature fluctuations of the microwave, background induced by a local overdensity, of size larger than the Local Supercluster, that may eventually account for a substantial fraction of the observed dipole anisotropy, and briefly mention the new prospects of observing them opened by space-borne experiments currently in project. We also show that useful information on the large scale distribution of galaxies and, in particular, on the correlation function of rich clusters can be elicited from an analysis of the HEAO 1 A-2 all sky survey data, exploiting also the spectral resolution of this experiment.

The Motion of the Local Group Relative to the Nearest Clusters of Galaxies

Abstract: The motion of the Local Group relative to an ensemble of galaxy clusters between 4000 and 10000 km/s is within 250 km/s of that inferred from the microwave dipole anisotropy The one-dimensional peculiar velocities of the component clusters are less than 350 km/s with 90% confidence

Peculiar Velocities and Galaxy Formation

Abstract: The cosmic microwave background (CMB) dipole anisotropy (DA) (Lubin and Villela, this volume) implies a Local Group (LG) velocity v D = 640 ± 50Km s -1 relative to the comoving reference frame, in a direction which is 45° away from the Virgo cluster. The CMBDA seems to be consistent both in amplitude and in direction with the DA of the Hubble flow (780 ± 188km s -1) measured by Aaronson et al. (1985) in a set of 10 clusters at a distances 40 → 100 h -1 Mpc. Also, the IRAS point source catalogue exhibit a DA in the galaxy distribution in reasonable agreement in direction with the CMBDA (Yahil et al., 1985; Meiksin and Davis, 1985).