Showing papers by "Edward L. Wright published in 1995"

Far-infrared spectral observations of the galaxy by cobe

Abstract: We derive Galactic continuum spectra from 5-96 cm(-1) fromCOBE/FIRAS observations. The spectra are dominated by warm dust emission,which may be fitted with a single temperature in the range 16-21 K (fornu(2) emissivity) along each line of sight. Dust heated by the attenuatedradiation field in molecular clouds gives rise tointermediate-temperature (10-14 K) emission in the inner Galaxy only. Awidespread, very cold component (4-7 K) with optical depth that isspatially correlated with the warm component is also detected. The coldcomponent is unlikely to be due to very cold dust shielded from starlightbecause it is present at high latitude. We consider hypotheses that thecold component is due to enhanced submillimeter emissivity of the dustthat gives rise to the warm component, or that it may be due to verysmall, large, or fractal particles. Lack of substantial power above theemission from warm dust places strong constraints on the amount of coldgas in the Galaxy. The microwave sky brightness due to interstellar dustis dominated by the cold component, and its angular variation could limitour ability to discern primordial fluctuations in the cosmic microwavebackground radiation.

Observational confirmation of a circumsolar dust ring by the COBE satellite

Abstract: ASTEROID collisions are an important source of the dust particles in the zodiacal cloud1–3. These particles spiral in towards the Sun under the influence of drag forces4–6 and, in passing through the inner Solar System, are subject to gravitational perturbations by the planets, which may trap them (at least temporarily) in orbital resonances7–10. Recently, numerical simulations have shown that resonances with the Earth are particularly effective at trapping asteroidal dust, leading to the suggestion that the Earth may be embedded in a circumsolar ring of dust11. The azimuthal structure of this ring was predicted to be asymmetric, with the region trailing the Earth being substantially more dense than that in the leading direction11. This prediction is in both qualitative and quantitative agreement with the asymmetry in zodiacal light observed by the Infrared Astronomical Satellite (IRAS)11,12, but the IRAS data alone are equivocal because of calibration uncertainties and sparse coverage of elongation angle12. Here we report observations by the Diffuse Infrared Background Experiment13 (DIRBE) on the Cosmic Background Explorer satellite (COBE)14, which confirm both the existence of this ring and the predictions of its near-Earth structure.

Producing Mega-pixel CMB Maps from Differential Radiometer Data

Abstract: A major goal of cosmology is to obtain sensitive, high resolution maps of the Cosmic Microwave Background (CMB) anisotropy. Such maps, as would be produced by the recently proposed Microwave Anisotropy Probe (MAP), will contain a wealth of primary information about conditions in the early universe. To mitigate systematic effects when observing the microwave background, it is desirable for the raw data to be collected in differential form: as a set of temperature differences between points in the sky. However, the production of large (mega-pixel) maps from a set of temperature differences is a potentially severe computational challenge. We present a new technique for producing maps from differential radiometer data that has a computational cost that grows in the slowest possible way with increasing angular resolution and number of map pixels. The required central processor (CPU) time is proportional to the number of differential data points and the required random access memory (RAM) is proportional to the number of map pixels. We test our technique, and demonstrate its feasibility, by simulating one year of a space-borne anisotropy mission.

On the Density of PBH's in the Galactic Halo

Abstract: Calculations of the rate of local Primordial Black Hole explosions often assume that the PBH's can be highly concentrated into galaxies, thereby weakening the Page-Hawking limit on the cosmological density of PBH's. But if the PBH's are concentrated by a factor exceeding $c/(H_\circ R_\circ) \approx 4 \times 10^5$, where $R_\circ = 8.5$ kpc is the scale of the Milky Way, then the steady emission from the PBH's in the halo will produce an anisotropic high latitude diffuse gamma ray intensity larger than the observed anisotropy. This provides a limit on the rate-density of evaporating PBH's of $\lesssim 0.4$~pc$^{-3}$yr$^{-1}$ which is more than 6 orders of magnitude lower than recent experimental limits. However, the weak observed anisotropic high latitude diffuse gamma ray intensity is consistent with the idea that the dark matter that closes the Universe is Planck mass remnants of evaporated black holes.

Comments on the quasi-steady-state cosmology

Abstract: The Quasi-Steady-State Cosmology as proposed by Hoyle, Burbidge and Narlikar does not fit the observed facts of the Universe. In particular, it predicts that 75-90\% of the radio sources in the brightest sample that shows steeper than Euclidean source counts should be blueshifted.