arXiv subjects

Edward L. Wright

Publications and source records attributed to Edward L. Wright.

101 records · Page 6Linked to original sources

arXiv1997

Angular Power Spectra of the COBE DIRBE Maps

The angular power spectra of the infrared maps obtained by the DIRBE (Diffuse InfraRed Background Experiment) instrument on the COBE satellite have been obtained by two methods: the Hauser-Peebles method previously applied to the DMR maps, and by Fourier transforming portions of the all-sky maps projected onto a plane. The two methods give consistent results, and the power spectrum of the high-latitude dust emission is C_\ell \propto \ell^{-3} in the range 2 < \ell < 300.

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arXiv1997

The CMBR and the Seeds of Galaxies

The Cosmic Microwave Background Radiation (CMBR) is the radiation left over from the hot Big Bang. Its blackbody spectrum and small anisotropy provide clues about the origin and early evolution of the Universe. In particular, the spectrum of the CMBR rules out many non-gravitational models of structure formation, and the anisotropy of the CMBR provides a measure of the gravitational potential at the time of last scattering, about 300,000 years after the Big Bang. The density inhomogeneities needed to produce the gravitational potential perturbations traced by the CMBR have grown to become the galaxies, clusters of galaxies, and superclusters that we see today.

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arXiv1996

COBE Observations of Interstellar Line Emission

The FIRAS instrument on the COBE satellite has conducted an unbiased survey of the far-infrared emission from our Galaxy. The first results of this survey were reported by Wright et al. (1991), and later conclusions were reported in Bennett et al. (1994). I report the results of analyses of this spectral survey, which includes emission lines from 158 micron C+, 122 micron and 205 micron N+, 370 micron and 609 micron neutral C, and CO J=2-1 through 5-4. The morphological distribution along the galactic plane (b=0 deg) for all the spectral line emission, and the high galactic latitude intensities of the strong C+ and 205 micron N+ emission are discussed. The high galactic latitude intensity of the 158 micron fine structure transition from C+ is I = (1.43 +/- 0.12)*1E-6 csc|b| erg/cm^2/s/sr for |b| > 15 deg and it decreases more rapidly than the far infrared intensity with increasing galactic latitude.

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arXiv1996

Scanning and Mapping Strategies for CMB Experiments

CMB anisotropy experiments seeking to make maps with more pixels than the 6144 pixels used by the COBE DMR need to address the practical issues of the computer time and storage required to make maps. A simple, repetitive scan pattern reduces these requirements but leaves the experiment vulnerable to systematic errors and striping in the maps. In this paper I give a time-ordered method for map-making with one-horned experiments that has reasonable memory and CPU needs but can handle complex COBE-like scans paths and 1/f noise.

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arXiv1995

Producing Mega-pixel CMB Maps from Differential Radiometer Data

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.

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arXiv1995

On the Density of PBH's in the Galactic Halo

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.

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arXiv1994

Comments on the Quasi-Steady-State Cosmology

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.

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arXiv1994

Dark Matter in the Light of COBE

The observations of all three COBE instruments are examined for the effects of dark matter. The anisotropy measured by the DMR, and especially the degree-scale ground- and balloon-based experiments, is only compatible with large-scale structure formation by gravity if the Universe is dominated by non-baryonic dark matter. The FIRAS instrument measures the total power radiated by cold dust, and thus places tight limits on the absorption of starlight by very cold gas and dust in the outer Milky Way. The DIRBE instrument measures the infrared background, and will place tight limits on the emission by low mass stars in the Galactic halo.

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arXiv1994

Comparison of Spectral Index Determinations

The index $n$ of a power law power spectrum of primordial density fluctuations, $P(k) \propto k^n$, has been estimated using many different techniques. The most precise compare the COBE DMR large angular scale $ΔT$ to the amplitude of the large scale structure, but these are also the most model-dependent. The COBE DMR $ΔT$ has also been compared to the degree-scale $ΔT$ from several experiments. And finally, a relatively model-independent value of $n$ can derived from the COBE data alone, but the small range of angular scales covered by COBE limits the precision of these methods.

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arXiv1994

COBE Tutorial and Recent Results

Some of the technical details involved in taking and analyzing data from COBE are discussed, and recent results from the FIRAS and DMR experiments are summarized. Some of the cosmological implications of these recent data are presented.

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arXiv1993

Cosmology/COBE

Abbreviated abstract of an invited talk at the International Cosmic Ray Conference in Calgary, July 1993: The results from the COBE satellite are in close agreement with the predictions of the standard hot Big Bang model, suggesting that the Universe was once hot, dense and isothermal, giving a background radiation spectrum that is close to a perfect blackbody. The spectrum observed by the FIRAS instrument places strong limits on events and scenarios occurring later than 1 year after the Big Bang. The observation of intrinsic anisotropy of the microwave background by the DMR instrument provides a measurement of the magnitude of the gravitational potential fluctuations that existed at decoupling. These potential perturbations were either produced in an inflationary epoch, or else they are initial conditions dating from t = 0. The angular power spectrum of dT is compatible with the inflationary scenario. The observed amplitude of dT can be used to restrict theories of the fundamental structure of matter on micro-physical scales and at energies higher than that of the most energetic cosmic rays. The DIRBE instrument will provide greatly improved data on extragalactic IR backgrounds after the strong foreground emission is subtracted.

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