102,019 research outputs found
FORMATION AND EVOLUTION OF EARLY DISTORTIONS OF THE MICROWAVE BACKGROUND SPECTRUM - A NUMERICAL STUDY
No full textWe present the results of an extensive numerical study on the formation and evolution of early distortions of the microwave background spectrum. The thermalization redshift, Z(therm), of arbitrary amounts of energy has been accurately determined. Simple formulae, yielding Z(therm) as a function of the baryon density and of the chemical potential are given. The process of relaxation to a stationary spectrum (Bose-Einstein like) is investigated in detail; several earlier conclusions are revised. An analytic formula which provides a very accurate description of the final stationary spectrum is presented and used to reassess the observational constraints on the chemical potential. We also give simple formulae, yielding, as a function of the baryon density and of the chemical potential, the wavelength at which the maximum distortion occurs and the amplitude of the distortion
Differential Information on the Evolution of Extragalactic Sources from Spectral Index Distributions
No full textThe dependence of the average spectral index of extragalactic sources on luminosity in complete samples selected at different frequencies is shown to vary in a manner that directly reflects their evolutionary properties. In particular, easily recognizable features are introduced by a luminosity dependent evolution and by the presence of a cutoff in the redshift distribution. The expected dependence on luminosity of the average optical to X-ray energy index αox for X-ray selected active galactic nuclei is discussed in some detail
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