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  • 1
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    A search for the Sunyaev-Zel'dovich effect at millimeter wavelengths (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is believed that X-ray emission from clusters of galaxies represents thermal bremsstrahlung from a hot plasma. According to Sunyaev and Zel'dovich (1972), the plasma column density and temperature derived from this model imply a measurable distortion of the cosmic background radiation (CBR) in the cluster direction. This distortion results from the Compton scattering of the CBR photons by the electrons in the plasma, resulting in an average increase of each photon. This process, known as the Sunyaev-Zel'dovich effect, is photon conserving and 'shifts' the CBR spectrum to higher frequencies. The result is a decrease of flux at frequencies below 7.5 per cm (the Rayleigh-Jeans region), and an increase above. The investigation is concerned with measurements of the Sunyaev-Zel'dovich effect at frequencies in the range from 3 to 10 per cm. Attention is given to the employed observing and analysis technique, and an initial null result for the cluster Abell 1795.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 271; Aug. 1
    Format: text
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  • 2
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    Neutral hydrogen in the direction of the Small Magellatic Cloud and the limits of an extragalactic soft X-ray flux (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Previously reported X-ray data from the vicinity of the Small Magellanic Cloud (SMC) have been reanalyzed using H I data from a more detailed and sensitive 21-cm survey of this region. The results support the previous conclusion: assuming that the interstellar material absorbs according to the cross sections of Brown and Gould (1970), at least 75 per cent of the observed 0.25-keV X-ray flux is of local origin. The corollary problem of placing a cosmologically useful upper limit on the extragalactic flux will be difficult to solve until the behavior of the local component is better understood; but if the local flux is isotropic, a 3-sigma upper limit of 240 photons per (sq cm s sr keV) at 0.25 keV may be placed on a flux originating beyond the SMC. Tables of H I column density are given for an area 30 deg by 30 deg about the SMC. The high-velocity component, presumably associated with the Magellanic Cloud system, and the galactic disk component are tabulated separately.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; 209; Oct. 1
    Format: text
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  • 3
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    Interpretation of the cosmic microwave background radiation anisotropy detected by the COBE Differential Microwave Radiometer (1992)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The large-scale cosmic background anisotropy detected by the COBE Differential Microwave Radiometer (DMR) instrument is compared to the sensitive previous measurements on various angular scales, and to the predictions of a wide variety of models of structure formation driven by gravitational instability. The observed anisotropy is consistent with all previously measured upper limits and with a number of dynamical models of structure formation. For example, the data agree with an unbiased cold dark matter (CDM) model with H0 = 50 km/s Mpc and Delta-M/M = 1 in a 16 Mpc radius sphere. Other models, such as CDM plus massive neutrinos (hot dark matter (HDM)), or CDM with a nonzero cosmological constant are also consistent with the COBE detection and can provide the extra power seen on 5-10,000 km/s scales.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 396; 1, Se; L13-L18
    Format: text
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  • 4
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    Preliminary separation of galactic and cosmic microwave emission for the COBE Differential Microwave Radiometer (1992)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: Preliminary models of microwave emission from the Milky Way Galaxy based on COBE and other data are constructed for the purpose of distinguishing cosmic and Galactic signals. Differential Microwave Radiometer (DMR) maps, with the modeled Galactic emission removed, are fitted for a quadrupole distribution. Autocorrelation functions for individual Galactic components are presented. When Galactic emission is removed from the DMR data, the residual fluctuations are virtually unaffected, and therefore they are not dominated by any known Galactic emission component.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 396; 1, Se; L7-L12
    Format: text
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