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  • ASTROPHYSICS  (7)
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  • 1
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    Contributions of low-luminosity sources to the X-ray background (1989)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: HEAO 1 A-2 data are used to determine hard X-ray fluxes, or upper limits, for complete optically selected samples of active and normal galaxies, in order to estimate or to constrain their local X-ray luminosity functions. It is found that the luminosity function of Seyfert nuclei must flatten down drastically shortly below the observational limit of Piccinotti et al (1982); little can be added by dwarf active nuclei hidden in otherwise normal galaxies. Also analyzed is the possible contribution to the X-ray background from galaxies with strong star-formation activity, in the light of the possibility of a substantial cosmological evolution suggested by recent radio and IRAS data.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 344; 125-134
    Format: text
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  • 2
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    Constraints on large-scale clustering from the autocorrelation properties of the X-ray background (1990)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Expectations for the angular correlation function of intensity fluctuations of the extragalacitc 2-10 keV X-ray background are discussed in relation to the two-point spatial correlation functions, xi(r), of X-ray sources. A simple analytic formula for the amplitude of intensity correlations, Gamma(theta), holding in the low-redshift, small-separation approximation, is derived. The HEAO 1 A-2 upper limits on Gamma(theta) have been exploited to derive constraints on the local xi(r) functions of rich clusters of galaxies, of AGNs, and on the AGN-cluster cross-correlation, as well as on evolution of the correlation functions with cosmic time. X-ray data are found to be compatible with the Bahcall and Soneira estimates of xi(cluster-cluster) as well as with the results of recent studies of quasar clustering.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 351; 22-30
    Format: text
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  • 3
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    Observations of the nucleus of M100 (1981)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The galaxy M100 = NGC 4321 is a spiral galaxy in which a bright Type II Supernova was discovered on April 19, 1979. Its spectral evolution was followed with IUE for more than two months (refs. 1,2). At all epochs, the spectrum was dominated by continuous radiation on which emission and absorption features were superimposed. The equivalent width of most of the absorption features appeared not to vary with time suggesting that they originated in the interstellar media of M100 and our own galaxy.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 725-728
    Format: application/pdf
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  • 4
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    An X-ray study of M51 (NGC 5194) and its companion (NGC 5195) (1985)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Observations of NGC 5194/95 with the Einstein HRI show a very strong nuclear X-ray source, surrounded by a diffuse flux, three point sources, and the companion. The diffuse flux, which correlates well with the radio continuum, is likely to originate from the disk population with an age of approximately 2.1 billion yrs. The large luminosity from the nuclear source, together with optical and radio observations, shows that it belongs to the low luminosity active nuclei, thus extending this class to luminosities of less than about 10 to the 40th erg/s.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Space Science Reviews (ISSN 0038-6308); 40; 643-646
    Format: text
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  • 5
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    X-ray continuum and iron K emission line from the radio galaxy 3C 390.3 (1994)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: X-ray properties of the radio galaxy 3C 390.3 were investigated using the European X-ray Observatory Satellite (EXOSAT) and Ginga satellites. Long-term, large-amplitude X-ray intensity changes were detected over a period extending from 1984 through 1991, and high-quality X-ray spectra were obtained especially with Ginga. The X-ray continuum spectra were described with power-law model with photon slope in the range 1.5-1.8, and the slope flattened as the 2-20 keV luminosity decreased by 40%. There was a first detection of the iron emission line from this source at the 90% confidence level. An upper limit was derived on the thermal X-ray component. X-ray emission mechanisms and possible origins of the long-term variation are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 420; 1; p. 143-151
    Format: text
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  • 6
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    The most luminous far-infrared extragalactic sources (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Extremely luminous far-infrared sources are difficult to explain as active sites of star formation, because their ratios of optical-to-infrared luminosities are extremely low. It is shown that brief intervals during which interacting galaxies collide can account for extremely high (more than 10 to the 11th) solar luminosities. The small fraction of the population that exhibits extreme luminosity also roughly equals the fraction of spiral galaxies expected to be observed undergoing collisions at any given time. A number of potential tests that would distinguish the model from others is proposed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 315; 28-45
    Format: text
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  • 7
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    An X-ray study of M51 (NGC 5194) and its companion (NGC 5195) (1985)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: The galaxy M51 and its companion NGC 5195 were observed with the Einstein High-Resolution Imager. The X-ray observations led to the detection of both galaxies with (0.2-4.0 keV) X-ray luminosities of 3.0 x 10 to the 40th ergs/s and 2.1 x 10 to the 39th ergs/s respectively. M51 and its companion are compared to other spiral and irregular galaxies observed in X-rays, and the various components of the X-ray emission of M51 (i.e., nucleus, point sources, and unresolved extended emission) are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 298; 259-267
    Format: text
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