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  • ASTROPHYSICS  (12)
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  • 1
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    On the problems associated with the rapidly varying compact nonthermal sources (1975)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Difficulties and possible interpretations are discussed for observations of extragalactic compact nonthermal radio sources. The sources considered are those which have been identified optically with normal and peculiar galaxies, quasars, N galaxies, and BL Lacertae objects. Optical, infrared, and radio flux variations in different sources are noted along with difficulties associated with determining angular sizes from interferometric measurements. It is suggested that the ultimate origin of the infrared flux is probably a nonthermal synchrotron mechanism in some sources and absorption and reradiation of ultraviolet synchrotron radiation by dust in others. Model calculations of compact sources are reviewed, emphasizing equipartition of energy, total energies, the importance of the Compton effect, and sources which present severe difficulties for the theory of a canonical incoherent electron-synchrotron source.
    Keywords: ASTROPHYSICS
    Type: Comments on Modern Physics; vol. 6
    Format: text
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  • 2
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    Empirical evidence concerning absorption lines and radiation pressure in quasi-stellar objects (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Empirical spectroscopic evidence is examined for the hypothesis that radiation pressure having large gradients with wavelength plays a crucial role in maintaining patterns of redshift differences in quasars. Seventy-four absorption-line redshift systems in 32 quasars and two Seyfert galaxies are analyzed and discussed in terms of the radiation-pressure line-locking hypothesis. Redshift line ratios greater than unity are computed for each quasar and plotted as histograms. Ratios which may indicate line and edge locking are identified, including those of the C IV and Mg II doublets and those of the N III/C III, He II/O III, C II/He I, Ly-beta/H I, and H I/He I ionization edges.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 202; Dec. 1
    Format: text
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  • 3
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    Physical conditions and the locations of the absorption-line systems in the QSO 3C 286 and the BL Lacertae object PKS 0735 + 178 (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 200; Sept. 15
    Format: text
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  • 4
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    An analysis of the spectrum of the large-redshift quasi-stellar object OQ 172 (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 193; Nov. 1
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  • 5
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    Physics of compact nonthermal sources. III - Energetic considerations (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The energy content of the compact incoherent electron-synchrotron sources 3C 84, 3C 120, 3C 273, 3C 279, 3C 454.3, CTA 102, 3C 446, PKS 2134+004, VRO 42.22.01 and OJ 287 is calculated on the assumption that the low-frequency turnovers in the radio spectrum are due to self-absorption and that the electron distribution is isotropic. The dependence of the source parameters on various modifications of the standard assumptions is determined. These involve relativistic motions, alternate explanations for the low-frequency turnover, proton-synchrotron radiation, and distance to the source. The canonical interpretation is found to be accurate in many respects; some of the difficulties and ways of dealing with them are discussed in detail.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 193; Oct. 1
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  • 6
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    The log N-log S curve for 3CR radio galaxies and the problem of identifying faint radio galaxies (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The log N-log S slope of optically identified galaxies in the 3CR catalog is analyzed for galaxies with flux levels greater than 10 Jy and located at galactic latitudes greater than 7 deg. For the 86 galaxies with known redshifts, the slope is found to be about 1.16; for all 119 galaxies, the slope is found to be about 1.50. If the 113 unidentified sources are included, the slope steepens to about 1.81. It is shown that this steepness is caused by the unidentified sources. Assuming that the slope is due to evolution at redshifts of 1 to 3 and that the unidentified sources are bright ellipticals, the mean redshifts and apparent brightnesses of these galaxies are calculated. The results indicate that it is impossible to observe the unidentified sources with existing ground-based telescopes, implying that it is presently impossible to establish directly that evolution is responsible for the steep log N-log S curve of the 3CR galaxies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 205; Apr. 15
    Format: text
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  • 7
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    On possible associations of quasi-stellar objects and radio galaxies with rich clusters of galaxies (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A comparison of the cataloged coordinates of QSOs and of 3CR galaxies with those of Abell's rich clusters of galaxies yields the following results: (1) There is no statistically significant evidence that high-redshift QSOs lie preferentially close to Abell clusters. (2) There is no statistically significant evidence that low-redshift QSOs lie preferentially close to Abell clusters. (3) There is (as is well known) highly significant evidence that 3CR galaxies lie preferentially close to Abell clusters. (4) The distributions of angular separations between QSOs and clusters and between 3CR galaxies and clusters differ at statistically significant (but not highly significant) levels. In view of these results, a generic relationship between low-redshift QSOs and radio galaxies seems questionable. This result for the QSOs is also entirely consistent with the idea that they are 'local' objects with redshifts of noncosmological origin.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 216
    Format: text
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  • 8
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    Intergalactic matter and radiation and its bearing on galaxy formation and evolution (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: An up-dated review is given of the evidence for the presence of intergalactic matter and radiation in the Universe. It is concluded that the only important constituents which may make a sizable contribution to the total mass-energy are intergalactic gas and condensed objects with a very high mass-to-light ratio. If the QSOs are not at cosmological distances, cold atomic hydrogen may still be the most important constituent and may contribute much more mass than do the galaxies. The X-ray observations still do not unambiguously show that very hot gas is present, though it is very likely on general grounds that some hot gas is present in clusters of galaxies. The question of whether or not large amounts of matter, enough to close the Universe, are present, remains unsettled. From the theoretical standpoint the answer depends almost completely on the approach taken to the problem of galaxy formation and to the cosmological model which is favored.
    Keywords: ASTROPHYSICS
    Type: The formation and dynamics of galaxies; Symposium; Aug 12, 1973 - Aug 15, 1973; Canberra; Australia
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  • 9
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    A study of the absorption-line spectra of six high-redshift quasi-stellar objects (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: High-resolution spectrograms of six QSOs with apparent visual magnitudes of 17.0 to 18.5 and redshifts greater than 2 are studied for absorption lines. Accurate wavelengths are measured for all the absorption lines that could be detected, attempts are made to identify redshift systems, and the redshifts in each object are examined. Analysis of the absorption-line spectra shows that: (1) a large number of redshifts covering a wide range of values are present in five of the QSOs; (2) about two-thirds of the absorption lines remain unidentified, cannot be of Galactic origin, and are not associated with existing redshift systems; (3) many comparatively small absorption redshifts exist which, if they are due to intervening galaxies, must be produced by very large halos; and (4) in one QSO there is a possible redshift system containing five lines with an absorption redshift that is significantly greater than the emission redshift.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 224
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  • 10
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    Absorption in the spectra of quasi-stellar objects and BL Lacertae objects (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Observations of absorption in the spectra of 64 QSOs and two BL Lac objects are reviewed. Criteria for selecting the absorption-line objects are discussed along with line identifications, properties of identified absorption systems, the observed absence of variability in the absorption lines, the redshift distribution, line locking, and absorption shortward of the Lyman limit. The possibility of noncosmological redshifts is noted, and two interpretations of the absorption-line data are considered: (1) the 'intrinsic' hypothesis that the absorptions arise in gas associated with the QSOs and (2) the 'intervening' hypothesis that they are produced by intervening galaxies, galactic halos, or intergalactic clouds intersected by the line of sight to a QSO. Direct observational tests for the location of the absorbing hydrogen in several individual objects are described. It is concluded that no conclusive observational evidence exists which is capable of establishing whether the absorption is intrinsic or intervening.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific; vol. 90
    Format: text
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