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  • ASTROPHYSICS  (6)
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  • 1
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    Pruning the Lyman alpha forest of Q1331+170 (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A multitude of absorption lines seen shortward of QSO Ly-alpha emission, that cannot be traced to heavy element absorption systems, are assumed to be Ly-alpha lines arising in intervening clouds. Studies of these Ly-alpha clouds, typically done at 1 A or lower resolution, have shown N(H1) approximately equal to 10(exp 13) - 10(exp 17) sq cm and b approximately equal to 35 km/s. Sargent et al 1980, on the basis of a flat pair velocity correlation function (PVCF), argued that these clouds are intergalactic. But Crotts 1989 showed that the strong Ly-alpha lines are spatially clustered. High resolution studies of Webb 1987 and Rauch et al 1992 also report some evidence for weak clustering, but overall such high resolution studies have been rare. A study of the Ly-alpha forest of Q1331 + 170 over x(sub abs) = 1.60 - 2.19 based on 18 km/s resolution data at S/N approximately equal to 15, with metal-line deblending incorporated.
    Keywords: ASTROPHYSICS
    Type: NASA. Ames Research Center, The Evolution of Galaxies and Their Environment; p 141-142
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Interstellar clouds near the sun (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Present knowledge concerning interstellar clouds near the sun is reviewed. The distribution and chracteristics of this interstellar dust and gas are described, and interstellar wind flowing through the solar system is discussed. Evidence is presented for a flow of more distant interstellar material past the solar system. Possible effects of an encounter between the solar system and a cloud core embedded in this low-density flow are examined. It is likely that the solar system is heading for condensations within 100 pc and that encounters may occur in the next 0.1 to 1 Myr. Such encounters could trigger global weather effects, including surface cooling and increased precipitation.
    Keywords: ASTROPHYSICS
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Probing the Galactic halo along the 3C 273 sight line using IUE (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: High-resolution spectra of the QSO 3C 273 were obtained in 1989 and added to two spectra recorded in 1982. The coadded spectra represent 600,000 s of integration at a resolution of 30 km/s from 1200 to 2000 A. The line of sight passes through the Virgo Cluster the entire halo of the Milky Way, at Galactic latitude b = 64 deg, and foreground X-ray-emitting material from local disturbed gas. The observed equivalent width of Galactic C IV is greater than the equivalent width of C II, a situation that is uncommon in local gas but is often found in QSO absorption line systems. The lines of C IV, Al III, and Si IV may arise in an extended halo or may be associated with local disturbed gas in a radio loop. The remaining detected species (H I, C II, Si II) arise predominately from the local gas. Most of the gas is probably within 5 kpc, but no firm conclusion is reached. Possible detection of interstellar absorption due to the Virgo Cluster is discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 381; 55-62
    Format: text
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  • 4
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    Interstellar absorption lines in the galaxy NGC 1705 (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The possibility is considered, and shown to be plausible, that the strong C IV and Si IV absorption lines in low-resolution ultraviolet spectra of gas-rich dwarf galaxies are primarily interstellar, not stellar as has been supposed. The argument is based on analogies with H II regions in the Local Group, on low-resolution equivalent width measurements of gas-rich dwarf galaxies from the literature and on high-resolution UV spectra of NGC 1705.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 351; 412-417
    Format: text
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  • 5
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    On the origin of some QSO absorption lines (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Some QSO absorption-line systems (QSOALSs) may arise when a QSO sight line intersects a Magellanic-type irregular galaxy (i.e., a gas-rich dwarf). Much of the complexity in the line profiles of metals can be naturally explained in this manner. The frequency of occurrence of QSOALSs then requires that much of the mass of modern galaxies once resided in a halo of gas-rich dwarfs (at the epoch of QSOALS formation).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 311; 610-616
    Format: text
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  • 6
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    An inhomogeneous reference catalogue of identified intervening heavy element systems in spectra of QSOs (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Identifications of heavy element line systems, observed in spectra of quasi-stellar objects between 1965 and 1989 inclusive, are collected and tabulated with references. Each system is assigned a quality grade based on the apparent reliability of the data. The highest quality systems are used to characterize the absorbers as a sample. A decrease in C IV line strength with redshift (z), and the corresponding decrease in line density per unit z with z are confirmed. The weakest C IV systems, at high z, are accompanied by relatively stronger Si IV lines, compared to the relative line strengths at low z. The space density of systems with strong lines of first ions is nearly independent of z below z = 3, though it drops at z greater than 3. Preliminary tests for quasar lensing by intervening systems and for clustering of absorbers on large scales are presented.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 250; 24-49
    Format: text
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