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  • ASTROPHYSICS  (7)
  • 1985-1989  (7)
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  • ASTROPHYSICS  (7)
Years
Year
  • 1
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    Are the virial masses of clusters smaller than we think? (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The constraints that the available X-ray spectral and imaging data place on the mass distribution and mass to light ratio of rich clusters are considered. It was found for the best determined cases that the mass to light ratio is less than 125 h sub 50 at radii exceeding 1 h sub 50 Mpc. The mass to light ratio is approximately constant at radii exceeding 1 h sub 50 Mpc but may rise to values of roughly 200 h sub 50 in the central regions. The fraction of the total mass that is in baryons, primarily the hot X-ray emitting gas, is roughly 30 percent thus setting the mass to light ratio of the dark material to roughly 70. The model that fits the X-ray data for Coma is in good agreement with the observed optical velocity dispersion vs. radius data.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 317; 593-600
    Format: text
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  • 2
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    Are the virial masses of clusters smaller than we think? (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The constraints that the available X-ray spectral and imaging data place on the mass distribution and mass to light ratio of rich clusters are considered. It was found for the best determined cases that the mass to light ratio is less than 125 h sub 50 at radii exceeding 1 h sub 50 Mpc. The mass to light ratio is approximately constant at radii exceeding 1 h sub 50 Mpc but may rise to values of roughly 200 h sub 50 in the central regions. The fraction of the total mass that is in baryons, primarily the hot X-ray emitting gas, is roughly 30% thus setting the mass to light ratio of the dark material to roughly 70. The model that fits the X-ray data for Coma is in good agreement with the observed optical velocity dispersion vs. radius data.
    Keywords: ASTROPHYSICS
    Type: NASA-TM-89268 , NAS 1.15:89268
    Format: application/pdf
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  • 3
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    Optical absorption from the high-velocity neutral hydrogen complex C in the spectrum of the RR Lyrae star BT Draconis (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The detection of interstellar Na D absorption lines at a local standard of rest (LSR) velocity of -85 km/s is reported, together with tentative detections of further Na D lines at -133 km/s and -110 km/s, in the spectrum of the RR Lyrae star BT Draconis which lies toward the high-velocity neutral hydrogen complex C (LSR velocity around -115 km/s). This suggests an upper limit of 2.1 kpc on the distance to this high-velocity complex, and indicates that the complex has near-cosmic metallicity. This result strongly favors either a model in which complex C is formed by infalling material in the halo, which has originated in the Galactic disk, or one in which it is part of a large relatively local shell structure.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 293; L15-L18
    Format: text
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  • 4
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    Gas in and toward the Magellanic Clouds (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Attention is given to the Ca II K absorption spectra of 48 early-type supergiants in the SMC and LMC, with a view to the Clouds' possible fragmentary nature and the distance of the gas responsible for the absorption lines at 60 and 120 km/sec. The comparison of the spectra obtained with H I measurements toward the Clouds indicates that in both Clouds, the velocity components in the neutral hydrogen distribution lie at different distances along the line of sight. Good agreement is found between the radial velocity shown in absorbing material and the radial velocity spread predicted by Murai and Fujimoto's (1980) dynamical model of the formation of the Magellanic Stream by tidal stripping. It is speculated that both the SMC and LMC are extended and fragmented along the line of sight.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 303; 198-215
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  • 5
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    Long-slit spectroscopy of gas in the cores of X-ray luminous clusters (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The results of long-slit spectroscopy obtained for the core regions of 14 clusters of galaxies are reported. The data are presented in detail. It is shown that the presence of optical emission is tied to the properties of the hot gas in the cluster and not to the morphology of the central galaxy or cluster, demonstrating that the optical systems are indeed formed by the cooling of hot gas. Cooling flows occur when the gas density exceeds a critical central value which corresponds to a cooling time scale which, it is argued, weakly favors low values of H(0). The kinematics of the gas flows are discussed. The excitation mechanisms, correlation of optical emission with radio properties, and upper limits on coronal line strengths from the hot gas are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 59; 447-498
    Format: text
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  • 6
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    On the gravitational stability of the interstellar medium in spiral arms (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The dynamics of self-gravitating gaseous density perturbations in the tightly wound spiral-arm model of the forcing potential (Brown 1969) is investigated. The cloud ensemble of the cold phase of the interstellar medium is regarded as a collisional gas whose 'molecules' are the clouds themselves, and the dynamical evolution of density perturbations is calculated assuming this gas obeys a polytropic pressure-density law. It is suggested that the formation of extreme Population I objects found predominantly along the arms of Sb/Sc systems is regulated by an overall energy balance in the cloud fluid. A single parameter is found which appears to characterize the flow's gravitational response to perturbations; this spiral parameter, Q-sub-sp, differs from the Toomre Q parameter by a factor of the square root of the density enhancement at the shock. It is necessary but not sufficient that Q-sub-sp be less than unity for significant growth to occur.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 297; 61-75
    Format: text
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  • 7
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    Kinematic evidence of satellite galaxy populations in the potential wells of first-ranked cluster galaxies (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The velocities of 38 centrally positioned galaxies (r much less than 100 kpc) were measured relative to the velocity of the first-ranked galaxy in 14 rich clusters. Analysis of the velocity distribution function of this sample and of previous data shows that the population cannot be fit by a single Gaussian. An adequate fit is obtained if 60 percent of the objects lie in a Gaussian with sigma = 250 km/s and the remainder in a population with sigma = 1400 km/s. All previous data sets are individually consistent with this conclusion. This suggests that there is a bound population of galaxies in the potential well of the central galaxy in addition to the normal population of the cluster core. This is taken as supporting evidence for the galactic cannibalism model of cD galaxy formation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 305; L39-L43
    Format: text
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