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  • 1
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    The ethynyl radical C2H - A new interstellar molecule (1974)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Four new interstellar lines have been detected near 87.3 GHz. Based on laboratory ESR data these lines have been positively defined as hyperfine components of the lowest rotational transition of the ethynyl radical C2H. The observations gave precise values for the C2H rotation, spin-doubling, and hyperfine constants. C2H is probably one of the most abundant interstellar polyatomic molecules yet detected.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 193; Nov. 1
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  • 2
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    The onset of galactic winds in early-type galaxies (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Researchers report on a program using Einstein x ray observations of the x ray spectra and surface brightness profiles (or extents) of a large sample of early-type (elliptical and SO) galaxies for which the goal is to determine the critical optical luminosity for which galactic winds are important. For galaxies in which the x ray emission is dominated by hydrostatic coronae, the x ray spectra will be relatively soft (characterized by a temperature of approx. 10 to the 7th power K), while for galaxies with a galactic wind, the emission will be dominated by the spectrally harder discrete sources (since the x ray emission from the wind is essentially negligible). In this new sample of 180 galaxies, there are 28 early type galaxies with sufficient counts to obtain a spectrum with the Einstein Image Proportional Counter (IPC). This sample more than doubles the total number of early-type galaxies in earlier compilations (Forman, Jones, and Tucker 1985; Canizares et al. 1987). The new spectral observations will help determine the critical optical luminosity for the onset of galactic winds which is important for understanding the chemical evolution of galaxies and of the intergalactic medium. The implications of galactic winds for the heavy element enrichment and energy content of the intracluster medium are discussed.
    Keywords: ASTROPHYSICS
    Type: NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers; p 185-187
    Format: application/pdf
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  • 3
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    Alternatives to the existence of large cooling flows (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Arguments against the existence of large-scale cooling flows in clusters of galaxies are presented. The evidence for cooling flows is all circumstantial, consisting of observations of cool gas or hot gas with a radiative cooling time less than the Hubble time, or a central peak in the X-ray surface brightness profile. There is no evidence for large quantities (several tens to several hundreds of solar masses per year) of matter actually flowing anywhere. On the contrary, several lines of evidence suggest thaat cooling flows, if they exist, must be suppressed by one to two orders of magnitude from the values implied by simple estimates based on the radiative cooling time of the X-ray emitting gas. Two heat sources which might accomplish this, thermal conduction and relativistic particles, are considered, and an alternative to the standard model for cooling flows is presented: an accretion flow with feedback wherein the accretion of gas into a massive black hole in the central galaxy generates high energy particles that heat the gas and act to limit the accretion.
    Keywords: ASTROPHYSICS
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  • 4
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    Thermal conduction and heating by nonthermal electrons in the X-ray halo of M87 (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A hydrostatic model for the X-ray halo around the giant elliptical galaxy M87 is presented. It is shown that by taking into account the processes of thermal conduction, and nonthermal heating by relativistic electrons in the radio lobes, a self-consistent hydrostatic model can be constructed. There is no need to invoke radiative accretion or the suppression of thermal conductivity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 267; April 15
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  • 5
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    The relationship between the X-ray and optical luminosities for QSOs (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A study of simple models for the optical and X-ray luminosities of QSOs shows that a thick accretion disk around a black hole is consistent with the observed dependence of the X-ray luminosity L(x) on the optical luminosity L(opt) to the bth power, with b roughly in the range 0.5-0.8. The disk is expected to be thick since the sources are accreting at rates near the Edington limit. Using the model of McMillan, Lightman, and Cohn (1981) for the gas supply rate, the evolution of L(opt) is predicted to be proportional to t/t(0) to the -8/3 and that of L(x) is predicted to be proportional to t/t(0) to the -2.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 271; Aug. 15
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  • 6
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    The mass of Tycho's supernova remnant as determined from a high-resolution X-ray map (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: High resolution Einstein Observatory X ray images of Tycho's supernova remnant (SNR) are discussed. The object has features of a shock heated shell in the interstellar medium, accompanied by an inner shell with clumped ejecta. The measurements were made for 22 hr on Feb. 8, 1979, revealing a circular SNR, a thin emission shelf at the outer edge of the remnant, no emission in the central object, and most emissions concentrated in small, clumpy objects within a spherical shell. Three components of the X ray emission were identified, and calculations of the swept-up mass, the diffuse component of the ejecta shell, and the clumpy ejecta are reported to be 2.2, 1.2, and 0.7 solar mass, respectively. The SNR is concluded to be at an evolutionary stage between uniform expansion and adiabatic changes.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 266
    Format: text
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  • 7
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    X-ray emission from compact groups of galaxies (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The existence of very compact groups, or 'poor clusters,' of galaxies as a category of X-ray source is reported. By analogy with X-ray emission from clusters of galaxies, it is assumed that the extended X-ray emission is due to thermal bremsstrahlung from hot gas in the groups. The derived X-ray temperatures, luminosities, and sizes are similar to those for X-ray emitting, rich clusters of galaxies. It is inferred that these groups are in a late evolutionary stage because of the presence of a dominant galaxy, the absence of spiral galaxies, and the short cooling time inferred for 2A 0335 + 096.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 238
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  • 8
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    Cluster of galaxies as a probe of the intergalactic medium (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The use of galactic clusters as probes of the intercluster medium is discussed, and the effects of a postulated hot intercluster medium on the diffuse gas associated with clusters of galaxies is examined. It is shown that diffuse intracluster gas, which is observed at X-ray wavelengths, is a powerful probe of intergalactic space. The consequences of conduction are explored and the existence and properties of the intracluster gas are used to constrain the temperature and density of a uniform gas filling the universe. The effects of a nonuniform medium on the results are discussed and it is shown that for plausible scenarios the evaporative mass loss rates are insensitive to changes in the density and temperature of the intracluster medium in the vicinity of clusters. The parameters such a gas would have to have in order to explain the larger energy per unit mass found in the intracluster gas compared to that in galaxies are calculated.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 277; 19-26
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  • 9
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    Hot coronae around early-type galaxies (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The analysis of the X-ray emission from a sample of 55 bright early-type galaxies shows that hot gaseous coronae are a common and perhaps ubiquitous feature of such systems. The X-ray emission can be explained most naturally as thermal bremsstrahlung from hot gas which may be accumulated from mass loss during normal stellar evolution. The presence of these coronae shows that matter previously thought to be expelled in a galactic wind is instead stored in a hot galactic corona which may be heated and powered by supernova explosions. Perhaps the single most important feature of these coronae is that they provide a unique tracer of the gravitational potential in the outer regions of bright early-type galaxies. In this paper the X-ray properties of these coronae and their implications for the presence of massive dark halos around individual early-type galaxies are discussed. Total masses of early-type galaxies up to 5 trillion solar masses are found.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 293; 102-119
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  • 10
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    A luminosity-temperature relation for cluster X-ray sources (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Luminosity-temperature (L-T) relations are derived for a self-gravitating isothermal gas sphere and for an isothermal gas sphere in hydrostatic equilibrium with the total mass of a cluster of galaxies. The relationships are compared with X-ray data for 13 clusters of galaxies. The L-T relation for the self-gravitating isothermal gas sphere is found to predict X-ray luminosities that are considerably larger than those observed, and the corresponding model is ruled out. It is shown, however, that the L-T relation for the isothermal gas sphere in hydrostatic equilibrium with total cluster mass is consistent with X-ray observations for reasonable choices of the ratio between central density and confining-mass density. Core radii or gas temperatures are predicted for five of the 13 clusters considered.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 229
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