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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1979

Evolutional schemes for objects with active nuclei

The observational properties of quasistellar objects (QSO) reveal that they are extremely violent nuclei of distant galaxies, but the evolutionary stage of these galaxies is still undetermined. Various published attempts to classify QSO under different criteria - including the one based on the morphological type of the surrounding galaxy E- or S- are analyzed. There are evidences that radioactive quasars reside in E-, while radio-quiet quasars reside in both E- and S- systems. The latter may be evolutionary connected to Seyfert-like objects. A correlation between the nuclei activity level in systems of different morphological type and the relative amount of gas in them is noted. From the point of view of activity level and the duration of active stage of nuclei it is concluded that an interaction of galaxies with the intergalactic medium is of particular importance and must be most conspicuous in spheriodal systems of central regions of rich clusters, in tight groups and binary galaxies.

Komberg, B. V.↗
NASA NTRS1979

The diffuse X-ray background spectrum from 3 to 50keV

The spectrum of the extragalactic diffuse X-ray background was measured with the GSFC cosmic X-ray experiment on HEAO-1 for regions of the sky away from known point sources and more than 20 deg from the galactic plane. A total exposure of 80 sq m-sec-sr is available at present. Free-free emission from an optically thin plasma of 40 plus or minus 5 keV provides an excellent description of the observed spectrum from 3 to 50 keV. This spectral shape is confirmed by measurements from 5 separate layers of three independent detectors. With an estimated absolute precision of about 10 percent, the intensity of the emission at 10 keV is 3.2 keV/keV-sq cm-sec-sr, a value consistent with the average of previously reported spectra. No other spectral features, such as iron line emission, are evident. This spectrum is not typical of known extragalactic objects. A uniform hot intergalactic medium of approximately 36 percent of the closure density of the universe would produce such a flux, although non-uniform models indicating less total matter are probably more realistic.

Marshall, F. E.↗
NASA NTRS1980

The diffuse X-ray background spectrum from 3 to 50 keV

The spectrum of the extragalactic diffuse X-ray background has been measured with the GSFC Cosmic X-ray Experiment on HEAO 1 for regions of the sky away from known point sources and more than 20 deg from the galactic plane. A total exposure of 80 sq m-s-sr is available at present. Free-free emission from an optically thin plasma of 40 plus or minus 5 keV provides an excellent description of the observed spectrum from 3 to 50 keV. This spectral shape is confirmed by measurements from five separate layers of three independent detectors. With an estimated absolute precision of about 10%, the intensity of the emission at 10keV is 3.2 keV/keV/sq cm/s/sr, a value consistent with the average of previously reported spectra. A uniform hot intergalactic medium of approximately 36% of the closure density of the universe would produce such a flux, although nonuniform models indicating less total matter are probably more realistic.

Marshall, F. E.↗
NASA NTRS1980

Residual fluctuations in the matter and radiation distribution after the decoupling epoch

The residual spectra of matter and radiation fluctuations in the early universe are investigated, and the evolution of primordial adiabatic and isothermal fluctuations through the decoupling epoch is studied. Amplification of adiabatic density fluctuations during decoupling, or velocity 'overshoot', is largely suppressed by Compton drag. Consequently, the amplitude of density fluctuations entering the horizon prior to decoupling is larger than hitherto assumed in the adiabatic theory. Damping of primordial adiabatic density fluctuations by an order of magnitude occurs on mass-scales of 3 x 10 to the 13th solar masses (Omega = 1) or 10 to the 14th solar masses (Omega = 0.2). Comparison of the residual radiation fluctuations with observational limits indicates that the adiabatic theory is only acceptable if re-ionization of the intergalactic medium results in additional scattering of the radiation after decoupling. Primordial isothermal fluctuations are found to yield radiation fluctuations which are insensitive to the assumed spectrum and lie a factor of about 5 below current limits

Silk, J.↗
NASA NTRS1980

Cold dense photoionized universes

This investigation employs a computer code, initially constructed for modeling the evolution of a hot dense intergalactic medium (IGM), to study some properties of a cold dense IGM photoionized by QSOs. Within the observational constraints set by flux measurements in the far-ultraviolet, night sky brightness, and hard X-ray region, and the optical depth limits on various QSO spectra, it determines some allowable scenarios for a range of QSO spectral indices (alpha) and cutoff energies. With H(0) = 50 km/s-Mpc, closure density of an IGM (composed of H and He in their cosmic ratio) is possible only if alpha is greater than or equal to 0.1, a circumstance not likely to prevail; the most probable value, alpha = -0.7, implies an upper limit density about 0.35 of closure, which is somewhat larger than previous estimates. These estimates are substantially independent of whether or not QSOs produce the observed diffuse extragalactic X-ray background; such QSO spectral details are critical, however, in determining the ionization of heavy elements that are expected to contaminate a pure primeval plasma.

Sherman, R. D.↗
NASA NTRS1979

Detection of X-ray emission from distant clusters of galaxies

The paper reports the first extensive detection of X-ray emission from clusters of galaxies at cosmological distances. The properties of these objects are similar to those observed in objects at low redshifts. The 0.5-4.5 keV luminosities are in the range of less than 1 x 10 to the 43rd to 2 x 10 to the 45th ergs/s; the core radii are on the order of 0.5 Mpc; and Bautz-Morgan type I clusters are more luminous than types II or III. The observations are consistent with models assuming an evolving cluster potential and moderately efficient galaxy formation, but do not require them when observational selection is considered. X-ray observations of the 3C 295 cluster indicate that there is sufficient intergalactic medium to cause stripping of the cluster spirals, but the colors of these galaxies imply that they have not been stripped. A possible explanation of this discrepancy is discussed.

Henry, J. P.↗
NASA NTRS1981

Quasar number density evolution

A simple model of quasar number density evolution is presented based on the occurrence of quasar-like radio galaxies (i.e., strong optical emission lines and type 2 radio morphology) exclusively in regions of low galaxy and intergalactic medium (IGM) density. This suggests a limit for the IGM density of 10 to the -4th (+ or - 1) per cu cm below which quasars are allowed to form and above which they are not allowed. In the recent past (z not greater than 1), the inferred quasar environments are the outskirts of clusters and near the centers of groups of galaxies. However, models of rich cluster evolution consistent with current X-ray observations predict gas densities of less than 10 to the -4th per cu cm in cluster cores in the more distant past (z between 1 and 5). This suggests that quasars were allowed to form in the cores of rich clusters at those epochs, which explains both the rich absorption spectra of high-redshift quasars and the absence of clusters surrounding quasars at lower redshift.

Stocke, J. T.↗
NASA NTRS1982

Cosmological constraints on hot plasma in a closed universe

A hot uniform collisionally heated intergalactic medium (IGM) at closure density is reconsidered. Optical depth measurements, plasma cooling and ionic abundances during the recombination epoch are discussed. The data are used to calculate X-radiation at critical energies. The results indicate a present temperature from 160,000 to 4,200,000 K if the reheating of the IGM ceased at the latest possible time. As cessation of heating moves to earlier times, the range of present plasma temperature narrows until at the earliest possible cessation time only about 160,000 K is acceptable. Relevant formulae are provided to modify these numbers as new data become available. This IGM avoids any hard X-ray production and thus assumes that discrete sources alone constitute the entire cosmic X-ray background.

Sherman, R. D.↗
NASA NTRS1982

Supernovae and the formation of galaxies

Attention is given to the cumulative effect of many SNs in a galaxy, especially a young galaxy, as well as the effect of the blast wave resulting from the combination of all individual SNs on the intergalactic medium (IGM). It is suggested that the IGM can be shock-heated by this process, so that in the late stages of an individual expanding galaxy's shock a shell may form whose mass is many times greater than that of the seed galaxy. If this shell fragments, due to gravitational instability, it will give rise to a new generation of galaxies. SN explosions may thereby provide a hydrodynamic amplifier of some significance in the process of galaxy formation.

Ostriker, J. P.↗
NASA NTRS1983

Radio and X-ray observations of the radio halo source in A1367

Radio and X-ray observations of the 'radio halo' in A1367 are presented. The radio spectral index distribution is derived combining data at 610 and 1415 MHz taken with the Westerbork Synthesis Radio Telescope (WSRT). A high-resolution Very Large Array (VLA) map allows us to discriminate between the extended cluster emission and a triple radio source associated with a background stellar object (most probably a QSO) which appears projected onto it. X-ray observations taken with the high-resolution imager on board the Einstein satellite reveal an X-ray source associated with this background object. A second weak X-ray enhancement is found projected onto the extended radio component. Inverse Compton scattering of the synchrotron-emitting particles provides a possible interpretation of such a source. The presence of large-scale magnetic fields and particle acceleration due to the turbulent motion of galaxies through the intergalactic medium is discussed in relationship to the observed peculiarities of the galaxies found in this region.

Gavazzi, G.↗
NASA NTRS1983

Soft X-ray spectral observations of quasars and high X-ray luminosity Seyfert galaxies

Results of the analysis of 28 Einstein SSS observations of 15 high X-ray luminosity (L(x) 10 to the 435 power erg/s) quasars and Seyfert type 1 nuclei are presented. The 0.75-4.5 keV spectra are in general well fit by a simple model consisting of a power law plus absorption by cold gas. The averager spectral index alpha is 0.66 + or - .36, consistent with alpha for the spectrum of these objects above 2 keV. In all but one case, no evidence was found for intrinsic absorption, with an upper limit of 2 x 10 to the 21st power/sq cm. Neither was evidence found for partial covering of the active nucleus by dense, cold matter (N(H) 10 to the 22nd power/sq cm; the average upper limit on the partial covering fraction is 0.5. There is no obvious correlation between spectral index and 0175-4.5 keV X-ray luminosity (which ranges from 3 x 10 to the 43rd to 47th powers erg/s or with other source properties. The lack of intrinsic X-ray absorption allows us to place constraints on the density and temperature of the broad-line emission region, and narrow line emission region, and the intergalactic medium.

Petre, R.↗
NASA NTRS1984

X-ray spectra of clusters of galaxies

The X-ray emission from luminous clusters of galaxies is dominated by thermal bremsstrahlung from an intergalactic medium. The central density of the gas is strongly correlated with the X-ray surface brightness. The X-ray surface brightness S(sigma) of many clusters is well modeled by a law of the form S(sigma) alpha S(o) 1 + R(2)/A(2) to the minus 3 beta + 1/2 power with beta approximately equal to 0.66. However, this model does not fit the X-ray spectral or optical galaxy counts well. In clusters with cooling flows in their center there is a strong correlation between the cooling rates of X-ray emitting material and optical H alpha emission. It is not clear, at present, what percentage of the virial mass of the cluster is in hot gas but if beta = 0.66, it is possible for the values to be of the order of 1/2. Spatially resoled X-ray spectroscopy is necessary to determine this value with any accuracy.

Mushotzky, R. F.↗
NASA NTRS1984

A sharp X-ray absorption feature in the BL Lacertae object PKS 2155-304

The present absorption feature from PKS 2155-304 appears at 600 eV and extends to higher energies by 50-100 eV, in a 0.38-1.6 keV spectrum that can be fitted by a single absorption edge or through plus two power laws, with slopes that are consistent with simultaneous measurements of the 2-10 keV flux. Ionized oxygen absorption is the most likely cause of this sharp feature, in the form of a K edge of O VIII, or an O VIII Lyman-alpha resonance absorption trough from high velocity material, or an O VIII Lyman-alpha absorption trough from a hot, O-rich intergalactic medium with near critical density.

Kruper, J.↗
NASA NTRS1984

Soft X-ray spectral observations of quasars and high X-ray luminosity Seyfert galaxies

Results of the analysis of 28 Einstein SSS observations of 15 high X-ray luminosity (L(x) 10 to the 435 power erg/s) quasars and Seyfert type 1 nuclei are presented. The 0.75-4.5 keV spectra are in general well fit by a simple model consisting of a power law plus absorption by cold gas. The average spectral index alpha is 0.66 + or -0.36, consistent with alpha for the spectrum of these objects above 2 keV. In all but one case, no evidence was found for intrinsic absorption, with an upper limit of 2 x 10 to the 21st power/sq cm. Neither was evidence found for partial covering of the active nucleus by dense, cold matter (N sub H greater than 10 to the 22nd power/sq cm); the average upper limit on the partial covering fraction is 0.5. There is no obvious correlation between spectral index and 0.75-4.5 keV X-ray luminosity (which ranges from 3 x 10 to the 43rd to 47th powers erg/s) or with other source properties. The lack of intrinsic X-ray absorption allows us to place constraints on the density and temperature of the broad-line emission region, and narrow line emission region, and the intergalactic medium. Previously announced in STAR as N84-14082

Petre, R.↗
NASA NTRS1986

Second generation spectrograph for the Hubble Space Telescope

The preliminary design for the Space Telescope Imaging Spectrograph (STIS), which has been selected by NASA for definition study for future flight as a second-generation instrument on the Hubble Space Telescope (HST), is presented. STIS is a two-dimensional spectrograph that will operate from 1050 A to 11,000 A at the limiting HST resolution of 0.05 arcsec FWHM, with spectral resolutions of 100, 1200, 20,000, and 100,000 and a maximum field-of-view of 50 x 50 arcsec. Its basic operating modes include echelle model, long slit mode, slitless spectrograph mode, coronographic spectroscopy, photon time-tagging, and direct imaging. Research objectives are active galactic nuclei, the intergalactic medium, global properties of galaxies, the origin of stellar systems, stelalr spectral variability, and spectrographic mapping of solar system processes.

Woodgate, B. E.↗
NASA NTRS1988

Energetic constraints on spectral distortions of the microwave background

The energetic constraints on mechanisms for producing the spectral distortion of the microwave background claimed by Matsumoto et al., (1988) are investigated in the light of the new upper bounds on the cosmological baryon density derived by Kawano et al., (1988) from primordial nucleosynthesis. The thermal emission from dust heated by stars at large redshift and Compton scattering by a hot intergalactic medium heated by supernova explosions are considered, and it is concluded that both mechanisms fail on energetic grounds if they rely on stars formed with the same mass function as is observed in the solar neighborhood.

Lacey, Cedric G.↗
NASA NTRS1988

The abundances of carbon and nitrogen in I Zw 18

The first measurements of the semiforbidden C III 1909 A and forbidden N II 6583 A emission lines in I Zw 18 are reported. These data are combined with previously published spectrophotometry in order to derive the carbon and nitrogen abundances in I Zw 18 with the aid of a nebular model. The CNO abundances in I Zw 18 are found to exceed those found in the Magellanic Clouds and other well-observed oxygen-poor irregular galaxies and are more similar to those in the sun and nearby Galactic H II regions. It is argued that I Zw 18 may be older and more chemically evolved than previously believed, and that its extremely low O/H results from escape of O-rich supernova ejecta from the Galaxy or from dilution by accretion of primordial gas. Alternatively, I Zw 18 may have formed from a preenriched intergalactic medium. Spectroscopic diagnostics for composite photoionization models to fit the spectrum of I Zw 18 are discussed.

Dufour, Reginald J.↗
NASA NTRS1989

Theories of the X ray background

Theories of the X-ray background are analyzed. Starburst and probably hard X-ray binary models can be dismissed on the basis of exorbitant energy requirements while the hot diffuse intergalactic medium fails to reproduce the residual spectrum. Active Galactic Nuclei (AGN) models are only viable if there is a class of AGN which puts out the bulk of its energy in the hard X-rays.

Cowie, Lennox L.↗