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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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At least 127 records · Page 7
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NASA NTRS1982

X-ray-imaging observations of clusters of galaxies

Einstein X-ray imaging observations, made to illustrate the variety of phenomena that can be considered through X-ray image analysis, are presented. Attention is given to general cluster properties and intracluster gas. Individual clusters are discussed (considering classification and dynamical evolution), and X-ray images are used to determine cluster mass distribution and to examine distant clusters. X-ray observations have contributed information in regard to processes affecting galaxies, the intracluster medium, and the cluster itself. Analyses have traced massive halos around dominant galaxies in unevolved clusters, and have helped define the cluster gravitational potential. In addition, multi-component double clusters have been discovered, and material which has been ram-pressure stripped from a hot corona around the M86 galaxy in Virgo was observed. Finally, quantitative estimates of the fractions of young and evolved clusters and determinations of total cluster mass are possible using X-ray observations.

Forman, W.↗
NASA NTRS1983

NGC 315 - High-velocity H I in an active elliptical galaxy

The detection of high-velocity H I in absorption against the nuclear continuum source in the giant elliptical galaxy NGC 315 is reported. The absorption line is found to be highly blueshifted in the reference frame of the galaxy with a projected velocity toward the galaxy of 490 km/s. The absorption line is very strong (244 + or - 4 mJy), consisting of two components with very narrow velocity widths of 2.5 km/s (FWHM) each and peak optical depths of 0.9 and 0.2. The kinetic temperature must be 150 K if the line widths are due entirely to thermal broadening, while the neutral gas column densities implied are 2-5 x 10 to the 20th hydrogen atoms/sq cm. No OH in absorption was detected in these clouds to a limiting peak optical depth of 0.04, although this result is consistent with either a galactic or extragalactic origin of the clouds. It is suggested that these clouds may have condensed out of a large unobserved galactic halo of gas, or they may reside in or have been captured from the intracluster medium.

Dressel, L. L.↗
NASA NTRS1983

The evolution of clusters of galaxies. I - Very rich clusters

A multiple one-body Monte Carlo code is used to investigate the evolution of galaxies in a steady cluster potential under the influence of dynamical friction, two-body relaxation, tidal stripping, and galaxy mergers. The basic assumptions, estimated time scales, method and computer program, and effects of uncertainties in galaxy encounter physics are addressed. Numerical experiments in which the mass initially carried by galaxies and the mass function are varied are reported. It is shown that the formation of a very massive cluster galaxy depends critically on the number of galaxies, the initial division of cluster material between galaxies and a smooth intracluster medium, the mass spectrum of the galaxies, and chance. By the end of all simulations, less than half of the mass in the central regions of the cluster is bound to galaxies. It appears possible to produce any of the Bautz-Morgan classes from very similar initial conditions.

Richstone, D. O.↗
NASA NTRS1983

The dynamics of rich clusters of galaxies. II - The Perseus cluster

The dynamics of the Perseus cluster are analyzed using self-consistent equilibrium analytical models. Using existing data in the literature plus new radial velocities reported here, composite surface density and velocity dispersion profiles are derived. These profiles have been compared with dynamical models described by Kent and Gunn (1982). The best fit suggest the presence of a significant degree of anisotropy in the velocity distribution: galaxy orbits are constrained to pass within a radius of seven cluster radii, or 1.3 deg of the cluster center. For Hubble constant = 50, a core radius of 340 kpc 11 arcmin and a mass to visual light ratio M/L = 300 are found. Using these results, X-ray observations of the intracluster medium in Perseus are reanalyzed. A previously noted discrepancy between the observed temperature of the hot gas and the cluster velocity dispersion is reduced but not eliminated. A cooling accretion flow previously deduced to exist in this cluster is shown to extend to only about one-third of the cluster radius.

Kent, S. M.↗
NASA NTRS1985

Gas deficiency in cluster galaxies - A comparison of nine clusters

The available 21 cm line data in the literature for galaxies in nine clusters is combined with new high-sensitivity observations of 51 galaxies in five of the nine clusters in order to test for discriminating circumstances between those clusters which show H I deficiency among their spiral population and those which do not. An H I deficiency for the complete cluster sample is derived employing a comparison sample of galaxies chosen from the Catalog of Isolated Galaxies. The deficiency and its radial dependence is summarized for each cluster and a composite. A comparison of the environments in different clusters leads to the conclusion that the occurrence of H I deficiency is correlated with the presence of a hot X-ray intracluster medium, and that an ongoing interaction process is active through the cores of X-ray clusters.

Giovanelli, R.↗
NASA NTRS1985

Where's the gas?

The recent finding of hot interstellar hydrogen gas in elliptical galaxies is discussed. The belief held until recently that elliptics had no such gas and thus were past their star-forming stage is contradicted by new evidence obtained primarily with the X-ray images from the Einstein satellite. The hot gas is present in far greater amounts than could be accounted for by an outflowing galactic wind. The gas exists in isolated elliptics as well as in cluster members and thus is not part of the intracluster medium. It is concluded that the gas must be forming new small stars, since few massive hot stars are visible in elliptical galaxies.

Maran, S. P.↗
NASA NTRS1985

X-rays from the radio halo of Virgo A = M87

The purpose of this study is to investigate in more detail the associated X-ray and radio emission in the Virgo A halo discovered by SGF. Improved Einstein HRI data and new radio maps obtained with the Very Large Array are described and the relation between the X-ray and radio structures is carefully examined. Several possible explanations are presented for the X-ray emission. The inverse compton model is found to be viable only if the magnetic field is variable and substantially weaker than the equipartition value. The principal alternative is excess thermal X-rays due to compression of the intracluster medium by the radio lobe. In either case, the association of such prominent radio and X-ray structures is unique among known radio galaxies.

Source record↗
NASA NTRS1987

Present star formation in sprials of the Virgo cluster

From a study of spiral galaxies in the Virgo Cluster (VC), it is shown that the RDDO anemics with smooth arms and no sign of present formation of (massive) stars have HI surface densities below a threshold value of 2 to 5 x 10 to the 20th power atoms/sq cm. This value is very consistent with predictions of theoretical models. It is likely that the HI disks of VC HI-deficient RDDO anemics were deeply affected by ram pressure stripping in the gaseous intracluster medium, while VC HI deficient RDDO spirals were only peripherally stripped.

Guiderdoni, B.↗
NASA NTRS1986

Observational constraints on bending the wide-angle tailed radio galaxy 1919+479

A wide range of new observations of the wide-angle tailed radio galaxy 1919+479 and its environs are presented. Multifrequency and multiconfiguration VLA observations are described, ranging in resolution from 0.7 arcsec to 40 arcsec. Distributions of source structures at different scale sizes, spectral indices, and polarizations are presented. Wide-field photographic and CCD imaging data are presented along with a review of the measured galaxy redshifts in the field. A newly reprocessed Einstein IPC X-ray image of the cluster is shown, and the X-ray emission's relationship to the radio morphology is described. The radio, optical, and X-ray data are used to constrain the cD galaxy dynamics and models for bending the radio structure. In particular, the possible role of jet collisions with clouds in the intracluster medium is considered. The applicability of cloud collision models to wide-angle tails in general is considered.

Burns, J. O.↗
NASA NTRS1986

Direct imaging of the extremely large host galaxy and gas cloud surrounding the quasar 3C275.1

Direct CCD images of the field of the quasar 3C275.1 have been obtained using v, r, and redshifted forbidden O II filters to study the ionized gas cloud surrounding the quasar and to determine the gross characteristics of the quasar host galaxy. The images show an elliptical substrate containing several bright knots and indicate that the host galaxy is extremely large and luminous. The host galaxy's luminosity, dimensions, and position at the cluster center suggest that it may be a cD or 'proto-cD'. The nebulosity may be accreting matter from a 'cooling flow' of the intracluster medium. Alternatively, the quasar and the surrounding galaxy and gas cloud may be the result of repeated galaxy collisions.

Hintzen, Paul↗
NASA NTRS1988

Comparative properties of Virgo Cluster dwarf irregulars and spirals

The optical and neutral hydrogen data for all spiral and late-type dwarf irregular galaxies in the Virgo Cluster catalog are analyzed. In particular, the continuity of optical properties, hydrogen masses, and dynamical properties are examined as functions of morphology and luminosity from the largest spirals through the faintest dwarfs (omitting blue compact dwarf galaxies); the effects of environment on H I content; mass segregation; and the Tully-Fisher relations. The spiral plus dwarf sample forms a continuous but nonhomologous sequence. Indicative dynamical mass-to-light ratios are relatively constant throughout; hydrogen mass-to-light ratios show only a slight increase with decreasing luminosity. The Tully-Fisher relations extend with continuous slope from spirals through dwarfs. The dwarfs show some evidence of ram-pressure stripping by the intracluster medium, but as a group do not seem to be stripped more heavily than spirals. There is no evidence of mass segregation even for the very low mass dwarfs versus giant spirals.

Hoffman, G. Lyle↗
NASA NTRS1986

X-ray observations of clusters - Physical implications

The X-ray properties of clusters of galaxies and elliptical galaxies are reviewed, with an emphasis on cooling flows and their effects on the structure and energetics of radio sources. It is found that the radial profiles of the hot (10 to the 8th K) diffuse (n = about 0.001/cu cm) gas in clusters do not require heating of the intracluster medium after the formation of the cluster. Consideration is given to theoretical formulas for cooling rates, the possible reasons for the observed correlation between cooling flows and the presence of a dominant central galaxy, cooling-flow models of elliptical galaxies, and the significant shear in the velocity field of a cooling flow.

Sarazin, Craig L.↗
NASA NTRS1986

X-ray observations of distant blue clusters of galaxies

X-ray observations are reported for a sample of distant clusters for which the percentage of apparent cluster members that are blue has been determined optically. The X-ray properties of the clusters are not simply related to the optical properties. The X-ray observations do not support models in which blue galaxies change color as a result of ram-pressure stripping, or in which star formation is triggered by interaction with an intracluster medium. The data lend some support to the idea that blue galaxies in distant clusters are being observed immediately after the removal of galactic halos, and before the interstellar medium is depleted (Larson et al., 1980).

Lea, Susan M.↗
NASA NTRS1988

X-ray emission lines from cooling flows

Techniques employing individual X-ray line strengths to estimate the rate at which gas cools in the intracluster medium are discussed. It is demonstrated that departures from ionization equilibrium in the cooling plasma are not important at X-ray temperatures. Nonrestrictive upper limits are obtained for four cooling flow clusters. The results favor the existence of substantial cooling flows and argue against the dominance of conduction or other heat sources.

Canizares, Claude R.↗
NASA NTRS1990

Einstein observations of the Hydra A cluster and the efficiency of galaxy formation in groups and clusters

The Einstein imaging proportional counter observations of the poor cluster of galaxies centered on the radio galaxy Hydra A are examined. From the surface brightness profile, it is found that the X-ray-emitting gas in the Hydra A cluster must be condensing out of the intracluster medium at a rate of 600 solar masses/yr. This is one of the largest mass deposition rates observed in a cluster of galaxies. The ratio of gas mass to stellar mass is compared for a variety of systems, showing that this ratio correlates with the gas temperature.

David, L. P.↗
NASA NTRS1990

H I absorption toward cooling flows in clusters of galaxies

An H I survey of 14 cooling flow clusters and two noncooling flow clusters was conducted, and H I absorption features were detected against the nuclear radio continuum sources of two cooling flow dominant (CFD) galaxies, 2A 0335 + 096 and MKW3s. The absorption features are broad and redshifted with respect to the stellar absorption-line velocity of the CFDs by 90-225 km/s. This indicates that the H I is falling onto, and is probably gravitationally bound to, the CFDs. The kinematics of the H I clouds suggest a possible kinematic link between the warm and cold phases of the intracluster medium. The clouds are orders of magnitude smaller in radius and mass and larger in density than Galactic H I clouds. The detected CFDs have mass-accretion rates that are about 2.5 times larger than the CFDs that were not detected.

Mcnamara, Brian R.↗
NASA NTRS1990

Stripping of gas and dust from the elliptical galaxy M86

Past observations of the x ray morphology of M86 have revealed that the galaxy is experiencing ram-pressure stripping due to its large velocity (1500 km s(-1)) relative to the intracluster medium of Virgo (Forman et al. 1979, Fabian, Schwartz, and Forman 1980). Observations indicate that the x ray emitting gas in the plume of M86 is still being produced from the continual heating of gas and dust stripped from nearer the galaxy's center. Researchers obtained two-dimensional Infrared Astronomy Satellite (IRAS) images of M86 which have revealed that there are two spatially separated regions of emission, one at 60 microns and the other at 100 microns of the IRAS wavebands. The 100 microns emission, presumably from cool dust (at approximately 20 K), appears to be located near the center of the galaxy together with HI (detected by Bregman, Roberts and Giovanelli 1988), while the 60 microns emission appears to lie more than 3 arcminutes away from the optical center in a direction slightly south of the center of the plume. Optical images produced by scanning U.K. Schmidt plates, reveal asymmetric isophotal contours along the major axis of the galaxy (first reported by Nulsen and Carter in 1987, which they propose as excess emission due to star formation). This excess optical emission is co-incident with the direction of the 60 micron infra-red emission.

White, D. A.↗
NASA NTRS1990

NGC 4438: Ram pressure sweeping of a tidally disrupted galaxy

NGC 4438 is the highly HI deficient peculiar spiral in the center of the Virgo cluster. Observations are given of the neutral hydrogen emission obtained with the Very Large Array (VLA) in the D-array configuration. These observations map out the total HI as determined from single dish measurements, and show the hydrogen to be confined to a region about one third the size of the optical disk and displaced to the side of the galaxy opposite M87. The hydrogen content of the galaxy is over an order of magnitude less than that expected for a galaxy of its type. The data suggest that the HI deficiency is a result of ram pressure stripping of the gas in the outer regions of the galaxy by the hot intracluster medium after being tidally perturbed.

Hibbard, J. E.↗