Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “GALAXIES”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Narrow-line Seyfert galaxies with permitted Fe II emission Markarian 507, 5C 3.100, and I Zw 1

Optical, X-ray and and/or IR spectra of Mrk 507, 5C 3.100 and I Zw 1 are compared in a discussion of the bases for classifications of Seyfert 1 and 2 galaxies. Einstein Observatory X ray data indicate that the Seyfert designation requires a continuum extending to X-rays in order to account for permitted Fe II lines observed in Seyfert galaxies. It is suggested that the IR luminosity of I Zw 1, which exceeds the X-ray luminosity by two orders of magnitude, may be accounted for by interaction between companion galaxies. The presence or absence of dense clouds such as those in I Zw 1 is identified as the factor which separates Seyfert galaxies into two mutually exclusive ranges in X-ray luminosity.

Halpern, J. P.↗
NASA NTRS1987

H I detection survey of a complete magnitude-limited sample of dwarf irregular galaxies in the Virgo Cluster area

New single-beam Arecibo H I observations of 298 late-type galaxies in the Virgo Cluster drawn mostly from the new catalog of Binggeli, Sandage, and Tammann (1985) are presented. Two hundred seventeen of these constitute a magnitude-limited 'complete sample' of such galaxies, types Sdm through Im and BCD. Sixty-one percent of this 'complete sample' was detected, greatly enhancing the store of redshifts and H I masses for such galaxies in the Virgo Cluster. For detected galaxies, heliocentric velocities, 50 percent profile widths, and single-beam fluxes are presented. For those that escaped detection, upper limits are computed to the flux appropriate to the redshift range (-600 to +3000 km/s).

Hoffman, G. Lyle↗
NASA NTRS1987

IRAS 00521-7054 - An unusually warm galaxy

IRAS 00521 - 7054 is a galaxy that lies behind the Small Magellanic Cloud. Its infrared energy distribution is quite unusual in that it has exceptionally red 0.6-10-micron colors, while its 12-100-micron spectrum is among the warmest known for a galaxy or quasar, with a peak at 25 microns and an integrated luminosity of close to 10 to the 12th solar luminosity. Its optical spectrum is characteristic of a Seyfert 2 galaxy: low-ionization forbidden lines and H-alpha have FWHM 500 km/s, with some evidence for a much broader component of the H-alpha line. A plausible model is that a central nonthermal source is the dominant source of luminosity, but it is heavily obscured by dust and is thus observed indirectly through reradiation of its flux by the surrounding material. This galaxy may then be a good example of an object in the process of developing into a 'classical' quasar.

Frogel, Jay A.↗
NASA NTRS1987

A catalog of galaxies in Hercules from the Palomar Sky Survey and the Minnesota Automated Plate Scanner

The development of galaxies catalogs from the Palomar Sky Survey using the Minnesota Automated Plate Scanner (APS) is examined. The design and operation of APS are described. The algorithm used to distinguish stars from galaxies is discussed, and the completeness and confusion of the algorithm as a function of magnitude are estimated. The quality of the photometric calibration for galaxy magnitudes and surface-brightness thresholds is evaluated. The relation between the distribution of colors and morphological types is studied. The luminosity functions for Hercules galaxies are calculated and presented. The catalog generated using the APS is 80 percent complete; photometry good to 0.23 mag rms is possible; and J-F colors are good to 0.17 mag rms.

Dickey, John M.↗
NASA NTRS1987

The continuum of type 1 Seyfert galaxies. I - A single form modified by the effects of dust

Broad-band measurements from 1 to 20 microns of 26 emission-line active galactic nuclei (AGNs), mainly Seyfert 1 galaxies, have been made. These data have been combined with previous optical and infrared photometry and IRAS 12, 25, 60 and 100 micron fluxes, giving a total sample of 37 AGNs, all of which have hard X-ray measurements. The sample includes all the emission-line AGNs identified in the Piccinotti et al. (1982) survey. When corrected for stellar contributions in the near-infrared, the continuum energy distributions can be classified observationally into three types: (1) bare, minimally reddened AGNs; (2) reddened AGNs; and (3) AGNs for which the far-infrared emission is contaminated by the host galaxy. These classifications reflect a range of luminosities and different environments rather than intrinsic differences in the primary continuum of the AGNs. The data are consistent with a single underlying form of active galaxy continuum modified by the presence of dust and of the host galaxy.

Ward, Martin↗
NASA NTRS1987

1E 0116.3-0116 - A peculiar, X-ray-bright early-type galaxy

The identification of 1E 0116.3-0116 with an E3 galaxy belonging to a sparse group of galaxies makes this object worthy of study. The optical spectrum of the galaxy exhibits no nuclear activity, and its radio emission is consistent with early-type galaxy status. In the event that the gas is isothermal, its surface brightness profile yields a total mass greater than 10 to the 13th solar masses. The cooling time of the gas is on average of the same order as the Hubble time.

Maccagni, D.↗
NASA NTRS1987

The red/infrared evolution in galaxies - Effect of the stars on the asymptotic giant branch

The effect of including the asymptotic giant branch (AGB) population in a spectral synthesis model of galaxy evolution is examined. Stars on the AGB are luminous enough and also evolve rapidly enough to affect the evolution of red and infrared colors in galaxies. The validity of using infrared colors as distance indicators to galaxies is then investigated in detail. It is found that for z of 1 or less infrared colors of model galaxies behave linearly with redshift.

Chokshi, Arati↗
NASA NTRS1987

Infrared emission and tidal interactions of spiral galaxies

Computer simulations of tidal interactions of spiral galaxies are used to attempt to understand recent discoveries about infrared (IR) emitting galaxies. It is found that the stronger tidal perturbation by a companion the more disk gas clouds are thrown into nucleus crossing orbits and the greater the velocity jumps crossing spiral arms. Both these tidally created characteristics would create more IR emission by high speed cloud collisions and more IR via effects of recently formed stars. This expectation at greater tidal perturbation matches the observation of greater IR emission for spiral galaxies with closer and/or more massive companions. The greater collision velocities found at stronger perturbations on the models will also result in higher dust temperature in the colliding clouds. In the IR pairs examined, most have only one member, the larger, detected and when both are detected, the larger is always the more luminous. In simulations and in a simple analytic description of the strong distance dependence of the tidal force, it is found that the big galaxy of a pair is more strongly affected than the small.

Byrd, Gene G.↗
NASA NTRS1987

A deep redshift survey of field galaxies. Comments on the reality of the Butcher-Oemler effect

A spectroscopic survey of over 400 field galaxies has been completed in three fields for which we have deep UBVI photographic photometry. The galaxies typically range from B=20 to 22 and possess redshifts z from 0.1 to 0.5 that are often quite spiky in distribution. Little, if any, luminosity evolution is observed up to redshifts z approx 0.5. By such redshifts, however, an unexpectedly large fraction of luminous galaxies has very blue intrinsic colors that suggest extensive star formation; in contrast, the reddest galaxies still have colors that match those of present-day ellipticals.

Koo, David C.↗
NASA NTRS1987

Steady state cooling flow models for normal elliptical galaxies

An extensive grid of steady state cooling flow models for the hot gas in elliptical galaxies is calculated. The effects of allowing inflow of surrounding gas and varying the supernova heating rate, the mass distribution of the galaxy, the rate of stellar mass loss, and the outer boundary pressure are studied. The X-ray luminosities, spectra, and surface brightness profiles of the galaxies are computed. In all of the models, the gas density varies approximately as r exp -3/2. In the models with heavy halos, the X-ray and optical surface brightnesses are nearly proportional to one another within individual galaxies, and the temperature profiles are roughly isothermal.

Sarazin, Craig L.↗
NASA NTRS1987

Far-infrared properties of cluster galaxies

Far-infrared properties are derived for a sample of over 200 galaxies in seven clusters: A262, Cancer, A1367, A1656 (Coma), A2147, A2151 (Hercules), and Pegasus. The IR-selected sample consists almost entirely of IR normal galaxies, with Log of L(FIR) = 9.79 solar luminosities, Log of L(FIR)/L(B) = 0.79, and Log of S(100 microns)/S(60 microns) = 0.42. None of the sample galaxies has Log of L(FIR) greater than 11.0 solar luminosities, and only one has a FIR-to-blue luminosity ratio greater than 10. No significant differences are found in the FIR properties of HI-deficient and HI-normal cluster galaxies.

Bicay, Michael D.↗
NASA NTRS1987

Arecibo observations of IRAS galaxies at 21 and 18 centimeters

Arecibo observations at 21 cm and 18 cm of a sample of galaxies selected for their intense far-infrared (FIR) emission are reported. The objective was to search for H I absorption and OH maser emission. No new cases were found. The significance of this null result is discussed both in terms of spatial distribution of the interstellar gas and dust and in terms of the continuum luminosity of the nucleus. Nevertheless, the H I profiles are extraordinary in that most are convex (single peak). This may suggest disruption of the disk rotation system in some cases. Little correlation is found between the hydrogen mass of these galaxies and their FIR luminosity. Comparison of these quantities suggests that the dust in these galaxies is under conditions very different from the solar neighborhood. Much more of the FIR emission apparently comes from H II regions than in normal galaxies. There is an excellent correlation between IR flux and radio continuum flux. The ratio of these two is the same as for normal spirals, which is surprising considering the many variables which could change this ratio.

Garwood, Robert W.↗
NASA NTRS1987

Quasar absorption lines and galaxy halos

The evolution of the halo environments of the Galaxy and of other galaxies at early epochs is discussed, summarizing the results of observations of quasar absorption lines obtained with the IUE satellite since its launch in 1978. Topics addressed include the Ly-alpha forest, nearby galaxies, displaced absorption systems, and systems with z(a) approximately equal to z(e). The data are presented in sample spectra and graphs and described in detail. It is suggested that definitive answers on the production of quasar absorption lines by the extended gaseous halos and/or disks of distant galaxies must await the higher-quality observational data to become available with the Hubble Space Telescope.

Bergeron, Jacqueline↗
NASA NTRS1987

Models of ring galaxies. II - Extended starbursts

Numerical models of the development of star-formation bursts in collisional ring galaxies are presented. To extend the work of Appleton and Struck-Marcell (1987) target disks which have relatively high mean cloud mass and gas density are emphasized. In such cases, even relatively low mass intruder galaxies are capable of triggering intense star-formation bursts in the density waves. Although the bursts are very short-lived in any individual gas element, pressure effects stimulate neighboring gas elements to burst, which can result in a sustained enhancement in the net star-formation rate. The results are capable of explaining the high far-infrared fluxes observed in righ galaxies and provide clues to the development of starburst activity in other colliding galaxies.

Struck-Marcell, Curtis↗
NASA NTRS1988

A five-band study of spiral galaxies - X-ray, optical, near- and far-infrared, and radio continuum correlations

A statistical analysis is given of the relationships between global emission properties of spiral galaxies, including the radio continuum, far-infared, near-infrared H-band, optical (B), and X-ray emission. Different properties are observed in early-type and in late-type spiral galaxies, which can be ascribed to the presence of prominent bulges in the former. In late-type spirals, the statistical properties of the emission at different wavelengths are consistent with a common disk/arm origin. The power-law exponents of the correlations are consistent with a steeper IMF in low-luminosity galaxies and with the presence of an obscured starburst component in high-luminosity galaxies. The strongest correlation of the radio continuum luminosity with any other variable is with the far-infrared, suggesting that the radio emission is disjoint from the older low-mass stellar component.

Fabbiano, G.↗
NASA NTRS1988

The morphology of multiple-nucleus brightest cluster galaxies

The morphology of high SNR CCD images of 16 multiple-nucleus brightest cluster galaxies is studied using an algorithm that models images of the systems as the line-of-sight superposition of normal elliptical galaxies. The algorithm is applied initially to the classic multiple-nucleus cD galaxy in A2199. Evidence is found suggestive of deep interpenetrating high-speed encounters by its secondaries. The interactions effects studied include noncentric isophotes, brightness profile effects, excess light around primary galaxies, and dynamical friction wakes. The results show that in many cases multiple systems are interacting systems.

Lauer, Tod R.↗
NASA NTRS1988

4C 40.36 - A radio galaxy at a redshift of 2.3

Long-slit spectroscopy of a faint extended optical object identified with the radio source 4C 40.36 is presented. Three emission lines are detected. Their wavelengths match those of C IV 1549 A, He II 1640 A, and semiforbidden C III 1909 A to within 0.5 percent for a redshift of z = 2.269. The extended continuum emission (20 kpc) together with the large equivalent widths (about 100 A) and narrow profiles (1500 km/s) of the emission lines, all show that 4C 40.36 is a galaxy with properties similar to those of other distant radio galaxies. The redshift of 4C 40.36, however, considerably exceeds that of the most distant radio galaxy (3C 326.1 at z = 1.825) known to date. 4C 40.36 is of additional interest as an excellent example of the recently discovered phenomenon of alignment between the optical and radio axes of powerful distant radio galaxies. The object was investigated as part of a survey of ultra-steep spectrum radio sources, and it is shown that the selection criteria used to discover 4C 40.36 result in a sample of objects having a relatively low dispersion of monochromatic radio luminosities.

Chambers, K. C.↗
NASA NTRS1988

Statistics of galaxy orientations - Morphology and large-scale structure

Using the Uppsala General Catalog of bright galaxies and the northern and southern maps of the Lick counts of galaxies, statistical evidence of a morphology-orientation effect is found. Major axes of elliptical galaxies are preferentially oriented along the large-scale features of the Lick maps. However, the orientations of the major axes of spiral and lenticular galaxies show no clear signs of significant nonrandom behavior at a level of less than about one-fifth of the effect seen for ellipticals. The angular scale of the detected alignment effect for Uppsala ellipticals extends to at least theta of about 2 deg, which at a redshift of z of about 0.02 corresponds to a linear scale of about 2/h Mpc.

Lambas, Diego G.↗

Refine your search to explore more results.