Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “E+A 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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1969

Penetrating radiations

High energy electromagnetic radiation and energetic particles from sun, galaxies, and nuclear explosions in spacecraft environment

Gaines, E. E.↗
NASA NTRS1972

The spectra of two galaxies near PKS 2251 + 11.

Determination of redshifts for two galaxies in the group associated with the quasi-stellar source PKS 2251 + 11 from the measurements of the H and K absorption lines of Ca II. The measured redshift of the brighter galaxy is within 60 km/sec of the redshift of the quasi-stellar source. The other differs by 1000 km/sec. Strong hydrogen-line emission reported earlier for the brighter galaxy was not detected.

Robinson, L. B.↗
NASA NTRS1977

A study of the luminosity function for field galaxies

Nine determinations of the luminosity function (LF) for field galaxies are analyzed and compared. Corrections for differences in Hubble constants, magnitude systems, galactic absorption functions, and definitions of the LF are necessary prior to comparison. Errors in previous comparisons are pointed out. After these corrections, eight of the nine determinations are in fairly good agreement. The discrepancy in the ninth appears to be mainly an incompleteness effect. The LF data suggest that there is little if any distinction between field galaxies and those in small groups.

Felten, J. E.↗
NASA NTRS1977

Final SAS-2 gamma-ray results on sources in the galactic anticenter region

Final results are presented for SAS-2 observations of high-energy gamma-rays from the galactic anticenter region. Three main gamma-ray features are shown to characterize this region: a localized source associated with the Crab Nebula and its pulsar, another localized source near galactic coordinates 195 deg, +5 deg, and a general enhancement of the diffuse background 10 to 15 deg south of the galactic plane, which is associated with the Gould Belt. For the Crab, it is found that the radiation is mostly pulsed, the pulsed fraction increases with energy, and the intensity of the radiation in the main and interpulse peaks is approximately the same. The other localized source, provisionally designated as gamma 195+5, is found to have a harder spectrum than the Crab but no obvious radio counterpart; emission from an external galaxy is ruled out.

Thompson, D. J.↗
NASA NTRS1979

HEAO A-2 extragalactic results

Results from the HEAO A-2 experiment concerning the extragalactic X-ray sky are discussed. All-sky maps of hard X-ray sources detected are presented reflecting the temporal variability of the sources that make up the extragalactic X-ray sky. Most of the identified extragalactic objects are not clusters of galaxies but isolated galaxies. Spectra for sources representing classes of active galz galaxies, BL Lacertae objects, and N galaxies are discussed in order of luminosity.

Boldt, E. A.↗
NASA NTRS1982

The nucleus of M81 - Simultaneous 2.3 and 8.3 GHz Mark III VLBI observations

Mark III very long baseline interferometry (VLBI) observations have been made of the nucleus in the normal galaxy M81 (NGC 3031) simultaneously at 2.3 and 8.3 GHz, and it was found that nearly 100% of the flux density of the nuclear region originates in an elongated radio core with linear dimensions 1000-4000 AU, dependent on frequency. This galactic nucleus is the most compact observed in any extragalactic source. The position coincides with that of the nucleus at optical and X-ray wavelengths within the larger uncertainties of the latter two. The position angle of the major axis of the M81 nucleus is within 3 deg of 75 deg at 2.3 GHz and within 6 deg of 50 deg at 8.3 GHz and is frequency dependent at the 4 sigma level. These values straddle the 62 deg position angle of the projection on the sky of the rotation axis of the galaxy. The spectrum of the core is slightly inverted, and the length of its major axis decreases with frequency. These results are consistent with the emission's being incoherent electron synchrotron radiation from an inhomogeneous region with an optical depth varying along the rotation axis of the galaxy.

Bartel, N.↗
NASA NTRS1987

Submm observations of IRAS galaxies

Twenty-six galaxies from the Infrared Astronomy Satellite (IRAS) point source catalog were observed at 250 and 1300 microns. The Far Infrared (FIR) spectra from 25 to 1300 microns are interpreted in terms of two dust components of about 16 and 53 K. Flux densities at 1300 microns are used to estimate the total gas mass M sub g. The warm dust luminosity L sup W is considered to be proportional to M sub g sup 0.9 in the mass range 3 x 10 to the 8th is equal to or less than M sub g/solar mass is equal to or less than 10 to the 12th power. The efficiency of star formation seems to be four times higher in barred and peculiar galaxies than in Sc types.

Chini, R.↗
NASA NTRS1987

Cosmic-ray elemental abundances from 1 to 10 GeV per amu for boron through nickel

The relative abundances of cosmic-ray nuclei in the charge range boron through nickel over the energy range 1-10 GeV per amu were measured with a balloon-borne detector. The instrument consists of a scintillation and Cerenkov counter telescope with a multiwire proportional chamber hodoscope and has been flown in four high-altitude balloon flights. Good charge resolution (sigma = 0.2 charge units at iron) and high statistical accuracy have been achieved. These data are used to derive the energy dependence of the leakage path length using the leaky box model of propagation and confinement in the galaxy. This energy dependence is found to be best fit by lambda = E(tot) exp -n, where n = 0.49 + or - 0.06 over 1-10 GeV per amu. Relative abundances at the source are consistent with an energy-independent composition.

Dwyer, Robert↗
NASA NTRS1990

The Energetic Gamma-Ray Experiment Telescope (EGRET) Science Symposium

The principle purpose of this symposium is to provide the EGRET (Energetic Gamma-Ray Experiment Telescope) scientists with an opportunity to study and improve their understanding of high energy gamma ray astronomy. The Symposium began with the galactic diffusion radiation both because of its importance in studying galactic cosmic rays, galactic structure, and dynamic balance, and because an understanding of its characteristics is important in the study of galactic sources. The galactic objects to be reviewed included pulsars, bursts, solar flares, and other galactic sources of several types. The symposium papers then proceeded outward from the Milky Way to normal galaxies, active galaxies, and the extragalactic diffuse radiation.

Fichtel, Carl E.↗
NASA NTRS1990

Accounting for the dispersion in the x ray properties of early-type galaxies

The x ray luminosities of early-type galaxies are correlated with their optical (e.g., blue) luminosities (L sub X approx. L sub B exp 1.6), but the x ray luminosities exhibit considerable scatter for a given optical luminosity L sub B. This dispersion in x ray luminosity is much greater than the dispersion of other properties of early-type galaxies (for a given L sub B), such as luminosity scale-length, velocity dispersion, color, and metallicity. Here, researchers consider several possible sources for the dispersion in x ray luminosity. Some of the scatter in x ray luminosity may result from stellar population variations between galaxies with similar L sub B. Since the x ray emitting gas is from accumulated stellar mass loss, the L sub X dispersion may be due to variations in integrated stellar mass loss rates. Another possible cause of the L sub X dispersion may be variations in the amount of cool material in the galaxies; cool gas may act as an energy sink for the hot gas. Infrared emission may be used to trace such cool material, so researchers look for a correlation between the infrared emission and the x ray emission of early-type galaxies at fixed L sub B. Velocity dispersion variations between galaxies of similar L sub B may also contribute to the L sub X dispersion. The most likely a priori source of the dispersion in L sub X is probably the varying amount of ram-pressure stripping in a range of galaxy environments. The hot gaseous halos of early-type galaxies can be stripped in encounters with other galaxies or with ambient cluster gas if the intracluster gas is sufficiently dense. Researchers find that the most likely cause of dispersion in the x ray properties of early type galaxies is probably the ram-pressure stripping of gaseous halos from galaxies. For a sample of 81 early-type galaxies with x ray luminosities or upper limits derived from Einstein Observatory observations (CFT) researchers calculated the cumulative distribution of angular distances between the x ray sample members and bright galaxies from the Revised Shapley - Ames catalog. Collectively, galaxies with low x ray luminosities (for a given L sub B) tend to be in denser environments than galaxies with higher x ray luminosities.

White, Raymond E., III↗
NASA NTRS1991

Were small galaxies once the dominant cosmological population?

Redshifts and K magnitudes have been obtained for a small but complete sample of 22 galaxies with B magnitudes down to 24. In the luminosity range B = 23-24, the B-band galaxy counts are dominated by a population of small blue galaxies at z roughly 0.25, which may collectively contain as much baryonic matter as the normal galaxies. It is possible either that these earlier galaxies have undergone merging to create the present galaxy population, or that they represent a quite different galactic population which has now faded or disappeared. Either possibility has considerable implications for understanding of galaxy formation.

Cowie, L. L.↗
NASA NTRS1994

Conditions in the z = 0.692 absorber toward 3CR 286

We present Hubble Space Telescope/Faint Object Spectrograph (HST/FOS) ultraviolet and ground-based optical spectra of the z = 0.692 21 cm absorption system in the quasi-stellar object (QSO) 3CR 286. The strength of the damped Lyman-alpha absorption implies an H I column density, N(H I) approximately 2 x 10(exp 21)/sq cm. We derive a high spin temperature for the H I gas, T(sub s) greater than or approximately equal to 10(exp 3) K, as has been found for other high-redshift 21 cm absorbing systems; at least 80% of the H I is hotter than 1200 K. Curve-of-growth analysis yields Mg(+) and Fe(+) abundances which are approximately 1-2 dex below solar values; the Ca(+) abundance is even lower implying some depletion onto dust grains. The H2 fraction is not high. We speculate that the high inferred T(sub s) for the gas may reflect continuing active star formation at the 5-8 Gyr look-back time to the absorbing galaxy.

Cohen, Ross D.↗
NASA NTRS2012

Origin of 12 micrometer Emission Across Galaxy Populations from Wise and ADSS Surveys

We cross-matched Wide-field Infrared Survey Explorer sources brighter than 1 mJy at 12 micron with the Sloan Digital Sky Survey galaxy spectroscopic catalog to produce a sample of approx. 10(exp 5) galaxies at z = 0.08, the largest of its kind. This sample is dominated (70%) by star-forming (SF) galaxies from the blue sequence, with total IR luminosities in the range approx 10(exp 8)-10(exp 12) Solar L. We identify which stellar populations are responsible for most of the 12 micron emission. We find that most (approx 80%) of the 12 micron emission in SF galaxies is produced by stellar populations younger than 0.6 Gyr. In contrast, the 12 micron emission in weak active galactic nuclei (AGNs; L [O iii] < 10(exo 7) solar L ) is produced by older stars, with ages of approx 1-3 Gyr. We find that L(sub 12 micron) linearly correlates with stellar mass for SF galaxies. At fixed 12 micron luminosity, weak AGNs deviate toward higher masses since they tend to be hosted by massive, early-type galaxies with older stellar populations. SF galaxies and weak AGNs follow different L(sub 12 micron) - SFR (star formation rate) relations, with weak AGNs showing excess 12 micron emission at low SFR (0.02-1 solar M /yr). This is likely due to dust grains heated by older stars. While the specific star formation rate (SSFR) of SF galaxies is nearly constant, the SSFR of weak AGNs decreases by approx 3 orders of magnitude, reflecting the very different star formation efficiencies between SF galaxies and massive, early-type galaxies. Stronger type II AGNs in our sample (L(sub [O iii]) > 10(exp 7) solar L ), act as an extension of massive SF galaxies, connecting the SF and weak AGN sequences. This suggests a picture where galaxies form stars normally until an AGN (possibly after a starburst episode) starts to gradually quench the SF activity. We also find that 4.6-12 micron color is a useful first-order indicator of SF activity in a galaxy when no other data are available.

Donso, E.↗