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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 NTRS1976

Energy spectra of X-ray clusters of galaxies

A procedure for estimating the ranges of parameters that describe the spectra of X-rays from clusters of galaxies is presented. The applicability of the method is proved by statistical simulations of cluster spectra; such a proof is necessary because of the nonlinearity of the spectral functions. Implications for the spectra of the Perseus, Coma, and Virgo clusters are discussed. The procedure can be applied in more general problems of parameter estimation.

Avni, Y.↗
NASA NTRS1988

Clustering correlations and limits on cosmological gravitational waves

A cosmological background of gravitational waves induces angular deviations in the propagation of light traversing it. All observed astrophysical sources might therefore have varying apparent positions, with the time dependence set by the wave period. Wavelengths greater than a kiloparsec are examined, so the positions are frozen but in general correlated. Comparison with observed galaxy-galaxy n-point correlation functions provide a spectrum-independent limit on the energy density of gravitational waves with wavelengths between a few tens of kiloparsecs and a few hundred megaparsecs of Omega(GW) less than 0.001.

Linder, Eric V.↗
NASA NTRS2021

RELICS-DP7: Spectroscopic Confirmation of a Dichromatic Primeval Galaxy atz∼7

We report the discovery of a spectroscopically confirmed strong Lyαemitter atz=7.0281±0.0003, observed as part of the Reionization Lensing Cluster Survey(RELICS). This galaxy, dubbed“Dichromatic Primeval Galaxy”atz∼7(DP7), shows two distinct components. While fairly unremarkable in terms of its ultraviolet(UV)luminosity(~L0.3UV*,whereLUV*is the characteristic luminosity), DP7 has one of the highest observed Lyαequivalent widths(EWs)amongLyαemitters atz>6(>200Åin the rest frame). The strong Lyαemission generally suggests a young metal-poor, low-dust galaxy; however, we find that the UV slopeβof the galaxy as a whole is redder than typical star-forming galaxies at these redshifts,−1.13±0.84, likely indicating, on average, a considerable amount of dust obscuration, or an older stellar population. When we measureβfor the two components separately, however, we find evidence of differing UVcolors, suggesting two separate stellar populations. Also, we find that Lyαis spatially extended and likely larger than the galaxy size, hinting to the possible existence of a Lyαhalo. Rejuvenation or merging events could explain these results.Either scenario requires an extreme stellar population, possibly including a component of Population III stars, or an obscured active galactic nucleus. DP7, with its low UV luminosity and high LyαEW, represents the typical galaxies that are thought to be the major contribution to the reionization of the universe, and for this reason DP7 is an excellent target for follow-up with the James Webb Space Telescope

Debora Pelliccia↗
NASA NTRS1988

Measuring the topology of large-scale structure in the universe

An algorithm for quantitatively measuring the topology of large-scale structure has now been applied to a large number of observational data sets. The present paper summarizes and provides an overview of some of these observational results. On scales significantly larger than the correlation length, larger than about 1200 km/s, the cluster and galaxy data are fully consistent with a sponge-like random phase topology. At a smoothing length of about 600 km/s, however, the observed genus curves show a small shift in the direction of a meatball topology. Cold dark matter (CDM) models show similar shifts at these scales but not generally as large as those seen in the data. Bubble models, with voids completely surrounded on all sides by wall of galaxies, show shifts in the opposite direction. The CDM model is overall the most successful in explaining the data.

Gott, J. Richard, III↗
NASA NTRS1994

Baryonic dark clusters in galactic halos and their observable consequences

We consider the possibility that approximately 10% of the mass of a typical galaxy halo is in the form of massive (approximately 10(exp 7) solar masses), compact (escape speeds approximately 100 km/s) baryonic clusters made of neutron stars (approximately 10% by mass), black holes (less than or approximately equal to 1%) and brown dwarfs, asteroids, and other low-mass debris (approximately 90%). These general properties are consistent with several different observational and phenomenological constraints on cluster properties subject to the condition that neutron stars comprise approximately 1% of the total halo mass. Such compact, dark clusters could be the sites of a variety of collisional phenomena involving neutron stars. We find that integrated out to the Hubble distance approximately one neutron star-neutron star or neutron star-black hole collision occurs daily. Of order 0.1-1 asteroid-neutron star collisions may also happen daily in the halo of the Milky Way if there is roughly equal cluster mass per logarithmic particle mass interval between asteroids and brown dwarfs. These event rates are comparable to the frequency of gamma-ray burst detections by the Burst and Transient Source Experiment (BATSE) on the Compton Observatory, implying that if dark halo clusters are the sites of most gamma-ray bursts, perhaps approximately 90% of all bursts are extragalactic, but approximately 10% are galactic. It is possible that dark clusters of the kind discussed here could be detected directly by the Infrared Space Observatory (ISO) or Space Infrared Telescope Facility (SIRTF). If the clusters considered in this paper exist, they should produce spatially correlated gravitational microlensing of stars in the Large Magellanic Cloud (LMC). If 10% of the halo is in the form of dark baryonic clusters, and the remaining 90% is in brown dwarfs and other dark objects which are either unclustered or collected into low-mass clusters, then we expect that two events within approximately 1 min of one another are likely to be seen after a total of order 20-30 microlenses have been detected.

Wasserman, Ira↗
NASA NTRS1989

A search for X-ray emission associated with the great attractor

A search is reported for X-ray emission associated with the object, dubbed the 'great attractor', which has been postulated as the cause of the coherent deviations from the Hubble flow which are observed in nearby parts of the universe. The hypothesis that a substantial fraction of the dynamical mass of the great attractor exists in the form of rich clusters of galaxies is ruled out. The possibility is considered that a substantial fraction of the mass of the great attractor could exist in a form which would increase the apparently diffuse X-ray surface brightness. The observational upper limit to the diffuse X-ray sky surface brightness enhancement in the general direction of the great attractor allows interesting limits to be set on the fraction of the dynamical mass of the great attractor which can exist in the form of X-ray-luminous material.

Jahoda, Keith↗
NASA NTRS1991

Northern dwarf and low surface brightness galaxies. IV - The large-scale space distribution

Results are reported from a statistical analysis of published observational data on a sample of 860 northern dwarf and low-surface-brightness (D/LSB) galaxies with delta = 0 deg or greater and b between -40 and 40 deg, selected from the Uppsala General Catalogue of Galaxies (Nilson et al., 1973). The results are presented in extensive redshift/space maps, histograms, graphs and tables and characterized in detail. It is shown that the distribution of D/LSB galaxies closely resembles that of bright galaxies, apparently ruling out biased-star-formation models predicting a uniform distribution of D/LSBs. Although bright galaxies outside clusters are somewhat more clustered than the H I-rich D/LSBs, the latters' pairwise peculiar velocity (460 + or - 50 km/sec) is similar to that of the former.

Thuan, Trinh X.↗
NASA NTRS1976

X-radiation from clusters of galaxies: Spectral evidence for a hot evolved gas

OSO-8 observations of the X-ray flux in the range 2-60 keV from the Virgo, Perseus, and Coma Clusters provide strong evidence for the thermal origin of the radiation, including iron line emission. The data are adequately described by emission from an isothermal plasma with an iron abundance in near agreement with cosmic levels. A power law description is generally less acceptable and is ruled out in the case of Perseus. Implications on the origin of the cluster gas are discussed.

Serlemitsos, P. J.↗
NASA NTRS1991

Luminous clusters of Wolf-Rayet stars in the SBmIII galaxy NGC 4214

Observations are reported of strong broad emission lines attributed to WR stars in the spectra of several bright knots in the nearby Magellanic irregular galaxy NGC 4214 (classified as type SBmIII), in addition to the emission produced by the more prevalent WN stars). Data are presented on measurements of the line fluxes, the line equivalent widths, and continuum flux densities in the four observed knots, showing that the strongest WR lines generally appear in knots having the most luminous stellar continuum. The significance of this observation is discussed.

Sargent, Wallace L. W.↗
NASA NTRS1981

Relativistic astrophysics - The view from Texas in Baltimore /Review/

Recent observational and theoretical work presented at the Tenth Texas Symposium on Relativistic Astrophysics held in Baltimore, Maryland from December 15-19, 1980, is outlined. Areas covered include the theoretical foundations of relativistic astrophysics in general relativity, quantum gravitational theory and the association of grand unification with astronomical and cosmological issues, the cosmic microwave, X-ray, gamma-ray, UV, cosmic ray and gravitational wave backgrounds, the current expansion rate and average mass-energy density of the universe, and mechanisms of galaxy formation. Also discussed are the characteristics of active galaxies and clusters emitting in the gamma-ray and X-ray regions, and compact objects formed from supernova explosions, including pulsars, X-ray-emitting neutron stars, Sco X-1 and SS 433, gamma-ray sources, and X-ray and gamma-ray bursters.

Trimble, V. L.↗
NASA NTRS1987

Molecular gas in the starburt nucleus of M82

The 7" resolution CO observations of the central 1 kpc of M82 have resolved 2 components of molecular gas: (1) a high concentration in the central 700 pc x 200 pc, and (2) extended features that may be gas expelled from the central concentration. The central concentration of molecular gas falls in the same confines as the other tracers of recent star formation, and may be identified directly with the star burst region. The molecular gas in the star burst nucleus of M82 appears to be highly disturbed and has high kinetic temperature, likely consequences of the high density of young star clusters. Stellar winds and subsequent supernovae from the star clusters can effectively sweep up the interstellar medium. The spatial distribution and kinematics of the nuclear concentration of the molecular gas, as well as the 2 micron light distribution, suggest the presence of a stellar bar in M82. Comparisons of the M82 star burst nucleus to a sample of IR luminous galaxies suggest that star burst regions in general may have a higher gas temperature and much higher L sub IR/M sub H2 that the galactic disk, and that the L sub IR of the star burst regions may be essentially proportional to their area.

Lo, K. Y.↗
NASA NTRS1990

Color excesses, intrinsic colors, and absolute magnitudes of Galactic and Large Magellanic Cloud Wolf-Rayet stars

A new method of determining the color excesses of WR stars in the Galaxy and the LMC has been developed and is used to determine the excesses for 44 Galactic and 32 LMC WR stars. The excesses are combined with line-free, narrow-band spectrophotometry to derive intrinsic colors of the WR stars of nearly all spectral subtypes. No correlation of UV spectral index or intrinsic colors with spectral subtype is found for the samples of single WN or WC stars. There is evidence that early WN stars in the LMC have flatter UV continua and redder intrinsic colors than early WN stars in the Galaxy. No separation is found between the values derived for Galactic WC stars and those obtained for LMC WC stars. The intrinsic colors are compared with those calculated from model atmospheres of WR stars and generally good agreement is found. Absolute magnitudes are derived for WR stars in the LMC and for those Galactic WR stars located in clusters and associations for which there are reliable distance estimates.

Vacca, William D.↗
NASA NTRS1979

GSFC Contributions to the NATO X-ray Astronomy Institute, Erice, July 1979

An overview of X-ray astronomical spectroscopy in general is presented and results obtained by HEAO 1 and 2 as well as earlier spacecraft are examined. Particular emphasis is given to the spectra of supernova remnants; galactic binary X-ray sources, cataclysmic variables, bulges, pulsars, and stars; the active nuclei of Seyfert 1 galaxy, BL Lac, and quasars; the diffuse X-ray background; and galactic clusters.

Holt, S. S.↗
NASA NTRS1977

X-radiation from clusters of galaxies - Spectral evidence for a hot evolved gas

OSO-8 observations of the X-ray flux in the range between 2 and 60 keV from the Virgo, Perseus, and Coma clusters provide strong evidence for the thermal origin of the radiation, including iron-line emission. The data are adequately described by emission from an isothermal plasma with an iron abundance in near agreement with cosmic levels. A power-law description is generally less acceptable and is ruled out in the case of Perseus. Implications of the origin of the cluster gas are discussed.

Serlemitsos, P. J.↗
NASA NTRS1981

HEAO A-2 observations of non-Abell Zwicky clusters containing extended radio sources

Burns and Owen's sample of 25 4C radio sources which coincide with Zwicky clusters of galaxies has been searched for X-ray emission using the HEAO 1 A-2 experiment. X-ray emission was detected from five sources at the 3sigma level, two of which exceeded 5sigma. Positions and 90% X-ray error boxes are given for each of the five sources detected. The clusters surveyed are non-Abell clusters which would generally not be expected to be detectable with the A-2 experiment. The search for X-ray emission was prompted by the knowledge of the existence of extended radio sources in the clusters. The relaxed structure of these sources implies the presence of a relatively dense intracluster medium which is expected to produce thermal bremsstrahlung X-ray emission.

Holman, G. D.↗
NASA NTRS1987

Intermediate-age core helium burning stars and the distance to the Magellanic Clouds

The luminosities of the core helium burning stars in six Magellanic Cloud intermediate-age star clusters, whose ages have recently been determined from photometry reaching below the main-sequence turnoff, are compared with the predictions of a new grid of theoretical models. It is found that for the so-called 'short' distance moduli consistent results can be achieved with moderate amounts of mass loss from the main sequence to the core helium burning stage for the older clusters, and with rather more substantial mass loss for the younger objects. For the 'long' moduli, however, the results of the comparison give inconsistent results in that the required masses for the clump stars generally exceed the corresponding turnoff masses, in some cases by several tenths of a solar mass. The results support the adoption of smaller distances to these galaxies.

Seidel, E.↗
NASA NTRS1988

Low luminosity radio galaxies - Effects of gaseous environment

X-ray data from the Einstein Observatory have been collected for a number of low luminosity B2 radio galaxies, in order to study the effect of gas pressure on radio sources. Generally, the thermal pressure of the X-ray emitting gas is sufficient to confine most of the radio components. Various possibilities are given for sources where thermal pressure significantly exceeds the nonthermal pressure. For radio lobes, an inverse correlation is found between the central densities of the cluster gas and the size of the radio structures. For jets, a study of the pressure ratios is given for different distances from the radio core. In a few cases, pressure imbalance is found in the outer regions of the jets. However, from depolarization data, this is unlikely to be produced by a large thermal component inside the radio jets.

Morganti, R.↗
NASA NTRS1988

Atlas of Galaxies Useful for Measuring the Cosmological Distance Scale

A critical first step in determining distances to galaxies is to measure some property of primary objects such as stars of specific types, H II regions, and supernovae remnants that are resolved out of the general galactic star content. With the completion of the Mount Wilson/Palomar/Las Campanas survey of bright galaxies in 1985, excellent large-scale photographs of the complete Shapley-Ames sample were on hand. Most of the galaxies useful for distance scale calibration are in this collection. This atlas contains photographs of 322 galaxies including the majority of all Shapley-Ames bright galaxies, plus cluster members in the Virgo Cluster core that might be usefully resolved by the Hubble Space Telescope (HST). Because of crowding and high background-disk surface brightness, the choice of field position is crucial for programs involving resolution of particular galaxies into stars. The purpose of this atlas is to facilitate this choice. Enough information is given herein (coordinates of the galaxy centers and the scale of the photography) to allow optimum placement of the HST wide-field planetary camera format of approximately 150 arc-seconds on a side.

Sandage, Allan↗