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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Hot gas metallicity and the history of supernova activity in elliptical galaxies

Calculations of the dynamical evolution of the hot interstellar medium (ISM) in a massive elliptical galaxy are described, with a variety of past variations of the SN rate being assumed. The investigation focuses on iron enrichment in the ISM. The equivalent widths of the 6.7-keV iron line are calculated as a function of redshift and of galactic projected radius. The present-day interstellar gas in elliptical galaxies contains a fossil record of past SN activity that can be determined from measurements of iron line equivalent widths at several projected radii in the galaxy. It is proposed that the ISM iron abundance is likely to be quite inhomogeneous. The hydrogen-free ejecta of type Ia SN also result in pronounced ISM abundance inhomogeneities that probably eventually cool and move in pressure equilibrium with the local ISM flow velocity. The 6.7-keV iron line emission is greater if the iron is confined to ionized regions of pure iron.

Loewenstein, Michael↗
NASA NTRS1975

Development of a comet as it pursues its orbit

The properties of cometary dust-swarms in almost parabolic long-period orbits are examined. The effect of passage of the solar system through interstellar gas clouds is shown to be capable of affecting substantially the angular momentum of a comet about the sun, thus accounting for the existence of comets with high values of perihelion distance. The same process would enable cometary particles to adsorb interstellar gases and regenerate their gas content.

Lyttleton, R. A.↗
NASA NTRS1982

Acoustic waves in supernova remnants

When the Mach number of a supernova shock wave, propagating through the hot interstellar gas, is less than the critical value 2.76, the interaction of the shock with an interstellar cloud produces a reflected pressure pulse that propagates away from the cloud as an acoustic wave. A preliminary analysis indicates that about 4% of the energy of an exploding supernova shell is converted into such waves. When the postshock gas temperature exceeds 2 x 10 to the 6th K, waves as short as 6 pc are damped in less than a wavelength, returning the energy to the hot gas. Longer waves, especially at late stages, are less strongly damped, and are superposed in the hot gas to create a fluctuating magnetoacoustic field, with typical periods of about 100,000 years. In the warm neutral clouds at temperatures of about 8000 K these waves are rapidly damped by plasma slip (ambipolar diffusion), providing a heat source that may account for the temperatures of these clouds.

Spitzer, L., Jr.↗
NASA NTRS1988

Superbubbles in disk galaxies

Correlated supernovae from an OB association create a superbubble: a large, thin, shell of cold gas surrounding a hot pressurized interior. Because supernova blast waves usually become subsonic before reaching the walls of the shell or cooling radiatively, the energy input from supernovae may be reasonably approximated as a continuous luminosity. Using the Kompaneets (thin-shell) approximation, the growth of superbubbles in various stratified atmospheres is numerically modeled. A dimensionless quantity predicts whether a superbubble will blow out of the H I disk of a spiral galaxy (and begin to accelerate upward) or collapse. Superbubbles blow out of the H I layer when they have a radius in the plane between one and two scale heights. They blow out only one side of a disk galaxy if their centers are more than 50-60 p above the plane and the gas layer has density and scale height typical of the Milky Way. Fingers of warm interstellar gas intrude into the hot interior when the superbubble overtakes dense clouds.

Mac Low, Mordecai-Mark↗
DOE OSTI2012

Gamma-ray observations of the Orion Molecular Clouds with the Fermi Large Area Telescope

We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between ~100 MeV and ~100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to ~10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity-integrated CO intensity (W CO) at a 1° × 1° pixel level. The correlation is found to be linear over a W CO range of ~10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The W CO-to-mass conversion factor, X CO, is found to be ~2.3 × 10 20 cm -2 (K km s –1 ) –1 for the high-longitude part of Orion A (l > 212°), ~1.7 times higher than ~1.3 × 10 20 found for the rest of Orion A and B. We interpret the apparent high X CO in the high-longitude region of Orion A in the light of recent works proposing a nonlinear relation between H2 and CO densities in the diffuse molecular gas. W CO decreases faster than the H 2 column density in the region making the gas "darker" to W CO.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2012

Gamma-Ray Observations of the Orion Molecular Clouds with the Fermi Large Area Telescope

We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between approx 100 MeV and approx 100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to approx 10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity-integrated CO intensity (W(sub CO)) at a 1 deg 1 deg pixel level. The correlation is found to be linear over a W(sub CO) range of approx 10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The W(sub CO)-to-mass conversion factor, X(sub CO), is found to be approx 2.3 10(exp 20) / sq cm (K km/s)(exp -1) for the high-longitude part of Orion A (l > 212 deg), approx 1.7 times higher than approx 1.3 10(exp 20) found for the rest of Orion A and B. We interpret the apparent high X(sub CO) in the high-longitude region of Orion A in the light of recent works proposing a nonlinear relation between H2 and CO densities in the diffuse molecular gas.W(sub CO) decreases faster than the H2 column density in the region making the gas "darker" to W(sub CO).

Ackermann, M.↗
NASA NTRS1986

Cooling flows in ellipticals and the nature of radio galaxies

Analytical arguments are presented to demonstrate that the morphology of the host galaxy will influence the type of radio signature emitted by the nucleus, which is in many cases presumed to a black hole. The types of matter inflows and consequent shapes of the accretion disks around the nuclei of spiral and elliptical galaxies are discussed. If the inflowing matter is predominantly cold and clumpy, then stars will tend to form and only the available hot gas will descend into the center. Collimated radio jets will appear only in the presence of hot interstellar gas in elliptical galaxies and not in spiral galaxies. The implications of the predictions for the interpretation of observational data on, e.g., BL Lac objects and N galaxies are discussed.

Begelman, M. C.↗
DOE OSTI2016

PREDOMINANTLY LOW METALLICITIES MEASURED IN A STRATIFIED SAMPLE OF LYMAN LIMIT SYSTEMS AT Z = 3.7

We measured metallicities for 33 z = 3.4–4.2 absorption line systems drawn from a sample of H i-selected-Lyman limit systems (LLSs) identified in Sloan Digital Sky Survey (SDSS) quasar spectra and stratified based on metal line features. We obtained higher-resolution spectra with the Keck Echellette Spectrograph and Imager, selecting targets according to our stratification scheme in an effort to fully sample the LLS population metallicity distribution. We established a plausible range of H i column densities and measured column densities (or limits) for ions of carbon, silicon, and aluminum, finding ionization-corrected metallicities or upper limits. Interestingly, our ionization models were better constrained with enhanced α -to-aluminum abundances, with a median abundance ratio of [ α /Al] = 0.3. Measured metallicities were generally low, ranging from [M/H] = −3 to −1.68, with even lower metallicities likely for some systems with upper limits. Using survival statistics to incorporate limits, we constructed the cumulative distribution function (CDF) for LLS metallicities. Recent models of galaxy evolution propose that galaxies replenish their gas from the low-metallicity intergalactic medium (IGM) via high-density H i “flows” and eject enriched interstellar gas via outflows. Thus, there has been some expectation that LLSs at the peak of cosmic star formation ( z ≈ 3) might have a bimodal metallicity distribution. We modeled our CDF as a mix of two Gaussian distributions, one reflecting the metallicity of the IGM and the other representative of the interstellar medium of star-forming galaxies. This bimodal distribution yielded a poor fit. A single Gaussian distribution better represented the sample with a low mean metallicity of [M/H] ≈ −2.5.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1977

Apollo-Soyuz pamphlet no. 3: Sun, stars, in between

The structure of the sun and its surface temperature and brightness are discussed as background for explaining the ASTP joint experiment to photograph the solar corona from Soyuz while the Apollo spacecraft created an artificial eclipse by blocking out the sun. Stellar spectra, stellar evolution, and the Milky Way galaxy are explored in relation to the MA-083 experiment to survey the sky for extreme ultraviolet sources and background radiation. Interstellar gas and the spectrum of helium are discussed in relation to the MA-088 experiment designed to detect interstellar helium entering the solar system and to measure its density and motion.

Page, L. W.↗
NASA NTRS2019

Correlation between SFR Surface Density and Thermal Pressure of Ionized Gas in Local Analogs of High-redshift Galaxies

We explore the relation between the star formation rate (SFR) surface density (integration of SFR) and the interstellar gas pressure for nearby compact starburst galaxies. The sample consists of 17 green peas and 19 Lyman break analogs (LBAs). Green peas are nearby analogs of Ly alpha emitters at high redshift and LBAs are nearby analogs of Lyman break galaxies at high redshift. We measure the sizes of green peas using Hubble Space Telescope Cosmic Origins Spectrograph near-UV images with a spatial resolution of approximately 0.05 arcsec. We estimate the gas thermal pressure in H II regions by P equals N (sub total)Tk (sub B) approximately or equal to 2n (sub e)Tk (sub B). The electron density is derived using the [S II] doublet at 6716,6731 Angstroms and the temperature is calculated from the [O III] lines. The correlation is characterized by the integration of SFR equals 2.40 times 10 (sup -3) times solar mass per year per square kiloparsec times ((P divided by k (sub B)) divided by (10 ( sup 4) per cubic centimeter times K)) times (sup 1.33). Green peas and LBAs have high integration of SFR up to 1.2 solar masses per year per square kiloparsec and high thermal pressure in the H II region up to P divided by k (sub B) approximating 10 (sup 7.2) K cubic centimeters. These values are at the highest end of the range seen in nearby starburst galaxies. The high gas pressure and the correlation are in agreement with those found instar-forming galaxies at redshift approximating 2.5. These extreme pressures are shown to be responsible for driving galactic winds in nearby starbursts. These outflows may be crucial in enabling Ly alpha and Lyman-continuum to escape.

Galaxies: Evolution↗
NASA NTRS1989

The carbon chemistry of meteorites: Relationships to comets

The carbonaceous meteorites exhibiting alteration by liquid water bear a strong relationship to comets. Not only is their elemental composition closer to solar in relative abundances than other meteorites, they are water rich; and they contain isotopic compositions among refractory and volatile elements indicative of presolar components. Some of these isotopic anomalies occur in organic compounds and carbonaceous grains signifying the presence of discrete and identifiable carbon components derived from interstellar and circumstellar matter. Insofar as comets and meteorites are ultimately formed from interstellar gas and dust, and comets have been subjected to considerably less aqueous and thermal evolution than carbonaceous meteorites, the interstellar imprint should be much stronger and better preserved in comets.

Chang, S.↗
NASA NTRS1996

[A NASA / University Joint Venture in Space Science]

MILAGRO is a water-Cherenkov detector for observing cosmic gamma rays over a broad energy range of 100 GeV to 100 TeV. MILAGRO will be the first detector that has sensitivity overlapping both air-Cherenkov and air-shower detectors. With this detector scientists in the collaboration will study previously observed celestial sources at their known emission energies, extend these observations into a new energy regime, and search for new sources at unexplored energies. The diffuse gamma-radiation component in our galaxy, which originates from interactions of cosmic rays with interstellar gas and photons, provides important information about the density, distribution, and spectrum of the cosmic rays that pervade the interstellar medium. Events in the Compton Gamma Ray Observatory (GRO) are being observed up to about 30 GeV, differing by slightly more than order of magnitude from the low energy threshold of MILAGRO. By looking in coincidence at sources, correlated observations will greatly extend the astrophysics potential of MILAGRO and NASA's GRO. A survey of cosmic-ray observatories is being prepared for scientists and others to provide a resource and reference which describes high energy cosmic-ray research activities around the world. This summary presents information about each research group, such as names of principal investigators, number of persons in the collaboration, energy range, sensitivity, angular resolution, and surface area of detector. Similarly, a survey of gamma-ray telescopes is being prepared to provide a resource and reference which describes gamma-ray telescopes for investigating galactic diffuse gamma-ray flux currently observed in the GeV energy range, but is expected to extend into the TeV range. Two undergraduate students are compiling information about gamma-ray telescopes and high energy cosmic-ray observatories for these surveys. Funding for this project was provided by the Arkansas Space Grant Consortium. Also enclosed Appendix A, B, C, D and E.

Wold, Donald C.↗
DOE OSTI2013

ANOMALOUS DIFFUSE INTERSTELLAR BANDS IN THE SPECTRUM OF HERSCHEL 36. I. OBSERVATIONS OF ROTATIONALLY EXCITED CH AND CH{sup +} ABSORPTION AND STRONG, EXTENDED REDWARD WINGS ON SEVERAL DIBs

Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 A are found in absorption along the line of sight to Herschel 36, the star illuminating the bright Hourglass region of the H II region Messier 8. Interstellar absorption from excited CH{sup +} in the J = 1 level and from excited CH in the J = 3/2 level is also seen. To our knowledge, neither those excited molecular lines nor such strongly extended DIBs have previously been seen in absorption from interstellar gas. These unusual features appear to arise in a small region near Herschel 36 which contains most of the neutral interstellar material in the sight line. The CH{sup +} and CH in that region are radiatively excited by strong far-IR radiation from the adjacent infrared source Her 36 SE. Similarly, the broadening of the DIBs toward Herschel 36 may be due to radiative pumping of closely spaced high-J rotational levels of relatively small, polar carrier molecules. If this picture of excited rotational states for the DIB carriers is correct and applicable to most DIBs, the 2.7 K cosmic microwave background may set the minimum widths (about 0.35 A) of known DIBs, with molecular processes and/or local radiation fields producing the larger widths found for the broader DIBs. Despite the intense local UV radiation field within the cluster NGC 6530, no previously undetected DIBs stronger than 10 mA in equivalent width are found in the optical spectrum of Herschel 36, suggesting that neither dissociation nor ionization of the carriers of the known DIBs by this intense field creates new carriers with easily detectable DIB-like features. Possibly related profile anomalies for several other DIBs are noted.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

What Sets the Slope of the Molecular Kennicutt–Schmidt Relation?

The surface densities of molecular gas, Σ H 2 , and the star formation rate (SFR), Σ * , correlate almost linearly on kiloparsec scales in observed star-forming (non-starburst) galaxies. We explore the origin of the linear slope of this correlation using a suite of isolated galaxy L * simulations. We show that in simulations with efficient feedback, the slope of the Σ * – Σ H 2 relation on kiloparsec scales is insensitive to the slope of the ρ * – ρ relation assumed at the resolution scale. We also find that the slope on kiloparsec scales depends on the criteria used to identify star-forming gas, with a linear slope arising in simulations that identify star-forming gas using a virial parameter threshold. This behavior can be understood using a simple theoretical model based on conservation of interstellar gas mass as the gas cycles between atomic, molecular, and star-forming states under the influence of feedback and dynamical processes. In particular, we show that the linear slope emerges when feedback efficiently regulates and stirs the evolution of dense, molecular gas. As a result we show that the model also provides insights into the likely origin of the relation between the SFR and molecular gas in real galaxies on different scales.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1992

The origin of broad emission lines in the extragalactic giant H II region NGC 2363

High signal-to-noise long-slit spectra have been obtained of the giant H II region NGC 2363 located in the dwarf SBm galaxy NGC 2366. A discovery of low-intensity broad spectral components (FWHM is approximately equal to 40 A or 2400 km/s) in the bright nebular lines H-alpha, H-beta, and forbidden O III is reported. The broad spectral components are detected over a large spatial extent (not less than 500 pc) centered on the nebula. Several mechanisms for broadening nebular lines are explored: stellar winds, Thomson scattering by hot gas, supernova remnants, and superbubble blowout. All mechanisms have problems. Superbubble blowout, which is the only known mechanism capable of accelerating interstellar gas over such a volume of space, does not appear consistent with the physical properties of the H II region NGC 2363 or with the nature of the host galaxy. It is concluded that the broad nebular lines are probably due to very high velocity gas whose origin is, at present, unknown.

Roy, Jean-Rene↗
DOE OSTI2020

The effect of ram-pressure stripping on dwarf galaxies

ABSTRACT Ram-pressure stripping (RPS) is a well observed phenomenon of massive spiral galaxies passing through the hot intracluster medium (ICM) of galaxy clusters. For dwarf galaxies (DGs) within a cluster, the transformation from gaseous to gas-poor systems by RPS is not easily observed and must happen in the outskirts of clusters. In a few objects in close by galaxy clusters and the field, RPS has been observed. Since cluster early-type DGs also show a large variety of internal structures (unexpected central gas reservoirs, blue stellar cores, composite radial stellar profiles), we aim in this study to investigate how ram pressure (RP) affects the interstellar gas content and therefore the star formation (SF) activity. Using a series of numerical simulations, we quantify the dependence of the stripped-off gas on the velocity of the infalling DGs and on the ambient ICM density. We demonstrated that SF can be either suppressed or triggered by RP depending on the ICM density and the DGs mass. Under some conditions, RP can compress the gas, so that it is unexpectedly retained in the central DG region and forms stars. When gas clouds are still bound against stripping but lifted from a thin disc and fall back, their new stars form an ellipsoidal (young) stellar population already with a larger velocity dispersion without the necessity of harassment. Most spectacularly, star clusters can form downstream in stripped-off massive gas clouds in the case of strong RP. We compare our results to observations.

Steyrleithner, P.↗
NASA NTRS2006

Difficulties in Laboratory Studies and Astronomical Observations of Organic Molecules: Hydroxyacetone and Lactic Acid

For the past 35 years, radio astronomy has revealed a rich organic chemistry in the interstellar gas, which is exceptionally complex towards active star-forming regions. New solar systems condense out of this gas and may influence the evolution of life on newly formed planets. Much of the biologically important functionality is present among the some 130 gas-phase molecules found to date, including alcohols, aldehydes, ketones, acids, amines, amides and even the simplest sugar - glycolaldehyde. Still, many unidentified interstellar radio signals remain, and their identification relies on further laboratory study. The molecules hydroxyacetone and lactic acid are relatively small organic molecules, but possess rather complex rotational spectra owing to their high asymmetry. Hydroxyacetone is particularly problematic because it possess a very low barrier to internal rotation, and exhibits strong coupling of the free-rotor states with the overall rotation of the molecule. As in the case of acetamide, a full decomposition method was employed to order the resultant eigenstates onto normal asymmetric top eigenvectors.

Apponi, A. J.↗