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At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

VERY LARGE ARRAY MAPPING OF THE CO(1-0) LINE IN SMM J14011+0252

We present high-resolution CO(1-0) observations of the lensed submillimeter galaxy (SMG) SMM J14011+0252 at z = 2.6. Comparison to the previously detected CO(3-2) line gives an intensity ratio of r {sub 3,1} = 0.97 {+-} 0.16 in temperature units, larger than is typical for SMGs but within the range seen in the low-z ultraluminous infrared galaxy population. Combining our new data with previous mid-J CO observations, we perform a single-phase large velocity gradient (LVG) analysis to constrain the physical conditions of the molecular gas. Acceptable models have significant degeneracies between parameters, even when we rule out all models that produce optically thin emission, but we find that the bulk of the molecular gas has T {sub kin} = 20-60 K, n{sub H{sub 2}}{approx}10{sup 4}-10{sup 5} cm{sup -3}, and N {sub CO}/{Delta}v = 10{sup 17.00{+-}0.25} cm{sup -2} km{sup -1} s. For our best-fit models to self-consistently recover a typical CO-to-H{sub 2} abundance and a plausible degree of virialization, the local velocity gradient in the molecular gas must be substantially larger than its galaxy-wide average. This conclusion is consistent with a scenario in which SMM J14011+0252 has a fairly face-on orientation and a molecular interstellar medium composed of many unresolved clouds. Using previous H{alpha} observations, we find that SMM J14011+0252 has a spatially resolved star formation rate versus molecular gas surface density relation inconsistent with those of 'normal' local star-forming galaxies, even if we adopt a local 'disk-like' CO-to-H{sub 2} conversion factor as motivated by our LVG analysis. This discrepancy supports the inference of a star formation relation for high-z starbursts distinct from the local relation that is not solely due to differing choices of gas mass conversion factor.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

Multi-spectral Observations of the Star Formation: the Role of Far Infrared Photometry

The study and analysis of complex astrophysical process requires a multispectral approach employing many of the tools of modern astronomy. The study of the interaction of early type stars with the interstellar medium is an example of this point. Two examples of multi-spectral studies of individual objects are reviewed. The predominent theme is the combination of high resolution far infrared photometry, radio images and millimeter-wave spectroscopy with the radio sensitive to the ionization, the millimeter-wave lines showing the structure and excitation of the gas and the far infrared providing a picture of the energetics of the dust which connects the star to the interstellar medium. Multispectral observations of FIRSSE and IRAS objects are discussed.

Schwartz, P. R.↗
DOE OSTI2012

MONTE CARLO CALCULATION OF THE TRANSLATIONAL RELAXATION OF SUPERTHERMAL H ATOMS IN THERMAL H{sub 2} GAS

A simple and reliable method to study the translational relaxation of 'hot' H atoms following their production by chemical mechanisms is proposed. The problem is relevant to interstellar medium, shocks, photospheres, and atmospheric entry problems. It is shown that the thermalization of H atoms can be conveniently studied by the Monte Carlo method, including the thermal distribution of background molecules, and sets the basis for further investigations. The transport cross section is determined by the inversion of transport data. The collision density of H atoms in H{sub 2} gas is also calculated and discussed in the context of simple theories. The application of the results to astrophysical problems is outlined, including numerical results for the reaction H + H{sub 2}O {yields} H{sub 2} + OH. An approximate analytical formula for the reaction probability during H atom thermalization is proposed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

From the laboratory to space: unveiling isomeric diversity of C 5 H 2 in the reaction of tricarbon (C 3 , X 1 Σ g + ) with the vinyl radical (C 2 H 3 , X 2 A′)

By connecting laboratory dynamics with cosmic observables, this work highlights the critical role of reactions between highly reactive species in shaping the molecular inventory of the interstellar medium and opens new windows into the spectroscopically elusive corners of astrochemical complexity. The gas phase formation of distinct C 5 H 2 isomers is explored through the bimolecular reaction of tricarbon (C 3 , X 1 Σ + g ) with the vinyl radical (C 2 H 3 , X 2 A′) at a collision energy of 44 ± 1 kJ mol −1 employing the crossed molecular beam technique augmented by electronic structure and Rice–Ramsperger–Kassel–Marcus (RRKM) calculations. This barrierless and exoergic reaction follows indirect dynamics and is initiated by the addition of tricarbon to the radical center of the vinyl radical forming a Cs symmetric doublet collisional complex (CCCCHCH 2 ). Subsequent low-barrier isomerization steps culminate in the resonantly stabilized 2,4-pentadiynyl-1 radical (CHCCCCH 2 ), which decomposes via atomic hydrogen loss. Statistical calculations identify linear, triplet pentadiynylidene (p2, X 3 Σ − g ) as the dominant product, while singlet carbenes ethynylcyclopropenylidene (p1, X 1 A′), pentatetraenylidene (p3, X 1 A 1 ), and ethynylpropadienylidene (p4, X 1 A′) are formed with lower branching ratios. The least stable isomer, 2-cyclopropen-1-ylidenethenylidene (‘eiffelene’; p5, X 1 A 1 ), remains thermodynamically feasible, but exhibits negligible branching ratios. Two isomers detected in TMC-1 to date (p1 and p3) possess significant dipole moments making them amenable to radio telescopic observations, whereas linear pentadiynylidene (p2; D ∞h ) is only traceable via infrared spectroscopy or through its cyanopentadiynylidene derivative (HCCCCCCN). This study highlights the isomer diversity accessed in the low temperature hydrocarbon chemistry of barrierless and exoergic bimolecular reactions involving two unstable, reactants in cold molecular clouds.

Medvedkov, Iakov A. [University of Hawai'i at Mano↗
DOE OSTI2013

EXPLORING IO'S ATMOSPHERIC COMPOSITION WITH APEX: FIRST MEASUREMENT OF {sup 34}SO{sub 2} AND TENTATIVE DETECTION OF KCl

The composition of Io's tenuous atmosphere is poorly constrained. Only the major species SO{sub 2} and a handful of minor species have been positively identified, but a variety of other molecular species should be present, based on thermochemical equilibrium models of volcanic gas chemistry and the composition of Io's environment. This paper focuses on the spectral search for expected yet undetected molecular species (KCl, SiO, S{sub 2}O) and isotopes ({sup 34}SO{sub 2}). We analyze a disk-averaged spectrum of a potentially line-rich spectral window around 345 GHz, obtained in 2010 at the APEX 12 m antenna. Using different models assuming either extended atmospheric distributions or a purely volcanically sustained atmosphere, we tentatively measure the KCl relative abundance with respect to SO{sub 2} and derive a range of 4 × 10{sup –4}-8 × 10{sup –3}. We do not detect SiO or S{sub 2}O and present new upper limits on their abundances. We also present the first measurement of the {sup 34}S/{sup 32}S isotopic ratio in gas phase on Io, which appears to be twice as high as the Earth and interstellar medium reference values. Strong lines of SO{sub 2} and SO are also analyzed to check for longitudinal variations of column density and relative abundance. Our models show that, based on their predicted relative abundance with respect to SO{sub 2} in volcanic plumes, both the tentative KCl detection and SiO upper limit are compatible with a purely volcanic origin for these species.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

X-ray scaling relations of “core” and “coreless” E and S0 galaxies

We have re-examined the two X-ray scaling relations of early-type galaxies (ETGs), L{sub X,GAS}–L{sub K} and L{sub X,GAS}–T{sub GAS}, using 61 ATLAS{sup 3D} E and S0 galaxies observed with Chandra (including ROSAT results for a few X-ray bright galaxies with extended hot gas). With this sample, which doubles the number of ETGs available for study we confirm the strong, steep correlations reported by Boroson et al. Moreover, the larger sample allows us to investigate the effect of structural and dynamical properties of ETGs in these relations. Using the sub-sample of 11 “genuine” E galaxies with central surface brightness cores, slow stellar rotations and old stellar populations, we find that the scatter of the correlations is strongly reduced, yielding an extremely tight relation of the form L{sub X,GAS} ∼ T{sub GAS}{sup 4.5±0.3}. The rms deviation is only 0.13 dex. For the gas-rich galaxies in this sample (L{sub X,GAS} > 10{sup 40} erg s{sup −1}), this relation is consistent with recent simulations for velocity dispersion supported E galaxies. However, the tight L{sub X,GAS}–T{sub GAS} relation of genuine E galaxies extends down into the L{sub X} ∼ 10{sup 38} erg s{sup −1} range, where simulations predict the gas to be in outflow/wind state, with resulting L{sub X} much lower than observed in our sample. The observed correlation may suggest the presence of small bound hot halos even in this low luminosity range. At the high luminosity end, the L{sub X,GAS}–T{sub GAS} correlation of core elliptical galaxies is similar to that found in samples of cD galaxies and groups, but shifted down toward relatively lower L{sub X,GAS} for a given T{sub GAS}. In particular cDs, central dominant galaxies sitting at the bottom of the potential well imposed by the group dark matter, have an order of magnitude higher L{sub X,GAS} than our sample core galaxies for the same L{sub K} and T{sub GAS}. We suggest that enhanced cooling in cDs, which have higher hot gas densities and lower entropies, could lower T{sub GAS} to the range observed in giant Es; this conclusion is supported by the presence of extended cold gas in several cDs. Instead, in the sub-sample of coreless ETGs—these galaxies also tend to show stellar rotation, a flattened galaxy figure and rejuvenation of the stellar population—L{sub X,GAS} and T{sub GAS} are not correlated. The L{sub X}−T{sub GAS} distribution of coreless ETGs is a scatter diagram clustered at L{sub X,GAS} < 10{sup 40} erg s{sup −1}, similar to that reported for the hot interstellar medium (ISM) of spiral galaxies, suggesting that both the energy input from star formation and the effect of galactic rotation and flattening may disrupt the hot ISM.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1976

Radio detections of cometary molecular transitions: A review

Radio detections of CH, OH, HCN, CH3CN, and several unidentified species in comet Kohoutek and the detection of H2O emission from comet Bradfield are discussed in terms of the similarities and differences between cometary molecules and interstellar molecules. Emphasis is placed on excitation and chemistry. The observed projected densities and resulting gas production rates are considered along with the feasibility of future radio molecular observations of comets.

Snyder, L. E.↗
NASA NTRS1979

Interstellar bullets - H2O masers and Herbig-Haro objects

The paper considers the energy input to H2O masers in a dense molecular cloud and analyzes the response time scales for both collisional and radiative pump models. Specific mechanisms for magnetic energy input are given. The evolution of dense H2O maser clouds is studied in the environment of a young pre-main-sequence star that has developed an appreciable supersonic wind. It is shown that compact clouds can be ejected at high velocity to distances of order 1 pc. It is suggested that these clouds (referred to as interstellar bullets) might explain the phenomena of Herbig-Haro objects and high-velocity gas motions observed near compact infrared objects.

Norman, C.↗
NASA NTRS1980

The diffuse UV background

The diffuse radiation field in the UV (900-3,000 A) affects the structure of galactic molecular clouds and conveys important information concerning the physical characteristics and spatial distribution of gas and dust in the universe. Continuum emission in this range is probably dominated by interstellar dust scattering in our galaxy. For view directions and angular resolutions allowing observations in the rifts between galactic dust clouds, the background due to the integrated light of spiral galaxies may be detected, providing important information on their structure and evolution. The redshifted emission from an intergalactic medium may be observable in the regions between nearby bright galaxies. Present observations provide weak constraints on the radiation field required to ionize the intergalactic medium at the level required by the Gunn-Peterson test.

Paresce, F.↗
NASA NTRS1984

Spiral structure and star formation. II - Stellar lifetimes and cloud kinematics

The reliability studies using continuum gas dynamical calculations becomes questionable in connection with the apparent clumpiness of the Galaxy's interstellar medium (ISM). Roberts and Hausman (1984) have, therefore, presented a detailed model of a disk galaxy in which the ISM consists entirely of 'cloud particles', which orbit ballistically in the galaxy's gravitational field, collide inelastically with one another, and give birth to and subsequently interact with young star associations. The effects of changing the clouds's collisional mean free path have been examined, and the variations in the young star system's spiral morphology have been explored. The present investigation is concerned with a further study of this clumpy, cloudy ISM model, taking into account longer mean free path models likely to be appropriate for systems of molecular clouds. Attention is also given to the kinematics of clouds as they orbit under the influence of galactic gravity, collisions, and supernova remnants.

Hausman, M. A.↗
NASA NTRS1987

Element abundances in the interstellar atomic material

In the interstellar medium, a significant fraction of the free atoms for elements heavier than helium must have condensed into solids, in the form of small, interstellar dust grains. Observations of optical and ultraviolet absorption lines in the spectra of hot stars indicate that the depletions below the cosmic abundances of various elements range from almost none at all to a factor of 0.0001 and seem to be enhanced along lines of sight with higher mean density. Other methods of measuring abundances confirm the absorption line results. The available evidence supports the notion that the grains form in both the atmospheres of cool stars and in dense interstellar clouds, and they are destroyed by shocks which frequently pass through the low density gas.

Jenkins, Edward B.↗
NASA NTRS1988

Formation of particulates by ion bombardment of cryogenic ice mixtures

An analysis of the particulates which form upon the bombardment of a gaseous mixture reflecting cosmic molecular abundances with H2(+) ions accelerated at 350 keV. The model of Black and Dalgarno (1977) for the Zeta Oph cloud and an observational determination of the interstellar Ar abundances (Simpson et al., 1986) are used to determine the abundances of the gas mixture. The characteristics of the resulting residue are examined, including photographs and absorbance spectra. The possible astrophysical implications of the experiment are discussed.

Wdowiak, T. J.↗
NASA NTRS1991

Probing the Galactic halo along the 3C 273 sight line using IUE

High-resolution spectra of the QSO 3C 273 were obtained in 1989 and added to two spectra recorded in 1982. The coadded spectra represent 600,000 s of integration at a resolution of 30 km/s from 1200 to 2000 A. The line of sight passes through the Virgo Cluster the entire halo of the Milky Way, at Galactic latitude b = 64 deg, and foreground X-ray-emitting material from local disturbed gas. The observed equivalent width of Galactic C IV is greater than the equivalent width of C II, a situation that is uncommon in local gas but is often found in QSO absorption line systems. The lines of C IV, Al III, and Si IV may arise in an extended halo or may be associated with local disturbed gas in a radio loop. The remaining detected species (H I, C II, Si II) arise predominately from the local gas. Most of the gas is probably within 5 kpc, but no firm conclusion is reached. Possible detection of interstellar absorption due to the Virgo Cluster is discussed.

Burks, Geoffrey S.↗
NASA NTRS1993

On the origin of the Z-shaped narrow-line region in the Seyfert galaxy NGC 3516

A kinematic study has been carried out of the line-emitting gas in the Seyfert galaxy NGC 3516. The existence of two curved filaments in the central 2.5 kpc of this galaxy, which give Z-shaped appearance to its NLR. A precessing twin-jet model in which the line-emitting material is entrained by a precessing radio jet and kept ionized by the nuclear ionization field can explain the kinematic data of the brightest emission rather well. If this model is valid, this would make NGC 3516 the least luminous known active galaxy with a precessing jet. An alternative scenario assumes that the curved inner filaments represent gas entrained by a radio jet which is deflected by ram pressure from the rotation interstellar medium of the galaxy.

Veilleux, Sylvain↗
NASA NTRS2000

JSC Stardust Curation Team

STARDUST, a NASA Discovery-class mission, is the first to return samples from a comet. Grains from comet Wild 2's coma-the gas and dust envelope that surrounds the nucleus-will be collected as well as interstellar dust. The mission which launched on February 7, 1999 will encounter the comet on January 10, 2004. As the spacecraft passes through the coma, a tray of silica aerogel will be exposed, and coma grains will impact there and become captured. Following the collection, the aerogel tray is closed for return to Earth in 2006. A dust impact mass spectrometer on board the STARDUST spacecraft will be used to gather spectra. of dust during the entire mission, including the coma passage. This instrument will be the best chance to obtain data on volatile grains, which will not be well-collected in the aerogel. The dust impact mass spectrometer will also be used to study the composition of interstellar grains. In the past 5 years, analysis of data from dust detectors aboard the Ulysses and Galileo spacecraft have revealed that there is a stream of interstellar dust flowing through our solar system. These grains will be captured during the cruise phase of the STARDUST mission, as the spacecraft travels toward the comet. The sample return capsule will parachute to Earth in February 2006, and will land in western Utah. Once on y the ground, the sample return capsule will be placed into a dry nitrogen environment and flown to the curation lab at JSC.

Zolensky, Michael E.↗
NASA NTRS2001

Interfaces in N51D

We obtained Far Ultraviolet Spectroscopic Explorer (FUSE) observations of four stars in the superbubble N51D in order to use the OVI interstellar absorption lines to study the interface between the hot (10(exp 6) K) interior gas and the surrounding warm (10(exp 4) K) dense shell.

Chu, You-Hua↗
NASA NTRS1996

Observations of Ices in Star-Forming Regions

Ground-based, air-borne, and space-based infrared spectra of protostars show prominent absorption features at 3.08, 3.54, 4.23, 4.67, 4.9, 6.0, 6.85, and 7.6 micrometers. These features are due to simple molecules such as H2O, CH3OH, CO2, CO, OCS, and CH4 in accreted icy grain mantles. These studies have revealed the presence of several independent ice components, often along the same line of sight. The observations and proposed identifications will be reviewed with the emphasis on recent results from ISO and on the organic inventory of interstellar ices. These molecular grain mantles are thought to form by accretion and reaction of gas phase species on a grain surface. Observed abundances will be compared with theoretical calculations and the important grain surface routes will be delineated. The importance of the 'diffusion' limit will be emphasized.

Tielens, Alexander G. G. M.↗