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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 397 records · Page 22
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NASA NTRS1989

Does CO trace H2 at high galactic latitude

A CO survey of 342 Infrared Excess Clouds (IRECs) distributed uniformly across the sky is presented. Following comparison of the integrated CO brightness with the 100 micron infrared brightness B(sub 4) obtained from the IRAS data, evidence was found for a threshold in B(sub 4) of 4-5 MJy sr(exp -1) below which CO does not form. Evidence is also presented that the threshold effect can be seen within an individual cloud, providing evidence for a phase transition between atomic and molecular gas. While the main thrust was to examine the CO content of the IRECs, it was also attempted to detect CO toward a number of UV stars so that CO brightness could be correlated with direct measurements of H2 column density and E(B-V). Of the 26 observed stars CO was detected toward 6. It is consistent with the results obtained using infrared data.

Bazell, David↗
NASA NTRS1990

The kinematics and morphology of NGC 520: One, two, or three galaxies

The peculiar galaxy NGC 520 (Arp 157) is often interpreted as an interacting pair of galaxies. The identification of the two bulges and overall morphology of the two galaxies has long been a puzzle which the authors attempt to solve here. New longslit optical spectroscopy and near-infrared images of NGC 520 are presented. These data suggest that the northwest peak is the bulge of one of two galaxies in the system. The other larger bulge is clearly evident in the K band image in the middle of the dust lane. The stellar radial velocity profile in the central 10 seconds of the larger bulge is consistent with counterrotation seen in the molecular gas component. This kinematic subsystem could be the remains of a merged gas-rich irregular.

Stanford, S. A.↗
NASA NTRS1990

On the H2 line emission from NGC 6240 and other starburst galaxies

The origin of the powerful H2 line emission from the starburst galaxy NGC 6240 is considered. It is argued that shock waves do not appear to be able to account directly for the observed H2 emission. A new scenario is proposed in which the emission originates in molecular gas which has been abruptly exposed to intense X-ray irradiation. The required X-rays could come from a variety of sources, including SNRs or high-velocity collisions between clouds.

Draine, B. T.↗
NASA NTRS1990

CO observations of galaxies 1985-1989

This catalog lists all publications containing new observations of CO isotopes in galaxies that have appeared since the submission of Verter (1985) and before the end of 1989. For each publication the number and nature of the observations are summarized. Condensations of this information can be used to evaluate the current status and direction of observational research on molecular gas in external galaxies.

Verter, Frances↗
NASA NTRS1991

High-resolution CO observations of luminous infrared galaxies with large L(ir)/L(B) ratios - IRAS 10173 + 0828, Zw 049.057, IRAS 17208 - 0014

The Owens Valley mm-wave interferometer has been used for high-resolution (about 3-7 arcsec) mapping of CO emission in three luminous IRAS galaxies: IRAS 17208 - 0014, 15107 + 0724, and IRAS 10173 + 0828. These galaxies are among the most extreme, in terms of their L(ir)/L(B) ratio, for objects in the IRAS Bright Galaxy Surveys. The CO emission detected in the three galaxies originates from a single region centered on the IRAS emission peak. These observations have shown that these galaxies have similar values for the global L(ir)/M(H2) ratio, for the surface density of molecular gas in their central regions and for the extinction toward the nucleus (above 300 mag). A high L(ir)/L(B) ratio seems to be a good predictor for both a high global L(ir)/M(H2) ratio and very large central H2 surface densities.

Planesas, P.↗
NASA NTRS1991

The rate and efficiency of high-mass star formation along the Hubble sequence

Data obtained with IRAS are used to compare and contrast the global star formation rates for a galactic sample which represents essentially all known noninteracting spiral and lenticular galaxies within 40 Mpc. The distribution of 60 micron luminosity is similar for spirals of types Sa-Scd inclusively, although the luminosities of the very early and very late types are, on average, one order of magnitude lower. High-mass star formation rates are similar for early, intermediate, and late type spirals, and the average high-mass star formation rate per unit molecular gas mass is independent of type for spiral galaxies. A remarkable homogeneity exists in the high-mass star-forming capabilities of spiral galaxies, particularly among the Sa-Scd types. The Hubble sequence is therefore not a sequence in the present-day rate or production efficiency of high-mass stars.

Devereux, Nicholas A.↗
NASA NTRS1991

A second outflow from L1551/IRS 5?

The detection of previously unreported high-velocity emission in the L1551 moleculaar cloud is reported. This emission may represent high-velocity molecular gas deflected out of the IRS 5 outflow or may indeed represent another independent outflow whose origin is IRS 5 or L1551NE. This region is revealed to be far more complex than previously suspected.

Moriarty-Schieven, G. H.↗
NASA NTRS1991

The Berkeley tunable far infrared laser spectrometers

A detailed description is presented for a tunable far infrared laser spectrometer based on frequency mixing of an optically pumped molecular gas laser with tunable microwave radiation in a Schottky point contact diode. The system has been operated on over 30 laser lines in the range 10-100/cm and exhibits a maximum absorption sensitivity near one part in a million. Each laser line can be tuned by + or - 110 GHz with first-order sidebands.

Blake, G. A.↗
NASA NTRS1992

Near-infrared images and color maps of Arp 220

Near-infrared images (1.3-3.7 microns) are presented for the nuclear region of Arp 220. Color maps in J - H and H - K reveal steep gradients, and the two nuclei previously detected at 20 cm and 2.2 microns appear on the J - H image as peaks separated by 1 arcsec. Hot dust emission (T about 1000 K) at 3.7 microns and extremely red J - H and H - K colors are found for both nuclei. The increasingly red color approaching the center of the galaxy are explained most naturally by a mixture of extinction and emission by increasing amounts of hot dust. The near-infrared emission is consistent with a circumnuclear starburst extending to a radius of about 1.5 kpc from the nuclei; further from the center the colors are consistent with a normal late-type stellar population. Inside a radius of 1 kpc the color maps show a NE-SW elongation that aligns with the concentration of molecular gas seen in CO images. The observed 3.7-micron luminosity, when corrected for nuclear extinction determined by 10-micron silicate absorption measurements and normalized by the bolometric luminosity, is consistent with UV-excess quasars and is about 10 times greater than that found in infrared luminous starburst galaxies.

Mazzarella, J. M.↗
NASA NTRS1991

Star formation - Observations

Star-formation theories can be tested in light of observational evidence of star formation scenarios on the scales of galaxies, Galactic molecular clouds, and individual star-formation regions. Attention is presently given to the relative importance of atomic and molecular gas in star formation, the role of stimulated star formation, the existence of disks around stars undergoing formation, and the effect of spiral density waves. Attention is given to the processes of cloud cores and core collapse. The development of a theory of binary star formation will require the resolution of the issue as to the presence of a disk in the formation scenario, as indicated by the observation of spectral lines at higher resolutions.

Evans, Neal J., II↗
NASA NTRS1993

Feeding IC 342: The nuclear spiral of a starburst galaxy

IC 342 is a large nearby (1.8 Mpc, Turner and Hurt, 1991, hereafter T&H) spiral galaxy undergoing a moderate nuclear starburst. T&H have previously mapped the inner arcminute in CO-13(1-0) using the Owens Valley Millimeter Interferometer and found evidence that the nuclear molecular gas takes the form of spiral arms in a density wave pattern. They suggest that radial streaming along the arms may channel gas from the exterior of the galaxy into the nucleus, feeding the starburst. We have mapped the CO-12(1-0) emission of the inner 2 kpc of IC 342 at 2.8 inch resolution using the Owens Valley Radio Observatory (OVRO) Millimeter Interferometer. The greater sensitivity of CO-12 observations has allowed us to trace the spiral pattern out to a total extent of greater than 1 kpc. The CO-12 observations extend considerably the structure observed at CO-13 and offer further evidence that a spiral density wave may extend from the disk into the nucleus of IC 342.

Levine, D.↗
NASA NTRS1993

Is a local bar a good place to find a companion? The near infrared morphology of Maffei 2

Maffei 2 is one of the closest large spiral galaxies lying just beyond the Local Group. It would probably be one of the most heavily studied galaxies in the sky were it not for the approximately 5 magnitudes of visual extinction resulting from its position behind the Galactic plane. It is the site of a burst of nuclear star formation indicated by strong infrared and radii continuum emission. Interferometric maps of CO-12 and CO-13 emission indicate that star formation is associated with a barlike structure consisting of arms of molecular gas that extend from within approximately 50 pc of the dynamical center out to a radius of at least 500 pc. HI maps have shown the galaxy to have an angular extent of approximately 15 feet and a neutral gas mass typical of a large spiral galaxy.

Hurt, Robert L.↗
NASA NTRS1993

Infrared fine-structure line diagnostics of shrouded active galactic nuclei

Far-infrared spectroscopy of celestial objects will improve dramatically in the coming decade, allowing astronomers to use fine-structure line emission to probe photoionized regions obscured in the optical band by thick clouds of dust. The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H(beta) in luminosity. This paper shows how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of (Ne V) emission in particular will distinguish shrouded AGN's from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

Voit, G. M.↗
NASA NTRS1993

A (12)CO J = 2-1 map of the disk of Centaurus A: Evidence for large scale heating in the dust lane

Centaurus A (NGC 5128) is a nearby (3 Mpc) elliptical galaxy with a prominent dust lane, extensive radio lobes, and a compact radio continuum source, suggestive of nuclear activity. As a consequence of its peculiar morphology, this merger candidate has been the subject of much attention, particularly at optical wavelengths. Unfortunately the high and patchy extinction in the disk, aggravated by the warped structure of the dust lane, has severely hindered investigations into the properties of the interstellar medium, particularly with regard to the extent of star formation. Here we present a map of the (12)CO J = 2-1 line throughout the dust lane which, when combined with a previously measured (12)CO J = 1-0 map and data on molecular absorption lines observed against the compact non-thermal continuum source, offers insight into the excitation conditions of the molecular gas.

Wild, W.↗
NASA NTRS1992

Infrared fine-structure line diagnostics of shrouded active galactic nuclei

The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H-beta in luminosity. We show how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of Ne v emission in particular will distinguish shrouded AGNs from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

Voit, G. M.↗
NASA NTRS1992

Mid-infrared rotational line emission from interstellar molecular hydrogen

The line emission from the v = 0-0 S(0), S(2), and S(3), and the v = 1-0 and v = 2-1 S(1) transitions of molecular hydrogen in clouds exposed to high FUV fluxes and in shocks is modeled. Particular attention is given to the lowest pure rotational H2 transitions at 20 and 17 microns, respectively. It is found that, in photodissociation regions (PDRs), the emission comes from warm (greater than about 100 k) molecular gas, situated at optical depths greater than about 1, beyond the hot atomic surface layer of the clouds. For FUV fields, G0 = 1000 to 100,000 times the average interstellar field densities n = 10 exp 3 - 10 exp 7/cu cm, the typical line intensities are in the range 10 exp -6 to 10 exp -4 ergs/s sq cm sr. The predictions for the line intensities from both C-type and J-type shock models are compared. The results are applied to recent observations of the 0-0 S(1) transition in both the PDR and the shocked gas in Orion.

Burton, Michael G.↗
NASA NTRS1992

Ultraviolet emission in the dark cloud toward HD 62542

We have obtained low resolution IUE short wavelength spectra at several positions within a ridge of molecular gas within the Gunn Nebula. Optical absorption line measurements toward HD 62542 indicate moderately high densities within the ridge. The physical appearance of the ridge, along with H-alpha and IRAS images of the nebula, suggest that winds and radiation from Gamma Vel and Zeta Pup are heating and compressing the ridge. The IUE spectra revealed faint C II and C III emission at one position, while C IV was weakly detected at another. The former are interpreted as arising in photoionized gas while the latter probably arises in a shocked wind striking the ridge. No detections were made at other positions in the ridge.

O'Donnell, James E.↗
NASA NTRS1993

The observation of correlated velocity structures in a translucent molecular cloud and implications for turbulence

We present a formaldehyde map of the translucent high-latitude molecular cloud MBM 16. The molecular gas traced by the H2CO is located in spatially distinct large structures that exhibit velocity coherence on a scale of 0.5 pc. These structures are not pressure-confined and are probably not self-gravitating. They may be transient structures. If so, we suggest that they are produced by shear flows whose scale length is of order the size of the cloud.

Magnani, L.↗