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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 NTRS1993

A Hubble Space Telescope planetary camera view of giant H II regions - The Wolf-Rayet content of NGC 595 and NGC 604 in M33

We present images of NGC 595 and NGC 604, the most massive giant H II regions in M33, obtained with the Planetary Camera aboard the HST in order to study their WR population. Fourteen WR and/or Of candidates are detected in NGC 604, and eleven in NGC 595. All previously claimed 'superluminous' WR stars are found to be tight (diameter less than 3 pc) stellar aggregates containing one (or sometimes more) normal WR star. As suspected from ground-based data, the WR/O number ratio is significantly higher in NGC 595 (about 0.3) than in NGC 604 (about 0.1). The WR stars may be major contributors to the output of mechanical power and energy into the interstellar medium in both clusters. Over the observable initial mass range, the initial mass functions (IMFs) have similar slopes. These IMFs are somewhat flatter than those generally derived for massive stars in the Galaxy or the Magellanic Clouds.

Drissen, Laurent↗
NASA NTRS1993

Broad band X-ray Telescope observations of the hot interstellar media in NGC 1399 and NGC 4472

We present our analysis and interpretation of spatially resolved X-ray spectroscopy of the elliptical galaxies NGC 1399 and NGC 4472 obtained with the Broad Band X-Ray Telescope. The X-ray emission from both galaxies is dominated by thermal emission from a hot interstellar medium. The temperature of the plasma in NGC 1399 is 1.0-1.2 keV with a mild positive temperature gradient; for NGC 4472 the average temperature is 0.7-1.0 keV. The temperature of NGC 1399, when combined with other X-ray and optical data, implies that, if the gas is gravitationally confined, about 70 percent of the mass inside a radius of about 8.6 arcmin (38 kpc) is nonluminous. The derived metallicities and metallicity gradients are consistent with optically determined stellar metallicities, and allow surprisingly small upper limits to be placed on Type Ia supernovae rates in both galaxies. The implications of this for the gasdynamical evolution of the two galaxies are discussed. Limits on the oxygen-to-iron ratio and the line-of-sight column density are derived. There is a possible detection of cold gas in the line of sight to NGC 1399 that exceeds the Galactic value. Constraints on the contribution from a harder spectral component are placed, and likely candidates for the origin of this secondary component are evaluated.

Serlemitsos, P. J.↗
NASA NTRS1994

The Reddening law outside the local group galaxies: The case of NGC 7552 and NGC 5236

The dust reddening law from the UV to the near-IR for the extended regions of galaxies is here derived from the spectral distributions of the starburst spiral galaxies NGC 7552 and NGC 5236. The centers of these galaxies have similar absorption and emission line spectra, differing only if the strength of their interstellar lines and in the continuum distribution, with NGC 7552 appearing more reddened than NGC 5236. The disk of NGC 7552 is more inclined, and there is evidence that its center is observed through additional foreground dust and gas clouds, as compared to the center of NGC 5236. While the galaxies can be expected to have similar dust content, they are known to have different dust path lengths to our line of sight. Therefore, differences in the shape of the spectra can be attributed mainly to the effects of dust, allowing us to probe for the first time the properties of the reddening law outside the local group of galaxies. We derive the reddening law based on the optical depth of the emission line of H Alpha and H Beta and also based on the continuum distribtuion. We find that the optical depth from the emission line regions are about twice the optical depth of the continuum regions. Thus, dereddening a starburst galaxy by scaling the Milky Way reddening laws to optical depths obtained from the H Alpha/H Beta line ratio overcompensates for the effect of dust.

Kinney, Anne L.↗
NASA NTRS1994

Soft X-ray observations of the interacting galaxies NGC 1808 and NGC 1792

The soft X-ray emission from both galaxies NGC 1808 and NGC 1792, which we investigated using the ROSAT HRI and Position Sensitive Proportional Counter (PSPC), comes most probably from X-ray binaries and/or from hot ionized gas in powerful supernovae and supernova remnants. The distribution of the soft X-ray emission in NGC 1808, which is very well correlated with the distribution of 'radio knots' in the central starburst, suggests that hot gas dominates the emission in the ROSAT band. This is consistent with the results of PSPC observations by Junkes et al. The total soft X-ray luminosity in the ROSAT band of NGC 1808 of 1.2 x 10(exp 41) ergs/s is relatively high compared with other nearby starburst galaxies. Soft X-ray emission of diffuse hot ionized gas that is associated with the outflow traced by the conspicuous dust filaments protruding from the plane has been detected. Its luminosity in the ROSAT band is greater than or equal to 3 x 10(exp 39) ergs/s, i.e., several percent of the total soft X-ray luminosity. Thus, NGC 1808 is another example for a 'superwind' galaxy. The soft X-ray radiation from NGC 1792 is more likely to be dominated by a population of high-mass X-ray binaries or young powerful supernovae which are associated with the high-level star formation going on in the very prominent H II regions along its spiral arms, with possibly an additional contribution of diffuse hot ionized gas. The soft X-ray luminosities of individual sources lie in the range of 5 x 10(exp 38) to 2.7 x 10(exp 39) ergs/s, thus exceeding by far the Eddington luminosity of an accreting neutron star. The peaks of some of these soft X-ray luminous sources are offset with respect to the H II regions by a few hundred parsecs. Accordingly, if the soft X-ray sources should originate from the H II regions, their relative velocities with respect to the ambient medium have to be as high as approximately 100 km/s.

Dahlem, Michael↗
NASA NTRS1974

Observations of the infrared radiation from the nuclei of NGC 1068 and NGC 4151

Data resulting from monitoring the flux of radiation at 11 microns from NGC 1068 and NGC 4151 are presented. There is some evidence for changes of flux of 50% on a time scale of approximately 100 days from NGC 4151. This evidence is suggestive but not compelling. Limits are set on the possible change of the 11-micron flux from NGC 1068. The energy distribution of radiation from NGC 1068 between 8 and 13 microns has been shown to have no spectral features within the accuracy and resolution of our measurement. This is in contrast to energy distributions observed from galactic sources in which the source of energy is generally interpreted as thermal reradiation from grains.

Stein, W. A.↗
NASA NTRS1987

CCD photometry of globular cluster core structure. I - NGC 6388, NGC 6624, and M15: One flat core and two cusps

The first results of a major survey of globular cluster core structure are reported. Surface brightness profiles for three clusters are presented: one with a normal flat core profile (NGC 6388), and two with central cusps (NGC 6624 and M15). The profiles are fitted with both seeing-convolved King models and seeing-convolved power laws. A King model provides a reasonable fit to the entire profile of NGC 6388, but there are no acceptable King profiles for NGC 6624 and M15. For these two clusters, a seeing-convolved power law provides a good fit to the inner part of the profile, while a King model gives a good fit to the outer part of the profile. The interpretation of the measured power-law slopes of the central surface brightness cusps of NGC 6624 and M15 are discussed in terms of models for core collapse in a multicomponent cluster.

Lugger, Phyllis M.↗
NASA NTRS1988

Two compact planetary nebulae of moderate excitation - NGC 6565 (3-4.5 deg) and NGC 6644 (8-7.2 deg)

Data obtained with an image-tube scanner at the 3-m Shane telescope are combined with IUE data to obtain plasma diagnostics and chemical compositions for two planetary nebulae of moderately high excitation. Theoretical nebular models were calculated using stellar fluxes given by Husfeld et al. (1984) for T(asterisk) = 85,000 K, log g = 4.72, and elemental abundances were obtained by fitting theoretical to observed line intensities and also by using the model to determine ionization correction factors to be applied to observed ionic concentrations. Although C appears to be about 1.5 times as abundant in NGC 6644 as in NGC 6565, N, O, Ne, S, Cl, and Ar are depleted by factors ranging from 2 to 6 in NGC 6644 as compared to NGC 6565. The high-velocity object, NGC 6644, was evidently made from a less metal-rich mixture than the sun.

Aller, Lawrence H.↗
NASA NTRS1994

Detection of CO J = 2 goes to 1 emission from the polar rings of NGC 2685 and NGC 4650A

We report the detection of the J = 2 goes to 1 (230 GHz) line of carbon monoxide in the polar rings of the galaxies NGC 2685 and NGC 4650A, and we use the results in a simple analysis of the composition of the neutral interstellar medium therein. Only 17%-35% of the gas mass of the NGC 4650A ring is provided by molecular clouds, perhaps consistent with the conventional picture of the origin of polar rings in the capture of a dwarf galaxy or tidal mass transfer from a spiral galaxy. The polar ring of NGC 2685, however, is quite rich in molecular matter, with an H2 mass greater than the neutral atomic hydrogen mass. Such a composition may be difficult to explain with the picture that applies to NGC 4650A.

Watson, Dan M.↗
NASA NTRS1994

Hubble Space Telescope imaging of super-star clusters in NGC 1569 and NGC 1705

We examine the structural properties of three super-star clusters in the nearby, H I-rich galaxies NGC 1569 and NGC 1705. The clusters, which have total absolute V magnitudes between -13.3 and -14.1, appear to be point sources on ground-based images but are partially resolved in new images obtained with the Hubble Space Telescope (HST) Planetary Camera. From deconvolved V- and I-band images we find that the three clusters have very compact cores with extended halos that are partially resolved into individual stars. Using new distances to the galaxies derived from color-magnitude diagrams for field stars, we find that the half-light radii are 2.2-3.4 pc. The cluster in NGC 1705 is barely resolved in the HST images. The clusters in NGC 1569, on the other hand, show significant substructure in their cores and ellipticities that are comparable to the flattenings seen in young clusters in the Large Magellanic Cloud (LMC). The clusters show internal (V-I) color gradients. The properties of these clusters are similar to R136, the core of the luminous star-forming complex 30 Doradus in the LMC, except that R136 has a lower luminosity and central surface brightness. The half-light surface brightness of the brightest cluster (NGC 1569 A) is 1.3 x 10(exp 6) L(sub v) solar/ sq cm, which is over 65 times higher than R136 and 1200 times higher than the mean rich LMC star cluster other than R136 after allowing for aging effects. The next brightest clusters in each of these galaxies are greater than or = 2 mag fainter. Thus, the super-star clusters represent an extreme but uncommon mode of star formation. In terms of luminosity and size, they appear to be good analogs of young globular clusters.

O'Connell, Robert W.↗
NASA NTRS1979

VLBI observations of galactic nuclei at 18 centimeters - NGC 1052, NGC 4278, M82, and M104

Compact radio sources about a light year in size have been detected in the nuclei of the galaxies NGC 1052, NGC 3034 (M82), NGC 4278, and NGC 4594 (M104) at a wavelength of 18 cm. The compact nucleus detected in M81 at 6 cm was not seen at 18 cm. The compact source in M82 is unique among extragalactic sources in its size-spectrum relationship. It is either broadened by scattering within M82 or it lies behind, and is absorbed by, an H II region. In these galaxies, the size of the nuclear radio source at 18 cm is larger than it is at higher frequencies. The nucleus of the giant radio galaxy DA 240 was not detected.

Shaffer, D. B.↗
NASA NTRS1985

Kinematics and ionization of extended ionized gas in active galaxies. I - The X-ray luminous galaxies NGC 2110, NGC 5506, and MCG -5-23-16

Direct CCD imaging and long-slit Vidicon spectroscopy have been used to map the emission-line ratios, profiles, and velocity fields over the extended narrow-line regions in three nearby Seyfert galaxies, NGC 2110, NGC 5506, and MCG -5-23-16. The gas in the letter is spatially unresolved. Similarities between the other two nebulae include the excitation mechanism (photoionization by a central nonthermal source) and the overall profiles of the very broad emission lines close to the nucleus. The nebulae are, however, quite different in their global kinematic behavior. In NGC 2110, the gas appears to lie in a disk or flattened spheroid and to be in ordered rotation, with a classical rotation curve, about an axis parallel to the minor axis of the stellar isophotes. The velocity field of NGC 5506 is quite irregular, but a component of rotation in the plane of the galaxy seems to exist.

Wilson, A. S.↗
NASA NTRS1993

Interaction of NGC 2276 with the NGC 2300 group - Fabry-Perot observations of the H-alpha velocity field

We report kinematic observations of H-alpha emission from the spiral galaxy NGC 2276 obtained with a Fabry-Perot Camera. The 'bow shock' appearance and enhanced star formation in NGC 2276 have been attributed by Mulchaey et al. (1993) to a ram-pressure interaction with the dense IGM detected in ROSAT observations of the NGC 2300 group of galaxies. Along the 'bow shock' limb of the galaxy, we observe strong H-alpha emission and significant kinematic perturbations located immediately interior to an abrupt decrease in the scale length of the optical disk. Although ram-pressure forces may be important in the evolution of the outer gaseous disk, the peculiar kinematics and the truncation in the stellar disk are difficult to explain in a ram-pressure model; a more likely cause is tidal interaction, probably with the elliptical galaxy NGC 2300.

Gruendl, Robert A.↗
NASA NTRS2012

Black Holes in Bulgeless Galaxies: An XMM-Newton Investigation of NGC 3367 AND NGC 4536

The vast majority of optically identified active galactic nuclei (AGNs) in the local Universe reside in host galaxies with prominent bulges, supporting the hypothesis that black hole formation and growth is fundamentally connected to the build-up of galaxy bulges. However, recent mid-infrared spectroscopic studies with Spitzer of a sample of optically "normal" late-type galaxies reveal remarkably the presence of high-ionization [NeV] lines in several sources, providing strong evidence for AGNs in these galaxies. We present follow-up X-ray observations recently obtained with XMM-Newton of two such sources, the late-type optically normal galaxies NGC 3367 and NGC 4536. Both sources are detected in our observations. Detailed spectral analysis reveals that for both galaxies, the 2-10 keV emission is dominated by a power law with an X-ray luminosity in the L(sub 2- 10 keV) approximates 10(exp 39) - 10(exp 40) ergs/s range, consistent with low luminosity AGNs. While there is a possibility that X-ray binaries account for some fraction of the observed X-ray luminosity, we argue that this fraction is negligible. These observations therefore add to the growing evidence that the fraction of late-type galaxies hosting AGNs is significantly underestimated using optical observations alone. A comparison of the midinfrared [NeV] luminosity and the X-ray luminosities suggests the presence of an additional highly absorbed X-ray source in both galaxies, and that the black hole masses are in the range of 10(exp 5) - 10(exp 7) solar M for NGC 3367 and 10(exp 4) - (exp 10) solar M for NGC 4536

McAlpine, W.↗
DOE OSTI2024

Spectral study of star-forming rings in S0 galaxies of Dorado group – NGC 1533 and NGC 1543

ABSTRACT We have fulfilled a detailed long-slit spectroscopic analysis for two SB0 galaxies – NGC 1533 and NGC 1543, – belonging to the Dorado group. Our spectral data reveal asymmetric decoupled kinematics of the stars and ionized gas in these barred lenticular galaxies that give evidences for external origin of the gas in the rings. We have calculated the star formation rates in the rings by using the ultraviolet fluxes of the rings corrected for the foreground and intrinsic absorption; and we have estimated parameters of the stellar populations in the inner parts of the galaxies confirming that they are old – except the nucleus of NGC 1543, which demonstrates signatures of rejuvenation less than 5 Gyr ago.

Proshina, Irina S.↗
NASA NTRS1980

Optical polarization of the Seyfert galaxies Mrk 3, Mrk 231, NGC 3227 and NGC 3516

The paper presents intermediate resolution observations of the emission line and continuum polarization of the Seyfert galaxies Mrk 3, Mrk 231, NGC 3227, and NGC 3516. The polarization shows a strong wavelength dependence with the polarization increasing smoothly into the blue for each galaxy. This wavelength dependence, together with the presence of polarized H(alpha) emission, indicates that the polarization of each galaxy is caused by an asymmetric dust envelope surrounding the nucleus. Observations of the polarization of the /O III/ lambda 5007 emission in Mrk 3 and NGC 3227, and the polarization through the nonstellar Na ID line absorption in Mrk 231 are used to place constraints on the extent of the polarizing clouds in these galaxies. No polarization variability was detected with time-bases ranging from a few weeks to three years.

Thompson, I.↗
NASA NTRS1983

Star formation in blue galaxies. I - Ultraviolet, optical, and infrared observations of NGC 4214 and NGC 4670

NGC 4214 and NGC 4760 have been observed between 1150 A and 1950 A with the IUE satellite, and new infrared and optical broad-band photometry have been obtained. The spectra of both galaxies are dominated by O stars, and, in the spectrum of NGC 4214, the C IV 1550 A line exhibits a P Cygni profile indicative of hot stars with large mass-loss rates. Although the optical spectra of both galaxies are dominated by strong narrow emission lines, no strong emission lines are seen in the UV (the observed Ly-alpha flux is dominated by geocoronal emission). Both galaxies contain giant H II region complexes in which the energy (in particular, the H-beta luminosity and the ultraviolet continuum) is provided by several hundred O stars. The comparison of the observed UVOIR energy distributions with evolutionary population models indicates that the regions observed consist of young 'bursts' of star formation superposed on an underlying old population. The initial mass function for this epoch of star formation is constrained to be similar in slope to or flatter than the Salpeter function.

Geller, M. J.↗
NASA NTRS1987

Fine-scale motion in NGC 6514 and NGC 6523

Velocity maps of the inner regions of the bright H II regions NGC 6514 and NGC 6523 were made with unprecedented spatial and spectral resolution in the 5007 A line of forbidden O III. In addition to the advantages of an instrumental full width at half-maximum intensity of only 5.4 km/s, the small thermal width of the heavy oxygen ion also allows determination of accurate line widths and velocities. The CCD spectra were numerically fitted to Gaussian line profiles and revealed two separate velocity systems in NGC 6523. The data sets of radial velocities were used to derive the dependence of the most probable turbulent velocities upon the sample sizes, and the spatial dependence of the structure function. These relationships are the basic functions for comparison with the predictions of the models for turbulence in H II regions.

O'Dell, C. R.↗
NASA NTRS1990

Parsec-Scale Penetration of UV into Molecular Clouds: CII 158 Micron Mapping of W3, NGC 1977, and NGC 2023

The spatial distribution of the 158 microns CII fine structure line in the galactic sources W3, NGC 1977, and NGC 2023 is mapped. The emission arises from warm (100 to 300 K), dense photodissociation regions at the surface of molecular gas. In all three sources, the emission extends over parsec scales or greater. For W3 and NGC 1977, where the UV source/molecular cloud geometry presents an edge on view of the variation of CII intensity into the molecular gas, two dimensional models of the CII emission which include the effects of gas clumping and scattering by dust on the transport of UV photons are constructed. The observed CII distribution and intensity is well modeled by a clumpy or filamentary distribution to the molecular gas, with a clump/interclump gas density ratio of 100 or more, which allows deep penetration of carbon ionizing UV photons into the clouds. The penetration of UV into clumped molecular clouds may also explain the extended far IR continuum emission from these sources. The total luminosity of CII emission from a clumpy molecular cloud with adjacent or embedded octave band stars can be as much as an order of magnitude higher than the CII luminosity of a uniform cloud. In addition, the extended penetration of UV into molecular clouds will affect the abundances of atomic and molecular species and increase the fractional ionization of interclump gas and UV illuminated clump surfaces.

Howe, J. E.↗