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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Probing the rapid formation of black holes and their Galaxy hosts in QSOs

Using the modelling code x-cigale, we reproduced the spectral energy distributions (SEDs) of 1359 SDSS quasi-stellar objects (QSOs) within the redshift range 0 < z < 4, for which we have NIR/MIR fluxes with the highest quality and spectral data characterizing their supermassive black hole (SMBHs). Consistent with a rapid formation of the host galaxies, the star formation histories (SFHs) have small e-folding, at most 750 Myr using an SFH function for spiral or 1000 Myr using one for elliptical. Above z ∼ 1.6, the two solutions are degenerate, the SEDs being dominated by the active galactic nucleus (AGN) continuum and high star formation rates (SFRs), typical of starburst galaxies, while at lower redshifts the starburst nature of the host, independent from its morphology, is better reproduced by a spiral SFH. In general, the SFR increases with the redshift, the mass of the bulge, the AGN luminosity, and Eddington ratio, suggesting there is no evidence of AGN quenching of star formation. Comparing the specific BH accretion rate (BHAR) with specific SFR, all the QSOs at any redshift trace a linear sequence below the Eddington luminosity, in parallel and above the one-to-one relation, implying that QSOs are in a special phase of evolution during which the growth in mass of their SMBH is more rapid than the growth in mass of their galaxy hosts. This particular phase is consistent with a scenario where the galaxy hosts of QSOs in the past grew in mass more rapidly than their SMBHs, suggesting that a high star formation efficiency during their formation was responsible in limiting their masses.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1999

Rossi X-Ray Timing Explorer Observations of the Gamma-Ray Blazar PKS 2155-304

PKS 2155-304 is the archetypical X-ray-selected BL Lac object (XBL). It is one of the brightest BL Lacs at x-ray through optical wavelengths where it has a relatively featureless continuum and displays rapid, large amplitude variability. This continuum is thought to be direct synchrotron emission from a distribution of ultra-relativistic electrons which extends to unusually high energies (Edelson et al. 1995). The gamma-ray emission from PKS 2155-304 constitutes a second, separate, spectral component. Observations with the EGRET telescope aboard the Compton Gamma Ray Observatory (CGRO) show that the spectral energy distribution of this gamma-ray component must peak at energies above 10 GeV (Vestrand et al. 1995). This, plus the realization that the extension of the synchrotron component into the x-ray band meant that ambient photons would be scattered to TeV energies, led to predictions that PKS 2155-304 would be a detectable TeV gamma ray source (Vestrand et al. 1995; Stecker et al. 1996). The University of Durham group has recently reported the discovery of TeV gamma ray emission from PKS 2155-304 (Chadwick et al. 1998, 1999) . The TeV emission was detected in 1996 September and 1997 October/November, with the largest fluxes being measured in 1997 November. During 1997 November, we detected a record high GeV gamma-ray flux from PKS 2155-304 with CGRO/EGRET (Sreekumar and Vestrand 1997) and subsequently very high x-ray fluxes were measured with BeppoSAX (Chiapeeti et al. 1997). Here we report on the record x-ray fluxes measured with the Rossi X-Ray Timing Explorer (RXTE) during the GeV/TeV outburst.

Vestrand, W. Thomas↗
NASA NTRS1997

Blazar studies with CGRO and INTEGRAL

Issues involved in galaxy unification through the two scenarios of unification through evolution and unification through orientation are reviewed, and the importance of observations at soft gamma ray energies for the characterization of the properties of blazars is discussed. The observation of blazars with the International Gamma Ray Astrophysics Laboratory (INTEGRAL) and the Compton Gamma Ray Observatory (CGRO) is considered. The spectral density field is described and the spectral energy distributions of different classes of galaxies are detailed. It is concluded that the scientific returns expected from INTEGRAL include: the strongest gamma ray tests for beaming gamma-gamma transparency arguments and the Elliot-Shapiro relationship; the discovery that infrared luminous galaxies harbor and fuel supermassive black holes; the discovery of variable spectral hardenings in quasars, and the identification of trends in the high energy behavior of radio galaxies, radio quasars and blazars.

Dermer, Charles D.↗
DOE OSTI2020

Surrogate modelling the Baryonic Universe – I. The colour of star formation

The spectral energy distribution of a galaxy emerges from the complex interplay of many physical ingredients, including its star formation history (SFH), metallicity evolution, and dust properties. Using GALAXPY , a new galaxy spectral prediction tool, and SFHs predicted by the empirical model UNIVERSEMACHINE and the cosmological hydrodynamical simulation IllustrisTNG, we isolate the influence of SFH on optical and near-infrared colours from 320 to 1080 Å at z = 0. By carrying out a principal component analysis, we demonstrate that physically motivated SFH variations modify galaxy colours along a single direction in colour space: the SFH-direction. We find that the projection of a galaxy’s present-day colours on to the SFH-direction is almost completely regulated by the fraction of stellar mass that the galaxy formed over the last billion years. Together with cosmic downsizing, this results in galaxies becoming redder as their host halo mass increases. We additionally study the change in galaxy colours due to variations in metallicity, dust attenuation, and nebular emission lines, finding that these properties vary broad-band colours along distinct directions in colour space relative to the SFH-direction. Finally, we show that the colours of low-redshift Sloan Digital Sky Survey galaxies span an ellipsoid with significant extent along two independent dimensions, and that the SFH-direction is well-aligned with the major axis of this ellipsoid. Our analysis supports the conclusion that variations in SFH are the dominant influence on present-day galaxy colours, and that the nature of this influence is strikingly simple.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Circumstellar dust emission models

We present the wavelength-dependent absorption coefficient K(sub lambda) the scattering coefficient o(sub lambda), the albedo w(sub lambda), and the average cosine of the scattering phase function g(sub lambda) between 0.0912 micrometers and 1000 micrometers for four interstellar medium grain models. These grain models are used in a radiation transfer code to calculate the properties of dust shells surrounding a newly formed O star. For each shell model a distribution of 25 grain sizes and two compositions were used in our calculations. The spectral type of the central star (O6 ZAMS), the geometry (shell), and circumstellar density distribution (constant) are the same in all models, so that different model predictions result entirely from differences in grain properties. For each grain type the models predict the emergent spectral energy distribution with wavelength, the optical depth with wavelength, and the mean dust temperature with distance from the central star. In addition, we find the emitted envelope flux (total flux minus the direct stellar contribution) included within an angular radius theta for several wavelengths between 2.2 micrometers and 100 micrometers. It is found that large differences in the emitted spectrum can occur when grains with different optical constants and size distributions are used.

Wolfire, Mark G.↗
NASA NTRS1980

Ultraviolet, visual, and infrared observations of the peculiar Be star HD 45677

The peculiar Be star HD 45677 was observed at low and high resolution by the IUE, and nearly simultaneous optical and IR observations were obtained with ground-based telescopes. These data were used to produce a spectral energy distribution extending from 0.12 to 12.6 microns in order to investigate the conversion of UV to IR radiation in the circumstellar dust shell. The high-resolution spectra indicate a spectral type of B2 in agreement with the optical classification.

Sitko, M. L.↗
NASA NTRS1986

Short time Fourier analysis of the electromyogram - Fast movements and constant contraction

Short-time Fourier analysis was applied to surface electromyograms (EMG) recorded during rapid movements, and during isometric contractions at constant forces. A portion of the data to be transformed by multiplying the signal by a Hamming window was selected, and then the discrete Fourier transform was computed. Shifting the window along the data record, a new spectrum was computed each 10 ms. The transformed data were displayed in spectograms or 'voiceprints'. This short-time technique made it possible to see time-dependencies in the EMG that are normally averaged in the Fourier analysis of these signals. Spectra of EMGs during isometric contractions at constant force vary in the short (10-20 ms) term. Short-time spectra from EMGs recorded during rapid movements were much less variable. The windowing technique picked out the typical 'three-burst pattern' in EMG's from both wrist and head movements. Spectra during the bursts were more consistent than those during isometric contractions. Furthermore, there was a consistent shift in spectral statistics in the course of the three bursts. Both the center frequency and the variance of the spectral energy distribution grew from the first burst to the second burst in the same muscle. The analogy between EMGs and speech signals is extended to argue for future applicability of short-time spectral analysis of EMG.

Hannaford, Blake↗
DOE OSTI2024

Emission line predictions for mock galaxy catalogues: a new differentiable and empirical mapping from DESI

ABSTRACT We present a simple, differentiable method for predicting emission line strengths from rest-frame optical continua using an empirically determined mapping. Extensive work has been done to develop mock galaxy catalogues that include robust predictions for galaxy photometry, but reliably predicting the strengths of emission lines has remained challenging. Our new mapping is a simple neural network implemented using the JAX Python automatic differentiation library. It is trained on Dark Energy Spectroscopic Instrument Early Release data to predict the equivalent widths (EWs) of the eight brightest optical emission lines (including H α, H β, [O ii], and [O iii]) from a galaxy’s rest-frame optical continuum. The predicted EW distributions are consistent with the observed ones when noise is accounted for, and we find Spearman’s rank correlation coefficient ρs > 0.87 between predictions and observations for most lines. Using a non-linear dimensionality reduction technique, we show that this is true for galaxies across the full range of observed spectral energy distributions. In addition, we find that adding measurement uncertainties to the predicted line strengths is essential for reproducing the distribution of observed line-ratios in the BPT diagram. Our trained network can easily be incorporated into a differentiable stellar population synthesis pipeline without hindering differentiability or scalability with GPUs. A synthetic catalogue generated with such a pipeline can be used to characterize and account for biases in the spectroscopic training sets used for training and calibration of photo-z’s, improving the modelling of systematic incompleteness for the Rubin Observatory LSST and other surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2014

STAR Formation Histories Across the Interacting Galaxy NGC 6872, the Largest-Known Spiral

NGC6872, hereafter the Condor, is a large spiral galaxy that is interacting with its closest companion, the S0 galaxy IC 4970. The extent of the Condor provides an opportunity for detailed investigation of the impact of the interaction on the current star formation rate and its history across the galaxy, on the age and spatial distribution of its stellar population, and on the mechanism that drives the star formation activity. To address these issues we analyzed the far-ultraviolet (FUV) to near-infrared (near-IR) spectral energy distribution of seventeen 10 kpc diameter regions across the galaxy, and derived their star formation history, current star formation rate, and stellar population and mass. We find that most of the star formation takes place in the extended arms, with very little star formation in the central 5 kpc of the galaxy, in contrast to what was predicted from previous numerical simulations. There is a trend of increasing star formation activity with distance from the nucleus of the galaxy, and no evidence for a recent increase in the current star formation rate due to the interaction. The nucleus itself shows no significant current star formation activity. The extent of the Condor also provides an opportunity to test the applicability of a single standard prescription for conversion of the FUV + IR (22 micrometer) intensities to a star formation rate for all regions. We find that the conversion factor differs from region to region, arising from regional differences in the stellar populations.

Histories↗
NASA NTRS2010

Herschel-ATLAS: Dust Temperature and Redshift Distribution of SPIRE and PACS Detected Sources Using Submillimetre Colours

We present colour-colour diagrams of detected sources in the Herschel-ATLAS Science Demonstration Field from 100 to 500/microns using both PACS and SPIRE. We fit isothermal modified-blackbody spectral energy distribution (SED) models in order to extract the dust temperature of sources with counterparts in GAMA or SDSS with either a spectroscopic or a photometric redshift. For a subsample of 331 sources detected in at least three FIR bands with significance greater than 30 sigma, we find an average dust temperature of (28 plus or minus 8)K. For sources with no known redshifts, we populate the colour-colour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters and compare to colours of observed sources to establish the redshift distribution of those samples. For another subsample of 1686 sources with fluxes above 35 mJy at 350 microns and detected at 250 and 500 microns with a significance greater than 3sigma, we find an average redshift of 2.2 plus or minus 0.6.

Amblard, A.↗
NASA NTRS2022

The Population of Galactic Centre Filaments – III. Candidate Radio and Stellar Sources

Recent MeerKAT radio continuum observations of the Galactic Centre at 20 cm show a large population of non-thermal radio filaments (NRFs) in the inner few hundred pc of the Galaxy. We have selected a sample of 57 radio sources, mainly compact objects, in the MeerKAT mosaic image that appear to be associated with NRFs. The selected sources are about four times the number of radio point sources associated with filaments than would be expected by random chance. Furthermore, an apparent correlation between bright IR stars and NRFs is inferred from their similar latitude distributions, suggesting that they both co-exist within the same region. To examine if compact radio sources are related to compact IR sources, we have used archival 2MASS, and Spitzer data to make spectral energy distribution of individual stellar sources coincident or close to radio sources. We provide a catalogue of radio and IR sources for future detailed observations to investigate a potential three-way physical association between NRFs, compact radio and IR stellar sources. This association is suggested by models in which NRFs are cometary tails produced by the interaction of a large-scale nuclear outflow with stellar wind bubbles in the Galactic Centre.

plasmas↗
DOE OSTI2022

Candidate cosmic filament in the GJ526 field, mapped with the NIKA2 camera

Distinctive large-scale structures have been identified in the spatial distribution of optical galaxies up to redshift z ~ 1. In the more distant universe, the relationship between the dust-obscured population of star-forming galaxies observed at millimetre wavelengths and the network of cosmic filaments of dark matter apparent in all cosmological hydrodynamical simulations is still under study. Using the NIKA2 dual-band millimetre camera, we mapped a field of ~90 arcmin 2 in the direction of the star GJ526 simultaneously in its 1.15-mm and 2.0-mm continuum wavebands to investigate the nature of the quasi-alignment of five sources found ten years earlier with the MAMBO camera at 1.2 mm. We find that these sources are not clumps of a circumstellar debris disc around this star as initially hypothesized. Rather, they must be dust-obscured star-forming galaxies, or sub-millimetre galaxies (SMGs), in the distant background. The new NIKA2 map at 1.15 mm reveals a total of seven SMGs distributed in projection on the sky along a filament-like structure crossing the whole observed field. Furthermore, we show that the NIKA2 and supplemental Herschel photometric data are compatible with a model of the spectral energy distributions (SEDs) of these sources when a common redshift of 2.5 and typical values of the dust parameters for SMGs are adopted. Hence, we speculate that these SMGs might be located in a filament of the distant ‘cosmic web’. The length of this candidate cosmic filament crossing the whole map is at least 4 cMpc (comoving), and the separations between sources are between 0.25 cMpc and 1.25 cMpc at this redshift, in line with expectations from cosmological simulations. Nonetheless, further observations to determine the precise spectroscopic redshifts of these sources are required to definitively support this hypothesis of SMGs embedded in a cosmic filament of dark matter.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

Low-luminosity active galaxies: Are they similar to Seyfert galaxies?

A careful X-ray study of five low-luminosity active galactic nuclei (LLAGNs) was conducted to address specifically the issue of whether the dominant X-ray production mechanism is the same at all luminosities in AGNs. The sample consists of three Seyfert 1 galaxies (NGC 4639, NGC 5033, and NGC 5273), and two low-ionization nuclear emission-line regions (NGC 3642 and NGC 4278) having a weak broad component of H-alpha emission. We find that the X-ray emission (ROSAT High Resolution Interferometer (HRI)) is mostly or entirely nuclear (less than or approximately = 500 pc) despite the low X-ray luminosities (approximately 9 x 10(exp 40) ergs/s) of the sample. The correlation between X-ray luminosity and the broad H-alpha emission-line luminosity observed in high-luminosity active galaxies continues down to the low-luminosity range; the mean L(sub X)/L(sub H-alpha) ratio of LLAGNs is approximately 14, while that of AGNs is approximately 29. ROSAT Position Sensitive Proportional Counter (PSPC) observations of three LLAGNs in our sample indicate that the 0.2-2.2 keV X-ray spectral energy distributions are similar to those seen in Seyfert nuclei but do not have high intrinsic absorbing columns. Using existing ultraviolet data for four LLAGNs, we find that the 'optical' (2500 A) to X-ray spectral index (alpha(sub OX)) has an average upper limit of 1.6; for comparison, the measured value in AGNs is typically 1.4, while that in M81 (the prototypical LLAGN) is 1.0.

Koratkar, A.↗
NASA NTRS2012

Gamma-Ray Activity in the Crab Nebula: The Exceptional Flare of April 2011

The Large Area Telescope on board the Fermi satellite observed a gamma-ray flare in the Crab nebula lasting for approximately nine days in April of 2011. The source, which at optical wavelengths has a size of approximately 11 ly across, doubled its gamma-ray flux within eight hours. The peak photon flux was (186 +/- 6) x 10(exp -7) /square cm/s above 100 MeV, which corresponds to a 30-fold increase compared to the average value. During the flare, a new component emerged in the spectral energy distribution, which peaked at an energy of (375 +/- 26) MeV at flare maximum. The observations imply that the emission region was relativistically beamed toward us and that variations in its motion are responsible for the observed spectral variability.

Buehler, R.↗
NASA NTRS1999

Exploring the Full Range of Properties of Quasar Spectral Distribution

The aim of this work is to obtain multi-wavelength supporting data for the sample of quasars and active galaxies observed in the far-infrared (IR) by ISO as part of our Key Project on quasars and active galaxies. This dataset then provides complete spectral energy distributions (radio-X-ray) of the ISO sample in order to fully delineate the continuum shapes and to allow detailed modeling of that continuum. The report is made up of a short project summary, and a bibliography of published papers, proceedings and presentations.

Wilkes, B.↗
NASA NTRS2006

The X-ray Emitting Components towards l = 111 deg: The Local Hot Bubble and Beyond

We have obtained an XMM-Newton spectrum of the diffuse X-ray emission towards (l, b) = (111.14,1.11), a line of sight with a relatively simple distribution of absorbing clouds; > 9 x 10(exp 19)/sq cm at R>170 pc, a 6 x 10(exp 21)/sq cm molecular cloud at 2.5-3.3 kpc, and a total column of 1.2 x 10(exp 22)/sq cm. We find that the analysis of the XMM-Newton spectrum in conjunction with the RASS spectral energy distribution for the same direction requires three thermal components to be well fit: a "standard" Local Hot Bubble component with kT = 0.089, a component beyond the molecular cloud with kT = 0.59, and a component before the molecular cloud with kT = 0.21. The strength of the O VII 0.56 keV line from the Local Hot Bubble, 2.1+/-0.7 photons/sq cm/s/sr, is consistent with other recent measures. The 0.21 keV component has an emission measure of 0.0022+/-0.0006 pc and is not localized save as diffuse emission within the Galactic plane; it is the best candidate for a pervasive hot medium. The spatial separation of the approx. 0.2 keV component from the approx. 0.6 keV component suggests that the spectral decompositions of the emission from late-type spiral disks found in the literature do represent real temperature components rather than reflecting more complex temperature distributions.

Kuntz, K. D.↗
DOE OSTI2020

A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). III. Discovery of a z = 4.72 Radio Galaxy with the Lyman Break Technique

We report a discovery of a z = 4.72 radio galaxy, HSC J083913.17+011308.1, using the Lyman break technique with the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) catalog for Very Large Array Faint Images of the Radio Sky at Twenty centimeter radio sources. The number of known high-z radio galaxies (HzRGs) at z > 3 is quite small to constrain the evolution of HzRGs so far. The deep and wide-area optical survey by HSC-SSP enables us to apply the Lyman break technique to a large search for HzRGs. For an HzRG candidate among pre-selected r-band dropouts with a radio detection, a follow-up optical spectroscopy with the Gemini Multi-Object Spectrographs (GMOS)/Gemini has been performed. The obtained spectrum presents a clear Lyα emission line redshifted to z = 4.72. The spectral energy distribution fitting analysis with the rest-frame UV and optical photometries suggests the massive nature of this HzRG with logM{sub ∗}/M{sub ⊙}=11.4. The small equivalent width of Lyα and the moderately red UV colors indicate its dusty host galaxy, implying a chemically evolved and dusty system. The radio spectral index does not meet a criterion for an ultra-steep spectrum, α{sub 1400}{sup 325} of −1.1 and α{sub 1400}{sup 150} of −0.9, demonstrating that the HSC-SSP survey compensates for a subpopulation of HzRGs that are missed in surveys focusing on an ultra-steep spectral index.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

A pulsation phase-dependent dust shell model of OH 26.5 + 0.6

The spectral energy distribution of the radio-luminous OH/IR star 26.5 + 0.6 was modeled as a function of pulsation phase, using standard radiative-transfer techniques but with more self-consistent input parameters based partly on pulsation model calculations. The changes in spectral shape and overall intensity are easily explained in terms of the radial movement of the dust condensation radius with the changing luminosity of the star. The derived amplitude of the bolometric light curve is only 1.2 mag, considerably less than expected.

Suh, Kyung-Won↗