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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
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NASA NTRS2013

The Nature of the Unresolved Extragalactic Cosmic Soft X-Ray Background

In this paper we investigate the power spectrum of the unresolved 0.5-2 keV cosmic X-ray background (CXB) with deep Chandra 4-Msec (Ms) observations in the Chandra Deep Field South (CDFS). We measured a signal that, on scales >30 arcsec, is significantly higher than the shot noise and is increasing with angular scale. We interpreted this signal as the joint contribution of clustered undetected sources like active galactic nuclei (AGN), galaxies and the intergalactic medium (IGM). The power of unresolved cosmic source fluctuations accounts for approximately 12 per cent of the 0.5-2 keV extragalactic CXB. Overall, our modelling predicts that approximately 20 per cent of the unresolved CXB flux is produced by low-luminosity AGN, approximately 25 per cent by galaxies and approximately 55 per cent by the IGM. We do not find any direct evidence of the so-called 'warm hot intergalactic medium' (i.e. matter with 10(exp 5) less than T less than 10(exp 7) K and density contrast delta less than 1000), but we estimated that it could produce about 1/7 of the unresolved CXB. We placed an upper limit on the space density of postulated X-ray-emitting early black holes at z greater than 7.5 and compared it with supermassive black hole evolution models.

galaxies↗
NASA NTRS2024

JWST Mid-Infrared Spectroscopy Resolves Gas, Dust, and Ice in Young Stellar Objects in the Large Magellanic Cloud

In this work, we present spectra of 11 young stellar objects (YSOs) taken with the Mid-Infrared Instrument (MIRI) / Medium Resolution Spectroscopy (MRS) instrument onboard the James Webb Space Telescope (JWST). The YSOs are located in the N79 region of the Large Magellanic Cloud (LMC), an active star forming region with hundreds of Spitzer - and Herschel-identified YSOs and host to super star cluster (SSC) candidate H72.97-69.39. The three giant molecular clouds (GMCs) in N79 (East, West, and South) have varying star formation rates and stellar populations. MRS follow-up observations of four Spitzer -identified YSOs in N79 East, West, and South reveal that what seemed to be a single, massive YSO is actually a cluster of YSOs. We discuss the emission and absorption lines of six YSOs which have complete or almost-complete spectral coverage from 4.9 – 27.9 µm. YSO Y3, located in N79 East, is the youngest source in this study and likely to be less than 10,000 years old inferred from the prominent CH 4 , NH 3 , CH 3 OH, CH 3 OCHO, and CO 2 ice absorption features. The most luminous source is the central ionizing YSO of SSC H72.97-69.39, Y4, which has dozens of fine-structure and H 2 emission lines. Unlike the other YSOs in this work, Y4 has no polyaromatic hydrocarbon (PAH) emission lines due to the intense ionizing radiation destroying these large carbon chain molecules. The mass accretion rate based on H I (7-6) line luminosity of YSOs Y1, Y2, Y4, and Y9 range between 1.22 × 10 −4 – 1.89 × 10 −2 M ⊙ yr −1 For the first time in the mid-infrared, we are able to resolve individual high-mass protostars forming in small clusters in an extra-galactic environment like the LMC.

Omnarayni Nayak↗
NASA NTRS1976

An X-ray redshift measure for clusters of galaxies up to z not less than 1

Correlated measurements of redshifted iron line emission and apparent surface brightness are suggested for unambiguously defining intrinsic X-ray characteristics for clusters of galaxies up to z not less than 1. If some of the weak unidentified high-galactic-latitude X-ray sources are clusters at z roughly equal to 1-3, then such correlated measurements should be feasible within the complement of instruments aboard the HEAO-B orbiting X-ray telescope observatory. In addition, those clusters at z less than 1 would require spectral data from broader bandwidth experiments, such as the all-sky survey to be provided by the proportional counters aboard the first mission of the High Energy Astronomy Observatory (HEAO-A).

Boldt, E.↗
NASA NTRS1976

An X-ray red-shift test for clusters of galaxies up to Z greater than or equal to 1

Correlated measurements of red-shifted iron line emission and apparent surface brightness are suggested for unambiguously defining intrinsic X-ray characteristics for clusters of galaxies up to z greater than or equal to 1. If some of the weak unidentified high galactic latitude X-ray sources are clusters at z approximately 1-3, then such correlated measurements should be feasible witin the complement of instruments aboard the HEAO-B orbiting X-ray telescope observatory. In addition, those clusters at z less than 1 would require spectral data from broader bandwidth experiments, such as the all-sky survey to be provided by the proportional counters aboard the first mission of the High Energy Astronomy Observatory (HEAO-A).

Boldt, E. A.↗
NASA NTRS1998

An Extraordinary Cluster of Massive Young Stars in the Milky Way's Nucleus

The mass distribution of newborn stars is key to the evolution of galaxies, as it determines whether a galaxy's interstellar medium is funneled predominantly into dim, long-lived, low-mass stars, as is the case in normal galactic disks, or into bright, short-lived, massive stars, as is perhaps the case in starburst nuclei.

milky way stars galactic disks stellar clusters↗
NASA NTRS2017

The XXL Survey: First Results and Future

The XXL survey currently covers two 25 deg2 patches with XMM observations of approximately 10 ks. We summarize the scientific results associated with the first release of the XXL dataset, which occurred in mid-2016.We review several arguments for increasing the survey depth to 40 ks during the next decade of XMM operations. X-ray(zeta less than 2) cluster, (zeta less than 4) active galactic nuclei (AGN), and cosmic background survey science will then benefit from an extraordinary data reservoir. This, combined with deep multi-lambda observations, will lead to solid standalone cosmological constraints and provide a wealth of information on the formation and evolution of AGN, clusters, and the X-ray background. In particular, it will offer a unique opportunity to pinpoint the zeta greater than1 cluster density. It will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA and Euclid missions.

general↗
NASA NTRS2000

The Age of the Inner Halo Globular Cluster NGC 6652

Hubble Space Telescope (HST) (V,I) photometry has been obtained for the inner halo globular cluster NGC 6652. The photometry reaches approximately 4 mag below the turn-off and includes a well populated horizontal branch (HB). This cluster is located close to the Galactic center at RGC approximately equal to 2.0 kpc with a reddening of E(V-I) = 0.15 +/- 0.02 and has a metallicity of [Fe/H] approximately equal to -0.85. Based upon DELTA V (sup SGB) (sub HB), NGC 6652 is 11.7 plus or minus 1.6 Gyr old. Using A HB precise differential ages for 47 Tuc (a thick disk globular), M107 and NGC 1851 (both halo clusters) were obtained. NGC 6652 appears to be the same age as 47 Tuc and NGC 1851 (within +/- 1.2 Gyr), while there is a slight suggestion that M107 is older than NGC 6652 by 2.3 +/- 1.5 Gyr. As this is a less than 2 sigma result, this issue needs to be investigated further before a definitive statement regarding the relative age of M107 and NGC 6652 may be made.

Chaboyer, Brian↗
NASA NTRS2008

An Eccentric Binary Millisecond Pulsar in the Galactic Plane

Binary pulsar systems are superb probes of stellar and binary evolution and the physics of extreme environments. In a survey with the Arecibo telescope, we have found PSR J1903+0327, a radio pulsar with a rotational period of 2.15 milliseconds in a highly eccentric (e = 0.44) 95-day orbit around a solar mass (M.) companion. Infrared observations identify a possible main-sequence companion star. Conventional binary stellar evolution models predict neither large orbital eccentricities nor main-sequence companions around millisecond pulsars. Alternative formation scenarios involve recycling a neutron star in a globular cluster, then ejecting it into the Galactic disk, or membership in a hierarchical triple system. A relativistic analysis of timing observations of the pulsar finds its mass to be 1.74 +/- 0.04 Solar Mass, an unusually high value.

Champion, David J.↗
NASA NTRS1990

H I absorption limits and emission mapping for high-velocity clouds

Systematic emission and absorption surveys have been conducted for high-velocity H I in the direction of 63 bright continuum sources. High-velocity emisison is detected along 18 of these 63 directions with a threshold about a factor of 2 better than previous, much more extensive surveys. No high-velocity absorption was found in any of the directions. The sky distribution of the high-velocity emission and the column density distribution agree with larger surveys. Detailed emission maps in the vicinity of each continuum source show that the variations in column density within a high-velocity cloud are similar to the variations between high-velocity clouds. A previously discovered high-velocity cloud at high galactic latitude, in the direction of part of the Virgo Cluster of galaxies, was mapped. This small cloud is moving away from the galactic plane at v greater than 30 km/s and is probably not self-gravitating.

Colgan, Sean W. J.↗
NASA NTRS1984

Inflow of halo gas from the direction of the Galactic north pole

A far-UV echelle spectrum has been obtained of the UV-bright star vZ1128 in the globular cluster M3. This cluster lies in a direction 11 deg off the Galactic north pole at a distance of about 10 kpc. Only the usually strong interstellar lines are recognizable in the faint spectrum, and they show absorption at velocities from near +40 km/s to -100 km/s. Since in the direction observed the line-of-sight component of the Milky Way rotation is negligible, the detected velocities demonstrate for this direction the motion of gas from the Milky Way halo toward the disk. Gas returning to the disk in a galactic fountainlike flow may explain the observations.

De Boer, K. S.↗
NASA NTRS1983

The spatial correlation function of rich clusters of galaxies

A series of objective statistical estimators is applied to directly study the three-dimensional distribution of rich clusters, using a recently completed redshift sample of 104 Abell clusters out to distance class four and galactic latitude of 30 deg or more. The sample and the relevant positional and redshift selection effects are discussed, and the two-point angular correlation function and nearest-neighbor distribution of clusters in the sample are determined, as well as in the larger D = 5+6 sample and in several subsamples of different richness classes and latitude zones. The redshift correlation function of clusters for various angular separations on the sky is examined as a test for the reality of the observed angular correlations. The two-point spatial correlation function of clusters in the sample is determined, and the consistency among the three observed correlation functions is tested. A model that describes all the observed correlations is presented.

Bahcall, N. A.↗
NASA NTRS1991

Thermal instabilities in proto-globular clusters resulting from time-dependent potentials

In this paper a scenario is proposed to explain the lack of young globular clusters in the Galaxy. It is argued that the formation of the Galactic disk would induce tidal compressions on protoglobular clouds during passage through the Galactic disk. Such a compression would trigger the onset of thermal instability in typical protoglobular cluster clouds, leading to rapid cooling and contraction and subsequent star formation. The clouds are thus unlikely to survive several passages through the Galactic disk following its formation. Instabilities preferentially occur in clouds with relatively high metallicity and with orbits lying more nearly in the plane of the Galaxy, possibly leading to the formation of a population of clusters with small orbital inclination, similar to the population of disk clusters observed in the Galaxy.

Murray, Stephen D.↗
NASA NTRS1981

Study of the fluctuations in the cosmic X-ray background

The emerging picture indicates that neither the total cosmic X-ray background (CXB) flux nor the fluctuations are completely dominated by any single class of sources. Quasars clearly contribute a substantial fraction of the total flux while galaxy cluster X-ray sources and galactic nuclear activity also make nonnegligible contributions. It appears that from the large angular scale CXB galaxy correlations that no class of relatively low liminosity X-ray sources associated with galaxies can play a major role in supplying the total flux. The origin of the fluctuations looks more complex. It is hard to avoid the conclusion that the NGP-SGP difference and some other features of the CXB map are associated with the local anisotropy in the galactic distribution (the local supercluster). It also appears reasonable to some suppose that at least some large angular structures in the CXB are due to emission from hot galactic halo gs.

Turner, E. L.↗
NASA NTRS1985

Local density maxima - Progenitors of structure

Beginning with a short review of the observational data and of some previous theoretical ideas and numerical simulations, the question is addressed of how the large-scale structure that emerges around local density maxima depends on the nature of the primordial density perturbations field. The density contrast profile around local maxima is given, to a good approximation, by the primordial two-point correlation function. The mean number density of objects of a given core mass is calculated as a function of the primordial power spectrum, p(k). In an open universe, rich clusters should have halos steeper than galactic haloes. The observed structure is found to be consistent with omega-sub-zero less than 1.0 and n = -1.

Hoffman, Y.↗
NASA NTRS1993

Results from the Far Ultraviolet Space Telescope (FAUST)

We present early results from the Far Ultraviolet Space Telescope (FAUST), which flew in March 1992 with the ATLAS space shuttle mission. The telescope provides wide-field images in the far ultraviolet (1400-1800 A). Studies underway using the data obtained on this mission include establishing the brightness and distribution of far ultraviolet stars in the halo of our Galaxy, establishing the far ultraviolet properties of nearby galaxies and nearby clusters of galaxies, analyzing the diffuse galactic light, and searching for the origin of the extragalactic ultraviolet light. We discuss the instrument performance, and early results from these observations.

Sasseen, T. P.↗
NASA NTRS2009

Fermi at Six Months

An overview of the Fermi Gamma-ray Space Telescope's first 6 months in operation is provided. The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy rage 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. It contains a Large Area Telescope capable of viewing the entire sky every 3 hours and a Gamma-ray Burst Monitor for viewing the entire unocculted sky. Since its launch on June 11, 2008 Fermi has provided information on pulsars, gamma ray bursts, relativistic jets, the active galactic nucleus, and a globular star cluster. This presentation describes Fermi's development, mission, instruments and recent findings.

Hays, Elizabeth↗
NASA NTRS2020

Mock Catalogs for the Extragalactic X-ray Sky: Simulating AGN Surveys with ATHENA and with the AXIS Probe

We present a series of new, publicly available mock catalogs of X-ray selected active galactic nuclei (AGNs), nonactive galaxies, and clusters of galaxies. These mocks are based on up-to-date observational results on the demographic of extragalactic X-ray sources and their extrapolations. They reach fluxes below 10-20 erg cm-2 s-1 in the 0.5–2 keV band, that is, more than an order of magnitude below the predicted limits of future deep fields, and they therefore represent an important tool for simulating extragalactic X-ray surveys with both current and future telescopes. We used our mocks to perform a set of end-to-end simulations of X-ray surveys with the forthcoming ATHENA mission and with the AXIS probe, a subarcsecond resolution X-ray mission concept proposed to the Astro 2020 Decadal Survey. We find that these proposed, next generation surveys may transform our knowledge of the deep X-ray Universe. As an example, in a total observing time of 15 Ms, AXIS would detect ~225 000 AGNs and ~50 000 nonactive galaxies, reaching a flux limit of f0:5-2 ~ 5 x 10-19 erg cm-2 s-1 in the 0.5–2 keV band, with an improvement of over an order of magnitude with respect to surveys with current X-ray facilities. Consequently, 90% of these sources would be detected for the first time in the X-rays. Furthermore, we show that deep and wide X-ray surveys with instruments such as AXIS and ATHENA are expected to detect ~20 000 z > 3 AGNs and ~250 sources at redshift z > 6, thus opening a new window of knowledge on the evolution of AGNs over cosmic time and putting strong constraints on the predictions of theoretical models of black hole seed accretion in the early universe.

X-ray galaxies↗
NASA NTRS1983

X-ray emission from the Pleiades cluster

The detection and identification of H0344+24, a new X-ray source located in the Pleiades cluster, is reported, based on observations made with HEAO A-2 low-energy detector 1 in the 0.15-3.0-keV energy band in August, 1977. The 90-percent-confidence error box for the new source is centered at 03 h 44.1 min right ascension (1950), near the center star of the 500-star Pleiades cluster, 25-eta-Tau. Since no likely galactic or extragalactic source of X-rays was found in a catalog search of the error-box region, identification of the source with the Pleiades cluster is considered secure. X-ray luminosity of the source is calculated to be about 10 to the 32nd ergs/sec, based on a distance of 125 pc. The X-ray characteristics of the Pleiades stars are discussed, and it is concluded that H0344+24 can best be explained as the integrated X-ray emission of all the B and F stars in the cluster.

Agrawal, P. C.↗