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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 NTRS2019

2 mm GISMO Observations of the Galactic Center. I. Dust Emission

The Central Molecular Zone (CMZ), covering the inner ~1degree of the Galactic plane has been mapped at 2 mm using the GISMO bolometric camera on the 30 m IRAM telescope. The 21" resolution maps show abundant emission from cold molecular clouds, from star forming regions, and from one of the Galactic center nonthermal filaments. In this work we use the Herschel Hi-GAL data to model the dust emission across the Galactic center. We find that a single-temperature fit can describe the 160 - 500 mu m emission for most lines of sight, if the long-wavelength dust emissivity scales as lambda (exp beta) with beta approximately equal 2.25. This dust model is extrapolated to predict the 2 mm dust emission. Subtraction of the model from the GISMO data provides a clearer look at the 2 mm emission of star-forming regions and the brightest nonthermal lament.

Richard G Arendt↗
NASA NTRS2007

Determination of the Far-Infrared Cosmic Background Using COBE/DIRBE and WHAM Data

Determination of the cosmic infrared background (CIB) at far infrared wavelengths using COBE/DIRBE data is limited by the accuracy to which foreground interplanetary and Galactic dust emission can be modeled and subtracted. Previous determinations of the far infrared CIB (e.g., Hauser et al. 1998) were based on the detection of residual isotropic emission in skymaps from which the emission from interplanetary dust and the neutral interstellar medium were removed. In this paper we use the Wisconsin H(alpha) Mapper (WHAM) Northern Sky Survey as a tracer of the ionized medium to examine the effect of this foreground component on determination of the CIB. We decompose the DIRBE far infrared data for five high Galactic latitude regions into HI- and H(alpha)- correlated components and a residual component. Eased on FUSE H2 absorption line observations, the contribution of a11 H2-correlated component is expected to he negligible. We find the H(alpha)-correlated component to be consistent with zero for each region, and we find that addition of an H(alpha)-correlated component in modeling the foreground emission has negligible effect on derived CIB results. Our CIB detections and 2(sigma) upper limits are essentially the same as those derived by Hauser et al. and are given by (nu)I(sub nu)(nW/sq m/sr) < 75, < 32, 25+/-8, and 13+/-3 at gamma = 60, 100, 140, and 240 microns, respectively. Our residuals have not been subjected to a detailed anisotropy test, so our CIB results do not supersede those of Hauser et al. Mie derive upper limits on the 100 micron emissivity of the ionized medium that are typically about 40% of the 100 micron emissivity of the neutral atomic medium. This low value may be caused in part by a lower dust-to-gas mass ratio in the ionized medium than in the neutral medium, and in part by a shortcoming of using H(alpha) intensity as a tracer of far infrared emission. If H(alpha) is not a reliable tracer, our analysis would underestimate the emissivity of the ionized medium, and both our analysis and the Hauser et al. analysis may slightly overestimate the CIB. We estimate the possible effect for the CIB to be only about 5%, which is much smaller than the quoted uncertainties. From a comparison of the Hauser et al. CIB results with the integrated galaxy brightness from Spitzer source counts, we obtain 2(sigma) upper limits on a possible diffuse CIB component that are 26 nW/sq m/sr at 140 microns and 8.5 nW/sq m/sr at 240 microns.

Odegard, N.↗
NASA NTRS1983

Was the Big Bang hot?

Techniques for verifying the spectrum defined by Woody and Richards (WR, 1981), which serves as a base for dust-distorted models of the 3 K background, are discussed. WR detected a sharp deviation from the Planck curve in the 3 K background. The absolute intensity of the background may be determined by the frequency dependence of the dipole anisotropy of the background or the frequency dependence effect in galactic clusters. Both methods involve the Doppler shift; analytical formulae are defined for characterization of the dipole anisotropy. The measurement of the 30-300 GHz spectra of cold galactic dust may reveal the presence of significant amounts of needle-shaped grains, which would in turn support a theory of a cold Big Bang.

Wright, E. L.↗
NASA NTRS1994

Ly(alpha) emission and absorption features in the spectra of galaxies

The combined effects of interstellar dust absorption and of scattering by hydrogen atoms may give rise to a Ly(alpha) spectral feature of negative equivalent width, as has been observed in several star-forming galaxies. By considering the transfer of Ly(alpha) line radiation and of neighboring stellar continuum radiation within a dusty galaxy, we find that dust absorption has three effects: (1) it reduces the apparent ultraviolet continuum luminosity at all wavelengths; (2) it preferentially decreases the apparent Ly(alpha) line luminosity from H II regions; and (3) it creates an 'attenuation feature' in the continuum spectrum -- centered at the Ly(alpha) rest frequency -- which occurs because the attenuation of the stellar continuum radiation increases as the Ly(alpha) rest frequency is approached, due to the effects of scattering by hydrogen atoms. For plausible values of the galactic dust content and of the disk thickness, these effects can lead to a negative net Ly(alpha) equivalent width, even for galaxies in which the unattenuated spectrum would show a strong Ly(alpha) emission line.

Chen, W. L.↗
NASA NTRS1976

The cosmic far-infrared background at high galactic latitudes

Far-infrared background fluxes from various cosmic sources are predicted. These fluxes lie near the high frequency side of the blackbody radiation spectrum. These sources could account for a significant fraction of the background radiation at frequencies above 400 GHz which might be misinterpreted as a comptonization distortion of the blackbody radiation. Particular attention is paid to the possible contributions from external galaxies, rich clusters of galaxies and from galactic dust emission.

Stecker, F. W.↗
NASA NTRS1977

The cosmic far-infrared background at high galactic latitudes

Far-infrared background fluxes from various cosmic sources are predicted. These fluxes lie near the high-frequency side of the blackbody radiation spectrum. The sources could account for a significant fraction of the background radiation at frequencies above 400 GHz, which might be misinterpreted as a 'Comptonization' distortion of the blackbody radiation. Particular attention is paid to the possible contributions from external galaxies, from rich clusters of galaxies, and from galactic dust emission.

Stecker, F. W.↗
NASA NTRS1991

Preliminary spectral observations of the Galaxy with a 7 deg beam by the Cosmic Background Explorer (COBE)

The FIR absolute spectrophotometer (FIRAS) on the Cosmic Background Explorer (COBE) has carried out the first all-sky spectral line survey in the FIR region, as well as mapping spectra of the Galactic dust distribution at below 100 microns. Lines of forbidden C I, C II, and N II, as well as of CO are all clearly detected. The mean line intensities are interpreted in terms of the heating and cooling of the multiple phases of the interstellar gas. In addition, an average spectrum of the galaxy is constructed and searched for weak lines. The spectrum of the galaxy observed by FIRAS has two major components: a continuous spectrum due to interstellar dust heated by starlight, and a line spectrum dominated by the strong 158-micron line from singly ionized carbon, with a spatial distribution similar to the dust distribution, and a luminosity of 0.3 percent of the dust luminosity. There are in addition moderately strong 122- and 205.3-micron lines, identified as coming from singly-ionized nitrogen. Maps of the emission by dust and forbidden C II and N II are presented.

Wright, E. L.↗
NASA NTRS1991

Cosmological gamma-ray bursts

The distribution in angle and flux of gamma-ray bursts indicates that the majority of gamma-ray bursters are at cosmological distances, i.e., at z of about 1. The rate is then about 10 exp -8/yr in a galaxy like the Milky Way, i.e., orders of magnitude lower than the estimated rate for collisions between neutron stars in close binary systems. The energy per burst is about 10 exp 51 ergs, assuming isotropic emission. The events appear to be less energetic and more frequent if their emission is strongly beamed. Some tests for the distance scale are discussed: a correlation between the burst's strength and its spectrum; the absorption by the Galactic gas below about 2 keV; the X-ray tails caused by forward scattering by the Galactic dust; about 1 month recurrence of some bursts caused by gravitational lensing by foreground galaxies; and a search for gamma-ray bursts in M31. The bursts appear to be a manifestation of something exotic, but conventional compact objects can provide an explanation. The best possibility is offered by a decay of a bindary composed of a spinning-stellar-mass black-hole primary and a neutron or a strange-quark star secondary. In the final phase the secondary is tidally disrupted, forms an accretion disk, and up to 10 exp 54 ergs are released. A very small fraction of this energy powers the gamma-ray burst.

Paczynski, Bohdan↗
NASA NTRS1994

Science with High Spatial Resolution Far-Infrared Data

The goal of this workshop was to discuss new science and techniques relevant to high spatial resolution processing of far-infrared data, with particular focus on high resolution processing of IRAS data. Users of the maximum correlation method, maximum entropy, and other resolution enhancement algorithms applicable to far-infrared data gathered at the Infrared Processing and Analysis Center (IPAC) for two days in June 1993 to compare techniques and discuss new results. During a special session on the third day, interested astronomers were introduced to IRAS HIRES processing, which is IPAC's implementation of the maximum correlation method to the IRAS data. Topics discussed during the workshop included: (1) image reconstruction; (2) random noise; (3) imagery; (4) interacting galaxies; (5) spiral galaxies; (6) galactic dust and elliptical galaxies; (7) star formation in Seyfert galaxies; (8) wavelet analysis; and (9) supernova remnants.

Terebey, Susan↗
NASA NTRS2001

The Sunyaev-Zeldovich Effect Spectrum of Abell 2163

We present a measurement of the Sunyaev-Zeldovich effect (SZE) at 30 GHz for the galaxy cluster Abell 2163. Combining this data point with previous measurements at 140, 220, and 270 GHz from the SuZIE and Daibolo experiments, we construct them most complete SZE spectrum to date. The spectrum is fitted to determine the compton y parameter and the peculiar velocity for this cluster; our results are y_0=3.6 x 10(circumflex)4 and v_p=360 km s(circumflex)-1. These results include corrections for contamination by Galactic dust emission; we find the contamination level to be much less than previously reported. The dust emission, while strong, is distributed over much larger angular scales than the cluster signal and contributes little to the measured signal when the proper SZE observing strategy is taken into account.

LaRoque, S.↗
NASA NTRS2002

The Long Duration Flight of the TopHat Experiment

TopHat is a balloon-borne instrument designed to operate on the top of a balloon. From this location, the experiment could efficiently observe using a clean beam with extremely low sidelobes. The experiment was designed to scan a large portion of the sky directly above it and to map the anisotropy of the Cosmic Microwave Background (CMBR) and thermal emission from galactic dust. The instrument used a one meter class telescope with a five band single pixel radiometer spanning the frequency range from 150-600 GHz. The radiometer used bolometric detectors operating at approx. 250 mK. Here, we will report on the flight of the TopHat experiment over Antarctica in January, 2001 and describe the scientific goals, the operation, and in-flight performance.

Silverberg, R.↗
NASA NTRS2002

The Sunyaev-Zel'dovich Effect Spectrum of Abell 2163

We present an interferometric measurement of the Sunyaev-Zel'dovich effect (SZE) at 1 cm for the galaxy cluster Abell 2163. We combine this data point with previous measurements at 1.1, 1.4, and 2.1 mm from the SuZIE experiment to construct the most complete SZE spectrum to date. The intensity in four wavelength bands is fit to determine the Compton y-parameter (y(sub 0)) and the peculiar velocity (v(sub p)) for this cluster. Our results are y(sub 0) = 3.56((sup +0.41+0.27)(sub -0.41-0.19)) X 10(exp -4) and v(sub p) = 410((sup +1030+460) (sub -850-440)) km s(exp -1) where we list statistical and systematic uncertainties, respectively, at 68% confidence. These results include corrections for contamination by Galactic dust emission. We find less contamination by dust emission than previously reported. The dust emission is distributed over much larger angular scales than the cluster signal and contributes little to the measured signal when the details of the SZE observing strategy are taken into account.

LaRoque, S. J.↗
NASA NTRS2010

The Primordial Inflation Polarization Explorer (PIPER)

The Primordial Inflation Polarization Explorer (PIPER) is it balloon-borne instrument designed to search for the faint signature of inflation in the polarized component of the cosmic microwave background (C-N-113). Each flight will be configured for a single frequency, but in order to aid in the removal of the polarized foreground signal due to Galactic dust, the filters will be changed between flights. In this way, the CMB polarization at a total of four different frequencies (200, 270, 350, and 600 GHz) will be, measured on large angular scales. PIPER consists of a pair of cryogenic telescopes, one for measuring each of Stokes Q and U in the instrument frame. Each telescope receives both linear orthogonal polarizations in two 32 x 40 element planar arrays that utilize Transition-Edge Sensors (TES). The first element in each telescope is a variable-delay polarization modulator (VPM) that fully modulates the linear Stokes parameter to which the telescope is sensitive. There are several advantages to this architecture. First, by modulating at the front of the optics, instrumental polarization is unmodulated and is therefore cleanly separated from source polarization. Second, by implementing this system with the appropriate symmetry, systematic effects can be further mitigated. In the PIPER design, many of the. systematics are manifest in the unmeasured linear Stokes parameter for each telescope and this can be separated from the desired signal. Finally, the modulation cycle never mixes the Q and U linear Stokes parameters, and thus residuals in the modulation do not twist the observed polarization vector. This is advantageous because measuring the angle of linear polarization is critical for separating the inflationary signal from other polarized components.

Chuss, David T.↗
NASA NTRS2011

Correlations in the (Sub)Mil1imeter Background from ACT x BLAST

We present measurements of the auto- and cross-frequency correlation power spectra of the cosmic (sub)millimeter background at: 250, 350, and 500 microns (1200, 860, and 600 GHz) from observations made with the Balloon-borne Large Aperture Submillimeter Telescope, BLAST; and at 1380 and 2030 microns (218 and 148 GHz) from observations made with the Atacama Cosmology Telescope, ACT. The overlapping observations cover 8.6 deg(sup 2) in an area relatively free of Galactic dust near the south ecliptic pole (SEP). The ACT bands are sensitive to radiation from the CMB, the Sunyaev-Zel'dovich (SZ) effect from galaxy clusters, and to emission by radio and dusty star-forming galaxies (DSFGs), while the dominant contribution to the BLAST bands is from DSFGs. We confirm and extend the BLAST analysis of clustering with an independent pipeline, and also detect correlations between the ACT and BLAST maps at over 25(sigma) significance, which we interpret as a detection of the DSFGs in the ACT maps. In addition to a Poisson component in the cross-frequency power spectra, we detect a clustered signal at 4(sigma), and using a model for the DSFG evolution and number counts, we successfully fit all our spectra with a linear clustering model and a bias that depends only on red shift and not on scale. Finally, the data are compared to, and generally agree with, phenomenological models for the DSFG population. This study represents a first of its kind, and demonstrates the constraining power of the cross-frequency correlation technique to constrain models for the DSFGs. Similar analyses with more data will impose tight constraints 011 future models.

Hajian, Amir↗
NASA NTRS2010

The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave Background Power Spectrum at 148 AND 218 GHz from the 2008 Southern Survey

We present measurements of the cosmic microwave background (CMB) power spectrum made by the Atacama Cosmology Telescope at 148 GHz and 218 GHz, as well as the cross-frequency spectrum between the two channels. Our results dearly show the second through the seventh acoustic peaks in the CMB power spectrum. The measurements of these higher-order peaks provide an additional test of the ACDM cosmological model. At l > 3000, we detect power in excess of the primary anisotropy spectrum of the CMB. At lower multipoles 500 < l < 3000, we find evidence for gravitational lensing of the CMB in the power spectrum at the 2.8(sigma) level. We also detect a low level of Galactic dust in our maps, which demonstrates that we can recover known faint, diffuse signals.

Das, Sudeep↗
NASA NTRS2020

The Atacama Cosmology Telescope: arcminute-resolution maps of 18,000 square degrees of the microwave sky from ACT 2008-2018 data combined with Planck

This paper presents a maximum-likelihood algorithm for combining sky maps with disparate sky coverage, angular resolution and spatially varying anisotropic noise into a single map of the sky. We use this to merge hundreds of individual maps covering the 2008–2018 ACT observing seasons, resulting in by far the deepest ACT maps released so far. We also combine the maps with the full Planck maps, resulting in maps that have the best features of both Planck and ACT: Planck’s nearly white noise on intermediate and large angular scales and ACT’s high-resolution and sensitivity on small angular scales. The maps cover over 18 000 square degrees, nearly half the full sky, at 100, 150 and 220 GHz. They reveal 4 000 optically-confirmed clusters through the Sunyaev Zel’dovich effect (SZ) and 18 500 point source candidates at > 5σ, the largest single collection of SZ clusters and millimeter wave sources to date. The multi-frequency maps provide millimeter images of nearby galaxies and individual Milky Way nebulae, and even clear detections of several nearby stars. Other anticipated uses of these maps include, for example, thermal SZ and kinematic SZ cluster stacking, CMB cluster lensing and galactic dust science. The method itself has negligible bias. However, due to the preliminary nature of some of the component data sets, we caution that these maps should not be used for precision cosmological analysis. The maps are part of ACT DR5, and will be made available on LAMBDA no later than three months after the journal publication of this article, along with an interactive sky atlas.

Sigurd Naess↗
NASA NTRS1993

Design and Results of Differential Microwave Radiometers (DMR) on COBE

The Differential Microwave Radiometer (DMR) experiment on the Cosmic Background Explorer is in the final year of a scheduled four years of operation to measure large- and intermediate-scale anisotropies in the Cosmic Microwave Background (CMB). The DMR instrument comprises two independent radiometers at each of three frequencies, 31.5 53, and 90 GHz, where the frequencies were chosen to best separate the CMB from the foreground emissions from galactic dust and electrons...

Kogut, Alan J.↗
NASA NTRS2018

PICO - the Probe of Inflation and Cosmic Origins

The Probe of Inflation and Cosmic Origins (PICO) is a NASA-funded study of a Probe-class mission concept. The top-level science objectives are to probe the physics of the Big Bang by measuring or constraining the energy scale of inflation, probe fundamental physics by measuring the number of light particles in the Universe and the sum of neutrino masses, to measure the reionization history of the Universe, and to understand the mechanisms driving the cosmic star formation history, and the physics of the galactic magnetic field. PICO would have multiple frequency bands between 21 and 799 GHz, and would survey the entire sky, producing maps of the polarization of the cosmic microwave background radiation, of galactic dust, of synchrotron radiation, and of various populations of point sources. Several instrument configurations, optical systems, cooling architectures, and detector and readout technologies have been and continue to be considered in the development of the mission concept. We will present a snapshot of the baseline mission concept currently under development.

Bonato, Matteo↗