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S. H. Moseley

Publications and source records attributed to S. H. Moseley.

45 records · Page 3Linked to original sources
arXiv2002

Probing the Invisible Universe: The Case for Far-IR/Submillimeter Interferometry

The question "How did we get here and what will the future bring?" captures the human imagination and the attention of the National Academy of Science's Astronomy and Astrophysics Survey Commitee (AASC). Fulfillment of this "fundamental goal" requires astronomers to have sensitive, high angular and spectral resolution observations in the far-infrared/submillimeter (far-IR/sub-mm) spectral region. With half the luminosity of the universe and vital information about galaxy, star and planet formation, observations in this spectral region require capabilities similar to those currently available or planned at shorter wavelengths. In this paper we summarize the scientific motivation, some mission concepts and technology requirements for far-IR/sub-mm space interferometers that can be developed in the 2010-2020 timeframe.

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arXiv2000

Calibrating Array Detectors

The development of sensitive large format imaging arrays for the infrared promises to provide revolutionary capabilities for space astronomy. For example, the Infrared Array Camera (IRAC) on SIRTF will use four 256 x 256 arrays to provide background limited high spatial resolution images of the sky in the 3 to 8 micron spectral region. In order to reach the performance limits possible with this generation of sensitive detectors, calibration procedures must be developed so that uncertainties in detector calibration will always be dominated by photon statistics from the dark sky as a major system noise source. In the near infrared, where the faint extragalactic sky is observed through the scattered and reemitted zodiacal light from our solar system, calibration is particularly important. Faint sources must be detected on this brighter local foreground. We present a procedure for calibrating imaging systems and analyzing such data. In our approach, by proper choice of observing strategy, information about detector parameters is encoded in the sky measurements. Proper analysis allows us to simultaneously solve for sky brightness and detector parameters, and provides accurate formal error estimates. This approach allows us to extract the calibration from the observations themselves; little or no additional information is necessary to allow full interpretation of the data. Further, this approach allows refinement and verification of detector parameters during the mission, and thus does not depend on a priori knowledge of the system or ground calibration for interpretation of images.

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arXiv1999

Newly Synthesized Elements and Pristine Dust in the Cassiopeia A Supernova Remnant

Spectroscopic observations at 2.4 - 45 microns of the young supernova remnant Cas A with the Infrared Space Observatory (ISO) Short Wavelength Spectrometer (SWS) reveal strong emission lines of O, Ne, Si, S, and Ar. These lines are observed at high velocities (several thousand km/s), and are therefore associated with the supernova ejecta known as the fast-moving knots (FMKs). Continuum emission from dust is also seen in the Cas A spectrum. The continuum strength is spatially well correlated with the O and Ar line strengths, indicating that the dust emission also arises from the FMKs. The dust continuum has an emission feature at ~22 microns which cannot be fit by typical astronomical silicates, but can be fit with a particular class of silicate minerals. This suggests that the dust in Cas A is silicate material that has freshly condensed from the Cas A ejecta into a mineral form that is uncharacteristic of typical ISM dust grains.

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arXiv1998

Submillimeter Imaging of NGC 891 with SHARC

The advent of submillimeter wavelength array cameras operating on large ground-based telescopes is revolutionizing imaging at these wavelengths, enabling high-resolution submillimeter surveys of dust emission in star-forming regions and galaxies. Here we present a recent 350 micron image of the edge-on galaxy NGC 891, which was obtained with the Submillimeter High Angular Resolution Camera (SHARC) at the Caltech Submillimeter Observatory (CSO). We find that high resolution submillimeter data is a vital complement to shorter wavelength satellite data, which enables a reliable separation of the cold dust component seen at millimeter wavelengths from the warmer component which dominates the far-infrared (FIR) luminosity.

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arXiv1998

The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background: II. Model of the Interplanetary Dust Cloud

The COBE Diffuse Infrared Background Experiment (DIRBE) was designed to search for the cosmic infrared background (CIB) radiation. Scattered light and thermal emission from the interplanetary dust (IPD) are major contributors to the diffuse sky brightness at most infrared wavelengths. Accurate removal of this zodiacal light foreground is a necessary step toward a direct measurement of the CIB. The zodiacal light foreground contribution in each of the 10 DIRBE wavelength bands ranging from 1.25 to 240 microns is distinguished by its apparent seasonal variation over the whole sky. This contribution has been extracted by fitting the brightness calculated from a parameterized physical model to the time variation of the all-sky DIRBE measurements over 10 months of observations. The model brightness is evaluated as the integral along the line of sight of the product of a source function and a three-dimensional dust density distribution function. The dust density distribution is composed of multiple components: a smooth cloud, three asteroidal dust bands, and a circumsolar ring near 1 A.U. By using a directly measurable quantity which relates only to the IPD cloud, we exclude other contributors to the sky brightness from the IPD model. Using the IPD model described here, high-quality maps of the infrared sky with the zodiacal foreground removed have been generated. Imperfections in the model reveal themselves as low-level systematic artifacts in the residual maps which correlate with components of the IPD. The most evident of these artifacts are located near the ecliptic plane in the mid-infrared, and are less than 2% of the zodiacal foreground brightness. Uncertainties associated with the model are discussed, including implications for the CIB search.

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arXiv1998

The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background: I. Limits and Detections

The DIRBE on the COBE spacecraft was designed primarily to conduct systematic search for an isotropic CIB in ten photometric bands from 1.25 to 240 microns. The results of that search are presented here. Conservative limits on the CIB are obtained from the minimum observed brightness in all-sky maps at each wavelength, with the faintest limits in the DIRBE spectral range being at 3.5 microns (νI_ν< 64 nW/m^2/sr, 95% CL) and at 240 microns (νI_ν< 28 nW/m^2/sr, 95% CL). The bright foregrounds from interplanetary dust scattering and emission, stars, and interstellar dust emission are the principal impediments to the DIRBE measurements of the CIB. These foregrounds have been modeled and removed from the sky maps. Assessment of the random and systematic uncertainties in the residuals and tests for isotropy show that only the 140 and 240 microns data provide candidate detections of the CIB. The residuals and their uncertainties provide CIB upper limits more restrictive than the dark sky limits at wavelengths from 1.25 to 100 microns. No plausible solar system or Galactic source of the observed 140 and 240 microns residuals can be identified, leading to the conclusion that the CIB has been detected at levels of νI_ν= 25+-7 and 14+-3 nW/m^2/sr at 140 and 240 microns respectively. The integrated energy from 140 to 240 microns, 10.3 nW/m^2/sr, is about twice the integrated optical light from the galaxies in the Hubble Deep Field, suggesting that star formation might have been heavily enshrouded by dust at high redshift. The detections and upper limits reported here provide new constraints on models of the history of energy-releasing processes and dust production since the decoupling of the cosmic microwave background from matter.

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arXiv1998

The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background: III. Separation of Galactic Emission from the Infrared Sky Brightness

The Cosmic Infrared Background (CIB) is hidden behind veils of foreground emission from our own solar system and Galaxy. This paper describes procedures for removing the Galactic IR emission from the 1.25 - 240 micron COBE DIRBE maps as steps toward the ultimate goal of detecting the CIB. The Galactic emission models are carefully chosen and constructed so that the isotropic CIB is completely retained in the residual sky maps. We start with DIRBE data from which the scattered light and thermal emission of the interplanetary dust (IPD) cloud have already been removed. Locations affected by the emission from bright compact and stellar sources are excluded from the analysis. The unresolved emission of faint stars at near- and mid-IR wavelengths is represented by a model based on Galactic source counts. The 100 micron DIRBE observations are used as the spatial template for the interstellar medium (ISM) emission at high latitudes. Correlation of the 100 micron data with H I column density allows us to isolate the component of the observed emission that is associated with the ISM. Limits are established on the far-IR emissivity of the diffuse ionized medium, which indicate a lower emissivity per H nucleus than in the neutral medium. At 240 micron, we find that adding a second spatial template to the ISM model can greatly improve the accuracy of the model at low latitudes. The crucial product of this analysis is a set of all-sky IR maps from which the Galactic (and IPD) emission has been removed. We discuss systematic uncertainties and potential errors in the foreground subtraction process that may have an impact on studies seeking to detect the CIB in the residual maps.

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arXiv1993

Morphology of the Interstellar Cooling Lines Detected by COBE

The FIRAS instrument on the COBE satellite has conducted an unbiased survey of the far-infrared emission from our Galaxy. The first results of this survey were reported by Wright et al. (1991). We report the results of new analyses of this spectral survey, which includes emission lines from 158 um C+, 122 um and 205 um N+, 370 um and 609 um C, and CO J=2-1 through 5-4. We report the morphological distribution along the galactic plane (b=0) of the spectral line emission, and the high galactic latitude intensities of the C+ and 205 um N+ emission. The high galactic latitude intensity cosecant of the 158 um fine structure transition from C+ is presented, and C+ is seen to decrease more rapidly than the far infrared intensity with increasing galactic latitude. C+ and H I emission are closely correlated with a C+ cooling rate of (2.65 +/- 0.15)x10^{-26} erg/s/H-atom. We conclude that this emission arises almost entirely from the Cold Neutral Medium. The high galactic latitude intensity of the 205 um fine structure transition from N+ arises entirely from the Warm Ionized Medium, and its cosecant is presented. We estimate the total ionizing photon rate in the Galaxy to be 3.5x10^{53} ionizing photons per second, based on the 205 um N+ transition.

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