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J. C. Mather

Publications and source records attributed to J. C. Mather.

At least 37 records · Page 2Linked to original sources
arXiv2000

Multi-Read Out Data Simulator

We present a data simulation package designed to create a series of simulated data samples for a detector with non-destructive sampling capability. The original intent of this software was to provide a method for generating simulated images for the Next Generation Space Telescope, but it is general enough to apply to almost any non-destructive detector or instrument. MultiDataSim can be used to generate "practice" sampling strategies for an instrument or field-of-view, and thus can be used to identify optimal observation strategies.

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arXiv1999

Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. III. Power spectrum analysis and excess isotropic component of fluctuations

The cosmic infrared background (CIB) radiation is the cosmic repository for energy release throughout the history of the universe. Using the all-sky data from the COBE DIRBE instrument at wavelengths 1.25 - 100 mic we attempt to measure the CIB fluctuations. In the near-IR, foreground emission is dominated by small scale structure due to stars in the Galaxy. There we find a strong correlation between the amplitude of the fluctuations and Galactic latitude after removing bright foreground stars. Using data outside the Galactic plane ($|b| > 20°$) and away from the center ($90°< l <270°$) we extrapolate the amplitude of the fluctuations to cosec$|b|=0$. We find a positive intercept of $δF_{\rm rms} = 15.5^{+3.7}_{-7.0},5.9^{+1.6}_{-3.7}, 2.4^{+0.5}_{-0.9}, 2.0^{+0.25}_{-0.5}$ nW/m2/sr at 1.25, 2.2,3.5 and 4.9 mic respectively, where the errors are the range of 92% confidence limits. For color subtracted maps between band 1 and 2 we find the isotropic part of the fluctuations at $7.6^{+1.2}_{-2.4}$ nW/m2/sr. Based on detailed numerical and analytic models, this residual is not likely to originate from the Galaxy, our clipping algorithm, or instrumental noise. We demonstrate that the residuals from the fit used in the extrapolation are distributed isotropically and suggest that this extra variance may result from structure in the CIB. For $2°< θ< 15^°$, a power-spectrum analysis yields firm upper limits of $(θ/5^°) \timesδF_{\rm rms} (θ) < $ 6, 2.5, 0.8, 0.5 nW/m2/sr at 1.25, 2.2, 3.5 and 4.9 mic respectively. From 10-100 mic, the upper limits <1 nW/m2/sr.

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arXiv1999

COBE-FIRAS Observations of Galactic Lines

The COBE Far InfraRed Absolute Spectrophotometer (FIRAS) observations constitute an unbiased survey over the wavelength range from 100 um to 1 cm over 99% of the sky. Improved calibration of the FIRAS instrument and the inclusion of all of the FIRAS data allow an improved signal to noise determination of the spectral lines by a factor of ~2 over our previous results. The resolution is low (0.45 cm^{-1}) so only the strongest lines are observable. The CO chain from J=1-0 to J=8-7 is observed towards the Galactic center. The line ratios are roughly consistent with a 40 K excitation temperature. The 157.7 um C II and 205.3 um N II lines are observable over most of the sky. The 370.4 um and 609.1 um lines of C I, and the 121.9 um line of N II are observed in the Galactic plane. The line ratios at the Galactic center are consistent with a density of n_0 ~30 cm^{-3} and a UV flux of G_0 ~15 uW m^{-2} sr^{-1} (10 Habing units). The 269 um H2O line is observed toward the Galactic center in absorption.

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arXiv1998

Calibrator Design for the COBE Far Infrared Absolute Spectrophotometer (FIRAS)

The photometric errors of the external calibrator for the FIRAS instrument on the COBE are smaller than the measurement errors on the cosmic microwave background (CMBR) spectrum (typically 0.02 MJy/sr, 1 sigma), and smaller than 0.01% of the peak brightness of the CMBR. The calibrator is a re-entrant cone, shaped like a trumpet mute, made of Eccosorb iron-loaded epoxy. It fills the entire beam of the instrument and is the source of its accuracy. Its known errors are caused by reflections, temperature gradients, and leakage through the material and around the edge. Estimates and limits are given for all known error sources. Improvements in understanding the temperature measurements of the calibrator allow an improved CMBR temperature determination of 2.725 +/- 0.002 K.

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arXiv1998

Cosmic Ray Rejection and Image Processing Aboard The Next Generation Space Telescope

The NASA Yardstick design for the Integrated Science Instrument Module (ISIM) utilizes 64 1k x 1k InSb imagers. Since multiple readouts per image are required to remove cosmic ray events and to reduce the readout noise, the implied downlink rates can approach 0.7 Tbytes per day. These would exceed the downlink capabilities of RF links from L2 or more distant orbits. Some form of on-board data analysis and compression is mandatory: a factor of 100 compression for an L2 orbit, factors of 1000-10000 for a 1 AU drift-away or 1 x 3 AU elliptical orbit. Supported by funding from JPL to study the uses of low-cost, on- board parallel processors, we are studying algorithms and architectures to perform cosmic-ray rejection and lossless compression of the NIR images, while optimizing the resulting signal- to-noise.

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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 Spectrum of the Extragalactic Far Infrared Background from the COBE Firas Observations

The COBE FIRAS data contain foreground emission from interplanetary, Galactic interstellar dust and extragalactic background emission. We use three different methods to separate the various emission components, and derive the spectrum of the extragalactic Far InfraRed Background (FIRB). Each method relies on a different set of assumptions, which affect the FIRB spectrum in different ways. Despite this, the FIRB spectra derived by these different methods are remarkably similar. The average spectrum that we derive in the ν= 5 - 80 cm^{-1} (2000-125 \um) frequency interval is: I(ν) = (1.3 \pm 0.4)\times10^{-5} (ν/ν_0)^{0.64 \pm 0.12} P_ν(18.5 \pm 1.2 K), where ν_0=100 cm^{-1} (λ_0=100 \um) and P is the Planck function. The derived FIRB spectrum is consistent with the DIRBE 140 and 240 \um detections. The total intensity received in the 5 - 80 cm^{-1} frequency interval is 14 nW m^{-2} sr^{-1}, and comprises about 20% of the total intensity expected from the energy release from nucleosynthesis throughout the history of the universe.

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arXiv1997

Comparison of the COBE FIRAS and DIRBE Calibrations

We compare the independent FIRAS and DIRBE observations from the COBE in the wavelength range 100-300 microns. This cross calibration provides checks of both data sets. The results show that the data sets are consistent within the estimated gain and offset uncertainties of the two instruments. They show the possibility of improving the gain and offset determination of DIRBE at 140 and 240 microns.

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arXiv1997

Quasi-stationary States of Dust Flows Under Poynting-Robertson Drag: New Analytical and Numerical Solutions

The effect of solar or stellar radiation on dust particles' trajectories (the Poynting-Robertson drag) has been studied by a number of authors and applied to interplanetary dust dynamics in numerical computations. Meanwhile some important features of dust flows can be studied analytically by implementing our novel hydrodynamical approach to use the continuity equation written in the particle's orbital elements as coordinates (Gor'kavyi, Ozernoy, & Mather 1997). By employing this approach and integrating the continuity equation, we are able to find two integrals of motion when the Poynting-Robertson drag dominates the dissipative forces in the dust flow. These integrals of motion enable us to explore basic characteristics of dust flows from any sources in the Solar system (such as asteroids, comets, Kuiper belt, etc.) or in another planetary system. In particular, we have reproduced the classical solution $n(r)\propto r^{-1}$ that approximately represents the overall distribution of dust in the Solar system. We have also investigated various factors that could be responsible for the deviations of the power law index in $n(r)\propto r^δ$ from $δ=-1$, including the influences of the orbital characteristics of dust sources, the evaporation of dust particles, as well as mixtures of dust particles of both asteroidal and cometary origin. We have calculated the masses and number densities of asteroidal and cometary components of the zodiacal cloud at different distances from the Sun.

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arXiv1997

The Spectrum of the CMB Anisotropy from the Combined COBE FIRAS and DMR Observations

We analyze the Cosmic Microwave Background (CMB) anisotropy data from the independent COBE FIRAS and DMR observations. We extract the frequency spectrum of the FIRAS signal that has the spatial distribution seen by DMR and show that it is consistent with CMB temperature fluctuations in the radiation well into the Wien region of the spectrum. Conversely, we form a map of the Planckian component of the sky temperature from FIRAS and show that it correlates with the DMR anisotropy map. The rms fluctuations at angular scales of 7 degrees are 48 \pm 14 uK for the FIRAS data compared with 35 \pm 2 uK for the DMR data and 31 \pm 6 uK for the correlated combination (1 sigma uncertainties). The consistency of these data, from very different instruments with very different observing strategies, provide compelling support for the interpretation that the signal seen by DMR is, in fact, temperature anisotropy of cosmological origin. The data also limit rms fluctuations in the Compton y parameter, observable via the Sunyaev- Zel'dovich effect, to Delta_y < 3 x 10^{-6} (95% CL) on 7 degree angular scales.

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arXiv1997

Limits on the cosmic infrared background from clustering in COBE/DIRBE maps

We discuss a new method of estimating the cosmic infrared background (CIB) from the spatial properties of infrared maps and give the limits on the CIB from applying it to the COBE/DIRBE maps. The strongest limits are obtained at mid- to far-IR where foregrounds are bright, but smooth. If the CIB comes from matter clustered like galaxies, the smoothness of the maps implies CIB levels less than $\sim$(10-15) nW/m$^2$/sr over this wavelength range.

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arXiv1996

Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. An all-sky survey of $C(0)$

We measure the smoothness of the infrared sky using the COBE DIRBE maps, and obtain interesting limits on the production of the diffuse cosmic infrared background (CIB) light by matter clustered like galaxies. The predicted fluctuations of the CIB with the DIRBE beam size of 0.7° are of the order of 10\%, and the maps are smooth at the level of $δνI_ν\sim $ a few \nwm2sr rms from 2.2 to 100 \um. The lowest numbers are achieved at mid- to far-IR where the foreground is bright but smooth; they are $\sqrt{C(0)}$$\leq$$(1-1.5)$ \nwm2sr at $λ=$ 10-100 \um. If the CIB comes from clustered matter evolving according to typical scenarios, then the smoothness of the maps implies CIB levels less than $\sim (10-15) $ \nwm2sr over this wavelength range.

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arXiv1996

The Cosmic Microwave Background Spectrum from the Full COBE/FIRAS Data Set

We have refined the analysis of the data from the FIRAS (Far InfraRed Absolute Spectrophotometer) on board the COBE (COsmic Background Explorer). The FIRAS measures the difference between the cosmic microwave background and a precise blackbody spectrum. We find new tighter upper limits on general deviations from a blackbody spectrum. The RMS deviations are less than 50 parts per million of the peak of the CMBR. For the Comptonization and chemical potential we find $|y| < 15\times10^{-6}$ and $|μ| < 9\times10^{-5}$ (95\% CL). There are also refinements in the absolute temperature, 2.728 $\pm$ 0.004 K (95\% CL), and dipole direction, $(\ell,b)=(264.14^\circ\pm0.30, 48.26^\circ\pm0.30)$ (95\% CL), and amplitude, $3.372 \pm 0.007$ mK (95\% CL). All of these results agree with our previous publications.

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arXiv1996

Clustering of Diffuse Infrared Background Light

The cosmic infrared background from galaxies should have a minimum fluctuation of the order of 10\% on angular scales probed by the DIRBE (Diffuse Infrared Background Experiment) on board COBE (Cosmic Background Explorer). We present the theoretical basis for the analysis and discuss the all-sky all-wavelengths survey that we conducted. We further show that a linear combination of maps at different wavelengths can greatly reduce the fluctuations produced by foreground stars in the near-IR, while not eliminating the fluctuations of the background from high redshift galaxies. The method is potentially very powerful, especially at wavelengths in the mid- to far-IR where the foreground is bright but smooth.

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arXiv1996

Clustering of DIRBE Light and IR Background

We outline a new method for estimating the cosmic infrared background using the spatial and spectral correlation properties of infrared maps. The cosmic infrared background from galaxies should have a minimum fluctuation of the order of 10\% on angular scales of the order of 1°. We show that a linear combination of maps at different wavelengths can greatly reduce the fluctuations produced by foreground stars, while not eliminating the fluctuations of the background from high redshift galaxies. The method is potentially very powerful, especially at wavelengths where the foreground is bright but smooth.

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arXiv1996

Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. I. $C(0)$ and limits on the near-IR background

This paper is devoted to studying the CIB through its correlation properties. We studied the limits on CIB anisotropy in the near IR (1.25, 2.2, and 3.5 \um, or $J,\;K,\;L$) bands at a scale of 0.7° using the COBE\footnote{ The National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) is responsible for the design, development, and operation of the {\it COBE}. Scientific guidance is provided by the {\it COBE} Science Working Group. GSFC is also responsible for the development of the analysis software and for the production of the mission data sets.} Diffuse Infrared Background Experiment (DIRBE) data. In single bands we obtain the upper limits on the zero-lag correlation signal $C(0)= \langle(νδI_ν)^2\rangle < 3.6 \times 10^{-16},\; 5.1 \times 10^{-17},\; 5.7 \times 10^{-18}$ \w2m4sr2 for the $J,K,L$ bands respectively. The DIRBE data exhibit a clear color between the various bands with a small dispersion. On the other hand most of the CIB is expected to come from redshifted galaxies and thus should have different color properties. We use this observation to develop a `color subtraction' method of linear combinations of maps at two different bands. This method is expected to suppress the dominant fluctuations from foreground stars and nearby galaxies, while not reducing (or perhaps even amplifying) the extragalactic contribution to $C(0)$. Applying this technique gives significantly lower and more isotropic limits.

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arXiv1995

FAR-INFRARED SPECTRAL OBSERVATIONS OF THE GALAXY BY COBE

We derive Galactic continuum spectra from 5-96/cm from COBE/FIRAS observations. The spectra are dominated by warm dust emission, which may be fit with a single temperature in the range 16-21 K (for nu^2 emissivity) along each line of sight. Dust heated by the attenuated radiation field in molecular clouds gives rise to intermediate temperature (10-14 K) emission in the inner Galaxy only. A widespread, very cold component (4-7 K) with optical depth that is spatially correlated with the warm component is also detected. The cold component is unlikely to be due to very cold dust shielded from starlight, because it is present at high latitude. We consider hypotheses that the cold component is due to enhanced submillimeter emissivity of the dust that gives rise to the warm component, or that it may be due to very small, large, or fractal particles. Lack of substantial power above the emission from warm dust places strong constraints on the amount of cold gas in the Galaxy. The microwave sky brightness due to interstellar dust is dominated by the cold component, and its angular variation could limit our ability to discern primordial fluctuations in the cosmic microwave background radiation.

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