494 research outputs found
Assessment of Models of Galactic Thermal Dust Emission Using COBE/FIRAS and COBE/DIRBE Observations
Accurate modeling of the spectrum of thermal dust emission at millimeter
wavelengths is important for improving the accuracy of foreground subtraction
for CMB measurements, for improving the accuracy with which the contributions
of different foreground emission components can be determined, and for
improving our understanding of dust composition and dust physics. We fit four
models of dust emission to high Galactic latitude COBE/FIRAS and COBE/DIRBE
observations from 3 millimeters to 100 microns and compare the quality of the
fits. We consider the two-level systems model because it provides a physically
motivated explanation for the observed long wavelength flattening of the dust
spectrum and the anticorrelation between emissivity index and dust temperature.
We consider the model of Finkbeiner, Davis, and Schlegel because it has been
widely used for CMB studies, and the generalized version of this model recently
applied to Planck data by Meisner and Finkbeiner. For comparison we have also
fit a phenomenological model consisting of the sum of two graybody components.
We find that the two-graybody model gives the best fit and the FDS model gives
a significantly poorer fit than the other models. The Meisner and Finkbeiner
model and the two-level systems model remain viable for use in Galactic
foreground subtraction, but the FIRAS data do not have sufficient
signal-to-noise ratio to provide a strong test of the predicted spectrum at
millimeter wavelengths.Comment: 17 pages, 7 figures. Accepted for publication in Ap
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 (\nu I_\nu < 64 nW/m^2/sr, 95% CL) and at 240 microns (\nu I_\nu < 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 \nu I_\nu = 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.Comment: 26 pages and 5 figures, accepted for publication in the Astrophyical
Journa
A Novel Approach to Constrain the Escape Fraction and Dust Content at High Redshift Using the Cosmic Infrared Background Fractional Anisotropy
The Cosmic Infrared Background (CIB) provides an opportunity to constrain
many properties of the high redshift (z>6) stellar population as a whole. This
background, specifically, from 1 to 200 microns, will contain any information
about the era of reionization and the stars responsible for producing these
ionizing photons. In this paper, we look at the fractional anisotropy delta I/I
of this high redshift population, which is the ratio of the magnitude of the
fluctuations (delta I) and the mean intensity (I). We show that this can be
used to constrain the escape fraction of the population as a whole. The
magnitude of the fluctuations of the CIB depend on the escape fraction, while
the mean intensity does not. This results in lower values of the escape
fraction producing higher values of the fractional anisotropy. This difference
is predicted to be larger at the longer wavelengths bands (above 10 microns),
albeit it is also much harder to observe in that range. We show that the
fractional anisotropy can also be used to separate a dusty from a dust-free
population. Finally, we discuss the constraints provided by current
observations on the CIB fractional anisotropy.Comment: 8 pages, 4 figures, accepted to ApJ, some clarifications added,
matches accepted versio
Detection of the Cosmic Far-Infrared Background in the AKARI Deep Field South
We report the detection and measurement of the absolute brightness and
spatial fluctuations of the cosmic infrared background (CIB) with the AKARI
satellite. We have carried out observations at 65, 90, 140 and 160 um as a
cosmological survey in AKARI Deep Field South (ADF-S), which is one of the
lowest cirrus regions with contiguous area on the sky. After removing bright
galaxies and subtracting zodiacal and Galactic foregrounds from the measured
sky brightness, we have successfully measured the CIB brightness and its
fluctuations across a wide range of angular scales from arcminutes to degrees.
The measured CIB brightness is consistent with previous results reported from
COBE data but significantly higher than the lower limits at 70 and 160 um
obtained with the Spitzer satellite from the stacking analysis of 24-um
selected sources. The discrepancy with the Spitzer result is possibly due to a
new galaxy population at high redshift obscured by hot dust. From power
spectrum analysis at 90 um, three components are identified: shot noise due to
individual galaxies; Galactic cirrus emission dominating at the largest angular
scales of a few degrees; and an additional component at an intermediate angular
scale of 10-30 arcminutes, possibly due to galaxy clustering. The spectral
shape of the clustering component at 90 um is very similar to that at longer
wavelengths as observed by Spitzer and BLAST. Moreover, the color of the
fluctuations indicates that the clustering component is as red as
Ultra-luminous infrared galaxies (ULIRGs) at high redshift, These galaxies are
not likely to be the majority of the CIB emission at 90 um, but responsible for
the clustering component. Our results provide new constraints on the evolution
and clustering properties of distant infrared galaxies.Comment: 50 pages, 15 figures, submitted to Ap
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