1,243 research outputs found
FIRBACK: II. Data Reduction and Calibration of the 170 micron ISO Deep Cosmological Survey
We present the final reduction and calibration of the FIRBACK ISOPHOT data.
FIRBACK is a deep cosmological survey performed at 170 microns. This paper
deals with the ISOPHOT C200 camera with the C160 filter. We review the whole
data reduction process and compare our final calibration with DIRBE (for the
extended emission) and IRAS (for point sources). The FIRBACK source extraction
and galaxy counts is discussed in a companion paper (Dole et al., 2001).Comment: Accepted for publication in A&A. 9 pages, includes new aa.cls. Also
available (with better quality figures) at http://wwwfirback.ias.u-psud.fr
and http://mips.as.arizona.edu/~hdole/firback (new aa.cls is here
Power Spectrum Analysis of Far-IR Background Fluctuations in 160 Micron Maps From the Multiband Imaging Photometer for Spitzer
We describe data reduction and analysis of fluctuations in the cosmic far-IR
background (CFIB) in observations with the Multiband Imaging Photometer for
Spitzer (MIPS) instrument 160 micron detectors. We analyzed observations of an
8.5 square degree region in the Lockman Hole, part of the largest low-cirrus
mapping observation with this instrument. We measured the power spectrum of the
CFIB in these observations by fitting a power law to the IR cirrus component,
the dominant foreground contaminant, and subtracting this cirrus signal. The
CFIB power spectrum in the range 0.2 arc min^{-1} <k< 0.5 arc min^{-1} is
consistent with previous measurements of a relatively flat component. However,
we find a large power excess at low k, which falls steeply to the flat
component in the range 0.03 arc min^{-1} <k< 0.1 arc min^{-1}. This low-k power
spectrum excess is consistent with predictions of a source clustering
"signature". This is the first report of such a detection in the far-IR.Comment: This is the version of the paper accepted by A&A, which includes
various changes and new material. The superior-quality PDF with integrated
figures may be downloaded at
http://www-astro.lbl.gov/~bruce/spitzerpaper1/cfibaa_pub.pdf 15 pages,
figures integrated with text. This paper supersedes astro-ph/050416
IRIS: A new generation of IRAS maps
The Infrared Astronomical Satellite (IRAS) had a tremendous impact on many
areas of modern astrophysics. In particular it revealed the ubiquity of
infrared cirrus that are a spectacular manifestation of the interstellar medium
complexity but also an important foreground for observational cosmology. With
the forthcoming Planck satellite there is a need for all-sky complementary data
sets with arcminute resolution that can bring informations on specific
foreground emissions that contaminate the Cosmic Microwave Background
radiation. With its 4 arcmin resolution matching perfectly the high-frequency
bands of Planck, IRAS is a natural data set to study the variations of dust
properties at all scales. But the latest version of the images delivered by the
IRAS team (the ISSA plates) suffer from calibration, zero level and striping
problems that can preclude its use, especially at 12 and 25 micron. In this
paper we present how we proceeded to solve each of these problems and enhance
significantly the general quality of the ISSA plates in the four bands (12, 25,
60 and 100 micron). This new generation of IRAS images, called IRIS, benefits
from a better zodiacal light subtraction, from a calibration and zero level
compatible with DIRBE, and from a better destriping. At 100 micron the IRIS
product is also a significant improvement from the Schlegel et al. (1998) maps.
IRIS keeps the full ISSA resolution, it includes well calibrated point sources
and the diffuse emission calibration at scales smaller than 1 degree was
corrected for the variation of the IRAS detector responsivity with scale and
brightness. The uncertainty on the IRIS calibration and zero level are
dominated by the uncertainty on the DIRBE calibration and on the accuracy of
the zodiacal light model.Comment: 16 pages, 17 figures, accepted for publication in ApJ (Suppl). Higher
resolution version available at
http://www.cita.utoronto.ca/~mamd/IRIS/IrisTechnical.htm
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 H I and H-alpha
correlated components and a residual component. 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_nu (nW m-2 sr-1) < 75, < 32, 25 +- 8, and 13 +- 3 at 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. We
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.Comment: 38 pages, 8 figures. Accepted for publication in Ap
The Near Infrared Background: Interplanetary Dust or Primordial Stars?
The intensity of the diffuse ~ 1 - 4 micron sky emission from which solar
system and Galactic foregrounds have been subtracted is in excess of that
expected from energy released by galaxies and stars that formed during the z <
5 redshift interval (Arendt & Dwek 2003, Matsumoto et al. 2005). The spectral
signature of this excess near-infrared background light (NIRBL) component is
almost identical to that of reflected sunlight from the interplanetary dust
cloud, and could therefore be the result of the incomplete subtraction of this
foreground emission component from the diffuse sky maps. Alternatively, this
emission component could be extragalactic. Its spectral signature is consistent
with that of redshifted continuum and recombination line emission from HII
regions formed by the first generation of very massive stars. In this paper we
analyze the implications of this spectral component for the formation rate of
these Population III stars, the redshift interval during which they formed, the
reionization of the universe and evolution of collapsed halo masses. We find
that to reproduce the intensity and spectral shape of the NIRBL requires a peak
star formation rate that is higher by about a factor of 4 to 10 compared to
those derived from hierarchical models. Furthermore, an extragalactic origin
for the NIRBL leads to physically unrealistic absorption-corrected spectra of
distant TeV blazars. All these results suggest that Pop III stars contribute
only a fraction of the NIRBL intensity with zodiacal light, star forming
galaxies, and/or non-nuclear sources giving rise to the remaining fraction.Comment: 28 pages including 7 embedded figures. Submitted to Ap
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