5,353 research outputs found
Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. An all-sky survey of
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\deg\ are of the order
of 10\%, and the maps are smooth at the level of 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
\nwm2sr at 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 \nwm2sr
over this wavelength range.Comment: 15 pages (LATEX) with 2 figures and 1 plate; Ap. J. Letters, in pres
Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. I. 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 ) bands at a scale of 0.7\deg\ 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 \w2m4sr2 for the
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 . Applying this technique gives significantly lower and more isotropic
limits.Comment: 44 pages postcript; includes 5 tables, 14 figures. Astrophysical
Journal, in pres
Demonstrating the negligible contribution of optical ACS/HST galaxies to source-subtracted cosmic infrared background fluctuations in deep IRAC/Spitzer images
We study the possible contribution of optical galaxies detected with the {\it
Hubble} ACS instrument to the near-IR cosmic infrared (CIB) fluctuations in
deep {\it Spitzer} images. The {\it Spitzer} data used in this analysis are
obtained in the course of the GOODS project from which we select four
independent regions observed at both 3.6 and 4.5
\um. ACS source catalogs for all of these areas are used to construct maps
containing only their emissions in the ACS -bands. We find that
deep Spitzer data exhibit CIB fluctuations remaining after removal of
foreground galaxies of a very different clustering pattern at both 3.6 and 4.5
\um than the ACS galaxies could contribute. We also find that there are very
good correlations between the ACS galaxies and the {\it removed} galaxies in
the Spitzer maps, but practically no correlations remain with the residual
Spitzer maps used to identify the CIB fluctuations. These contributions become
negligible on larger scales used to probe the CIB fluctuations arising from
clustering. This means that the ACS galaxies cannot contribute to the
large-scale CIB fluctuations found in the residual Spitzer data. The absence of
their contributions also means that the CIB fluctuations arise at z\gsim 7.5
as the Lyman break of their sources must be redshifted past the longest ACS
band, or the fluctuations have to originate in the more local but extremely low
luminosity galaxies.Comment: Ap.J.Letters, in press. Minor revisions to mathc the accepted versio
New measurements of cosmic infrared background fluctuations from early epochs
Cosmic infrared background fluctuations may contain measurable contribution
from objects inaccessible to current telescopic studies, such as the first
stars and other luminous objects in the first Gyr of the Universe's evolution.
In an attempt to uncover this contribution we have analyzed the GOODS data
obtained with the Spitzer IRAC instrument, which are deeper and cover larger
scales than the Spitzer data we have previously analyzed. Here we report these
new measurements of the cosmic infrared background (CIB) fluctuations remaining
after removing cosmic sources to fainter levels than before. The remaining
anisotropies on scales > 0.5 arcmin have a significant clustering component
with a low shot-noise contribution. We show that these fluctuations cannot be
accounted for by instrumental effects, nor by the Solar system and Galactic
foreground emissions and must arise from extragalactic sources.Comment: Ap.J.Letters, in pres
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\deg. 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.Comment: 7 pages postcript, talk at "Unveiling the cosmic infrared background"
workshop, College Park, M
Cosmic Infrared Background Fluctuations and Zodiacal Light
We have performed a specific observational test to measure the effect that
the zodiacal light can have on measurements of the spatial fluctuations of the
near-IR background. Previous estimates of possible fluctuations caused by
zodiacal light have often been extrapolated from observations of the thermal
emission at longer wavelengths and low angular resolution, or from IRAC
observations of high latitude fields where zodiacal light is faint and not
strongly varying with time. The new observations analyzed here target the
COSMOS field, at low ecliptic latitude where the zodiacal light intensity
varies by factors of over the range of solar elongations at which the
field can be observed. We find that the white noise component of the spatial
power spectrum of the background is correlated with the modeled zodiacal light
intensity. Roughly half of the measured white noise is correlated with the
zodiacal light, but a more detailed interpretation of the white noise is
hampered by systematic uncertainties that are evident in the zodiacal light
model. At large angular scales () where excess power above the
white noise is observed, we find no correlation of the power with the modeled
intensity of the zodiacal light. This test clearly indicates that the large
scale power in the infrared background is not being caused by the zodiacal
light.Comment: 17 pp. Accepted for publication in the Ap
Aperiodic invariant continua for surface homeomorphisms
We prove that if a homeomorphism of a closed orientable surface S has no
wandering points and leaves invariant a compact, connected set K which contains
no periodic points, then either K=S and S is a torus, or is the
intersection of a decreasing sequence of annuli. A version for non-orientable
surfaces is given.Comment: 8 pages, to appear in Mathematische Zeitschrif
Quantitative evaluation of polymer gel dosimeters by broadband ultrasound attenuation
Ultrasound has been examined previously as an alternative readout method for irradiated polymer gel dosimeters, with authors reporting varying dose response to ultrasound transmission measurements. In this current work we extend previous work to measure the broadband ultrasound attenuation (BUA) response of irradiated PAGAT gel dosimeters, using a novel ultrasound computed tomography system
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