A. Kashlinsky et S. Odenwald, Clustering of the diffuse infrared light from the COBE DIRBE maps. III. Power spectrum analysis and excess isotropic component of fluctuations, ASTROPHYS J, 528(1), 2000, pp. 74-95
The cosmic infrared background (CIB) radiation is the cosmic repository for
energy release throughout the history of the universe. The spatial fluctua
tions of the CIB resulting from galaxy clustering are expected to be at lea
st a few percent on scales of a degree, depending on the luminosity and clu
stering history of the early universe. Using the all-sky data from the COBE
DIRBE instrument at wavelengths 1.25-100 mu m, we attempt to measure the C
IB fluctuations. In the near-IR, foreground emission is dominated by small-
scale structure due to stars in the Galaxy. There we find a strong correlat
ion between the amplitude of the fluctuations and Galactic latitude after r
emoving bright foreground stars. Using data outside the Galactic plane (\ b
\ > 20 degrees) and away from the center (90 degrees < l < 270 degrees), w
e extrapolate the amplitude of the fluctuations to csc \ b \ = 0. We find p
ositive intercepts of delta F-rms = 15.5(-7.0)(+3.7), 5.9(-3.7)(+1.6), 2.4(
-0.9)(+0.5), and 2.0(-0.5)(+0.25) nW m(-2) sr(-1) at 1.25, 2.2, 3.5, and 4.
9 mu m, respectively, where the errors are the range of 92% confidence limi
ts. For color subtracted maps between band 1 and 2 we find the isotropic pa
rt of the fluctuations at 7.6(-2.4)(+1.2) nW m(-2) sr(-1). Based on detaile
d numerical and analytic models, this residual is not likely to originate f
rom the Galaxy, our clipping algorithm, or instrumental noise. We demonstra
te that the residuals from the lit used in the extrapolation are distribute
d isotropically and suggest that this extra variance may result from struct
ure in the GIB. We also obtain a positive intercept from a linear combinati
on of maps at 1.25 and 2.2 mu m. For 2 degrees < theta < 15 degrees, a powe
r-spectrum analysis yields firm upper limits of (theta/5 degrees) x delta F
-rms(theta) < 6, 2.5, 0.8, and 0.5 nW m(-2) sr(-1) at 1.25, 2.2, 3.5, and 4
.9 mu m, respectively. From 10 to 100 mu m, the dominant foregrounds are em
ission by dust in the solar system and the Galaxy. The upper limits on the
CIB fluctuations are below 1 nW m-2 sr-l there and are lowest ( less than o
r equal to 0.5 nW m(-2) sr(-1)) at 25 mu m.