Issue |
A&A
Volume 379, Number 3, December I 2001
|
|
---|---|---|
Page(s) | 1161 - 1169 | |
Section | Numerical methods and codes | |
DOI | https://doi.org/10.1051/0004-6361:20011394 | |
Published online | 15 December 2001 |
Sky confusion noise in the far-infrared: Cirrus, galaxies and the cosmic far-infrared background *
1
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
2
Konkoly Observatory of the Hungarian Academy of Sciences, PO Box 67, 1525 Budapest, Hungary
3
Helsinki University Observatory, Tähtitorninmäki, PO Box 14, 00014 University of Helsinki, Helsinki
Corresponding author: Cs. Kiss, pkisscs@konkoly.hu
Received:
31
January
2001
Accepted:
26
September
2001
We examined the sky confusion noise in 40 sky regions by analysing
175 far-infrared (90-200 μm) maps obtained with ISOPHOT,
the photometer on-board the Infrared Space Observatory.
For cirrus fields with
MJy sr-1 the
formula based on IRAS data (Helou & Beichman [CITE])
predicts confusion noise values within a factor of 2
of our measurements.
The dependence of the sky confusion noise on the
surface brightness was determined for the wavelength range
m.
We verified that the confusion noise
scales as
, independent
of the wavelength and confirmed
for
μm.
The scaling of the noise value at different separations
between target and reference positions was investigated
for the first time, providing a practical formula.
Since our results confirm the applicability of the
Helou & Beichman ([CITE]) formula,
the cirrus confusion noise predictions made for future space missions
with telescopes of a similar size can be trusted.
At 90 and 170 μm a noise term with a Poissonian spatial
distribution was detected in the faintest fields
(
-5 MJy sr-1), which we interpret
as fluctuations in the Cosmic Far-Infrared Background (CFIRB).
Applying ratios of the fluctuation amplitude to the absolute level
of 10% and 7% at 90 and 170 μm, respectively, as supported by
model calculations,
we achieved a new simultaneous determination of the fluctuation
amplitudes and the surface brightness of the CFIRB.
The fluctuation amplitudes are
mJy and
mJy at 90 and 170 μm, respectively.
We obtained a CFIRB surface brightness of
MJy sr-1
(
=
nW m-2 sr-1)
at 170 μm and an upper limit of 1.1 MJy sr-1
(
= 37 nW m-2 sr-1) at 90 μm.
Key words: methods: observational / ISM: structure / infrared: ISM
© ESO, 2001
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