Sky confusion noise in the far-infrared: Cirrus, galaxies and the cosmic far-infrared background
C. Kiss, á, brahá, P. m, U. Klaas, M. Juvela, D. Lemke;
AaA, 2001, 379, 1161
ABSTRACT:We examined the sky confusion noise in 40 sky regions by analysing 175 far-infrared (90-200 mu m) maps obtained with ISOPHOT, the photometer on-board the Infrared Space Observatory.For cirrus fields with < B > > 5 MJy sr-1 the formula based on IRAS data (Helou & Beichman \cite{Helou+Beichman_90}) 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 90 <= lambda <= 200 mu m.
We verified that the confusion noise scales as N ~ < B > 1.5, independent of the wavelength and confirmed N ~ lambda 2.5 for lambda >= 100 mu m.
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{Helou+Beichman_90}) formula, the cirrus confusion noise predictions made for future space missions with telescopes of a similar size can be trusted.
At 90 and 170 mu m a noise term with a Poissonian spatial distribution was detected in the faintest fields (< B > <= 3-5 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 mu m, 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 7 +/- 2 mJy and 15 +/- 4 mJy at 90 and 170 mu m, respectively.
We obtained a CFIRB surface brightness of B0 = 0.8 +/- 0.2 MJy sr-1 (nu Inu = 14 +/- 3 nW m-2 sr-1) at 170 mu m and an upper limit of 1.1 MJy sr-1 (nu Inu = 37 nW m-2 sr-1) at 90 mu m.
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA.
KEYWORDS: methods: observational, ism: structure, infrared: ism: continuum
PERSOKEY:statistical analysis, fir, iso, component separation, cib, ,
CODE: kiss2001