KISAG - Science

Extragalactic background

Fluctuations of the far-infrared extragalactic background

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 I_nu = 14 +/- 3 nW m^-2 sr^-1) at 170 mu m and an upper limit of 1.1 MJy sr^-1 (nu I_nu = 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.

Authors: Kiss, Cs.; Ábrahám, P.; Klaas, U.; Juvela, M.; Lemke, D.

Journal: Astronomy and Astrophysics, v.379, p.1161-1169 (2001)

Absolute surface brightness observations with ISOPHOT

Future project ...

Spatial structure of galactic cirrus

Confusion noise

Authors: Kiss, Cs.; Ábrahám, P.; Klaas, U.; Juvela, M.; Lemke, D.

Journal: Astronomy and Astrophysics, v.379, p.1161-1169 (2001)

Fourier analysis of far-infrared cirrus maps

We examined the Fourier power spectrum characteristics of cirrus structures in 13 sky fields with faint to bright cirrus emission observed with ISOPHOT in the 90-200 mu m wavelength range in order to study variations of the spectral index alpha . We found that alpha varies from field to field with -5.3 le alpha le -2.1. It depends on the absolute surface brightness and on the hydrogen column density. We also found different spectral indices for the same sky region at different wavelengths. Longer wavelength measurements show steeper power spectra. This can be explained by the presence of dust at various temperatures, in particular of a cold extended component. For the faintest areas of the far-infrared sky we derive a wavelength-independent spectral index of alpha = -2.3 +/- 0.6 for the cirrus power spectrum. The application of the correct spectral index is a precondition for the proper disentanglement of the cirrus foreground component of the Cosmic Far-Infrared Background and its fluctuations.

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 United Kingdom) and with the participation of ISAS and NASA.

Authors: Kiss, Cs.; Ábrahám, P.; Klaas, U.; Lemke, D.; Héraudeau, Ph.; del Burgo, C.; Herbstmeier, U.

Journal: Astronomy and Astrophysics, v.399, p.177-185 (2003)

Zodiacal light

Structure of the Zodiacal light cloud

ISO performed an extensive observing programme on the infrared zodiacal light, including multi-filter photometry of the global brightness distribution, observations of the asteroidal bands and cometary dust trails, and investigation of the small scale brightness fluctuation. The detailed determination of the spectral energy distribution of the zodiacal light, including mid-infrared spectrophotometry, opens the possibility for the separation of the main components of the infrared sky. The mid-infrared spectrum may provide information on the nature of the constituents, and on the size distribution of the interplanetary grains. Two years after the ISO mission we review the observations and summarize the results of ISOPHOT and ISOCAM.

Authors: Ábrahám, P.; Leinert, C.; Lemke, D.

Journal: Dust in the Solar System and Other Planetary Systems, Proceedings of the IAU Colloquium 181 held at the University of Kent, Canterbury, UK, 4-10 April 2000. Edited by S.F. Green, I.P. Williams, J.A.M. McDonnell and N. McBride. Oxford: Pergamon, 2002, 414 p. COSPAR colloquia series, Vol. 15. ISBN 0080441947., p.111

Mid-infrared spectrum of the Zodiacal light

We present 29 mid-infrared spectra of the zodiacal light distributed over the sky. The observed 5.9-11.7 mu m spectral shapes are well represented by blackbody radiation with colour temperatures in the range of 255<= T<= 300 K. The spectra are smooth and featureless. The variation of the temperature can be explained by the geometrical distribution of dust in the inner solar system. This result indicates that although the interplanetary dust particles originate from discrete sources (comets, asteroids) the interplanetary cloud of today seems to be well mixed in terms of grain composition and size distribution.

Authors: Leinert, Ch.; Ábrahám, P.; Acosta-Pulido, J.; Lemke, D.; Siebenmorgen, R.

Journal: Astronomy and Astrophysics, v.393, p.1073-1079 (2002)