EDP Sciences
Free Access
Volume 399, Number 1, February III 2003
Page(s) 177 - 185
Section Formation, structure and evolution of stars
DOI https://doi.org/10.1051/0004-6361:20021787

A&A 399, 177-185 (2003)
DOI: 10.1051/0004-6361:20021787

Small-scale structure of the galactic cirrus emission

Cs. Kiss1, 2, P. Ábrahám1, 2, U. Klaas1, D. Lemke1, Ph. Héraudeau1, C. del Burgo1 and U. Herbstmeier1

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

(Received 18 March 2002 / Accepted 22 November 2002)

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  $\pm$ 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.

Key words: ISM: structure -- infrared: ISM

Offprint request: Cs. Kiss, pkisscs@konkoly.hu

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