Small-scale structure of the galactic cirrus emission
del Burgo, C.; Ábrahám, P.; Lemke, D.; Klaas, U.; Kiss, Cs.; Herbstmeier, U.; Héraudeau, Ph.
Germany, Hungary
Abstract
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.