Properties of Galactic cirrus clouds observed by BOOMERanG

The physical properties of galactic cirrus emission are not well characterized. BOOMERANG is a balloonborne
experiment designed to study the cosmic microwave background at high angular resolution in the millimeter
range. The BOOMERANG 245 and 345 GHz channels are sensitive to interstellar signals, in a spectral
range intermediate between FIR and microwave frequencies. We look for physical characteristics of cirrus
structures in a region at high galactic latitudes (b -40 ) where BOOMERANG performed its deepest integration,
combining the BOOMERANG data with other available datasets at different wavelengths. We have
detected 8 emission patches in the 345 GHz map, consistent with cirrus dust in the Infrared Astronomical Satellite
maps. The analysis technique we have developed allows to identify the location and the shape of cirrus
clouds, and to extract the flux from observationswith different instruments at differentwavelengths and angular
resolutions. We study the integrated flux emitted from these cirrus clouds using data from Infrared Astronomical
Satellite (IRAS), DIRBE, BOOMERANG and Wilkinson Microwave Anisotropy Probe in the frequency
range 23–3000 GHz (13 mm 100 μm wavelength). We fit the measured spectral energy distributions with a
combination of a grey body and a power-law spectra considering two models for the thermal emission. The
temperature of the thermal dust component varies in the 7 – 20 K range and its emissivity spectral index is in
the 1 – 5 range. We identified a physical relation between temperature and spectral index as had been proposed
in previous works. This technique can be proficiently used for the forthcoming Planck and Herschel missions
data.

Faculty of the European Space Astronomy Center (ESAC-ESA). Italian Space Agency, contracts COFIS, BOOMERANG and HiGal

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