Istituto di Scienza e Tecnologie dell'Informazione     
Maino D., Farusi A., Baccigalupi C., Perrotta F., Banday A. J., Bedini L., Burigana C., De Zotti G., Górski K. M., Emanuele S. All-sky astrophysical component separation with Fast Independent Component Analysis (FASTICA). 3137, Technical report, 2001.
We present a new, fast, algorithm for the separation of astrophysical components superposed in maps of the sky. The algorithm, based on the independent component analysis (ICA) technique, is aimed at recovering both the spatial pattern and the frequency scalings of the emissions from statistically independent astrophysical processes, present along the line-of-sight, from multi-frequency observations, without any a priori assumption on properties of the components to be separated, except that all of them, but at most one, must have non-Gaussian distributions. The analysis starts from very simple toy-models of the sky emission in order to assess the quality of the reconstruction when inputs are well known and controlled. In particular we study the dependence of the results of separation conducted on and off the galactic plane independently, showing that optimal separation is achieved for sky regions where components are smoothly distributed. Then we move to more realistic applications on simulated observations of the microwave sky with angular resolution and instrumental noise at the mean nominal levels for the PLANCK satellite. We consider several PLANCK observation channels containing the most important known diffuse signals: the cosmic microwave background (CMB), galactic synchrotron, dust and free-free emissions. A method for calibrating the reconstructed maps of each component at each frequency has been devised. The spatial patterns of all the components have been recovered on all scales probed by the instrument. In particular, the CMB angular power spectrum is recovered at the percent level up to lmax = 2000. Frequency scalings and normalization have been recovered with better than 1% precision for all the components at frequencies and in sky regions where their signal-to-noise ratio is more than 1.5; the error increases at about 10% level for signal-to-noise ratios =1. Runs have been performed on a Pentium III 600 MHz computer; although the computing time slightly depends on the number of channels and components to be recovered, FASTICA is an extremely promising technique for analyzing the maps that will be obtained by the forthcoming high resolution CMB experiments.
Subject Independent component analysis
J.2 Astronomy
85-08 Computational methods

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