Using alpha-stable distributions to model the P(D) distribution of point sources in CMB sky maps

We present a new approach to the statistical modelling of point source counts in astronomical images. The approach is based on the theory of alpha-stable distributions. We show that the distribution of the intensity fluctuations produced by a generic point source population belongs to the alpha-stable family of distributions. With the alpha-stable model it is possible to totally describe the non-Gaussian distribution with a few parameters which are closely related to the parameters describing the source counts. Using statistical tools available in the signal processing literature, we show how to estimate these parameters in an easy and fast way. Then we apply the method to Cosmic Microwave Background (CMB) observations where point sources appear as superimposed to the cosmological signal as well as the instrumental noise, and propose a method to statistically disentangle these contributions. In the case of the Planck mission, our technique is able to determine the parameters of the dominant point source populations with relative errors < %5 for the 30 GHz and 857 GHz channels. The formalism and methods presented here can be useful also for other experiments in other frequency ranges such as X-rays or radio Astronomy.