A combined multifrequency map for point source subtraction

A method is proposed for combining multifrequency maps in order to produce a catalogue of extragalactic point sources using data from future high-precision satellite experiments. We have found the optimal way of combining maps at different frequencies in order to maximize the signal (point sources) to noise (rest of the signal) ratio. Our approach is a natural multifrequency generalization of the bandpass filter introduced by Tegmark & de Oliveira-Costa. We show that combination of different frequency maps gives us the possibility of creating a more complete catalogue of point sources.