2011A&A...528A..75R

In experimental microwave maps, point sources can strongly affect the estimate of the power spectrum and/or the test of Gaussianity of the cosmic microwave background (CMB) component. As a consequence, their removal from the sky maps represents a critical step in the analysis of the CMB data. Before removing a source, however, it is necessary to detect it, and source extraction is a delicate preliminary operation. In the literature, various techniques have been presented to detect point sources in the sky maps. The most sophisticated ones exploit the multi-frequency nature of the observations that is typical of the CMB experiments. These techniques have ``optimal'' theoretical properties and, at least in principle, are capable of remarkable performances. Yet they are fairly difficult to use, which deteriorates the quality of the obtainable results. We present a new technique, the weighted matched filter (WMF), which is quite simple to use and therefore more robust in practical applications. This technique shows particular efficiency in the detection of sources whose spectra have a slope different from zero. We apply this method to three Southern Hemisphere sky regions - each with an area of 400deg² - of the seven-year Wilkinson Microwave Anisotropy Probe (WMAP) maps and compare the resulting sources with those of the two seven-year WMAP point source catalogues. In these selected regions we find seven additional sources not previously listed in WMAP catalogues and discuss their most likely identification and spectral properties.