Extragalactic point source detection in Wilkinson Microwave Anisotropy Probe 7-year data at 61 and 94 GHz

The detection of point sources in cosmic microwave background maps is usually based on a single-frequency approach, whereby maps at each frequency are filtered separately and the spectral information on the sources is derived combining the results at the different frequencies. In contrast, in the case of multifrequency detection methods, source detection and spectral information are tightly interconnected in order to increase the source detection efficiency.

In this work we apply the matched multifilter method to the detection of point sources in the Wilkinson Microwave Anisotropy Probe (WMAP) 7-year data at 61 and 94 GHz. This linear filtering technique takes into account the spatial and the cross-power spectrum information at the same time using the spectral behaviour of the sources without making any a priori assumption about it. We follow a two-step approach. First, we do a blind detection of the sources over the whole sky. Secondly, we do a refined local analysis at their positions to improve the signal-to-noise ratio of the detections. At 94 GHz we detect 129 5σ objects at |b| > 5° (excluding the Large Magellanic Cloud region); 119 of them are reliable extragalactic sources and 104 of these 119 lie outside the WMAP Point Source Catalogue mask. Nine of the total 129 detections are known Galactic sources or lie in regions of intense Galactic emission and one additional (weak) high Galactic latitude source has no counterpart in low-frequency radio catalogues. Our results constitute a substantial improvement over the New Extragalactic WMAP Point Source (NEWPS) 3-year catalogue.