Extragalactic point source detection in WMAP 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. On the contrary, in the case of multi-frequency 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 WMAP 7yr 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. Second, we do a refined analysis at their positions to improve the signal-to-noise ratio. At 94 GHz we detect 157 5σ objects at |b| > 5 ◦ (excluding the Large Magellanic Cloud region); 111 of them lie outside the WMAP Point Source Catalog mask. 28 of our detections are known Galactic sources or lie in regions of intense Galactic emission. All the other 129 have counterparts in lower frequency radio catalogues and are presumably extragalactic; 18 of them are not included in the WMAP 7yr catalogue. Our results constitute a substantial improvement over the WMAP Five-Band Point Source Catalog, which contains 87 5σ detections at 94 GHz.