In Brief

The Cosmic Background Imager (CBI) is a 13-element interferometer meant to study the anisotropies of the comic microwave background radiation at high angular scales. Among the most prominent sources of secondary anisotropies is known to be the extragalactic foreground radio sources. In the particular case of CBI, there are as many as almost 6000 that could potentially contaminate the observed data.

The strategy to attack the problem has been the identification of those sources are not bright enough to contribute significant flux at the frequency regime of CBI (26-36 GHz). That is done on the basis of the extrapolation of flux at 1.4 GHz as extracted from the NVSS catalog with a three-point spectral index as that is computed from observations at 1.4, 4.85 and 10,45 GHz.  The former being extracted from the NVSS and the latter two observed at one of the two largest fully steerable telescopes, the 100-m telescope in Effelsberg.