Stacking catalogue sources in WMAP data

Abstract

We stack Wilkinson Microwave Anisotropy Probe (WMAP) 7-yr temperature data around extragalactic point sources, showing that the profiles are consistent with WMAP's beam models, in disagreement with the findings of Sawangwit and Shanks. These results require the point source catalogue's selection to be free from biases due to cosmic microwave background (CMB) fluctuations. We compare profiles from sources in the standard WMAP catalogue, the WMAP catalogue selected from a CMB-free combination of data and the NRAO VLA Sky Survey catalogue, and quantify the agreement with fits to simple parametric beam models. We estimate the biases in source profiles due to alignments with positive CMB fluctuations, finding them roughly consistent with those biases found with the WMAP standard catalogue. Addressing those biases, we find source spectral indices significantly steeper than those found by WMAP, with strong evidence for spectral steepening above 61 GHz. We re-analyse parameters with a revised source correction, finding an ns increase by up to ˜0.3s. Finally, we discuss implications for current CMB experiments.