Stacking catalog sources in WMAP data

TL;DR

This study analyzes WMAP 7-year data to verify beam profiles and source spectral indices, revealing biases and spectral steepening that impact CMB power spectrum corrections and primordial spectrum interpretations.

Contribution

It provides a detailed comparison of source profiles from different catalogs, quantifies biases due to CMB fluctuations, and finds steeper spectral indices above 61 GHz, refining point source corrections.

Findings

Profiles consistent with WMAP beam models

Biases due to CMB fluctuations are quantified

Spectral indices are steeper above 61 GHz

Abstract

We stack WMAP 7-year temperature data around extragalactic point sources, showing that the profiles are consistent with WMAP's beam models, in disagreement with the findings of Sawangwit & Shanks (2010). These results require that the source sample's selection is not biased by CMB fluctuations. We compare profiles from sources in the standard WMAP catalog, the WMAP catalog selected from a CMB-free combination of data, and the NVSS catalog, 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 catalog. Addressing those biases, we find source spectral indices significantly steeper than those used by WMAP, with strong evidence for spectral steepening above 61 GHz. Such changes modify the power spectrum correction required for unresolved point sources, and tend to weaken somewhat the evidence for deviation from a Harrison-Zel'dovich primordial spectrum, but more analysis is required. Finally, we discuss implications for current CMB experiments.