Point Source Contamination in CMB Non-Gaussianity Analyses

TL;DR

This paper investigates how point sources like SZ clusters and radio sources bias non-Gaussianity measurements in the CMB, finding that their effect is significant but insufficient to explain high $f_{NL}$ values, emphasizing the need for accurate source modeling.

Contribution

It quantifies the bias from point sources on $f_{NL}$ estimates for WMAP and Planck, highlighting the importance of source properties in primordial non-Gaussianity analysis.

Findings

Point sources bias $f_{NL}$ by up to 0.35 in WMAP bands.

Bias in Planck bands ranges from -0.48 to 1.3.

Source properties critically affect bias estimates.

Abstract

In this paper we analyze the biasing effect of point sources, either thermal Sunyaev-Zeldovich clusters or standard radio sources, on the estimated strength of the non-Gaussianity in the Cosmic Microwave Background (CMB). We show that the biggest contribution comes from the cross--correlation of the CMB with the matter density rather than from the poisson term which is conventionally assumed in these calculations. For the three year WMAP data, we estimate that point sources could produce a non--Gaussian signature equivalent to a bias in $f_{NL}$ of $0.35, 0.24, -0.097, -0.13$ in the Ka, Q, V and W bands respectively. The level of bias we find is largely insufficient to explain the very high $f_{NL}$ values recently detected by Yadav and Wandelt. For Planck, we estimate the point source bispectra to contaminate the $f_{NL}$ estimator with a bias of $1.3, 0.34, -0.25, -0.48$ at $30, 44, 70, 100 {\rm GHz}$ respectively. These results depend on the assumed redshift distribution of the point sources. However, given the projected Planck sensitivity of $\Delta f_{NL} \simeq 5$ (95 % C.L.), a good estimate of point sources' properties including their number density and redshift distribution is essential before deriving strong conclusions on primordial non--Gaussianity.