Non-Gaussianity from extragalactic point-sources

TL;DR

This paper analyzes the non-Gaussianity caused by extragalactic point sources in the CMB, introducing a new parametrization for their bispectrum and assessing their impact on primordial non-Gaussianity estimates.

Contribution

It presents a novel parametrization for visualizing the bispectrum of extragalactic sources and evaluates their frequency, scale dependence, and impact on primordial non-Gaussianity.

Findings

IR source clustering significantly enhances non-Gaussianity

Bispectrum peaks in squeezed triangle configurations

Masking reduces radio source bias but not IR source bias

Abstract

The population of compact extragalactic sources contribute to the non-Gaussianity at Cosmic Microwave Background frequencies. We study their non-Gaussianity using publicly available full-sky simulations. We introduce a parametrisation to visualise efficiently the bispectrum and we describe the scale and frequency dependences of the bispectrum of radio and IR point-sources. We show that the bispectrum is well fitted by an analytical prescription. We find that the clustering of IR sources enhances their non-Gaussianity by several orders of magnitude, and that their bispectrum peaks in the squeezed triangles. Examining the impact of these sources on primordial non-Gaussianity estimation, we find that radio sources yield an important positive bias to local fNL at low frequencies but this bias is efficiently reduced by masking detectable sources. IR sources produce a negative bias at high frequencies, which is not dimmed by the masking, as their clustering is dominated by faint sources.