Impact of Secondary non-Gaussianities on the Search for Primordial Non-Gaussianity with CMB Maps

TL;DR

This paper investigates how secondary non-Gaussianities can bias the measurement of primordial non-Gaussianity in CMB maps, especially at small angular scales, highlighting the need for joint estimation methods.

Contribution

It demonstrates that secondary non-Gaussianities can significantly bias f_NL estimates at small scales, challenging the common assumption of negligible bias.

Findings

Bias from secondary non-Gaussianities is non-negligible at small scales.

Joint estimation of primordial and secondary contributions is necessary.

Bias impact is significant for f_NL around 5 to 10.

Abstract

When constraining the primordial non-Gaussianity parameter f_NL with cosmic microwave background anisotropy maps, the bias resulting from the covariance between primordial non-Gaussianity and secondary non-Gaussianities to the estimator of f_NL is generally assumed to be negligible. We show that this assumption may not hold when attempting to measure the primordial non-Gaussianity out to angular scales below a few tens arcminutes with an experiment like Planck, especially if the primordial non-Gaussianity parameter is around the minimum detectability level with f_NL between 5 and 10. In future, it will be necessary to jointly estimate the combined primordial and secondary contributions to the CMB bispectrum and establish f_NL by properly accounting for the confusion from secondary non-Gaussianities.