Impact of secondary non-Gaussianities on the search for primordial non-Gaussianity with CMB maps

When constraining the primordial non-Gaussianity parameter $f_{\mathrm{NL}}$ with cosmic microwave background anisotropy maps, the bias resulting from the covariance between primordial non-Gaussianity and secondary non-Gaussianities to the estimator of $f_{\mathrm{NL}}$ 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 $f_{\mathrm{NL}}$ between 5 and 10. In the future, it will be necessary to jointly estimate the combined primordial and secondary contributions to the cosmic microwave background bispectrum and establish $f_{\mathrm{NL}}$ by properly accounting for the confusion from secondary non-Gaussianities.