We study the impact of cosmological parameters ’ uncertainties on estimates of the primordial NG parameter f _ { NL } in local and equilateral models of non-Gaussianity .
We show that propagating these errors increases the f _ { NL } 1 \sigma uncertainty by a term { \delta f _ { NL } ^ { local } / f _ { NL } ^ { local } } \simeq 16 \% for WMAP and { \delta f _ { NL } ^ { local } / f _ { NL } ^ { local } } \simeq 5 \% for Planck in the local case , whereas for equilateral configurations the correction term are { \delta f _ { NL } ^ { equil } / f _ { NL } ^ { equil } } \simeq 14 \% and { \delta f _ { NL } ^ { equil } / f _ { NL } ^ { equil } } \simeq 4 \% , respectively .
If we assume for f _ { NL } ^ { local } a central value \langle f _ { NL } ^ { local } \rangle \simeq 60 , according to recent WMAP 5-years estimates , we obtain for Planck a final correction \Delta f _ { NL } ^ { local } \simeq 3 .
Although not dramatic , this correction is at the level of the expected estimator uncertainty for Planck , and should then be taken into account when quoting the significance of an eventual future detection .
In current estimates of f _ { NL } the cosmological parameters are held fixed at their best-fit values .
We finally note that the impact of uncertainties in the cosmological parameters on the final f _ { NL } error bar would become totally negligible if the parameters were allowed to vary in the analysis and then marginalized over .