Non-Gaussianity and Minkowski functionals: forecasts for Planck

We study Minkowski functionals as probes of primordial non-Gaussianity in the cosmic microwave background, specifically for the estimate of the primordial 'local' bi-spectrum parameter f(NL), with instrumental parameters which should be appropriate for the Planck experiment. We use a maximum likelihood approach, which we couple with various filtering methods and test thoroughly for convergence. We included the effect of inhomogeneous noise as well as astrophysical biases induced by point sources and by the contamination from the Galaxy. We find that when Wiener filtered maps are used (rather than simply smoothed with Gaussian), the expected error on the measurement of f(NL) should be as small as Delta f(NL) similar or equal to 10 when combining the three channels at 100, 143 and 217 GHz in the Planck extended mission setup. This result is fairly insensitive to the non-homogeneous nature of the noise, at least for realistic hitmaps expected from Planck. We then estimate the bias induced on the measurement of f(NL) by point sources in those three channels. With the appropriate masking of the bright sources, this bias can be reduced to a negligible level in the 100 and 143 GHz channels. It remains significant in the 217 GHz channel, but can be corrected for. The Galactic foreground biases are quite important and present a complex dependence on sky coverage: making them negligible will depend strongly on the quality of the component separation methods.